Summary:
The rapid development of water plant automation and the emergence of problems are the most significant features of water plant automation in recent years. 
With the rapid development of automation technology, system control equipment and electromechanical instrumentation equipment, filter tank automation, pharmaceutical injection automation, pump station automation, and water quality inspection automation technology are becoming more and more mature. Water plant automation projects have been implemented in large and medium-sized cities in China. Good technical environment. In fact, since the 90s of last century, the domestic water plant automation has made great progress.
At present, during the construction and expansion of large and medium-sized urban water plants in the country, relying mainly on the introduction of foreign capital and a full set of equipment technologies, the average level of automation technology in water plants is higher; while the medium and small-sized water plants mainly achieve automation by retrofitting old water plants, their characteristics are: The design work is based on localization, and equipment selection is combined with Chinese and foreign. Due to the relatively weak technological power of small and medium-sized water plants, the maintenance of automation in production has certain technical difficulties. Although the domestic water plant automation has made great progress, but by the domestic economy, technical conditions, the water plant automation is achieved under certain conditions, with water plant pumping station automation, for example, domestic motor, switchgear and other equipment quality is often Failure to meet the requirements of automation control, coupled with the lack of a unified planning of the water supply network, resulting in the pump station automation equipment can only rely on imported equipment, resulting in large investment, no obvious benefits, high maintenance costs, and many pumping station automation can only achieve the pump Automatic switching and speed regulation.
According to the practice of automation design and transformation, with reference to the experience of water plant operation and management, we believe that the automation of domestic water plants has formed a certain pattern, and there are also some obvious problems that we need to solve in practice. 
I. Main modes and issues for automatic design of water plants
The application of programmable logic controllers and computers is a feature of water plant automation. At present, three kinds of control systems are used in China; SCADA, DCS, and PLC+PC. Which PLC + PC controller is more popular. The system can achieve distributed control, system stability is good, development, operation is simple, and better meet the domestic water plant automation monitoring and protection requirements. Water plant automation control process design using PLC+PC system generally adopts the following mode. 
1.1 Communication Master Station
The major and medium-sized water plant main stations are mainly equipped with three monitoring computers: one for processing production data reports and two for production monitoring (one for use and one for preparation). Production monitoring computer configuration fault alarm printing function and real-time print alarm items. The main station generally sets the alarm bell to strengthen the alarm function. According to actual needs, monitoring computers can also be set up in the offices of management departments so that managers can keep abreast of the production situation. 
The interference of network communication lines should be fully considered in the design. The communication cable should not have a split port. Although the communication cable has a shielding layer, it should be reinforced with a metal pipe in addition to the communication cable (the communication cable includes the instrument signal communication line), and the wiring should avoid strong electrical equipment such as transformers. , high-voltage cables, to avoid electromagnetic interference. 
1.2 Dosing station
Dosing station equipment mainly consists of automatic control systems, executing agencies, and meters. The automatic control system generally adopts PLC, and is mainly responsible for completing the data collection of the dosing station. In the design of the dosing station, there is a common problem that the PLC does not completely collect the output signals of the instruments and devices. Due to the different instrumentation and equipment used by various water plants, the designers did not fully understand the functions of the equipment when designing and lacked the ability to monitor the auxiliary data of the equipment. The general configuration of the implementing agencies are: chlorine injection, ammonia injection equipment, water purification agent (coagulant and coagulant, etc.) equipment, chlorine leakage, ammonia leak alarm, chlorine, ammonia bottle scales and flow meters. Some water plants are also equipped with water purification agent mixing equipment and caustic soda dosing equipment. For the production data, the chlorinator and ammonia dosing amount, the stroke of the metering pump, the frequency, and the weighing scale value are mainly collected. The number of alarm points for the high and low vacuum control valves in the equipment is relatively small. These switch quantity warning signals can provide clear guidance for equipment maintenance and help producers manage and maintain equipment. It is especially suitable for small and medium-sized water plants that lack technical strength. The dosing station is generally equipped with a water quality meter room, a raw water high turbidity meter and a flow meter, and some water plants also have an ammonia nitrogen meter. In actual operation, the use cycle of the instrumentation sensor of the dosing station should be compiled into a corresponding alarm program to promptly remind the production personnel to maintain and replace. 
1.3 Reaction tank and sedimentation tank station
The station's control equipment consists of mud discharge valves and mud discharge machines. For mud discharge valves, two types of working modes, automatic cycle mud dumping and computer remote mud draining, can be realized. A specific problem must be considered when setting up the mud discharging program: Since the sewage discharge pipe or the sump volume of the water plant limits the amount of sewage discharged, separate the sewage from the filter tank, the sludge from the sludge discharger and the sewage from the discharge valve of the reaction tank, and drain the sewage valve group. To ensure production safety. 
In recent years, most of the water plants built use flat-flow sedimentation tanks. The sediment at the bottom of the pool is not evenly distributed. The sludge evacuator must travel at a variable speed. At present, the parallel-flow pond sludge evacuators are mostly operated by step-speed control. The running speed is controlled by several trip switches provided on the equilibria. According to the law of sedimentation in the bottom of the pool, it is better to design a stepless speed regulation operation, which can save the production water consumption and discharge mud more thoroughly. 
1.4 Filter and Backwash Stations
The station mainly completes the two control tasks of filtering water and coordinating the blower room recoil. Generally, the work status of the filter pool is divided into three types: water stoppage, water filtration, and backwash. The main collection of filter water level, head loss signal, processing back flush queue, maximum work cycle settings and other work. 
In the filtered water state, the control program uses the control function to achieve constant water level filtration, set the remote control filter tank mud drain valve, and the opening degree of the filter valve to handle sudden production problems. In the state of stopping the pool, all remote control operations of the valve are set to facilitate maintenance and other production work. 
Filter backwashing starts with two parameters of cycle and head loss, but there is little opportunity for head loss to initiate backwashing, and head loss pressure gauges need to be calibrated frequently after long-term operation. If they are not calibrated in time, their data is often unreliable. Gas-water mixed backwashing is divided into five price segments: filter water drain flushing, air-water mixed flushing, water flushing, and filter water inflow. When the filter is flushed with a Roots blower, the noise is large when starting the fan. Soft start using the inverter can reduce the noise pollution. In the process of water flushing, gas flushing, and gas-water mixing, the required gas and water volume are different. One fan and one pump are used. The Jiangbei Water Plant in Huizhou City under construction has adopted a new backflushing process: in the pure backwash of gas and water, 2 sets of fans and 2 sets of pumps are used respectively; when mixing air and water, 1 set of fans and 1 set are used. Water pump. In this way, the flow rate of backwash gas and water tends to be reasonable, but the control program is complicated. 
