Improvement of control circuit of feed pump

A co-generation plant in South China Sea 200 MW fire two generators, each unit is equipped with 2 feed pump group provided by the Swiss company Sulzer, mutual backup. Heat pump to manual control loop is US Westinghouse WDPF-Ⅱ type distributed control system is completed.

1 feed pump control circuit problems

Feed pumps in our factory commissioning, misoperation occurred many times during the trial run, resulting in substantial fluctuations in the drum water level, and caused several downtime. After analysis, to determine the feed pump control circuit has the following problems.

(1) feed pump recirculation door switch control signal generated by an analog electronic circuit given place (see FIG. 1), which loop interference signal due to a multi-spot, easy error signal, and the signal itself is poor accuracy, but also to cause the pump Unstable operation.

Figure 1 before the recycle gate control loop

(2) There is no linkage circuit when the pump is dumped, resulting in the standby pump unable to be put into operation in time, resulting in exceeding of the important parameters such as drum water level and even causing the boiler to extinguish the fire.

(3) A total of 21 point temperature protection measuring points such as bearing temperature, stator coil temperature, lubricating oil temperature, working oil temperature and sealing water temperature of front pump, motor, coupling and main pump of feed pump, Access to decentralized control system, in which a point of poor contact, interference and other failures, will cause the feed pump to jump, but also become a major risk to safe operation.

2 to pump control circuit transformation

In response to the above problems, after careful study of the water pump control software, and understand the relevant functions of the WDPF system, made the following changes to the feed pump control circuit.

(1) The front pump flow signal into the decentralized control system, converted to digital, increase the high and low comparison algorithm, the corresponding switch recirculation door, eliminating the recirculation door switch signal unreliable hidden trouble. Revised after the loop control loop shown in Figure 2.

(2) increase the feed pump linkage signal, due to the cause of the pump itself caused by the jump pump hair linkage signal. Linkage conditions completed by the computer software, an increase of computer output points and a linkage relay, increase the linkage circuit shown in Figure 3.

Figure 3 increase the feed pump linkage loop

(3) For the accidental jump caused by the occasional open circuit of the thermal resistance of the feed water pump, we take a 5 s delay increase for each point of the temperature and filter out the high-temperature false signal caused by the interference signal, and increase the computer software. When the heat Resistance signal exceeds 500 ℃, judged as open, will not cause jump pump. The modified high temperature pump circuit shown in Figure 4.

Figure 4 modified high temperature pump circuit jump

3 Conclusion

After the above measures are gradually implemented, the phenomenon of wrong jumping of feed pump in our factory disappears. As a result of the correct action of the feed pump protection circuit, the safety hazard of our factory is eliminated. At the same time, in the reform of the control loop of the feed pump, we also have a profound understanding of the powerful functions and convenient modification of the WDPF-II decentralized control system, and deeply feel that the large-scale thermal power plant is designed with advanced DCS decentralized control system. Its hardware and software System and other aspects are more stable and reliable, and has considerable flexibility, which laid a good foundation for the reliable operation of the thermal protection.

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