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SCRUBBER DESIGN (PACKED COLUMN)
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column
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packed
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scrubber
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- packed
- scrubber
| SCRUBBER DESIGN (PACKED COLUMN) | |||||||||||||
| Prepared by : | Column Tag No. | : | |||||||||||
| Checked by : | Job No. | : | |||||||||||
| Date : | Client | : | |||||||||||
| Project | : | ||||||||||||
| # | Input Data | Stream | : | HCL Vap. | |||||||||
| Packing type | = | Intallox Saddles | |||||||||||
| Packing size | = | 25 | mm | ||||||||||
| Packing MOC | = | PP | |||||||||||
| Gas pr. Drop / m bed | = | 15 | mmWC / m packing height | = | 147.1 | (N/m2)/m | |||||||
| Total packing height | = | 3.2 | m (including all packed beds) | ||||||||||
| Gas / Vapour Properties | |||||||||||||
| Gas / Air flow rate | = | 1000 | kg/h | OR | 0 | m3/h | |||||||
| = | 0.2778 | kg/s |
=
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0 | m3/s | ||||||||
| Gas pressure at entry | = | 1.0000 | atm | ||||||||||
| Gas temperature at entry | = | 30.00 | oC | = | 303.00 | oK | |||||||
| Gas / Air mol weight | = | 29 | |||||||||||
| Component to be scrubbed | |||||||||||||
| Component Name | = | HCL Vap | |||||||||||
| Component flow rate | = | 70 | Kg/h | ||||||||||
| % comp. in air/gas | = | 6 | % (v/v) | (presumed) / (given by client) / (by process cal.) | |||||||||
| Molecular weight of comp. | = | 36.5 | |||||||||||
| Liquid / Scrubbing media Properties | |||||||||||||
| Scrubbing media | = | 20% NaOH | |||||||||||
| Liquid flow rate, L | = | 77 | kg/h | ||||||||||
| = | 0.0214 | kg/s | |||||||||||
| Liquid Density, L |  |
= | 1100 | kg/m3 | Conversion : | ||||||||
| Liquid Viscosity, µL | = | 0.0035000 | Ns/m2 | 3.5 | Cp = | 0.00350000 | Ns/m2 | ||||||
| Packing factor, Fp | = | 21 | m-1 | ||||||||||
| Charac. Packing Factor,Cf | = | 33 | Ref. Table 6.3, Characterstics of Random packings | ||||||||||
| Conversion factor, J | = | 1.0 | factor for adequate liquid distribution & irrigation across the bed | ||||||||||
| Calculations | |||||||||||||
| TO CALCULATE COLUMN DIAMETER | |||||||||||||
| Since larger flow quantities are at the bottom for an absorber, the diameter will be chosen to | |||||||||||||
| accommodate the bottom conditions. | |||||||||||||
| To calculate Gas density | |||||||||||||
| Avg. molecular weight | = | 29.45 | Kg / Kmol | ||||||||||
| If gas flow rate is given in kg/h | If gas flow rate is given in m3/h | ||||||||||||
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| Gas in = | 0.009432183 | Kmol/s | Gas in | = (m3/s) x 273 | x | pr. in atm | x 1 | ||||||
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T in kelvin | 1.0 atm | 22.4 | ||||||||
| = | (kmol/s) x T in kelvin x 1.0 atm x 22.4 |  |
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| 273 pr. In atm 1 | = | 0 | Kmol/s | ||||||||||
| = | 0.234499 | m3/s | = | 0 | Kg/s | ||||||||
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| Select vol. flow rate and mass flow rate from above, | |||||||||||||
| Selected mass flow rate | = | 0.2777778 | Kg/s | ||||||||||
| Selected vol. Flow rate | = | 0.234499 | m3/s | ||||||||||
| Selected molar flow rate | = | 0.0094322 | Kmol/s | ||||||||||
| Therefore, gas density | = | 1.1846 | Kg/m3 | (mass flow rate / vol. Flow rate) | |||||||||
| To find L', G' and Tower c/s area | |||||||||||||
| Assuming essentially complete absorbtion, | |||||||||||||
| Component removed | = | 0.0207 | Kg/s | (molar flow rate x % comp. x mol. Wt.) | |||||||||
| Liquid leaving | = | 0.0420 | Kg/s | (Inlet liquid flow rate + comp. Removed) | |||||||||
   |
0.5 | = | 0.00497 | ||||||||||
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| Using | 0.00497 | as ordinate, | Refer fig.6.34 using a gas pressure drop of | 147.1 | (N/m2)/m | ||||||||
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= | 0.04 | (from graph) | ||||||||||
|
 |
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| Therefore, G' | = |  |
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|
0.5 | ||||||||
| Cf µL0.1 J | |||||||||||||
| = | 1.6665 | Kg / m2.s | |||||||||||
| Tower c/s area | = | 0.1667 | m2 | ( c/s area = mass flow rate / G' ) | |||||||||
| Tower diameter | = | 0.4607 | m | = | 460.7 | mm | |||||||
| = | 500 | mm | |||||||||||
| Corresponding c/s area | = | 0.1963 | m2 | ||||||||||
| TO ESTIMATE POWER REQUIREMENT | |||||||||||||