Recoil equipment can be made with domestic equipment. In order to overcome the failure problem of equipment in domestic start-up cabinets, monitoring data can be collected on the relevant relays, and software can be used to find that startup cabinets are malfunctioning when they are started or run to prevent further accidents. 
1.5 I. Secondary pump station
The automation of the pump station mainly includes: monitoring the operation of the pump and collecting the factory water quality data. 
The main data collected by the pump and motor includes the motor temperature, the front and rear bearing temperature of the pump, and the pump outlet pressure. In the past, there are many examples of automation of pumping stations that use frequency conversion to control two-stage constant pressure water supply. Due to the layout of the city's pipe network, the economic benefits of this technology are not obvious. Nowadays, most of the water plants have only guaranteed primary pumps. Station automation, secondary pump station semi-automatic. 
Factory water detection instruments mainly include: clean water turbidity meter, flow meter, residual chlorine detector, pressure gauge, PH meter and so on. In the water plant automation design, sampling points of the raw water and the water meter directly affect the real-time and accuracy of the instrument detection, thus affecting the automatic control. For example, the post-chlorination point of the Shakou Water Plant of Foshan City has no mixer in the water inlet pipe of the clear water tank in front of the clear water tank, and the residual chlorine sampling point is located on the water outlet pipe of the secondary pumping station, resulting in the detection of post-chlorine dosing and residual chlorine up to The lag of 2h caused a significant change in post-chlorination. Later, in the second-stage pumping station, an auxiliary chlorine injection point was added to shorten the detection delay of residual chlorine to 15 minutes, which improved the original chlorination. Therefore, in the automation design work, the design of automation should be closely linked with the design of the process system in order to ensure the entire system to achieve automatic control. 
The problem of lightning protection in automated waterworks cannot be ignored. Because of the lack of lightning protection measures in early-run automated water plants, the loss of their righteousness and control systems was severe due to lightning strikes. Taking the PLC system as an example, accidents caused by damage to the AD conversion module often occur due to the lightning of the instrument. In the past two years, there have been a large number of surge arrester products. The investment in lightning protection of automated water plants is very low, but its protection effect is very obvious. 
With the universal application of automation, the degree of automation of reliability and safety issues has gradually attracted attention. Many water plants are considering increasing the closed-circuit monitoring system in the design and directly monitoring some key production sites. The current closed-circuit monitoring system already has a simple alarm function, which can produce alarms for simple problems such as abnormal water levels. At present, closed-circuit monitors have gradually become an important part of the water plant automation system. 
II. Development direction and production management of water plant automation 2.1 Reducing investment, increasing the rate of domestic use of equipment and the intelligent degree of control software
In the early 90s of last century, in the automation design of water plants, over-reliance on imported equipment led to high system investment, low cost-effectiveness, and poor implementation in production and operation, leading to the automation of huge investment projects. The system becomes a fashionable and expensive decoration. With the introduction of domestic equipment of high quality and low cost into the automation of water plants, the rate of automated equipment design for water plants in China is constantly increasing, forcing foreign equipment to continue to decline in price, and the price/performance ratio is rising. It is precisely the application of domestic equipment, not only There has been a significant increase in the level and performance of automation, and the investment in the system has continued to decline. In fact, many water plant automations are based on the rational selection of control equipment and are configured with a combination of domestic and foreign equipment, effectively reducing automation investment. In addition, in the automatic operation process, the device often malfunctions or malfunctions, and it is necessary to enhance the reliability of the control system in the automation design work and improve the degree of intelligence of the control program. The technical personnel should be familiar with the performance of the equipment, accurately set the equipment monitoring alarm signal, play the function of automatic monitoring and protection, and strengthen the safety and reliability of the design scheme. 
2.2 Transform old water plants to realize the upgrading of water plants
The transformation of old water plants has become one of the most important tasks in the current automation of water works. The process, layout, and equipment of the old water plant vary widely. Each water plant transformation must be specifically analyzed. Only when the automation technology and the production process are reasonably combined can the purpose of successful transformation and investment saving be achieved. 
At present, most of the old water plant renovation work is mainly to improve the degree of automation of the water purification system. This is the choice made at the present stage according to the actual situation. The two major process filters and dosing of the water purification system are the focus. 
According to different types of filter, the equipment used is not completely the same, the main equipment for automatic filter configuration is: filter water level, head loss monitoring, post-filter water valve, backwash valve, water pump (fan), etc. Imported equipment has relatively good reliability; there are many products for valves and pumps (fans), and there is a large gap in performance. There are many problems in design selection. For the filter system, the automation transformation mainly has the following aspects:
A. Adjust the opening of the filtered water valve according to the change of the filter water level to achieve constant water level filtration. First, according to the actual site conditions, determine the constant water point (a point), through programming, constant water level can be input into the program. When the water intake increases and the water level rises above point a, the RN transmitter will immediately transfer the water level change to the filter tank PLC slave station. At this time, PLC will generate a control signal through calculation and increase the opening of the filtered water valve, so that the water level will drop to point a. On the contrary, when the water level is lower than the position of a, the PLC slave station will generate a control signal to reduce the opening of the filtered valve, so that when the water level rises to point a, the PLC slave station will generate a control signal to reduce the opening of the filtered valve. Degree, so that the water level rises to the position of a. In this way, through this control method, it is possible to ensure that the filter tank is filtered at a constant water level; this ensures the safe operation of the filter tank and the quality of the filtered water. In each filter, an obstruction sensor must be installed. The obstruction sensor inputs the blocking degree of the filter media to the PLC slave station in the standard signal mode (for example, 4-20mA corresponds to 0-250cm water column), when the blocking value is greater than the set value in the PLC (usually set to 180cm water column) , PLC will produce the corresponding control instructions, start the backwash pump, blower and a variety of valves, automatic backwash filter, and to achieve the flushing pump and blower cycle control. 
