Gasifying agents type at lower temperature effect on bubbling fluidised bed gasification for low rank coal

Abstract

Oxygen and steam as gasifying agents are preferred for gasification process compared to air due to the production of higher heating value of syngas and lower contents of diluents. Lower operating temperature is required for low rank coal (LRC) gasification process. This is because, carbon conversion will occur faster with high reactivity of LRC. Ash agglomeration formation is also prevented at lower operating temperature. Hydrodynamics of bubbling fluidisation and gasification process are expected to be affected with different gasifying agents and operating temperature. Computational fluid dynamics (CFD) method was used to select suitable superficial velocity for bubbling fluidised bed (BFB) simulation and explore the effects of different gasifying agents at a lower operating temperature. The model was validated with theoretical values and superficial velocities of three to four times the minimum velocity (3~4Umf) were selected due to its best uniform bubbling fluidisation. Different gasifying agents will produce different bubbling patterns which relates to the density and viscosity of the gasifying agents. Many and faster moving bubbles were produced when using oxygen and air at 1,073 K while no changes is detected when using steam. This concludes that air and oxygen as gasifying agents give higher effect to the bubbling hydrodynamics compared to selection of steam as gasifying agent.