Gasification of Indian Coal in a Tubular Coal Gasifier

In spite of the high ash content, Indian coals have been widely used for the generation of power and industrial steam in India. Being considered as the technology for future in terms of efficiency and cleaner environment, coal gasification carries much importance since India has a large amount of coal reserves. In this paper, the numerical simulations have been performed on gasification performance of three types of Indian coals in atmospheric as well as pressurized conditions in an entrained flow, air-blown tubular gasifier. In the model, continuous phase conservation equations are solved in an Eularian frame and those of particle phase are solved in a Lagrangian frame, with coupling between the two phases incorporated through interactive source terms. Phenomena such as devolatilisation, combustion of volatiles, char combustion & gasification and the dispersion of coal particles due to turbulence are taken into account. The P-1 model has been adopted for radiative heat transfer in which scattering is taken into account for the particles. It is observed that as the ash percentage increases, the heat and mass transfer are strongly affected and the gasification performance decreases. This is attributed to the lower char reactivity due to thick ash layers and lower oxygen and other gas diffusion rates. Various regions such as devolatilisation, combustion and gasification zones inside the gasifier have been identified using the temperature plots, devolatilisation plots and mass depletion histories of coal particles. The overall gasification performance indices such as carbon conversion, heating value of the exit gas and cold gas efficiency have been predicted.