Lecture 1 Overview of Water Treatment

1. Definition of water

Water is an irreplaceable resource for all living things (animals, plants, humans) to survive.

Second, the characteristics of the water supply industry:

1. lack of water resources

(1) Resource water shortage

(2) Water shortage

2. Monopoly

3. Service

4. social

5. public welfare

3. Basic knowledge of water treatment

1. purpose of water treatment

Remove impurities to make it meet certain water quality standards.

Impurities

2.1 According to its particle size and existing form

(1) Suspended substances: silt, clay, aquatic plants, algae, protozoa, bacteria, pathogenic bacteria, etc.

(2) Colloid: clay in water, silicic acid colloid, humic substance colloid

(3) Dissolved substances: Calcium, magnesium salts, other salts, oxygen, carbon dioxide and other dissolved gases

2.2 According to its nature

(1) Inorganic substances

(2) Organic matter

(3) Microorganisms

3. Types of water treatment

Water purification treatment (domestic and industrial water)

water treatment

Sewage Treatment (Wastewater Treatment)

4. water treatment

4.1 Water source

(1) Groundwater

(2) Surface water: rivers, rivers, lakes, reservoirs

Different water sources have different water treatment processes.

4.2 Characteristics of groundwater

(1) Colorless and transparent

(2) Contains a lot of dissolved salts

(3) High hardness

(4) Contains less bacteria

(5) The water temperature is low and the change is small

4.3 Groundwater treatment process

4.4 Characteristics of river water

(1) The turbidity is high and changes with the seasons

(2) Low chroma, low salt content and hardness

(3) Lots of bacteria

(4) The water temperature varies greatly

4.5 Characteristics of reservoir water

(1) Turbidity is low and changes with the seasons

(2) More algae and shellfish

(3) Lots of bacteria

(4) The water temperature varies greatly

4.6 Conventional surface water treatment process

4. Water quality

1. Physical indicators: water temperature, turbidity, suspended solids, color, smell, taste, etc.

2. Chemical indicators: pH value, hardness, sulfate, chloride, ammonia nitrogen, nitrite, nitrate, oxygen consumption, dissolved oxygen, iron, manganese, lead, mercury, hydride, phenolic compounds and other harmful or toxic substances, radioactive substances, etc.

3. Bacteria: bacteria, coliforms

4. Drinking Water Quality Standards

(1) National drinking water quality standards

(2) World Health Organization Drinking Water Quality Standards

(3) European Community Drinking Water Quality Standards

Five, the main water treatment process:

The purpose of water purification treatment is to remove suspended matter, colloids, germs and other harmful impurities that are harmful to human health and industrial production in raw water, so that the treated water meets the current national drinking water quality standards.

1 . The main unit process used:

1.1 Gas extraction (air lift)

Gas stripping or gas stripping is mainly used to remove dissolved gases in water, such as carbon dioxide, hydrogen sulfide, other substances that cause smell and taste, and volatile organic compounds (VOC). Oxygen also replenishes dissolved iron and manganese in water. Gas is also an important means of providing dissolution in biological treatment.

1.2 Coagulation and sedimentation

The coagulation process is to destabilize the colloid and aggregate into larger particles by adding chemicals to the water, so that it can be separated in the subsequent sedimentation process or intercepted in the filtration process. Coagulation, sedimentation, and filtration are the most important means to remove suspended matter. With the removal of suspended matter, microorganisms such as bacteria can also be reduced to a considerable extent. Coagulation also has a certain removal effect on macromolecular natural organic matter and synthetic organic matter.

1.3 Filtration

Oxidized iron and manganese can be effectively removed in filtration

1.4 Chemical precipitation

Generally used for softening treatment and removal of iron and manganese. Chemical precipitation is also effective for the removal of heavy metals and radioactive pollutants. Chemical precipitation can also remove some dissolved organic compounds and reduce viruses and bacteria. The use of lime for softening treatment and removal of heavy metals and radioactive pollutants is a common method used in chemical precipitation. Potassium permanganate and chlorine are the most common oxidizing agents used to precipitate dissolved iron and manganese.

1.5 Ion exchange

The most widely used fields of ion exchange in water treatment are water softening and desalination. Small softening units using ion exchange are sometimes more economical than lime softening and are easy to automate.

1.6 Membrane treatment

As a water purification process, membrane treatment has developed rapidly in recent years, including reverse osmosis, electrodialysis, microfiltration, ultrafiltration and nanofiltration.

1.7 Chemical oxidation and disinfection

The use of chemical oxidation and disinfection in water treatment can serve a variety of purposes, such as control of biological growth in pools and pipe networks, reduction of color, control of odor and taste, removal of specific organics, improvement of flocculation, oxidation of iron and manganese, and Disinfection etc. The most commonly used oxidants are chlorine, chloramine, ozone, chlorine dioxide, potassium permanganate, etc.

1.8 Adsorption

Activated carbon is mainly used for adsorption, and it is generally used for the removal of dissolved organic matter, the reduction of chroma, and the removal of substances that cause odor and taste.

1.9 Biological treatment

It mainly uses microorganisms to decompose pollutants. It has a good removal effect on ammonia nitrogen, and also has a certain removal effect on organic matter, chroma, iron, manganese, etc., and can reduce the amount of coagulant speculation in subsequent processes.

2. Conventional water treatment process:

(1) A simple process that only uses disinfection

(2) Using slow filter treatment process

(3) Direct filtration treatment process

(4) Coagulation, sedimentation, filtration treatment process

3. Strengthen the conventional water treatment process:

(1) Enhanced coagulation

Main method:

1) Increase the dosage of coagulant to destabilize the inorganic colloid.

2) Adjust the pH value. The pH value of water has a significant effect on the removal of organic matter.

3) Add flocculants to increase adsorption and bridging effects, so that organic matter is easily adhered by flocs and sinks.

4) Improve the mixing, flocculation and other facilities, and improve the hydraulic conditions so that the coagulant can fully play its role.

(2) Enhanced filtration

Main technical measures and technical keys:

1) Choose the right filter material

2) The backwashing of the filter should not only effectively wash away the accumulated mud, but also preserve a certain amount of biofilm on the surface of the filter material. The flushing method and strength should be determined through tests in combination with the selection of filter materials.

3) It is required that the water entering the filter tank has enough dissolved oxygen. The nitrification process of ammonia nitrogen needs to consume dissolved oxygen. When the dissolved oxygen in the raw water is low, the dissolved oxygen can be increased through aeration measures.

4) Do not add chlorine before filtration, and the backwash water should not contain residual chlorine.

5) The effect of the filter to remove ammonia nitrogen is closely related to the temperature.

4. High turbidity water treatment process:

Need to add flocculant and grit chamber

5. Low temperature and low turbidity water treatment process:

The effects of coagulation, flocculation, sedimentation and filtration are all affected at low temperature, but the main contradiction is that the flocculation process is not effective. During the flocculation process, larger flocs were not formed in the end, and the factor of low turbidity played an important role.

(1) Strengthen the coagulation process to promote the gradual formation of coarse flocs from the particles in the water so as to create good conditions for subsequent sedimentation and filtration.

(2) Use the residual activity of sludge to eliminate the deficiency of low turbidity. One is to return the backwash water to the mixing tank to mix with the raw water; the other is to use a mechanical stirring clarifier or a hydraulic circulation clarifier to return the sludge to the flocculation tank.

6. Slightly polluted water treatment process:

When conventional treatment is difficult to make slightly polluted raw water meet drinking water quality standards, the following measures can generally be adopted:

(1) Strengthen routine treatment, such as enhanced coagulation

(2) Increase pretreatment, such as biological pretreatment

(3) Increase post-treatment, such as activated carbon adsorption, biological activated carbon method, membrane treatment, etc. Post-treatment is also called advanced treatment, mainly including ozone, activated carbon, membrane treatment, etc.

7. Eutrophic lake water treatment process:

main problem:

(1) Water quality:

1) Algae

2) Biological smell

3) Iron and manganese

4) Ammonia nitrogen and COD

(2) Water treatment

1. 1. Factory water quality is poor
  2. Water production difficulties
  3. polluted environment

6. Pretreatment

1. High Turbidity Water Pretreatment

1.1 canal grit chamber

1.2 Advection sedimentation tank

1.3 radial flow sedimentation tank

1.4 Inclined tube sedimentation tank

1.5 Cyclone flocculation sedimentation tank

2. Chemical pretreatment

2.1 Chemical pre-oxidation

2.2 Ozone pre-oxidation

2.3 Potassium permanganate pre-oxidation

2.4 Prechlorination

2.5 Chlorine dioxide pre-oxidation

2.6 Ferrate compound agent pre-oxidation

3. Biological pretreatment

3.1 Biological contact oxidation pretreatment of granular filler

3.2 Biological contact oxidation pretreatment of elastic filler

3.3 Biological pretreatment of eutrophic source water

4. Powdered activated carbon adsorption pretreatment

Seven, coagulation

Coagulation is an important process in water treatment. Coagulation includes two stages of coagulation and flocculation. In water supply treatment, adding coagulants to raw water to destroy the stable state of colloidal particles in the water, making the particles easy to contact each other and adsorbing is called coagulation; under certain hydraulic conditions, through the collision and interaction between colloidal particles and other particles Aggregation, thereby forming flocculent substances that are easily separated from water, is called flocculation.

1. The coagulation process

Coagulation removes turbidity and color, and can partially remove inorganic and organic pollutants. In addition, coagulation is also one of the commonly used methods for the removal of synthetic surfactants, radioactive substances, plankton and algae.

2. Commonly used coagulation agents

2.1 Solid aluminum sulfate

2.2 Liquid aluminum sulfate

2.3 Alum

2.4 Ferrous sulfate (green vitriol)

2.5 iron trioxide

2.6 Basic Aluminum Chloride

2.7 Polyaluminum Chloride

3. Commonly used flocculants

3.1 Synthetic polymer flocculant (polyacrylamide)

3.2 Natural plant modified polymer flocculant (FN-A flocculant)

4. Commonly used coagulants

4.1 Chlorine

4.2 Quicklime

4.3 Sodium hydroxide

4.4 Activated silicon salt

4.5 bone glue

4.6 Sodium alginate

5. Coagulant dosing

5.1 Gravity dosing

5.2 Pressure dosing

5.3 Dosing system

6. Coagulant configuration

7. Dosing metering equipment

7.1 Orifice metering

7.2 Float cup measurement

7.3 Rotameter doser

7.4 Dosing metering pump

Driver (motor)
gear mechanism
piston
Pump head: ball check valve including diaphragm, suction port and discharge port
stroke adjuster
Accessories: including filter, pulse damper, back pressure valve, safety valve.

8. Mixing facilities

8.1 Pipeline Mixing

8.2 Mixing Tank Mixing

8.3 Mechanical stirring and mixing

8.4 Water pump mixing

8. Flocculation

1. The process of flocculation

The flocculation process is to make the particles with flocculation performance contact and collide with each other under the action of external force to form larger flocs to meet the requirements of sedimentation and separation. In water purification structures, the equipment that completes the flocculation process is called a flocculation tank. The flocculation process is a very important link in the whole water purification process.

2. Classification of flocculation tanks

2.1 Separator flocculation tank

2.2 folded plate flocculation tank

2.3 Mechanical flocculation tank

2.4 Grid flocculation tank

2.5 perforated swirl flocculation tank

2.6 wave plate flocculation tank

2.7 Swing type stirring flocculation tank

2.8 Contact flocculation tank

3. Technical parameters of flocculation tank

process	Velocity gradient G	Residence time (S)	Velocity Gradient GT
Mixed to flocculated distribution channel	100-150	Variety
High Energy Flocculation for Direct Filtration	20-75	900-1500	40000-75000
Conventional flocculation (before sinking)	10-60	1000-1500	30000-60000

9. Precipitation

1. Precipitation

Sedimentation process refers to the separation of suspended solids from water under the action of gravity. The precipitation process is a very important link in the whole water purification process.

2. Classification of structures during sedimentation

2.1 Sedimentation tank: remove impurities by sinking suspended particles

2.2 Air flotation tank: through the adsorption of micro-bubbles and suspended particles, the relative density is lower than that of water and floats up to remove impurities.

2.3 Clarification tank: through the contact and adsorption of the precipitated sludge and the suspended particles in the raw water, the sedimentation is accelerated to remove impurities.