B. The filtering effect depends on the filter structure. Whether or not this effect can be maintained often depends on a reasonable flush. In certain raw water quality, coagulant filling conditions and filtration rate conditions, the filtration effect is determined by the filter layer. The finer, deeper, and more uniform the filter layer, the better the filtration effect; the coarser, deeper and more uniform the filter layer is, the more muddy it is, ie the permissible filtration period, the filtration rate or the turbidity of the inlet water can be higher. After 1970, the United States generally used double-layer filter media, 0.5m coal (Es=1.0mm, Uc=1.5), 0.25m sand (Es=0.5mm, Uc=1.5). Here Es is the effective value path; Ue is the uniform coefficient. After 1980, deep (1.8m) thick (Es = 1.3mm, Uc = 1.5) coals and below 0.3m sand (Es = 0.75mm) (or none) prevailed. In recent years, coarse-grained (d=0.95mm) deep (L=1.2m) sand filter layers have been used in China. For coarse-grained deep filter media, the effluent turbidity can be ≤ 0.1 NTU even at higher filtration rates (15 to 20 m/hr). In order to ensure the filtering effect, a certain ratio should be maintained between the thickness L of the filter layer and the effective diameter d. Normal sand filter and standard double filter L/d ≥ 1000, coarse filter deep filter L/d ≥ 1300, in order to make water out When the turbidity reaches 0.1NTU, the L/d ratio needs to be increased by 25% on the basis of the double-layer filter and coarse-grained deep filter without polymer coagulant aid. Prof. Kawamura concluded that U.S. water plant filter operating experience suggests that when the filter layer thickness is less than 0.9 m, surface flushing and air water flushing are equally effective, and surface flushing is no less than gas water flushing. When >0.9m, it is advisable to flush with (or without) surface flushing. The technical transformation of the existing water plant filter tank is limited by the depth of the filter layer and even the flushing strength. To improve the filtering effect, the conventional filter tank should be changed to uniform particle filter material when it is sanded. The depth should be used as much as possible, and the uniformity coefficient should be as small as possible and the effective grain size should be as small as possible. The diameter is 1/1000 of the thickness, and the best flushing strength can meet the needs of the new filter layer. Otherwise, the addition of surface flushing, whether it is more thoroughly transformed into a coarse-grained deep filter tank is determined by a technical and economical comparison. 
C. In the transformation of the old water plant filter tank, through practice, it has been shown that the siphon filter, valveless filter, double-valve filter and ordinary fast filter tanks can be modified to double the output of the original filter tank. The original 1.5 to 2 times, 20% to 30% higher than the French Deliman V-type filter, the water quality is much better than the original filter, to the national requirements. The backwash system uses gas-water backwash, and the water distribution uses the latest plastic filter bricks. The backwash effect is good, the pool structure is simple, and the cost is low. All valves can use pneumatic valves. When they are normally filtered, they can run during power outages. The constant water level adjustment control is a no-power control system. The retrofit filter has all the features of a modern filter. Due to the superior backwash performance, the water consumption of the water plant is greatly saved, only one-tenth of the original, and the backwash is thorough, which is of great significance for reducing water plant consumption and saving water resources. Generally, the backwash water consumption of a waterworks is 5% to 10% of the water production, and a filter with good operating conditions takes 5% of the water consumption. For a water plant with a daily output of 10,000 tons, the daily water consumption is 500 tons. The annual consumption The amount of water is 180,000 tons, while the annual water consumption of the new filter is only 18,000 tons, saving 162,000 tons; if the water fee is 1.5 yuan/ton, it will save 243,000 yuan per year; for the 100,000 tons/day water plant, annual savings The cost of backwash water consumption alone was 2.43 million yuan. - That is to say, generally can recover the transformation cost within one year, and at the same time, the water supply capacity has multiplied, and a water plant becomes two water plants or three water plants. With less investment, shorter construction period, and quicker results, the huge investment in the construction or expansion of new water plants is eliminated, and its economic benefits are unlimited. 
In terms of the water plant dosing system, especially the water purification agent dosing, field technicians have conducted a lot of research. For the practical application of water purifiers, the following examples better reflect its development characteristics. The automated gravity reform of the high-pot of the water plant in the southeast of Fuzhou reflects the combination of old and new technologies. The transformation of the plant has captured the essence of the automation of pharmaceutical injection, using feedback signals to control the regulator, without changing the original building structure, and still relying on gravity as a driving force. The renovation work not only saves investment in civil engineering equipment, but also integrates the old and new production systems. Zhenjiang Jinxi Water Plant's casting automation reform, the use of raw water flow meter and filter water turbidity meter constitute a control system. The function of preventing mutations when controlling the water purifying agent dosage is weak. The fuzzy control function used by Minhang Water Plant in Shanghai improves the signal, so that the real-time performance of the dosage change with raw water parameters is strengthened, when the original water flow rate of change At 100%, the turbidity of the water before filtration can be maintained at about 5 NTU. All of these examples have successfully realized the automation of retrofitting of old water plant water purifiers. The investment cost is low and the effect is relatively good. All of them involve the research of the automation system, which reflects the trend of the in-depth development of the domestic water plant automation technology. The technicians have entered the self-research period from the simple introduction of the past. 
Xiamen Feihua Water Environmental Protection Technology Co., Ltd. has independently developed and developed an automated dosing system during the project implementation of the water plant's automatic twisting and dosing system. The control system uses turbidity control as the main line, and the system collects raw water flow and raw water turbidity. The control is the main line, and the system collects raw water flow, raw water turbidity and simulated inclined tube turbidity to carry out compound calculations. Simultaneously, the turbidity change of the precipitated water is considered, and the optimal dosing control amount is obtained on-line. Ensure that the amount of dosing can be reasonably reduced in the case of ensuring that the sedimentation water reaches the standard, and the dosing amount be adjusted in time when the raw water flow changes, and the dosing is automatically stopped when the raw water is stopped. The man-machine interface adopts industrial control computer and 21 "display, can integrate the system into the factory's existing management network, can carry out remote data review and system adjustment. It can dynamically select different pharmaceutical formulations online, adjust the control parameters online. Remote service software solves user's problems online in time, and the system mainly includes the following parts: on-site data acquisition and processing system, frequency conversion control system, metering pump liquid injection system, etc. The functional characteristics of each part are as follows:
A. Field data acquisition and processing system adopts Modicon (or AB company, SIEMENS, etc.) modular PLC, processor selects TSX Premium P57203M, equipped with MB+ network card, can communicate with other stations PLC, the system has reliable hardware, powerful software , It is a reliable guarantee for the automatic control of the water purification station. 
