Liquid absorption purification hydrogen production

Conventional Hydrogen Production Using Liquid Absorption Purification... 

Product purification. In a liquid absorption system, carbon dioxide is removed. The product gas undergoes a methanation step to remove the residual traces of carbon oxides. Recent SMR plants use a pressure swing absorption (PSA) unit instead, producing 99.99% pure hydrogen. 

Natural gas is processed mainly for the recovery of liquid hydrocarbons useful in gasoline, pure hydrocarbons as butane, propane, ethane, or mixtures of them, hydrogen sulfide (and sulfur or sulfuric acid), and carbon black but significant amounts of gas are also converted into ammonia, synthesized by the Fischer-Tropsch reaction, or oxidized into chemical products such as formaldehyde. Conventional operations, however, consist of mainly two operations, viz., recovery of liquids (absorption, etc.), and purification of the liquid. 

Numerous industrial operations involve a heat transfer between a liquid phase and a gaseous phase, with an important mass transfer effect, either as desorption-evaporation or as absorption-condensation. Here are some examples reconcentration, by evaporation, of solvents, toxic industrial effluents production, by absorption, of industrial aqueous acid solutions reversible or irreversible chemical reactions (oxidation, hydrogenation, sulfonation) purification of permanent gases (air, smoke) by scrubbing of soluble vapors desorbers and absorbers for heat pumps, where these two operations occur simultaneously. 

The absorption in alkanolamine solutions (MEA, DEA, ADIP, DGA, etc.) is the commercially most important process for the removal of CO2 from synthesis gas for ammonia and methanol production, for the production of hydrogen, in natural gas purification, coal liquefaction, and the like. In the present example a gas containing 13.55 mole-% of CO2 is to be purified by absorption into an aqueous solution of 13.6 wt-% MEA. The column, filled with 0.05 m steel Pall rings, has a diameter of 1.05 m and is operating at a temperature of 315 K and a pressure of 14.3 bars. The inlet flow rates of gas and liquid are 497 kmol/h and 76.9 mVh, respectively. Determine the packed column height necessary to reduce the mole fraction of CO2 to 5 x 10 at the top of the column. 

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