3. Sedimentation tank classification

3.1 Vertical flow sedimentation tank

3.2 radial flow sedimentation tank

3.3 Straight flow sedimentation tank

single layer sedimentation tank
Double sedimentation tank
multi-layer sedimentation tank
slope bottom sedimentation tank

4. Technical parameters of sedimentation tank (taking advection sedimentation as an example)

Horizontal velocity (mm/s)	Residence time (h)	Retention speed (m/h)	Remark
8-46	0.75-3.00	1.61-3.85

10. Clarification

1. Clarify

Clarification is a process in which the particles in the raw water and the sediment accumulated in the pond collide with each other, absorb and aggregate, and then form flocs and separate from the water, so that the raw water is clarified. The clarifier combines coagulation and solid-liquid separation, and is a water purification structure that completes the process of mixing, flocculation, and suspension separation in one pool.

2. Classification of clarifiers

2.1 Circulation (reflux) sludge type

mechanical stirring
hydraulic circulation

2.2 suspended sludge * sludge filter) type.

Pulse
suspended

3. Technical parameters of the clarifier

The residence time is generally 1.2-1.5h

Eleven, air flotation

1. Air flotation

The air flotation process adopts the artificial introduction of air bubbles into the water to make them adhere to the flocs, thereby greatly reducing the overall density of the flocs, and using the rising speed of the gas to force them to float up, so as to realize the rapid separation of solid and liquid. The purpose is to change the original simple solid-liquid two-phase separation into a more complex three-phase separation of gas, solid and liquid.

2. Classification of water purification and air flotation

2.1 Microporous air flotation method

2.2 Impeller spit air flotation method

2.3 Electrolytic condensation air flotation method

2.4 Vacuum release air flotation method

2.5 Pressure Vessel Floatation Method

2.6 Biological or chemical gas production method

12. Filtration

1. filter

Filtration generally refers to the process of intercepting impurities in water through the surface or filter layer of the filter medium. Filtration is an important part of most surface water treatment processes.

2. Classification of filters

2.1 According to the filter material

single layer filter
double layer filter
multi-layer filter media
Mixed media filter

2.2 According to the backwash water distribution system

(1) Low water head flushing (small resistance) filter

(2) Medium water head flushing (medium resistance) filter

(3) High head flushing (high resistance) filter

2.3 According to the direction of water flow

(1) Downflow filter

(2) Upflow filter

bidirectional flow filter

(4) Amplitude flow filter

2.4 According to the change of filtration rate

(1) Constant speed filter tank

(2) variable speed filter

2.5 According to the filter arrangement

(1) Ordinary (four valve) filter

(2) Double valve filter

(3) Valveless filter

Siphon filter
Mobile hood filter
V type filter

(7) flap filter

3. Filter material

Natural quartz sand, anthracite, granular activated carbon, garnet, ilmenite, etc.

4. Filter backwash

4.1 Filter backwashing method

According to the state of the filter layer: expansion flushing, micro-expansion flushing
According to the flushing method: water flushing, air-water backwashing, water flushing with surface flushing

4.2 Source of filter backwash water

(1) Direct backwashing after filtration

(2) Rinse with high-level pool water

5. Filter technical parameters

category	Particle size (mm)	Filter layer thickness (mm)	Filtration rate (m/h)
Quartz sand filter	0.5-1.2	700	8-10
double layer filter	Anthracite 0.8-1.8	300-400	10-14
double layer filter	quartz sand 0.5-1.2	400	10-14
Three layers of filter material	Anthracite 0.8-1.8	450	18-20
	quartz sand 0.5-1.2	230
	Heavy ore 0.25-0.5	70

13. Advanced processing

1. Activated carbon adsorption

2. Ozone activated carbon adsorption

14. Disinfection

1. Chlorine disinfection

The purpose of chlorine disinfection is to eliminate various bacteria, spores, viruses, etc. in water.

2. Factors affecting the disinfection process

(1) The type, concentration and distribution of microorganisms

(2) The characteristics, concentration and contact time of the disinfectant

(3) pH value, temperature, other organic matter or magazines in the water

3. Chloramine disinfection

Applicable scope:

Raw water has more organic matter.
The factory water pipeline is long.

4. Chlorine dioxide disinfection

5. Ozone disinfection

6. Other disinfection methods

(1) Ultraviolet disinfection method

(2) Electric field disinfection method

(3) Solid phase contact disinfection method

(4) Ultrasonic disinfection method

(5) Photocatalytic oxidation disinfection method

Lecture 2 Water plant equipment

one. Electrical Equipment

1. Water pump

1.1 Classification

(1) According to the principle, it is divided into vane pump, positive displacement pump and screw pump

(2) centrifugal pump

(3) Submersible centrifugal pump

(4) Axial flow pump and mixed flow pump

(5) Progressive cavity pump

(6) Diaphragm positive displacement pump

(7) Screw pump

2. motor

3. blower

3.1 Centrifugal blower

3.2 Roots blower

3. blower

3.1 Centrifugal blower

3.2 Roots blower

4. Air compressor

4.1 Sliding vane compressor

4.2 Screw compressors

4.3 Liquid Ring Compressor

4.4 Piston compressors

4.5 Diaphragm compressor

5. Grille decontamination machine

5.1 Mobile grid decontamination machine

5.2 Pin-tooth grill decontamination machine

5.3 High chain type automatic grill decontamination machine

5.4 Curved grill decontamination machine

5.5 Steel wire grille decontamination machine

5.6 Back rake type grill decontamination machine

5.7 Walking grill decontamination machine

6. Sand removal and sand water separation equipment

6.1 Grab type desander

6.2 Truss truck pump suction desander

6.3 Chain Bucket Desander

6.4 Sand water separator

6.5 Pressure type inclined plate sand remover

6.6 XS sand remover

7. mud scraper

7.1 Chain scraper type mud scraper

7.2 Truss car mud scraper

7.3 Rotary mud scraper

8. Suction dredge

8.1 Truss truck type suction dredger

8.2 Rotary suction dredge

9. Valve

9.1 Classification

(1) In terms of form, there are butterfly valves, gate valves, gate valves, and ball valves;

(2) In terms of function, there are mud discharge valve and check valve;

(3) There are manual valves, electric valves, and pneumatic valves in terms of execution methods.

10. Blender

2. Chlorination equipment

1. Major manufacturers

American WALLACE&TIERNAN company
American CAPITAL (capital) company
Germany ALLDOS company
Jesco UK

2. Form

wall mounted
cabinet

3. Composition of Chlorination System

⑴ Air source system

⑵ Vacuum chlorination system

⑶ Pressure water supply system

⑷ Electrical, control and testing instrument system

⑸ Chlorine gas leakage detection and safety protection system

3.1 Air source system

Generally, two groups of gas sources are set up, and each group of gas sources is composed of several chlorine bottles. After one group of chlorine cylinders is supplied with chlorine gas, the automatic switching device automatically switches to another group of chlorine cylinders to ensure continuous supply of chlorine gas. A chlorine gas filter is installed in the gas source so that the inlet valve of the vacuum regulator can work reliably.

Gas source switch: pressure switch, vacuum switch.

3.2 Vacuum chlorination system

The vacuum chlorination system includes:

⑴ Vacuum regulator:

Two vacuum regulators, one for use and one for standby. The vacuum regulator depressurizes the chlorine gas under positive pressure to a vacuum state. Only when the outlet of the vacuum regulator reaches a certain degree of vacuum, the inlet valve will open, otherwise it will be closed automatically, so that the system can operate in a safe vacuum state. The vacuum regulator consists of an inlet regulating valve and a pressure relief valve.

The function of the inlet regulating valve is that when the outlet of the regulator reaches above the set vacuum degree, the regulating valve will open, and the negative pressure chlorine gas will enter the chlorinator, otherwise the valve will close.

The function of the pressure release valve is that when the chlorination system is shut down, if the inlet valve cannot be completely closed, a small amount of chlorine gas will leak into the negative pressure chamber of the regulator, and a positive pressure will appear. At this time, the release valve will open to release the leaked chlorine gas. Discharge to a safe area.

⑵ Chlorinator

The standard chlorinator is equipped with a flow meter, a vacuum pressure gauge, a chlorination automatic regulating valve, a chlorination servo motor, and a compound ring controller (PCU unit). Choose a cabinet-type vacuum chlorinator, with a proportional flow controller (SCU unit) for the front chlorinator, and a compound ring control cabinet (PCU cabinet) for the rear chlorinator and supplementary chlorinator. For detailed control methods, see the control design section of the chlorine dosing room.

⑶ water ejector

The ejector generates the vacuum required for the system to work by the rapid flow of pressurized water. In order to prevent damage to the chlorinator due to backflow into the chlorinator when the chlorination is stopped, a check valve and a drain valve are provided in the injector. Chlorine gas and pressurized water form a chlorine solution during the water injection period, which is injected to the chlorine addition point through a diffuser.

3.3 Pressure water supply system

In order to ensure the pressure stability of the injector of the chlorination system, a pipeline booster pump is installed at each dosing point for boosting (a total of six pipeline booster pumps, five for one standby). This can ensure the stability of its pressure and facilitate the adjustment of automatic chlorine dosing. The pressure water supply system should be equipped with a pressure transmitter on each pressurized water pipe to facilitate timely alarm when the pressure is low . The inlet of the booster pump is equipped with a filter to prevent debris from entering the injector to affect chlorination or damage the injector.

3.4 Electrical, control and instrumentation systems

Contains the following sections:

⑴ Electric control part of chlorinator:

The electric control part of the chlorinator mainly includes an electrical junction box, a chlorination servo motor, a position transmitter, etc.

⑵ Residual chlorine analyzer:

The residual chlorine analyzer continuously measures the amount of free residual chlorine in water. The sampling point is set after the chlorination point of the filtered water. The residual chlorine analyzer outputs 4-20mA residual chlorine signal to the controller and PLC of the rear chlorination machine, and the chlorine addition controller realizes automatic chlorine addition control according to the detected flow rate and residual chlorine.

3.5 Chlorine leakage detection and safety protection system

The system includes:

⑴ Chlorine leakage alarm device:

The chlorine leakage alarm device contains two chlorine leakage probes, one is installed in the chlorine bottle room, and the other is installed in the chlorinator room. Each probe can be set with two levels of alarm. When the chlorine leak detector detects that the concentration of chlorine in the indoor air is higher than the allowable value, the chlorine leak detector will send an alarm and send the alarm signal to the PLC station, and the management computer will send out an audible and visual alarm.

⑵ Chlorine absorption device:

The chlorine absorption device is a domestic chlorine absorption device with a chlorine absorption capacity of 1 ton. This device is automatically activated when chlorine gas leaks to absorb the leaked chlorine gas to ensure personal safety.

⑶ Hydraulic electronic scale:

In order to ensure the safe operation of the chlorination system, prevent the backflow of chlorine gas, and grasp the weight of the remaining liquid chlorine in the chlorine bottle in time, a hydraulic electronic scale is equipped. The weight of the chlorine bottle is displayed on the spot.

3. Dosing equipment

1. Major manufacturers

(1) American Milton Roy Company

(2) American WALLACE&TIERNAN Company

(3) Germany ALLDOS company

(4) German ProMinent company

(4) Germany BRAN+LUEBBE company

2. Form

(1) Mechanical plunger pump

(2) Mechanical diaphragm pumps

(3) Hydraulic diaphragm pump

3. Dosing system process

The dosing system of the whole water plant consists of six parts:

⑴ Added commercial drugs

⑵ Liquid preparation and input part

⑶ Dosing equipment

⑷ Liquid medicine output part

⑸ Liquid dosing point

⑹ Electrical, control and testing instrument system

3.1 Added commercial drugs

The commercial drug to be added adopts liquid and solid aluminum sulfate. When injecting solid medicine, dilute it with water, stir it with compressed gas in the solution pool, and then use the metering pump for pressure dosing; if the medicine to be added is in liquid state, it can be directly input from the liquid storage pool into the solution pool for dilution, and in the solution pool Use compressed gas for stirring, and then use a metering pump for pressure dosing.

3.2 Liquid preparation and input part

⑴ Drug storage pools: Two drug storage pools are set up in the drug storehouse to store liquid medicines for preparation of dispensing and dosing.

(2) Stirring equipment: In order to cooperate with the dissolution of the drug and the smooth dosing of the drug, it is equipped with a compressed gas stirring device. The stirring equipment adopts blower for stirring. The advantage of choosing a blower for stirring is that the stirring is uniform, and since it does not directly contact with the medicine with the stirring equipment, it has no corrosive effect on the equipment.

