Thread Content
As the main equipment of thermal power plants, boilers are required to operate safely and for a long period of time. Scaling is the main factor affecting life and the requirements for water are relatively high. Boiler water is heated at a certain temperature and pressure to produce steam, and steam is used as the medium for heat transfer and power. For low-pressure and medium-pressure boilers, this type of boiler has slightly lower water quality requirements. ； High-pressure boilers have very high requirements for water quality. Most or all of the impurities that can cause corrosion and scaling of boilers, water supply systems and other thermal equipment, cause steam and water co-evaporation, and poison ion exchange resins, such as dissolved oxygen, soluble silica, iron and residual chlorine, should be removed. In boiler water treatment, ion exchange water treatment of boiler supplementary water is the most basic and important water treatment method. This method is used in all three power stations of our unit. After the ion exchange resin fails, alkali or acid must be added for reduction, thus producing a large amount of acid-base wastewater. Direct discharge not only affects the environment, but is also monitored by the environmental protection department, causing unnecessary losses and directly affecting economic benefits. 1. Acid-base wastewater treatment method Wastewater discharge * * The standard is that the pH value is between 6.0 and 8.5, so the basic method of wastewater treatment: Acidic water-alkali, alkaline water plus acid, that is, wastewater neutralization treatment, so that the pH value of wastewater reaches between 6.0 and 8.5 for qualified discharge. The ideal situation is to use an online treatment method, that is, while discharging, acid or alkali is added according to the detected PH value to reach the standard of neutral water. This is the goal pursued by our scientific and technical personnel. However, due to factors such as the quality of the incoming water and the lag in PH value detection, there are currently no cases of successful application in China. The wastewater treatment method of the second power station of my unit before the transformation was basically based on this principle, and a PLC programmable controller was used, but the effect was not ideal. Static treatment methods are now commonly used, that is, chemical wastewater is concentrated into a treatment tank, and neutralization is performed when the liquid level in the tank reaches a certain height. According to the characteristics of yin and yang bed reduced water, there are more yin and yang beds than yin beds. The wastewater in the treatment tank is generally acidic. Adding appropriate alkali for neutralization can reach the standard. How to add alkali and how much alkali to add are the main issues in our research. The past method relied on manual addition of alkali. Since there is no online pH meter, the alkali addition process can only be based on feeling. Either too much is added or too little is added. Therefore, our unit proposed to transform the original system and use computers to control the alkali addition process. The amount of alkali added is automatically determined by the computer based on the online pH value. Due to the large amount of wastewater treated every day, the wastewater treatment time in each pool is required to be as short as possible, that is, the pool is required to be mixed evenly quickly after the alkali is added. Mixed methods include: ①Add a mixer to the pool for mixing, such as the small neutralization pool solution before the transformation of the second power station ； ②Add a gas explosion head to the pool for stirring, such as the solution adopted by a power station to add alkali and gas explosion heads at multiple points. ； ③Add a circulation pump to circulate water, such as the alkali addition scheme in the circulation pipeline of the second power station. The alkali is not only mixed evenly in the pipeline, but also circulates in the pool to achieve uniformity. 2. Principle of computer-controlled acid-base wastewater treatment. The acid-base wastewater treatment site of the boiler water treatment system is relatively far away from the operation room. The strong current control cabinet is placed in the on-site control room. In order to prevent interference with the computer, it is controlled through an intermediate relay. The acid-base wastewater treatment site consists of a treatment tank, a storage tank, an alkali tank, an alkali-adding pump, a circulation pump or fan for stirring in the treatment tank, a pouring pump between the treatment tank and the storage tank, electric valves, and various measuring instruments. Data to be detected: The liquid level of the treatment pool and storage tank, the liquid level of the alkali tank, the pH value of the pipeline, the pH value of the pool, the pH value of the outflow and the flow rate. The equipment that needs to be controlled is: Principles of circulating liquid submersible pump or fan, water pouring pump, dosing metering pump, and electric valve: The measurement data directly enters the controller. The control of various motors is based on the switch output of the controller controlling the pull-in of the intermediate relay, and then the normally open contact of the intermediate relay controls the action of the contactor of each circuit of the on-site control cabinet, thereby starting or stopping the work of each equipment. At the same time, a pair of normally open contacts of the contactor are closed and fed back to the input relay of the relay cabinet. The contacts of the intermediate relay are used as switching inputs of the controller and are input to the computer to determine whether the equipment can start reliably and determine the operating status of the equipment. Figure 1 Control system structure diagram. The operation of each equipment can be operated in three places.: ①Operate with mouse on computer screen ； ②Operations on the on-site control cabinet panel ； ③Operation buttons next to the device. 