Comparison of wood combustion and gasification technologies in the context of the Swiss energy strategy 2050

Transcription

1 Comparison of wood combustion and gasification technologies in the context of the Swiss energy strategy 2050 Final report E4tech Sàrl for Swiss Competence Center for Energy Research February 2014 Strategic thinking in sustainable energy

2 Title: Client: Version: Comparison of wood combustion and gasification technologies Swiss Competence Center for Energy Research Final report Date: 26 February 2015 E4tech authors: Ausilio Bauen Maarten van den Berg (contact: Luca Bertuccioli Franz Lehner Yamini Panchaksharam Richard Taylor Francois Vuille Guillaume Wurlod E4tech Sàrl Av. Juste-Olivier Lausanne Switzerland Tel: Fax: Company number: CH

3 Contents Executive summary Introduction Woody bioenergy use in Switzerland The Swiss Energy Strategy 2050 and the role for bioenergy in the Energy Perspectives Sustainable bioenergy feedstock potential in Switzerland International wood trade Status of wood combustion and gasification technologies Overview and scoping of technologies Technology status and commercial prospects Combustion boiler Combustion boiler + steam turbine / ORC Gasification Technology overview Gasification + ICE Gasification + Liquid fuels synthesis Gasification + Methanation Summary Relevance of wood combustion and gasification technologies in the Swiss energy transition Energy system benefits from using woody biomass Greenhouse gas emissions savings from using woody biomass Emissions of air pollutants Barriers for using woody biomass in Switzerland Overall assessment of relevance of woody biomass technologies in Switzerland Relevance of Swiss research and industry Which technologies are being studied and commercialised in Switzerland? Opportunities for Swiss research and industry in developing wood combustion and gasification technologies Conclusions References Strategic thinking in sustainable energy

4 List of Figures Figure 1: Range of applicable scales for each technology family based on feedstock thermal input power... 8 Figure 2: Technology and commercial readiness indices for the technology families... 9 Figure 3: Final bioenergy demand for heat and mobility in Switzerland in different scenarios (PJ/year) Figure 4: Domestic biomass feedstock potentials for energy according to Steubing (2010) and Infras (2004) Figure 5: woody biomass feedstock potential in Switzerland (Steubing, 2010) Figure 6: wood energy use in Switzerland by feedstock type (source: SFOE, 2014) Figure 7: Global consumption of wood pellets (O'Carroll, 2012) Figure 8: Wood to bioenergy routes via combustion and gasification Figure 9: Technology Readiness Level (TRL) and Commercial Readiness Index (CRI) (ARENA, 2014).. 21 Figure 10: Range of applicable scales for each family of technologies based on biomass thermal input power Figure 11: Technology and commercial readiness indices for the technology families Figure 12: GHG emissions of bioenergy compared to incumbents (E4tech based on FOEN, 2009; SFOE, 2008; SFOE, 2012) Figure 13: GHG emissions of biomethane relative to natural gas (E4tech based on SFOE 2008) Figure 14: GHG emissions of biofuels relative to gasoline (E4tech based on SFOE 2008) Figure 15: NO x and PM10 emission performance of wood boilers compared to alternative heating technologies (E4tech based on FOEN 2009 and SFOE 2012) Figure 16: NO x and PM10 emissions of electricity from wood compared to natural gas (E4tech based on FOEN 2009 and SFOE 2012)

5 List of Tables Table 1: Competing fossil and renewable options of heat from woody biomass in Switzerland Table 2: Competing fossil and renewable options of electricity from woody biomass in Switzerland 37 Table 3: Competing fossil and renewable options of liquid fuel from woody biomass in Switzerland 38 Table 4: Competing fossil and renewable options of gaseous fuel from woody biomass in Switzerland Table 5: Energy system benefits from using woody biomass for different energy end-uses Table 6: Greenhouse gas emissions data used Table 7: Comparison of GHG emissions benefits Table 8: NO x and PM10 emission data used Table 9: Comparison of air emissions benefits Table 10: Logistic, regulatory and social barriers for wood combustion and gasification technologies at different scales in Switzerland Table 11: Overview of benefits and assessment of selected technologies

6 List of acronyms 1G 2G 3G BFB BIGCC BioSNG BIOSWEET BtL CCS CFB CHP CO CNG CRI CTI DD EF EPFL FAME FOEN FT GJ GWh ICE IEA LHV MSWI NEP ORC PJ PM POM PSI PtG PV SCCER SFOE TRL UD US US DoE VOC First generation biofuels: derived from sugar, lipid or starch extracted from a plant Second generation biofuels: derived from cellulose, hemicellulose, lignin or pectin Third generation biofuels: cellulose, hemicellulose, lignin or pectin Bubbling Fluidised Bed Biomass Integrated Gasification with Combined Cycle Bio Synthetic Natural Gas BIOmass for SWiss EnErgy future Biomass to liquids Carbon Capture and Storage Circulating Fluidised Bed Combined Heat and Power Carbon monoxide Compressed Natural Gas Commercial Readiness Index Commission for Technology and Innovation Downdraft fixed bed Entrained Flow École polytechnique fédérale de Lausanne Fatty Acid Methyl Ester Federal Office for the Environment Fischer Tropsch Gigajoule Gigawatt Hour Internal Combustion Engine International Energy Agency Lower Heating Value Municipal Solid Waste Incineration New Energy Policies (scenario) Organic Rankine Cycle Petajoule Particulate Matter Policy measures (scenario) Paul Scherrer Institute Power to Gas Photovoltaic Swiss Competence Centre for Energy Research Swiss Federal Office of Energy Technology Readiness Level Updraft fixed bed United States United States Department of Energy Volatile Organic Compounds 6