B. The frequency conversion control system mainly includes two parts: frequency conversion control and PLC control: the frequency converter selects Schneider's products and has stable performance and reliable operation. It uses two metering pumps, two frequency converters, and one set of control cabinets. Metering pump dosing system; the control cabinet controls the working status of the two metering pumps (including start, stop, manual, automatic and running frequency of the metering pump), and also collects the output frequency of the inverter. The frequency conversion cabinet PLC is connected to the pump house PLC through the MB+ network, which can be monitored centrally through the pump house PLC. 
C. The dosing pump liquid dosing system mainly includes the following parts: 1. Dosing pump main machine (use precision mechanical diaphragm dosing pump); 2. Y-type filter: Installed between the metering pump and the drug pool, filter out the liquid Dregs; 3, flow equalizer: installed at the outlet of the metering pump, to equalize the metering pump outlet flow while reducing the impact of liquid chemicals on the pipeline; 4, safety relief valve: installed at the outlet of the metering pump to prevent the pipe from clogging and produce high pressure Damage to pipelines and molds; 5ã€Back pressure valve: prevent backflow and siphonage of metering pump; 6. Glass rotor flowmeter: intuitive display of dosing amount; 7. Optional automatic stroke regulator;
The relevant instrument is mainly a turbidity meter, and a turbidity meter with a cleaning device is used to drive the sampling cylinder of the turbidity meter at regular intervals by driving an ABS electric ball valve installed at the turbidity meter cleaning port. 
2.3 Strengthen Water Plant Automatic Production and Operation Management
Automated water plant production management is a problem that should be considered in the automation of the water plant. In actual production, many water plants have been operating for several years, and automation has become manual. This phenomenon has mostly appeared in the early construction of automated water plants. There are many reasons for this phenomenon. One is that the design ideas and solutions are not clear, and it is out of line with the actual water plant production management. For example, some water plants add an excessive amount of manual operation equipment while automating the design, which not only causes duplicate investment, but also causes the production personnel to produce incorrect dependency psychology. In addition, because the technicians do not understand the actual situation of the production, their design often differs from the actual production, causing partial failure of the automation design. The second reason is that production managers do not recognize the automation of water works. Some water plants will continue to divide employees into electricians, mechanics, waterworkers, and electricians of pumping rooms on a one-to-one basis in accordance with the old-fashioned water production model. The obvious separation of posts does not fully meet the needs of automated production in water plants. Automated water plants should implement safety benefit production management with a controlled system as a unit, unlike old water plants that implement management systems with isolated equipment. Third, managers cannot effectively master the technical maintenance work of automated water plants. Although current popular control systems have good reliability, different failures may occur due to aging of the equipment after several years of operation. Due to the aging of network communication lines caused by false alarm communications, component deformation caused by poor contact, individual component input points, etc., these require production management personnel in accordance with the actual situation in a timely manner to deal with equipment maintenance problems. 
Third, the water plant automation equipment selection
The selection of equipment is an important part of the design of the water plant automation system. The selection of equipment must meet the control requirements, and at the same time pay attention to the economical efficiency of equipment investment. At present, in the water plant automation design, the programmable logic controller, the main water quality meter, the filter valve, the input automation equipment and so on select the imported equipment. 
3.1 Reasonable selection of imported equipment
The selection of imported equipment requires an actual understanding of its performance, so that a reasonable choice of cost-effective equipment can be achieved. For example, water plants dosing, water quality testing automation equipment, there is a big difference in the price of imported equipment. Some foreign companies that develop the Chinese market earlier, such as the capital, W&T, have a wider market, and earlier in the Chinese market have higher quotations, and the quotations are not much reduced. The same equipment quotations are about 1/3 higher than other companies. On the contrary, for some companies with small market size, such as Erdos, Honeywell and other companies offer relatively low prices, their equipment performance is basically the same. Due to the fact that these companies do not use many products, their performance is not familiar to everyone. In the process of use, some technical explorations may be needed, so less choices are used. If companies have a certain amount of technical strength, they should seize the favorable market situation and adopt their products, which can greatly reduce the automation of water plants. Through extensive understanding of imported equipment, it is not difficult to find that different equipment quotes from the same company or vendor are also different, which also provides conditions for us to reduce investment in the selection of control equipment. 
Control equipment PLC foreign suppliers have entered the Chinese market, the more popular PLC brands include the United States AB, Germany's Siemens, Japan's Mitsubishi and France, Spain, South Korea's products. American AB company PLC software function is relatively complete (at present only AB company's products have a special fuzzy control function), but the price is higher, Mitsubishi PLC prices are relatively low, to meet the water plant automation control requirements. In addition, the monitoring system software is also an automatic design need to choose, more famous monitoring software is the United States FIX software, in addition to the domestic configuration king, Taiwan's Yanhuang, and many professional company's supporting software, can achieve a certain scale of water Factory automation monitoring requirements. 
3.2 Reasonably configure domestic equipment
At present, in the automation design work, domestic (or Sino-foreign joint venture) control equipment is selected to be more reliable: pressure sensors, flowmeters, turbidimeters, flowing current controllers, monitoring computers, various cables, and lightning protection devices. There are more brands of products for selection, only the use of good quality control equipment can meet the water plant automation control requirements, to meet the design reliability requirements. In general, the product reliability of joint ventures or wholly-owned enterprises adopting imported technology can be comparable to that of imported equipment. For example, the water level gauge, the degree of clogging of the V-type filter, and the domestically produced products using the E+H company's technology have the same performance and appearance as the imported products. The price difference is more than 1/3. By understanding product performance, designing different equipment to be applied in the water plant control system is the best way to reduce the automation investment in the water plant. Therefore, in the water plant automation design work, a reasonable choice of equipment can significantly reduce investment. 
The common filter in a water plant is a gas-water backwash V-filter, and one of the key points in water plant automation is the filter station. The filter tube gallery basically uses pneumatic butterfly valves. There are a number of products from Europe and the United States that are used in local water plants, and domestic pneumatic valves are used less frequently. In the actual automation reform, part of the filter valve can be made of domestic pneumatic valves, and the production performance is also better. 
Water plant automation design and transformation should follow the principles of safety, reliability and economy, sum up experiences, integrate automation technology and water production technology, and continuously develop and improve the automation level of water plants in practice.
