Off-design characteristics of a novel integrated system of coal-fired cogeneration unit and compressed air energy storage

Abstract

The regulation range of heat-power ratio in conventional coal-fired cogeneration unit of heat and power (CHP) is limited, which makes the previous determination of electricity by heat can't meet both the heat and power load, and results in relatively low efficiency. In this paper, a new integrated system of coal-fired CHP unit with compressed air energy storage (CAES) system is studied, which can greatly adjust the heat-power ratio. During heat enhanced period (increasing heat-power ratio), CAES stores electric energy and makes the compression heat supply to the users. During power enhanced (reducing heat-power ratio), CAES discharges energy and absorbs CHP extraction heat to use in CAES expander. As the regulation of heat-power ratio is a process of variable working conditions, a detailed off-design model of the integrated system is established. The influence of the key parameters on the system off-design characteristics is revealed. The research shows that the CAES air flow rate has a great impact on the integrated system's efficiency and heat-power ratio, while the CAES chamber pressure has the least impact on the integrated system's efficiency. Under different CAES air flow rates and air chamber pressures, the fuel ratio corresponding to the highest exergy efficiency in the two periods is the same, which is about 0.92. Finally, a case study is made on the data of an industry park, which shows that the integrated system can well follow the heat and power demand with relatively high efficiency.