7 Executive summary With the Energy Strategy 2050 the Swiss government has formulated an ambitious strategy for the Swiss energy system in which nuclear energy is phased out, efficiency measures reduce energy demand and renewable forms of energy displace nuclear and large shares of conventional fossil energy. To speed up the transition, the government increased financial support for energy research and has, amongst other things, facilitated the creation of seven Swiss Competence Centres in Energy Research (SCCER). The SCCER BIOSWEET (BIOmass for SWiss EnErgy future) which is coordinated by PSI, focuses on increasing the contribution of biomass to the Swiss energy system and has formulated a vision that by 2050 bioenergy could contribute an additional 100 PJ to the Swiss energy demand: 33 PJ from woody biomass, 33 PJ from bio-wastes and manure and 33 PJ from algae. This report is the result of a request from the Commission for Technology and Innovation (CTI) to the SCCER BIOSWEET to provide an independent comparison of wood combustion and wood gasification technologies and their potential impact on the Swiss energy transition. The report discusses woody biomass use for energy in Switzerland, the sustainable potentials and the projected bioenergy demand in the Energy Perspectives 2050 (Chapter 2); the status of wood combustion and gasification technologies (Chapter 3); the relevance of wood combustion and gasification technologies in the Swiss energy transition (Chapter 4); and the relevance of Swiss research and industry activities (Chapter 5). Wood biomass use in Switzerland Between 1990 and 2007 wood energy use in Switzerland stayed approximately constant between 30 and 35 PJ per year (weather-adjusted). Since 2008 however, consumption of wood for energy purposes has increased significantly, reaching a new peak of 46 PJ in 2013 (SFOE, 2014). In the New Energy Policies (NEP) scenario of the Energy Perspectives 2050 (Prognos, 2012) bioenergy plays an important role. Final bioenergy demand in Switzerland for heat and mobility purpose is projected to increase from 39 PJ in 2010 to 67 PJ in 2050, equivalent to about 15% of the total final energy demand. Reductions in the heat demand in the built environment and the rise of competing heating technologies (solar thermal, heat pumps) in the NEP scenario leads to a declining role for wood for heat beyond 2020 and the wood demand drops from 35 PJ in 2020 to 16 PJ in Even though the electricity generation from wood (excluding MSW power plants) increases from 1 PJ in 2013 (SFOE, 2014) to 4 PJ in 2050 (supply variant C&E, E in Prognos, 2012), the overall wood demand decrease opens up opportunities for other uses of wood. The sustainable wood potential of forest wood and waste wood for energy use in Switzerland is estimated to be around 42 PJ today (Steubing, 2010) and to increase to between 50 and 62 PJ in 2040 (Infras, 2004). Comparing this to the wood energy demand for heat in the NEP scenario in 2050 (16 PJ) and for electricity in the supply variant C&E, E (4 PJ) this means that between 30 and 42 PJ could be available for energy purposes in Switzerland. 7

8 Status of wood combustion and gasification technologies Within combustion and gasification there are multiple ways to convert wood into useful energy. In this study, we differentiate between five broad wood combustion and wood gasification technology families and assess their capability to deliver heat, power, liquid fuel and gaseous fuel: Combustion boiler to heat Combustion boiler + steam turbine / Organic Rankine Cycle (ORC) to electricity and heat Gasification + ICE to electricity and heat Gasification + synthesis to liquid fuel Gasification + methanation to gaseous fuel The technology families differ from one another on a number of different metrics: requirements for the downstream process, feedstock conversion efficiency, plant costs, the scales at which they can be operated and their technological maturity. The last two aspects are of most interest in the context of the relevance of the technologies to the Swiss Energy Strategy Figure 1 below shows which scales the different technologies are most suitable for when operated commercially. Heat-only applications are the only applications relevant at the smallest scale. CHP applications span from small scale (with gasification and ICE) to very large scale (with boiler and steam turbine). When technologically mature, the gasification + methanation route is expected to be applicable at about 30 MW scale whereas the gasification + synthesis to liquid fuel route is currently applicable at about 250 MW scale. It cannot be excluded however that research and development on, for instance, smaller reactors, makes these synthesis routes economically viable at smaller scale in the future. Figure 1: Range of applicable scales for each technology family based on feedstock thermal input power The technology and commercial readiness assessment (Figure 2) shows that all technologies are at least at the Technology Readiness Level 9 (system launch, test and operation) and Commercial Readiness Index 2 (Commercial trial at small scale). The gasification families (ICE, synthesis, 8

9 methanation) are behind the combustion families which all have multiple commercial applications (Commercial Readiness Index 4). The least mature technologies (gasification + synthesis to liquid fuel or methanation) have a significant number of projects in the pipeline with several developers planning to build early commercial plants. Gasification + methanation Gasification + synthesis Gasification + ICE Boiler + ORC Boiler + steam turbine Boiler TRL CRI Figure 2: Technology and commercial readiness indices for the technology families Relevance of wood combustion and gasification technologies in the Swiss energy transition The relevance of the combustion and gasification families to the Swiss energy transition has been assessed on the basis of the energy end services they can provide and the related energy system benefits, greenhouse gas emissions, air pollutant emissions as well as on the non-technical deployment barriers. Wood for heat only (combustion) Wood boilers can have a positive impact on the energy system when electric heating is displaced or avoided by decreasing the seasonal supply and demand gap in winter. GHG savings however are small compared to electric but more than 90% compared to heating oil and natural gas. Air pollution emissions increase compared to natural gas and alternative renewable technologies. Non-technical barriers are low making decentralised wood combustion for generating heat a useful application of woody biomass in Switzerland. Wood for electricity (combustion and gasification) Using wood for electricity (combined with heat, which is currently required to receive the feed-in tariff in Switzerland) increases the renewable electricity supply in Switzerland. The ORC and gasification + ICE technologies in particular have the additional benefit of being able to increase the load balancing capacity of the grid. The GHG intensity of electricity from woody biomass (typically between gco 2 /kwh) does not provide any GHG savings compared to the current Swiss production mix (24 gco 2 /kwh) but has similar emissions compared to the current Swiss consumption 9

