Steam regeneration

Solvent recovery with adsorption is most feasible when the reusable solvent is valuable and is readily separated from the regeneration agent. When steam-regenerated activated-carbon adsorption is employed, the solvent should be immiscible with water. If more than one compound is to be recycled, the compounds should be easily separated or reused as a mixture. Only very large solvent users can afford the cost of solvent purification by distillation. ... 

The subsequent reaction of the reduced iron oxide with steam regenerates the original oxidized form of iron oxide (i.e., magnetite) and yields pure hydrogen (mixed with unreacted steam) as follows ... 

In pathway B in Fig. 14.3, H2S is first removed by absorption and then enters a clean gas shift section. Catalysts used are standard HTS catalysts. The use of LTS catalysts is only possible when sulfur is removed to very low levels (<0.01 ppm), using a Rectisol (methanol) solvent [6], Downstream the WGS section C02 is removed by absorption. When partial pressures are high (>1.5 MPa, [6]) a physical solvent (e.g., methanol) can be used. Physical solvents can be easily regenerated by flashing at reduced pressures. At lower C02 partial pressures a chemical solvent [e.g., mono-ethyl amine (MEA)] is used, which requires energy input for steam regeneration of the solvent. 

Reductions in adsorption capacity after the first steam regeneration. 

During the regeneration process, the contaminants are desorbed and a waste stream is produced. For instance, during steam regeneration a mixture of water and organics from the condensed desorbed vapor is produced. Thus, a regeneration process should be accompanied by a waste treatment apparatus. 

Steam regeneration is most commonly applied to activated carbon that has been used in the removal and/or recovery of solvents from gases. At volatile organic compound (VOC) concentration levels from 500 to 15,000 ppm, recovery of the VOC from the stream used for regeneration is economically justified. Below about 500 ppm, recovery is not economically justifiable, but environmental concerns often dictate adsorption followed by destruction. While activated carbon is also used to remove similar chemicals from water and wastewater, regeneration by steam is not usual. The reason is that the water-treatment carbon contains 1 to 5 kg of water per kg of adsorbent that must be removed by drying before regeneration or an excessive amount of superheated steam will be needed. In water treatment. 

Adsorbent particle size Working charge Steam solvent ratio Adsorbent void volume Steam regeneration temperature Inert gas regenerant temperature Regeneration time Number of adsorbers... 

The regeneration of activated carbon beds used in gas phase adsorption requires less severe conditions than for liquid phase processes. Regeneration can be conducted in situ by stripping with steam. Newer and more efficient systems use regeneration by hot inert gas, nominally at 350°F, to recover a greater portion of contaminants with their subsequent recovery. This is particularly attractive if the disposal of condensate from steam regeneration becomes a problem [73]. 

The catalytic effect of accumulated metals is especially marked with calcium [39, 40], The presence of 2.3% calcium increases the mass loss for steam regeneration at 850°C by a factor of 5 and for CO2 by a ffctor of 25 at the same temperature compared to the respective rates observed in the absence of calcium [41]. 

Alvarez-Trevit, J. A. Steam Regeneration of Activated Carbon Adsorbents, Ph.D. diss.. The University of Texas at Austin, 1995. 

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