Biomass for Power Generation and CHP

PROCESSES – Biomass combustion is a carbon-free process because the resulting CO2 was previously captured by the plants being combusted. At present, biomass co-firing in modern coal power plants with efficiencies up to 45% is the most cost-effective biomass use for power generation. Due to feedstock availability issues, dedicated biomass plants for combined heat & power (CHP), are typically of smaller size and lower electrical efficiency compared to coal plants (30%-34% using dry biomass, and around 22% for municipal solid waste). In cogeneration mode the total efficiency may reach 85%-90%. Biomass integrated gasification in gas-turbine plants (BIG/GT) is not yet commercial, but integrated gasification combined cycles (IGCC) using black-liquor (a by-product from the pulp & paper industry) are already in use. Anaerobic digestion to produce biogas is expanding in small, off-grid applications. Bio-refineries may open the door to combined, cost-effective production of bio-chemicals, electricity and biofuels. TYPICAL COSTS – Because of the variety of feedstocks and processes, costs of bio-power vary widely. Co-firing in coal power plants requires limited incremental investment ($50-$250/kW) and the electricity cost may be competitive (US$ 20/MWh) if local feedstock is available at low cost (no transportation). For biomass typical cost of $3-$3.5/GJ, the electricity cost may exceed $30-$50/MWh. Due to their small size, dedicated biomass power plants are more expensive ($1500-$3000/kW) than coal plants. Electricity costs in cogeneration mode range from $40 to $90/MWh. Electricity cost from new gasification plants is around $100-$130/MWh, but with significant reduction potential in the future. STATUS –Abundant resources and favourable policies are enabling bio-power to expand in Northern Europe (mostly co-generation from wood residues), in the United States and in countries producing sugar cane bagasse (e.g. Brazil). Proliferation of small projects, including digesters for off-grid applications, is recorded in both OECD and emerging economies. Global biomass electricity capacity is in the range of 47 GW, with 2–3 GW added in 2005. Associated investment accounted for 7% of total investment in renewable energy capacity in 2005 ($38 billion excluding large hydro). POTENTIAL & BARRIERS – In the short term, co-firing remains the most cost-effective use of biomass for power generation, along with small-scale, off-grid use. In the mid-long term, BIG/GT plants and biorefineries could expand significantly. IEA projections suggest that the biomass share in electricity production may increase from the current 1.3% to some 3%-5% by 2050 (IEA ETP, 2006), depending on assumptions. This is a small contribution compared to the estimated total biomass potential (10%-20% of primary energy supply by 2050), but biomass are also used for heat generation and to produce fuels for transport. Main barriers remain costs; conversion efficiency; transportation cost; feedstock availability (competition with industry and biofuels for feedstock, and with food and fiber production for arable land); lack of supply logistics; risks associated with intensive farming (fertilizers, chemicals, biodiversity).