Experiment Research On Method Of Feed Water Control For Supercritical Once-through Boiler

In the increasingly severe shortage of fuel and resources, it becomes a trend that the generator sets go forward to high parameter and large capacity to meet the needs of China’s actual situation and the national economic development. At present, supercritical units is increasingly becoming the main unit among thermal power generating units. Unlike traditional drum boiler, once-through boiler is used in supercritical units, the control system of which has character of multivariate, strong coupling, nonlinear. Once-through boiler feed water is from liquid into vapor instantaneously, with no fixed boundaries, so a higher demand is for feed water control.Feed water control system is a subsystem of the supercritical unit control system, but it plays an extremely important role in the entire unit and is the most important and most complex control sub-loop of once-through boiler. Once-through boiler feed water control is base on the water to coal ratio, while there is also the correction link, the correction signal mainly including intermediate point temperature and intermediate point’s enthalpy. The tasks of once-through boiler feed water control are not only controlling the main steam temperature, but also involving load control, in order to ensure the safe and stable operation of the unit.The author takes2×660MW supercritical once-through boiler of DingZhou power plant as the research object in this paper, uses feed water control system based on intermediate point’s enthalpy adjust and design the feedwater control logic. Firstly, this paper analyzes the character of feedwater control system during start-up and wet state,and proposes the process of wet-dry state transfer; Secondly, this paper taked about the research on feedwater control system of dry state in supercritical once-through boiler, involing the design of feedwater control logic diagram, load regulation and the factors affecting water-coal ratio, and analyzed the feedwater control process in load-up and load-down based on the actual situation of DingZhou power plant. Finally, according to kinds of RB situations, the RB feedwater control of coal mill, forced fan-induced draft fan, air pre-heater, feed water pump and primary air fan in medium-load and high-load operating conditions are studied experimentally, and the adjustment process is analyzed.