The steam generator has the task to change the chemcial energy which was changed to heat in the firing process, into enthalphy of a high pressure steam, making the unit a heat exchanger. At the beginning of its development it had been simply a heated container to generate saturated steam. The steam generator consists of the two main systems: "firing" and "evaporation". In the firing system, one differentiates between fixed bed and grid firing (combustion on a fixed or movable grid), the fluidized bed firing (combustable material is fanned with air forming a fluidized bed) and burner firing (the combustible material is injected into the burning chamber together with air). In steam generation processes, one differentiates between natural circulation, forced circulation and forced flow systems. The picture shows a boiler with combustion firing (combustion firing for oil, gas) and forced circulation firing. The finely ground coal is supplied with air (oxygen supply) and comusted in the combination burners.
The coal dust is combusted and the heat is transmitted to the evaporator pipes in order to produce steam The light combustion residue (flyash) is carried along by the fluegas, the heavy residue (flyash) is removed at the bottom of the boiler. |
The superheater has the task of bringing the high temperature steam to the required temperature. The feedwater is heated through the fluegases. In the fluegas feedwater heaters (economizer, Eco), the heat remaining in the fluegases behind the evaporator heater surface and superheater, is utilised, thus increasing the effectiveness of the boiler. The air heater also uses the remaining heat of the fluegas in which heat is transmitted to the combustion air. This results in improved combustion performance. The fresh air blower transports the combustion air through the air intake to the combustion burner. The water/steam separation is carried out in socalled steam drums. For effective steam separation, an adequately large separation surface between the water and the steam phase must be available. The fresh steam produced is rerouted through the superheater to the steam turbine. The fluegas reaches the fluegas cleaning plant behind the air heater. |
