Gas outlet temperature of the gasifier and utilization of sensible heat
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May I ask: 1. What is the approximate exit temperature of the gas produced by fluidized-bed gasification and gas-flow bed gasification of low-rank coals (such as lignite) at the outlet of the gasification furnace? 2. How is the sensible heat of the high-temperature coal gas leaving the gasifier utilized? Thank you all.
Some background: In existing industrial plants, there are two common processes for recovering the heat from high-temperature syngas (1300–1500 degrees). One is the waste heat recovery process represented by Shell’s dry coal powder gasifier, while the other is the quenching process represented by GE’s water-coal slurry gasifier. The so-called waste heat recovery process refers to a technological process that utilizes heat exchange equipment (i.e., waste heat boilers) to directly recover the sensible heat of high-temperature syngas, thereby generating high-temperature and high-pressure steam. The quenching process involves first cooling the high-temperature syngas with water to a lower temperature, and then using heat exchange equipment to recover the latent heat of the cooled syngas, thereby generating steam at a lower temperature and pressure. This type of steam has a narrower range of applications compared to steam at high temperature and pressure, and its utility value is relatively lower as well.
The exit temperature of the fluidized bed gasifier is generally around 1000°C; after passing through a cyclone separator, the gas enters a waste heat boiler where the sensible heat is recovered, and medium- and low-pressure steam is generated for reuse. The exit temperature of the furnace chamber in a fluidized bed gasifier can exceed 1200°C. Heat recovery in such gasifiers is mainly achieved through either a waste heat boiler system or a quenching system (with gasifiers that may use either water-cooled walls or refractory bricks). In the waste heat boiler system, heat is exchanged via water-cooled walls and waste heat boilers, after which the steam is separated from the water in the steam drum to produce medium-pressure steam for reuse ； In the latter case, after the high-temperature syngas is quenched with water, most of its thermal energy is carried away by the quenching water; the high-pressure and high-temperature quenched ash water is then used to recover steam and condensate through flash evaporation.