Clean fossil-fuelled power generation

ARTICLE IN PRESS Energy Policy 36 (2008) 4310–4316 Contents lists available at ScienceDirect Energy Policy journal homepage: www.elsevier.com/locate/enpol Clean fossil-fuelled power generation$ Tony Oliver K-S Tech Ltd., Tanglewood, Woodland Avenue, Cranleigh, Surrey GU6 7HZ, UK a r t i c l e in f o Keywords: Clean fossil a b s t r a c t Using fossil fuels is likely to remain the dominant means of producing electricity in 2030 and even 2050, partly because power stations have long lives. There are two main ways of reducing CO2 emissions from fossil-fuelled power plants. These are carbon capture and storage (CCS), which can produce near-zero CO2 emissions, and increases in plant efficiency, which can give rise to significant reductions in CO2 emissions and to reduced costs. If a typical UK coal-fired plant was replaced by today’s best available technology, it would lead to reductions of around 25% in emissions of CO2 per MW h of electricity produced. Future technologies are targeting even larger reductions in emissions, as well as providing a route, with CCS, to zero emissions. These two routes are linked and they are both essential activities on the pathway to zero emissions. This paper focuses on the second route and also covers an additional third route for reducing emissions, the use of biomass. It discusses the current status of the science and technologies for fossil-fuelled power generation and outlines likely future technologies, development targets and timescales. This is followed by a description of the scientific and technological developments that are needed to meet these challenges. Once built, a power plant can last for over 40 years, so the ability to upgrade and retrofit a plant during its lifetime is important. & 2008 Queen’s Printer and Controller of HMSO. Published by Elsevier Ltd. All rights reserved. 1. Current status In its World Energy Outlook, the International Energy Agency (2004) looks out to 2030 and predicts that globally, fossil fuels will remain the dominant means of producing electricity. New power plants with a capacity of 1400 GW are expected to be built to 2030, and most of these are predicted to be fossil fuelled. (Compare this with the current, total installed capacity of 76 GW in the UK.) Power plant lifetimes can often exceed 40 years, so it is easy to postulate that fossil-fuel power generation will still be dominant in 2050, particularly considering the large amounts of new fossil plant being built and planned in China and south-east Asia. This places great importance on our ability to produce new fossil-fuelled technologies that have low CO2 emissions and also on new technologies suitable for upgrading plant to reduce their current level of emissions of NOx, SOx and, in particular, CO2. The Government has recognised the importance of fossil fuels in power generation and has produced a corresponding strategy (Department of Trade and Industry, 2005) for developing carbon abatement technologies. The objective of the strategy is: ‘‘To ensure the UK takes a leading role in the development and $ While the Government Office for Science commissioned this review, the views are those of the author(s), are independent of Government, and do not constitute Government policy. commercialisation of Carbon Abatement Technologies that can make a significant and affordable reduction in CO2 emissions from fossil fuel use’’. Both Government and industry (Department of Trade and Industry, 2005) have recognised that there are two main routes for reducing CO2 emissions from fossil-fuelled power plant (see Fig. 1):  carbon capture and storage (CCS), which can produce near-zero CO2 emissions; and  increases in plant efficiency, which can give rise to significant reductions in CO2 emissions and to reduced costs of electricity. As may be seen from Fig. 1, these two routes are linked and they are both essential activities in the pathway to zero emissions. This paper focuses on the second route, while being directly complementary to the first—it is essential that CCS is based on the most efficient underlying technology because of the efficiency penalty associated with CCS. An additional third route for reducing emissions will also be covered here, this being the use of biomass such as energy crops, food-processing residues or forestry waste. Biomass can be co-fired with coal, replacing some of the coal with a renewable fuel, or it can be used in dedicated biomass plant. Fossil-fuelled power generation technologies have improved continuously since the first steam engines of the industrial 0301-4215/$ - see front matter & 2008 Queen’s Printer and Controller of HMSO. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.enpol.2008.09.062 ARTICLE IN PRESS 4311 T. Oliver / Energy Policy 36 (2008) 4310–4316 Strategy trajectories Key issue will be value of CO2 'Zero emissions' trajectory (= C) Carbon reduction 'Increased efficiency' trajectory (= E) Zero emissions will need the most efficient plant Near-term Mid-term Long-term Time Fig. 1. Strategy trajectories and their interactions. Table 1 Status of plant types (2004) Technology Status Capital costs (£/kWe($/kWe)) Performance Issues Pulverised coal with flue gas desulphurisation and selective catalytic reduction Commercial, strong position, supercritical 850 (1300) Up to 46% efficiency Leading, proven technology Integrated gasification combined cycle High-efficiency plant at commercial demo stage 1100 (1700) Depends a lot on gas turbine: 41–45% efficiency Perceived as clean Reliability of gas turbine Complex Fluidised bed combustion Commercial, niche market for poor fuels and expanding market position 800–1000 (1200–1500) Up to 40% efficiency Competitive