⑶ Liquid medicine delivery pipeline: composed of PVC pipe, PVC electric ball valve and manual ball valve. ABS pipes are also available.

⑷ Diluted and dissolved water pipes: composed of PVC pipes, electric valves and manual ball valves. ABS pipes are also available.

3.3 Dosing equipment

The dosing equipment adopts a metering pump that can be adjusted by variable frequency and stroke .

3.4 Liquid medicine output part

⑴ Pulse damper

The pulse damper is composed of upper and lower chambers and a middle diaphragm. The upper chamber is filled with inert gas, and the lower chamber is connected to the liquid outlet pipeline, forming a gaseous compressible space in the liquid outlet pipeline, thereby reducing the impact of pulsating liquid flow on the plastic PVC pipe. The impact of the road makes the output liquid flow more stable.

⑵ Safety valve

Avoid overpressure at the pipeline or pump head due to valve misoperation or pipeline blockage, resulting in equipment damage or accidents. In the case of overpressure, the safety valve opens and the liquid medicine is introduced into the medicine pool.

⑶ Back pressure valve

Maintain pump outlet pressure to prevent siphon phenomenon.

⑷ Syringe

Made of PVC material, with check valve to prevent backflow.

3.5 Throw Points

The dosing point is set on the outlet main pipe of the surge well before the mixing equipment (pipeline mixer).

3.6 Electrical, control testing and instrumentation systems

⑴ Stroke servo motor

The stroke servo motor receives a standard signal of 4-20mA and automatically adjusts the stroke length (0-100%) of the metering pump. There are two ways of stroke remote adjustment: remote manual adjustment and automatic adjustment. The remote manual adjustment is to adjust the stroke through the buttons on the stroke controller. The automatic adjustment is that the stroke drive servo motor receives the 4-20mA signal output by the PLC to adjust the stroke.

⑵ Frequency converter

By changing the power supply frequency, the speed of the metering pump motor is adjusted to adjust the dosage. There are two ways of frequency adjustment: keyboard operation and remote adjustment. Keyboard operation is to adjust the frequency through the buttons on the keyboard of the frequency converter. Remote adjustment is to receive the 4-20mA or 0-5V signal output by PLC to adjust the frequency.

⑶ Ultrasonic liquid level gauge:

It is used to measure the liquid level of the medicine pool, and send the liquid level value to the PLC of the dosing station. When the measured liquid level is lower than the set value, the PLC realizes it by controlling the switch of the electric ball valve in the dosing system. Automatic switching of medicine pool.

4. Meter

1. Classification of instruments

Water plants use online meters

(1) Process instruments: water level gauge, pressure transmitter, flow meter, differential pressure gauge, etc.

(2) Water quality instruments: temperature meter, PH value meter, turbidity meter, ammonia nitrogen analyzer, SCD (dissociated current meter), residual chlorine analyzer, dissolved oxygen meter, etc.

(3) Electrical instruments: Ammeter, Voltmeter, Active Power Meter, Reactive Power Meter, Power Factor Meter, Electricity Meter (All these instruments output standard signals of 4-20mA or 1-5V.)

2. The output signal of the meter

(1) 4-20mA current

(2) 0-5V voltage

Pulse signal

3. Common Instruments

3.1 Turbidimeter

3.1.1 Category

(1) High Turbidimeter

(2) Low Turbidimeter

3.1.2 Major Manufacturers

(1) American HACH Company

(2) American HF Company

(3) Germany E+H Company

3.2 Flow meter

3.2.1 Category

(1) Electromagnetic flowmeter

(2) Ultrasonic flowmeter (sub-bundle type and plug-in type)

(3) Turbine flowmeter

3.2.2 Major Manufacturers

(1) Shanghai Guanghua Company

(2) Siemens AG, Germany

(3) Germany E+H Company

3.3 pH meter

(1) Siemens AG, Germany

(2) Germany E+H Company

(3) Germany ALLDOS company

(4) American HACH Company

(5) American Milton Roy Company

3.4 Residual Chlorine Analyzer

(1) American W&T Corporation

(2) American CAPITAL company

(3) Germany ALLDOS company

(4) American HACH Company

3.5 Swimming current meter

(1) American Milton Roy Company

(2) British SCD instrument

(3) American HF Company

(4) Beijing Single Factor Company

3.6 Level gauge

3.6.1 Form

(1) Contact type (drop-in type)

(2) Non-contact (ultrasonic and radar)

3.6.2 Major Manufacturers

(1) Siemens AG, Germany

(2) Germany E+H Company

(3) American Rosemount Corporation

3.7 Pressure transmitter

3.7.1 Form

(1) pressure sensitive

(2) capacitive

3.7.2 Major Manufacturers

(1) Siemens AG, Germany

(2) Germany E+H Company

(3) American Rosemount Corporation

five. Electrical Equipment

1. Power supply

Requires secondary power supply (2 incoming lines, one for backup and one for use) Low voltage 380V AC (for general water intake pumps); high voltage 6KV or 10KV (for water delivery pumps)

2. Power distribution equipment

Transformers, incoming line cabinets, capacitor cabinets, switch cabinets, metering cabinets, connection cabinets (two-way incoming line connection) and control cabinets.

3. Electrical control equipment (devices)

six. Automatic control equipment

1. Programmable Logic Controller (PLC)

2. Industrial Control Computer (IPC)

3. Computer (PC)

4. Control cabinet

5. control box

6. Internet equipment

7. Monitoring equipment

Lecture 3 Introduction to Automatic Control System of Waterworks

one. basic concept

1. Open loop system: A control system without a feedback signal.

2. Closed-loop control: a control system with a feedback signal.

two. Automatic control system structure

1. Centralized

2. Decentralized

3. Distributed: decentralized control, centralized management.

three. Composition of water plant automatic control system

1. Controller

Programmable Logic Controller (PLC)
Industrial Control Computer (IPC)
Computer (PC)

2. structure

Generally, the "reaction﹑precipitation" station is merged into the "dosing" station, and the "power distribution" station is merged into the "water delivery" station.

4. Selection of PLC

The control system engineering developed by our company generally uses PLCs from AB, Schneider, and Siemens.

1. American Rockwell Corporation

1.1 Products

(1) PLC5 series

(2) ControlLogix series

(3) SLC500 series

(4) MicroLogix series (1000 type; 1200 type; 1500 type).

1.2 Network

(1) DH+ network (Data Hight Plus)………………………………38K/s

(2) DH485 network……………………………………… 19.6K/s

(3) Industrial Ethernet………………………………………….10M/S

(4) Control Net………………………………………………..5M/s

(5) Driver Net…………………………………………………

2. Schneider Corporation

Schneider's products include American Modicom products and French TE products.

2.1 Products

(1) Modicom products include 984 series, Quantum series and Momentum series.

(2) TE products include Preminm series, Micro series and Nano series.

2.2 Network

(1) MB+ network……………………………………………………..1M/s

(2) Industrial Ethernet……………………………………..10M/S

(3) TE network has:

UNI-TELWAY

TELWAY

FIPWAY

ETHWAY

3. Siemens

3.1 Products

(1) S5 series

(2) S7-400 series

(3) S7-300 series

(4) S7-200 series.

3.2 Network

(1) Industrial Ethernet

(2) Profbus-DA

(3) Profbus-DP

(4) Profbus-FMS

Four, PLC module type

(1) DI—digital input

(2) DO—switch output

(3) AI—analog input (0-5V, 4-20mA)

(4) AO—analog output (0-5V, 4-20mA)

(5) PI—pulse count input

(6) RI—thermocouple input

Five, automatic control system PLC programming, the programming method to be followed

(1) Top-down, step by step refinement.

(2) Modular-structured

(3) Addressing skills

6. Lower computer programming

(1) Ladder diagram

(2) Statement list

(3) SFC

7. The upper computer programming generally uses the configuration method.

8. Requirements for the automatic control system of the water plant

1. Control design of water intake pumping station

1.1 PLC control object

⑴ Intake pump, outlet valve, vacuum solenoid valve

⑵ Sewage pump

⑶ vacuum pump

1.2 Monitoring objects

⑴ Intake pump running status

●Remote control

●Manual

● run

●stop

●Fault

●This running time

●Cumulative running time

●Last downtime

●This startup time

⑵ Electrical parameters of water intake pump room:

●Phase current: I1, I2, I3

●Effective residual current: Io

●Voltage: U21, U32, U13, V1, V2, V3)

●Residual voltage: Vo

●Active power: P

●Reactive power: Q

●Power factor

●Frequency

●Active energy: -Wh

●Reactive power: -VARh

⑶ Control cabinet status: closing, opening, fault

⑷ Status of water intake outlet valve: manual, automatic, fully open, fully closed, fault

⑸ Water pump outlet pressure

⑹ The pressure of the main water intake pipe

⑺ Suction well water level

⑻ Raw water flow, daily water intake, cumulative water intake

⑼ Raw water turbidity

⑽ PH value of raw water

⑾ Raw water ammonia nitrogen

⑿ Raw water temperature

⒀ Dissolved oxygen in raw water

⒁ High water level of drainage well

⒂ Drain pump status

⒃ Vacuum pump status

⒄ The status of the vacuum solenoid valve of the water intake pump

1.3 Control method of water intake pump

1.3.1 Automatic control mode

According to the water level of the clear water pool, the PLC realizes automatic start/stop of the fixed pump to control the water intake pump; and detects the operating conditions and data of the pump, and performs fault protection for the controlled equipment.

In the configuration man-machine interface, the operator can set the upper limit water level, ultra-high limit water level, low water level, and ultra-low limit stop water pump water level of the clean water tank. The specific control method should be perfected according to the user's process requirements.

When the water level of the suction well of the water intake room drops to the ultra-low limit water level, the PLC automatically stops the water intake pump.

1.3.2 Manual control mode of central control

The PLC receives the commands issued by the computer in the central control room through the keyboard or mouse, starts/stops the water pump unit, and performs fault protection for the controlled equipment.

1.3.3 Local manual control mode of water intake pump

In the manual mode, the on/off control of the water pump unit is carried out through the button on the local switch cabinet. PLC only detects it and does not perform fault protection.

1.3.4 Water intake pump protection measures

⑴ Over-current pre-alarm:

When the pump motor current is greater than the pre-alarm current setting value, the computer will give an audible and visual alarm.

⑵ Overcurrent fault:

When the current of the water pump motor is greater than the rated current, the water outlet valve and the water pump will be closed immediately, and the computer will alarm with sound and light.

⑶ Empty car failure:

When the current of the water pump motor is less than the rated current or the water outlet pressure is lower than the normal value, it is an empty pump failure, immediately shut down for protection, and the computer sounds and lights alarm.

⑷ Electrical failure:

After the water pump motor starts and runs normally, if the running signal continues to lose for 5 seconds, it is an "electrical" failure, the PLC will stop immediately for protection, and the computer will alarm with sound and light.

1.4 Fault monitoring and protection of power transformation and distribution system

PLC automatically detects current and voltage signals, and PLC automatically judges "overvoltage fault", "undervoltage fault", "overcurrent fault", "disconnection fault" and other faults of power transformation and distribution systems detected by PLC. According to the different conditions of various faults, the screen cabinets of the power transformation and distribution equipment will be protected accordingly, and sound and light alarms will be given.

1.5 Drain pump control

The drainage pump is automatically controlled on the spot according to the water level of the drainage well, and the PLC only detects and alarms it.

1.6 Vacuum system control

When starting a water intake pump, the PLC automatically opens the vacuum solenoid valve to check the vacuum degree, and starts the vacuum pump until the vacuum is formed when the vacuum degree is not enough.

