Experimental investigation and modelling study of long stick wood gasification in a top lit updraft fixed bed gasifier

We present results of an experimental study on long stick wood gasification, in an attempt to reduce wood gathering for gasification. This paper presents the results from experiments and the analyses of gasification using sticks with length similar to 68 cm and diameter similar to 6 cm. The moisture content of the wood was 25%. This top lit updraft gasifier operates with 180 W of blower power air supply to produce 9-10 kW of thermal energy, an energy yield of similar to 50/1. Results were obtained for various flow conditions with airflow rates ranging from 25 to 45 m(3)/h. For modelling, the flaming pyrolysis time for long stick wood in the gasifier is calculated to be 2.1 min. The length of the flaming pyrolysis zone and char gasification zone is found to be 37 cm and 36 cm respectively. The turn down ratio for the gasification is around 2. The rate of feed was between 9 and 10 kg/h and the gasifier operated continuously for 5 h in two runs to study the gasifier reliability. The performance studies in specific gasification rate, equivalence ratio, turn down ratio, superficial velocity, airflow, and gas flow are analyzed. The temperature ranged from 1185 K in the combustion zone to 400 K in the drying zone. The gas and airflows can be converted to the Air/Fuel equivalence ratio, the most important aspect of gasifier operation. The equivalence ratio shows operation in a combustion mode (6.3) at start up; in a flaming pyrolysis mode (1.2) for the middle part of the run; and in the charcoal gasification mode (5.7) at the end of the run. Measurement of the equivalence ratio is a simple way of analyzing the behaviour of the gasifier. From the results of present investigation, it is revealed that the top lit updraft gasifier is more suitable for long stick wood as feed when compared to conventional updraft gasifier. (c) 2007 Elsevier Ltd. All rights reserved.