Combustion is a commercial technology with traditional fuels such as wood residues and MSW (incineration) and several successful applications can be identified worldwide.
Combustion is a commercial technology with traditional fuels such as wood residues and MSW (incineration) and several successful applications can be identified worldwide. However, in order to increase the range of applications and thus the market for combustion technologies, new applications have to be developed for the more complex feedstocks such as straw, grasses, and mixtures of several different fuels. Grate systems are the preferred type of combustor due to their reliability and industrial experience especially for small to medium size applications (0.5 - 5 MWe). Fluidized bed combustors have been proven very successful due to the relative easy scale up and their capacity to operate with a variety of fuels so long as the bed sintering (due to the high ash content of some of the biomass fuels) can be effectively controlled. This has been demonstrated even with some difficult fuels such as poultry litter. The main range of applications for fluidized bed systems is for the medium to the large scale (3 - 20 MWe). A new market has started to develop and it concerns the incineration of RDF in fluidized bed systems with several plants already in operation. There is nevertheless need for long term operation of fluidized bed systems in order to prove their reliability. Overall the main emphasis for future technical development should focus in using more difficult feedstocks and multi-fuel operation. In addition, the industry should follow the advances on materials made by the coal boiler technology in using supercritical steam conditions in view of increasing the conversion efficiency to electricity. This improves the overall process efficiency and the economics. The MSW incineration industry has initiated activities in this area aiming to increase the efficiency to electricity from the present level of 20-23% to above 30%. Combined Heat and Power (CHP) applications offer the best economic viability due to the sale of heat to district heating networks or industrial users. 3.1.2 Gasification Gasification only now, after about 3 decades of R&D work, appears to be ready to achieve commercialisation status. The main problem with gasification has always been the efficient removal of tar and there is general agreement in the industry that this can only be efficiently achieved with catalytic reforming of the tar. On the large scale applications, the successful operation of the Varnamo plant (6 MWe + 9 MWth, Foster Wheeler) in Sweden for over 3,800 hours on Integrated Gasification Combined Cycle provided credibility and the expected operation of the ARBRE plant (8MWe, TPS) in the UK during the first months of 2001 will be the first step towards commercialisation of the IGCC technology. Serious delays have been reported with the Brazilian project (32 MWe, TPS), however, it is expected that this project will also been implemented soon. The Battelle technology has also been successfully demonstrated at the Burlington, Vermont, project in the US. The co-gasification applications have been very successful and the demonstration of the BioCoComb plant (10 MWth) in Zeltweg, Austria and the Lahti plant (40-70 MWth) in Finland have provided confidence in this relative simple application. The expected operation of the AMER plant (56 MWth) will also further increase the reliability of this type of application. The above three plants are based on different manufacturers (Austrian Energy, Foster Wheeler and Lurgi respectively) while all three gasifiers are circulating fluidized bed systems. There is still no reliable technology for the small scale applications, <500 kWe, however, BTG plans to demonstrate a reverse flow catalytic bed which is claimed to eliminate tar in small to medium size plants. It should be noted that all small-scale plants are based on moving bed gasifiers. In the medium range applications there are efforts underway to demonstrate the effectiveness of Ni-based catalyst but these projects still have to be implemented. ¬Future R&D work should focus on the effective removal of tar and the various catalytic systems must prove their reliability and especially their economic viability based on an acceptable lifetime of the catalysts. In addition, the gasification technologies should aim to widen the range of fuels acceptable by the gasifiers such as fuels of high ash content and multi-fuel operation. For this to be achieved it is necessary to pay attention to feeding systems especially whenever difficult feedstocks such as bagasse, grasses and fluff RDF are to be used. RDF and waste recovered fuels will become more important in the near future for gasification applications. Thus the experiences gained by the Greve in Chianti plant (TPS, under modifications to increase the electricity output from 2.5 to about 6.0 MWe) will be valuable. Renewed interest has also been demonstrated for the production of synthesis gas and it's subsequent conversion to methanol as has been demonstrated by the novel methanol to gasoline process in New Zealand or Fischer- Tropsch synthesis products as demonstrated by SASOL in South Africa. Various Dutch research centres have proposed a once through configuration for methanol combined with an IGCC in order to improve the overall economics and process efficiency. 