Cement, Energy & Environment

power plants. The other advantage of biomass co– firing is that the incremental investment for burning biomass in coal fired plants is significantly lower than the cost of dedicated biomass power. At present, co-firing projects in coa l-fired power plants exceed the biomass capacity of dedicated biomass plants. The Clean Development Mechanism (COM) recognizes biomass co-firing as a way to reduce C0 2 emissions in developing countries. The indicators developed by international organizations to measure the sustainability of bio-energy (including protection of soil and water resources, bio-diversity, land allocation and tenure, and food prices) need to be integrated into the relevant policy measures. The costs of biomass acquisition and transportation determine to a large extent the economic feasibility of co-firing. The acquisition costs depend on possible competition with other biomass energy uses (e.g. biofuels) or non-energy applications. In developing countries , the use of waste streams from agriculture and forestry may also create additional value and job opportunities while contributing to rural development. Co-fi ring Technologies Direct co-firing is the simplest, cheapest and most common option . Biomass can either be milled jointly with the coal (i.e. typically less than 5 per cent in terms of energy content) or pre-milled and then fed separately into the same boiler. Indirect co-firing is a less common process in which a gasifier converts the solid biomass into a fuel gas that is then burned with coal in the same boiler. Though more expensive because of the additional technical equipment (i.e. the gasifier), this option allows for a greater variety and higher percentages of biomass to be used. Parallel co– firing requires a separate biomass boiler that supplies steam to the same steam cycle. This method allows for high biomass percentages and is frequently used in pulp and paper industrial facilities to make use of by-products from paper production, such as bark and waste wood. Process and Technology Status Biomass co-firing consists of burning biomass along with coal in coal-fired power plants. Compared to power plants burning 100 per cent biomass, co-firing offers several advantages , including lower capital costs, higher efficiency, improved economies of scale and lower electricity costs due to the larger size and the superior performance of modern coal power plants. At present, some 230 power and combined heat and power (CHP) plants use co-firing , mostly in northern Europe and the United States, with a capacity of 50-700 MW. Co-firing in CHP plants is currently the most competitive option to exploit the biomass energy potential for both electricity and heat production. Performance and Costs The net electric efficiency of a co-fired coal/biomass power plant ranges from 36-44 per cent, depending on plant technology, size, quality and share of biomass . While a 20 per cent co-firing (as energy content) is currently feasible and more than 50 per cent is technically achievable, the usual biomass share today is below 5 per cent and rarely exceeds 10 per cent on a continuous basis. A high biomass share means lower GHG emissions. It is estimated that 1-10 per cent biomass co-firing in coal power plants could reduce C0 2 emissions from 45 million to 450 million tonnes per year by 2035, if no biomass upstream emissions are included. However, high biomass shares involve technical issues, such as securing sufficient biomass , as well as potential combustion problems , such as slagging , fouling (which reduces heat transfer) and corrosion. The overall cost of co-firing is sensitive to the plant location and the key cost element is the biomass feedstock. The investment cost for retrofitting a coal-fired power plant for co-firing is in the range of 430-500 USD/Kw for co-feed plants, 760-900 USD/Kw for separate feed plants and 3,000-4,000 USD/Kw for indirect co-firing. These costs are still significantly lower than the cost of dedicated 100 per cent biomass power plants. Co-Firing Potential The substitution of 10 per cent of the global coal-fired capacity by co-firing would result in about 150 GW biomass capacity. In comparison, today's co-firing capacity is estimated at between 1-1 0 GW (the variability being associated with the actual biomass share in co-firing plants),and the • 1-