The operation control method Bog multistage displacement compressor

The present invention provides a method for controlling the operation of a boil off gas multistage displacement compressor, capable of preventing the temperature of low pressure stage-side discharge gas from exceeding a temperature allowable for the operation, even when the temperature of low pressure stage-side suction gas is higher than that in a steady operation. For achieving the above-mentioned object, according to a first aspect of the present invention, there is provided a method for controlling the operation of a boil off gas multistage displacement compressor including plural stages of displacement compression sections, which are connected with each other, for compressing boil off gas generated from liquefied natural gas, includes: in case of a predetermined condition, making a ratio of a load on a low pressure stage compression section to a load on a high pressure stage compression section in the boil off gas multistage displacement compressor (load ratio) smaller than load ratios in case of conditions other than the predetermined condition. A suction temperature of the low pressure stage compression section of the boil off gas multistage displacement compressor is made detectable, and the predetermined condition is a condition where a detected temperature of the suction temperature is not lower than a first preset temperature.