3.1.3 Pyrolysis The main type of pyrolysis technology under development at present for biomass feedstocks is fast pyrolysis for liquids while slow pyrolysis technologies for RDF are starting to be demonstrated. The Canadian companies Ensyn, Pyrovac and Dynamotive are considered the technology leaders, however as there is not a reasonable market in North America all these companies are looking in the EU as the main market. Ensyn are operating several plants up to 84 t/d wood feed in the USA and Canada for products for the food industry and chemicals. ENEL's Bastardo plant (Ensyn technology, 10 t/d wood feed) in Perugia, Italy, although commissioned, has still to operate under full capacity effectively while the Pyrovac plant (84 t/d feed, mainly bark) in Jonquiere Canada has yet to achieve continuous operation for more than 24 hours. In the EU there are mainly three technologies under development, the rotating cone of BTG, Netherlands, the fluid bed of Wellman, UK, and the ablative type of fast pyrolysis at Aston University, UK. From these, the BTG process has been successfully operated at pilot scale at up to 6 t/d and a demonstration project to scale up the technology is underway in the Netherlands. The Wellman technology has only been operated at pilot scale while the Aston University process is at laboratory scale. There are some attempts to demonstrate medium capacity fast pyrolysis plants, however, these continue to face technical problems which in some cases are related to the effective heat transfer at high heating rates between the heat carrier and the finely chopped biomass particles or to the rapid quenching of the pyrolysis vapours to freeze any further reactions. These problems result in variations in the bio-oil quality and its consistency, which present uncertainties in the marketing of the fuel. Several studies are underway investigating the production of chemicals from fast pyrolysis oils but only Ensyn has reached commercial status with the Red Arrow plants in the USA, which focus on food flavourings, although there is considerable interest in adhesives and resins for the wood products industries. A significant amount of work has also been undertaken for testing the bio-oil in engines and boilers for power and or heat production. Since fast pyrolysis is a relative recent technology, it is understandable that technical problems still have to be overcome before commercial status can be achieved, however, there are reasonable expectations that within the next 5 - 8 years sufficient reliability and experience will have been gained to warranty commercial scale plants. Slow pyrolysis for waste has been attempted for several years based on rotary kiln systems, however, these processes failed to convince the waste management industry that they were a serious competitor to incineration. Recent attempts have been undertaken based on pyrolysis of waste followed by combustion of the gas and vapour products with incineration of the char for power and/or heat generation. The most credible projects are those of Siemens at Furth and Thermoselect in Karlsruhe Germany but significantly longer performance is required before such processes will prove their techno-economic viability. In general the efficiency to power is lower for pyrolysis but it offers better control of contaminants, while on the other hand the environmental impact is higher for incineration. Future work will have to concentrate on increasing the reliability of the various technologies and improving the performance of combustion equipment for bio-oil. In addition, attention must be paid in better characterisation and eventual standardisation of the bio-oil for wider market penetration. 3 2 Biological Processes 3.2.1 Fermentation Ethanol, an anaerobic product of microbial etabolism can be recovered relatively easily through conventional distillation recovery methods. The production of industrial ethanol from integrated grain milling plants and sugar crops is a mature technology and has been successfully implemented in Brazil and the US. On the other hand, the absence of appropriate legislation has limited significantly the production of ethanol in the EU. The last decade, ethanol production from lignocellulosic materials has received increased attention by the research community and technical breakthroughs have been reported in the US and Canada. 3.2.2 Anaerobic Digestion Liquid phase anaerobic digestion (dry solid matter in the digester in the range of 5 - 10 wt%) can be considered a commercial technology and several companies offer various technical solutions to a variety of effluents and substrates. Recent work has focused on multi-substrate operation with attention on the biodegradable traction of MSW especially in Denmark. Both for biogas and landfill gas, purification technologies have been developed to remove carbon dioxide and other corrosive gases (such as hydrogen sulphide) for utilisation of the rich methane gas as transport fuel. If the biogas or landfill gas can be purified extensively, then they can be used as a renewable substitute for natural gas in several applications. Solid state anaerobic digestion (dry solid matter in the digester in the range of 30 - 35 wt%) is a technology approaching commercial status with Organic Waste Systems of Belgium and Valorga of France as the leaders and main competitors. Solid state operation results in significantly higher biogas productivity rates than liquid phase and a better quality of compost due to the mesophilic operation I (about 50 - 55 °C). 