Absorption regeneration

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... 

The Shell Sulfinol Process is used for removal of acidic constituents such as H2S, CO2, COS, etc. from a gas stream. Improved performance over other processes is due to the use of an organic solvent, Sulfolane (tetrahydrothiophene dioxide), mixed with an aqueous alkanolamine. Relative proportions of Sulfolane, alkanolamine, and water, as well as the operating conditions, are tailored for each specific application. Simultaneous physical and chemical absorption under feed gas conditions is provided by this Sulfinol solvent. Regeneration is accomplished by release of the acidic constituents at near atmospheric pressure and a somewhat elevated temperature. The flow scheme (Figure 4) is very similar to that of an aqueous alkanolamine system since it involves only absorption, regeneration and heat exchange under typical alkanolamine treater conditions. 

RAR [Recycle Absorption Regeneration] A process for extracting traces of sulfur compounds from the effluent gases from the Claus process by use of a selective amine absorbent. Developed by KTI. 

The first industrial facility dates from 1965. Others have followed suit, but they are essentially built at locations belonging to Union Carbide. The process employs dimethyl-acetamide, containing 10 per cent weight water, as solvent In its latest version, it comprises a single absorption/regeneration step. 

To be truly competitive, the removal of the acid gas components H2S and CO2, be it trim or bulk, complete or partial, requires the optimum choice of an activator together with a carefully crafted know-how in solvent absorption/regeneration process design. The Elf Activated MDEA process developed by Total is probably the most cost-effective solution today to meet the widest range of applications from complete CO2 removal to bulk H2S and/or CO2 removal even for acid gas re-injection projects. The historical R D efforts of Elf Aquitaine coupled with current resources of Total allows this MDEA process to be credited with the most significant know-how back-up technology base on the market today. 

In contrast MEA absorption-regeneration operates on a temperature differential with absorption at a relatively low temperature, 27°-60°C, and regeneration at 100 -140 C. Thus, it is necessary to cool the incoming gas to the absorber and to heat the MEA solution in the regenerator with steam. The MEA process has been improved by the addition of promoters and corrosion inhibitors, thereby lowering heat requirements. 

Aqueous alkanolamine solutions are frequently used for removal of acidic gases such as carbon dioxide and hydrogen sulfide from gas streams in the natural gas, synthetic, and refinery industries. Several options are available for removing acid gases, but by far the most popular is the absorption by amine based solvents such as monoethanolamine (MEA), diglycolamine (DGA), diethanolamine (DEA), di-isopropanolamine (DIPA), triethanolamine (TEA), N-methyldiethanolamine (MDEA), 2-amino-2-methyl-l-propanol (AMP), and 2-piperidineethanol (2-PE) in reversible absorption-regeneration processes [1]. 

The process uses a conventional absorption-regeneration cycle in which a thermally unstable compound is formed during absorption and decomposed by an increase in temperature and the presence of stripping vapor during regeneration. The chemistry is simple and can be represented approximately by the conversion of monoanunonium phosphate to diammonium phosphate as follows ... 

Since with each absorption-regeneration cycle some carbon dioxide would be lost fiom the system, all of the potassium in the solution would eventually be converted to potassium bisulfide which was found to be essentially non-regenerable according to the following reaction (Tosh et al., 1960) ... 

The chemistry of the H2S removal cycle is uniquely based on an arsenic-activated potassium carbonate solution, and is quite complex. The overall reaction mechanism of the absorption-regeneration cycle can be represented in a simplified form by the following equations ... 

In cases where both selective sulfur removal and complete carbon dioxide removal are required, such as with coal-derived substitute natural gases, two successive independent absorption-regeneration cycles are used as shown in Figure 14-8. Various flow schemes are discussed in. some detail by Van Deraerschot and Valentine (1976) and Sweny (1980). These authors claim that, with proper plant design, removal of sulfur compounds to concentrations as low as a few parts per million can be achieved with relatively low co-absorption of carbon dioxide. 

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