CD1002 17th Contribution 7/3/2005 12:01 Page 2 These articles were produced by the Implementing Agreement on Bioenergy, which forms part of a programme of international energy technology collaboration undertaken under the auspices of the. U P D A T E Co-firing Biomass with Coal Bioenergy is gaining attention worldwide as a renewable energy option. One of the current Tasks of is concerned with biomass combustion and co-firing. Some of the recent work of this Task has focussed on co-firing biomass with coal. Overview There has been remarkably rapid progress over the past 5-10 years in the development of the coutilisation of biomass materials in coal-fired power plants. The use of biomass in existing coal-fired power plants was among the first commercial options. The reasons for this were the direct reduction of CO 2 emissions by replacing coal and also utilisation of the existing infrastructure for energy-efficient power supply - thereby minimising investment costs. A recent inventory of the application of co-firing worldwide has indicated that more than 150 coalfired power plants have experience with co-firing biomass or waste, at least on a trial basis. The power plants involved are in the range 50-700 MW e although a number of very small plants have also been involved. The co-firing activities have involved all of the commercially significant solid fossil fuels, including lignites, sub-bituminous coals, bituminous coals, anthracites, and petroleum coke. These fuels have been co-fired with a very wide range of biomass material, including herbaceous and woody materials, wet and dry agricultural residues and energy crops. This experience has shown how the technical risks associated with co-firing in different types of coal-fired power plants can be reduced to an acceptable level through proper selection of biomass type and co-firing technology. There are three co-firing options for biomass materials in coal-fired boilers, and all of these options have been demonstrated at industrial scale, viz: Direct co-firing is the least expensive, most straightforward, and most commonly applied approach. The biomass and the coal are burned in the coal boiler furnace, using the same or separate mills and burners, depending principally on the biomass fuel characteristics. Another option is to install a biomass gasifier to convert the solid biomass into a fuel gas, which can be burned in the coal boiler furnace. This approach can offer a high degree of fuel flexibility, and the fuel gas can be cleaned prior to combustion to minimise the impact of the products of combustion of the fuel gas on the performance and integrity of the boiler. This approach has been applied, for instance, in the Zeltweg plant in Austria, the Lahti plant in Finland and the AMERGAS project in the Netherlands. A third option is to install a completely separate biomass boiler and utilise the steam produced in the coal power plant steam system. This approach has been applied, for instance, in the Avedøre Unit 2 Project in Denmark. Conclusions There is now fairly wide experience of the successful co-firing of biomass materials in coal-
CD1002 17th Contribution 7/3/2005 12:01 Page 3 fired power plant boilers worldwide, covering a wide variety of combinations of fuels and boiler plant configurations. Based on this experience, it is possible to draw a number of general conclusions, viz: Biomass co-firing has been demonstrated successfully in more than 150 installations worldwide, for most combinations of fuel and boiler type. The electrical conversion efficiencies for the biomass, when co-fired in coal-fired plants, are similar to those for coal, i.e. they are significantly higher than those for small, dedicated biomass power plants based on similar energy conversion technologies. Co-firing in existing coal-fired boilers is, in almost all cases, the lowest cost biomass power production option, and can be implemented relatively quickly. Well-managed biomass co-firing projects involve low levels of technical risk. In addition to the reduction of CO 2 emissions, biomass co-firing may also lead to reductions in the emissions of other pollutants. Overall, believes that the co-firing of biomass in existing coal-fired boilers provides an attractive approach to nearly every aspect of the development of biomass-to-energy capacity in a number of countries. Direct co-firing of woodchips with coal. (Courtesy Delta Electricity, Australia) Baxter, L.L., Rumminger, M., Lind, T., Tillman, D. and Hughes, E. 2000. Co-firing Biomass in Coal Boilers: Pilot- and Utility-scale Experiences. Biomass for Energy and Industry: 1st World Conference and Technology Exhibition, Seville, Spain. Tillman, D., Hughes, E. and Gold, B.A. 1994. Co-firing of biofuels in coal fired boilers: Results of case study analysis. 1st Biomass Conference of the Americas, Burlington, VT. Koppejan, J. Overview of experiences with cofiring biomass in coal power plants, Task 32: Biomass Combustion and Co-firing. In prep. Koppejan, J., van Loo, S. et al. 2002. Handbook of Biomass Combustion and Co-firing, IEA Bioenergy Task 32: Biomass Combustion and Cofiring, Twente University Press. The New Liquid Biofuel Age Another programme in is Task 39 Liquid Biofuels from Biomass. This Task continues to promote technology and support policies for the economic production and distribution of liquid biofuels from biomass. Some recent developments in liquid biofuel commercialisation are outlined below. Bio-based ethanol production World production of bio-based ethanol is primarily from sugarcane (Brazil) and corn starch (USA), and totals over 30 billion litres annually, as shown in Figure 1. A dramatic increase in world ethanol production has been seen since 2000, corresponding with rapid increases in the price of oil and uncertainty over the supply of fossil resources.