2. Dosing control design

2.1 Control object

⑴Coagulant metering pump

⑵ Add coagulant and add coagulant aid mixer system

⑶ solution pool water inlet electric valve

⑷Electric valve for dispensing medicine from the solution pool

⑸Solution pool intake electric valve

⑹Solution pool feeding electric valve

⑺Electric valve for dispensing medicine from the medicine storage pool

⑻Dosing and stirring device electric valve for medicine discharge

⑼ Coagulant metering pump outlet electric valve

⑽ Stirring blower

⑾ Stirring blower electric valve

⑿Dosing and stirring device

⒀ Sewage pump

2.2 Monitoring objects

(1) Turbidity:

●Raw water turbidity

●Turbidity of sedimentation tank effluent

●Turbidity of filtered water

●Turbidity of factory water

(2) Source water dissolved oxygen

(3) Source water ammonia nitrogen

(4) pH value

●pH value of source water

●pH value after precipitation

●pH value of factory water

(5) Source water temperature

(6) Residual chlorine

●Residual chlorine in water after precipitation

●Residual chlorine in filtered water

●Residual chlorine in factory water

(7) Raw water flow

●Raw water flow

●Filtered water flow

(8) Liquid level

●Solution tank liquid level

●Reservoir liquid level

●Dosing device liquid level

(9) Dosing flow rate

●dosing flow

(10) Electric valve status

●Status of the water inlet electric valve of the solution pool: manual, automatic, fully open, fully closed, fault

●Status of the electric valve for dispensing medicine in the solution pool: manual, automatic, fully open, fully closed, fault

The state of the electric valve of the intake air of the solution pool: manual, automatic, fully open, fully closed, fault

●Status of the electric valve for feeding medicine in the solution pool: manual, automatic, fully open, fully closed, fault

●Status of the electric valve for medicine discharge in the medicine storage pool: manual, automatic, fully open, fully closed, fault

●Status of the electric valve of the drug dosing and stirring device: manual, automatic, fully open, fully closed, fault

●Status of the electric valve at the outlet of the coagulant metering pump: manual, automatic, fully open, fully closed, fault

Stirring blower electric valve status: manual, automatic, fully open, fully closed, fault

●Status of the electric valve for feeding medicine in the solution pool: manual, automatic, fully open, fully closed, fault

●Status of the electric valve for medicine discharge in the medicine storage pool: manual, automatic, fully open, fully closed, fault

●Status of the electric valve of the drug dosing and stirring device: manual, automatic, fully open, fully closed, fault

(11) Metering pump status

●Remote control

●Manual

● run

●stop

●Fault

●Stroke,

●Frequency

●This running time

●Cumulative running time

(12) Stirring blower status

●Manual

●Auto

● run

●stop

●Fault

●This running time

●Cumulative running time

2.3 Control design of dosing system

2.3.1 Preparation of liquid medicine

The preparation of the medicinal solution is completed in the medicinal reservoir and the solution reservoir. The dissolution of the solution pool is fixed, and after the concentrated liquid of the drug storage pool enters the solution pool, it is filled with water for dilution and stirring. There are two ways of automatic medicine liquid dispensing: manual dispensing by upper computer and fully automatic dispensing.

The process of automatic liquid configuration is as follows:

(1) The upper computer manually selects the dispensing

The operator selects the dispensing mode as "host computer manual dispensing" mode, and the upper computer manual dispensing is beneficial for the operator to monitor the entire dispensing process.

When the liquid level of the working solution pool drops to the set level, the PLC automatically closes the outlet valve of the medicine pool, and at the same time opens the outlet valve of the spare medicine pool to ensure continuous medicine supply, and at the same time sends an "empty pool" alarm signal to request dispensing . After the operator receives the "empty pool" alarm signal, he presses the "dispensing" button on the host computer, and the PLC automatically enters the dispensing program: the PLC opens the medicine outlet valve of the medicine storage tank, and then opens the medicine inlet valve of the solution pool. Because the liquid level value of the dope flowing into the solution pool each time is constant, the water intake capacity is also constant, and the prepared concentration is also basically fixed. When the liquid level of concentrated liquid flowing into the solution pool is equal to the set feed liquid level, the PLC automatically opens the water inlet valve of the solution pool. When the water level rises to the set water level, the water inlet valve is closed and the stirring blower is turned on. The stirring time can be set by the computer. Certainly. After the dissolution process is completed, the drug pool automatically enters the standby state.

(2) Fully automatic dispensing

The operator selects the dispensing mode as "full automatic dispensing", and the fully automatic dispensing is conducive to completing the entire dispensing process when no one is on duty.

When the liquid level of the working solution pool drops to the set level, the PLC automatically closes the outlet valve of the medicine pool, and at the same time opens the outlet valve of the spare medicine pool to ensure continuous medicine supply, and at the same time sends an "empty pool" alarm signal to request dispensing . Ten minutes after the "empty pool" alarm signal, the PLC automatically enters the dispensing program: the PLC opens the medicine outlet valve of the medicine storage pool, and then opens the medicine inlet valve of the solution pool. Because the liquid level value of the dope flowing into the solution pool each time is constant, the water intake capacity is also constant, and the prepared concentration is also basically fixed. When the liquid level of concentrated liquid flowing into the solution pool is equal to the set feed liquid level, the PLC automatically opens the water inlet valve of the solution pool. When the water level rises to the set water level, the water inlet valve is closed and the stirring blower is turned on. The stirring time can be set by the computer. Certainly. After the dissolution process is completed, the drug pool automatically enters the standby state.

2.3.2 Automatic switching of medicine pool

There are two medicine pools, one for use and one for standby. When the liquid level of the medicine pool drops to the set level, the PLC will automatically close the outlet valve of the medicine pool, and at the same time open the outlet valve of the spare medicine pool to ensure continuous medicine supply, and at the same time send out " Empty tank” alarm signal, request dispensing.

2.3.3 Stirring of the medicine pool

The medicine pool in use is automatically stirred for a few minutes at regular intervals, and the time is adjustable (manually set by the computer in the central control room). PLC detects the liquid flow, the operating frequency and stroke of the dosing pump, and calculates the dosing flow. If the actual measured dosing flow rate is lower than 40% of the expected dosing flow rate, the PLC determines that the dosing pipeline is blocked and issues a fault alarm.

2.3.4 Dosing control principle and comparison

Timely and accurate dosing of the required coagulant dosage according to the change of water quality and quantity is the key issue to obtain perfect coagulation effect. In the past, it was manually operated, and the dosing was judged by the turbidity after precipitation and the shape of alum flowers in the reaction tank. The hysteresis factor is strong and the continuity is poor, so the dosage is difficult to be accurate. Consumption of alum is often greater than the actual demand. Since the 1980s, people have explored various automatic dosing technologies for feedforward control based on raw water quality. In the world, such as mathematical model method, model filter method and flowing current method, etc., but due to the change of factors affecting the coagulation effect of raw water (flow, turbidity, pH, alkalinity, temperature, oxygen consumption and ammonia nitrogen, etc.) Too much, so that the automatic control effect of adding coagulant is difficult to stabilize, the interference is strong, and the operation is unsatisfactory, which has become a difficult problem and the focus of realizing the automation of water plants.

The purpose of implementing automatic coagulant filling is first to stabilize water quality, secondly to save a certain amount of coagulant due to reasonable filling, and thirdly to save labor. There are usually two considerations about the goal of water quality. One is that under the same conditions, the turbidity of the filtered water is basically proportional to the turbidity of the water to be filtered, so the turbidity of the effluent from the sedimentation tank is required to meet a certain target requirement; the other One is to use the turbidity of the filtered water as the target requirement, which includes factors such as changes in the filtration characteristics and operating conditions of the filter when the raw water quality changes greatly. Usually, the turbidity of the sedimentation tank effluent is used as the control target for coagulant injection. In addition to stably reducing the turbidity of the factory water to a certain target value, the implementation of coagulant filling automation also requires cost reduction. There are many ways to add coagulant control. At present, the following types are commonly used in China:

(1) Use a streaming current detector (SCD) to control the dosing.

(2) Using the single factor method to control the dosing.

(3) The underwater photographic analysis method of "alum flower" using the reaction pool is usually called FCD (Flocclation Control Device) technology.

(4) Self-built mathematical models for raw water turbidity, temperature, PH value, flow and other factors are used, and the turbidity after precipitation is used as a feedback reference value for control.

The principle of the single factor method is essentially the same as that of the streaming current method, except that the measuring instrument is made in China. This method has no advantages in terms of equipment performance or price.

The principle of underwater photography is very good, but it is very difficult to implement it, and there are not many implementations in China.

The methods of self-built mathematical models are some individual examples and cannot be promoted as experience.

The coagulant injection is automatically controlled by a streaming current detector (SCD). In this scheme, a streaming current detector (SCD) is used to implement automatic control of coagulant injection. There are many successful examples of this program both at home and abroad, and we have adopted it in most projects and received good results. Some of the unsatisfactory results of individual use mainly have the following reasons:

(1) The installation location of the sampling point and the SCD instrument is not suitable, the instrument is easily disturbed by the external environment, and the automatic control of dosing will fail;

⑵The SCD instrument is not regularly maintained;

(3) Part of the medicament has an adsorption effect on the SCD probe;

(4) Improper selection of control model

The measurement of the streaming current (SCD) value is also the indirect measurement of the streaming potential (Zeat value). The SCD value when the sedimentation tank effluent turbidity target is required is used as the set value, the measured flow current value is compared with the set value, and the dosage is adjusted in time through the PID adjustment of the controller. There are two control models in this way. One is to use the flow current value (SCD value) feedback to control the frequency of the coagulant dosing pump through PID adjustment when the raw water flow rate changes little or does not change suddenly, so that the SCD value is controlled within the set range. To achieve the goal of controlling the turbidity of the effluent from the sedimentation tank, the control model is shown in Figure 1.

The control mathematical model shown in Figure 1 is as follows:

IO=KP(E)+Ki∫0t(e)dt+Kd*d(E)/dt+B

Among them: IO=controller output (4~20mA)

B=Output Compensation or Feedforward

E= Deviation (setpoint SP-process variable PV)

KP=proportional gain

Ki = integral gain (1/sec)

Kd = differential regulation (sec)

For the control model one (see Figure 1), due to the single-loop control, the frequency of the dosing pump is controlled by the SCD value feedback through the PID adjustment output. This control model does not require the raw water flow rate, which can reduce the raw water flow meter, and at the same time, the dosing pump does not need to automatically adjust the stroke. If there is a raw water flow signal, the output compensation or feedforward B takes a value proportional to the raw water flow. Due to the slow response of the SCD instrument, it is not suitable for water plants with large changes in raw water flow or frequent sudden changes.

The other is the flow current value as the controlled object, the raw water flow rate is used to control the frequency of the coagulant injection pump, and the SCD value feedback controls the stroke of the coagulant injection pump through PID adjustment. The control model is shown in Figure 2.

For control model 2 (see Figure 2), due to the use of dual-loop control, that is, the frequency of the dosing pump is controlled by the raw water flow rate, and the SCD value feedback controls the stroke of the dosing pump through PID adjustment. The control model requires raw water flow signal and dosing pump stroke automatic adjustment device. The output compensation or feed-forward B of this control model can be set to zero.

The SCD setting value generally varies with the seasons and the raw water quality. The setting value of SCD can be determined according to the stirring experiment.

The PID adjustment parameters are set according to the raw water quality and experience. The function of proportional (P) adjustment is to quickly adjust the size of the deviation. If the deviation is large, the adjustment effect will be large, and if the deviation is small, the adjustment effect will be small. Integral (I) adjustment effect is to gradually change the adjustment effect. If the deviation is large, the adjustment effect changes quickly, and vice versa. The role of differential (D) regulation is to quickly eliminate the deviation. According to experience, the differential gain Kd value should not be too large.

The mathematical model of its control is:

IO=Km*Kf*Qm+(1-Km)[KP(E)+Ki∫0t(e)dt+Kd*d(E)/dt+B]

Among them: IO=controller output (4~20mA)

B=Output Compensation or Feedforward

E= Deviation (setpoint SP-process variable PV)

KP=proportional gain

Ki = integral gain (1/sec)

Kd = differential regulation (sec)

Km=composite ring coefficient (less than 1)

Kf=proportionality factor

Qm=instantaneous flow of raw water

This program adopts the second control model. This control model has been adopted by us in many projects and has received good results.

According to the instantaneous flow rate of raw water, the maximum and minimum value of the dosing output are limited to ensure that the frequency and stroke of the metering pump operate within a certain range.

FCD underwater photography method (hereinafter referred to as FCD), its principle is advanced, and it is also a new topic of water treatment that European countries are studying in recent years. Due to the complexity of its mathematical calculation model, it is difficult to implement it, and it is implemented in some water plants in China. FCD technology is jointly developed and researched by the Water Supply Committee of the Water Industry Branch of the China Civil Engineering Society and the Science and Technology Committee of the China Urban Water Supply Association and Shanghai University. Applying the latest flocculation control theory in the world today, directly using the relationship between the floc shape and quantity after flocculation, the dosing metering and the effect of the sedimentation tank, the complex automatic process of dosing is expressed with simple and intuitive images and accurate data. Reflect the coagulation effect and reasonably determine the optimal dosage. Thus, the dosing automation control has reached a new level. And created two online measurement and control instruments, the display flocculation control device FCD and the flocculation display device FMD.

