PDF Publication Title:
Text from PDF Page: 015
Pressure Swing Adsorption: In a pressure swing adsorption system, the pressure is used to selectively adsorb and desorb individual VOCs based on their molecular characteristics and affinity for the adsorbent used. The method relies on the fact that more VOC is adsorbed at higher pressure. In these systems, the pressure is raised during the adsorption cycle and reduced during the regeneration cycle. When the adsorbent is saturated, the waste stream is stopped and the pressure of the adsorber vessel is reduced. The reduction in pressure results in desorption of the VOC, thereby regenerating the adsorbent. Pressure swing adsorption systems have been used to control gasoline vapors from storage tank vents. [19] 1.5 Adsorption Theory At equilibrium, the quantity of gas that is adsorbed on activated carbon is a function of the adsorption temperature and pressure, the chemical species being adsorbed, and the carbon characteristics, such as carbon particle size and pore structure. For a given adsorbent-VOC combination at a given temperature, an adsorption isotherm can be constructed that shows the relationship between the mass of adsorbate per unit weight of adsorbent (i.e., the “equilibrium adsorptivity”) to the partial pressure of the VOC in the gas stream. Figure 1.5 shows a set of typical adsorption isotherms for VOC adsorption on activated carbon. As shown in the graph, the adsorptivity increases with increasing VOC partial pressure and decreases with increasing temperature. Isotherms with this convex shape are designated as “Type I” isotherms. The Freundlich isotherm in equation 1.1 can be fit to a portion of a Type I curve and is commonly used in the industrial design of adsorbers.[2] where we = P = k,m = we kPm equilibrium adsorptivity (lb adsorbate/lb adsorbent) partial pressure of VOC in gas stream (psia) empirical parameters (1.1) The treatment of adsorption from gas mixtures is complex and beyond the scope of this chapter. However, where two VOCs in a gas mixture have nearly identical adsorption isotherms, the VOC with the lower vapor pressure will displace the VOC with the higher vapor pressure even when the latter VOC has previously adsorbed to the carbon surface. Thus, during the course of the adsorption cycle the carbon’s capacity for a higher vapor pressure constituent decreases. This phenomenon should be considered when sizing the adsorber. To be conservative, the adsorption cycle requirements should be based on the least adsorbable component in a mixture and the desorption cycle should be based on the most adsorbable component.[1] The equilibrium adsorptivity is the maximum amount of adsorbate the carbon can hold at a given temperature and VOC partial pressure. In actual control systems where there are not two beds operating in series, however, the entire carbon bed is never allowed to reach equilibrium. Instead, once the outlet concentration reaches a preset limit (the “breakthrough concentration”), 1-11PDF Image | Carbon Adsorbers
PDF Search Title:
Carbon AdsorbersOriginal File Name Searched:
final_carbonadsorberschapter_7thedition.pdfDIY PDF Search: Google It | Yahoo | Bing
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
Heat Pumps CO2 ORC Heat Pump System Platform More Info
CONTACT TEL: 608-238-6001 Email: greg@infinityturbine.com (Standard Web Page)