The rapid development of water plant automation and the emergence of problems are the most significant features of water plant automation in recent years. 
With the rapid development of automation technology, system control equipment and electromechanical instrumentation equipment, filter tank automation, pharmaceutical injection automation, pump station automation, and water quality inspection automation technology are becoming more and more mature. Water plant automation projects have been implemented in large and medium-sized cities in China. Good technical environment. In fact, since the 90s of last century, the domestic water plant automation has made great progress.
At present, during the construction and expansion of large and medium-sized urban water plants in the country, relying mainly on the introduction of foreign capital and a full set of equipment technologies, the average level of automation technology in water plants is higher; while the medium and small-sized water plants mainly achieve automation by retrofitting old water plants, their characteristics are: The design work is based on localization, and equipment selection is combined with Chinese and foreign. Due to the relatively weak technological power of small and medium-sized water plants, the maintenance of automation in production has certain technical difficulties. Although the domestic water plant automation has made great progress, but by the domestic economy, technical conditions, the water plant automation is achieved under certain conditions, with water plant pumping station automation, for example, domestic motor, switchgear and other equipment quality is often Failure to meet the requirements of automation control, coupled with the lack of a unified planning of the water supply network, resulting in the pump station automation equipment can only rely on imported equipment, resulting in large investment, no obvious benefits, high maintenance costs, and many pumping station automation can only achieve the pump Automatic switching and speed regulation.
According to the practice of automation design and transformation, with reference to the experience of water plant operation and management, we believe that the automation of domestic water plants has formed a certain pattern, and there are also some obvious problems that we need to solve in practice. 
I. Main modes and issues for automatic design of water plants
The application of programmable logic controllers and computers is a feature of water plant automation. At present, three kinds of control systems are used in China; SCADA, DCS, and PLC+PC. Which PLC + PC controller is more popular. The system can achieve distributed control, system stability is good, development, operation is simple, and better meet the domestic water plant automation monitoring and protection requirements. Water plant automation control process design using PLC+PC system generally adopts the following mode. 
1.1 Communication Master Station
The major and medium-sized water plant main stations are mainly equipped with three monitoring computers: one for processing production data reports and two for production monitoring (one for use and one for preparation). Production monitoring computer configuration fault alarm printing function and real-time print alarm items. The main station generally sets the alarm bell to strengthen the alarm function. According to actual needs, monitoring computers can also be set up in the offices of management departments so that managers can keep abreast of the production situation. 
The interference of network communication lines should be fully considered in the design. The communication cable should not have a split port. Although the communication cable has a shielding layer, it should be reinforced with a metal pipe in addition to the communication cable (the communication cable includes the instrument signal communication line), and the wiring should avoid strong electrical equipment such as transformers. , high-voltage cables, to avoid electromagnetic interference. 
1.2 Dosing station
Dosing station equipment mainly consists of automatic control systems, executing agencies, and meters. The automatic control system generally adopts PLC, and is mainly responsible for completing the data collection of the dosing station. In the design of the dosing station, there is a common problem that the PLC does not completely collect the output signals of the instruments and devices. Due to the different instrumentation and equipment used by various water plants, the designers did not fully understand the functions of the equipment when designing and lacked the ability to monitor the auxiliary data of the equipment. The general configuration of the implementing agencies are: chlorine injection, ammonia injection equipment, water purification agent (coagulant and coagulant, etc.) equipment, chlorine leakage, ammonia leak alarm, chlorine, ammonia bottle scales and flow meters. Some water plants are also equipped with water purification agent mixing equipment and caustic soda dosing equipment. For the production data, the chlorinator and ammonia dosing amount, the stroke of the metering pump, the frequency, and the weighing scale value are mainly collected. The number of alarm points for the high and low vacuum control valves in the equipment is relatively small. These switch quantity warning signals can provide clear guidance for equipment maintenance and help producers manage and maintain equipment. It is especially suitable for small and medium-sized water plants that lack technical strength. The dosing station is generally equipped with a water quality meter room, a raw water high turbidity meter and a flow meter, and some water plants also have an ammonia nitrogen meter. In actual operation, the use cycle of the instrumentation sensor of the dosing station should be compiled into a corresponding alarm program to promptly remind the production personnel to maintain and replace. 
1.3 Reaction tank and sedimentation tank station
The station's control equipment consists of mud discharge valves and mud discharge machines. For mud discharge valves, two types of working modes, automatic cycle mud dumping and computer remote mud draining, can be realized. A specific problem must be considered when setting up the mud discharging program: Since the sewage discharge pipe or the sump volume of the water plant limits the amount of sewage discharged, separate the sewage from the filter tank, the sludge from the sludge discharger and the sewage from the discharge valve of the reaction tank, and drain the sewage valve group. To ensure production safety. 
In recent years, most of the water plants built use flat-flow sedimentation tanks. The sediment at the bottom of the pool is not evenly distributed. The sludge evacuator must travel at a variable speed. At present, the parallel-flow pond sludge evacuators are mostly operated by step-speed control. The running speed is controlled by several trip switches provided on the equilibria. According to the law of sedimentation in the bottom of the pool, it is better to design a stepless speed regulation operation, which can save the production water consumption and discharge mud more thoroughly. 
1.4 Filter and Backwash Stations
The station mainly completes the two control tasks of filtering water and coordinating the blower room recoil. Generally, the work status of the filter pool is divided into three types: water stoppage, water filtration, and backwash. The main collection of filter water level, head loss signal, processing back flush queue, maximum work cycle settings and other work. 
In the filtered water state, the control program uses the control function to achieve constant water level filtration, set the remote control filter tank mud drain valve, and the opening degree of the filter valve to handle sudden production problems. In the state of stopping the pool, all remote control operations of the valve are set to facilitate maintenance and other production work. 
Filter backwashing starts with two parameters of cycle and head loss, but there is little opportunity for head loss to initiate backwashing, and head loss pressure gauges need to be calibrated frequently after long-term operation. If they are not calibrated in time, their data is often unreliable. Gas-water mixed backwashing is divided into five price segments: filter water drain flushing, air-water mixed flushing, water flushing, and filter water inflow. When the filter is flushed with a Roots blower, the noise is large when starting the fan. Soft start using the inverter can reduce the noise pollution. In the process of water flushing, gas flushing, and gas-water mixing, the required gas and water volume are different. One fan and one pump are used. The Jiangbei Water Plant in Huizhou City under construction has adopted a new backflushing process: in the pure backwash of gas and water, 2 sets of fans and 2 sets of pumps are used respectively; when mixing air and water, 1 set of fans and 1 set are used. Water pump. In this way, the flow rate of backwash gas and water tends to be reasonable, but the control program is complicated. 
