Hot carbonate regeneration

Design Theory, Simplified Design Procedures, Column Diameter Selection, Water Deaeration, Water Decarbonation, Ammonia Stripping, Amine Regeneration, Hot Carbonate Regeneration, Side Strippers, Example Problem, Notation, References... 

Another successful C02 absorbent utilizing chemical interaction has been potassium carbonate used in the "hot carbonate process." The C02 absorption and absorbent regeneration occur at about the same temperature of 225°F in this process. C02 absorption occurs at high pressure and the sorbent regeneration occurs due to lowering of pressure with steam stripping. The absorption/regeneration reactions are represented as... 

Hot carbonates are well suited for the removal of C02 at moderate or high levels in the presence of little or no H2S. The process acquired its name from the use of elevated temperatures in both the absorber and the regenerator (110—115°C). Hot carbonates such as the Benfield and the Koppers Vacuum Carbonate utilize K2C03 to remove H2S, COS, and C02 from gas streams [35]. Their heat requirements and high solvent circulation make hot carbonates more expensive than other acid gas removal processes. Other hot carbonate processes, including the Catacarb and the Giammarco-Vetrocoke processes, use catalysts, corrosion inhibitors, and/or activators to enhance the removal of the acid gases. Hot carbonate-promoted systems are able to decrease the C02 level from 1% to 0.1%. Promoters include DEA, amine borates, and hindered amines [36]. 

Yun J.-H., Choi D.-K., and Moon H., Benzene adsorption and hot purge regeneration in activated carbons. Chem. Eng, Set 55(2000) pp. S8S7-S872. 

Bercic, G. Pintar, A., and Levee, J., Desorption of phenol from activated carbon by hot water regeneration (desorption isotherms), Ind. Eng. Chem. Res.. 35(12), 4619-4625 (1996). 

Because the bulk of the solvent is recirculated without cooling, there is only a small sensible heat load. The heat of reaction with K2CO3 is only 270 Btu/lb of CO2 absorbed. This is one-third the heat of reaction of CO2 with MEA therefore, the heat load on a hot carbonate system per pound of CO2 absorbed and regenerated is lower than for an amine solvent system. 

The regeneration of a hot carbonate solution requires reversal of Equation 4-18 or 4-19 ... 

Generally it is uneconomical to regenerate a solvent down to a bicarbonate content so low that it permits reduction of the CO2 in the absorber outlet gas below 1,500 mol ppm for a typical unpromoted hot carbonate system. Although some promoted systems claim to be able to... 

Detailed modeling of CO2 absorption by the hot carbonate process is demanding. One such analysis, along with references to earlier literature, is available in Sanyal et al. (1988). in actual operation, the absorbent, e.g. the aqueous K2CO3 solution, loaded with CO2 is regenerated in a separate column, a stripper, by a C02-free vapor, say steam at a lower pressure, e.g. 0.14 MPa, when the absorber operates at a much higher pressure, say 2.2 MPa. 

Arsenite Solutions. Addition of essentially stoichiometric proportions of arsenic trioxide to aqueous sodiiun or potassium carbonate solutions results in a marked increase in the rate of absorption and desorption of carbon dioxide, as compared with conventional carbonate solutions. Figure 5-31 illustrates this phenomenon by comparing, qualitatively, the rate of absorption of carbon dioxide at 1 atm partial pressure and room temperature in 40% potassium carbonate and in a typical solution used in the Giarrunarco-Vetrocoke process (Riesen-feld and Mullowney, 1959). The effects of the more rapid absorption and desorption are appreciable savings in regeneration heat, reduction in equipment size, and production of treated gas of higher purity than is possible with ordinary hot carbonate solutions. 

When the bed is saturated, regeneration of the adsorbent is necessary. Carbon beds are typically regenerated with steam, hot air, or a combination of vacuum and hot gas. 

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