Question 10.4: Outline the methodology for the determination of the pretrea...
Outline the methodology for the determination of the pretreatment requirements of a gasphase carbon adsorption system.
The methodology for determining the carbon adsorption pretreatment requirements for an emission stream is outlined in the following three steps:
Step 1: Cooling Consideration
T_{e} = ــــــــــــــــــــــــــــــــــــــºF
When the temperature of the emission stream is higher than 130ºF, a heat exchanger is needed to lower the temperature to below 130ºF or less. Refer to a suitable reference for the calculation procedures.
Step 2: Dehumidification Consideration
R_{hum} = ــــــــــــــــــــــــــــــــــــــ \%
When the relative humidity is above 50\% and the HAP concentration is less than 1000 ppmv, a condenser may be used to cool and condense the water vapor in the emission stream, which will reduce the relative humidity of the emission stream.
Step 3: High VOC Concentration Consideration
HAP_{e} = ــــــــــــــــــــــــــــــــــــــppmv
When the flammable vapors are present in the emission stream, they must be limited to below 25\% of their LEL.
LEL= ــــــــــــــــــــــــــــــــــــــppmv (see Table 2)
25\% LEL = 0.25LEL = ــــــــــــــــــــــــــــــــــــــppmv
Carbon beds have a maximum practical inlet concentration for HAP of 10,000 ppmv. Greater inlet concentrations may not able to be treated by carbon.
| Table 2 Flammability Characteristics of Combustible Organic Compounds in Air^{a,b} |
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| Compound | Mol. Wt. | LEL^{a} (\% vol) | UEL^{a} (\% vol) |
| Methane | 16.04 | 5.0 | 15.0 |
| Ethane | 30.07 | 3.0 | 12.4 |
| Propane | 44.09 | 2.1 | 9.5 |
| n-Butane | 58.12 | 1.8 | 8.4 |
| n-Pentane | 72.15 | 1.4 | 7.8 |
| n-Hexane | 86.17 | 1.2 | 7.4 |
| n-Heptane | 100.20 | 1.05 | 6.7 |
| n-Octane | 114.28 | 0.95 | 3.2 |
| n-Nonane | 128.25 | 0.85 | 2.9 |
| n-Decane | 142.28 | 0.75 | 5.6 |
| n-Undecane | 156.30 | 0.68 | |
| n-Dodecane | 170.33 | 0.60 | |
| n-Tridecane | 184.36 | 0.55 | |
| n-Tetradecane | 208.38 | 0.50 | |
| n-Pentadecane | 212.41 | 0.46 | |
| n-Hexadecane | 226.44 | 0.43 | |
| Ethylene | 28.05 | 2.7 | 36.0 |
| Propylene | 42.08 | 2.4 | 11.0 |
| Butene-1 | 56.10 | 1.7 | 9.7 |
| cis-Butene-2 | 56.10 | 1.8 | 9.7 |
| Isobutylene | 56.10 | 1.8 | 9.6 |
| 3-Methyl-butene-1 | 70.13 | 1.5 | 9.1 |
| Propadiene | 40.06 | 2.6 | |
| 1,3-Butadiene | 54.09 | 2.0 | 12.0 |
| Acetylene | 2.5 | 100.0 | |
| Methyl acetylene | 1.7 | ||
| Benzene | 78.11 | 1.3 | 7.0 |
| Toluene | 92.13 | 1.2 | 7.1 |
| Ethyl benzene | 106.16 | 1.0 | 6.7 |
| o-Xylene | 106.16 | 1.1 | 6.4 |
| m-Xylene | 106.16 | 1.1 | 6.4 |
| p-Xylene | 106.16 | 1.1 | 6.6 |
| Cumene | 120.19 | 0.88 | 6.5 |
| p-Cumene | 134.21 | 0.85 | 6.5 |
| Cyclopropane | 42.08 | 2.4 | 10.4 |
| Cyclobutane | 56.10 | 1.8 | |
| Cyclopentane | 70.13 | 1.5 | |
| Cyclohexane | 84.16 | 1.3 | 7.8 |
| Ethyl cyclobutane | 84.16 | 1.2 | 7.7 |
| Cycloheptane | 98.18 | 1.1 | 6.7 |
| Methyl cyclohexane | 98.18 | 1.1 | 6.7 |
| Ethyl cyclopentane | 98.18 | 1.1 | 6.7 |
| Ethyl cyclohexane | 112.21 | 0.95 | 6.6 |
| Methyl alcohol | 32.04 | 6.7 | 36.0 |
| Ethyl alcohol | 46.07 | 3.3 | 19.0 |
| n-Propyl alcohol | 60.09 | 2.2 | 14.0 |
| n-Butyl alcohol | 74.12 | 1.7 | 12.0 |
| n-Amyl alcohol | 88.15 | 1.2 | 10.0 |
| n-Hexyl alcohol | 102.17 | 1.2 | 7.9 |
| Dimethyl ether | 46.07 | 3.4 | 27.0 |
| Diethyl ether | 74.12 | 1.9 | 36.0 |
| Ethyl propl ether | 88.15 | 1.7 | 9.0 |
| Diisopropyl ether | 102.17 | 1.4 | 7.9 |
| Acetaldehyde | 44.05 | 4.0 | 36.0 |
| Propionaldehyde | 58.08 | 2.9 | 14.0 |
| Acetone | 58.08 | 2.6 | 13.0 |
| Methyl ethyl ketone | 72.10 | 1.9 | 10.0 |
| Methyl propyl ketone | 86.13 | 1.6 | 8.2 |
| Diethyl ketone | 86.13 | 1.6 | |
| Methyl butyl ketone | 100.16 | 1.4 | 8.0 |
_{}^{a}\textrm{LEL}: lower explosive limit; UEL: upper explosive limit.