Compressor Flexibility Issues, Efficiency, and Options (Research)
Operational flexibility in natural gas compression is normally achieved through off design operation, recycling flow, throttling compressor suction, or adjusting pipeline pressures all of which result in a loss of efficiency. With pipeline flow volatility and thus the need for greater compression flexibility expected to increase significantly in the future, GRI sponsored a study conducted by Southwest Research Institute to characterize the need for flexible compression and to identify associated technology options, needs, and benefits. Any project to increase compression flexibility should have a goal to increase overall compression efficiency. This paper quantifies several of the common causes of lower efficiency due to wide ranging operations and describes several technology options for increased efficiency under expanded operating conditions. Estimates of the loss of efficiency, based on typical conditions, when throttling suction pressure, recycling flow, or operating near 50% of rated load are presented in the paper. The overall effect on efficiency of reducing pipeline pressures to increase load at a compressor station is estimated. Several technology options identified during the GRI study on flexible compression are described and considered in terms of increased efficiency. A total of ten concepts, some available and in use or only requiring minor adaptation and some requiring moderate to major levels of development are presented for industry's review.