NOVELTY - The device comprises a cooling tank (E1), a rectifying tower (T1), a low pressure and high pressure rectifying tower, a first and second separator and a refrigerant return passage. The low pressure rectifying tower comprises a tower top condenser (E3) and tower reboiler (E2). The high pressure rectifying tower comprises a tower kettle and tower top condenser. The cooling tank comprises a first liquid-phase mixed refrigerant inlet and a second liquid phase mixed refrigerant inlet. The first liquid-phase mixed refrigerant inlet is connected with a liquid cooling box of a channel.    USE - The device is useful for producing liquefied natural gas such as nitrogen, carbon monoxide and methane gas by dehydrogenation gas.    ADVANTAGE - The device is capable of economically producing the liquefied natural gas such as nitrogen, carbon monoxide and methane gas by dehydrogenation gas with less energy consumption in an environmentally friendly manner.    DETAILED DESCRIPTION - The device comprises a cooling tank (E1), a rectifying tower (T1), a first separator, a second separator and a refrigerant return passage. The rectifying tower comprises a low pressure rectifying tower and a high pressure rectifying tower. The low pressure rectifying tower comprises a fist tower top condenser (E3) and a tower reboiler (E2). The high pressure rectifying tower comprises a tower kettle and a second tower top condenser. The cooling tank comprises a first liquid-phase mixed refrigerant inlet and a second liquid phase mixed refrigerant inlet. The first liquid-phase mixed refrigerant inlet is connected with a liquid cooling box of a channel. A first liquid phase channel leads out a pipeline from a tail end of a particular stage of a heat exchanger in a cold box by a first throttle valve, which is connected with a refrigerant return passage cooling tank. The cold box is connected with the second liquid phase mixed refrigerant inlet. The second liquid phase mixed refrigerant inlet is connected with a second liquid cooling box of the channel. The second liquid phase channel leads out the pipeline from the tail end of a other specific grade heat exchanger via a second throttle valve (V2), which is connected with the refrigerant return passage cooling tank. The refrigerant return passage cooling tank is connected with the cooling box of a second gas channel. The second gas channel is connected to a methane gas inlet and a methane liquid outlet. The methane liquid outlet of the low pressure rectifying tower bottom reboiler and methane liquid inlet are connected with the cooling of a mixed stream passage. The mixed stream passage is connected to a mixing stream inlet and a mixed stream outlet. The mixed stream inlet area is located in the intermediate heat exchanger. The mixed stream inlet of the low pressure rectifying tower, the tower bottom reboiler and methane liquid outlet are connected with the mixed stream outlet of the high pressure rectifying tower. The high pressure rectifying tower and mixed stream inlet are connected with the cooling tank of liquefied natural gas passage. The liquefied natural gas passage is connected with a liquefied natural gas inlet on the cooling intermediate heat exchanger and a liquefied natural gas outlet. The low pressure rectifying tower bottom reboiler and a bottom of the liquefied natural gas outlet are connected with the cooling tank of a liquid nitrogen channel. The liquid nitrogen channel comprises a liquid nitrogen inlet and a liquid nitrogen outlet. The liquid nitrogen outlet pipeline through the fourth throttle valve, which is connected with the low pressure rectifying tower condenser through the fifth flow valve. The fifth flow valve is connected with the high pressure distillation tower top condenser, which is connected with the cooling box and an air channel. The air channel is connected with a gas nitrogen outlet and gas nitrogen inlet. The nitrogen gas inlet is connected with low pressure rectifying tower condenser and high pressure rectifying tower condenser, which is connected with the outlet at the top. A cold tank of hydrogen-rich gas passage is connected with a hydrogen-rich gas outlet and a hydrogen inlet. The hydrogen-rich gas inlet and the second separator are connected with the outlet at a top. A cold tank of nitrogen enriched passage is connected with the nitrogen-enriched and nitrogen-enriched inlet. The nitrogen-enriched first separator inlet is connected with a top part is connected with the light phase outlet of the low pressure rectifying tower bottom reboiler and comprising a methane liquid inlet, a methane liquid outlet and a liquefied natural gas outlet. The tower top condenser inlet of the low pressure rectifying tower is connected with an inlet of the first separator. The air outlet of the top part is connected with the nitrogen inlet of the cooling box. The tower kettle of the high pressure rectifying tower is provided with the outlet. The outlet on a bottom is connected by a sixth throttle valve and a middle part of the low pressure rectifying tower, and is provided with an inlet and is connected with the mixed stream of cooling outlet pipeline of a water tank. An air-inlet of the top part outlet of the cooling box is connected with the bottom outlet of the first separator in a low pressure rectifying tower. The outlet at the top is connected with the bottom outlet of a nitrogen-enriched air outlet. The nitrogen-enriched air outlet is connected with cooling tank and the second high pressure rectifying tower. The top of hydrogen-rich gas outlet is connected with the inlet of the cooling tank. The first gas channel is led from a third level heat exchanger. The third throttle valve and return passage are connects the refrigerant.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a device for producing liquefied natural gas. asteriskasteriskLISTNasteriskasterisk(E1) Cooling box#(E2) Tower bottom reboiler#(E3) Tower top condenser#(T1) Rectifying tower#(V2) Second throttle valve.asteriskasterisk/LISTPasteriskasterisk