3.2.3 Composting Aerobic composting is a commercial technology with demonstrated reliable performance is several projects. However, the economics of composting are strongly related to the quality of the compost and to a strong market for the compost that is not always evident. Composting source separated or "green" waste results in compost of higher quality due to the absence of plastics or other contamination. Except for the need of standards on the quality of the compost, there is no strong justification for extensive R&D work. The R&D needs for the biological processes are related to pilot plant/industrial scale demonstration of ethanol form lignocellulosic feedstocks with increased yields, to the fine tuning of solid state digestion technologies and to the improved purification of biogas and landfill gas for various applications such as transport fuel or supply of methane in natural gas networks. 3. ENVIRONMENTAL PROTECTION Bioenergy is considered as the resource with the highest environmental impact amongst the renewable energy sources and this does not refer to incineration or waste treatment only, but it even applies to wood combustion. This is due to the fact that there are always residues (such as ash and liquid effluents) to be disposed off and practically in all applications there is a stack or a chimney. This may induce the general public to relate bioenergy plants to coal fired plants, incinerators and in general emission of gaseous pollutants. It is therefore mandatory that all Bioenergy technologies must carefully and convincingly address the problem of emissions if they are ever going to be accepted by the general public, the political establishment and subsequently the industry. Practically in all Bioenergy applications at the end the energy carrier (biogas, fuel gas, bio-oil, ethanol, solid fuel or hydrogen) will be used in a combustionprocess to release the chemical energy of the carrier. It is therefore of critical importance that emissions from the combustion of all energy carriers are minimised to whatever possible extend. It is preferable whenever possible to try to reduce the concentration of the pollutants in the energy carrier before it's combustion so as to minimise or eliminate emissions of sulphur oxides, heavy metals, halogenated compounds and other pollutants. This can (be achieved in gasification or pyrolysis processes, however, it is not possible for combustion unless extensive feedstock pretreatment takes place which is always relative expensive. In the medium term future this can prove an advantage for gasification and pyrolysis processes for contaminated biomass or waste recovered fuels in relation to combustion. Although there has been significant progress in the reduction of emissions for all the above pollutants, this is a field where the R&D work should be intensified. This is becoming even more critical as waste recovered fuels and contaminated biomass such as demolition wood are becoming an important cheap resource in countries where there is scarcity of other biomass feedstocks. ETHANOL FUEL PROGRAM EVOLUTION The fuel ethanol program in Brazil was formally established in 1975, aiming at reducing oil imports. Other important considerations were: the existing know-how in fuel ethanol production/utilization; land and labor availability; and low sugar prices in the world market. After 1980, with the ethanol-dedicate engines, local environmental benefits became evident (elimination of Pb in gasoline blends; lower CO emissions; less aggressive HC and NOx). The global environmental benefits, with a substantial reduction in CO2 net emissions, was well quantified in 1990.  The program was established within the context of a strong government intervention in the sugar cane sector; before 1975 sugar was produced and commercialized within "production quotas", and all exports were made by the government. In the 90's all the production/commercialization of sugar and ethanol were totally de-regulated as follows: From 1975 - 80's Ethanol: - Level of guaranteed purchase, at controlled prices - "Fixed" ratio of ethanol/gasoline selling prices: 0.59 (1975) 0.75 (1989) - Low interest rate in loans for investment (1980-1985) Sugar: Government issued "production quotas" Exports: by the Government * 1990 Sugar Exports Privatized * 1994 Ethanol: 22% ethanol in gasoline blends * 1995 Sugar: de-regulation (end of quotas) * 1997 Anhydrous ethanol (blends) de-regulation (end of quotas and controlled prices) * Ethanol: 24% ethanol in gasoline blends * Hydrated ethanol (E 1 00): de-regulation Those policies and the world market positions for sugar and oil resulted in productions as are summarized in Figure 1. It is important to see the sugar cane availability, its causes and consequences, to understand the possibilities today. Figure Figure 1: Production - Brazil  Internal sugar consumption in Brazil grew in the expected way, somewhat above population growth in some periods. Sugar cane growth from 120 M ton to 240 Mt (from 1979 to 85) was almost entirely driven by the E-l00 (dedicated ethanol car) in the period. In the following years production stabilized; the government policy of paying the producer according to officially audited production costs was gradually abandoned (if not officially), and the "fixed" ratio of pump price ethanol/gasoline increased from 0.59 to 0.75. Sugar exports were privatized in 1990, and a shortage of ethanol (1989-90) led to consumer mistrust and very rapid decline in sales of ethanol dedicated vehicles. In the 90's, the export privatization and the very competitive production costs led to an extraordinary increase in sugar exports (from 1.5 to 11 M ton sugar) pushing sugar cane production to the 300 MT level; this was stabilized again by the drop in sugar prices and the over supply of ethanol in the 97-2000 period. In the same period, the relative utilization of sugar cane for ethanol or sugar is