We did not find results for: In cfbc boiler drum level control with vfd whether its possible to maintain level?
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The drum level control will likely be a three-element control if the boiler load changes 25%. The output of the drum level controller would control the boiler feedwater supply valve. The boiler feedwater supply valve manages delivery of the correct amount of feedwater mass inflow to balance with the steam mass outflow and the drum level trim. There is plenty of information on one, two and three-element drum level control available from a simple web search. I assume the VFD that you mention is for the boiler feedwater control. Boiler feedwater pressure must always be above the drum pressure for feedwater to flow into the drum. VFDs on the boiler feedwater pumps would be used for improved feedwater (supply) pressure control. Evaluate the pressure versus flow characteristic available from the pump(s) though their feasible range of speeds. From that, it will become evident that the pressure drop across the feedwater supply valve can be kept fixed through the use of a VFD speed control matched to the characteristics of the feedwater supply valve (or a pressure measurement across the feedwater valve). A constant pressure drop across the feedwater supply valve would achieve... * improved efficiency because of reduced pressure loss * reduction of pumping power * reduction of feedwater control valve wear at low flows * improved control since the feedwater supply valve would be consistently operating at its designed pressure drop * improved control due to constant loop gain
