Electrolytic seawater chlorination system is the sterilization treatment of seawater in DC cooling water system, and provides sodium hypochlorite solution for seawater pretreatment system and boiler recharge water treatment system. Solve many problems such as sea organisms, bacteria and algae attached to the cooling water pipe and condenser copper pipe, reducing the flow area affecting the water transmission capacity, reducing the cooling efficiency of the condenser, forcing the unit to reduce the load operation affecting the power generation. This paper mainly introduces the composition, process introduction and design characteristics of the chlorine making system, and focuses on the system debugging and the treatment and feedback of the problems in the debugging process. Good system debugging is the basis of the safe operation of the unit, and good experience feedback has the value of popularization and reference.
Systematic review
BLUEWAV electrolytic seawater chlorine production device is composed of filtration system, sodium hypochlorite generation system, sodium hypochlorite storage and hydrogen discharge system, dosing system, pickling system and other process parts as well as matching electrical and automatic control system.
Process flow
The seawater is lifted from the seawater intake pump station by the seawater booster pump, into the automatic flushing filter, filtered again, injected into the BLUEWAV sodium hypochlorite generator electrolytic cell for electrolysis, and the generated sodium hypochlorite solution enters the sodium hypochlorite storage tank. When the liquid level of the sodium hypochlorite storage tank reaches a certain height, the sodium hypochlorite solution is added to the dosing point through the continuous dosing pump and the impact dosing pump. The by-product hydrogen produced by the sodium hypochlorite generator in the electrolytic process is sent into the sodium hypochlorite storage tank together with the electrolyte, the gas-liquid separation is carried out in the storage tank, the air is blown into the storage tank through the fan, the hydrogen concentration is diluted to less than 1%, and then the storage top hood is safely discharged to the atmosphere. At the same time, the electrolytic process will produce calcium and magnesium scale attached to the electrolytic cell, and the system is equipped with a pickling system to regularly pickling the electrolytic cell.
Design specification
Two sets of BLUEWAV electrolytic seawater sodium hypochlorite production equipment with a yield of 30kg/h are set up. During normal operation, two sets of chlorine production equipment are run at the same time. The circulating water volume of each unit is about 22,788m /h, and the water volume of seawater pretreatment is about 250m/h. The DC cooling water system is continuously fed with 1mg/L dosage and supplemented with 3mg/L dosage twice a day, each lasting half an hour impact feeding. The seawater pretreatment system is continuously fed with the dosage of 5-8mg/L, and the seawater is taken to the front pool of the circulating pipe, the water temperature is 20-34℃, and the pressure is 0.4-0.45MPa. The function and role of the rectifier power supply is to convert the alternating current supplied by the rectifier transformer into direct current 1700A and 64V to the electrolyzer. 380V,50Hz power supply is connected to the low-voltage PDC MCC. In addition to the sodium hypochlorite storage tank and fan, the other equipment is arranged in the chlorine making room.
System debugging procedure
In the installation stage, the manufacturer will present the PLC logic configuration of the upper computer, and the operator will determine the system operation screen and put forward modification suggestions. The debugging personnel should intervene to supervise the trial operation and transfer of the chlorine making system monomer, find out the problem as soon as possible, and check whether there is wrong installation at the valve and instrument measuring point. The chlorine making system belongs to the dangerous area. Check the system according to the design and installation drawings in advance, including civil construction, piping, equipment, lighting, anti-corrosion, ventilation, etc.
Pre-commissioning phase
The thermal debugging personnel shall make joint adjustment of the system valve and measuring point, and cooperate with the determination of valve switching time, the valve interlock protection test, the system equipment static interlock protection test, and the rectifier electrical static test: inform the installation personnel to remove the raw water pipe before the automatic cleaning filter, start the seawater raw pump to flush the pipe, and flush until the water is cleared. In order to avoid damage to the equipment due to impurities in the pipeline in the later test. The automatic cleaning filter is put into the medium pressure difference switch and time setting, which need to be dynamically adjusted to confirm the normal operation.
Static filling test of sodium hypochlorite generator, sodium hypochlorite storage tank and pickling tank to check whether there are loopholes, and cooperate with the technical personnel of the manufacturer to verify the residual chlorine meter and gas leak detector to ensure normal operation. Manually start the raw seawater pump, adjust the pressure test of the chlorine making system equipment and pipelines to the working pressure, ensure that there is no leakage point of the equipment and pipelines, sodium hypochlorite generator and pickling pipeline with salt water removal dynamic leak check. Test the continuous dosing pump, impact dosing pump, seawater raw water pretreatment dosing pump and waste water pump for 8 hours to check whether the output and pipeline tightness are normal. Meanwhile, test the hydrogen exhaust fan for 8 hours.
