Skid mounted coalbed methane deacidification equipment

Coalbed methane deacidification gaspurifyThe process basically includes raw material gasDeacidification, dehydration, and mercury removalsystemProcess technology,FirstAfter pre-treatment, the wellbore gas enters the purification block directly. The deacidification process (mainly referring to carbon dioxide and hydrogen sulfide) uses solvent absorption method, and the absorbent isMDEA； The dehydration process uses molecular sieves to remove trace amounts of water; The removed heavy hydrocarbons are directly sent to the flare system for combustion treatment; The mercury removal process adopts the sulfur leaching activated carbon adsorption method;

1Complete set of equipment for deacidification of coalbed methaneoffCO₂Process Selection

The content of natural gasCO₂Collectively referred to as acidic gases, their presence can cause metal corrosion and pollute the environment. In addition,CO₂Excessive content will reduce the calorific value of natural gas. Therefore, it is necessary to strictly control the content of acidic components in natural gas to meet the requirements of process and product quality.

The methods used for removing acid gas from natural gas include solvent absorption, physical absorption, oxidation-reduction, and molecular sieve adsorption. The currently widely used solvent absorption method. It is a desulfurization method based on reversible chemical reactions and using alkaline solvents as absorbents. The solvent and acid components in the feed gas are mainlyCO₂）Reacting to generate compounds; The rich solution that absorbs acid gas can decompose and release acid gas under the conditions of increasing temperature and decreasing pressure, thereby achieving the regeneration and utilization of solvents.

The solvent used in solvent absorption method is generally alkylamine, mainly monoethanolamine（MEA）、 Diethylamine (DEA), diisopropanolamine (DIPA), methyl diethanolamine (MDEA), etc. From the perspectives of applicability and economy, this plan chooses methyl diethanolamine (MDEA) as the solvent for removing acidic gases.

MDEA (N-Methyldiethanolamine), also known as N-methyldiethanolamine, has the molecular formula CH₃-N(CH₂CH₂OH)₂, molecular weight119.2, boiling point 246-248 ℃, flash point 260 ℃, freezing point -21 ℃, latent heat of vaporization 519.16kJ/kg, miscible with water and alcohol, slightly soluble in ether. Under certain conditions, it has strong absorption capacity for acidic gases such as carbon dioxide, with low reaction heat, low desorption temperature, stable chemical properties, non-toxic and non degradable.

pureMDEA solution and CO₂No reaction occurs, but its aqueous solution isCO₂The reaction can be expressed as follows:

CO₂ + H₂O == H⁺ + HCO₃^- (1)

H⁺ + R₂NCH₃ == R₂NCH₃H⁺ (2)

Formula（1) Controlled by liquid film, the reaction rate is extremely slow, and equation (2) is an instantaneous reversible reaction. Therefore, equation (1) represents the absorption of CO by MDEA₂The control steps are to accelerate the absorption rateAdd activator (R) to MDEA solution₂^/NH）Afterwards, the reaction proceeds according to the following equation:

R₂^/NH + CO₂ == R₂^/NCOOH (3)

R₂^/NCOOH + R₂NCH₃ + H₂O ==R₂^/NH + R₂CH₃NH⁺HCO₃^- (4)

(3)+(4)：

R₂NCH₃+ CO₂ + H₂O == R₂CH₃NH⁺HCO₃^- (5)

By formula（3) It can be inferred from (5) that the activator has absorbed CO₂Transfer to the liquid phaseCO₂This greatly accelerates the reaction speed.MDEA molecules contain a tertiary amine group that absorbs CO₂Afterwards, bicarbonate is generated, and the heat required for heating and regeneration is much lower than that required for the formation of amino formate salts from secondary amines.

From the perspectives of energy consumption, processing scale, and investment operating costs,The MDEA amine liquid method is the most suitable process, so this plan chooses the MDEA amine liquid method for acid removal gas.

The raw material gas enters the deacidification unit, which uses MDEA Solution formulaRemoving impurities from the raw gas using the method CO2 and H2S Waiting for acidic gases.

Natural gas enters from the lower part of the absorption tower and passes through the tower from bottom to top; *After regeneration MDEA 溶liquid(Poor liquid)）Entering from the top of the absorption tower, passing through the tower from top to bottom, and flowing in the opposite direction MDEA solutionFully contact with natural gas in the absorption tower, the CO2 Absorbed and entering the liquid phase, unabsorbedThe components are drawn out from the top of the absorption tower and enter the decarbonization gas cooler and separator. Gas from the decarbonization gas separatorEnter the raw material gas drying unit, and the condensate goes to the flash evaporation tank.

Processed natural CO2 Content less than 50ppmV，H2S Content less than 4 ppmV.

absorbed CO2 of MDEA The solution is called rich liquid and sent to the flash evaporation tower. The natural gas produced by depressurization flash evaporation is sent to the fuel system. After flash evaporation, the rich solution exchanges heat with the solution (lean solution) flowing out from the bottom of the regeneration tower, and then heats up to～ Go to the upper part of the regeneration tower at 98 ℃ and perform stripping regeneration in the tower until the lean liquid degree reaches the target.

The lean solution from the regeneration tower passes through the lean and rich liquid heat exchanger and lean liquid cooler, and is cooled to~After being pressurized by the lean solution pump at 40 ℃, it enters from the upper part of the absorption tower.

The gas at the top outlet of the regeneration tower enters the acid gas separator through the acid gas cooler, and the gas from the acid gas separator is sent to the acid gas discharge system. The condensate is pressurized by the recovery pump and sent to the flash separator.

The heat source of the regeneration tower reboiler is provided by the heat transfer oil from the heat transfer oil system. The main process equipment of this unit is absorption tower and regeneration tower.

2. Coalbed methane deacidification gasDehydration process selection

The presence of water in natural gas often causes serious consequences: water and natural gas form hydrates under certain conditions, blocking pipelines and affecting the cooling and liquefaction process; In addition, the presence of moisture can also cause unnecessary power consumption; Due to the low liquefaction temperature of natural gas, the presence of water can also cause equipment freezing and blockage, so dehydration is necessary.

The natural gas dehydration process generally includes three categories: low-temperature dehydration, solid desiccant adsorption, and solvent absorption. Cryogenic separation is mainly used to avoid the formation of hydrates in natural gas at low temperatures, but its allowed low temperatures are limited and cannot meet the requirements for natural gas liquefaction; Solvent absorption usually includes concentrated acids (usually organic acids such as concentrated phosphoric acid), glycerol (commonly triethylene glycol), etc., but these methods have low dehydration depth and cannot be used in cryogenic devices; The common methods for solid desiccant dehydration are silica gel method, molecular sieve method, or a combination of these two methods.

Natural gas liquefaction dehydration must adopt solid adsorption method. Due to the strong adsorption selectivity, high adsorption characteristics under low water vapor partial pressure, and the ability to further remove residual acidic gases of molecular sieves, this scheme adopts4A molecular sieve is used as a dehydration adsorbent.

3Coalbed methane deacidification gasSelection of mercury removal process

At present, there are mainly two types of mercury removal processes: the United StatesUOP's HgSIV molecular sieve adsorption method and the use of sulfur impregnated activated carbon to chemically react mercury with sulfur to produce * and adsorb it on activated carbon. The former has high cost and is suitable for situations with high mercury content; The latter has low operating costs and is suitable for situations with low mercury content.

On the one hand,The operating cost of HgSIV molecular sieve is very high; On the other hand, the mercury content in the feed gas of this device is relatively low. Therefore, our company has successful experience in using sulfur impregnated activated carbon for mercury removal.