Feb 28, 2005 - coal plants appear to be an alternative for the future. .... will also identify some successful coal gasification projects in North America to highlight .... is the concept of changing the coal to a gas before burning and electricity ...
Coal Gasification BUEC 560 Prof Joseph Doucet
Prepared by:
Cheng-Hsin Chang 28 February 2005
Executive Summary Coal is widely known as a cheap and dirty fuel. Despite that reputation, coal-fired plants once dominated the electricity generation market.
Nevertheless, with the
emergence of cheap natural gas and the increasing importance attached to protecting the environment, that market landscape has changed. The coal industry has slowed in pace and although coal is still cheap, it has failed to compete with clean-burning natural gas. However, the same two causes of coal’s decline may serve as catalysts for new technology in the future.
Increased natural gas prices, increased focus on reduced
emissions and the wealth of coal reserves have recently stimulated the research and development of coal gasification. Now, Integrated Gasification Combined Cycle (IGCC) coal plants appear to be an alternative for the future. IGCC plants boast negligible pollution emissions, reduced carbon dioxide emissions (greenhouse gases), reduced solid wastes and increased efficiencies compared to conventional coal plants. These benefits are not without barriers. IGCC plants are capital intensive at $1400/KW hence relatively uncompetitive when compared to natural gas plants. Gasification technology is still developing and generally unproven as it generates twice the amount of carbon dioxide as natural gas plants. Based on world coal reserves of more than 200 years, it is clear that IGCC will continue to be developed as the most probable replacement for conventional coal plants. Whether coal gasification is the final answer will depend on natural gas reserves, prices and IGCC technological advances. Coal gasification is a promising technology that needs to be further developed until it can become economically viable for the future of the coal industry.
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Table of Contents Executive Summary ......................................................................................................... ii Table of Contents............................................................................................................ iii List of Figures ............................................................................................................ iii 1. Introduction................................................................................................................. 1 2. Conventional Coal ...................................................................................................... 2 3. Coal Gasification ........................................................................................................ 5 4. Current US Programs .................................................................................................. 8 5. Future Demands ........................................................................................................ 11 6. Conclusion ................................................................................................................ 13 References...................................................................................................................... 14 End Notes....................................................................................................................... 15
List of Figures Figure 1 – Proved Coal Reserves at end of 2003................................................................ 1 Figure 2 – Pulverized Coal (PC) fired plant ....................................................................... 3 Figure 3 - Coal and Gas Prices ........................................................................................... 4 Figure 4 - Integrated Gasification Combined Cycle ........................................................... 5 Figure 5 - Polk Power Station............................................................................................. 9 Figure 6 - World Energy Demand .................................................................................... 11
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1. Introduction Coal has been a source of energy for man and has contributed to the development of great historical events since 1,000 BC. Coal has satisfied simple needs such as cooking and heating. It also spurred on the development of the steam engine for transportation and was instrumental during the industrial revolution. Now coal is but one input in the fuel mix for electricity generation among many man has discovered. In the past two decades, the lower cost of generation through natural gas and increased awareness of the environment have led to a decline in the development of coal-fired plants. Nevertheless, coal is still abundant around the modern world (Figure 1). For this very reason, coal is beginning to regain its prominent position in the world energy market. The development of an Integrated Gasification Combined Cycle (IGCC) coal plant could represent the future of the coal industry. IGCC development has stemmed from poor conventional coal practices, environmental concerns, increasing natural gas prices and growing energy demands around the world.
Figure 1 – Proved Coal Reserves at end of 20031
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This paper will discuss the comparison of conventional coal plant operations to coal gasification based on an integrated gasification combined cycle system. This paper will also identify some successful coal gasification projects in North America to highlight recent technological developments in gasification highlighting some of the positive and negative advantages of IGCC. Finally, it will present the outlook for the coal industry and coal gasification.
2. Conventional Coal Historically, coal was a great source of energy, accounting for 74% of the world energy consumption in 19372. Since the discovery of oil and natural gas, along with the increase of technology to allow for the cheap harnessing of energy, coal has declined in use. Coal is now primarily used for electricity generation, accounting for 40% of the world’s electricity supply. Coal consumption has in fact increased by 50% from 1975 to 1990. Although not as widely used for different applications, coal is still the most abundant of all fossil fuels in the world. Its reserves are at 60% compared to oil and natural gas, which are each at 20%3.
