The E-Gas Process
The E-Gas process utilizes a two-stage gasifier with a coal-slurry feed and is currently the only two-stage process with an operating commercial-scale demonstration plant.
The E-Gas process was developed by Dow, which started in 1978 with a 12t/d pilot plant operating in Plaquemine, Louisiana. This was followed by a 550 t/d demonstration plant (in 1983) and a 1600 t/d 165 MW IGCC production facility (1987), both at the same site. Based on these results a 2500 t/d coal (2100 t/d petcoke) commercial unit was built at the Wabash River site in Terra Haute, Indiana, as part of a repowering project. This Wabash River Plant began operations in 1996. The unit is equipped with a spare gasifier. The reactor has an insulated brick lining similar to Texaco gasifiers. The overall efficiency is about 40% HHV.
The E-Gas gasifier is a two-stage coal-water slurry-feed entrained slagging gasifier. It was originally designed for the gasification of sub-bituminous coal, although more recently high-sulfur (up to 5.9 wt% on a dry basis) Midwestern bituminous coal has been used. The combination of a coal-water slurry and a low-rank coal in a single - stage gasifier would result in a low-efficiency and high-oxygen consumption. By adding a second nonslagging stage this problem was avoided. In the process scheme (see Figure 5-21) the sub-bituminous coal-water slurry is injected into the hot gases from the first slagging stage resulting in a much cooler exit gas which contains some char. This mixture, with a temperature of about 1040°C, passes through a fire-tube syngas cooler, after which the char is separated from the gas in a particulate-removal unit
featuring metal candle filters. The char is then injected together with oxygen and/or steam into the first slagging stage with a temperature of about 1400°C. The advantage of this process is that although a sub-bituminous coal is used and introduced into the gasifier as a coal-water slurry, the slagging part of the gasifier sees a feed upgraded by a dry char stream that requires relatively little oxygen to be gasified. The waste heat from this stage is then used in the nonslagging stage to free the feed of all the water, as well to supply the heat for some pyrolysis reactions.
The slag is quenched in a water bath in the bottom of the slagging reactor. It is then crushed and, via a continuous pressure let-down system, brought to ambient pressure. The E-Gas process is the only process where no lock hoppers are used for this purpose.