Question 10.8: Outline the step-by-step procedures for calculating the stea...
Outline the step-by-step procedures for calculating the steam requirements (lb steam/min-ft²), of a fixed-bed carbon adsorption system.
The step-by-step procedures for calculating the steam requirements of a fixed-bed regenerative carbon system are summarized as follows:
Step 1: Carbon Adsorber Efficiency
For a given HAP outlet concentration (HAP_{e}), the adsorption time (θ_{ad}), the regeneration time (θ_{reg}),and the steam requirement (St) can be determined using Table 3.
θ_{ad} = ــــــــــــــــــــــــــــــــــــــh
θ_{reg}= ــــــــــــــــــــــــــــــــــــــh
St = ــــــــــــــــــــــــــــــــــــــlb steam/lb carbon
| Table 3 Carbon Adsorber System Efficiency Variables |
||
| Steam requirement for regeneration, St (lb steam/lb carbon) | ||
| 0.3 | 1.0 | |
| Outlet HAP concentration, HAP_{o} (ppmv) | 70 | 10–12 |
| Adsorption cycle time,^{a} θ_{ad} (h) | 2 | 2 |
| Regeneration cycle time,^{a} θ_{reg} (h) | 2 | 2 |
_{}^{a}\textrm{In } some instances, cycle times may be considerably longer than the values given here. The values in this table are approximate, not definitive.
Step 2: Steam Required for Regeneration
Calculate the steam requirement using
Q_{s} =NA [St(C'_{req})/(θ_{req} − θ_{dry-cool})]/60 (10)
Q_{s} = ــــــــــــــــــــــــــــــــــــــ lb/h
Calculate Q_{s}/A_{bed}:
A_{bed} =Q'_{e,a}/U_{e} (10a)
A_{bed} = ــــــــــــــــــــــــــــــــــــــft²
Q_{s}/A_{bed} = ــــــــــــــــــــــــــــــــــــــlb steam/min-ft²
Typically, the Q_{s}/A_{bed} is limited to 4 lb steam/min-ft² to prevent fluidization of the carbon bed. Assume Q_{dry-cool} = 0.25 h, if no information is available.