Moving Bed Gasification

At regular intervals, the gas outlet is mechanically cleaned by a scraper on-line to prevent fouling by caking solids. All coal feeding, ash discharge and outlet cleaning operations are fully automated. They are controlled by hydraulic systems whose operating cycles are appropriately adjusted to the properties of the coals to be handled. 

The reaction space itself is enclosed by an inner shell with relatively thin walls which is accommodated inside the thick-walled pressure vessel. The space between the inner and outer shells is filled with boiling water to cool the inside. This boiling water is pressurized to a level slightly higher than the reactor pressure it is used to generate steam which can be added to the gasifying agent. 

Ash discharge through a lock has already been mentioned before. The procedure is analogous to coal feeding. The ash lock is pressurized by means of 

According to the diagram shown here, the major part of the remaining heat in the raw gas is used in a downstream heat exchanger to heat up boiler feed water before the raw gas flows through a trim cooler to be cooled to ambient temperature. Needless to say, other ways of utilizing the heat are conceivable from case to case. 

If not used as quench water, the tar and oi -laden gas liquor from the waste heat boiler is split up in the tar separator (see Sect. 5.1) into a dusty tar, a thin tar, and a gas liquor fraction. The condensate from the feed water preheater, like some of the condensate from the waste heat boiler, is used as quench water in the wash cooler. The trim cooler condensate, which essentially contains only hydrocarbons with boiling points of less than 100 °C, is sent to the oil separator to be separated into an oil fraction and a gas liquor fraction. The gas liquor passes an additional oil trap and then goes to the Phenosolvan unit. 

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In the case of lump coal feeding into gasifiers (e.g., countercurrent moving-bed gasification), the moisture content is usually not that critical. One should keep in mind that the feed moisture ends up as wastewater contaminated with hydrocarbons, which needs to be treated. 

The mass flow rate of the gasifying agent steam WHaO.ga (all mass flows in kg/s) does not include the coal moisture Wh20,w and the decomposition water from coal pyrolysis WH20,pyr- The mass flow of residual steam in the raw gas is represented by WH20,rg [9]. In case of moving-bed gasification, sometimes only the injected steam is balanced [2]. 

Characteristics of moving-bed gasifiers are low gasification temperatures, relatively low oxygen requirements, relatively high methane content in... 

The importance of these concepts can be illustrated by the extent to which the pyrolysis reactions contribute to gas produdion. In a moving-bed gasifier (e.g., producer-gas gasifier), the particle is heated through several distinct thermal zones. At the initial heat-up zone, coal carbonization or devolatilization dominates. In the successively hotter zones, char devolatihzation, char gasification, and fixed carbon... 

There are three main types of gasification technology entrained flow, fluidized bed, and moving bed. All of these can... 

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