Syngas Cleanup

The raw syngas produced by the gasification of various feedstocks is similar. The main gas components are hydrogen (H2) and carbon monoxide (CO), carbon dioxide (C02), water vapor (H20), and various impurities. However, the concentrations of these various components depend on the feedstock composition and the specific gasification process employed. 

There are numerous commercial processes available to remove the sulfur content from syngas, ranging from throwaway regenerable adsorbent-type to regen-erable solvent-type processes. Solvent-type processes are of primary interest for sulfur removal from syngas. The solvent-type processes can be divided into three types  

There are many commercial installations of each type, treating a variety of natural gas and syngas streams. For syngas treatment, the principal chemical-type 

The principal challenge of the sulfur removal processes is to reduce the sulfur compounds in the syngas to a low enough level to meet the requirements of downstream processes and prevailing emission regulations, and to do so as economically as possible. This would not be a problem if only H2S were present, since H2S is easily removed by most processes down to very low levels. However, the solubility of COS in both types of solvents is much lower than that of H2S, making it more difficult to remove. 

At high syngas pressure, physical solvent-based processes become increasingly attractive, for example, the Rectisol and Selexol processes. There are more than 55 Selexol plants worldwide, treating natural and syngas.51 The Selexol process solvent is a mixture of dimethyl ethers of polyethylene glycol, and has the formulation 

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Fig. 3. LP Oxo liquid recycle flow scheme A and B, reactors C, vaporizer D, catchpot E, stabilizer F, syngas cleanup and G, propylene cleanup.

Syngas cleanup system - low or high temperature and processes used to remove sulfur, nitrogen, particulates, and other compounds that may impact the suitability of the syngas for specific applications (i.e., turbine and fuel cell for electric power generation, hydrogen production, liquid fuel production, or chemical production). 

Although biomass-to-methanol technology has yet to be commercialized, laboratory technology suggests that commercial production would be feasible at a cost of about 0.20/L. Assuming that expected improvements in syngas cleanup and a reduction in feedstock costs are realized, the costs may be reduced to the target of 0.15/L as eady as 1998. 

The typical steps for syngas gas cleanup include particle removal, COS hydrolysis, acid gas cooling, sulfur removal, and sulfur recovery. C02 sequestration can be implemented in an IGCC plant by adding additional units in the syngas cleanup section. 

Cold syngas cleanup Cold syngas cleanup Hot syngas cleanup... 

Ultra clean transportation fuels can be made from coal via four sequential steps including coal gasification, syngas cleanup, F-T (Fischer-Tropsch) synthesis, and F-T product workup. These fuels are known as CTL (coal-to-liquids) fuels to differentiate them from GTL (gas-to-liquids) and... 

The Rectisol process superstructure for syngas cleanup designed for the Kellogg-Rust-Westinghouse IGCC application. 

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