Adsorption systems design

Standardized canister and panel adsorption system designs are offered by the manufacturers. Typically, thin beds 1 to 2 in. thick are used to minimize pressure drop. Face velocities are in the range of about 30 to 60 ft/min. A common design for large systems uses many rectangular panels 1 to 2 ft on each side, arranged in a housing to create an accordion-folded, extended. sur-... 

Design Methods. Improvements ia the ability to predict multicomponent equilibrium and mass-transfer rate performance will allow significant improvements ia the design of new adsorption systems and ia the energy efficiency of existing systems. 

Adsorption systems employing molecular sieves are available for feed gases having low acid gas concentrations. Another option is based on the use of polymeric, semipermeable membranes which rely on the higher solubiHties and diffusion rates of carbon dioxide and hydrogen sulfide in the polymeric material relative to methane for membrane selectivity and separation of the various constituents. Membrane units have been designed that are effective at small and medium flow rates for the bulk removal of carbon dioxide. 

Other types of regenerators designed for specific adsorption systems may use solvents and chemicals to remove susceptible adsorbates (51), steam or heated inert gas to recover volatile organic solvents (52), and biological systems in which organics adsorbed on the activated carbon during water treatment are continuously degraded (53). 

Adsorption-Control Equipment If a gas stream must be treated for a short period, nsnally only one adsorption unit is necessary, provided, of course, that a sufficient time interval is available between adsorption cycles to permit regeneration. However, this is usually not the case. Since an nninternipted flow of treated gas is often required, it is necessary to employ one or more units capable of operating in this fashion. The units are designed to handle gas flows without interruption and are charac terized by their mode of contact, either staged or continuous. By far the most common type of adsorption system used to remove an objectionable pollutant from a gas stream consists of a number of fixed-bed units operating in such a sequence that the gas flow remains nninternipted. A two- or three-bed system is nsn ly... 

Equilibrium Considerations - Most of the adsorption data available from the literature are equilibrium data. Equilibrium data are useful in determining the maximum adsorbent loading which can be obtained for a specific adsorbate-adsorbent system under given operating conditions. However, equilibrium data by themselves are insufficient for design of an adsorption system. Overall mass transfer rate data are also necessary. 

Engineering Considerations To effect the good engineering design of an activated carbon adsorption system, it is first necessary to obtain information on the following the actual cubic feet per minute (ACFM) of air to be processed by the adsorber, the temperature of gas stream, the material(s) to be absorbed, the concentration of the material to be adsorbed, and if the intended application is air pollution control such as odor control - then the odor threshold of the material to be adsorbed. In addition, data is needed on the presence of other constituents in the gas stream, and whether or not solvent recovery is economical. 

Solvent reeovery systems would also neeessitate the speeifieation of eondenser duties, distillation tower sizes, holding tanks, piping, and valves. It is important to note that the engineering design of an adsorption system should be based on pilot data for the partieular system. Information ean usually be obtained direetly from the adsorbent manufaeturer. The overall size of the unit is determined primarily by eeonomie eonsiderations, balaneing the operating eosts against the eapital eosts. 

The main factors in the design of an adsorption system are the (1) Carbon consumption - The amount of earbon required to treat the liquid or gas, normally expressed per unit of the fluid treated and (2) Contact time - For a fixed flow rate, the contact time is directly proportional to the volume of carbon and is the main factor influencing the size of the adsorption system and capital cost. 

Lukchis, G.M. Adsorption Systems, Part II Equipment Design, Chemical Engineering, July 9, 1973, p. 83. 

Jiang, L., V.G. Fox, and L.T. Biegler, Simulation and optimal design of multi-Bed pressure swing adsorption systems, AIChE ]., 50, 2904-2917, 2004. 

Bulletin 23-56c, Calgon Carbon Corporation, Pittsburgh, Pa., 1986. White and Barkley, The Design of Pressure Swing Adsorption Systems, Chem. Eng. Prog., January 1989. 

The forgoing derivation and wave speed values will be found very helpful in discussing design methodologies for all adsorption systems. 

This discussion lays out the basic concepts involved in design using water as the subject contaminant. In the next sections we examine a handful of commercially relevant adsorptive separations. We find that the design ideas are all readily transferable but that in each application there are additional special considerations that enter into the sizing of the adsorption system. 

The USEPA surveys identified four resin adsorption systems in the pesticide industry [7]. Phenol, pesticide, and diene compounds are all effectively removed by these systems. At least one system realized a significant product recovery via regeneration and distillation. The design surface loading rates vary from 1.0 to 4.0 gpm/ft with empty bed contact times of 7.5 to 30 minutes. 

Adsorption systems make use of the fact that VOCs are attracted to and will adsorb to (attach to the surface of) certain special materials, the most common of which is activated charcoal. Activated charcoal consists of finely divided particles of charcoal. Flue gases containing VOCs are passed through a chamber and over a bed of the adsorbent, where they collect on its surface. The system may be designed such that the VOCs can then be removed from the... 

Another adsorption system evaluated was a high-volume, high-pressure, macroporous-resin-based concentrator system designed to provide a 10,000-fold concentrate. This system used four stainless steel columns in series. Columns one through four were filled with AG MP-1 (Bio-Rad), AG MP-50 (Bio-Rad), XAD-2 (Rohm and Haas), and XAD-7 (Rohm and Haas), respectively. Unlike the other adsorption processes, a pump system was employed for both the adsorption and desorption phases of the evaluation. The use of acetonitrile as the elution solvent permitted UV monitoring of the eluant. 

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