A Dutta, Animesh creator Bhattacharya, Sribas C. Chairperson Surapong Chiraratananon Examination Committee Kumar, Sivanappan Examination Committee Pham, H.L. Examination Committee The Royal Netherlands Government Scholarship donor text series technical report th Bangkok Asian Institute of Technology 1998 continuing eng 86 leaves The present study was undertaken for getting low tar gas by improving the multi stage/hybrid gasification processes. Experimental investigation of hybrid updraft-downdraft gasification and hybrid wood-charcoal gasification was conducted. Two-stage briquette gasification and two-stage wood gasification with preheater was also carried out in this regard. The performance measures included the tar content, gas composition and net heating value of the producer gas. The results of the investigation revealed the followings. Although tar content of the product gas in briquette gasification was found higher than wood gasification; the difference in tar content diminished significantly at higher flow rates and a higher net heating value of gas was obtained. But pressure drop gradient (~p/cm) across the reactor bed for briquette gasification was found 4 to 6 times than that of wood gasification. In hybrid updraft downdraft gasification, for six of the nine experimental runs, a tar free gas was obtained in the down draft end. A very high concentration of CO and a very low concentration of H2 and C02 was found in the product gas. It also seems to be potential for cogeneration. Hybrid wood charcoal gasifier was also shown promising in respect to get higher net heating value of gas and the lowest tar content was found only 9.83 mg/Nm3 in this unit. Two-stage wood gasifier with preheater shows an exemplary idea for using in an Internal Combustion Engine as nearly tar free gas was obtained by supplying preheated air to the gasifier and the exhaust gas from the engines has the potential to heat the inlet air of the gasifier. For five of the experimental runs, tar content of the gas was found below 10 mg/Nm3 which can be possible to used in engine without scrubbing by heating the supply air in the range of 250-185 °C. For all of these cases except two-stage briquette gasification, an exceptionally high temperature was obtained in the combustion/reduction zone that helped to crack the tar. It was also found that for a particular primary air flow rate, increase in the secondary and tertiary air flow between the operation limit resulted in decrease in tar content as well as C02 and H2 concentration while that of CO increases. A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development Thesis (M.Eng.) - Asian Institute of Technology, 1998 Biomass energy Asian Institute of Technology. http://203.159.5.9/ait-thesis/detail.php?q=B13315 http://203.159.5.9/ait-thesis/detail.php?q=B13315 120399 20260818223006.0