Mathematical Modelling of a Bubbling Fluidized Bed Gasifier for High Ash Indian Coal

Fluidized bed gasifiers are used in a large number of process industries such as petrochemical, refinery, agrochemical, fine chemicals, and fertilizers. Formation of synthesis gas (CO + H₂) from coal is a viable method, as it produces the “building block” molecules for the further down streaming process which can be used to produce both fuel and chemicals such as Methanol and Dimethyl Ether (DME). Various technical challenges faced while using high ash Indian coal includes erosion in the process equipment’s, poor emissivity and flame temperature, and low radiative heat transfer. In order to make the process commercially viable we need to develop an efficient system to handle Indian coal and find a scalable way for the generation of synthesis gas. Thus, in this study, 1D non-isothermal steady state mathematical model was developed for gasification of “Indian coal” in a bubbling fluidized bed coal gasifier by incorporating steady state mass conservation equations for “total flow” of gaseous species along the bed height. This model incorporates the effect of hydrodynamic behaviour of the bed and complex reactions such as coal devolatilization, homogeneous, and heterogeneous reactions. Steady state energy balance equations for solid fuel, gas phase and inert bed material were written to predict the average temperature variation along the height of gasifier. Continuity equation for the variation of superficial gas velocity and other hydrodynamic parameters such as bubble diameter and bubble rise velocity were also written. Pre-exponential factor for both homogeneous and heterogeneous reactions were fitted by using genetic algorithm to match the exit synthesis gas composition obtained from actual Indian coal gasifier. The simulation results thus obtained were in good agreement with the results obtained from actual Indian coal gasifier. The proposed model can be used to scale-up, operational control, or improving the design of any bubbling fluidized bed gasifier.