Recoil equipment can be made with domestic equipment. In order to overcome the failure problem of equipment in domestic start-up cabinets, monitoring data can be collected on the relevant relays, and software can be used to find that startup cabinets are malfunctioning when they are started or run to prevent further accidents. 
1.5 I. Secondary pump station
The automation of the pump station mainly includes: monitoring the operation of the pump and collecting the factory water quality data. 
The main data collected by the pump and motor includes the motor temperature, the front and rear bearing temperature of the pump, and the pump outlet pressure. In the past, there are many examples of automation of pumping stations that use frequency conversion to control two-stage constant pressure water supply. Due to the layout of the city's pipe network, the economic benefits of this technology are not obvious. Nowadays, most of the water plants have only guaranteed primary pumps. Station automation, secondary pump station semi-automatic. 
Factory water detection instruments mainly include: clean water turbidity meter, flow meter, residual chlorine detector, pressure gauge, PH meter and so on. In the water plant automation design, sampling points of the raw water and the water meter directly affect the real-time and accuracy of the instrument detection, thus affecting the automatic control. For example, the post-chlorination point of the Shakou Water Plant of Foshan City has no mixer in the water inlet pipe of the clear water tank in front of the clear water tank, and the residual chlorine sampling point is located on the water outlet pipe of the secondary pumping station, resulting in the detection of post-chlorine dosing and residual chlorine up to The lag of 2h caused a significant change in post-chlorination. Later, in the second-stage pumping station, an auxiliary chlorine injection point was added to shorten the detection delay of residual chlorine to 15 minutes, which improved the original chlorination. Therefore, in the automation design work, the design of automation should be closely linked with the design of the process system in order to ensure the entire system to achieve automatic control. 
The problem of lightning protection in automated waterworks cannot be ignored. Because of the lack of lightning protection measures in early-run automated water plants, the loss of their righteousness and control systems was severe due to lightning strikes. Taking the PLC system as an example, accidents caused by damage to the AD conversion module often occur due to the lightning of the instrument. In the past two years, there have been a large number of surge arrester products. The investment in lightning protection of automated water plants is very low, but its protection effect is very obvious. 
With the universal application of automation, the degree of automation of reliability and safety issues has gradually attracted attention. Many water plants are considering increasing the closed-circuit monitoring system in the design and directly monitoring some key production sites. The current closed-circuit monitoring system already has a simple alarm function, which can produce alarms for simple problems such as abnormal water levels. At present, closed-circuit monitors have gradually become an important part of the water plant automation system. 
II. Development direction and production management of water plant automation 2.1 Reducing investment, increasing the rate of domestic use of equipment and the intelligent degree of control software
In the early 90s of last century, in the automation design of water plants, over-reliance on imported equipment led to high system investment, low cost-effectiveness, and poor implementation in production and operation, leading to the automation of huge investment projects. The system becomes a fashionable and expensive decoration. With the introduction of domestic equipment of high quality and low cost into the automation of water plants, the rate of automated equipment design for water plants in China is constantly increasing, forcing foreign equipment to continue to decline in price, and the price/performance ratio is rising. It is precisely the application of domestic equipment, not only There has been a significant increase in the level and performance of automation, and the investment in the system has continued to decline. In fact, many water plant automations are based on the rational selection of control equipment and are configured with a combination of domestic and foreign equipment, effectively reducing automation investment. In addition, in the automatic operation process, the device often malfunctions or malfunctions, and it is necessary to enhance the reliability of the control system in the automation design work and improve the degree of intelligence of the control program. The technical personnel should be familiar with the performance of the equipment, accurately set the equipment monitoring alarm signal, play the function of automatic monitoring and protection, and strengthen the safety and reliability of the design scheme. 
2.2 Transform old water plants to realize the upgrading of water plants
The transformation of old water plants has become one of the most important tasks in the current automation of water works. The process, layout, and equipment of the old water plant vary widely. Each water plant transformation must be specifically analyzed. Only when the automation technology and the production process are reasonably combined can the purpose of successful transformation and investment saving be achieved. 
At present, most of the old water plant renovation work is mainly to improve the degree of automation of the water purification system. This is the choice made at the present stage according to the actual situation. The two major process filters and dosing of the water purification system are the focus. 
According to different types of filter, the equipment used is not completely the same, the main equipment for automatic filter configuration is: filter water level, head loss monitoring, post-filter water valve, backwash valve, water pump (fan), etc. Imported equipment has relatively good reliability; there are many products for valves and pumps (fans), and there is a large gap in performance. There are many problems in design selection. For the filter system, the automation transformation mainly has the following aspects:
A. Adjust the opening of the filtered water valve according to the change of the filter water level to achieve constant water level filtration. First, according to the actual site conditions, determine the constant water point (a point), through programming, constant water level can be input into the program. When the water intake increases and the water level rises above point a, the RN transmitter will immediately transfer the water level change to the filter tank PLC slave station. At this time, PLC will generate a control signal through calculation and increase the opening of the filtered water valve, so that the water level will drop to point a. On the contrary, when the water level is lower than the position of a, the PLC slave station will generate a control signal to reduce the opening of the filtered valve, so that when the water level rises to point a, the PLC slave station will generate a control signal to reduce the opening of the filtered valve. Degree, so that the water level rises to the position of a. In this way, through this control method, it is possible to ensure that the filter tank is filtered at a constant water level; this ensures the safe operation of the filter tank and the quality of the filtered water. In each filter, an obstruction sensor must be installed. The obstruction sensor inputs the blocking degree of the filter media to the PLC slave station in the standard signal mode (for example, 4-20mA corresponds to 0-250cm water column), when the blocking value is greater than the set value in the PLC (usually set to 180cm water column) , PLC will produce the corresponding control instructions, start the backwash pump, blower and a variety of valves, automatic backwash filter, and to achieve the flushing pump and blower cycle control. 
