Production of Middle Caloric Fuel Gas from Coal by Dual-Bed Gasification Technology

A coal gasification technology for producing middle caloric fuel gas using granular coal is urgently required in China considering the huge energy demand required for project development. This work demonstrated the dual-bed gasification technology on a pilot plant (1000 tons of coal/a) mainly consisting of a fluidized-bed gasifier and a pneumatic combustor using the coal with a particle size of less than 20 mm. Simulation was performed with Aspen Plus to investigate the feasibility of producing a middle caloric fuel gas. It was found that, with a bituminite powdered coal as fuel and air as the gasifying reagent, the pilot plant could operate steadily within a given duration of 16 h. At a gasifier temperature of 900 degrees C and combustor temperature of 980 degrees C, a fuel gas with 1680 kcal N-1 m(-3) of high heating value (HHV) was produced at an equivalence ratio (ER) of 0.089 (defined as the ratio of the oxygen mole in air supplied in the gasifier to the oxygen mole needed for burning the fed coal completely). The heating value of fuel gas could be enhanced by introducing steam as a supplementary reagent to the gasifier while reducing the air required. Gasification simulation of 10 tons of coal/h indicated that a fuel gas with above 2000 kcal N-1 m(-3) of HHV could be obtained with an ER of less than 0.10 and a steam/coal ratio larger than 0.48. The study suggested that dual-bed gasification technology could be employed for producing a middle caloric fuel gas using granular coal with a size of less than 20 mm.