Biomass Co-Firing

One of the most effective ways of reducing pollution associated with burning coal for electricity is to directly replace it with a renewable fuel of similar quality, usually wood. 

While wood and other biomass can substitute for some quantity of coal-fired generation, physical differences in the two fuels as well as insufficient total energy resources in sustainably managed biomass make it an insufficient replacement to match the raw power and infrastructure in place for coal-fired utility generation. 

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Wind offshore Wind onshore Tide and wave Solar thermal electricity Photovoltaics Hydro small-scale Hydro large-scale Geothermal electricity Biowaste (Solid) biomass (Solid) biomass co-firing Biogas... 

Several issues clearly remain regarding how blending biomass and coal will affect combustion performance, emissions, fouling and slagging propensities, corrosion, and ash salability. Nevertheless, several utilities have tested biomass/coal co-firing in utility boilers and the Electric Power Research Institute funded a study in 1997 to establish biomass co-firing guidelines.580... 

Prabir, B., Butler, J., and Leon, M. 2011. Biomass co-firing options on the emission rednction and electricity generation costs in coal-fired power plants. Renewable Energy. 36 282-288. 

V. Nast, G. Ekschele, and W. Hutchinson, "TDE Co-firing Experience in a Cyclone Boiler," Proceedings, Strategic Benefits of Biomass and Waste Fuels Conference, EPRI, Washington, D.C., 1993. 

Pyrolysis oil (bio-oil) is produced in fast and flash pyrolysis processes and can be used for indirect co-firing for power production in conventional power plants and potentially as a high energy density intermediate for the final production of chemicals and/or transportation fuels. Gas chromatographic analysis of the liqtrid fraction of pyrolysis products from beech wood is given in Table 3.6 (Demirbas, 2007). Biocmde resrrlts from severe hydrothermal upgrading (HTU) of relatively wet biomass and potentially can be used for the production of materials, chemicals,... 

There are three major types of processes for direct combustion of waste biomass water-wall incineration, supplementary fuel co-firing with coal or oil, and fluidized bed combustion. 

We note in passing that countries with large deposits of coal are unlikely to switch to biomass-only combustion and are likely to opt for co-firing instead. The operating temperature is partly determined by the composition of the ash-forming compounds present in the biomass. 

There are some 200 producers of biomass power product in the U.S. alone. The majority — more than two-thirds — use forest products, and just under one-third use landfill gas as the primary fuel source. In some cases, especially where the cost of biomass is very low, it is co-fired with a fossil fuel, such as coal, to lower the overall cost of the electricity produced. 

In addition to co-firing, there are three other types of biomass electricity-generation systems direct-fired, gasification, and modular. Of these, the most commonly used is direct-fired. In this system, biomass fuel is burned in a boiler to produce high-pressure steam, which then drives turbines to produce electricity. The drawback to these types of power plants is that they tend to be small scale and are not very efficient. Costs also tend to be relatively high, at nine cents per kilowatt-hour, versus only 2.1 cents per kilowatt-hour for some co-fired plants.31... 

Annamalai K, Wooldridge M. Co-firing of coal and biomass fuel blends. Prog Energy Combust Sci. 2001 27 171-214. 

Overgaard P, Sander B, Junker H, Friborg K, Larsen O-H. Two years operational experience and further development of full-scale co-firing of straw. In 2nd World Conf. on Biomass for Energy, Industry and Climate Protection 2004 May 10-14 Rome, Italy, p. 1261-4. 

Biomass and coal have fundamentally different fuel properties that can lead to benefits or deterrents to co-firing. For instance, biomass is a more volatile fuel than coal and has higher oxygen content. Coal, on the other hand, has more fixed carbon than biomass. Wood fuels tend to contain very little ash (on the order of 1% ash or less) and consequently increasing the ratio of wood in biomass/coal blends can reduce the amount of ash that needs to be disposed. A negative aspect of biomass is that it can contain more chlorine than coal. This is particularly true for some grasses, straws, and other agricultural residues. 

When biomass is co-fired with coal (even in small percentages), the alkali metals in biomass ash can alter the properties of the resulting mixed ash. This could have a significant impact on the coal plant s operating and maintenance costs or even operability. The addition of biomass to a coal-fired power plant can also nullify ash sales contracts for coal flyash. Biomass ash components in feedstocks may also reduce the long-term efficiency and effectiveness of certain (selective catalytic reduction, SCR) systems for the selective catalytic reduction ofNOx. 

Fuel preparation and whether to premix the biomass and coal or introduce the two fuels separately into the boiler is another important issue that needs to be addressed for successful implementation of co-firing. Fuel handling of biomass in co-firing systems will need to be demonstrated with a variety of biomass feedstocks—such as switchgrass, willow, and energy cane—to take advantage of lower cost biomass residues and future energy crops. 

The use of biomass (residues), when co-fired (e.g., with coal) and coupled to subsequent carbon sequestration, might be an important technical option for achieving zero emission and, potentially, a net reduction of atmospheric C02. 

At present the most reliable applications for biomass gasification are co-firing and direct firing of the fuel gas in a boiler for heat or steam cycle. These applications present the least technical risks as the problem of tar is avoided and therefore the main task of the industry is to increase their market penetration. It is important that more plants will be built and operated in existing markets in order to increase the degree of confidence for the users and especially the utilities as well as to improve the industrial capabilities with various problematic but cheap fuels. 

Lin W, et al. (1999) Agglomeration in fluidized bed combustion of biomass -mechanisms and co-firing with coal. In Proceedings in I5th International Conference on Fluidized Bed Combustion, May 16-19, Savannah, Georgia, 12. ... 

ABSTRACT Calcium-enriched bio-oil (CEB) can be used for flue gas desulfurisation in coal and waste combustion chambers. It is produced by mixing biomass derived fast pyrolysis oil with calcium oxide. The aim of the proposed project is to develop a technology i) to produce calcium-enriched bio-oil with a calcium content of 13 wt,%, and ii) to test the CEB in a combustion chamber by co-firing it with a sufur-containing fuel. In this paper the production method of CEB will be elucidated, and small-scale experiments related to CEB spraying will be presented. Finally, co-combustion experiments of a sulfur-containing fuel with CEB in a small flame tunnel (20 kW, ) will be reported. 

Studies should be continued into the properties of biomass fuels and blends, with reference to mitigating the impacts of fouling, corrosion, and other detrimental effects on plant efficiency, operation, and maintenance (particularly in co-fired systems). 

Johnson, D.K., Tilhnan, D.A., Miller, B.G., Pisupati, S.V., and Clifford, D.J. 2001. Characterizing biomass fuels for CO firing applications. Proceedings. 2001 Joint International Combustion Symposium. American Flame Research Committee, Kauai, Hawaii, September. 

Maciejewska, A., Veringa, H., Sanders, J, and Peteves, S.D. 2006. Co-firing of biomass with coal Constraints and role of biomass pre-treatment. Report No. EUR 22461 EN. Institute of Energy, European Commission, Luxembourg. 

Bio-briquettes (biomass briquettes) are a biofuel substitute to coal and charcoal. They are used to heat industrial boilers in order to produce electricity from steam. The most common use of biobriquettes is in the developing world, where energy sources are not as widely available. There has been a move to the use of briquettes in the developed world throngh the nse of co-firing, when the briquettes are combined with coal in order to create the heat supplied to the boiler. This reduces carbon dioxide emissions by partially replacing coal used in power plants with materials that are already contained in the carbon cycle. 

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