What are the advantages and disadvantages of the quenching method at the outlet of the gasifier?
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Shell uses gas quenching for the outlet gas of its gasification furnace, while Texaco employs water quenching. Please evaluate the advantages and disadvantages of these two methods in terms of environmental impact, heat utilization, energy savings, equipment investment, risks, and operability.
The syngas produced by Shell’s gasifier is quenched using gas as it leaves the reactor; this syngas is suitable for IGCC power generation； Texaco uses water quenching, and syngas is suitable for producing methanol and synthetic ammonia
The composition of the syngas does not change when gas quenching is used. The purpose of quenching is to convert the liquid slag into a solid state, thereby reducing its viscosity and preventing scaling in subsequent systems. In addition to lowering the temperature, liquid quenching also removes solid impurities and readily soluble gaseous components, turning the liquid slag into small solid particles； This caused certain changes in the components of the syngas; the water content at the outlet reached saturation, and the unremoved acidic components could cause corrosion to the subsequent systems.
From the perspective of coal gasification technology, a comparison is made between the pulverized coal gasification process and the water-coal slurry gasification process: Shell’s pulverized coal gasification method uses dry powder as the feed material and solid slag as the waste product; it features high cold gas efficiency, high carbon conversion rates, and is energy-saving. The downside is that a single unit requires a large investment, and there is no backup unit; therefore, if the unit fails, it will inevitably affect the annual effective operating time. By using the cold air heat exchange section to recover heat, the device operates for a short time, resulting in frequent malfunctions. The water-coal slurry clean gasification technology uses water-coal slurry as the feed material and employs wet slag discharge; its cold gas efficiency is lower than that of dry powder processes, and its carbon conversion rate is also lower. It is energy-saving and environmentally friendly, requires less investment in equipment, comes with backup units, and features a high annual operational rate.
Shell’s quenching method is designed for the subsequent waste boiler process, and the intention behind it is good. However, given the current low number of Shell furnaces that are operating, it is still too early to make comparisons with Texaco.