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Gas scrubbing is a process where a gas is removed from a mixture by contact with a liquid solvent. It is commonly used in packed towers or columns to remove impurities or recover gases. The solubility of the gas solute in the liquid solvent is the theory behind gas scrubbing. Temperature and pressure affect the solubility of the solute gas in the liquid phase. Packed towers or columns are used for gas scrubbing, where solute-containing gas enters the bottom of the column and travels up through the packing.
Gas scrubbing, also known as gas sorption, is a process in which a gas is removed from a mixture through contact with a liquid solvent. Gas scrubbing is a common purification technique in the chemical process industries and is most commonly performed in structures known as packed towers or packed columns. This technique can be used to remove impurities or to recover gases.
Gas scrubbers are commonly used to separate gases such as hydrogen sulfide (H2S) and carbon dioxide (CO2) from natural gas, syngas and flue gas. In these cases, solute materials must be removed from the product gases due to performance, health and environmental concerns. In other cases, the solute gas itself may be the intended end product and, after being absorbed into the liquid solvent, is recovered.
The theory behind gas scrubbing lies in the solubility of the gas solute in the liquid solvent. Solvents are specifically chosen to extract solvent gas from a gaseous mixture. For example, CO2 is soluble in an aqueous solution of ethanolamine. If a gaseous stream of nitrogen and CO2 were to come into contact with ethanolamine, the CO2 would be more likely to dissolve in the solution, leaving a gaseous mixture composed primarily of nitrogen.
For gas scrubbing to work efficiently, there must be good contact between the liquid and gaseous phases. Temperature and pressure can also affect the solubility of the solute gas in the liquid phase. The correct values for these process variables can be determined by experimentation or determined with process simulation software. The equilibrium between temperature and pressure will depend on the capacities of the packed column and the solubility of other gases in the mixture.
Gas scrubbing is usually done in packed towers or packed columns. These columns are similar in shape to distillation columns but contain tower packings instead of trays. These packings fill the center of the column and come in many different shapes, materials and sizes. Raschig rings, Pall rings, Berl saddles and Intalox® saddles are common types of seals. Gaskets are used to increase the surface area and ensure good contact between the gas and the medium.
In general, solute-containing gas, or rich gas, enters the bottom of the column and travels up through the packing. Fresh liquid enters the top of the column and passes through a liquid distributor, which distributes the liquid evenly throughout the packaging. After the purge, the solute-free or lean gas exits the top of the column. The solute-rich liquid, or hard liquor, exits the bottom column.
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