show in Figure 2, as well as the ethanol penetration in the Otto-cycle engine cars, in Brazil. BIOMASS FOR ENERGY OR MATERIALS INTRODUCTION Greenhouse gas (GHG) emission reduction is one of the most important environmental challenges for the next decades. Carbon dioxide (CO2) is the most important greenhouse gas, representing approximately three-quarters of the total GHG emissions. Biomass strategies pose an important option for CO2 emission reduction since CO2 is fixed during the biomass growth stage. Biomass can subsequently be used as a renewable resource, with zero net CO2 emissions. This is the basis for all biomass strategies (i.e. groups of activities with similar characteristics, concerning agriculture and forestry and aiming for GHG emission mitigation). The following biomass strategies can be discerned: * Carbon storage above ground in new forests; * Carbon storage below ground in soils; * Carbon storage in wood materials and products; * Substitution of energy carriers with biomass; * Substitution of materials with biomass; * Energy recovery from process waste and post¬ consumer waste. The land availability and the biomass yield per hectare limit the total amount of biomass. Different biomass strategies compete for the limited amount of biomass and land available. Moreover, these strategies compete with other strategies for GHG emission reduction (e.g. other renewables, energy efficiency). A lot of attention has been paid to carbon storage strategies, to substitution of energy carriers and to materials substitution (e.g. 1-3). However, little attention has been paid to the interaction and the cost-effectiveness of these strategies. The pervasiveness of GHG emissions complicates the analysis: many GHG emission reduction strategies influence each other's efficiency. For example emission reduction because of a switch to bioelectricity reduces the potential for emission reduction based on the increased efficiency of household equipment. The assessment of biomass strategies is further complicated by co-production and cascading: by-products from wood sawing and waste materials can be used for energy recovery. This illustrates why the assessment of biomass strategies is complicated, and why different studies result in different recommendations, depending on the scope of the study. This study focuses on Western Europe. Current European policies with regard to biomass are aiming for bioenergy, especially electricity production (4). Transportation fuel research activities have been reduced in the last decade. As of yet, biomaterials strategies have received little attention from a GHG emission point of view. Some reforestation activities represent a continuation of a trend that started decades ago. It is unclear whether the current European biomass policy trends are optimal, given the conflicting study results and rapid technological change. For this reason, an energy and materials' systems engineering model has been developed in order to analyse the optimal use of biomass from agriculture and forestry for energy and/or materials. The selection of optimal biomass strategies has been investigated in the framework of the BRED (Biomass for greenhouse gas emission Reduction) project. MODEL CHARACTERISTICS The MARKAL linear programming model was developed 20 years ago within the IEA/ETSAP (International Energy Agency/Energy Technology Systems Analysis programme) framework (5). MARKAL is an acronym for MARKet Allocation. A MARKAL model is a representation of (part ot) the economy of a region. The economy is modelled as a system, represented by processes with physical and monetary flows between these processes. The processes represent all activities that are necessary to provide products and services. Special emphasis is given to new emerging technologies and their potential integration in the energy and materials system. A MARKAL model calculates the least-cost system configuration that meets the fixed demand for products and services given a number of constraints. The selection of process alternatives is based on discounted full life cycle costs. Biofuels for example are characterised by higher costs than fossil fuels, but lower GHG emissions. Consequently, biofuels will only be selected if GHG emissions are endogenised in the costs. This is done on the basis of emission permit prices. Figure. 1 Figure 1: Biomass model structure MARKAL is a dynamic model. The time span modelled is generally covering a period of decades. Within such a time horizon, technological change will be a major driving force for a changing systems configuration. Price elasticities of demand are endogenised in the MARKAL Elastic Demand algorithm (6). The least-cost system optimisation algorithm represents the market mechanism. The model user defines the database of processes and the constraints for individual processes and for the region as a whole. Constraints are for example determined by the availability of resources or environmental policy goals. Processes are characterised by their physical inputs and outputs of energy and materials, by their costs and by their environmental impacts. Many products and services can be generated through a number of alternative processes (e.g. electricity production can be based on coal, gas or biomass). The model database contains 1500 processes, covering the whole life cycle for both energy carriers and materials 'from cradle to grave'. The MARKAL MATTER 4.2 model has been used for this analysis. Documentation on input data and analysis results can be found on the internet (7) and in a large number of publications (e.g. 8,9). The model covers more than 25 energy carriers and 150 materials. More than 100 products represent the applications of these materials. 