In 2001, these reserves were estimated to
sufficiently provide for about 216 years of production compared to oil and natural gas, at 40 and 62 years respectively. In North America, coal represents approximately 91% of all reserves. In terms of Canadian reserves, there are approximately 90 years worth of coal reserves compared to eight and nine years for oil and natural gas.
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Canada is home to 24 coal electricity generating facilities that account for 20% of the total electricity generation, second only to hydropower. Most of these coal plants are traditional coal-fired plants that are based on a pulverized coal (PC) plant (Figure 2). These traditional plants simply take raw coal and pulverize it for burning. The resulting heat is then used for creating steam to turn turbines, generating electricity.
This
traditional method of generation is quite inefficient at only 33-38% system efficiency, heat rates of 10,000 BTU/KWh, as well as emitting high concentrations of nitrogen
Figure 2 – Pulverized Coal (PC) fired plant4
oxides (NOx), sulphur oxide (SOx), carbon dioxide (CO2) and other particulates. Nitrogen oxide and sulphur oxide are key actors in creating smog and acid rain. Carbon dioxide has been identified as a major contributor to greenhouse gases, which cause global warming. Due to growing concerns for the environment, many upgrades have been added to the process for minimizing NOx and SOx emissions. These upgrades (scrubbers) come at a high cost and still leave coal plants as heavy polluters compared to natural gas plants. Consider a simple case study of a 500-megawatt coal plant5, which generates approximately 3.5 billion kilowatt-hours per year of electricity through burning 1,430,000 tons of coal along with leaving 2.2 billion gallons of water and 146,000 tons of
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limestone. The same plant emits approximately 10,000 tons of sulphur oxide (SOx), 10,200 tons of nitrogen oxide (NOx), 3.7 million tons of carbon dioxide (CO2), 500 tons of small particles, 220 tons of hydrocarbons, 720 tons of carbon monoxide (CO), 125,000 tons of ash and 193,000 tons for sludge from its smokestacks.
Natural gas burns far cleaner than coal since it is a gas. Natural gas has no solid waste material such as ash and it emits 43% fewer carbon molecules per unit of energy released. Natural gas also produces low emissions of sulphur oxide (SOx) and particulate matter. With these competitive emission results and lower costs, natural gas has become a favoured alternative to coal. Throughout the past two decades, natural gas plants have been appearing while coal plants have been aging. The increased pressure for global environmental protection, with goals set out by programs such as the Kyoto protocol, has compounded the challenges for coal plants.
Kyoto has set out a goal to reduce
greenhouse gases by 5.2% from levels taken in 1990. However, the coal industry is not a sunset industry yet. Although there is high pressure from low natural gas prices and Coal and Gas Prices 40.00
30.00 4.0
25.00 20.00
3.0
15.00
2.0
10.00 1.0 0.0 1985
concern
environmental
protection,
for coal
35.00
5.0
5.00 1990
1995
2000
0.00 2005
Coal - US $/ tonne
Gas - US $/ MMBTU
6.0
increased
retains the largest supply of energy reserves in the world.
Coal
technology has been increasing and with rising natural gas costs
Year Natural Gas
Figure 3 - Coal and Gas Prices6
Coal
(Figure 3), more utilities are reinvestigating the future economics
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of the coal industry. It is quite clear from Figure 3 that coal prices have been declining steadily for the past two decades, but have risen recently, while natural gas prices have been steadily rising. However, capital costs for coal and natural gas plants are still dramatically different as coal plants cost approximately $1300/KW, while natural gas plants cost $600/KW. Based on these concerns for environment and costs, the coal industry has been actively working on improving coal plants for the future.
3. Coal Gasification One solution that is gaining more attention is coal gasification. Coal gasification is the concept of changing the coal to a gas before burning and electricity generation. There are three types of gasification processes currently: the moving bed, fluidized bed and the entrained flow. The most popular gasification method is used in Integrated Gasification Combine Cycle (IGCC) coal plants (entrained flow method), Figure 4.
