The increasing deployment of renewable energy requires larger flexibility in the energy system, in which conventional combined heat and power (CHP) plants are also an important source of flexibility. However, the provision of flexibility depends on the operation region of a CHP plant, i.e., the electricity and heat production of a CHP plant are inter-related.
Therefore, this paper aimed to assess the flexibility of coal-based CHP plants in various heating modes. To this aim, various heating modes of CHP plants, including: main steam bypass heating, reheat steam bypass heating, intermediate-pressure turbine (IPT) outlet steam heating, high back-pressure (HBP) heating, and low-pressure turbine zero output (LZO) heating, were respectively investigated. An energy balance matrix method was employed to determine the operation regions of CHP plants in various heating modes.
Results show that, compared with other heating modes, CHP plants in the reheat steam bypass heating mode and in the HBP heating mode can provide larger power-adjustment flexibilities without affecting heating loads. This implies that CHPs in these heating modes can obtain larger profits on a day-ahead market. A CHP plant in the LZO heating mode can reduce its power load to the lowest level and thus it yields the largest flexibility for accommodating renewable energy.
Keywords Flexibility, Combined heat and power, District heating, Operation region, Energy balance matrix