Working principle of FCD:

Underwater camera is carried out in real time, and the moving images of flocs (alum flowers) are captured, which are enlarged and sent to the computer image interface, and the display screen directly displays the image of the distribution state of flocs in water after flocculation. And the real-time image processing is carried out by the computer to calculate the parameters related to the turbidity of the effluent of the sedimentation tank, calculate the real-time "equivalent diameter" value of the "floccule", and combine the set target value and water inflow to calculate the amount of alum liquid filling , and then converted into a standard current signal to control the filling pump, realize automatic control, and optimize the dosing of the medicine.

At the same time, FCD adopts the turbidity feedback method after precipitation to correct the deviation caused by various factors and make the control more accurate. Since the system adopts the concept of the equivalent diameter of floc particles to replace the overall effect of flocculation, the turbidity of the effluent is judged, and the dosage should be calculated, which avoids the hysteresis problem caused by the traditional use of turbidity control after precipitation.

After years of experimental research, the "equivalent diameter" of flocculation has established a new concept reflecting the effect of flocculation. According to the study, this concept value reflects the representative value of all particles when they are settled in the sedimentation tank. It is also a representative value for judging the sedimentation effect under a certain amount of flocculant injection. The use of "equivalent diameter" avoids the interference of different water quality of raw water and various influencing factors that cause the flocculation effect. Directly judge whether the turbidity of the effluent of the sedimentation water meets the target. If the FCD technology is successfully applied, it will be scientific and intelligent beyond the judgment of an experienced operator on the sedimentation effect at the side of the sedimentation tank.

At present, the best method for domestic application is: use the self-built mathematical model of raw water turbidity, temperature, PH value, raw water flow and other factors to form an adaptive feedforward control, use the FCD value as the middle feed, and use the turbidity after precipitation as the control. Three-level control of feedback.

The FCD value is used as the controlled object, and the frequency of the coagulant dosing pump is controlled by the self-built mathematical model of the raw water flow rate. The FCD value feedback controls the stroke of the coagulant injection pump through PID adjustment, and the turbidity after sedimentation is used as the feedback The control model is shown in Figure 2.

For control model 2 (see Figure 2), due to the use of multi-level loop control, that is, the frequency of the dosing pump is controlled by the raw water flow rate, and the FCD value feedback controls the stroke of the dosing pump through PID adjustment, and the final control is based on the water turbidity after precipitation The target value is fed back to correct the three-level control model of dosing. This control model requires a raw water flow signal and an automatic adjustment device for the stroke of the dosing pump.

The FCD setting value generally varies with the difference of raw water turbidity and raw water flow. The setting value of FCD can be fuzzily corrected by the computer itself.

The mathematical model of its control is:

IO1=Km1*Kf*Q1+(1-Km1)[KP1(E) +Kd1*d(E)/dt+B1]

IO2=Km2*Kf*Q2+(1-Km2)[KP2(E)+Ki2∫0t(e)dt+Kd2*d(E)/dt+B2

Among them: IO1, IO2 = controller output (4~20mA)

B=Output Compensation or Feedforward

E= Deviation (setpoint SP-process variable PV)

KP=proportional gain

Ki = integral gain (1/sec)

Kd = differential regulation (sec)

Km=composite ring coefficient (less than 1)

Kf=proportionality factor

Q=instantaneous flow of raw water

The most common disturbance is the change of raw water flow, which is also one of the main disturbance factors. It can be known from the function of the working principle of the metering pump:

q=K·60/P(1-S) fH=KfH (q is output flow, K characteristic constant, P pole pairs, S slip, F other possible disturbance parameters)

Usually we can replace the F(IO1) function by converting q into a current value when F=1.

2.3.5 Failsafe

PLC provides fault protection (open fault and close fault) for electric ball valve of medicine pool. Open fault: In the one-step start/stop program, after the program issues the "open valve" command, the PLC judges it as "open fault" when it is not fully opened or is still in the closed position within the set time (determined by the actual debugging), Immediately cut off the power supply of the valve and stop the pump, and issue a fault alarm. Closing fault: In the one-step start/stop program, after the program issues the "closing valve" command, the PLC judges it as "closing fault" when it is not fully closed or is still in the open position within the set time (determined by the actual debugging), Immediately cut off the power supply of the valve and stop the pump, and issue a fault alarm.

2.3.6 Medicine pool overrun alarm

When the liquid in the medicine pool exceeds its set upper or lower limit, the computer will send out an audible and visual alarm to remind the on-duty personnel for immediate treatment.

2.3.7 Dosing control method

⑴ Automatic control

According to the determined control mode, realize automatic dosing, automatic detection of working conditions and data, and protection of the controlled equipment.

⑵Central control manual control

The PLC receives commands from the computer in the central control room through the keyboard or mouse, starts/stops the dosing pumps, valves and other controlled equipment, remotely adjusts the frequency and stroke of the dosing pumps, and performs fault protection for the controlled equipment.

⑶ Manual control

In the manual state, PLC only detects and does not perform fault protection. The on/off control of the dosing pump is carried out through the buttons on the on-site dosing control cabinet or the box, the frequency is adjusted through the keyboard on the frequency converter, and the stroke is adjusted through the switch button on the hand operator of the control cabinet.

3. Chlorination control design

3.1 Control object

(1) Chlorinator

(2) Inline booster pump

(3) Chlorine leakage alarm

(4) Chlorine absorption device

(5) Chlorine gas pressure switching system

3.2 Detection object

(1) The operating status of the chlorinator

●Manual

●Auto

● run

●stop

●Opening

(2) Chlorination switching system operating status

(3) Chlorine bottle weight

(4) Chlorine leakage alarm: chlorine leakage alarm between chlorine bottles, chlorine leakage alarm between chlorine addition

(5) Operating status of chlorine gas absorption device

●Corrosion-resistant pump status: running, stopping, fault

●Exhaust fan status: running, stopping, failure

(6) Running status of pipeline booster pump

●Manual

●Auto

● run

●stop

●Fault

(7) Sampling pump status

●Manual

●Auto

● run

●stop

●Fault

(8) Status of the axial flow fan between the chlorine cylinders

●Manual

●Auto

● run

●stop

●Fault

3.3 Chlorination control design

Chlorination control system consists of chlorine bottle, electric ball valve, filter, vacuum regulator, chlorination machine, water injector, vacuum automatic switching device and chlorine leakage detection probe, etc. The vacuum switching device can make the two sets of chlorine bottles switch between empty bottles and full bottles automatically.

In order to grasp whether the chlorination is in the state of manual or automatic chlorination, the manual/automatic selection signal of the chlorinator is drawn in the chlorinator.

3.3.1 Pre-chlorination control design

The function of pre-chlorination is mainly to prevent algae and destroy colloids, so pre-chlorination is generally added in proportion to the flow of raw water. The mathematical model of control is as follows:

IO=Kf*Qm where: IO=controller output (4-20mA)

Kf=proportionality factor

Qm=instantaneous flow of raw water

The setting of the proportional coefficient Kf depends on the amount of chlorine added before.

The pre-chlorination control process is completed by the controller that comes with the chlorinator, and the PLC is only used to detect production conditions and data.

3.3.2 Post-chlorination control design

Post-chlorination is directly related to the qualification rate and stability of residual chlorine in the factory. In post-chlorination control, free residual chlorine contained in water is used as the controlled object. Its control model is shown in the figure below. The filtered water flow rate is used as feed-forward, and the free residual chlorine after mixing at the dosing point is used as feedback. The amount of chlorine added is controlled through PID adjustment, so that the free residual chlorine is controlled within the set range, so as to achieve disinfection and maintain a certain residual chlorine. purpose in the network. The mathematical model of PID control is similar to adding coagulant.

Km*Kf*Qm+(1-Km)[KP(E)+Ki∫0t(e)dt+Kd*d(E)/dt+B]

Among them: IO=controller output (4~20mA)

B=Output Compensation or Feedforward

E= Deviation (setpoint SP-process variable PV)

KP=proportional gain

Ki = integral gain (1/sec)

Kd = differential regulation (sec)

Km=composite ring coefficient (less than 1)

Kf=proportionality factor

Qm=Instantaneous flow rate of filtered water

Its output compensation or feed-forward B takes a value proportional to the filtered water flow. The setting value of free residual chlorine is set according to the water quality requirements to ensure that the free residual chlorine at the end of the pipe network meets the national standard. With the change of climate, the situation of water supply network and the quality of raw water, the set value of free residual chlorine will also change accordingly.

The post-chlorination control process can be completed by the controller that comes with the chlorinator, or it can be controlled and detected by PLC for production conditions and data. Due to the powerful calculation function of the PLC processor, only the PLC can fully simulate this function of the above-mentioned chlorination principle; and the controller (PCU) unit that comes with the chlorinator is actually a single-chip processor inside, and then communicates with peripherals. The drive system is integrated as an overall controller.

3.3 Supplementary chlorine control design

Supplementary chlorine is directly related to the qualification rate and stability of residual chlorine in the factory. In the control of supplementary chlorine, the free residual chlorine contained in water is used as the controlled object. Its control model is shown in the figure below. The flow rate of the factory water is used as feedforward, and the free residual chlorine of the factory water is used as feedback. The amount of chlorine added is controlled through PID adjustment, so that the free residual chlorine is controlled within the set range, so as to achieve disinfection and maintain a certain amount of residual chlorine in the pipe network. the goal of. The mathematical model of PID control is similar to that of post-chlorination.

IO=Km*Kf*Qm+(1-Km)[KP(E)+Ki∫0t(e)dt+Kd*d(E)/dt+B]

Among them: IO=controller output (4~20mA)

B=Output Compensation or Feedforward

E= Deviation (setpoint SP-process variable PV)

KP=proportional gain

Ki = integral gain (1/sec)

Kd = differential regulation (sec)

Km=composite ring coefficient (less than 1)

Kf=proportionality factor

Qm=Instantaneous flow rate of filtered water

Its output compensation or feed-forward B takes a value proportional to the factory water flow. The setting value of free residual chlorine is set according to the water quality requirements to ensure that the free residual chlorine at the end of the pipe network meets the national standard. With the change of climate, the situation of water supply network and the quality of raw water, the set value of free residual chlorine will also change accordingly.

The control process of supplementary chlorine can be completed by the controller that comes with the chlorinator, or it can control and detect the production conditions and data through PLC. Due to the powerful calculation function of the PLC processor, only the PLC can fully simulate this function of the above-mentioned chlorination principle; and the controller (PCU) unit that comes with the chlorinator is actually a single-chip processor inside, and then communicates with peripherals. The drive system is integrated as an overall controller.

3.4 Main Factors Affecting Chlorination Effect

⑴ The purpose of adding chlorine is for disinfection. In the chlorine addition control, the free residual chlorine in the water is generally used as the controlled object, and the free residual chlorine in the factory water is kept within a certain range. However, the ammonia nitrogen in raw water plays a very important role in the formation of free residual chlorine after chlorination. Because ammonia nitrogen and chlorine form chloramine in water, the ammonia nitrogen in raw water has a great influence on the formation of free residual chlorine after chlorination, especially in water plants with large changes in raw water ammonia nitrogen, it is difficult to use free residual chlorine as the object of control. To achieve the desired effect, in this case, the total chlorine can be used as a comparative reference.

(2) The length of sampling time directly affects the effect of chlorine addition. Usually, the post-chlorination is fully mixed after chlorine dosing, and the sampling time should be shortened as much as possible, generally 3 minutes is appropriate. There are usually two ways to shorten the sampling time: one is to shorten the length of the sampling water pipe as much as possible; the other is to increase the flow rate of the sampling water pipe.

⑶ The correctness of the detection value of the residual chlorine analyzer is the key to controlling the addition of chlorine. Due to the zero drift of the residual chlorine analyzer, it should be calibrated regularly. During calibration, samples should be taken near the probe of the residual chlorine analyzer, and analyzed immediately, and the residual chlorine value detected manually should be calibrated to the residual chlorine analyzer. The manual detection of residual chlorine must be timely, otherwise what is detected is not free residual chlorine but total chlorine.

⑷ The flow rate of the filtered water is greatly changed due to the sludge discharge of the reaction sedimentation tank and the backwashing of the filter tank. It is also an important factor affecting chlorine addition.

Because the factors affecting post-chlorination control are more complicated, the control is more troublesome. Based on the above factors, the compound loop control with proportional plus PID is much better than the effect of PID control alone.