10 grid mix (122 gco 2 /kwh). With the combustion route air pollution emissions will increase compared to conventional electricity generation but with the gasification + ICE route, emissions of NO x and PM10 can be better controlled with syngas cleaning. In practice, emissions are most likely to be driven by the regulations which will specify the allowable emissions levels and thus the required control technologies. Wood has a role to play in the Swiss energy system but siting issues (i.e., finding end-users for the heat, logistics and permitting) are likely to hamper its deployment. Wood for liquid and gaseous fuels (gasification) The gasification + synthesis to liquid biofuels and gasification + methanation routes obviously reduce the reliance on fossil fuels. Indirectly they can also lower future electricity demand when considered as a sustainable alternative to electric mobility. The potential GHG emissions savings compared to their fossil counterparts are more than 80% making them quite significant. Air pollution emissions are expected to be similar to conventional fuels. When techno-economically feasible, gasification to liquid and gaseous fuel would be the best use of woody biomass in Switzerland as they provide a unique alternative to step up the volume of renewable liquid and gaseous fuel. Aside from the relatively technological maturity, a large challenge for deploying wood gasification to liquid or gaseous fuel plants in Switzerland is feedstock logistics required for typical plant sizes (around 250 MW for liquid fuel and around 30 MW for gaseous fuel). In the light of the relatively low and scattered Swiss wood resource potential, it is unlikely that a gasification + synthesis to liquid biofuel plant will be realised in Switzerland. The 1.2 PJ wood required for a 30 MW gasification + methanation plant is however more likely to be realisable in the future. Conclusion On the basis of the above analysis by energy end-use we conclude that combustion and gasification of woody biomass can both bring significant benefits to the Swiss energy system. Wood use for energy purposes is limited by the sustainable wood potential and will therefore not be the most important renewable energy source of the future Swiss energy system. However, it is an important piece of the puzzle and has a unique storage potential, both as feedstock and in the form of its liquid and gaseous end-products. Wood combustion technologies are mature and have advantages compared to fossil fuels. From an energy system efficiency and climate change mitigation point of view the highest benefits however can be obtained when wood is used in gasification routes. Woodderived gaseous biofuels (and liquid biofuels imported from abroad) could provide a significant portion of the fuel demand in the transport sector, which has, aside from electrification, few other viable renewable alternatives in the near future. Before gasification can fulfil its promise in Switzerland, the affordability, simplicity, reliability and maintainability of the woody biomass to gaseous fuel technology needs to be improved. Swiss research institutes, which have groups focusing on these technological challenges as well as on mapping and securing supply chains, can contribute to the required technology advancement. 10

11 1 Introduction Together with partners PSI has successfully applied for an SCCER in the biomass area and now coordinates the BIOmass for SWiss EnErgy future (BIOSWEET) consortium. The focus of the activity, in line with the "Coordinated Energy Research in Switzerland" action plan is mainly on the production of biogas from wood, agricultural residues and algae via advanced fermentation, gasification and hydrothermal conversion pathways. In addition to these areas, PSI and its partners proposed researching advanced combined heat and power (CHP) concepts to generate electricity and heat from woody biomass. The overarching goal of the research is to push the current conversion and efficiency limits significantly to exploit the valuable biomass resources to the highest possible extent in order to approach the BIOSWEET vision of 100 Petajoules of additional sustainable energy for Switzerland by The Commission for Technology and Innovation (CTI) has requested the SCCER BIOSWEET consortium to provide a study showing the comparison of the impact to the energy revolution in Switzerland of both research topics wood combustion and wood gasification. In this context PSI has asked E4tech, as an independent advisor with specific bioenergy expertise, to determine the impact wood gasification and combustion technologies could have on the Swiss energy strategy 2050 by means of a literature study. This report is the result of PSI s request to E4tech and provides answers to the following main research questions: What is the commercial status/maturity (i.e. Technology Readiness Level) of the various conventional and advanced wood combustion and wood gasification technologies? What are their development needs, how likely are they to be deployed and in what time horizon? What role could woody biomass play in the future Swiss energy system and what could it contribute to the Energy Strategy 2050 of the Confederation? How can Swiss research and industry contribute to and benefit from the further development of wood combustion and wood gasification technologies? 11

