Thermal swing processes

Nelson, T.O., P.D. Box, D.A. Green, and R.P. Gupta, Carbon Dioxide Recovery from Power Plant Flue Gas using Supported Carbonate Sorbents in a Thermal Swing Process, Sixth Annual Conference on Carbon Capture and Sequestration, Pittsburgh, PA, May 2007. 

FIGURE 11.15. Schematic diagram of a typical thermal swing process for sweetening of sour gas. (From ref. 22, copyright John Wiley Sons, Inc., 1978 reprinted with permission.)... 

From a thermodynamic perspective the essential difference between PSA and thermal swing processes is that in the PSA system the energy recfuired to achieve the separation is put into the system as mechanical work rather than as heat. Since mechanical energy is generally more expensive than heat, efficient utilization of energy is essential for an economic PSA system. Such considerations become especially important in the larger scale units. 

A practical problem in thermal swing processes is the reduction in the capacity or life of the adsorbent when it is subjected to repeated thermal cycling. Another problem is the formation of coke in applications in which reactive hydrocarbons are exposed to elevated temperatures during the desorption/regeneration step. 

The drying of air and other gaseous streams may be accomplished by thermal swing processes. Pressure swing adsorption operation can, however, achieve even lower dewpoints than thermal swing operation and has... 

Commercial applications of thermal swing processes are more commonly for the purification of gases and liquids than for the bulk separation of gases. 

Figure 7.9 Sweetening of sour gas stream by a thermal swing process (source Chi and Cummings 1978).

The first point to be made in this regard is in relation to the relative rapidity of cycle times in pressure swing processes compared with those for thermal swing processes. Further reduction in the cycle time of PSA processes produces greater cycle efficiency with increased rates of production of the desired component. Sircar and Hanley (1995) of Air Products and Chemicals Inc., described a model rapid pressure swing adsorption (RPSA) process in which the rates of adsorption and desorption were expressed in terms of a linear driving force (q.v. Section 4.4) and equal times were allocated to adsorption and desorption. The ratio of the net rate of adsorption, R, to the steady state adsorption capacity, q, was shown to be ... 

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