Floating pressure control for a gas distribution system

Abstract

In a process in which a compressor feeds gas to a manifold which in turn supplies a controlled flow of gas to each of a plurality of users in parallel operation, method and apparatus are provided for controlling the back pressure acting against the compressor. The back pressure is manipulated to substantially optimize operation of the compressor. Since user demand for the gas varies over wide ranges, the control system automatically reduces back pressure acting against the compressor during periods of low loads by incrementally opening the control valve to one of the plurality of users. The reduced back pressure causes each on line control valve to move toward a more open position to maintain its set point. The pressure reduction continues in increments until one of the plurality of on line control valves reaches a maximum desired open position. The condition of a control valve exceeding a maximum desired open position is also sensed and the back pressure is then increased to cause the plurality of valves to move toward a closed position. The pressure increase cycle continues until all on line valves achieve a position less than the high limit. At this time the decrease/increase pressure is repeated so that the actual back pressure is floating, being dependent on user demand for the gas.