B. The filtering effect depends on the filter structure. Whether or not this effect can be maintained often depends on a reasonable flush. In certain raw water quality, coagulant filling conditions and filtration rate conditions, the filtration effect is determined by the filter layer. The finer, deeper, and more uniform the filter layer, the better the filtration effect; the coarser, deeper and more uniform the filter layer is, the more muddy it is, ie the permissible filtration period, the filtration rate or the turbidity of the inlet water can be higher. After 1970, the United States generally used double-layer filter media, 0.5m coal (Es=1.0mm, Uc=1.5), 0.25m sand (Es=0.5mm, Uc=1.5). Here Es is the effective value path; Ue is the uniform coefficient. After 1980, deep (1.8m) thick (Es = 1.3mm, Uc = 1.5) coals and below 0.3m sand (Es = 0.75mm) (or none) prevailed. In recent years, coarse-grained (d=0.95mm) deep (L=1.2m) sand filter layers have been used in China. For coarse-grained deep filter media, the effluent turbidity can be ≤ 0.1 NTU even at higher filtration rates (15 to 20 m/hr). In order to ensure the filtering effect, a certain ratio should be maintained between the thickness L of the filter layer and the effective diameter d. Normal sand filter and standard double filter L/d ≥ 1000, coarse filter deep filter L/d ≥ 1300, in order to make water out When the turbidity reaches 0.1NTU, the L/d ratio needs to be increased by 25% on the basis of the double-layer filter and coarse-grained deep filter without polymer coagulant aid. Prof. Kawamura concluded that U.S. water plant filter operating experience suggests that when the filter layer thickness is less than 0.9 m, surface flushing and air water flushing are equally effective, and surface flushing is no less than gas water flushing. When >0.9m, it is advisable to flush with (or without) surface flushing. The technical transformation of the existing water plant filter tank is limited by the depth of the filter layer and even the flushing strength. To improve the filtering effect, the conventional filter tank should be changed to uniform particle filter material when it is sanded. The depth should be used as much as possible, and the uniformity coefficient should be as small as possible and the effective grain size should be as small as possible. The diameter is 1/1000 of the thickness, and the best flushing strength can meet the needs of the new filter layer. Otherwise, the addition of surface flushing, whether it is more thoroughly transformed into a coarse-grained deep filter tank is determined by a technical and economical comparison. 
C. In the transformation of the old water plant filter tank, through practice, it has been shown that the siphon filter, valveless filter, double-valve filter and ordinary fast filter tanks can be modified to double the output of the original filter tank. The original 1.5 to 2 times, 20% to 30% higher than the French Deliman V-type filter, the water quality is much better than the original filter, to the national requirements. The backwash system uses gas-water backwash, and the water distribution uses the latest plastic filter bricks. The backwash effect is good, the pool structure is simple, and the cost is low. All valves can use pneumatic valves. When they are normally filtered, they can run during power outages. The constant water level adjustment control is a no-power control system. The retrofit filter has all the features of a modern filter. Due to the superior backwash performance, the water consumption of the water plant is greatly saved, only one-tenth of the original, and the backwash is thorough, which is of great significance for reducing water plant consumption and saving water resources. Generally, the backwash water consumption of a waterworks is 5% to 10% of the water production, and a filter with good operating conditions takes 5% of the water consumption. For a water plant with a daily output of 10,000 tons, the daily water consumption is 500 tons. The annual consumption The amount of water is 180,000 tons, while the annual water consumption of the new filter is only 18,000 tons, saving 162,000 tons; if the water fee is 1.5 yuan/ton, it will save 243,000 yuan per year; for the 100,000 tons/day water plant, annual savings The cost of backwash water consumption alone was 2.43 million yuan. - That is to say, generally can recover the transformation cost within one year, and at the same time, the water supply capacity has multiplied, and a water plant becomes two water plants or three water plants. With less investment, shorter construction period, and quicker results, the huge investment in the construction or expansion of new water plants is eliminated, and its economic benefits are unlimited. 
In terms of the water plant dosing system, especially the water purification agent dosing, field technicians have conducted a lot of research. For the practical application of water purifiers, the following examples better reflect its development characteristics. The automated gravity reform of the high-pot of the water plant in the southeast of Fuzhou reflects the combination of old and new technologies. The transformation of the plant has captured the essence of the automation of pharmaceutical injection, using feedback signals to control the regulator, without changing the original building structure, and still relying on gravity as a driving force. The renovation work not only saves investment in civil engineering equipment, but also integrates the old and new production systems. Zhenjiang Jinxi Water Plant's casting automation reform, the use of raw water flow meter and filter water turbidity meter constitute a control system. The function of preventing mutations when controlling the water purifying agent dosage is weak. The fuzzy control function used by Minhang Water Plant in Shanghai improves the signal, so that the real-time performance of the dosage change with raw water parameters is strengthened, when the original water flow rate of change At 100%, the turbidity of the water before filtration can be maintained at about 5 NTU. All of these examples have successfully realized the automation of retrofitting of old water plant water purifiers. The investment cost is low and the effect is relatively good. All of them involve the research of the automation system, which reflects the trend of the in-depth development of the domestic water plant automation technology. The technicians have entered the self-research period from the simple introduction of the past. 
Xiamen Feihua Water Environmental Protection Technology Co., Ltd. has independently developed and developed an automated dosing system during the project implementation of the water plant's automatic twisting and dosing system. The control system uses turbidity control as the main line, and the system collects raw water flow and raw water turbidity. The control is the main line, and the system collects raw water flow, raw water turbidity and simulated inclined tube turbidity to carry out compound calculations. Simultaneously, the turbidity change of the precipitated water is considered, and the optimal dosing control amount is obtained on-line. Ensure that the amount of dosing can be reasonably reduced in the case of ensuring that the sedimentation water reaches the standard, and the dosing amount be adjusted in time when the raw water flow changes, and the dosing is automatically stopped when the raw water is stopped. The man-machine interface adopts industrial control computer and 21 "display, can integrate the system into the factory's existing management network, can carry out remote data review and system adjustment. It can dynamically select different pharmaceutical formulations online, adjust the control parameters online. Remote service software solves user's problems online in time, and the system mainly includes the following parts: on-site data acquisition and processing system, frequency conversion control system, metering pump liquid injection system, etc. The functional characteristics of each part are as follows:
A. Field data acquisition and processing system adopts Modicon (or AB company, SIEMENS, etc.) modular PLC, processor selects TSX Premium P57203M, equipped with MB+ network card, can communicate with other stations PLC, the system has reliable hardware, powerful software , It is a reliable guarantee for the automatic control of the water purification station. 
