Device for producing LNG through coal bed gas

The utility model relates to a device for producing LNG through coal bed gas. The device is characterized in that the device comprises a nitrogen-methane expansion refrigeration system, the nitrogen-methane expansion refrigeration system comprises an expansion machine (9) and a compressor (5), an outlet of the expansion machine (9) is connected with an inlet of a secondary heat exchanger (2), an inlet of a primary heat exchanger (1) and an inlet of the compressor (5) in sequence through pipelines, the primary heat exchanger (1) is provided with a coal bed gas inlet and a coal bed gas outlet, the secondary heat exchanger (2) is provided with an LNG inlet and an LNG outlet, the coal bed gas outlet is communicated with a gas-liquid separation tank (4) through a throttling valve (3), and a liquid outlet of the gas-liquid separation tank (4) is communicated with the LNG inlet. According to the device, the purified coal bed gas is cooled based on the nitrogen-methane expansion refrigeration principle and can be mad