Quantitative Analysis of Energy Storage in Different Parts of Combined Heat and Power Plants

To increase the flexibility of power generation, the coal-fired combined heat and power (CHP) plants should make full use of their own energy storage (ES). Available ES exists mainly in boiler steam-water systems, in units' condensed water systems (CW), and in district heating networks (DHN). The goal of the paper is to analysis the ES quantitatively. And ES is characterized by ES coefficient, the maximum ES capacity and ES respond speed for power load. ES coefficient, the key parameter of ES capacity, represents the change in ES when unit process variable changes. For pressure, flow, and temperature variables, three kinds of mechanism methods (volume increment method, equivalent enthalpy drop method, and specific enthalpy increment method) are proposed to calculate ES coefficients. Then, the maximum ES capacity can be obtained by the product of ES coefficient and the limit value of the variable. Finally, ES respond speed for power load can be drawn from simulation. Calculation results and simulations show that ES in CW has small capacity 1.2 GJ but fast speed; ES in boiler has larger capacity 2.6 GJ and slower respond speed; ES in DHN is 374 GJ, which is two orders of magnitude larger than the previous two, and the response is relatively fast. Therefore, recommendations to increase power load flexibility are using ES in boiler and DHN to reduce fuel fluctuation when power load change frequently, using ES in CW to reduce load responding time, and using ES in DHN to expand load regulation range.