Reactors for Gasification

Figure 6.5 Three different designs of fixed bed reactors for gasification...

The second reactor is a combustor that bums the residual tar to provide the heat for gasification. 

The heat required for gasification is essentially supplied by the partial oxidation of the coal. Overall, the gasification reactions are exothermic, so waste heat boilers often are used at the gasifier effluent. The temperature, and therefore composition, of the product gas is dependent upon the amount of oxidant and steam, as well as the design of the reactor that each gasification process utilizes. 

Reactor Vessel used for gasification, liquefaction, and pyrolysis, with the three main types the moving packed bed, the entrained flow, and the fluidized bed reactor. 

A tube-wall reactor, in which the catalyst is coated on the tube wall, is conceptually ideally suited for highly exothermic and equilibrium-limited reactions because the heat generated at the wall can be rapidly taken away by the coolant. Previous work (1) has numerically demonstrated that for highly exothermic selectivity reactions, the optimized tube-wall reactor is superior from both steady state production and dynamic points of view to the fixed-bed reactor. Also, the tube-wall reactor is being advanced as a possible reactor for carrying out methanation in coal gasification plants (2). From a reaction engineering point of view, it therefore seems appropriate to analyze the reactor for the analytically resolvable case of complex first-order isothermal reactions. 

A set of 17 reactions was written to simulate the reactor events and they included 1 reaction for drying, 8 parallel reactions for devolatilization, 5 reactions for gasification and 3 reactions for combustion. The kinetic and thermodynamic parameters for these reactions were derived for a Wyoming subbituminous coal. 

Volkmann, D. and Just, T., Refractories for Gasification Reactors A Gasification Technology Supplier s Point of View, Refractories Applications and News, 9, 11-16, 2004. 

This process uses a fluid-bed unit that is especially designed for gasification of brown and hard coals, peat, and biomass. In the case of brown coal, predried feed at 12 wt % moisture is fed along with oxygen and steam to the reactor which operates at 750 to 800°C and 2.53 MPa. 

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