for low-grade fuels Fuel cells Some are commercial Small types at commercial demo 41700 (42500) 40–60% efficiency, depending on type Still developing, costs falling Could be significant for distributed generation Gas turbines Commercial, strong position 330–470 (500–700) for 41 MWe Small: 33% Mid: 42% Mid-size and micros currently niche Included in combined heat and power Combined cycle gas turbines 60% Up to 50% for large internal combustion engines Internal combustion engines Commercial, strong position for distributed generation 270–400 (400–600) Leading, proven technology for up to 20 MW Hydrogen-fuelled Pilot-scale demos N/A Unknown (zero CO2 from plant) Could need new infrastructure Novel cycles Demos N/A Targeting 50–70% For example, Kalina, CO2 recycling, recuperation, condensing cycles Note: N/A: no commercial plant. revolution. The main pathways to increased efficiency currently include:  gas turbines for higher-temperature gas combustion and hence improved efficiencies; and  improved gasifiers for converting coal and heavy oils to  advanced boilers to produce steam at higher temperatures and  pressures; improved steam turbines to handle higher temperatures and pressures and to convert thermal energy with greater efficiency; synthesis gas. The main fossil-fuel power generation technologies and their status (Advanced Power Generation Technology ARTICLE IN PRESS 4312 T. Oliver / Energy Policy 36 (2008) 4310–4316 Forum, 2004) are shown in Table 1. The main technologies in use today for centralised plant are pulverised coal and gas turbines. The historical improvement in fossil plant efficiency is shown in Fig. 2 for coal and gas. The average efficiency for coal-fired power plant in the UK is around 35%. If this plant was replaced by today’s best available technology, which would have an efficiency of around 45%, it would lead to reductions of around 25% in emissions of CO2 per MW of electricity produced. The improvements in efficiency require advances in enabling technologies, systems and underpinning sciences such as in high-temperature materials, modelling and simulation to optimise combustion processes, process heat integration, novel sensors and advanced control systems. While much has been achieved, there is still substantial potential for further improvement. For example, as can be seen from Table 1, current best available technologies for coal have conversion efficiencies of up to 46–47%, but there is potential to increase this to 60%. Similarly for natural gas power generation, efficiencies could be increased from the present 55–60% to 70–75%. The coal-fired technologies are also relevant to electricity generation from biomass. Using current plant technology and current biomass stock to produce a constant 10 MWe with an efficiency of 35% requires approximately 4000 ha of biomass planting. Achieving 60% efficiency for solid fuels would result in a reduction of this acreage by approximately 40% or would produce approximately 70% more CO2-neutral power from the same acreage. Fig. 2. Efficiency improvements and impact on CO2 emissions. Table 2 Technology targets for fossil-fuel plant Electrical efficiency using coal Electrical efficiency using gas CO2, NOx, SOx, particulate emissions Reliability, availability and maintainability (RAM) Costs 2005+ 2010+ 2020+ Best available technology Best available technology Best available technology Best available technology Cost-effective generation 50% 65% Near zero Better than current values Cost-effective generation 60% 70–75% ARTICLE IN PRESS 4313 T. Oliver / Energy Policy 36 (2008) 4310–4316 be done as soon as possible and early enough to allow commercial plants to be built on the scale necessary to meet the challenges of CO2 reduction. These technologies need to include both coal and gas and be suitable for new plants and for retrofit to existing plant. To achieve this, the industry (Advanced Power Generation Technology Forum, 2004) has set some ‘stretch’ development 2. Future technologies and development goals The primary goal is to contribute significantly to UK targets on competitiveness and security of supply and global targets on reducing CO2 emissions by demonstrating a range of costcompetitive fossil-fuelled power plant technologies. This needs to Steam Gasifier Desulphurisation Boiler feed water Coal Steam turbine and generator Water wash Ash/slag Gas turbine Air Oxygen Nitrogen Air separation unit Coal preparation Air Heat recovery boiler Heat recovery steam generator Chimney Steam HP pump GT system Air Feed water Steam turbine Combustor Condenser LP pump N-gas To deaerator Hydrogen fuel Anode 4H + 4e + Electrolyte Cathode +- 2H2 H ions pass through -+ O + 4e + 4H 2 2 LOAD 2HO Oxygen, usually from the air Fig. 3. Principles of advanced power generation technologies: (a) integrated gasifier combined cycle; (b) combined cycle gas turbine; and (c) fuel cell principle (example shown is the alkaline fuel cell). ARTICLE IN PRESS 4314 T. Oliver / Energy Policy 36 (2008) 4310–4316 Table 3 Matrix of options Short term Medium term Long term Pulverised coal Gas turbines Circulating fluidised beds Pulverised coal (ultra-supercritical) Gas turbines Circulating fluidised beds (supercritical) Gas turbine hybrids (limited market penetration) Gasification (limited market penetration) Fuel cells (limited market penetration) Gasification Fuel cells Gas turbines/gas turbine hybrids Novel cycles targets for the near and medium term and these are given in Table 2. There are several power plant technologies for fossil fuels and biomass at various stages of research or development that may have the potential to meet the targets and aim points in a costeffective way within the specified timeframe. For centralised