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the cost is so much higher for “B”: basically you get what you pay for. Multicomponent adsorption is complex, as alluded to before. Since this is a small application, delving into equilibria and column modeling is not justified. We can instead assume that the lighter components are displaced by the heavier components. The flow rate, up to 10 cfm at 80°F, amounts to 9.1 scfm or 1.52 lbmol/hr. From that we can estimate the time “on-line” provided by either adsorbent for each compound, assuming that they adsorb independently, and completely (no premature breakthrough). The best choice appears to be carbon “B,” since it offers a longer time on-line than carbon “A” for the critical component, MEK, and the ratio is greater than the cost differential. Table 4. Estimated loadings and service times of emitted components (at 100 ppm each) for activated carbons “A” and “B” at 80°F. Component Name Methyl Ethyl Ketone Toluene n-Hexane Carbon “A” 7.5 19.6 12.3 Carbon “B” “B”/“A” 13.2 1.76 28.8 1.47 19.1 1.55 Loading (lb/100 lb) Loading Mol.Wt. (g/mol) 72.10 92.14 86.18 Max. On-Line (hr/100 lb) “A” “B” 683 1203 1398 2054 938 1456 The final consideration is the type and cost of equipment. Modular units come packed with 150 to 500 lb of carbon. These can be installed and removed quickly, and returned to the manufacturer on an exchange basis (possibly avoiding “hazardous waste” aspects). One of the smaller units could be packed with 4x6 mesh carbon, and could handle up to 100 cfm. Furthermore, it could be viewed as having 50 lb allotments per contaminant. According to Table 4, there would be some safety factor for an “on-line” time of 600 hr, but not much. Depending on the vendor, the cost per drum would be in the range of $600. Even at this low a cost, it might be possible to justify a small PSA unit that would recover concentrated vapor (for incineration), or a condensed product. Such systems are not yet available “off-the-shelf,” however. 2. dilute aqueous emissions An analogous situation exists when a noxious or valuable contaminant is present in water. Examples are: the silver-laden waste from photographic developing that used to be discarded, or well-water containing sulfur or iron, or dozens of wastewater applications. For example, a difficult application is removal of halogenated phenolics from wastewater. The equilibration time for activated carbon is long, which means that the diffusivity is low, and that the breakthrough curve could be very distended. Let’s look at a specific case, say, 1 mg/l (or 1000 ppm) of 2-chlorophenol in 100 gpm water, with a minimum “on-line” time of 500 hr. The report by Dobbs and Cohen that was mentioned earlier indicates that Filtrasorb-300 (Calgon Corp.) adsorbs 57.1 mg/g at this concentration. They also noted that a fine powder (200x400 mesh, or 0.05 mm diameter) required about 2 hr to equilibrate. Equation (8) gives us an idea of how long a 2 mm diameter granule might take. Namely, the parameter Deff t/2 would be constant, as would the effective diffusivity. Thus, t3 mm = t0.05 mm (3 mm /0.05 mm)2 or 300 days! This material cannot be expected to exhibit a step change upon breakthrough. Therefore, a large safety factor is essential. It is also a valid reason for using a slurry of carbon in the powdered form, even though a downstream filter is required to recover the waste. 19PDF Image | ADSORBENT SELECTION
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CO2 Organic Rankine Cycle Experimenter Platform The supercritical CO2 phase change system is both a heat pump and organic rankine cycle which can be used for those purposes and as a supercritical extractor for advanced subcritical and supercritical extraction technology. Uses include producing nanoparticles, precious metal CO2 extraction, lithium battery recycling, and other applications... More Info
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