Figure 4 - Integrated Gasification Combined Cycle7
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The process begins with the feedstock, coal going into a gasifier. The gasifier converts the coal into a gas through heat and high pressure mixing with air or pure oxygen. This process is tightly controlled so as not to burn off too much of the fuel as a synthetic gas, “syngas”, is produced. The syngas is a mixture composed primarily of hydrogen (H2), carbon monoxide (CO) and other gaseous constituents.
C + ½ O2 (heat + gasification) → CO
}
C + H2O (heat + gasification) → CO + H2
Syngas
This process also facilitates a cleaner separation of the solid materials from the coal instead of the traditional ash that results. The syngas is then treated for the removal of hydrogen sulphide (separates to hydrogen and sulphur), ammonia and particulate matter. The cleaned syngas is then burned as a fuel in a combustion turbine, similar to that of a natural gas turbine. The resulting hot air is used to generate electricity through the turbine and the exhaust heat is recovered into a heat exchanger that creates steam and generates electricity through a second turbine. This duel system is commonly known as a combined cycle, which allows for a more efficient process of generation. This combined cycle can currently operate with 45% efficiency (heat rates of 8400 to 8600 BTU/KWh range) and future growth to 60% efficiency or higher, well above current coal plants but below natural gas plants. This higher efficiency not only saves money for the plant but it also reduces the waste of coal resources and allows for extension of resource reserves. The efficiency also lowers the emissions of carbon dioxide (CO2) by as much as 40% compared to conventional coal plants. The nature of the gasification process also reduces
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sulphur oxides (SOx) and even eliminates nitrogen oxides (NOx), therefore making great strides in almost near zero emissions for actors in acid rain and smog. The use of pure oxygen in the gasifier also allows for easier separation of carbon dioxide (CO2). Although the emissions of carbon dioxide are reduced, they are still a major problem as a greenhouse gas.
The Integrated Gasification Combined Cycle (IGCC) plant is still costly, at $1400/KW for capital investment, and uncompetitive compared to natural gas and conventional coal plants. The carbon dioxide (CO2) emissions still double that of natural gas plants. The possibility of sequestering carbon dioxide (CO2) would only add to the costs, unless a positive use could be found for the CO2 (currently, possible uses are being explored in drilling activities). However, other economic benefits could be factored into the IGCC process, such as reduced costs of cleaning ash, ability to sell the separated sulphur or ammonia, and the production of pure hydrogen for future fuel cell technologies. This system can also be used with a variety of feedstock beyond simply coal, adding flexibility for future feedstock costs. The design can also be conducted as upgrades to current coal plants, which will potentially reduce the capital costs required for future projects. The increased use of gasifiers are also continually improving its efficiencies and lowering capital costs. Currently, there are approximately 385 gasifiers in operation on 117 projects worldwide for production of liquid fuels, chemicals, synthetic natural gas and ammonia for fertilizer demonstrating the positive potential for further improvements. Capital cost cuts will continue as gas turbine technology advances and becomes more efficient. Furthermore, the continued difference between coal and
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natural gas prices may work in favour of coal technologies if natural gas continues to rise in price.
4. Current US Programs Although the Integrated Gasification Combined Cycle (IGCC) plants are still developing, the technology has been promoted since the 1980s through the US Department of Energy (DOE). Throughout the 1980s and 1990s, the Department of Energy started the “Clean Coal Technology” program, which combined joint ventures with public and private sectors to develop and demonstrate technologies for burning coal cleanly. This was a significant program as it generated demonstrations that were large enough to move onto commercialization of technology for the industry. The program consisted of 35 projects and the participation of 18 States. The original goals of the program were the reduction of acid rain and smog agents, namely sulphur dioxide and nitrogen oxide. The program targeted three main areas of interest: environmental control technologies, coal processing for clean fuels, and advanced electric power generation. For IGCC projects, the main boost for advancement came in 1990 when the Department of Energy introduced federal cost sharing through the Clean Coal Technology program for the construction of the first commercial IGCC plants. Four major projects were built: the Polk Power Station in Florida, the Wabash River Coal Gasification plant in Indiana, Kentucky Pioneer IGCC Demonstration Project in Kentucky, and the Pinon Pine IGCC Power Project in Nevada. Further momentum was added to the program as the federal government implemented the Clean Coal Power Initiative (CCPI) in 2002 to further
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reduce emissions through committing $2 billion dollars over a 10 year period to develop and demonstrate new technologies for burning coal cleanly.
