I. Introduction Qinshan 3 desalted water system, including UF, Three reverse osmosis and ion exchange treatment, ultrafiltration as an important level of water treatment equipment, mainly removal of the gel to ensure the normal operation of reverse osmosis. Since October 2002 has been put into operation ultrafiltration, ultrafiltration equipment, the original design because the high inlet pressure, there has been a large number of damaged membrane, membrane rupture of the shell quality of the effluent water quality can not meet the requirements of reverse osmosis water, making the rear anti- osmosis equipment operating conditions deteriorate, the membrane blocked the increase of fresh water and desalination water flow rate has dropped faster, < / Span> run the cycles. Ultrafiltration equipment in order to ensure normal Stable operation, to extend the service life of membrane, ultrafiltration has been under the control of the process layout and features of the system was reformed. Transformation, using the programmable control technology (PLC), optimize system pressure regulator, solutions of the problem conditions the pressure ultrafiltration device. II Process Analysis Field use of the ultrafiltration device total of two, parallel operation. Each device has two columns (A / B) the 11 ultrafiltration membrane. Ultrafiltration device starts, will automatically enter the back wash and quick wash mode, then enter the normal operation mode, Body; mso-ascii-font-family: Times New Roman ; mso-hansi-font-family: Times New Roman "> in the run to set the time interval (or manual), will repeat Anti-wash and quick wash operation mode, shown in Figure 1. normal operation, pumping water from the ultrafiltration feed pump to the equipment imported by the V1 / V2 into the membrane, the water output products from the V3, V5 / V6 will be filtered The brine discharge; when laundering, B running, but V3 closed, B to give the product water anti-A, from V9 / V10 through V12 exhaust; Times New Roman; mso-ascii-font-family: Times New Roman ; mso-hansi-font-family: Times New Roman "> quick wash, the ultrafiltration device entrance valve is closed, fast red pump water from the tank sent through the filter device, V7 / V8 open back tank from the V11, then, A running back wash B group. 2 ultrafiltration device is running the same, but the two devices, the time staggered, followed by anti-wash and fast wash. In the ultrafiltration operation, feed water pump outlet pressure is 500 ± 10kPa (head 50.3 m). as a floor pump in the water plant, water plant and the ultrafiltration device 2 Times New Roman ; mso-hansi-font-family: Times New Roman "> F (about 10 meters away from the floor), ultrafiltration equipment, the actual working pressure of the entrance 400 ± 20kPa, factory manuals in the ultrafiltration membrane maximum inlet pressure of 690kPa. in accordance with design requirements, equipment can function properly. but the end of 2003 (one year operation of the equipment so), site 1 / 3 of the membrane modules of different degrees of membrane rupture silk, export quality Jiju deterioration. ultrafiltration membrane manufacturers by consulting the same type of ultrafiltration membrane modules of information, that the technical parameters of the entrance to the maximum pressure of 310kPa. the scene is much larger than the pump outlet pressure ultrafiltration membrane modules of work pressure. resolved Design operating pressure is too high sense of urgency. In addition to salt water as the blood of power station, therefore,span lang = "EN-US">, in order to achieve the purpose of supply-demand is an ideal solution. Water treatment system is currently using PLC control. PLC control system with the transformation of short cycle, High reliability, and this program has a large number of applications in domestic water treatment systems, technology is mature. So, add the converter to finalize the adoption and use micro-PLC control system to achieve the purpose of process optimization equipment operation. 3, PLC control systems Because ultrafiltration device at different pressures for different operating conditions, while the ultrafiltration device lead to the pump outlet pressure is constant centrifugal pump. Use Pump an additional frequency converter power supply circuit, PLC control to adjust the pump by the power supply frequency, can achieve on-demand water supply purposes. The entire water treatment system uses a Rockwell s PLC control system, from the system and equipment maintenance facilities compatible with the point of view, decided to adopt the same company s PLC control products. (1) PLC control system hardware configuration According to the actual site conditions and control requirements, configuration of hardware PLC control system. As the three tied to the water pump placed in the water plant, 1st Floor, ultrafiltration equipment in Water 2 so-hansi-font-family: Times New Roman "> Building, 2nd floor, power supply at the water plant, water plant 2, duty officers to work the control room floor. Therefore, in order to facilitate monitoring, reconstruction of control equipment, including PLC control components and control the inverter can be placed outside the wall near Cable Bridge Department. on the general control requirements. normal operation: Pipe Pressure to keep to the pump for the set pressure, constant pressure water supply; anti-washing time: Keep Backwash pressure lower than the alarm value, according to the mother pipe to lower the pressure; quick wash end: the equipment required for the rapid restoration of the inlet pressure. new control equipment for input and output volume shown in Table 1. election Use font-family: Arial; mso-ascii-font-family: Times New Roman ; mso-hansi-font-family: Times New Roman "> of Within Inlay Open Guan Volume Lose Enter Lose Out Of Micro- Office Reason Device Micrologix1500 series 2 type composite structure, including the processor and with a rail base, covers an area of small, consistent with on-site space requirements. The series processors can expand by more than 100 I / O, Built-in PID man "> function, support for DF1 full-duplex, Half-duplex and network communication capabilities and equipment, meet the control requirements, it uses two 4 Channel analog input module 1769 - IF4, mutual isolation between channels, to capture the mother to pump control, Ultrafiltration pressure on import and export signals. In order to monitor equipment operation, with Panel View 600 s control panel, display device operating parameters, allows online modification settings. 