3.5 Chlorine leakage detection

The chlorine bottle room and the chlorinator room are equipped with chlorine leakage detectors, which will alarm when the concentration of chlorine leakage reaches a certain value, and start the exhaust machine and the chlorine gas absorption device.

3.6 Control of chlorine leakage absorption safety system

The chlorine absorption device is composed of absorption tower, fan, absorption liquid circulation pump and corresponding accessories. Due to the strengthening of air pollution control by environmental protection agencies, the current chlorine gas absorption device is characterized in that the tail gas does not discharge to the atmosphere, and is connected to the chlorine storehouse through a recovery pipe to form a closed loop system that does not pollute the environment.

When the chlorine leakage alarm device detects that the chlorine content in the air is greater than the set value, the chlorine leakage alarm device sends out a chlorine leakage alarm pre-alarm signal, automatically starts the chlorine gas absorption device, sends the alarm signal to the PLC, and the PLC sends the signal to the management computer. And sound and light alarm. The operation, stop and fault signals of fans and circulating pumps are sent to PLC.

3.7 Control of pipeline booster pump

The start-up of the booster pump and the chlorinator realizes linkage control, and an alarm signal of low pressure in the front and rear chlorination pipes is given. Three booster pumps are dual-purpose and one standby, and PLC automatically determines their standby. The automatic start and stop of the booster pump is adjusted and controlled by PLC according to the pipeline pressure.

4. Control design of reaction sedimentation tank

4.1 Control object

(1) 4 groups of reaction sedimentation tanks, each group of reaction sedimentation tanks has 6 groups of mud discharge valves

(2) 4 sludge discharge machines

4.2 Monitoring objects

(1) Status of mud discharge valve

●Manual

●Auto

●On

● off

●The last valve opening time

●The opening time of the valve

●Sludge discharge cycle

●Valve opening time

(2) Status of mud discharger

●Manual

●Auto

●Communication status

●forward

●Back

●The time of the last mud discharge

●This mud discharge time

●Sludge discharge cycle

●Submerge pump status

●Siphon state

(3) Turbidity

●Raw water turbidity

●Turbidity after precipitation

(4) Reaction sedimentation tank mud level

4.3 Control design of sludge discharge valve in flocculation tank

There are three ways to control the sludge discharge valve of the flocculation tank: local manual, remote manual and automatic control. Every two valves is a group, and only one group of valves can be opened at the same time, so as to ensure that the capacity of the drainage ditch and the drainage pump is not exceeded. The automatic control is determined by the sludge discharge cycle and valve opening time, which can be set on the computer, and the sludge discharge cycle can also be calculated according to the raw water flow and turbidity. The valve opening time is long and then short, that is, the mud discharge valve at the entrance of the flocculation tank has a long time to discharge mud, and the mud discharge valve at the outlet of the reaction tank has a short time to discharge mud.

4.4 Control design of mud scraper

The sedimentation tank scraper has three control methods: local manual, remote manual and automatic control. The automatic control is determined by the mud discharge period, which can be determined by calculating the raw water turbidity and raw water flow rate or manually set on the computer.

⑴ Local manual control mode

The mud scraping is manually controlled through the local control box on the mud scraper.

⑵ Remote manual control mode

The PLC receives instructions from the computer in the central control room through the keyboard or mouse to control the mud scraper.

⑶ Automatic control mode

PLC automatically detects the sludge discharge period, and when the sludge discharge period is up, the PLC automatically starts the sludge discharge machine for sludge discharge.

5. Filter control design

5.1 PLC control and detection object

5.1.1 Recoil PLC station control object

(1) Three backwash pumps and outlet valves

(2) Three blowers

(3) Two sampling water pumps

(4) Two air compressors

(5) Backwashing of the 16-grid filter

(6) Sedimentation tank mud scraper

5.1.2 Recoil PLC station monitoring object

(1) Turbidity

●Water turbidity after precipitation

●Turbidity of filtered water

●Turbidity of factory water

(2) Air compressor status

● run

●stop

●Fault

●Cumulative running time

(3) Control the state of the air circuit pressure line

●High pressure

●Low pressure

●pressure

(4) Running status of recoil pump

●Manual

●Auto

● run

●stop

●Fault

●Cumulative running time

(5) Blower running status

●Manual

●Auto

● run

●stop

●Fault

●Cumulative running time

●Outlet pressure

(6) flow rate

●Raw water flow

●Filtered water flow

(7) Status of mud scraper in sedimentation tank

●Manual

●Auto

●Communication status

●forward

●Back

●The time of the last mud discharge

●This mud discharge time

●Sludge discharge cycle

●Submerge pump status

●Siphon state

5.1.3 Filter station control object

(1) Inlet valve

(2) Drain valve

(3) Backwash air valve

(4) Backwash water valve

(5) Filtered water regulating valve

(6) Exhaust valve

5.1.4 Monitoring objects of grid filter station

(1) Water level of filter grid

(2) Clogging value of the filter grid (pressure difference value)

(3) Filtration time of the filter grid

(4) The state of the water valve after the filter grid is filtered

●Open in place

●Close in place

●Fault

●Valve opening

(5) Operating status of 16 grid filters

●On-site manual

●Central Control Manual

●Auto

●Filter

●Stop filtering

●Backwashing,

●Fault

(6) Operating state of pneumatic valve (switch type)

●Open in place

●Close in place

●Fault

(7) Diaphragm valve operating status

●On state

●Off state

5.2 Design of filter grid operating table

Each filter tank is equipped with a piano-style console, and each console is equipped with a small PLC. Control the valve of the filter grid during automatic filtration and backwashing, and exchange information with the backwashing PLC. The console performs manual filtering and backwashing control when the PLC fails or is debugged. Ensure that filtration and backwashing can still be performed in the event of PLC failure. When operating a filter grid, you can see the status of its valve, the opening of the regulating valve, the water level of the filter grid and other information.

The control cabinet includes:

⑴ Filtrated water valve opening indication and fault indication

⑵ The water level of the filter grid

⑶ filter grid manual / automatic switch

⑷ Filtered water regulating valve controller (can be adjusted manually)

⑸ Inlet valve switch, open position, close position, fault indicator light

⑹ Drain valve switch, open position, close position, fault indicator light

⑺ Exhaust valve switch, open position, close position, fault indicator light

⑻ Backwash gas valve switch, open position, close position, fault indicator light

⑼ Backwash water valve switch, open position, close position, fault indicator light

⑽ Manual/automatic transfer switch for each backwash pump

⑾ Backwash water pump switch, run, stop, fault indicator lights

⑿ Manual/automatic transfer switch for each blower

⒀ Backwash blower switch, run, stop, fault indicator light

Considering that the filter control room is relatively humid, and the chlorine gas emitted from the water has a certain corrosive effect on electrical equipment and components. Therefore, an imported piano table type operation cabinet with a higher protection level is selected. The control cabinet is used in many projects and has received good results. It is easy to operate, convenient and highly reliable, and is very popular among users.

5.3 Filter control design of the filter

There are two types of filter control: local/remote control. The on/off control of each valve of the filter tank is carried out through the button switch on the operation console, and the manual adjustment and automatic adjustment of the filtered water regulating valve are carried out through the hand operator. On the host computer, the filter can be turned on or the automatic filter can be stopped. The opening or stopping of the filter is calculated by the raw water flow, and the specific opening or stopping of the filter is determined by the first-open, first-stop queue.

⑴ Automatic filter control

In the automatic filtration state, during the filtration process of the filter, the PLC adjusts the opening of the filter outlet valve according to the change of the filter water level measured by the water level sensor, so as to ensure the constant water level of the filter. The water flow rate is used as feedforward and the filter water level is used as feedback, and PID regulation is used to control the opening of the filtered water regulating valve. The adjustment period is more than 1 minute, the water level adjustment range is less than 10mm, and the adjustment process is not affected by the degree of filter blockage and the change of water inflow into the filter tank.

⑵ Manual filter control in central control

Select manual filtering in the central control, and adjust and control the filtered water valve by manually inputting the opening of the filtered water valve (%).

⑶ Local automatic filter control

Utilize the hand operator in the local control cabinet to introduce the water level signal into the hand operator, and use the control function of the hand operator to automatically adjust and control the filtered water regulating valve. We use this method in many projects, and the effect is very good. This method can be independent of the PLC, that is, it can still ensure normal constant water level filtration when the PLC is not working, and it is very convenient and reliable to use.

⑷Manual local manual filter control

In the manual mode, the on/off control of the valve is performed through the button on the local centralized control cabinet, and the opening of the filtered water valve is adjusted through the button of the hand operator, so as to realize manual filtration.

5.4 Filter backwash control design

The flushing gas strength of the filter is 13-17L/s.m2; the air flushing strength is 13-17L/s.m2 and the water flushing strength is 3-4.5L/s.m2 when the air-water combined recoil; the water flushing strength is 4 -6L/s.m2; the surface sweeping intensity is 1.4-2.4L/s.m2.

There are three types of filter backwash control: local, remote and automatic. Backwashing of a certain filter can be forced on the host computer. Filter backwash has the following four backwash situations.

⑴ Manual backwashing:

When the on-site operation console is switched to manual, the operator uses the switch button on the filter on-site console to manually backwash a certain filter grid. The backwashing process should strictly follow the backwashing process and backwashing time. controlled by the operator.

⑵ Central control manual backwashing

When the local operation console is switched to automatic, the staff on duty in the central control room select manual backwashing on the computer, and use the mouse to request the filter to backwash immediately. The whole backwashing process is completed by PLC.

⑶ Filtering time exceeds the set time for backwashing

When the local operation console is switched to the automatic state and the computer in the central control room is set to the automatic backwashing state, the PLC will automatically record the filtration time. When the PLC detects that the filtration time (period) reaches the set value (can be set on the computer in the central control room ), when there is no backwashing in other filter grids, the PLC controls the backwashing, and the entire backflushing process is completely completed by the PLC.

⑷ The blockage value (pressure difference value) is greater than the set value for backwashing

When the local operation console is switched to the automatic state and the computer in the central control room is set to the automatic backwashing state, when the PLC detects that the differential pressure value (clogging value) reaches the set value (can be set, such as 1000mm) (indicating that its filter If there is a high degree of material clogging and backwashing is required), in the case of no backwashing in other filter cells, the PLC controls the backwashing, and the entire backflushing process is completely completed by the PLC.

After the manual backwashing and automatic backwashing of the central control are completed, it will automatically enter the filtration process. Recoil is divided into three stages:

⑴ Air flushing stage (1-5 minutes adjustable)

⑵ Air-water mixed backwash stage (4-6 minutes adjustable)

⑶ water rinsing phase (4-6 minutes adjustable)

In the backwashing process, in order to save the amount of flushing water, filtration is used to lower the water level , and then enter the normal backwashing process. Instead of draining lower the water level . The specific backwashing steps are as follows:

⑴ Close the inlet valve

(2) After filtering, the water regulating valve is opened to a certain opening degree, and the filtered water level is lowered to the set backwash water level (500mm above the filter material)

(3) Close the filtered water regulating valve and open the drain valve

⑷ Start the No. 1 blower and open the backwash valve

⑸ Start the No. 2 blower (air washing time 1 to 3 minutes)

⑹ Stop No. 1 blower

⑺ Start the No. 1 water pump and open the backwash valve (air and water washing time is 4 to 6 minutes)

⑻ Stop the No. 2 blower and close the backwash valve

⑼ Open the exhaust valve to the set time and then close the valve

⑽ Start the No. 2 water pump (water rinsing time 4-6 minutes)

⑾ Stop the No. 1 water pump

⑿ Stop the No. 2 water pump and close the backwash water valve

⒀ Go to filter status

5.5 Functional Design of Backwashing Judgment of Filter Grid

In the process of controlling the operation of the filter grid, the filter PLC constantly judges whether the filter grid needs to be backwashed.

5.5.1 Filter cycle

The owner determines the maximum filtration time of the filter grid according to the technical requirements of the water plant. When the filter grid is open and the filter is running, the PLC will start timing. When the filter time is greater than the set maximum filter cycle, it will immediately send a backwash request. ). After a filter grid sends a backwash request, if other filter grids are backwashing, the filter grid will continue to filter and wait for backwashing. The filter clock is reset (set to zero) immediately after the backwashing of the filter grid is completed.

