Resumen de Energy from Biomass: technology assessment of small-medium scale biomass conversion systems
Luis Leonardo Cutz Ijchajchal
Bioenergy is a key resource to addressing challenges such as climate change (anthropogenic CO? emissions), pollution (suspended particles), energy security and human well-being. Currently, most of the biomass produced worldwide is consumed for cooking and space heating which has raised concerns among governments and policy-makers, especially due to threats to human health. The present thesis focuses on studying the technical and economic feasibility of energy systems based on biomass. It is considered that the main problems regarding the deployment of biomass-based energy systems are: (a) use of traditional biomass; (b) selection of a biomass-based technology; (c) low diversification of the biomass portfolio. With regards to the use of traditional biomass, the thesis evaluates the impact of switching from a system dependent on traditional biomass to a centralized system using low-carbon technologies. The outcome is a model capable of estimating the net reduction of CO? emissions that could be obtained by displacing fuelwood and introducing modern biomass taking into account the CO? released not only in the production, collection, transport, pre-treatment and conversion of biomass but also the anthropogenic CO? emissions caused by shifting to alternative fuels to meet basic energy needs. Results show that even when households have to use alternatives fuels, burning biomass in combustion and gasification power plants still provide a significant reduction in CO? emissions. With regards to the selection of a biomass-based technology, this thesis includes a methodology to identify, evaluate and select the best suited technology for the conditions of a given biomass value chain. As any system is affected by the conditions where it is developed, biomass-based energy systems are strongly dependent on region/local conditions such as weather, type of biomass resources, among others. Thus, each region demands its own detailed study. Given the lack of studies related to bioenergy in developing regions such as Central America (CA), this thesis entails a full study case presentation for CA where 84% of the biomass produced is used for domestic cooking and heating. In this context, the thesis aims at improving the bioenergy assessment methodology by using a resource-focused approach to determine the key biomass resources in the region and a Multi-Actor Multi-Criteria Decision- Making method to identify a portfolio of thermochemical conversion technologies appropriate for CA, considering parameters that range from technical, economic, environmental to socio-political aspects. Furthermore, it includes a discussion about the barriers that have stopped the progress of biomass technologies and the challenges to achieve modern bioenergy systems in the region. Results reveal that the main source of biomass in CA is in the agricultural sector and the most appropriate technologies to transform CA’s biomass are improved cooking stoves and biomass combustion power plants. With respect to the diversification of the biomass portfolio, currently, sugarcane bagasse is the biomass mostly used in large scale applications for the production of combined heat and power (CHP) in developing countries. Using a demand-driven assessment this thesis aims to evaluate the potential for electricity and ethanol production in CA using sweet sorghum as an alternative sugar crop. Three scenarios were built to analyse sweet sorghum production in terms of the land where it can be cultivated: cropland, sugarcane land in fallow and land in continuous production (intercropping system). The land under permanent crops was not considered for this evaluation. It is estimated that sweet sorghum could supply around 10% of region’s electricity demand or supply the ethanol required to implement a 5% ethanol blending programme. Following this assessment, the thesis studies the integration of sweet sorghum into Central American sugar mills by using the existing machinery to process it. The short growing period of sweet sorghum would allow the CHP plants and distilleries to operate during off-season using sorghum bagasse and molasses as raw materials. This thesis provides a techno-economic analysis of the production of electricity and ethanol from sweet sorghum in a sugar mill. The data on various parameters used for techno-economic assessment were collected from an existing sugar mill and distillery in Central America. Results indicate that modern energy carriers from sweet sorghum can be produced at a competitive price under CA conditions and crucial variables determining the cost of electricity and ethanol are the installed capacity of the plant and crop yield.