12 2 Woody bioenergy use in Switzerland In this report the potential impacts of wood combustion and wood gasification technologies on the Swiss energy transition are reviewed. Even though wood is increasingly traded globally for energy purposes (Section 2.3) the domestic sustainable wood potential will be an important indicator for the amount of wood that can be used in the Swiss energy sector (the domestic sustainable wood potential as presented in literature is discussed in Section 2.2). Before we look at the characteristics of the selected combustion and gasification technologies in more detail in Chapter 3 and at their relevance to Switzerland in Chapter 4, we begin with a brief introduction of the Swiss bioenergy demand in the next section. 2.1 The Swiss Energy Strategy 2050 and the role for bioenergy in the Energy Perspectives 2050 The decision of the Swiss Federal Council and Parliament to phase out Switzerland s five nuclear facilities (announced in 2011) accelerated the plans to restructure the Swiss energy system and resulted in a long-term energy vision, the Energy Strategy 2050 and concrete policy packages. The Energy Strategy is informed by the Energy Perspectives (Prognos, 2012) which lays out a set of scenarios and variants between now and In the scenario where current policy measures are implemented effectively ( POM scenario), the projected total final energy demand decreases by 33% between 2010 and 2050 (from 841 PJ to 565 PJ). In the NEP scenario ( New Energy Policies the scenario at which the Energy Strategy 2050 is targeted) the final energy demand decreases even further, dropping 46% (from 841 PJ to 451 PJ). Bioenergy plays an important role in both the POM and NEP scenarios: total final bioenergy demand for heat and mobility in 2050 is projected to be 49 PJ in the POM scenario and close to 67 PJ in the NEP scenario (see Figure 3), equivalent to about 9% and 15% respectively of the total final energy demand in Switzerland in 2050 (compared to about 5% in 2014). In addition, the electricity generation from wood (excluding municipal solid waste incinerators) increases from 1 PJ in 2013 (SFOE, 2014) to 4 PJ in 2050 (supply variant C&E, E in Prognos, 2012) 1. The role of wood for heat in both the NEP and POM scenarios declines beyond 2020 in absolute terms (see Figure 3). The main reason for this is the lower heat demand in the built environment (a result of stringent energy efficiency standards for buildings) and the rise of competing technologies (solar thermal, heat pumps). However, despite the final wood energy demand for heat decreasing from 37 PJ in 2010 to 29 PJ in 2050, wood remains the most important bioenergy feedstock in the POM scenario, supplying about 60% of the combined heat and mobility bioenergy demand (49 PJ) in In the NEP scenario, the use of wood for heat drops significantly after 2020 (from 35 PJ in 2020 to 16 PJ in 2050), a result of using the sustainable feedstock potential for transport fuels rather than for heat. 1 It is assumed that electricity from wood is only generated in CHP plants so that only the additional energy input required to generate the electricity is accounted for here. In practice this means that the additional wood energy use is approximately equal to the electricity produced. This assumption makes sense if all the heat produced in CHP plants can be used to cover the forecasted heat demand. Otherwise more wood will be needed to produce electricity alone. 12

13 PJ / year Comparison of wood combustion and gasification technologies This is reflected in the projected demand for liquid biofuels in the NEP scenario which grows sharply from close to zero PJ in 2010 to 37 PJ in 2050 (55% of the combined bioenergy demand for heat and mobility) - about the same as the total woody bioenergy demand The NEP scenario suggests that beyond 2035, liquid biofuels come predominantly from second and third generation biofuels with up to 30 PJ of biofuel imports (Prognos, 2010). Bioenergy demand in Switzerland (POM and NEP scenario, heat and mobility) Liquid biofuels for transport 49.2 Biogas for transport Biogas, sewage gas Other solid biomass 10 Wood POM NEP POM NEP Figure 3: Final bioenergy demand for heat and mobility in Switzerland in different scenarios (PJ/year) As a consequence of the increased liquid biofuel demand, the biofuel share in liquid transport fuels (gasoline and diesel) will increase rapidly from less than 0.5% in 2014 to 8% (POM scenario) or 16% (NEP Scenario) by By 2030, the share of biofuels in the total transport fuel demand increases further to 27%. As concluded in a recent European study commissioned by fuel suppliers and car manufacturers (E4tech, 2013), it is unlikely that such high shares of biofuels can be taken up by the vehicle fleet in The fleet biofuel uptake capacity is constrained by blend walls which are the maximum biofuel concentrations that the engine or the emissions systems can tolerate. These are E10 for gasoline vehicles (5 10% ethanol in gasoline, depending on the model year of the vehicle) 2 and B7 for diesel vehicles (7% FAME in diesel) 3. Large scale penetration of drop-in biofuels is also unlikely in this timeframe as the supply of drop-in fuels will be too limited. The implications of the blend walls for the uptake of biofuel in the EU are laid out in the Auto-Fuel roadmap (E4tech, 2013). Uptake of biofuel shares above the current blend walls (7% for biodiesel and 10% for ethanol) requires adaptation of the fleet or production of drop-in fuels that are fully fungible with gasoline or diesel. Synthetic fuels produced from woody biomass are good candidates for producing drop-in biofuels, making the gasification process an important technology for the future, in particular if the NEP scenario were to become reality. 2 Ethanol concentrations higher than E10 are not tolerated by the engine as the higher oxygen content of ethanol compared to gasoline can lead to corrosion. 3 Newer diesel vehicles (EUR V onwards) have catalytic filters to reduce NO x and particulate matter emissions. These filters however can be damaged by the SO 2 in the biodiesel exhaust at concentrations higher than B7. 13

