1. Nonisothermal case: adiabatic approach Prof. Dr. Marco Mazzotti - Institut für Verfahrenstechnik

2. 1. Approach Therefore two new concepts become important: 1.Energy balances 2.Changes of L and G within the column In the adiabatic approach energy balances are calculated under following assumptions: There is no heat exchange through the walls of the column The gas and liquid stream leaving a stage are at the same temperature Calculating changes of L and G within the column are important when dealing with large solute fractions. This is often the case when calculating non-isothermal columns.

3. Once, pressure and initial composition and temperature of the solvent are set we can consider them as data. This is a list of known variables: Specifications y1y1 Gas final composition, y 1 G n+1 T G n+1 Data and set values y n+1 x0x0 Pressure, p Gas flow rate, G in Gas initial composition, y n+1 Solvent initial composition, x 0 Equilibrium data, y=f(x,T) p y = f(x,T) TL0TL0 Gas Temp. at inlet TG 1 Liquid Temp. at inlet, TL 2 LnLn TLnTLn Unknowns xnxn Solvent flow rate at inlet, L 2 Number of stages, n Solvent final composition, x n G1G1 L0 L0 n Solvent flow rate outlet, L 1 TG1TG1 Gas Temp. at outlet TG 2 Gas Temp. at outlet TL 1

4. 2. Balances Material Balance of column: The amount of liquid increases from the bottom to the top of the column. It is calculated by adding up the amount of solvent and the amount of absorbed solute. The same way the amount of gas is calculated. It deacreases from the top to the bottom of the column as the solute absorbs to the liquid. Energy Balance of column  H S represents the molar enthalpy of mixing or the integral heat of solution, at the prevailing concentration and at the base temperature T 0 J/(mol K)Heat capacitycp J/molChange of solute enthalpy between liquid and gas phase HsHs J/molEnthalpy at reference stateH0H0 J/molEnthalpyH

5. To solve the problem the gas outlet temperature and the amount of liquid solvent have to be estimated or calculated by a nother method, e.g. the isothermal approach 3. Solution of the system Now all necessary values of the bottom of the column can be calculated by the energy and mass balances. From the bottom of the column a new set of mass and material balances can be made including the first stage. (green canvas) From these balances all unknowns of the first stage can be calculated. This is repeated including one more stage every time until the required specification is reached.