B. The frequency conversion control system mainly includes two parts: frequency conversion control and PLC control: the frequency converter selects Schneider's products and has stable performance and reliable operation. It uses two metering pumps, two frequency converters, and one set of control cabinets. Metering pump dosing system; the control cabinet controls the working status of the two metering pumps (including start, stop, manual, automatic and running frequency of the metering pump), and also collects the output frequency of the inverter. The frequency conversion cabinet PLC is connected to the pump house PLC through the MB+ network, which can be monitored centrally through the pump house PLC. 
C. The dosing pump liquid dosing system mainly includes the following parts: 1. Dosing pump main machine (use precision mechanical diaphragm dosing pump); 2. Y-type filter: Installed between the metering pump and the drug pool, filter out the liquid Dregs; 3, flow equalizer: installed at the outlet of the metering pump, to equalize the metering pump outlet flow while reducing the impact of liquid chemicals on the pipeline; 4, safety relief valve: installed at the outlet of the metering pump to prevent the pipe from clogging and produce high pressure Damage to pipelines and molds; 5ã€Back pressure valve: prevent backflow and siphonage of metering pump; 6. Glass rotor flowmeter: intuitive display of dosing amount; 7. Optional automatic stroke regulator;
The relevant instrument is mainly a turbidity meter, and a turbidity meter with a cleaning device is used to drive the sampling cylinder of the turbidity meter at regular intervals by driving an ABS electric ball valve installed at the turbidity meter cleaning port. 
2.3 Strengthen Water Plant Automatic Production and Operation Management
Automated water plant production management is a problem that should be considered in the automation of the water plant. In actual production, many water plants have been operating for several years, and automation has become manual. This phenomenon has mostly appeared in the early construction of automated water plants. There are many reasons for this phenomenon. One is that the design ideas and solutions are not clear, and it is out of line with the actual water plant production management. For example, some water plants add an excessive amount of manual operation equipment while automating the design, which not only causes duplicate investment, but also causes the production personnel to produce incorrect dependency psychology. In addition, because the technicians do not understand the actual situation of the production, their design often differs from the actual production, causing partial failure of the automation design. The second reason is that production managers do not recognize the automation of water works. Some water plants will continue to divide employees into electricians, mechanics, waterworkers, and electricians of pumping rooms on a one-to-one basis in accordance with the old-fashioned water production model. The obvious separation of posts does not fully meet the needs of automated production in water plants. Automated water plants should implement safety benefit production management with a controlled system as a unit, unlike old water plants that implement management systems with isolated equipment. Third, managers cannot effectively master the technical maintenance work of automated water plants. Although current popular control systems have good reliability, different failures may occur due to aging of the equipment after several years of operation. Due to the aging of network communication lines caused by false alarm communications, component deformation caused by poor contact, individual component input points, etc., these require production management personnel in accordance with the actual situation in a timely manner to deal with equipment maintenance problems. 
Third, the water plant automation equipment selection
The selection of equipment is an important part of the design of the water plant automation system. The selection of equipment must meet the control requirements, and at the same time pay attention to the economical efficiency of equipment investment. At present, in the water plant automation design, the programmable logic controller, the main water quality meter, the filter valve, the input automation equipment and so on select the imported equipment. 
3.1 Reasonable selection of imported equipment
The selection of imported equipment requires an actual understanding of its performance, so that a reasonable choice of cost-effective equipment can be achieved. For example, water plants dosing, water quality testing automation equipment, there is a big difference in the price of imported equipment. Some foreign companies that develop the Chinese market earlier, such as the capital, W&T, have a wider market, and earlier in the Chinese market have higher quotations, and the quotations are not much reduced. The same equipment quotations are about 1/3 higher than other companies. On the contrary, for some companies with small market size, such as Erdos, Honeywell and other companies offer relatively low prices, their equipment performance is basically the same. Due to the fact that these companies do not use many products, their performance is not familiar to everyone. In the process of use, some technical explorations may be needed, so less choices are used. If companies have a certain amount of technical strength, they should seize the favorable market situation and adopt their products, which can greatly reduce the automation of water plants. Through extensive understanding of imported equipment, it is not difficult to find that different equipment quotes from the same company or vendor are also different, which also provides conditions for us to reduce investment in the selection of control equipment. 
Control equipment PLC foreign suppliers have entered the Chinese market, the more popular PLC brands include the United States AB, Germany's Siemens, Japan's Mitsubishi and France, Spain, South Korea's products. American AB company PLC software function is relatively complete (at present only AB company's products have a special fuzzy control function), but the price is higher, Mitsubishi PLC prices are relatively low, to meet the water plant automation control requirements. In addition, the monitoring system software is also an automatic design need to choose, more famous monitoring software is the United States FIX software, in addition to the domestic configuration king, Taiwan's Yanhuang, and many professional company's supporting software, can achieve a certain scale of water Factory automation monitoring requirements. 
3.2 Reasonably configure domestic equipment
At present, in the automation design work, domestic (or Sino-foreign joint venture) control equipment is selected to be more reliable: pressure sensors, flowmeters, turbidimeters, flowing current controllers, monitoring computers, various cables, and lightning protection devices. There are more brands of products for selection, only the use of good quality control equipment can meet the water plant automation control requirements, to meet the design reliability requirements. In general, the product reliability of joint ventures or wholly-owned enterprises adopting imported technology can be comparable to that of imported equipment. For example, the water level gauge, the degree of clogging of the V-type filter, and the domestically produced products using the E+H company's technology have the same performance and appearance as the imported products. The price difference is more than 1/3. By understanding product performance, designing different equipment to be applied in the water plant control system is the best way to reduce the automation investment in the water plant. Therefore, in the water plant automation design work, a reasonable choice of equipment can significantly reduce investment. 
The common filter in a water plant is a gas-water backwash V-filter, and one of the key points in water plant automation is the filter station. The filter tube gallery basically uses pneumatic butterfly valves. There are a number of products from Europe and the United States that are used in local water plants, and domestic pneumatic valves are used less frequently. In the actual automation reform, part of the filter valve can be made of domestic pneumatic valves, and the production performance is also better. 
Water plant automation design and transformation should follow the principles of safety, reliability and economy, sum up experiences, integrate automation technology and water production technology, and continuously develop and improve the automation level of water plants in practice.
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