14 PJ primary / year Comparison of wood combustion and gasification technologies 2.2 Sustainable bioenergy feedstock potential in Switzerland Estimates for the domestic sustainable bioenergy potential vary across the different literature sources, but orders of magnitude are very comparable. Discrepancies stem from the assumptions made with respect to, e.g., the fraction of agricultural or forest residues that can sustainably be removed, and the use of different biomass category definitions. In this chapter we discuss the Swiss bioenergy feedstock potential as presented in different studies. General bioenergy feedstock potential The Energy perspectives study (Prognos, 2012) uses an estimate for the sustainable bioenergy potential in 2040 based on a study conducted in 2004 (Infras, 2004). The range of this estimate (from conservative to optimistic) spans from 96 PJ to 127 PJ of primary energy per year, see Figure 4. In the NEP scenario the high end of this range is used as a ceiling for bioenergy use in Switzerland, irrespective of whether the bioenergy is sourced domestically or from abroad. A more recent study (Steubing, 2010) reports a sustainable biomass feedstock potential of 82 PJ which is more or less in line with Infras (2004) conservative 2025 estimate of 80 PJ. This however does not include energy crops and biomass from meadowland. Taking the average of the conservative to optimistic range presented in Infras (2004) gives a primary energy supply potential of 112 PJ, which is consistent with the 69 PJ final bioenergy demand of the NEP scenario in 2050, assuming 50% conversion efficiency for the biofuels share. 140 Domestic biomass feedstock potentials Meadows Energy crops and cultivated fields cons. opt. cons. opt. Organic waste (industrial, commercial, households) Agricultural residues and manure Waste wood (process) Waste wood (end of life) Forest wood, hedges and horticulture Steubing 2010 Infras 2004 Figure 4: Domestic biomass feedstock potentials for energy according to Steubing (2010) and Infras (2004) Woody biomass potential for energy purposes Of the total current domestic sustainable biomass potential of 82 PJ as reported by Steubing (2010), about half (42 PJ) is made up of woody biomass feedstock types: industrial residues (11%), waste wood (17%) and forest wood (72%, of which 22% is wood from landscape maintenance). Infras (2004) estimate a slightly higher range for the Swiss sustainable woody biomass potential for 2025 of 14

15 PJ primary / year Comparison of wood combustion and gasification technologies 50 PJ to 62 PJ (Figure 4). In a recent study, Thees et al. (2013) conclude that a total domestic sustainable potential of 36 PJ exists for forest wood (excluding waste wood and wood from landscape maintenance) to be available for energy purposes; 12 PJ more than the sustainable forest wood potential estimated by Steubing. Woody biomass feedstock potentials in Switzerland Sustainable potential Used potential Remaining potential Waste wood Wood from landscape maintenance Industrial wood residues Forest energy wood Figure 5: woody biomass feedstock potential in Switzerland (Steubing, 2010) Of the sustainable woody biomass potential estimated by Steubing, 64% is already used, leaving currently a remaining sustainable wood potential for energy purposes of 15.2 PJ (see Figure 5) of which 8 PJ is represented by forest wood (the same remaining forest wood potential is presented by Thees et al., 2013). For almost two decades, wood energy use in Switzerland stayed constant between 30 and 35 PJ per year (see Figure 6). Since 2008 however consumption of wood for energy purposes significantly increased, reaching a new peak of 47 PJ in The lion s share (93%) is used for heat in households (41%), industry (21%), the service sector (15%), district heating (14%), and in agriculture and forestry (1%). Only 7% of the woody biomass is used to produce electricity, part of which is generated in municipal solid waste incinerators (SFOE, 2014). 15

16 Figure 6: wood energy use in Switzerland by feedstock type (source: SFOE, 201 4) When comparing the sustainable wood energy potentials with the actual wood energy use in Switzerland we can conclude that a significant share of the sustainable potential is already used. If the 2013 wood energy use (47 PJ) were to stay constant, the conservative scenario of Infras would suggest that there is only an additional 3 PJ unused sustainable potential of forest wood in the 2040 horizon and an additional 15 PJ in the optimistic scenario. However, in the NEP scenario, the final energy demand for heat (which almost equals primary energy demand) drops from 37 PJ in 2010 to 35 PJ in 2020 and 16 PJ in 2050, while electricity from wood increases from 0.5 PJ in 2013 to 1.5 PJ in 2020 and 4 PJ in 2050 (supply variant C&E, E in Prognos, 2012) 4. This means that by 2050 the unused potential of woody biomass in Switzerland would be 30 PJ in the conservative scenario and 42 PJ in the optimistic scenario of Infras (comparing against the 2040 sustainable potentials). The sustainable potentials discussed here exclude imports. Wood is becoming a commodity and intercontinental trade (especially from the US to Europe) is on the rise. In this report we have considered the Swiss domestic sustainable wood potential as a basis for analysing woody biomass potential role in the Swiss energy transition. However, wood imports and or imports of final energy products derived from it (with the exception of heat) can be an economically attractive proposition and, if stringent criteria are met, a sustainable one too. A perspective on international wood trade and Swiss wood energy use beyond the generation from domestic feedstock is presented below. 2.3 International wood trade Wood for energy purposes, also called wood fuel, includes various forms of woody biomass such as chips, pellets, sawdust, charcoal and firewood. Fuel wood is traded globally but typical transport 4 It is assumed that electricity from wood is only generated in CHP plants so that only the additional energy input required to generate the electricity is accounted for here. In practice this means that the additional wood energy use is approximately equal to the electricity produced. This assumption makes sense if all the heat produced in CHP plants can be used to cover the forecasted heat demand. Otherwise more wood will be needed to produce electricity alone. 16