CD1002 17th Contribution 7/3/2005 12:01 Page 4 Biodiesel production Most biodiesel production is currently derived from oilseed plants such as canola (Europe), while smaller amounts are produced from waste animaland plant-derived oils (North America). Most production is centred in Europe, where 1.2 million tonnes of biodiesel was produced in 2002, equivalent to an increase of more than 37% when compared to 2001. North American production is significantly lower, at about 41,000 tonnes in 2002. Figure 1: Crude oil prices vs. ethanol production, 1980-2004 Rising demand for bio-based ethanol has increased the probability that other feedstocks, including lignocellulosic biomass, could become viable options for the biofuel industry. In particular, petroleum supplements including ethanol from lignocellulosic biomass (such as wood and agricultural residue) are receiving attention in North America for four main reasons: compatibility with existing distribution networks; ease of blending with gasoline for use; lower premiums for use under current North American taxation policies, as compared to diesel or biodiesel, and sufficient supply of lignocellulosic biomass exists to support a relatively large biomass-toethanol sector. A number of demonstration and pilot plants have recently been commissioned that will see lignocellulosic-based ethanol take a more predominant position in the biofuel industry. Demonstration plants include Iogen s facility in Ottawa, Canada, which is a $29 million, 40 ton/day facility that can process wheat straw and poplar. Abengoa is building a 200 million litre/year facility that will utilise 50% agricultural residues for feedstock in Castilla y Leon, Spain. In addition, other process development and pilot scale facilities can be found in Sweden, Canada, and the USA. Biodiesel is considered to be a likely alternative in Europe because of a diesel-friendly taxation structure, the nature of canola-based biodiesel, and the fact that close to 50% of new cars in Europe are powered by diesel engines. In North America, less than 1% of passenger vehicles are dieselpowered, which reduces the market for biodiesel products. An opportunity exists to improve the testing and regulation of biodiesel fuels for the international marketplace. Conclusions The development of liquid biofuels increasingly relies upon both technological improvement and political actions. To this end, Task 39 includes programmes that focus on technical progress in biomass-to-ethanol, promotion of biodiesel, and policy solutions for increased biofuel commercialisation. The Task collaboration has identified several key areas that need to be addressed as liquid biofuels become a more important component of the transportation fuel supply: There is a need for further research on primary technological hurdles in bio-based ethanol processes, such as pre-treatment and enzymatic hydrolysis of lignocellulosic feedstocks, and end uses for lignin. The availability of specific feedstocks must be better analysed to determine the potential volume of liquid biofuels that could be derived from the biomass industry.
