Absorber
DESIGN OF AN ABSORBER
Problem statement
To design an absorber (packed tower) for the absorption of 785.15 kg/h of sodium metabisulphite (Na2S2O5) at an average temperature of 68˚C and Y atm pressure with sulphur dioxide gas counter-currently reacting with Na2SO3 rich feed.
Introduction
Absorbers are vertical towers used in distillation, gas absorption and liquid-liquid extraction processes. Absorbers can be operated co-currently or counter currently. In the former, both fluids involved are fed into the unit from the same point causing them to flow along each other. In counter current operation, the liquid is fed at the top of the absorber, flows downwards and contacts with rising gas fed from beneath.
Absorbers can be classified as tray towers or packed towers. In tray towers, the interfacial surface area required for contact between the two fluids is provided by stepwisely arranged plates or trays whereas in packed towers, the interfacial surface area is provided by devices called packing. (Treybal, 1981)
The absorber used for this plant is a counter current packed tower.
Justification
The choice of a packed tower was influenced by the following factors;
1. The liquids involved in the reaction are corrosive and packed columns provide a cheaper solution around this problem since the packing can be easily replaced when the minimum degree of corrosion is reached
2. A lower liquid hold up is achieved in packed towers than in plate towers.
3. The pressure drop per equilibrium stage (HETP) is lower for packed columns.
(A) Chemical engineering design;
(i) Component specification
(ii) Calculation of liquid and gas flow rates
(iii) Selection of packing
(iv) Hold-down plates
(v) Packing support
(vi) Determination of column height
(vii) Determination of column diameter
(viii) Height of packing
(ix) Wetting rate
(x) Absorption factor
(xi) Average gas velocity in the packing
(B) Mechanical engineering design;
(i) Material of construction
(ii)
Problem statement
To design an absorber (packed tower) for the absorption of 785.15 kg/h of sodium metabisulphite (Na2S2O5) at an average temperature of 68˚C and Y atm pressure with sulphur dioxide gas counter-currently reacting with Na2SO3 rich feed.
Introduction
Absorbers are vertical towers used in distillation, gas absorption and liquid-liquid extraction processes. Absorbers can be operated co-currently or counter currently. In the former, both fluids involved are fed into the unit from the same point causing them to flow along each other. In counter current operation, the liquid is fed at the top of the absorber, flows downwards and contacts with rising gas fed from beneath.
Absorbers can be classified as tray towers or packed towers. In tray towers, the interfacial surface area required for contact between the two fluids is provided by stepwisely arranged plates or trays whereas in packed towers, the interfacial surface area is provided by devices called packing. (Treybal, 1981)
The absorber used for this plant is a counter current packed tower.
Justification
The choice of a packed tower was influenced by the following factors;
1. The liquids involved in the reaction are corrosive and packed columns provide a cheaper solution around this problem since the packing can be easily replaced when the minimum degree of corrosion is reached
2. A lower liquid hold up is achieved in packed towers than in plate towers.
3. The pressure drop per equilibrium stage (HETP) is lower for packed columns.
(A) Chemical engineering design;
(i) Component specification
(ii) Calculation of liquid and gas flow rates
(iii) Selection of packing
(iv) Hold-down plates
(v) Packing support
(vi) Determination of column height
(vii) Determination of column diameter
(viii) Height of packing
(ix) Wetting rate
(x) Absorption factor
(xi) Average gas velocity in the packing
(B) Mechanical engineering design;
(i) Material of construction
(ii)