Absorber Design 2024 -UPLOAD Copy.pptx

Gas absorber design basics

1. Packed Column As Gas Absorber Equipment Design

2. Column Design

3. Packed Bed Height Concept of HETP

4. HETP concept.. HETP (Height Equivalent to a Theoretical Plate) instead of a tray (plate) column, a packed column can be used for various unit operations such as continuous or batch distillation, or gas absorption

5. HETP concept.. What is “height equivalent to a theoretical plate (HETP)”? When packings are used instead of trays, the same enrichment of the vapour will occur over a certain height of packings, and this height is termed the height equivalent to a theoretical plate (HETP) It has been shown by Eckert (1975) that in distillation the HETP for a given type and size of packing is essentially constant, and independent of the system physical properties ;

6. HETP concept.. The following values for Pall rings can be used to make an approximate estimate of the bed height required. Size, mm HETP, m 25 (1 in.) 0.4 - 0.5 38 (1.5 in .) 0.6 - 0.75 50 (2 in.) 0.75 - 1.0

7. Calculation of HETP

8. For a Column…. 81 The relationship between transfer units and the height of an equivalent theoretical plate, HETP is given by: Value of m varies throughout a distillation so it will be necessary to calculate the HETP for each plate or a series of plates.

9. HETP in form of Transfer units (HTU/ NTU)

10. Absorption: packed Column Where the concentration of the solute is small, say dilute system, the height of packing Z can be calculated,… OR    

11. HETP in form of Transfer units (HTU/ NTU) For design purposes if we want to write HETP equations in terms of “transfer units” (HTU); …. the value of integral = the number of transfer units , and The group in front of the integral sign, = the height of a transfer unit .

12. overall gas-phase transfer units (NTU/HTU) For design purposes if we want to write HETP equations in terms of “transfer units” (NTU/HTU); …. Z = H OG * N OG Compare both equation… the value of integral = the number of transfer units, and The group in front of the integral sign, = the height of a transfer unit.

13. overall gas-phase transfer units (NTU/HTU) So for gas phase, N OG is the number of overall gas-phase transfer units H OG is the height of an overall gas-phase transfer unit      

14. overall gas-phase transfer units (NTU/HTU) For dilute systems , the number of transfer units is given by:

15. overall liquid-phase transfer units (NTU/HTU) For design purposes if we want to write HETP equations in terms of “transfer units” (HTU); …. Z = H OL N OL Compare both equation… the value of integral = the number of transfer units, and The group in front of the integral sign, = the height of a transfer unit.

16. overall liquid-phase transfer units (NTU/HTU) So for liquid phase, N OL is the number of overall liquid-phase transfer units H OL is the height of an overall liquid-phase transfer unit    

17. height of a transfer unit (HTU)   where m is the slope of the equilibrium line and Lm/Gm the slope of the operating line.

18. 19 Recommended design values, the pressure drop in mm water per m packing , are: Absorbers and strippers 15 to 50 mm Distillation, atmospheric and moderate pressure 40 to 80 mm Where the liquid is likely to foam, these values should be halved. Diameter Calculations for Packed bed column