Prof. Dr. Marco Mazzotti - Institut für Verfahrenstechnik Nonisothermal case: temperature profile in the column

This is a simple diagram showing the notation we will use later. The liquid enters the column at its top flowing by gravity trough the column. The gas enters at the bottom. With this configuration, work is not required for the flow transport. The heat of absorption of solute (gas) increases the temperature of the solution. When the gas (G) enters the column at about 10 to 20°C under the liquid temperature going out (L’), and the liquid is volatile, evaporation will cool down the liquid at the bottom of the column. This means that the temperature profile in the column will present a maximum near its bottom. You may print this out to have in mind the notation. The Absorption Scheme

Liquid temperature Absorption Column L h T T 2 = T 1 This diagram represents the temperature of the Liquid across the column. When the heat of absorption is not significant and the effect of liquid evaporation can be neglected, the adiabatic absorption column has a constant temperature along the height. 1 2

Liquid temperature Absorption Column L h T T2T2 Along the column, the absorption of gas increases the temperature. Gas and liquid temperatures are similar at the bottom, and the gas entering the column is already saturated. The changes in temperature are only due to the heat of absorption of solute gas. This is why temperature only increases along the column. T1T1 1 2

Liquid temperature Absorption Column L h T T2T2 T max Along the column, the absorption of gas increases the temperature. The gas enters the column at a lower temperature than the liquid and thus, at the bottom the evaporation of liquid is important. This is why the temperature decreases at the bottom. T1T1 1 2