17 distances depend on moisture content, heating value and bulk density of the feedstock type. Wood pellets perform best on these indicators and therefore represent the wood feedstock that is traded intercontinentally most. For European energy utilities, co-firing biomass in coal-fired power plants is one of the cheapest ways to increase the share of renewables in their electricity portfolio and meeting the EU renewable energy targets. Hence the EU-27 has become the largest producer of wood pellets with an estimated 10.5 million tonnes produced in 2012 (an increase of 57% compared to 2009) and net imports amounting to 4.5 million tonnes (EC, 2013). In 2012 most pellet imports came from North America (39%), Canada (30%) and Russia (14%). According to the same source, Switzerland produced 180,000 tonnes in 2012, imported 36,000 tonnes and exported 7,000 tonnes. In Europe on average almost 50% of the pellets is used for heating in the residential sector and the rest in industry, mainly to generate electricity. By contrast, Switzerland uses pellets almost only in the residential sector (Verhoest & Ryckmans, 2012). Globally the EU-27 is the largest consumer by far with about 70% of global consumption in The global demand is expected to grow rapidly and to almost quadruple between 2010 and 2020 (see Figure 7). This is mainly a result of the increased demand in the EU, which is driven by the 2020 renewable energy targets. Figure 7: Global consumption of wood pellets (O'Carroll, 2012) The Swiss perspective on import of wood bioenergy There are two ways to increase the woody biomass derived energy use in Switzerland: importing the feedstock or importing the final energy carrier. Advantages and disadvantages of these two alternatives are summarised below. 17

18 Importing the wood feedstock Depending on the energy end-use there are different arguments for importing wood. For the production of electricity and heat from wood, the most important argument for importing wood pellets in Europe is the attractive price of pellets from North America in combination with limited local supply and the storage capacity of the wood. This would not be very different for Switzerland although additional transport costs make the proposition slightly less attractive. In Switzerland, over the past six years, the pellet price has hovered around 8rp/kWh, about 2rp/kWh cheaper than heating oil and natural gas (with the exception of 2009 when heating oil dipped to around 7rp/kWh - the recent drop in crude prices suggests that the heating oil price will most likely drop too) (Prixpellets, 2015). Including costs for the installation and maintenance, a wood pellet system is slightly more expensive on a yearly basis than a system using natural gas or heating oil but in the same ballpark. Heating systems based on wood pellets are a viable, sustainable option in Switzerland. For liquid and gaseous biofuels there could be a different argument for importing woody biomass: reaping the benefits of deploying an advanced BtL or gasification plant. Domestic supply to deploy such a large facility (which is required to make the fuel competitive, see Section 3.1) is likely to be insufficient and hence would have to be complemented with wood from abroad. An important disadvantage of importing wood for any energy purpose from outside the EU is the risk of sustainability issues related to unsustainable forest management practices, or the perception thereof. Sourcing certified wood pellets could reduce this risk to some extent but an increase in wood energy use will offer ample sustainability challenges. Other arguments that speak against the import of woody biomass are the reduced energetic efficiency due to energy use in transport and the reduced security of supply. As long as pellets are a co-product of the wood industry (and from a sustainability perspective one could argue that this is a prerequisite), the supply of pellets depends on the health of the overall economy and the wood-using sectors in particular. Importing the final energy carrier An alternative way to increase the wood bioenergy consumption in Switzerland is to import the final energy carrier (with the exception of heat). A book and claim system with renewable certificates could be used for electricity and gaseous fuels (as well as liquid fuels that are already blended) produced close to the source of the woody biomass feedstock (e.g., Scandinavia) and delivered to Switzerland through the existing grids and distribution networks. The main advantages would be the ability to draw on a wider range or projects than are likely to be deployed in Switzerland and the flexibility to switch to alternatives if the wood energy sector does not develop. The main disadvantages would be a dependence on developments in other countries and a reduction in the Swiss electricity autonomy. 18

19 3 Status of wood combustion and gasification technologies In this chapter we start with a general overview of the combustion- and gasification-related wood to energy routes compared in this study (Section 3.1). Subsequently we discuss the characteristics, commercialisation status and techno-economics of the selected technologies. The results of the technology readiness assessment feed into Chapter 4, in which the relevance of the different wood combustion and gasification technologies for the Swiss energy transition is assessed. 3.1 Overview and scoping of technologies The aim of this study is to provide a comparative assessment of wood combustion and wood gasification technologies and their potential contributions to the Swiss energy transition. This translates into the question How can woody biomass best be used to be of greatest value to the Swiss energy system? To answer this question, we will compare different combustion and gasification technologies based on their techno-economic characteristics, the different energy services they can provide, and on their competitiveness compared to alternative fossil and renewable energy sources. A number of processes are required to convert the energy in woody biomass into the form of the end use. Depending on the quality of the wood and the chosen conversion technology, pre-treatment processes may be needed. In terms of the conversion processes, direct combustion of wood involves complete oxidation at very high temperatures, with the heat either used directly, used to generate electrical power, or to co-generate heat and electrical power. In the case of gasification, wood is first converted into a gas in a high temperature, low oxygen thermochemical process that produces synthesis gas. This syngas mainly contains hydrogen and carbon monoxide, and can then be used to produce heat and/or electrical power (through combustion of the syngas) or a range of chemicals, including liquid fuels (e.g., via Fischer-Tropsch or biological synthesis processes) and gaseous fuels (e.g., via methanation). Figure 8 presents a schematic of the main wood to bioenergy end-product routes using combustion or gasification technologies. Figure 8: Wood to bioenergy routes via combustion and gasification 19

