Decentralized electricity systems based on renewable energy sources are increasingly used in rural electrification worldwide as a competitive alternative to conventional grid-extension. Within this field, there is growing interest in biomass for heat and/or power supply, especially in developing countries .
Research Centers CEPIMA-GRECDH of the Universitat Politècnica de Catalunya are investigating modular gasification schemes as a technological solution to harness the energy potential from unused local agricultural and forestry residues in rural communities. Overall, the resulting gas, called producer gas, is cleaned before its final application in an internal combustion engine coupled to an electricity generator. The engine waste heat can also be captured and directed towards useful heating applications or biomass pre-treatment options. It is generally accepted that modular gasification may consider power up to 500kW .
A key component of CEPIMA-GRECDH groups' research is the pilot plant with a downdraft gasifier, currently being built at the School of Industrial Engineering of Barcelona. The main purpose of this pilot plant is to develop and test a pre-commercial unit working under real operating conditions. On the one hand, the main challenges are reducing tar production, thus allowing a wider variety of biomass fuels, and increasing the overall efficiency before commercialization. Otherwise, a main objective is to study the whole biomass-to-energy supply chain for the specific case of village electrification with mini-grids. It is precisely in this second point where this work is focused. Biomass downdraft gasification systems are well known options for clean and alternative small scale production of energy . Nevertheless, as Abe and co-workers  and other field experiences point out , several barriers for large scale implementation remain, which can be summarized as follows: Technical barrier; it includes problems related with the sizing of the installations due to non-realistic demand and resources estimations. The lack of information and training for correct plant maintenance, as well as the difficulties of acquiring spare parts. Financial barrier; it refers to the fact that these plants are often funded via donation programs without a proper planning and management scheme, both at the biomass resource level and at the electricity service level, thus making it very difficult to maintain a profitable plant. Political barrier; it makes reference to the lack of effective regulations and incentives along the bioenergy value chain (production, transformation, quality control, certification, energy generation, distribution and commercialization. Socio-economic barrier; here, the difficulty to change the everyday people habits are pointed out.
In this context, the main contribution of this work is to build up a model to represent, simulate and optimize the energy/biomass supply chain associated to rural electrification projects using biomass gasification. The final purpose is to obtain the “best” performance conditions taking into consideration the specific sources of raw material (types, production, location, seasonality), the demand (location, quantity), following a multi-objective optimization (for instance, financial and environmental points of view). This will allow overcoming technical and financial barriers.
The supply chain model is divided into two main blocks: Biomass and Energy. Input data to the model considers biomass sourcing, biomass pre-treatment before transportation, transportation between pre-treatment storage and energy generation points, energy generation, distribution and consumption. The problem is modeled using MILP techniques. The model is intended to support decision making in topics such as capacity size and location of pretreatment and energy generation units as well as the biomass sourcing profile for each time period so as to insure sustainability of the network. A case study that considers real data from villages located in Ghana is used to emphasize the benefits of the solution approach presented here as well as to discuss future extensions.
Acknowledgements Financial support received from ‘‘Generalitat de Catalunya'' with the European Social Fund (FI grants), the project EHMAN (DPI2009-09386) financed by the Spanish Ministry of Education and Science and the EU FEDER fund is fully appreciated.
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