power plant, the following have been judged to be the key medium- or longer-term technologies for UK research, development and demonstration:  Pulverised coal-fired plant equipped with flue gas desulphur    isation and operating at supercritical steam temperatures, possibly designed to be capture-ready for later addition of CCS. Circulating fluidised beds, which have combustion systems able to utilise low-grade coal, biomass and wastes and operating at supercritical steam temperatures. Integrated gasification combined cycle, in which coal or biomass is gasified; currently integrated with gas turbines but could also be integrated with fuel cells (see Fig. 3a). A gasifier could also be linked to an existing combined cycle gas turbine, allowing fuel switching from gas to coal/solid fuels. Gas turbines, which can be integrated with other plant such as in combined cycle gas turbines (see Fig. 3b). More complex cycles, such as wet cycles or inter-cooled recuperative cycles, can also be used. Fuel cells, a strong contender for distributed generation, could become a key component in any future hydrogen economy (see Fig. 3c). They could also be integrated with other technologies such as gas turbines and gasification for centralised power plant. The chosen key power plant technologies have the potential to achieve the aim points and this will result in significant reductions in CO2 emissions from future fossil-fuelled power plant. All these technologies could be used in a future supply system that needs to have a balanced portfolio to meet demand. The gasification technology also has the potential to produce hydrogen for the transport sector and the distributed generation sector with near-zero emissions, using coal and CCS or biomass as a feedstock. In order to meet the technology targets and challenges set out above, the priorities for the key plant technologies have been defined by industry and Government using the matrix of technology options shown in Table 3. Ultimately, new plant technologies will need to be demonstrated at full scale, hence the inclusion of physical demonstration in the list, both to gain operational experience and to reduce the investment risks attached to new untried designs. The timescales for demonstration are linked to the strategic target dates shown in Table 2. To be successful, the research and development themes will need to be driven by these same timescales. 3.1. Basic research This theme covers a broad range of activities, including the study of basic processes and research and development in relation to underpinning technologies that are incorporated into power generation plant and are crucial to its design and performance. Work of this type has traditionally been undertaken in universities and research establishments with input from industry. The main research areas are listed in Table 4. The main topics to be considered within these underpinning sciences were identified by the Advanced Power Generation Technology Forum (2004) as:  Combustion—Modelling, flame stability, pollutant production, co-firing with biomass, diagnostic techniques.  Materials—High-temperature materials, alloy development,            coatings, fracture mechanics, corrosion, fatigue, creep, materials processing, repair, lifetime prediction and modeling. Electrochemistry—fuel cells. Catalysts—Fuel cells, combustion, pollutant removal, gas separation, fuel processing. Membranes—Fuel cells, gas separation. Control and instrumentation—Intelligent, ‘wireless’ for harsh conditions. Fuel science—Hydrogen production from fossil fuels, decarbonisation of fossil fuels, gasification, ash properties, biomass. Manufacturing methods—Advanced materials, thin films, membranes, low-cost processes. Mathematical modelling—Fluid flow, heat transfer, interactions with chemistry, dynamic modelling, combustion modeling. Component life integrity—Lifing studies, creep, fatigue. Electronics—Electrical systems integration. Carbon clean-up—Preparation, including reforming, of fuels for fuel cells. Aerodynamics—Turbines, compressors. The benefits of basic research are threefold: 3. Themes for research, development and demonstration  It generates knowledge that diffuses into industry and can In order to develop these technologies, three main research, development and demonstration themes must be addressed:   basic research;  components and technologies; and  physical demonstration.  be integrated in the evolutionary development of existing systems. It supplies more innovative ideas for devices and processes for development into new products for manufacture. It provides a sustained supply to industry of high-quality engineers and scientists. ARTICLE IN PRESS Aerodynamics T. Oliver / Energy Policy 36 (2008) 4310–4316 * * * * * * * * The power plants of the future are likely to be more complex than those of today, with more integration of different supporting technologies. Some power plants may also be providing hydrogen as a by-product for transport or for distributed generation. This means that research, development and demonstration needs to consider not only the individual components and technologies but also their integration. This theme covers innovative design studies of the supporting technologies and their integration, up to and including the manufacture of small-scale prototypes. Work of this type tends to be undertaken through collaboration between universities, research organisations and industry. For the key medium- and longer-term power plant technologies, the following supporting technology areas that need further research, development and demonstration were identified by the Advanced Power Generation Technology Forum (2004) as:  Combustion technology—For gas turbines, pulverised coal-fired * * * * * plant and circulating fluidised beds plants.  