1769 - SDN scanning module for the device network communication, the exchange of information with the inverter. Original equipment and systems interact. Ultrafiltration device for removing salt water treatment system where the use of PLC control,E5 of the load line and the original contactor connected to the AC load line and the bottom of the contactor (load side), the rest of the circuit remain unchanged. This is the original circuit of AC contactor s main contacts change to frequency converter; Added PLC-CPU of the embedded switch output lines through the middle of the laying of relay isolation, to ultrafiltration feed pump control loop with the existing thermal protection normally closed contacts in series, failure to complete the inverter output to the original control loop, which feedback to the overall PLC. PLC-CUP embedded digital inputs, relay isolation by the middle of the laying of lines, to the ultrafiltration feed pump main circuit contactor auxiliary contacts, PLC on the membrane to the pump to achieve the status of collection; new plus PLC E6 hand. Control Net Contact . System System Mining Use Base On CAN technology Technique Of Set up Equipment Network (Devicenet), device net network is a flexible, Open network, is now widely used in field devices and communication between the controller, this 64 node Communication speed up to 500kbps, Multi-branch network,family: Times New Roman "> allowed within 500m of the device to support the 1769 - SDN scanner 4-20 sent word I / O data, polling information, support, modify the device parameters from the PLC program capability. use, the PLC and the local equipment - frequency converter through the device network connection. PLC to monitor the network on the inverter, saving PLC s I / O modules. network structure shown in Figure 2. PLC and inverter composed of 3 sets of equipment for a 4-node network , PLC as a network monitoring and management equipment to points A4 to point to point communication and human-machine interface (HMI) connection, HMI PLC to equipment on-line through all the nodes collected their equipment and PLC operation status, Failure, Frequency, Pressure parameters are displayed, at the same time failure alarm is given, and can adjust the device to run the actual operation of artificial parameters. (2) PLC control system software configuration Changes in the improvement of the configuration is Micrologix series PLC-CPU. PLC-CPU use RSlogic500 style = "font-family: Arial; mso-ascii-font-family: Times New Roman ; mso-hansi-font-family: Times New Roman "> editing software, optional ladder diagram, function chart, and Instruction List language and other editing. In programming design, using the current Qinshan three other PLC control system of nuclear heavy use of the ladder in the form. Ultrafiltration equipment to meet the various operating modes in the pressure on the import and export requirements, PLC through the collection, Analysis Operation and output control signal, and regulate power to the pump frequency, change the pump output pressure to achieve ultrafiltration equipment required to run. Ultrafiltration device is in run mode, when the PLC detects any one to pump contactor auxiliary contact closed when the normally open (closing command is given the original control system), automatic starting of the pump corresponding to the inverter, water pump home Pressure and water pumps for closed-loop frequency constitute, ; Mso-hansi-font-family: Times New Roman "> operation achieved by PI control. When the ultrafiltration device is in backwash mode, one device of a running back with back-pressure water cleaning product with the delivery The second group of devices. At this point, if the normal operating pressure directly against washing, because the equipment has been shut down exports of valves, back pressure will rise, more than requested value, or even result in the second group was reverse-torn membrane . To prevent the above from happening, this time on the need to reduce the frequency to the pump. When the ultrafiltration device quick wash in the next mode, the quick wash washing water in the tank just a separate anti-washed membrane. quick wash After ultrafiltration equipment running at this time if the frequency of drop just too much pressure equipment may not meet the entrance requirements, even to the pump because of the frequency close to 0; Mso-ascii-font-family: Times New Roman ; mso-hansi-font-family: Times New Roman "> and shutdown. This requires us to choose the right lower back pressure values of the starting frequency , Drop the appropriate frequency to avoid damage to membrane or the pressure too great influence over the frequency drop the follow-up operation mode device. After comprehensive consideration, reducing the frequency of calculation and initial field test back pressure value: P = aPD-15 including P values for the lower frequency of initial back pressure, a safety factor as, PD is back pressure setting, 15 is the average test value. aPD higher cleanliness in the film can be entered through the man-machine interface, the smaller the value, then a< 1; with the running time longer, lower membrane cleanliness, choose the larger back-pressure value, then a = 1. Frequency drop: dF = d (FO - FC) / Dt where dF is the frequency drop, FO normal operating frequency, FC for the anti-laundering Time frequency. Quick wash equipment given to the lowest frequency end, and then entered PI control equipment. FMIN = FO-FC 10 ≈ 25Hz which FMIN for a given minimum frequency, FO normal operating frequency, FC for the quick wash when the frequency is a test average of 10. To the pump outlet pressure is designed to 500kPa, 50Hz power outlet pressure during normal operation should be less than 400kPa, corresponding to frequency 35 ~ 40Hz, quick wash at the end of the low frequency ii-font-family: Times New Roman ; mso-hansi-font-family: Times New Roman "> by trial and estimates given to the lowest frequency of 25Hz. transformed continuous tracking device operating parameters, ultrafiltration device near the inlet pressure 15kPa 260kPa in expectations about stable operation, the membrane back pressure (25 ~ 35kPa) far below the set alarm value 55kPa the following operation, equipment running well. IV Conclusion The equipment modification, according to system of intermittent characteristics of the original balance to the system control mode, using the technology is mature, with the transformation of short cycle, scii-font-family: Times New Roman ; mso-hansi-font-family: Times New Roman "> reliable programmable controls, after 5 days of installation, Debugging, enter the test run. In a complete transformation to the pump and run the successful cases, a series of successively second and third sets of transformation. After transformation, the ultrafiltration device did not occur and the film documents the entrance overpressure damage events, equipment, normal and stable operation of the export quality to meet the design requirements. As in the transformation of the initial hardware configuration and software design of the original control system both hardware and software manufacturers use the same products, used the same ladder language for programming, to facilitate the field staff on the new control system control and improve the readability and maintainability of the modified system. Transformation, the first pump control to debug slightly longer than expected time,