20 There are multiple ways to convert wood into useful energy, and within combustion and gasification there are different generic types that vary in pre-treatment requirements, the temperature and pressure at which conversion takes place, how the biomass is fed into the gasifier or combustion chamber, the oxidant used (oxygen, air or steam), and whether the gasifier is directly heated (through partial combustion of the biomass feedstock), or indirectly heated using an external source. However, details of the specific technologies (e.g. updraft or downdraft gasifier, which are discussed in Section 3.2) do not have a major influence on the potential of the technology to play a role in the Swiss energy transition. In this study, we therefore use five broader wood combustion and wood gasification technology families and assess their capability to deliver energy (be it heat, power, liquid fuels and/or gaseous fuels) in a competitive environment: Combustion boiler to heat Combustion boiler + steam turbine / ORC to electricity and heat Gasification + ICE to electricity and heat Gasification + synthesis to liquid fuel Gasification + methanation to gaseous fuel Other gasifier applications exist, such as large scale biomass integrated gasification with combined cycle (BIGCC). However, BIGCC is only feasible at very large scale (typically over 150 MW th ) which is not realistic for the Swiss context given the limited sustainable woody biomass feedstock potential. 3.2 Technology status and commercial prospects In this section, in addition to a general description of the conversion technology family, we discuss: Feedstocks viable for the route, in terms of the likely types of feedstock that would be suitable for the gasification or combustion technology used, and how feedstock properties could affect the process Requirements of the downstream process, such as the degree to which syngas from the gasifier needs to be cleaned Process efficiency, accounting for the energy needed for feedstock preparation and drying, and to run the plant The development status of the system, in terms of whether it is at lab-scale, pilot stage, in demonstration, at commercial scale etc. Figure 9 shows the levels used in this assessment The typical throughput and physical scale of units, with likely minimum and maximum scales. Given that the technology families have different and sometimes multiple energy outputs, plant scales will be described based on thermal input to allow comparison across all the families. Costs, in terms of capital and operating costs, and the cost of the final product Technology commercialisation status metric In addition to the widely used technology readiness levels (TRL), the Australian Renewable Energy Agency (ARENA, 2014) has recently introduced the concept of commercial readiness index (CRI) which is particularly relevant to the technologies that are under consideration here because they span the range of commercial maturity from early commercial to widely deployed. We have adopted the CRI scale in the technology assessment below. 20

21 CRI 6 Bankable asset class 5 Widespread market competition 4 Multiple commercial applications TRL 3 Commercial scale up System test, launch and operations System/subsystem development Technology demonstration Technology development Research to prove feasibility Basic technology research Commercial trial, small scale 1 Hypothetical commercial proposition Figure 9: Technology Readiness Level (TRL) and Commercial Readiness Index (CRI) (ARENA, 2014) Please note that other organisations such as the European Commission (EC, 2014) have used different definitions of TRLs so the ratings below may differ from scorings in other publications Combustion boiler Technology description In a biomass boiler, the biomass fuel is burned to produce heat or steam that can be used for either process or space heating or to provide cooling using an absorption chiller. A typical biomass heat system comprises: Biomass handling where the fuel is discharged by delivery vehicle and held in storage until it is extracted to the boiler; Energy conversion conversion of the biomass in a boiler into heat or steam; Heat distribution heat is delivered from the boiler to the point of use. Biomass boilers for heating applications are available in a range of configurations depending on the scale and the intended biomass fuel type, in sizes from a few kilowatts up to several megawatts of thermal output. Broadly the combustion boiler configurations fall into five main categories which, in rough order of increasing thermal output are: Stoker burners: typically used for smaller applications below about 50 kw th, have a small grate and fuel inventory in the boiler resulting in a more responsive burner; Batch boilers: simple boilers also primarily for applications below about 50 kw th, where a large volume of fuel, typically split logs, is loaded into the boiler periodically; 21

22 Underfed stoker boilers: typically found in applications ranging from about kw th, these boilers have a slightly larger grate than stoker burners and are fed from the bottom to form a dome of combusting fuel; Moving grate boilers: most often found in applications larger than about 500 kw th, these boilers have a stepped grate down which the fuel progressively moves. The movement of the fuel down the grate helps to reduce clinkering the formation of large lumps of sintered ash and allows for carefully controlled combustion. This configuration has a larger grate and fuel inventory leading to a boiler with a slower response to load variations but that is also less sensitive to variations in feedstock. Fluidised bed boilers can either be of the bubbling (BFB) or circulating (CFB) varieties and are typically only used in applications larger than about 20 MW th. In fluidised bed combustion the fuel is combusted in a bed of sand that is kept fluidised by the circulation of air. Combustion in fluidised beds typically occurs at slightly lower temperatures than for grate combustors which reduces the risk of slagging and bed agglomeration. The large thermal mass of the bed makes the combustor largely insensitive to variations in feedstock. Fluidised bed boilers would typically not be used in a heat only configuration but have been included in this list for completeness. Feedstocks The range of allowable feedstock characteristics depends on the plant configuration and is listed below for each type. One of the most critical characteristics is moisture content with some boiler types requiring consistently dry feedstock and others being relatively insensitive to it: Stoker burners are most typically fuelled with pellets although units that operate on chipped wood exist. The small intense combustion zone and small fuel inventory in the boiler means that the boiler is more sensitive to fuel variability. The fuel particle size and moisture content must therefore be consistent. The fuel must typically have a moisture content less than about 30%. Batch boilers are most typically fuelled with standardized length split logs (e.g., 50 cm length). The fuel must be fairly dry, preferably with a moisture content of less than 25%. Underfed stoker boilers have a slightly larger fuel inventory than stoker burners and can thus tolerate a slightly larger range of fuel moisture contents and sizes. Moisture content typically needs to be in the 20-35% range although boilers with more refractory lining material can tolerate moisture contents up to 40%. Moving grate boilers have a wide tolerance of fuel types and moisture content (up to 60%) due to the relatively large fuel inventory in the boiler. Moving grate boilers are typically operated on wood chips and other waste woods, including wastes with higher ash content as the moving grate reduces the risk of clinkering. Pellets can be used but this may require flue gas recirculation to minimize temperatures over the grate; Fluidised bed boilers are designed to operate with an extremely wide range of feedstocks including those with high ash or moisture content such as sewage sludge and pulp and paper waste streams. For bubbling fluidised beds (BFB), feedstock size is not critical as oversize pieces of feedstock will be recirculated through the combustor until they are fully combusted. 22

