Heat and Power Applications of Advanced Biomass Gasifiers in New Zealand's Wood Industry A Chemical Equilibrium Model and Economic Feasibility Assessment

Abstract

The Biomass Integrated Gasification Application Systems (BIGAS) consortium is a research group whose focus is on developing modern biomass gasification technology for New Zealand's wood industry. This thesis is undertaken under objective four of the BIGAS consortium, whose goal is to develop modelling tools for aiding in the design of pilot-scale gasification plant and for assessing the economic feasibility of gasification energy plant. This thesis presents a chemical equilibrium-based gasification model and an economic feasibility assessment of gasification energy plant. Chemical equilibrium is proven to accurately predict product gas composition for large scale, greater than one megawatt thermal, updraft gasification. However, chemical equilibrium does not perform as well for small scale, 100 to 150 kilowatt thermal, Fast Internally Circulating Fluidised Bed (FICFB) gasification. Chemical equilibrium provides a number of insights on how altering gasification parameters will affect the composition of the product gas and will provide a useful tool in the design of pilot-scale plant. The economic model gives a basis for judging the optimal process and the overall appeal of integrating biomass gasification-based heat and power plants into New Zealand's MDF industry. The model is what Gerrard (2000) defines as a 'study estimate' model which has a probable range of accuracy of ±20% to ±30%. The modelling results show that gasification-gas engine plants are economically appealing when sized to meet the internal electricity demands of an MDF plant. However, biomass gasification combined cycle plants (BIGCC) and gasificationgas turbine plants are proven to be uneconomic in the New Zealand context.