Fuel gas supply system of lng carrier being attached engine using double fuel

A fuel gas supply system of an LNG carrier to which a dual fuel using engine is provided to install a one speed type compressor by installed a return line extending from a low capacity compressor to a liquid separator. A fuel gas supply system of an LNG carrier includes a liquid separator(3), a low capacity compressor(4), an after cooler/heater, and high capacity compressor bypass line, and a high capacity heater(9). The gas naturally evaporated in a cargo tank is supplied to the liquid separator. The low capacity compressor compresses the evaporated gas discharged from the liquid separator. The after cooler/heater cools and heat the gas discharged through the low capacity compressor. The high capacity compressor bypass line introduced the evaporated gas before the evaporated gas is introduced into the liquid separator. The high capacity heater controls the gas detouring the high capacity compressor to a temperature suitable for an engine. A line is installed from the low capacity compressor to the liquid separator so that a one speed type motor can be used in the low capacity compressor. The motor in the low capacity compressor is changed from two speed to one speed until the temperature of the evaporated gas reach a predetermined value by circulating the evaporated gas.