CD1002 17th Contribution 7/3/2005 12:01 Page 5 Process economics need to be improved. This is largely dependent on the results of research on feedstock availability and price. Standards and policies are required to improve commercialisation opportunities. Assistance from Professor Jack Saddler and Dr Warren Mabee in providing the details of this success story is gratefully acknowledged. Fulton, L. 2004. Biofuels for Transport: An International Perspective. Report to. Economagic.com. 2004. West Texas Intermediate Oil Prices. Online at www.economagic.com. Mabee, W.E. et al. 2004. Ethanol from Lignocellulosics. Report to IEA Task 39. Worgetter, M. et al. 2003. A Worldwide Review on Biodiesel Production. Report to IEA Task 39. National Biodiesel Board. 2004. Online at www.biodiesel.org. Reducing Dioxin Emissions to Air from MSW Combustion Task 36 Energy from Integrated Solid Waste Management, has covered a wide range of topics under its work programme. One of the more recent studies undertaken was to determine the effect that the introduction of the waste incineration directives had had on controlling dioxin emissions to air from MSW combustion plants. Introduction Poor environmental performance by early combustion plants, particularly in relation to dioxin emissions, led to widespread and vociferous public opposition in the late 1970s and early 1980s. Subsequently the EU took action to improve environmental standards for waste combustion with the introduction of the waste incineration directives (89/429/EEC and 89/369/EEC) in 1989. These directives aimed to reduce as far as possible the negative effects on the air, soil, surface water, and groundwater caused by emissions from MSW combustion plants. As a result, stringent operating conditions were introduced and minimum technical requirements for waste incineration and coincineration were set. This led to the closure of many small combustion plants as it was uneconomic to retrofit them to the new control standards. The directives have since been superseded by the Waste Incineration Directive (2000/76/EC). The Directive sets a new limit of 0.1 ng/m 3 for dioxins (i.e., no more than 1 part in 10 billion) in air emissions. The regulations applied immediately to all new plant from 28 December 2002 and to existing plant from 28 December 2005. To comply with the Waste Incineration Directive the following methods are employed to control emissions in modern MSW combustion plants. Emissions control Careful control of the combustion process is required to ensure that the temperatures are sufficiently high to destroy dioxins and other pollutants but not so high that nitrogen oxides (NO x ) formation becomes a problem or that dioxins are allowed to reform during the cooling of the flue gas. In modern waste combustion plants complex control systems are employed to ensure that these combustion processes are performed under the correct conditions of turbulence and temperature whilst maintaining a stable process. There are a range of designs for flue-gas cleaning equipment. The system for a modern plant typically consists of the following: Combustion control to ensure high degree of turbulence whilst ensuring high temperatures to destroy organic pollutants and subsequent control of the flue gas cooling to avoid reforming dioxins.
CD1002 17th Contribution 7/3/2005 12:01 Page 6 Acid gas scrubbing using a lime mixture injected into the gas stream, which reacts to neutralise the acid gases such as sulphur dioxide, hydrogen fluoride, and hydrogen chloride. Activated carbon or coal injection to the flue gas to remove organic compounds such as dioxins and volatile metals such as mercury and cadmium. Particulate (dust) removal using an electrostatic precipitator or filters. Measures to reduce emissions of oxides of nitrogen such as Selective Catalytic Reduction (SCR) or Selective Non-Catalytic Reduction (SNCR). These systems rely on chemicals such as ammonia or urea injected into the flue gas to destroy oxides of nitrogen. SCR requires the use of special catalysts and natural gas burners to reheat the flue gas to promote the reaction. Task 36 Study The Task reviewed information from the UK, the Netherlands, Norway, Sweden, Finland, and Denmark, with the aim of comparing data available before and after introduction of the European Directives. Based on the study it is possible to draw the following conclusions: Since 1990 overall emissions of dioxins, in all of the countries studied, have been reduced substantially. In the UK total emissions of dioxins to air were reduced from 1142 g I- TEQ/year in 1990 to 345 g I-TEQ/year in 1999 (see Figure 1); in Norway the corresponding numbers were 131 g I-TEQ in 1990 and 34 g I-TEQ in 2000. With proven combustion control and flue gas cleaning technology, it is possible to reduce the emissions of dioxins from incineration by up to 99%. In the UK in 1990 MSW combustion contributed about 52% of all dioxin emissions. In 1999, after enforcing the new EU regulations on dioxin emissions, the corresponding number was 1% as illustrated in Figure 1. Conclusion Overall, believes that combustion of MSW is no longer a major contributor to emissions of dioxins in countries where the new EU emissions regulations (or similar) have been enforced. Anon. Department for Food, Environment and Rural Affairs, Consultation on Dioxins and Dioxinlike PCBs in the UK Environment Report PB 6778, October 2002. Sorum, L. Dioxin emissions to air from MSW combustion Data from some IEA member countries. Figure 1: UK Dioxin Emissions to Air (1990 and 1999)