(622e) Bubbling Fluidized Bed Gasification of High Ash Pakistani Coal

Gasification has gained an increased interest among the major thermochemical conversion techniques: In accordance with increased thermal efficiency, Internal Gasification Combined Cycle is leading over other conventional methods to generate heat from the solid fuels. In gasification process, the composition of the produced synthesis gas can be linked to the different operating parameters like equivalence ratio, temperature etc. Bubbling fluidized bed is one of the most widely used technology particularly at moderate gasification capacities with low investment costs.

In this research work Bubbling fluidized bed gasifier (BFBG) was used to gasify the Pakistani high sulfur coal having low melting point ash. This type of coal could not be gasified in the other types of gasifiers due to the agglomeration problem. Focus of this research was to gasify this particular type of coal and to see the effect of parameters like temperature, bed voidage, equivalence ratio on the conversion and on the composition of product gas under atmospheric bubbling fluidized bed conditions. Lab scale BFBG with rating 7 KW is designed from the theoretical data available. It was made up of stainless steel with 0.1 m of internal diameter and 1.62 m of overall height. Quartz sand is used as a bed material. The bed inventory was maintained around 1800 g with an average size of 125μm. All hot metal surfaces of the gasifier have been insulated with ceramic fiber and wool. In order to maintain uniform flow of air, a wind box is designed beneath air distributor plate. There are three thermocouples around the bed at different locations. The heating jacket surrounding the bed is used for the pre-heating of sand by LPG burner. Sand is pre-heated up to 450⁰C by LPG burner, further temperature of bed was gradually increased by coal feeding up to 850⁰C. Minimum fluidization velocity was being calculated as 0.636 m/s. Sharig coal was used in this study and temperature was varied from 750⁰C to 85⁰C and equivalence ratio form 0.2 to 0.35. With the increase in temperature in the given range, CO increased from 8% to 21%, H₂ increased from 6% to 24%, while CO₂  decreased from 16% to 7% and methane decreased from 1.8% to 1.1%. The influence of the freeboard temperature on the synthesis gas composition was found to be less significant than dense bed temperature.  With the change in equivalence ratio from 0.2 to 0.35, CO/H₂ was found to decrease along with the decrease in CH₄ from 1.8% to 0.9%. An optimum value was found for this particular coal to get the maximum calorific value of the producer gas along with the smooth operation with- out the issue of bed agglomeration.