30 categories of waste materials are modelled. The model has been developed especially for the analysis - of GHG emission reduction strategies. Four GHG emission permit prices have been analysed: 20, 50, 100 and 200 EUR/t CO2, The base case is the run without a permit price. In the emission reduction cases, the permit prices increase from zero in the year 2000 to their maximum level in 2020 and stabilise afterwards. Figure 1 show a general overview of the model structure for biomass, showing the close relation between food, energy and materials crops. Europe is split into a northern region, a middle region and two southern regions in order to account for different climates and soil types. All important agricultural crop types are - covered (including energy crops like miscanthus and sweet sorghum). Afforestation (i.e. new forests on formerly agricultural soil, planted after 1990) is considered as a carbon storage strategy. Model input data for biomass (production and consumption processes) have been reported in five separate volumes (e.g. 10,11). With the MARKAL MATTER 4.2 model, three scenarios have been analysed: 1. Globalisation, characterised by rapid technological progress, globalisation of economic activities and market liberalisation 2. Fortress Europe, characterised by moderate economic development and heavy reliance on transportation and building sectors 3. Sustain, characterised by environmental reorientation of society (initiated by lifestyle changes) A more detailed discussion of the model and the results can be found in the final report (12). RESULTS Figure 2 shows the changes in agricultural land use for the 'Globalisation' scenario in - 2030. The figure shows the reference year 1990, the base case and permit price levels of 50,100 and 200 EUR/t CO2, In the base case and the 50 EURIt case, the use of biomass crops is negligible but some afforestation is introduced (based on a lower bound that represents current policy plans). Afforestation increases markedly in the 100 EURIt and 200 EUR/t cases and dominates biomass crops. The results show that the full land area is not yet used at lower, more realistic, permit price levels. This suggests that land availability should be no major issue in the biomass strategy discussion: the costs are the main driving force. The I preference for afforestation is a major difference with earlier modelling studies. Figure Figure 2: Agricultural land use, 'Globalisation', 2030 Western Europe has reached a status where its agricultural production potential exceeds food and fodder demand. This is largely accounted for by the steadily increasing agricultural productivity. If this trend continues, 10-20% of the agricultural land (both arable land and pastures) may become available for other purposes. If this land is used for high yield biomass crops, it can yield up to 500 Mt biomass per year. As a consequence, agricultural biomass crops can constitute an important option for GHG emission reduction. The results regarding biomass supply depend to a large extent on trends in agricultural productivity and trends in global markets for agricultural products. Extensification is not recommended from a GHG emission reduction point of view. The use of biomass for energy and materials applications will increase by up to 200 Mt (compared to the case with no permit price) if significant greenhouse gas policies (i.e. emission permit price of 200 EUR/t CO2) are introduced. The growth mainly takes place in the energy market. Also the materials market grows up to a permit price level of 100 EUR/t. Figures 3 and 4 show the division of biomass use (both from forestry and from agriculture) into energy and materials applications at a permit price level of 100 EUR/t CO2 in 2030. Figure Figure 3: Bioenergy applications, 100 EUR/t CO2, 2030 Figure 3 shows significant changes in the biomass use for energy purposes between 1990 and the base case in 2030. The total biomass use increases significantly from 80 Mt to 200 Mt. While the biomass use for heat production nearly disappears, the energy recovery from waste biomass (mainly for electricity production) increases significantly and remains at a constant level up to the 200 EUR/t permit price. The energy recovery from lignin (via gasification and subsequent cogeneration) increases at 100 EUR/t, but declines again at 200 EUR/t. These changes are related to the ethanol production from wood from 100 EUR/t upward, which results in lignin by-products that are used for energy recovery. However in the 200 EUR/t case, part of the residual lignin is used for Hydro Thermal Upgrading (HTU) oil production. From 50 EUR/t upward, biomass use increases significantly, up to 390 Mt biomass in the 200 EUR/t case. The main increase can be attributed to the production of transportation fuels, especially ethanol and (at 200 EUR/t) HTU biodiesel. Figure 3 shows that the differences between the scenarios are limited, indicating that the GHG permit price level has more impact than the scenario characteristics. Figure 4 shows an increase of the biomass used for materials applications from approximately 120 Mt in the reference year to 170 Mt in the 100 EUR/t case. The additional biomass is used as feedstock for petrochemicals, and a limited increase for construction materials. At higher permit price levels (200 EUR/t) feedstocks decline because HTU oil is applied in the transportation sector instead of for the production of biochemicals. Figure Figure 4: Biomaterials applications, 100 EUR/t CO2, 2030