| Efficiency of fan / blower | = | 60 | % | assumed / given | |||||||||
| To calculate pressure drop | |||||||||||||
| Pressure drop for irrigated | = | 470.72 | N/m2 | (pressure drop per m packing x total ht. of packing) | |||||||||
| packing | |||||||||||||
| For dry packing, | |||||||||||||
| O/L Gas flow rate, G' | = | 1.3095 | Kg / m2.s | (Gas inlet flow rate - Component removed) / c/s area | |||||||||
| O/L Gas pressure | = | 100854.28 | N/m2 | (subtracting pressure drop across packing) | |||||||||
| Gas density, G | |
= |   |
  |
 |
 |
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| 22.41m3/Kmol T in kelvin | 101330 | ||||||||||||
| = | 1.1605 | Kg/m3 | |||||||||||
| CD | = | 96.7 | Ref. Table 6.3, Characterstics of Random packings | ||||||||||
 |
= |  |
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| Z | |
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| = | 142.89 | N/m2 | |||||||||||
| Pressure drop for packing | = | 613.61 | N/m2 | (irrigated packing + dry packing) | |||||||||
| Pressure drop for internals | = | 25 | mmWC | (packing supports and liquid distributors) | |||||||||
| = | 245.17 | N/m2 | |||||||||||
| Gas velocity | = | 7.5 | m/s | ||||||||||
| Inlet expansion & outlet | = | 1.5 x Velocity heads | = | 1.5 x (V2 / 2g) | |||||||||
| contraction losses | = | 42.19 | N m / Kg | ||||||||||
| = | 49.97 | N/m2 | (divide by density) | ||||||||||
| Total pressure drop | = | 908.75 | N/m2 | (packing + internals + losses) | |||||||||
| Fan power output | = |  |
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| O/L gas density, Kg/m3 | |||||||||||||
| = | 201.35 | N .m / s | |||||||||||
| = | 0.20 | kW | |||||||||||
| Power for fan motor | = | 0.34 | kW | (fan power output / motor efficiency) | |||||||||
| = | 0.45 | hp | |||||||||||
| COLUMN DIAMETER / HYDRAULIC CHECK | |||||||||||||
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| Liq.-Vap. Flow factor, FLV | = | (L / V) x ( V / L) | |
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| = | 0.0025 | ||||||||||||
| Design for an initial pressure drop of | 15 | mm H2O /m packing | |||||||||||
| From K4 v/s FLV, | |||||||||||||
| K4 | = | 0.85 | |||||||||||
| K4 at flooding | = | 6.50 | |||||||||||
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| Trial % flooding | = | ( (K4 / K4 at flooding) ) x 100 | |||||||||||
| = | 36.1620 | ||||||||||||
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| Gas mass flow rate, Vm | = |  |
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| = | 3.7763 | kg/m2.s | |||||||||||
| Trial column c/s area | = | V / Vm | |||||||||||
| (Trial As) | |||||||||||||
| = | 0.0736 | m2 | |||||||||||
| Trial column dia., D | = | 0.3060 | m | D = |  |
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| Round off 'D' to nearest standard size | |||||||||||||
| Therefore, D | = | 0.500 | m | ||||||||||
| Column C/S area, As | = | 0.1963 | m2 |
As =
|
(pi/4) x D2 | ||||||||
| % flooding | = | 13.5472 | % flooding = Trial % flooding x (Trial As / As) | ||||||||||
| Conclusion | |||||||||||||
| Generally packed towers are designed for 50% -- 85% flooding. | |||||||||||||
| If flooding is to be reduced, | |||||||||||||
| (i) Select larger packing size and repeat the above steps. | |||||||||||||
| OR | |||||||||||||
| (ii) Increase the column diameter and repeat the above steps. | |||||||||||||
| HETP PREDICTION | |||||||||||||
| Norton's Correlation : | ln HETP = n - 0.187 ln + 0.213 ln µ |  |
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| Applicable when, | |||||||||||||
| liquid phase surface tension > 4 dyne/cm & < 36 dyne/cm | |||||||||||||
| liquid viscosity > 0.08 cP & < 0.83 cP | |||||||||||||
| Conversion : | |||||||||||||
| Input Data | 0.018 | N/m = | 18 | dyne/cm | |||||||||
| Liquid-phase | |||||||||||||
| Surface Tension, | |
= | 20 | dyne/cm | Norton's Correlation Applicable | ||||||||
| Liquid Viscosity | = | 3.5 | cP | Norton's Correlation NOT applicable | |||||||||
| n | = | 1.13080 | |||||||||||
| Calculation | |||||||||||||
| ln HETP | = | 0.8374366 | |||||||||||
| HETP | = | 2.3104368 | ft | ||||||||||
| = | 0.7042211 | m | |||||||||||
| For separations, less than 15 theoritical stages, a 20% design safety factor can be applied. | |||||||||||||
| Considering 20% safety factor, | |||||||||||||
| HETP | = | 0.8450653 | m | ||||||||||
| For separations, requiring 15 to 25 theoritical stages, a 15% design safety factor can be applied. | |||||||||||||
| Considering 15% safety factor, | |||||||||||||
| HETP | = | 0.8098543 | m | ||||||||||
