Superheater Steam Temperature Control Design And Investigation Of Wai Gao Qiao 1000MW Super-Supercritical Unit

It is difficult for instrument design that the pressure and temperature class of 1000 MW super-supercritical unit improves.This thesis gives a detail introduction to the system design of the superheater steam temperature of the Wai Gao Qiao 1000 MW super-supercritical unit in terms of instrument installment, instrument models, instrument pipe and valve, then offers a solution to the high parameter instrument design of the unit.The superheater steam temperature of the 1000 MW super-supercritical unit is one of the important parameters that ensures the unit a safe and economical work. High superheater steam temperature usually contributes to high thermal efficiency of the unit. But the too high temperature is not allowed by the metal material of the steam turbine. The reasons lie in two aspects: on one hand, though expensive heat-resisting and pressure-resisting materials are used in the unit, the superheater is usually located in high temperature zone and under high temperature, then the design value of the superheater temperature has almost approached the limiting temperature allowed by the steal material. On the other hand, the safety coefficient of the strength of steels is rather small, so it is dangerous if the superheater temperature goes beyond the limit. The task of the superheater steam temperature control is to keep the exit temperature of the heater within a certain range and offer protection to the heater so that the metal temperature of its tube wall does not surpass its limits. When the unit works in a normal state, the deviation between the superheater temperature and the rated value should not exceed±5℃. The superheater steam temperature may respond slowly and delay for a long time due to the large amount of metal material in the heated area of the boiler, slowing down the changes in temperature. Slow response and delay in time are both the features which are difficult to deal with in conventional control. Therefore, improved Smith predictor is introduced to solve this problem.According to the dynamic features of the superheater steam temperature which changes with the amount of spurting water and on the working principal of the Smith predictor , an improved Smith predictor is designed to solve the temperature control problem featuring big-delayed and big-lagged. Then the general PID cascade control system becomes single loop, the superheater steam control is quick-response not big-inertial.Simulation is also made through Matlab and the result shows that the improved Smith predictor can smoothly deal with the big-inertial and big-lagged problem. The real application of the unit also indicates the system can bring very good dynamic response and small static deviation, achieving satisfactory and effective control.This thesis can be divided into four parts: Part one gives an introduction to the background and current situation of the research task. Part two introduces the superheater steam temperature control system design of Wai Gao Qiao 1000 MW super-supercritical unit. Part three studies the superheater steam temperature control of the unit. Part four is the conclusion, offering method on how to overcome the influence of external interference on the improved Smith predictor and gives prospects for its future research.