Flexible operation control strategy for thermos-exchanger water level of two-by-one combined cycle gas turbine based on heat network storage utilization

Highlights: • A control-oriented dynamic model of thermal-supply of 2 × 1 CCGT is presented. • A pilot control strategy is proposed to enhance the stability of the TEWL. • Several control algorithms are designed and compared on stabilizing TEWL. • The pilot control strategy can greatly improve the operational flexibility of CCGT. The high penetration of renewable energy sources makes the two-by-one combined cycle gas-turbine (2 × 1 CCGT) with high operational flexibility (OPFL) become the mainstream of deep peak-load units. However, the thermos-exchanger water level (TEWL) often exceeds the limit and causes unit trip during flexible operations. For this reason, this paper proposes a flexible operational TEWL control strategy. First, by modeling and analyzing the thermodynamics of the thermal-supply system of 2 × 1 CCGT unit, the exhaust steam pressure of intermediate pressure cylinder (IPEP) is chosen as an upstream controlled variable with mathematical-model derived setpoint to stabilize the TEWL; Secondly, considering the heat storage utilization of heating network, the heating-network circulating water flow is selected as the manipulated variable of IPEP control, then forming a pilot IPEP control loop cooperating with the existing TEWL control loop to stabilize the TEWL. Several control algorithms are designed and compared to determine the most effective one for the IPEP pilot-TEWL control. The results show that the maximal deviation of TEWL can be reduced to 7 mm and the OPFL indexes can be significantly improved, i.e. the average power ramp rate is 6.74 MW/min, and the power capacity is 69.55 MW from 158 MW steam turbine.