The invention discloses a method for extracting
methane from
mixed gas containing the
methane,
hydrogen and
nitrogen. The method comprises the steps that feed gas is divided into two steams, namely, an air
stream A and an air
stream B, and the air
stream A enters a high-pressure
tower to be rectified and separated after being cooled through a main
heat exchanger; the air stream B is pumped out from the
heat exchanger after being cooled for a certain stage through the main
heat exchanger, the pumped-out air stream B is directly fed into a low-pressure
tower to be rectified after being depressurized, refrigerated and cooled through an expansion
machine, and a
liquid methane product is obtained at the
tower bottom. Or after the feed gas enters the main heat exchanger and is cooled to a certain stage, the feed gas is divided into the two streams, namely, the air stream A and the air stream B, wherein the air stream A continuously enters the main heat exchanger and is cooled, then the cooled air stream A enters the high-pressure tower to be rectified and separated, the air stream B is directly fed into the low-pressure tower to be rectified after being depressurized, refrigerated and cooled through the expansion
machine, and the
liquid methane product is obtained at the tower bottom. By means of the method for extracting the
methane from the
mixed gas containing the methane, the
hydrogen and the
nitrogen, non-pressurized liquified
natural gas with the purity being 98 percent or above can be directly obtained, the product does not need to be liquified again,
energy consumption can be greatly reduced, the
recovery rate of the methane can reach up to 99.5 percent, the
recovery rate of the
nitrogen can reach up to 99 percent, and the rewarmed nitrogen can be used as industrial nitrogen.