Flexible Power Generation Output with Optimization of District Heating Circulating Water Pump Operation

Currently improving the power output flexibility of the existing conventional generation units has been deemed as the most effective way to enhance the power system flexibility. Optimization of the auxiliary equipment of the unit such as pumps and fans is rarely studied for its influence on the flexible power generation output capability. Flexible power output capability of one example cogeneration unit in a power plant is analyzed based on built-up models of 620MW cogeneration unit using Ebsilon software. The flexible power output capability achieved and its economic benefit effect on the unit is studied in detail for the different circulation water pump operation modes. Peaking electricity cost is defined for comparing the opportunity cost incurred for realizing the flexible power output capability under different operation mode. Two district heating circulating water pump modes are considered. Under motor-driven operation mode, the district heating circulating water pumps can consume 8.715MW more electric power, which implies a same amount of flexible power output capability can be achieved. The calculated peaking electricity cost is 0.2499 Yuan/kW.h for achieving this flexible power output capability. It should be noted that the peaking electricity cost is decreased with increasing of the district heating circulating water flow, which implies that the power output flexibility should be better used when significant flexible power output capability is expected for high district heating load.