Low-NOx combustion for pulverised coal-fired plant and circulating fluidised beds plants.  Co-fuelling with biomass—Technologies for dealing with biomass together with fossil fuels.  Mercury capture—Removal of mercury from power plant * * * * * * * * * emissions. * Fuel science Manufacturing Mathematical models Component life integration Electronics * 3.2. Components and technologies  Fuel flexible gasification—For gasification with either coal   * * * * * * * * *      * * * * *    * *  (including low-rank coals), biomass or waste fuels. Optimisation and integration. Gasification—Durability of refractory, plant availability and cost reduction. Hot gas clean-up—Pollutant removal from higher temperature gas streams. High-temperature heat exchangers—For operating at higher temperatures. Hybrid or novel cycles—Development of existing technologies that will make up the cycle, systems integration etc. Reformers and fuelling for fuel cells—For use with fossil fuels. Electrochemical processes for fuel cells—For process development. Membranes—For fuel cells and gas separation (O2/N2, CO2/N2). Component integrity—For components operating in more extreme conditions. Control systems—For increased performance, reduced emissions, increased safety, etc. Fuel handling—Particularly for some biomasses. Plant manufacture—For advanced manufacturing methods giving high-quality components at lower cost. Virtual demonstration—Computer-based plant simulation systems that ultimately go beyond design to virtual demonstration. * * * * * * * * * * 4. Novel cycles for the longer term Gasification Fuel cells Gas turbines Pulverised coal-fired plant Circulating fluidised beds Novel cycles Technology Combustion Materials Electrochemistry Catalysts Membranes Control and instrumentation  Table 4 Basic research areas 4315 In addition to the key power plant technologies discussed above, there are some other cycles that are less developed but which could contribute in the longer term. Most of these are of interest because of their potential to reduce CO2 emissions for a given power output. Some of the cycles being considered are described below. Advanced gas turbine cycles: Several cycles are at various stages of development. These include cycles with recuperation, water injection or humid air, all of which are aiming at increasing efficiency. Hybrid cycles are also being investigated; one example being a fuel cell being integrated into a gas turbine cycle. ARTICLE IN PRESS 4316 T. Oliver / Energy Policy 36 (2008) 4310–4316 Direct coal-fired combined cycle plant: One variant of this is like an integrated gasification combined cycle plant in that a gas turbine and steam turbine can be used in a combined cycle. However, in this case, the coal is burnt directly in the gas turbine without previous gasification. The presence of coal particles inside the turbine pose technical problems, but the cycle has the potential to give efficiencies of over 50%. Underground coal gasification: For the UK, the interest in this technology is in the in situ gasification of deep underground coal seams that are difficult to mine. Oxygen and water are pumped into the underground seam where gasification takes place. The product gas is then brought to the surface and fed into a gas-fired power plant. Advanced gasification and polygeneration: For the longer term, more advanced gasification-based power cycles are being developed. Examples include incorporating fuel cell technology to enable a ‘triple cycle’ and perhaps ‘polygeneration’, with the power plant operating more as an ‘energy plant’ producing a slate of products from electricity and heat, to liquid transport fuels, specialty chemicals and hydrogen. CCS because they help offset the efficiency penalty that is associated with most CCS technologies. Government and industry research and development programmes are setting long-term targets for power plant efficiencies which, if they are achieved, will produce significant reductions in CO2 emissions compared to the current installed technologies. However, to reach these targets, it is essential that research and development is carried out on the key underpinning sciences. The development of a new power plant technology is expensive, with long lead-times and development of the underpinning sciences is a key component in this development. Also, once built, a power plant can last for over 40 years, so the ability to upgrade and retrofit a plant during its lifetime to meet new regulations etc. is also important. This again will put demands on the development of science and technology. For these reasons, the support of research, development and demonstration into technologies that will improve the efficiency of power plant is important and, in conjunction with CCS, will help deliver secure, clean electricity in the coming decades. References 5. Conclusions Globally, as well as in the UK, fossil-fuelled power generation is likely to remain the dominant means of producing electricity for the foreseeable future. Developments leading to increases in plant efficiency are vital because they lead directly to a reduction in CO2 emissions for a given power output. They are also beneficial for Advanced Power Generation Technology Forum, 2004. A Vision for Clean Fossil Power Generation, Advanced Power Generation Technology Forum, 2004. UK Foresight Programme, Department of Trade and Industry, London. Department of Trade and Industry, 2005. A Strategy for Developing Carbon Abatement Technologies for Fossil Use. Department of Trade and Industry, London. International Energy Agency, 2004. World Energy Outlook. International Energy Agency, Paris.