The Polk Power Station, Wabash River Coal plant and the Pinon Pine IGCC plant projects are all complete with promising results. The Polk Power Station (Figure 5) set out to demonstrate the commercial viability of an entrained-flow IGCC plant. The project was successful in removing over 97% of sulphur, limiting nitrogen oxide emissions to 0.7 lb/MWh (0.2 lb/MWh lower than the permitted limit) limiting particulate material emissions to 0.04 lb/MWh (5% lower than conventional coal plants) and carbon dioxide emissions to an average 7.2lb/hr (well below the 99 lb/hr permit). However, the project did observe poor carbon conversion at approximately 90% vice the expected 98% range of efficiency.
The overall project economics began with a capital cost of
$1650/KW (2001$) and the lessons learned have reduced capital costs to about $1300/KW (2001$)8. The Wabash Project had similar goals of developing an entrained flow system of IGCC but focused on the use of high-sulphur bituminous coal. The results were similar to that of the Polk Project, as it had observed good reductions in emissions of sulphur oxide, nitrogen oxide and carbon Figure 5 - Polk Power Station10
monoxide9. Finally, the Pinon Project set out
to demonstrate a fluidized-bed IGCC aided at operating low-BTU gas turbines. The emission results were also favourable in this project as sulphur oxide, nitrogen oxide and carbon dioxide were reduced by 95%, 70% and 20% less than conventional coal plants
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respectively11. The lessons learned and the success of these projects continues to bring the capital costs down and encourage further technology development for coal gasification.
Building on the success of the Clean Coal Technology program, the Department of Energy is now conducting research concentrating on improved efficiency, fuel flexibility and increasing economic benefits.
These are all being explored through
developing the flexibility of a variety of feedstock or combination of feedstocks. Reductions in costs of construction and operations continue to be a key issue in order to make IGCC coal plants competitive in the future against conventional coal plants and more importantly natural gas plants. Other options being researched are lowering costs of oxygen production for the gasification, increasing the efficiency of separating the syngas and its products to reduce losses, and improve carbon conversion percentages. Finally, additional work is being done on commercializing the waste products from the entire process in terms of the solid wastes, hydrogen and carbon dioxide.
All of these great initiatives and partnerships through the Department of Energy’s Office of Fossil Energy are working towards making coal gasification and clean coal a reality in the future. This is clearly stated in their program performance goal, “By 2010, develop advanced power systems capable of achieving up to 50 percent thermal efficiency at a capital cost of $1000 per kilowatt or less for a coal-based plant.”12
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5. Future Demands Based on the increasing energy demands around the world it is becoming very clear that the abundant reserves of coal cannot be overlooked in the future. However, mounting environmental concerns and lower costs of oil and natural gas are strong barriers for further development of coal plants. The forecast of world energy demands by the International Energy Agency clearly indicates that the current oil and natural gas reserves will not be sustainable in the future (Figure 6). Developing countries such as China, India and Brazil will demand more energy and fossil fuels at a rapid pace, overtaking the consumption demands of North America and Europe.
World Energy Demand
Mtoe (million tonnes of oil equivalent)
14000 12000
Other renewables
10000
Hydropower
8000
Nuclear power
6000
Coal
4000
Natural gas
2000
Oil
0 1971
2000
2010
2020
Year
Figure 6 - World Energy Demand13
These numbers combined with the distribution of world coal reserves (Figure 1) demonstrates the importance of promoting clean coal technology now. This sentiment is shared around the world as Integrated Gasification Combined Cycle plant projects are emerging in Europe, China, India, Japan, Australia and Britain. China, the world’s 11
largest producer and consumer of coal, has begun developing and researching coal gasification through joint projects lead by such companies as Shell. Similar projects in Japan included a joint venture with Chevron Texaco to build a 342-megawatt IGCC power plant. This trend also extends to many major private energy corporations such as American Electric Power (US’s largest utility), Cinergy, General Electric (GE), Chevron Texaco, Royal Dutch/Shell and Conoco Phillips who are all active in developing gasification technology or IGCC processes. These future demands and trends all support the fact that new coal technologies are very important for the world energy mix.
