Heat of regeneration

Primary alkanolamine solutions require a relatively high heat of regeneration. Also excessive temperatures or localized overheating in reboilers cause the MEA to decompose and form corrosive compounds. An inhibitor system, such as the Amine Guard system developed by Union Carbide, is an effective method of corrosion control (52). Inhibitors permit the use of higher (25—35%) concentration MEA solutions, thus allowing lower circulation rates and subsequendy lower regeneration duty. 

The relatively poor conductivity of a packed bed makes it difficult to get the heat of regeneration into the bed, either from a jacket or from coils embedded in the packing. This is more easily achieved by preheating the purge stream. Even in the best conditions, it takes time for the temperature of the bed to rise to the required level. Thermal regeneration is normally associated with long cycle times, measured in hours. Such cycles require large beds and, since the adsorption wave occupies only a small part of the bed on-line, the utilisation of the total adsorbent in the unit is low. 

In this case, carbon dioxide reacts reversibly in the adsorber with aqueous alkaline solutions to form a carbonate adduct (configuration 1). This adduct decomposes in the stripper upon heating. In early ammonia plants, an aqueous solution of 15-20 wt % monoethanolamine (MEA) was always standard for removing CO2. Primary alkanolamine solutions, however, require a relatively high heat of regeneration so that, nowadays, secondary and tertiary ethanol amines are mainly used. 

AH b heat of regeneration per mole of adsorbed meterial in a gas adsorption process... 

The overall reaction rate can be slow, which increases energy requirements. However, unlike MEA and DGA (discussed in Sections 4 and 5), MDEA is advantageous because it does not form any carbamate compounds (R2NCO2-R), and it has a low heat of regeneration [10]. Similarly, H2S is soluble in aqueous MDEA and follows electrolyte reactions (1) and (2) above, with additional reactimis (5) and (6) [8, 9] ... 

Important, high thermal efficiency possible by providing reaction heat from exothermic heat of regeneration Poor thermal efficiencies because of low circulation rate Control of temperature in narrow range essential for high reaction rate... 

CO,/CO mole ratio Heat of regeneration, Btu/lb deposit for these percentages of hydrogen ... 

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