3. Control system design 3.1 System hardware configuration The system adopts the control method of upper and lower computers. The upper computer uses an industrial PC and communicates with the lower computer using 485. The upper computer mainly displays the process flow screen, collects each point value in real time, dynamically displays the actual value on the screen, automatically saves each point value, automatically alarms, prints statistics, reports, etc. The lower computer adopts Taiwan ICP Corporation’s I-8811 embedded controller, which is composed of various AI, AO, DI, DO and other cards. Its function is that the on-site signal is transmitted to the signal processing card through the cable, and processed into a 1~5V DC signal that is easy for computer processing. After A/D conversion, it is uploaded to the host computer through 485. The input signal of each loop of the regulating loop is compared with the given signal transmitted from the host computer. If it exceeds the set adjustment deviation range, PID adjustment is performed according to the PID coefficient transmitted from the host computer. The result is processed by the output module to control the regulating valve. 3.2 System software design The monitoring software of the host computer adopts the iFIX2.6 version of Interllution Company. It is an integrated software package based on multi-tasking, multi-platform, good real-time performance and good openness. It integrates the most advanced modern software technologies such as COM/DCOM, OPC, VBA, ActiveX, etc., so that all application components can be seamlessly integrated into one system, and data can be easily shared on the network. The system generated by it is stable and reliable, and has been widely used in the field of industrial control. Taiwan ICP not only provides the test software of the controller, but also provides the interface program with iFIX for free. The system uses the configuration software iFIX product. After our secondary development, we combined the characteristics of this system to configure the various functional modules we need to complete the tasks we need. Configuration includes system configuration, real-time database configuration, historical database configuration, loop configuration, flow chart configuration, alarm configuration, etc. It is also more convenient to configure 8811 in iFIX monitoring software. The main contents include: ①Channel definition defines the communication path between iFIX SCADA nodes and process hardware, including the baud rate of the network hardware and other communication settings. ②Device definition, that is, defining a single device, the specified hardware type and different configurations of other devices. Including device name, device address, and device model. ③Poll record definition defines specified parameters in a device's data block. Including initial address and data type, as well as the definition of polling time and waiting time 3.3 Main functions of the control system ① Monitoring function: Detect and monitor parameters such as liquid level, acidity, and motor current in the treatment pool ； ②Real-time dynamic process flow display function: That is, the main screen of system operation and control, which displays the opening status of each valve in real time, whether the switching is successful, whether the pump is turned on, and for control points, displays the set value and actual value of the point, the liquid level, etc. ； ③Data processing functions: The system can automatically calculate the collected signals and output the corresponding control quantities. ； ④Control function: Automatically control the normal operation of the equipment according to the corresponding set value before operation, with manual and automatic switching ； ⑤Trend module: You can see the change curve of pH value with dosage and time. ； ⑥Alarm function: Alarms for various parameters exceeding limits or abnormal equipment status in the form of pictures and sound and light signals ； ⑦Report function: Daily reports, monthly reports and other forms can be automatically generated according to user requirements, and the report can be printed by selecting the print button on the screen. The report saving time needs to be determined, and the entire process parameters of automatic alkali addition can be queried and printed at any time. 3.4 Automatic neutralization treatment of wastewater Each treatment tank handles hundreds of tons of wastewater. The initial pH values vary greatly, and the sediments in the water are also different. It is difficult to use the traditional PID adjustment method to add alkali. We use simulated artificial alkali addition method. Before adding alkali, mix the wastewater evenly, measure the pH value, add alkali according to the pH value, and then judge after mixing evenly until the water quality is qualified. Automated processes for wastewater neutralization: When the treatment pool reaches a given water level, start the compressor, the gas explosion head in the pool begins to explode, stir, and after mixing evenly (the time can be set), measure the PH value in the pool. If the pool is acidic, the program controls to automatically add alkali to neutralize it, so that the pH value reaches the emission standard between 6 and 8.5. If the pH value is greater than 8.5, pump acidic water from the storage tank or pump part of the alkaline water from the treatment tank to the storage tank, then add part of the acidic water from the sun bed, mix it thoroughly to meet the discharge standard, and start the discharge valve to discharge. 4. Conclusion This system has been applied in the wastewater neutralization treatment transformation of the first and second power stations of our unit, achieving the expected results and improving the level of production automation. The method is feasible by simulating manual alkali addition. The system is versatile and can be used in power stations, pharmaceuticals, textiles and other industries.