Process and system for purifying, separating and liquefying nitrogen-and-oxygen-containing coal mine methane (CMM)

Abstract

The invention discloses a process and a system for purifying, separating and liquefying nitrogen-and-oxygen-containing coal mine methane (CMM). The process for purifying, separating and liquefying the nitrogen-and-oxygen-containing CMM comprises the following procedures of: pre-deoxidizing; pressurizing and cooling; deeply removing acid gas; deeply dehydrating and drying; deeply removing mercury and filtering; liquefying at low temperature; and rectifying at low temperature. The system for purifying, separating and liquefying the nitrogen-and-oxygen-containing CMM consists of a deep acid gas removing unit, a deep dehydrating and drying unit, a deep mercury removing and filtering unit, a low-temperature liquefying unit and a low-temperature rectifying unit. By the system, concentration of the produced liquefied natural gas (LNG) is as high as 99 percent, and the recovery rate of CH4 in the CMM is as high as 99 percent. The process and the system are favorable for recycling the CMM on a large scale, producing the LNG and reducing CMM accidents and environmental pollution.

Description

technical field [0001] The invention relates to a coal mine gas purification, separation and liquefaction process and a purification, separation and liquefaction system for nitrogen and oxygen-containing coal mine gas, which belong to the technical fields of chemical industry and low temperature. Background technique [0002] China's total resource reserves of coalbed methane are 36.8 trillion cubic meters, ranking third in the world, and the recoverable reserves are about 10 trillion cubic meters. Due to the different mining methods of coalbed methane, CH in coalbed methane 4 Concentrations can vary significantly. Coal mine methane (Coal Methane, CMM) refers to the CH produced through the underground coalbed methane extraction system and ground transportation system. 4 Coalbed methane with a concentration between 30% and 80% belongs to unconventional natural gas. Because a large amount of air components containing nitrogen and oxygen are mixed in the process of coal bed ...

AI Technical Summary

Problems solved by technology

In the above three patents, nitrogen-oxygen-containing coal mine gas is first pressurized and then deoxidized. During the compression and subsequent deoxygenation process, there is a danger of combustion and explosion; the removal of carbon dioxide by molecular sieve adsorption method is difficult to reach below 50ppm (V / V). It is easy to cause freezing blockage of the liquefied cold box; nitrogen expansion refrigeration is used, and energy consumption is high

200610080889.4 and 200620115881.2 patents use two-stage low-temperature rectification towers, which require an independent condenser, a lot of equipment, and complicated processes; since oxygen needs to be completely separated in the rectification tower, CH in the above-mentioned gas phase in the rectification tower 4 The concentration change will pass through the upper and lower explosion limit areas, and there is a danger of explosion

The 200620122543.1 patent uses a single-stage cryogenic rectification tower, which requires a separate condenser, and extracts CH from the middle side of the tower. 4 The mixed gas is vented, wasting resources

The patent requires that the CBM must first be pressurized and then concentrated CH by pressure swing adsorption 4 , the obtained desorbed gas is atmospheric pressure coalbed methane, and then undergoes multi-stage compression, which consumes a lot of energy; and in the process of pressure swing adsorption, CH 4 Adsorbed in the adsorbent, the change of its concentration must pass through the explosion limit area, and there is a danger of explosion

The patent with application number 200810229999.1 adopts the method of flash evaporation to separate nitrogen, and the flash steam carries a large amount of hydrocarbons to vent, CH 4 Low recovery rate and low LNG concentration

The patent with application number 201010155466.0 adopts multi-step fractional distillation and gas-liquid separation to remove nitrogen and oxygen, and set up a two-stage rectification tower, a nitrogen removal tower, and 3 low-temperature liquid pumps. There are many equipments, large investment, complex system, and difficult operation and maintenance.

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