Calculation for absorber stripper systems
Creators: name: Hadzihafizovic, Dzevad
Publisher: name: Dzevad Hadzihafizovic's Lab
Year: 2024

description: Absorption is a gas-liq mass transfer operation in which a component is transferred from thegas phase to the liquid. And the rate of absorption is determined by the rate of molecular diffusionthat largely controls this interphase mass transfer.The component which is absorbed is called solute and in which it is absorbed is called solvent.Generally, the solute enters the column in a gas introduced at the bottom of a column whilethe solvent is fed to the top as liquid. The solute is more or less soluble in the solvent while the carriergas is either insoluble or slightly soluble in the liquid phase. The absorbed gas and solvent leave atthe bottom and the unabsorbed components plus some of the liquid vaporized into the gas phaseleave as gas from the top.The absorbed solute may form a simple solution in the liquid phase or it may react chemicallywith a component in the liquid phase. Therefore, the absorption processes are conveniently dividedinto two main groups: • Physical Absorption - in which the process is solely physical and is limited to the formationof solution of the gas in the liquid, e.g., absorption of ammonia by water from an air-ammoniamixture; similarly liquid methanol at low temperature absorbs CO2and H2S at high pressureand forms their solution. • Chemical Absorption - in which absorption follows incipient chemical reaction, e.g., absorption of CO2in hot alkali and absorption of NOxin water.Gas absorption is a major unit operation for the selective removal of one or more components from a gas mixture by a suitable liquid forming a solutions of the gases upon absorption. The solventis regenerated from the solution by a process called Desorption. Desorption (or Stripping) is the just reverse of gas absorption. The rich solution, i.e., thesolvent loaded with absorbed solute (or solutes) is charged to the regeneration tower (i.e., strippingcolumn) at the top and the stripping stream (usually saturated steam) is introduced at the bottom.Upon gas-liq contact, mass transfer occurs in the opposite direction, i.e., physical transfer of solutefrom the liq phase to the gas phase. The lean solution (i.e., the solution stripped off much of its gasload) recovered from the bottom of the column is recycled to the absorption tower to ensure continuousoperation. 

Absorption and desorption are traditional thermal separation processes. A complete absorption process comprises an absorber and a desorber Figure 1.1. In the absorber the scrubbing liquor (solvent) is charged with the gaseous component (components) to the removed, and in the desorber (regenerator) it is regenerated or freed from thesubstances dissolved in it. The stripped solvent is pumped back to the absorption tower to completethe cycle. 

Be it absorption or desorption-the intimate gas-liq contact is essential in both cases and as such the effectiveness of the equipment is, by and large, determined by the success with which itpromotes contact between the two phases. Absorption differs from distillation in the following aspects: • Stripping vapor is generated in the distillation column by the partial evaporation of theliquid which is therefore at its boiling point, whereas in absorption the liquid is always wellbelow its boiling point.• Distillation is characterized by simultaneous molecular diffusion in both directions and inideal systems equimolar counter-diffusion occurs across the gas-liq phase boundaries ofthese two contacting streams. But in gas absorption, diffusion is chiefly unidirectional­the solute molecules are diffusing into the liquid while the movement in the reverse directionis practically very small. • The ratio of the liq flowrate to the gas flowrate is considerably greater in absorption than indistillation with the effect that the layout of trays is different in these two cases. • The primary objective of absorption is only solute recovery or solute removal while distillationinvolves separation of solutes from each other to any important extent.