POWER-GEN Europe and REWE 2017

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Increasing the Load Swing Capacity of Large Coal Fired Steam Generators by Online Coal Mass Flow Measurement and DCS Modifications (Room A)

renewable energy systems call for a higher load swing capacity of conventional coal fired power stations. Only by an increase in load gradient coal fired power stations will be able to contribute to grid stability for electrical distribution systems which have to absorb larger percentages of renewable energy. The limiting factor of large steam generators in load gradient is usually the pulverizer and it´s step response to changes in feeder settings. The pulverizer usually takes several minutes to react to changes in the feeder rate. The reason for this is the storage of coal wich is on the mill roller table as well as the circulation of the coal throughout the mill before it leaves the mill passing through the classifier. The paper discusses the use of online coal mass flow technology in order to characterize the mill behaviour and to accelerate the mill response by controlling mill parameters such as roller pressure, primary air temperature as well as primary air flow. Furthermore the use of an online coal mass flow signal in order to optimize the Boiler related Parameters such as feedwater, air flows etc. is discussed. Special attention is given to the use of state space controlers which help to produce a smooth signal with a low latency out of the raw coal mass flow signals. By this the coal mass flow signals can be used to optimise the boiler operation for higher load gradients and better secondary and primary control. The German power station Wilhelmshaven has implemented an on line coal mass flow system, which measures the coal mass flow on real time out of the mill classifier. In conjunction with a Kalmann-Filter implemented into the DCS system the load gradient as well as the capability for primary and secondary frequency control was optimised.