Design and application of the feed water control strategy for a 350Â MW circulating fluidized bed boiler

The delay and inertia of the supercritical circulating fluidized bed (CFB) boiler are larger than the traditional once-through pulverized coal-fired (PC) boiler. The ordinary feed water control strategy based on coal-water ratio has a poor performance when applied in CFB boiler. The paper explained the reason by analyzing the principle of the feed water control system in traditional PC boiler and combining with the characteristics of fuel combustion and heat transfer in CFB boiler. A double-feedforward self-balance feed water instruction was proposed based on the steam water balance theory. It contains the dynamic heat differential calculated by air and coal quantity and the load demand differential corrected by temperature. The proposed control strategy was applied in the actual operation of a supercritical 350 MW CFB unit. The result shows that it overcomes the large delay and inertia of the boiler and realizes the accurate feed water control when load changes, which has great significance for improving the control performance of CFB boilers.