Poly-Generation Using Biogas From Agricultural Wastes

Abstract

Across the world, many people, especially in rural communities, still lack access to secure, affordable electricity supplies. Many countries also lack or have under-developed indigenous fossil fuel resources, or rely on environmentally unfriendly fuels such as coal or Heavy Fuel Oil. Many under-developed regions though are blessed with considerable agricultural resources, and well-suited to Distributed Power Generation, where smaller decentralized power plants are located close to the actual energy consumers. Distributed Power eliminates the need for an electricity transmission grid, or reduces the investment costs necessary to strengthen the grid system, and helps ensure stable, secure electricity to support local economic growth. Agricultural wastes can be used as a locally available feedstock to produce the energy required to electrify regions and stimulate economic growth. This paper examines the benefits of applying Poly-generation — the production of multiple products at a single location — and examines a proposed bio-refinery scheme to produce ethanol from agricultural waste. The ethanol production process produces a waste biogas, which can then be used in a high efficiency Cogeneration (or Combined Heat and Power) plant as a fuel for gas turbines to generate electricity and steam (heat), not just for the bio-refinery but also local industry and businesses. By creating a high value product (ethanol) along with a free fuel, the bio-refinery acts as an anchor plant to provide reliable, affordable electricity to the local community. As well as providing economic benefits, such a concept has multiple environmental benefits as regions and nations try to combine growth in energy demand with reduction in global greenhouse gas emissions: agricultural residues that would otherwise have decayed emitting methane and CO2 into the atmosphere are used to create a high value product in ethanol, while using the biogas as a fuel displaces combustion of fossil fuels, reducing both combustion emissions and those associated with transportation of the fuel to the point of use.