Adsorption systems operation

Adsorption. Some organics are not removed in biological systems operating under normal conditions. Removal of residual organics can be achieved by adsorption. Both activated carbon and synthetic resins are used. As described earlier under pretreatment methods, regeneration of the activated carbon in a furnace can cause carbon losses of perhaps 5 to 10 percent. 

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... 

Industrial adsorption systems are engineered so that they operate in the region before the breakpoint and are continually regenerated by units. 

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. 

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. 

Adsorption, as ean readily be seen, is not an exaet seienee, but rather an art that draws on the experience of the design engineer. Various adsorber reeovery system operations are illustrated in Figures 26 and 27. 

Ching C. B., Ruthven D. M. (1985) An Experimental Study of a Simulated Counter-Current Adsorption System - I. Isothermal Steady State Operation, Chem. Eng. Sci. 40 877-885. 

In industrial operations, adsorption is accomplished primarily on the surfaces of internal passages within small porous particles. Three basic mass transfer processes occur in series (1) mass transfer from the bulk gas to the particle surface, (2) diffusion through the passages within the particle, and (3) adsorption on the internal particle surfaces. Each of the processes depends on the system operating conditions and the physical and chemical characteristics of the gas stream and the solid adsorbent. Often, one of the transfer processes will be significantly slower than the other two and will control the overall transfer rate. The other process will operate nearly at equilibrium. 

Model 4 system described contains steel pipes. Model 10 system described is backwashable. Systems include aU piping and manual valves to comprise a complete adsorption system, enabling all operations. Equipment costs include drawings, technical submittals, and provision of an operation and maintenance manual. Freight cost may need to be added for some models. 

The Molex process developed by U.O.P. is unique not only in its liquid-phase operation but also in its adsorption system (1-8). Its adsorption system consists of a single adsorption tower with multiple inlet-outlet points and a special rotary valve. The adsorption tower has many smaller adsorption chambers interconnected in series, and it operates under the so-called simulated moving bed operation. Instead of moving the adsorbent bed, the simulated moving bed operates by simultaneously advancing inlet-outlet points periodically. At any time, the adsorber has four zones—viz., adsorption, primary rectification, desorption, and secondary rectification zones, and these zones advance simultaneously as the rotary valve turns periodically. Desorption of n-paraffins is achieved by displacement. 

Figure 19.12. Batch parametric processing of solid-liquid interactions such as adsorption or ion exchange. The bottom reservoir and the bed interstices are filled with the initial concentration before pumping is started, (a) Arrangement of adsorbent bed and upper and lower reservoirs for batch separation, (b) Synchronization of temperature levels and directions of flow (positive upward), (c) Experimental separation of a toluene and n-hcptane liquid mixture with silica gel adsorbent using a batch parametric pump. (Reprinted from Wilhelm, 1968, with permission of the American Chemical Society), (d) Effect of cycle time t on reservoir concentrations of a closed system for an NaCl-H20 solution with an ion retardation resin adsorbent. The column is initially at equilibrium with 0.05M NaCl at 25°C and a = 0.8. The system operates at 5° and 55°C. [Sweed and Gregory, AIChE J. 17, 171 (1971)J.

Increased deterioration of the chemical program and the cooling system operation. The presence of slime, deposits, and general fouling permits adsorption of the chemical treatment into the slime and also product breakdown. Thus a higher bleed is required to reduce the level of contaminants, but chemical reserves also decrease, necessitating more... 

In summary, in operation of adsorption systems involving a localized and non-localized pair, selection of best separability is dependent both on the Henry constant and on the type of site interaction. Higher Henry constant combined with a localized site favours the employment of high pressure systems conversely, higher Henry constant combined with a non-localized site favours low pressure systems. The choice of appropriate temperatures depends on whether the Henry constants diverge or converge as the temperature is altered. 

Stewart and Hack (5.) have presented operating characteristics of pressure swing adsorption systems for reducing impurities in a hydrogen stream from 40 vol percent to 1 ppm. Impurities included ammonia, water, methane, carbon monoxide, carbon dioxide, nitrogen, and several hydrocarbons. In this study heatless adsorption is used to separate hydrogen sulfide-hydrogen mixtures and the experimental results are compared with theoretical models. 

It is worth mentioning here that comparisons between the efficiency of different MIP separation systems like two HPLC systems or two CEC systems, or an HPLC system with a CEC system, are quite difficult when the adsorption isotherms are nonlinear. One of the typical difficulties is that the phase ratios in the two systems may be different. The effect of phase ratio on the separation and particularly on the achievable optimum separation is a complex question even in linear chromatography. In nonlinear chromatography this is really difficult and also burdened by the differences between the isotherms of the two compounds to be separated. The complexity of this matter has been mostly overlooked in the MIP literature and the visual comparison of two separations in rather different systems, operated under very different conditions, has frequently lead to statements declaring one technique better than the other. 

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