23 Requirements of the downstream process There are no downstream processes for boilers in heat applications. However, larger biomass boilers, typically those larger than 100 kw th, may be subject to emissions regulations and may have abatement technologies such as cyclones, bag filters or electrostatic precipitators to remove particulates from the flue gas, as well as potentially for other emissions such as SO x and NO x (although these are typically not major concerns with biomass-fired boilers). In addition, most advanced biomass boilers have control systems that regulate the air and fuel supplies in the boiler and may also have oxygen and temperature probes to ensure that emissions are limited even during changes in boiler load. Efficiency The efficiency of biomass boilers is strongly dependent on the moisture content of the fuel, on the amount of excess air introduced into the boiler and on the percentage of any uncombusted fuel. Typical efficiency for boiler combustion units firing biomass is approximately 70 75% based on HHV. In recent years, condensing pellet boilers have also been introduced that have efficiencies as high as 94 95% although clearly such high efficiencies can only be achieved with tightly controlled fuel quality. Development status Biomass fired boilers for the provision of heat are a mature technology (TRL 9) with markets well established in mainland Europe and North America, with tens of thousands of units installed and millions of hours of operation logged. However, the primary market in terms of volume is the residential market and the supply of pellets to residential customers is still maturing which leads to biomass boilers being assessed as having a CRI of 4 5. Scale Biomass boilers range in size from a few kilowatts of thermal output for the smallest residential pellet boilers to 7 10 MW th. At larger scales, CHP installations are usually more financially attractive than heat only applications, plus the number of sites demanding very large quantities of heat is limited. Costs Installed costs for biomass boilers range dramatically with their size. Small essentially residential pellet boilers less than about 50 kw th cost in the range of 1,500 2,600 US$/kW th. Commercial units ranging in size from 100 to about 1 MW th, cost in the range of 600 1,300 US$/kW th. Whereas large units, in the MW th scale, cost in the range of US$/kW th (Holzenergie.ch, 2011; E4tech, 2014) Combustion boiler + steam turbine / ORC Technology description Biomass boilers for electricity generation can either be co-fired with other solid fuels or run just on biomass. Only dedicated biomass-fired systems will be considered in this section as co-firing with 23

24 other solid fuels such as coal is not relevant to the Swiss context. Please note that co-firing of biomass-derived synthetic natural gas (biosng) with natural gas will be discussed in Section 4.1. Biomass-fired power plants consist of three main sub-systems: Biomass handling where the fuel is discharged, prepared and stored until it is transported to the boiler; Energy conversion conversion of the biomass in a boiler into heat or steam; Power production and heat delivery conversion of the steam into electricity in a steam turbine generator, or of the heat into electricity using an organic Rankine cycle (ORC). The plants may also include heat delivery using hot water or steam extraction from the steam cycle or from the condenser of the ORC. Two main types of combustion systems are used for energy conversion for steam cycles: grate, pulverised and fluidised bed combustors. Grate boilers, described in Section 3.2.1, are typically only used in small to medium systems less than about 50 MW electrical capacity (or up to about 160 MW th input). Fluidised beds will typically be bubbling (BFB) or circulating (CFB) types and are used for systems larger than a few MW electrical capacity. For ORC plants, biomass boilers with thermal output of about 1 MW th to 10 MW th are required so these will typically be of the larger configurations discussed in Section 3.2.1, namely grate boilers or fluidised bed boilers for systems larger than about 2 MW th input. For steam plants used exclusively for electricity production, a standard condensing steam turbine cycle is used where remaining heat from all the steam from the turbine is eliminated in a condenser before the feedwater is sent back to the boiler. If the plant is also providing heat in a CHP application, a number of different configurations are possible. The heat load can take the place of the condenser, or alternately, intermediate pressure steam can be extracted from the turbine to meet the heat load with the remaining heat being eliminated in a condenser as before. Biomass-fired ORC plants will typically only be used in CHP applications due to their relatively low electrical efficiency. For ORC plants, heat is extracted from the ORC condenser and will be in the form of hot water, typically at about C due to the lower operating temperatures of the cycle. Advantages of the ORC approach are that the boiler is simplified due to lower operating pressures and temperatures and that the system is capable of a wider range of part load operating conditions than conventional steam plants. Feedstocks The range of feedstocks that can be used in the system depends on the type of combustor in the boiler. As for all biomass boilers, fuel moisture content is a critical parameter. Grate boilers can handle a reasonable range of fuel types and moisture contents up to 60% due to the relatively large fuel inventory in the boiler. Grate boilers are most typically operated on wood chips and other waste woods. Pellets can also be used but this may require flue gas recirculation to limit temperatures over the grate. Fluidised bed combustors can accept a very wide range of fuels including those with high moisture content due to the large thermal mass of the combustor bed and the stability that this provides to the combustion process. Essentially any form of woody biomass (e.g., chips, forestry and sawmill 24