5.5.2 Grid clogging value

The pressure difference between the top and bottom of the filter plate is used as the clogging degree of the filter material. When the clogging value (that is, the pressure difference reaches 1000mm) reaches the set value, it immediately sends a backwashing request to the PLC controlling the backflushing, and the PLC according to the request of each filter cell The sequence of backwashing arranges backwashing (arranged by the queue). After a filter grid sends a backwash request, if other filter grids are backwashing, the filter grid will continue to filter and wait for backwashing. The filter clock is reset (set to zero) immediately after the backwashing of the filter grid is completed.

5.5.3 Forced backwash

The operator sends a forced backwash command to the PLC for a certain filter grid through the mouse or keyboard, and the filter tank PLC automatically backwashes its filter grid after receiving the command. The filter clock is reset (set to zero) immediately after the backwashing of the filter grid is completed.

5.6 One-step start-stop design of backwash water pump

5.6.1 The process of opening the pump: closing the valve to start.

⑴ Pump start command

⑵ Check whether the water outlet valve is closed properly, if not, close it properly.

⑶ Start the water pump motor

⑷ When the running signal of the water pump motor arrives, the outlet pressure of the water pump is detected, and the valve is opened when it reaches the set value.

⑸ The valve is fully open

5.6.2 Pump stop process: close the valve and stop the pump

⑴ Pump stop command

⑵ Close the outlet valve

⑶ Valve closed in place

⑷ Stop pump motor

5.7 One-step start-stop design of backwash blower

5.7.1 The process of turning on the blower: opening the valve to start

⑴ Turn on the fan command

⑵ Open the bypass valve

⑶ Start the blower

⑷ Open the air valve

⑸ Close the bypass valve

5.7.2 The process of stopping the blower: stop and close the valve

⑴ Fan stop command

⑵ Open the bypass valve (unloading valve)

⑶ Close the outlet valve

⑷ Stop blower

⑸ Close the bypass valve (unloading valve)

5.8 Fault detection and protection design for each filter tank valve

⑴ After the flushing program issues the closing command of the filtered water regulating valve of the filter grid, if the closing valve is not in place within the set time, the PLC will fail to close the valve, cut off the power supply of the valve immediately, and give an alarm. Aborted flushing, requesting manual processing.

⑵ After the flushing program issues the opening/closing command of the inlet gate valve of the filter grid, if the opening/closing valve is not in place within the set time, and the PLC fails to open/close the valve, immediately cut off the power supply of the valve and give an alarm. Aborted flushing, requesting manual processing.

⑶ After the flushing program issues the opening command of the drain valve of the filter grid, if the opening of the valve is not in place within the set time, the PLC will fail to open the valve, cut off the power supply of the valve immediately, and give an alarm. Aborted flushing, requesting manual processing.

⑷ After the flushing program issues the valve opening command for the backwashing air valve of the filter grid, if the valve opening is not in place within the set time, and the PLC fails to open the valve, immediately cut off the power supply of the valve and give an alarm. Interrupt the flushing, shut down the backwash blower and other related equipment for protection, and request manual processing.

⑸ After the flushing program issues the valve opening command for the backwashing water valve of the filter grid, if the valve is not opened in place within the set time, and the PLC fails to open the valve, immediately cut off the power supply of the valve and give an alarm. Interrupt the flushing, shut down the backwashing water pump and other related equipment for protection, and request manual processing.

⑹ After the flushing program issues the closing command of the backwashing air valve of the filter grid, if the closing valve is not in place within the set time, the PLC will fail to open the valve, cut off the power supply of the valve immediately, and give an alarm. Backwashing continues.

⑺ After the flushing program issues the closing command of the backwashing water valve of the filter grid, if the closing valve is not in place within the set time, the PLC will fail to open the valve, cut off the power supply of the valve immediately, and give an alarm. Interrupt the flushing, shut down the backwashing water pump and other related equipment for protection, and request manual processing

5.9 Backwash pump fault detection and protection design

⑴ Over-current pre-alarm

When the backwash pump motor current is greater than the rated current, the computer will give an audible and visual alarm.

⑵ Overcurrent fault

When the motor current of the backwash water pump is greater than the rated current, the water outlet valve and the water pump will be closed immediately, and the computer will alarm with sound and light.

⑶ Empty vehicle failure

When the motor current of the backwash water pump is less than the rated current or the water outlet pressure is lower than the normal value, it is an empty car failure, immediately shut down for protection, and the computer sounds and lights alarm.

⑷ Electrical failure

After the backwashing water pump motor starts and runs normally, if the running signal continues to lose for 5 seconds, it is an "electrical" failure, the PLC will stop immediately for protection, and the computer will alarm with sound and light.

5.10 Fault detection and protection design of outlet valve of backwash pump

⑴ Valve opening failure

After the valve opening instruction is issued, if the valve opening is not in place within the set time, the PLC will make a valve opening failure, immediately cut off the power supply of the valve, stop the pump for protection of the backwashing water pump, and give an alarm.

⑵ Valve closing failure

After the valve closing command is issued, if the valve closing is not in place within the set time, the PLC will fail to close the valve, immediately cut off the power supply of the valve and give an alarm.

5.11 Backwash blower fault detection and protection design

⑴ Over-current pre-alarm

When the blower motor current is greater than the rated current, the computer will give an audible and visual alarm.

⑵ Overcurrent fault

When the current of the blower motor is greater than the rated current, the water outlet valve and the water pump will be closed immediately, and the computer will alarm with sound and light.

⑶ Empty vehicle failure

When the current of the blower motor is less than the rated current or the outlet water pressure is lower than the normal value, it is an empty car failure, and the machine will be shut down immediately for protection and the computer will alarm with sound and light.

⑷ Electrical failure

After the blower motor starts and runs normally, if the running signal continues to lose for 5 seconds, it is an "electrical" failure, the PLC will stop immediately for protection, and the computer will alarm with sound and light.

5.12 Fault detection and protection design of outlet valve of backwash blower

⑴ Valve opening failure

⑵ Valve closing failure

6. Control design of water pumping station

6.1 Control object

⑴ Water delivery pump

⑵ Water delivery pump outlet valve

⑶ pump room sewage pump

⑷ Incoming cabinet

⑸ Segmented cabinet

⑹ Transformer cabinet

⑺ Water intake pump outlet cabinet

⑻ Internal feedback speed control device

6.2 Monitoring objects

⑴ Operation status of outlet valve of water delivery pump

●Remote control

●Manual

●Open in place

●Close in place

●Fault

⑵ Running status of water delivery pump (fixed speed pump)

●Remote control

●Manual

● run

●stop

●This running time

●Cumulative running time

●Fault

●Last downtime

●This startup time

⑶ Running status of water delivery pump (variable speed pump)

●Remote control

●Manual

● run

●stop

●This running time

●Cumulative running time

●Fault

●Last downtime

●This startup time

●Frequency

(3) pH value

●pH value of raw water

●pH value of factory water

⑷ Flow

●Instantaneous flow of factory water

●Day water supply

●Cumulative water supply

⑸ Turbidity

●Raw water turbidity

●Turbidity after precipitation

●Turbidity of filtered water

●Turbidity of factory water

⑹ Residual chlorine

●Residual chlorine in filtered water

●Residual chlorine in factory water

⑺ Sewage pump running status

●Remote control

●Manual

● run

●stop

●Fault

⑻ State of transformer cabinet

●Close

●Opening

●Fault

⑼ Status of incoming cabinet

●Close

●Opening

●Fault

⑽ Electrical parameters

●Phase current: I1, I2, I3

●Effective residual current: Io

●Voltage: U21, U32, U13, V1, V2, V3)

●Residual voltage: Vo

●Active power: P

●Reactive power: Q

●Power factor

●Frequency

●Active energy: -Wh

●Reactive power: -VARh

⑾ Shimizu pond water level

⑿ Water pump outlet pressure

⒀ Suction well water level

⒁ Status of inverter control cabinet:

●Manual

●Auto

● run

●stop

●Fault

●This running time

●Cumulative running time

●Last downtime

●This startup time

6.3 Fixed speed pump control

6.3.1 Automatic control mode

According to the set factory water pressure, PLC automatically starts/stops the fixed pump and pump valve linkage; adjusts the speed of the speed regulating pump according to the set pressure; detects the operating conditions and data; detects the fault of the controlled equipment Protect.

6.3.2 Manual control mode of central control

The PLC receives the commands issued by the computer in the central control room through the keyboard or the mouse, stops the water pump unit and the water outlet valve, and performs fault protection for the controlled equipment.

6.3.3 Local manual control mode

In the manual mode, the on/off control of the water pump unit is carried out through the button on the local switch cabinet. PLC only detects it and does not perform fault protection.

6.4 Speed control

6.4.1 Automatic control

According to the set factory water pressure, the PLC operates the speed-regulating pump according to the set pressure; detects the operating conditions and data; and performs fault protection for the controlled equipment.

The speed regulation method mainly adopts constant pressure closed-loop control in time intervals, and the fact that its application in water plants can save energy, stabilize water supply, and reduce the number of pipe bursts has been widely recognized.

A variety of water supply modes are available for selection in the system setting, and fixed pumps and speed-regulating pumps are used together.

In order to adapt to the pressure/flow fluctuation characteristics of urban water supply, such as the flow fluctuation during the three peak water consumption periods during the day, as well as some other special applications, the system is designed with 6-stage timing pressure given control to meet the needs of use. The daily flow fluctuation and multi-stage pressure control curve are as follows (the pressure setting for the specific time period shall be agreed with the owner):

The scheme includes multi-period pressure given control on user's regular day and user-specified day. The regular day of the user refers to a date and time period other than the day specified by the user. User-designated day control includes the designation of Saturday or Sunday, and the designation of 3 date segments in the year/week cycle.

In the case of a sharp reduction in water supply at night (suitable for water plants with a small scale of water supply and mainly domestic water). Dormant pump control can be used. During the dormancy period, the dormant small pump works, and the control system only monitors the pipe network pressure. When the pipe network pressure is lower than the set value, the system automatically wakes up and the speed-regulating pump starts to work. When the pipe network pressure is higher than the set value, the system restarts Enter the dormant state, that is, only the dormant small pump is running. In this way, the control of the dormant pump is realized to maximize energy saving.

6.4.2 Manual control in the central control room

The PLC receives instructions from the computer in the central control room through the keyboard or mouse, starts/stops the water pump unit and the water outlet valve, adjusts the frequency of the inverter, and protects the controlled equipment from failure.

6.4.3 Local manual control mode

In the manual mode, the manual adjustment control is performed through the button frequency converter on the on-site switch cabinet. PLC only detects it and does not perform fault protection.

6.5 Water delivery pump protection measures

⑴ Over-current pre-alarm:

When the water pump motor current is greater than the pre-alarm current setting value, the computer will give an audible and visual alarm.

⑵ Overcurrent fault:

When the current of the water pump motor is greater than the rated current, the water outlet valve and the water pump will be closed immediately, and the computer will alarm with sound and light.

⑶ Empty car failure:

When the current of the water pump motor is less than the rated current or the water outlet pressure is lower than the normal value, it is an empty pump fault, immediately shut down for protection, and the computer gives an audible and visual alarm.

⑷ Electrical failure:

6.6 Fault detection and protection of outlet valve of water delivery pump

⑴ Valve opening failure

⑵ Valve closing failure

6.7 Fault monitoring and protection of power transformation and distribution system

PLC automatically detects current and voltage signals, and PLC automatically judges "overvoltage fault", "undervoltage fault", "overcurrent fault", "undercurrent fault" and other faults of power transformation and distribution systems detected by PLC. According to the different conditions of various faults, the screen cabinets of the power transformation and distribution equipment will be protected accordingly, and sound and light alarms will be given.

6.8 Fault monitoring and protection of other controlled equipment

PLC immediately protects the fault signals of other controlled equipment, such as sewage pumps, vacuum pumps, etc., and sends out sound and light alarms.

7 . Automatic control system function design

The automatic control system is an organic combination of hardware and software functions. An excellent automatic control system should have reasonable hardware configuration, complete and powerful software functions, friendly and sufficient man-machine interface, and the entire automatic control system is stable and reliable. Owners can use it with confidence. Even if there is a mistake in keyboard operation, the computer will block it, and immediately remind you with sound, and at the same time instruct you to operate on the CRT.

7.1 Functions of the automatic control system

The automatic control system of the water plant will realize the following major functions:

⑴ Data acquisition function

●Analog acquisition

The system collects and adjusts various instruments and various analog signals of the water plant.

●Switch value collection

The system collects switch values such as running, stopping, opening in place, closing in place, and faults of various equipment in the water plant.

