Modeling and Control of a Combined Heat and Power Unit with Two-Stage Bypass

Abstract

This paper presents a non-linear dynamic model of a combined heat and power (CHP) unit with two-stage bypass for the first time. This model is derived through an analysis of the material and energy balance of the CHP unit. The static parameters are determined via the design data of the CHP unit, and the dynamic parameters refer to model parameters of same type of units in other references. Based on the model, an optimized control scheme for the coordination system of the unit is proposed. This scheme introduces a stair-like feedforward-feedback predictive control algorithm to solve the control problem of large delays in boiler combustion, and integrates decoupling control to reduce the effect of external disturbance on the main steam pressure. Simulation results indicate that the model effectively reflects the dynamics of the CHP unit and can be used for designing and verifying its coordinated control system; the control scheme can achieve decoupling control of the CHP unit; the fluctuation of main steam pressure is considerably reduced; and the adjustment of coal feed flow is stable. In this case, the proposed scheme can guarantee the safe, stable and flexible operation of the unit and lay the foundation for decoupling the heat load-based constraint of CHP units, thereby expanding the access space of wind power in northern China.

Research on Modeling and Deep Peak Regulation Control of a Combined Heat and Power Unit

“…For bypass system [10], the steam flows into the cold section of the reheater increases with the opening of the HPB valve, since the resistance of the reheater remains unchanged, more steam flows through the reheater, resulting in the differential pressure of the reheater to increase. If the LPB valve is not opened in time, the exhaust steam pressure from HPC will be increased rapidly.…”

“…The main methods to decouple the constraint of CHP units are absorption heat pump (AHP) [8], [9], bypass [10], electric boiler) [11]- [13], heat storage tank [14], [15], low pressure cylinder (LPC) removal [16], high back pressure [17], etc. This paper mainly study a CHP unit with AHP and bypass systems.…”

“…Assume that the terminal difference of the heater θ HTR = 10 • C, then the outlet temperature of the heater is as show in Eq (10)…”

FCB system analysis and performance test results of 1000MW ultra supercritical coal fired power station

“…In the process of FCB, the generator outlet is cut off, while the steam turbine and boiler are in normal operation, or the boiler is in normal operation with the steam turbine shutting down [4] . Then, the bypass of the operating generator set is opened quickly, and the load of the boiler is reduced rapidly, so as to realize the rapid reduction of output and maintain the auxiliary power operation, commonly known as island operation [5] . For large-scale power plant such as 1000 MW units, if they have FCB function, they can completely or partially restore the auxiliary power operation of generating units through self-help mode in case of large-scale power grid failure, which further ensure the safety of the main equipments of the generating set.…”

Dynamic modeling for assessment of steam cycle operation in waste-fired combined heat and power plants

“…• Operational flexibility for variable power-to-heat ratio; by turbine bypass [8] and operation in backpressure or extraction mode [9]. • Optimization of district heating systems and CHP plant dispatch [10].…”