Hot-gas cleanup

Summary Reportfor Hot-Gas Cleanup, Compiled by Institute of Gas Technology, for International Energy Agency, IGT, Chicago, Dec. 1991, 50 pp. 

The total emissions of hazardous air pollutants from a CGCC plant having wet cleanup are expected to be at least an order of magnitude lower than those achievable from a modem coal-fired steam plant (41). Metals removal in hot-gas cleanup systems is still under development. 

Hot gas cleanup technology is currently under demonstration phase, but various demonstrations have not been successful so far. Wet scrubbing technology, though with a... 

Hot Gas Cleanup System Breakage of ceramic candle filters and stress corrosion cracking in heat exchangers has also been reported. 

Gasifiers typically produce contaminants that need to be removed before entering the fuel cell anode. These contaminants include H2S, COS, NH3, HCN, particulate, and tars, oils, and phenols. The contaminant levels are dependent upon both the fuel composition and the gasifier employed. There are two families of cleanup that can be utilized to remove the sulfur impurities hot and cold gas cleanup systems. The cold gas cleanup technology is commercial, has been proven over many years, and provides the system designer with several choices. The hot gas cleanup technology is still developmental and would likely need to be joined with low-temperature cleanup systems to remove the non-sulfur impurities in a fuel cell system. For example, tars, oils, phenols, and ammonia could all be removed in a low-temperature water quench followed by gas reheat. 

The typical fuel gas composition and contaminants from an air-blown gasifier that enter the MCFC at 650°C after hot gas cleanup, and the tolerance level of MCFCs to these contaminants are listed in Table 6-7 (58,71,72). It is apparent from this example that a wide spectrum of contaminants is present in coal-derived fuel gas. The removal of these contaminants can add considerably to the efficiency. A review of various options for gas cleanup is presented by Anderson and Garrigan (70) and Jalan et al. (73). 

Table 6-7 Gas Composition and Contaminants from Air-Blown Coal Gasifier After Hot Gas Cleanup, and Tolerance Limit of MCFCs to Contaminants... 

In a natural gas fueled PAFC, water is condensed out of the fuel stream going to the fuel cell to increase the partial pressure of hydrogen. In a coal gasification MCFC, water often is added to the fuel stream prior to the fuel cell to prevent soot formation. The addition of excess steam not only prevents the soot formation, but also causes a voltage drop of approximately 2 mV per each percentage point increase in steam content (45). The use of zinc ferrite hot gas cleanup can aggravate the soot formation problem because of the catalytic effect of the sorbent on carbon formation, and requires even higher moisture levels (46). 

MERC Hot Gas Cleanup Task Force, "Chemistry of Hot Gas Cleanup in Coal Gasification and Combustion," MERC/SP-78/2, February 1978. 

Acoustic Agglomeration of Power Plant Fly Ash for Environmental and Hot Gas Cleanup... 

What is the status of hot-gas cleanup technology And how would this affect the market for medium-Btu gas ... 

PANELIST CLARK In the case of medium-Btu gas, the effect of a hot-gas cleanup would depend on the end use of the gas. Most uses of gas have difficulty in utilizing thermal content of the gas efficiently. So in most cases, a hot-gas cleanup would give a rather small effect. 

If you are going to utilize the gas in a combustion turbine or where you could utilize the heat energy effectively and efficiently, you might have a case for hot-gas cleanup. 

Caballero, M. A., Cotella, J., Aznar, M. P., and Gil, J., Biomass gasification with air in fluidized bed. Hot gas cleanup with selected commercial and full-size nickel-based catalysts. Industrial Eng Chem Res 2000, 39 (5), 1143-1154. 

Pressurised gasification of biomass and fossil fuels in fluidised bed gasifiers, hot gas cleanup using ceramic filters and pressurised product gas combustion... 

---