●Pulse volume acquisition

The system collects various pulse quantities (flow, electricity, etc.) of the water plant.

⑵ Automatic detection function

The automatic detection function is to use the high-speed characteristics of the computer and PLC to automatically and continuously detect and record and display the water quality parameters (turbidity, residual chlorine, PH value, etc.), process parameters (pressure, differential pressure, etc.) of each process link in the water treatment process. , water level, liquid level, flow, weight), electrical parameters (current, voltage, active power, electricity) and other production data, as well as the operating conditions of the equipment (automatic, manual, running, stopping, fault, current running time, cumulative operating time, valve opening, valve closing, valve opening, etc.).

⑶ Automatic protection function

The computer and PLC automatically and continuously detect production data and equipment operation status, and conduct comprehensive analysis to comprehensively judge possible accidents in the user's production process, automatically alarm and automatically take measures to prevent the occurrence and expansion of accidents, and protect the safety of people and equipment wait.

⑷ Automatic control function

The computer and PLC can automatically start or stop certain equipment, or perform alternate operation, etc., according to the process conditions and control requirements, according to the logical sequence set by the specified time period. Automatically control the start/stop of chlorination, chemical dosing, filtration, backwashing, sludge discharge, and water pump.

⑸ Automatic adjustment function

According to the water level of the clear water tank, the PLC automatically adjusts the start and stop of the water intake pump, automatically adjusts the frequency and stroke of the dosing pump according to the raw water parameters, SCD value and the turbidity of the sedimentation tank, and automatically adjusts the filtered water valve according to the water level of the filter grid. According to the original water flow and the set parameters, the opening of the regulating valve of the chlorinator can be automatically adjusted to control the amount of chlorine added before, and the regulating valve of the chlorine addition can be automatically adjusted according to the flow rate of filtered water and the feedback of residual chlorine to control the amount of chlorine added, etc. .

⑹ System configuration and parameter setting functions

Authorized engineers can configure and parameterize the system.

⑺ Management function

According to the data collected by the production process instruments of the whole plant, the status signals and electrical data of the production equipment, as well as the laboratory data and other information, etc., coordinate and manage the production scheduling of the production process of the whole plant, print production reports, draw trend curves, and forecast There is an interface with the MIS of the water plant, which can be used for management work and other office automation application work if necessary.

Everything in the automatic control system is to serve the process and production, and it can guide the process, direct the production, ensure the water quality and pressure of the factory water meet the standards, and reduce the cost indicators such as chemical consumption, chlorine consumption, and electricity consumption, reduce labor intensity, and improve production. efficiency and improve the working environment.

7.2 Main functions of upper computer

There are three main functions of the host computer:

⑴ Management function

Generate a real-time dynamic diagram of the production process of the water plant, and provide a clear and friendly man-machine interface for the production staff on duty in the water plant. Vividly reflect the real-time data of the production process, complete the storage, display and query of alarms, historical data, and historical trend curves. Generate shift reports, daily reports, monthly reports and annual reports for various production and operation management.

⑵ Control function

Based on the graphical interface and Chinese prompts, the production duty personnel of the water plant use the keyboard or mouse of the computer to start or stop the equipment, set the control and adjustment parameters in the central control room.

⑶ Communication function

The communication between the automatic control system and other systems is completed through the computer in the central control room. For example, communication with various PLC stations on site, communication with analog display screens or large-screen projectors, communication with water plant management information system (MIS), communication with the company's water supply dispatching system, etc. wait.

7.3 Process control display function design

The process control display function is mainly man-machine interface function and interface function. The human-machine interface refers to the dynamic display of the real-time operating conditions of each process flow and process equipment in the whole plant on the computer or the local touch screen of the central control room (CCR) of the water plant, and the operating trend of the process control of dosing and chlorination. Water quality parameters (turbidity, PH value, residual chlorine), process parameters (water level, liquid level, pressure, pressure difference, flow rate, weight), electrical parameters and other production data. Make production management personnel understand the current production and operation status of the whole plant at a glance. It can monitor at multiple levels from the general drawing to the detailed drawing. The interface function refers to the clear and accurate operation instructions for production and management personnel and the shielding function for wrong operations.

⑴ Overall display

It can display the overview of the production system of the entire water plant, the process parameters of the entire plant, and the operation of the automatic control system.

⑵ Split screen display

It can display the operation status of each subsystem in split screen, and display the operation status and related parameters of the equipment monitored by each sub-control station in detail.

⑶ Trend display

It can display the change trend of all process parameters and electrical parameters in real time.

⑷ Graphic curve display

Graphs of parameters can be displayed individually or for four parameters.

⑸ Process flow display

It can display according to the technological process of water treatment, and display the operating status of the monitoring equipment and the parameters of the detection points.

⑹ Operating parameter display

It can display the start/stop time of main equipment, current running time, cumulative running time, etc.

⑺ Working condition display

●Manual in place: display “M”

●Auto: display "A"

●Run: display green

●Stop: display red

●Fault: flashing

●Valve open in place: display green

●Valve closed in place: display red

●Valve middle position: display yellow

●Valve failure: flashing

●Filtration by filter: display green

●Filter stop: display red

●Filter failure: flashing

●Backwash: yellow

●Specific failure: displayed in text

7.4 Event-driven and alarm function design

When a certain parameter exceeds the set value or the equipment breaks down, the management computer can send out sound and light alarm in time, and the display terminal will send out sound and flash to remind the on-duty personnel during the alarm, and display the corresponding prompt and picture at the same time, and record it in the alarm In the database, print in time. Alarm by flashing on the simulation screen. In addition, there is an alarm reset function. When the system displays the general diagram, sub-system diagram and individual equipment process diagram, it displays the fault registration form in the lower table column of the screen, so that the on-duty personnel can understand the fault status of the whole plant anytime and anywhere.

7.5 Operation window function design

The process equipment can be remotely controlled manually on the management computer. The on-duty staff selects the equipment to be operated with the mouse, and an operation window pops up, selects manual, and can control the start-stop or adjustment of the equipment through the keyboard or mouse. This provides great convenience for the on-duty personnel to deal with some emergencies. Can switch to remote manual control when needed. Can ensure the continuous and reliable operation of the system.

7.6 Function design of water plant production index table

On the management computer, no matter which screen you are in, you can use the mouse to select the icon of the production index table, and the production index table will pop up, displaying the main production indexes of the water plant in the form of a table. Make the staff on duty keep abreast of the production and operation of the whole plant.

7.7 Design of process parameter setting function

There are two types of process parameter settings:

⑴ Parameter setting

The SCD control value of the dosing system can be set on the management computer, the filter water level and backwash water level of the filter can be set, the sludge discharge period of the sludge discharge machine can be set, the sludge discharge cycle of the sludge discharge valve and the sludge discharge time can be set. , Filter backwash cycle setting, factory water pressure setting, factory water residual chlorine setting, etc.

⑵ Alarm limit setting

On the management computer, it is possible to set the upper and lower limit alarm water level of the water intake, the upper and lower alarm water level setting of the clear water tank, the upper and lower limit setting of the medicine tank liquid level, etc.

The setting values must be confirmed, and the computer must be shielded for wrong settings and out-of-range settings and send "error" information, requiring immediate correction.

7.8 Operation record function design

Calculate the current running time and cumulative running time of major equipment, calculate the daily water intake and cumulative water intake, calculate the current water supply volume and cumulative water supply volume, and record the last stop time and current start time of major equipment. Record the mud discharge time of the mud discharger and the mud discharge time of the mud discharge valve, etc.

7.9 Database management function design

Has strong database management functions. The entire system records the collected or calculated data in the SQL Server database of the server, and can realize seamless connection with the MIS of the water plant.

⑴ Establish a production log database

Record hourly raw production data for statistics and analysis.

⑵Establish production operation database

Record the operation data of the equipment so that the management personnel can grasp the current operation status and cumulative operation status of the equipment in time.

⑶ Establish fault database

Record system failures and PLC failures.

⑷ Establish alarm database

Record historical alarm database.

7.10 Data processing function design

It has a strong data processing function and can use online data and data in the database to calculate the main production indicators. (such as maximum value, minimum value, average value, water distribution power consumption, comprehensive power consumption, chemical consumption, chlorine consumption, cost, etc.).

⑴ Real-time data display

⑵ Automatic update of real-time data

⑶ Automatic saving and automatic deletion of real-time data

⑷ Convert real-time data into historical data for long-term storage.

⑸ Hourly data storage

⑹ Daily data storage

⑺ Record and calculate the start/stop time, current running time and cumulative running time of major equipment.

7.11 Report function design

⑴ Print/display the daily account of the water plant

⑵Print/display the daily operation report of water plant production

⑶ Print/display comprehensive daily report of water plant production

⑷ Print/display water plant production ledger

⑸ Print/display the monthly production report of the water plant

⑹ Print/display comprehensive monthly report of water plant production

⑺ Print/display the production season account of the water plant

⑻ Print/display comprehensive quarterly report of water plant production

⑼ Print/display the annual production account of the water plant

⑽ Print/display the annual report of water plant production and operation

⑾ Print/display comprehensive annual report of water plant production

⑿ Print/display alarm history

7.12 Curve function design

⑴ Print/display the daily change curve of the water level of the water intake well

⑵ Print/display the daily variation curve of raw water temperature

⑶ Print/display the daily variation curve of raw water turbidity

⑷ Print/display the daily change curve of raw water flow

⑸ Print/display raw water pH daily change curve

⑹ Print/display the daily change curve of dosing amount

⑺ Print/display the daily change curve of chlorine addition

⑻ Print/display the daily variation curve of the turbidity of the sedimentation tank effluent

⑼ Print/display the daily change curve of residual chlorine in the clear water pool

⑽ Print/display the daily change curve of the water level in the clear water tank

⑾ Print/display the daily variation curve of the factory water flow

⑿ Print/display the daily variation curve of factory water pressure

⒀ Print/display the diurnal change curve of residual chlorine in factory water

⒀ Print/display the daily variation curve of turbidity of factory water

⒁ Print/display the daily change curve of dissolved oxygen

⒂ Print/display the daily change curve of ammonia nitrogen

7.13 Self-diagnosis function of automatic control system

The system has a self-diagnosis function, which can self-diagnose the equipment in the automatic control system.

7.14 Power protection

The control room and PLC cabinet of the water plant are equipped with UPS power supply to provide power protection for indoor equipment to prevent equipment damage due to power fluctuations, system damage due to sudden power failure, or data loss.

7.15 Lightning protection measures

Install lightning protectors on the total power supply of the waterworks control room and PLC cabinet or box, and install lightning protectors on the power supply of major equipment. Install lightning protectors for instrument power and signals, and shield and install lightning protectors for automatic control network lines to protect the safety of equipment.

7.16 System Backup

The two computers in the control room of the water plant can serve as backups for each other. The server uses dual hard disks as disk mirroring to improve its reliability.

7.17 Data backup

The data backup function can be invoked for CD data backup.

7.18 System recovery

When the power failure or accident returns to normal, the system site will be recorded by the breakpoint of the system, and the system can resume from the breakpoint. The program system is restored from the CD.

7.19 Error Handling

If a non-fatal error occurs during system operation, the terminal will display an alarm message. But it does not stop the operation of the system. If a fatal error occurs during the operation of the system, the terminal will display the error message, record this message, and automatically return to the initial state.

7.20 Remote monitoring function

The system provides an Internet/Intranet interface, which can monitor the production and operation of the water plant through the company network on the Internet.

Water Treatment Automation Lecture Notes

Lecture 1 Overview of Water Treatment

4. Water quality

1 . The main unit process used:

2. Conventional water treatment process:

3. Strengthen the conventional water treatment process:

4. High turbidity water treatment process:

5. Low temperature and low turbidity water treatment process:

6. Slightly polluted water treatment process:

7. Eutrophic lake water treatment process:

Lecture 2 Water plant equipment

Lecture 3 Introduction to Automatic Control System of Waterworks

4. Selection of PLC

1. American Rockwell Corporation

2. Schneider Corporation

3. Siemens

Four, PLC module type

Five, automatic control system PLC programming, the programming method to be followed

7. The upper computer programming generally uses the configuration method.

8. Requirements for the automatic control system of the water plant

1. Control design of water intake pumping station

2. Dosing control design

3. Chlorination control design

4. Control design of reaction sedimentation tank

5. Filter control design

6. Control design of water pumping station

7 . Automatic control system function design

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