Enthalpy and Heat Balances

An enthalpy or heat balance for an absorber without heat losses as shown in Fig. 3-4 gives 

During the absorption of gases in solvents the heat of absorption is released and absorption is therefore an exothermic process. 

The heat of absorption is mainly taken up by the solvent, as heat transfer within the gas flow is poor and negligible. Therefore, during an adiabatic absorption process the temperature of the solvent increases 

Since an increase in the temperature from i,a to i.co occurs, this causes a decrease in the solvent absorption capacity of the soluted substance according to Henry s law. The absorption efficiency reduces due to an unfavorable equilibrium position at the higher temperature, (see Chapter 1.4.3.3). Consequently, isothermic absorption is aimed for in practice. The heat flux to be removed under isothermal absorption at (t / a = di u) follows from Eq. (3-7). 

Continuous removal of the heat of absorption is very difficult. The absorber is cooled stagewise if the absorption heat is considerable. 

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