A fossil-fired steam generator generates superheated steam with the aid of the heat generated as the result of the combustion of fossil fuels. Fossil-fired steam generators are mainly used in steam power plants, which predominantly serve the purpose of generating electricity, the steam generated being supplied to a steam turbine.
Along similar lines to the various pressure stages in a steam turbine, fossil-fired steam generators likewise encompass a plurality of pressure stages with different thermal states of the respective water-steam mixture contained therein. In the first (high) pressure stage, the flow medium runs on its flow path first through the economizers, which use residual heat to pre-heat the flow medium, and subsequently through various stages of evaporator and super heater heating surfaces. The flow medium is evaporated in theplant unit in a time frame of seconds are only possible with the aid of a co-ordinated interaction of the steam generator and the steam turbine. The contribution that the fossil-fired steam generator can make thereto is the use of its storage accumulators, that is, of the steam accumulator but also of the fuel accumulator, in addition to rapid changes in the controlling variables of feedwater, injection water, fuel and air.
This can ensue, for example, by the opening of partly throttled turbine valves of the steam turbine or of what is known as a step valve, by means of which the steam pressure is lowered upstream of the steam turbine. As a result, steam is released from the steam accumulator of the upstream fossil-fired steam generator and is