The Control System Of Boiler Feed Water And Ammonia, Hydrazine, And Ph Control Methods

This subject comes from the 1999's science and technology tackle key problem item of electric power Corp. of GanSu province. The aim of the subject is to study the design of the dosage, the control method about the auto-control of chemicals-adding and the value of pH of the boiler in the heat power plants. Presently, the adopted control method of the water supply and the drug adding (ammonia adding~. hydrazine adding.. phosphate adding)of the boiler in the most heat power plant is still manual sampling of the water supply, which is a kind of behindhand manual chemicals-adding method111 that starts and stops metering pump by hand after carrying through the analyse and measure of the pH and the density of hydrazine and phosphate-radical ions. It cannot adapt to the need of the change of the operating condition of the boiler at all. The chemicals?densities of the boiler system are not steady by turns and further more they wave in a sizable range. This not only wastes a lot of medicament but also leads to the oxidation corrosion of the copper pipes of the condenser of the boiler system. The pipes can even be broken by the corrosion and this can make machine stopped. Further more hydrazine is a kind of virulent carcinogen. One side it is prone to lead to environmental pollution when density is overtop, the other side when density is over low, except that the effect of carbon dioxide and oxygen is not good, it is also fall short of the anticipate aim of preventing corrosion and crustation of the heating power system of the boiler. Accordingly, it affects the secure and economic operation of the power station. This paper looks back the history of the control technology of the pH. On the base of analyzing and studying of the model of the pH and control method two new? kinds of control methods of pH were put forward, namely the algorithm of varying gain three-section nonlinear PID and integral fuzzy control(IFC), the control results via digital simulation with the process of the p1-I neutralization that has time lag indicated these two algorithms have the good performance in robustness, rapid response and control precision. Especially the IFC algorithm can over come the greater time delay in the process of the pH neutralization. The two methods are easy to design and be applied in practice. We adopt the SLC500 type PLC produced by A-B Corp. in America and the IPC-6980 industrial computer as controlled unit produced by Adventech Corp. in Taiwan. All of them combining these with the pH instrument, the hydrazine instrument, the electroconductibility instrument and the liquid level sensor compose a two stages monitor and control system. The industrial computer with RSView32 configuration software developed by the Rockwell Corp. in America servers as the RSView32 workstation connected to PLC with the RSLink in the form of direct communication. The interface of ammonia adding and hydrazine adding system(Technical flow chart interface, alarm menu, real-time trend graph, history trend graph and instrument stick graph) were programmed in RSView32 configuration software. The ladder diagram was written in RSView logix500 software. So the wholly auto-control process of the dosages and drugs adding of the boiler water supply system was realized. This is the first time on coming true the automated design of the dosages in the domestic.