Control system for variable pressure once-through boilers

摘要

A system for the operation of once-through boilers which utilizes variable throttle pressure over a very wide load operating range is disclosed. The system utilizes a valving arrangement permitting the turbine valve (22) to be opened to a predetermined open position, typically 70 percent of its full open position, as soon as possible during the system loading process, maintaining the turbine valve (22) in this predetermined open position while the flow of steam from the boiler is being varied by a control valve (40) and the output pressure of the boiler is varying accordingly, and then allowing the turbine valve (22) to open further from the predetermined open position when the system reaches full design pressure so as to vary the flow of steam from the boiler while the output pressure thereof is maintained substantially constant. In this manner, the boiler is operated at a variable output pressure over a very wide load operating range.