Experimental investigation of a downdraft biomass gasifier
Introduction
The utilisation of biomass is a very important source of energy in many parts of the world, especially for areas remote from supply of high-quality fossil fuels. Biomass energy conversion technologies especially pyrolysis and gasification have been substantially studied to promote renewable energy utilisation and solving partially the environmental issues. Various types of gasification systems have been developed and some of them are commercialised.
Narvaez et al. [1] have studied biomass gasification with air in a small pilot plant in a bubbling fluidised bed and the effect of several variables on the performance of the gasifier has been investigated. Brookes [2] discusses a gasifier for biomass waste and related volatile solids. Delgado et al. [3] discussed the upgrading (cleaning) of the raw hot gases from a bubbling fluidised bed biomass gasifier using cheap calcined minerals or rocks downstream from the gasifier. Goldman et al. [4] demonstrated the possibility of a two-phase counter-flow concept as a means of providing super adiabatic conditions, which are expected to enhance weak exothermic reactions and endothermic gasification reactions in the reforming zone. They have also developed a mathematical model based on a simplified case with a single source of reaction liberated energy to obtain temperature profiles in the gasification process. The United States Department of Energy has as a major goal in the development of cost-competitive technologies for the production of power from renewable biomass crops. Paisley and Anson [5] discussed the development and commercial demonstration of the Battelle high-through put gasification process power generating system. Hughes and Larson [6] used a modelling approach to simulate the effect of varying moisture content in the gasifier feed biomass. Jorapur and Rajvanshi [7] reported the commercial scale development of a gasification system using low-density biomass (sugar cane leaves and bagasse, bajra stalks, sweet sorghum stalks).
In the present paper, the results of the experimental investigation on a downdraft biomass gasifier are presented and discussed.
Section snippets
Experimental details
The experimental set-up consists of a blow-type downdraft gasifier with a cone structure, feeding system, start up system and an air supply system. Fig. 1 shows the main body made from a diameter mild steel pipe with a total height of . The cone structure lined with refractory cement is high, diameter at the top and diameter at the bottom. The cone is inclined at 60° to the horizontal to provide smooth gravitational movement of the wood to the combustion zone at the
Results and discussion
The performance of the biomass gasifier system is determined in terms of the cold gas and mass conversion efficiencies, the flow rate of the producer gas and the calorific value. The quality of the producer gas depends on various factors such as the moisture content of the feed, the air flow rate into the gasifier, the size of the wood, the position of the air inlet nozzle and the reduction zone volume. Gas analysis results are also presented to determine the development of the gas composition
Conclusion
An experimental investigation of a downdraft biomass gasifier is carried out using furniture wood and wood chips under various operating conditions. An increasing and then decreasing trend with equivalence ratio, with a peak at about 0.38, is seen for the CO and CH4. The variation of the calorific value with equivalence ratio shows a peak value indicating that there is an optimum equivalence ratio (0.38) for the best performance of the downdraft biomass gasifier. The gas production per unit
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