Shubham Goel

Understanding the mechanism of particle fragmentation, attrition, and agglomeration during coal and/or biomass gasification

Gasification of coal is now widely recognized as the core of clean coal technologies, particularly in the context of coal-to-liquids (CtL) technologies. There is significant interest on the Indian side, as part of a major government-backed initiative, to develop technology for conversion of high-ash (up to 45%) Indian coal to methanol (coal to methanol: CtM). With CO2 management being a strong driver for future gasification technologies, there is also interest in gasification of biomass, as well as blends of coal and biomass, in order to develop low-carbon (or ideally carbon-neutral) conversion of solid fuels to liquid fuels. For CtM technologies of the future, there is need to develop gasifiers which work with a suitable mixture of steam and neat oxygen (99%+ purity), so that downstream separation of waste gases (including N2) is less demanding. However, direct oxy-conversion puts several operational challenges on the gasifier, which motivates the present project. During actual operation of the gasifier, an examination of particle-scale phenomena on the solid fuel (coal, biomass, petcoke) reveals three complex phenomena: (a) fragmentation because of product gases (synthesis gas) expanding from the core of the solid particle and cracking up the ash layer, and because of percolation phenomena in the vicinity of the particle surface, which lead to fragmentation when the local porosity is sufficiently high; (b) attrition between colliding particles of the solid fuel, and between colliding particles of solid fuel and refractory (ash particles), leading to production of fines through mechanical action; (c) agglomeration possibly owing to the inorganic (ash) component of the coal particles approaching their liquidus temperature, and such colliding particles fusing to create larger agglomerates. Both processes (a) and (b) lead to production of fines, while process (c) leads to production of large agglomerates. Either of these lead to poor gasifier operation; (c) actually leads to catastrophic shutdown of the gasifier. These problems are significantly enhanced in direct oxygen firing (which is a must for future operations), and not at all understood in the context of high ash coals, or during gasification of coal and biomass or petcoke blends. The aim of the proposed project is to examine these phenomena through modelling the transport (multicomponent mass transfer and heat transfer) effects at the particle scale, while incorporating the structure evolution and particle fragmentation as the gasification proceeds. This part of the project will be executed both at IITD and UQ. At a later stage, the goal would be to embed these models into a reactor-scale (gasifier-scale) CFD code, and examine for the first time how such phenomena affect the global gasifier behaviour. This will be predominantly done at IITD, in collaboration with the UQ supervisor. Experiments may be conducted, as required, for validation of the multi-scale models, using equipment already in-place at IITD.