This paper evaluates the potential for flexible operation of combined heat and power plants, using previously validated steady-state and dynamic process models. The models compute the change in power and heat generation, as well as the response times of steam turbine extraction regulation. It is found that for small-to-medium sized plants, steam bypass could be a promising solution for regulation of power output, also in combination with boiler load changes. Rise times for load reductions by valve opening are within 30 s, independent of the extracted flow, and steam extractions/bypass can lead to power output reductions of up to 30% of rated power. However, plant specific design aspect may limit the achievable magnitude of load changes and must be considered.
Keywords combined heat and power, operational flexibility, district heating, steam extraction, dynamic modeling