Comparative Experiment on Tar Removal Methods in Fixed Bed Gasifier

摘要

Gasification is a thermo chemical transformation of a combustible solid in the presence of gaseous compound to produce producer gas, which is a mixture of Carbon monoxide, Hydrogen, Nitrogen, Carbon dioxide, Methane and traces of other hydrocarbons more commonly known as tar, resulting from an incomplete destruction of volatiles during different stage of transformation in the gasifier. Tar will impose serious limitations in the use of producer gas due to fouling of downstream process equipment, engine wear and high maintenance cost. Tar can be removed from producer gas by chemical and physical methods. Present study was carried out to study the removal of tar from selected biomass through physical method and catalytic cracking method. Catalytic cracking of tar was done with dolomite as tar cracking catalyst was carried out in this study. The selected biomass for the study was wood, arecanut husk and coconut shell. A dry filter with carbonized porous charcoal as bed material was designed and developed with a diameter of 15.5 cm, filter bed height of 60 cm, height of filter 90cm, superficial velocity of 0.06 m/s and residence time of 10 seconds to remove the tar coming after two condensers. By employing the filter, a tar conversion efficiency of 90.5 per cent was achieved. To reduce the tar further, dolomite was used as the catalyst. As the catalyst was added in the gasifier, the temperature gets increased from 675deg C to 935 deg C and the tar produced gets cracked in the gasifier. A tar conversion efficiency of 96.9% was attained by using dolomite as a catalyst. The mass closure and the energy closure for the gasifier were calculated as 98.04% and 98.55% respectively.