Mid-commissioning phase
After the completion of trial operation problems in the early stage of debugging, the system enters the middle stage of debugging, and the rectifier power supply of sodium hypochlorite generator is powered on, and the protection of the rectifier power supply itself (overcurrent protection, overvoltage protection, high temperature protection of the rectifier element, fast fuse protection, phase loss protection) is verified by test. Manually start the water supply of the system, start the exhaust fan and cooling water pump, and adjust the flow rate and pressure to normal operation: adjust the output current of the rectifier power supply 500A, 1000A, 1200A, 1500A, 1700A, run each current value for 1 hour, sample and analyze the effective concentration, check whether the transformer is abnormal, such as temperature, sound, etc. During the dosing pump system automatically, check the operation of the system. After confirming the normal operation parameters of the transformer, the system stops the rectifier and uses the seawater raw pump to flush the sodium hypochlorite generator. The two sets of chlorine system are programmed to start, adjust the current 1700A, run continuously for 8 hours, and check the operating parameters of the system.
Post-commissioning phase
After 20 days of normal operation of the chlorine making system, set the rectifier current of each chlorine making system to 500A, 1000A, 1200A, 1500A and 1700A. After running under the set current for 20 minutes, sample the sampling port to analyze the effective chlorine concentration, and acid wash the sodium hypochlorite generator. After pickling, the PH value of the liquid medicine was measured. After the chlorination system was put into operation, the rectifier current was 500A, 1000A, 1200A, 1500A, 1700A, and the effective chlorine concentration was analyzed by sampling again. The pickling effect was analyzed through the test.
Experience feedback
Sodium hypochlorite storage tank bottom sewage valve pipe and body interface is too high design problem Chlorine system long-term operation, produce a large number of secondary product salts gathered in the hypochlorite storage tank, can not be drained, easy to block the level meter and attached to the pump body and drug delivery system pipeline, communicate with the manufacturer, reduce the interface height, and set a certain inclined sewage pipe, sewage smooth.
The debrine cooling designed for the rectifier cabinet cannot meet the demand, resulting in a large temperature rise of the panel cabinet and internal equipment, especially in areas with high temperature. In order to improve the cooling effect, holes are opened on the side and top of the rectifier cabinet, and fans are added on the side to force ventilation of the rectifier cabinet. It ensures that the equipment does not overheat.
Automatic cleaning filter solenoid valve blockage
Automatic washing filter blowdown valve is a hydraulic diaphragm valve controlled by two-position three-way solenoid valve. Due to the high sand content of seawater, the solenoid valve is often blocked, and the pressure source cannot be opened and closed normally. The diaphragm valve cannot rise due to the accumulation of precipitated sand particles in the upper chamber filling the chamber, resulting in the valve failing to open and shut normally. After the transformation, the battery valve is not easy to plug, and the pneumatic diaphragm valve is on and off normally.
Logic optimization of hydrogen exhaust fan
The first version of the logic is a set of chlorine making device corresponding to a hydrogen exhaust fan, resulting in the exhaust fan can not achieve mutual backup state, and then change the logic, hydrogen exhaust fan is equipped with a master and backup button, after selecting the master and backup, the program control starts the main fan, the automatic stop condition is three seawater raw water pumps all stop feedback (thus judging that the two chlorine making devices stop running), the delay is 600 seconds.
The system is equipped with two sodium hypochlorite generators equipped with three seawater booster pumps with 10% output, and three seawater booster pumps with two uses and one standby one. The pump flow and pressure are 30m/h and 0.45MPa respectively. Because the route from the original seawater pump to the sodium hypochlorite storage tank in the system are all manual valves, if A set of chlorine making device is in operation and B set of chlorine making device is in use, Manual opening of the sodium hypochlorite generator outlet and inlet valve will cause the seawater diverting phenomenon, resulting in A set of incoming water flow below 18m/h, making the rectifier protection of A set of chlorine making device trip. Through the field flow test of three seawater raw pumps, it is determined that any sea water pump runs, when the second set is put into operation, the operating flow of the first set is reduced to 15.2m/h. Communicate with the manufacturer, the rectifier water flow is lower than 18m/h, 5s protection trip delay, changed to water flow is lower than 15m/h, 5s protection trip delay. Modify the value Modify any set of normal shutdown after the system flushing, the other set does not occur protection trip phenomenon.
BLUEWAV electrolytic seawater chlorine making system is responsible for the operation safety of DC cooling system and boiler recharge water system. The quality of commissioning is directly related to the safe and stable operation of condenser, and indirectly affects the normal operation of unit. The good commissioning and experience feedback of electrolytic seawater chlorine making system provide experience for the normal operation of power plant and the commissioning of similar units, which has important reference significance.
This article is reproduced from East China Electric Power Experimental Research Institute Co., LTD., China Energy Construction Group, Hangzhou 310000, Zhejiang, China