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6. Conclusion The coal industry is heading into the future with positive improvements. It is clear that the gasification of coal is a viable technology for the future but still faces several barriers in the short term. The barriers to entry for the development of further Integrated Gasification Combined Cycle (IGCC) coal plants are: •
Its high capital cost of $1400/KW that remains uncompetitive compared to conventional coal plants and natural gas plants;
•
The competitive prices of natural gas; and
•
Relative immaturity in technology.
Although based on the trend of support and development across North America, through such programs as Clean Coal Technology in the US, and around the world it is safe to say that IGCC coal plants have much to offer. The demonstrated advantages for IGCC are as follows: •
Almost zero emissions of SOx and NOx combined with reductions in CO2, solid wastes and pollutants;
•
Improved operating efficiencies to 45% and possible future efficiencies above 60%;
•
Improved economics of selling by-products such as sulphur and ammonia, along with possible integration with future fuel cell technologies through hydrogen; and
•
Flexibility with feedstock fuels and upgrade abilities to existing conventional coal and natural gas plants for cost reductions.
The benefits are great for this technology but until the barriers for entry begin to lower, IGCC will not progress at a competitive pace. However, continued support for research and development will pay high dividends for the future of world energy markets.
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References 1. Carlson, C.R. (2003), “Clean Coal Technologies: Can they help meet Alberta’s climate change commitments?”, paper for CABREE, Edmonton, Alberta, 2003. 2. Bonskowski, R. (2005), “The Outlook for Coal Utilization in the United States”, presentation for 2005 APEC Clean Fossil Energy Technical and Policy Seminar, Cebu, Philippines, 2005. EIA website. Internet: http://www.eia.doe.gov/cneaf/coal/page/f_p_coal/apec_jan2005_coal_outlook.pdf. 3. National Energy Board (2003). “Canada’s Energy Future Scenarios for Supply and Demand to 2025”, Calgary, AB. 4. Valenti, M., “Coal Gasification: An Alternative Energy Source is Coming of Age”, Mechanical Engineering, issue January 1992, pg 39-43. 5. Burr, M.T., “Coal Gasification Gets Real”, Public Utilities Fortnightly, issue January 2005, pg 42-47. 6. Valenti, M., “Bringing Coal into the 21st Century”, Mechanical Engineering, issue February 1995, pg. 68-74. 7. Pless, D.E. and Jenkins, S.D., “Coal’s Clean Comeback”, Civil Engineering, issue September 1996, pg. 46-49. 8. Canadian Clean Coal Technology Roadmap, Natural Resources Canada website. Internet: http://www.nrcan.gc.ca/es/etb/cetc/combustion/cctrm/htmldocs/news_e.html. 9. Coal in Alberta, Alberta’s Natural Resources website. Internet: http://collections.ic.gc.ca/ABresources/inventory/resources_hydro_coal_charact_alberta.h tml. 10. Coal, Natural Resources of Alberta website. Internet: http://www.lethsd.ab.ca/mmh/grade4/altaresources/coal.htm. 11. Coal, BP website. Internet: http://www.bp.com/subsection.do?categoryId=113&contentId=2014978. 12. Gasification Technology R&D, US DOE Office of Fossil Energy website. Internet: http://www.fe.doe.gov/programs/powersystems/gasification/index.html. 13. Remucal, J., “Clean Coal Technologies”, Your Planet Earth website. Internet: http://www.yourplanetearth.org/article.pl?sid=01/09/26/1634232. 14. Coal Gasification, Clean-Energy US website. Internet: http://www.clean-energy.us/. 15. Clean Energy, Union of Concerned Scientists website. Internet: http://www.ucsusa.org/clean_energy/renewable_energy/page.cfm?pageID=60. 16. Clark, P., “New Electricity Technology” presentation for TransAlta, Ft. McMurray, 2002. Internet: http://www.aeri.ab.ca/sec/new_res/docs/ASRA_pres_clarke.pdf. 17. Coal Combustion and Gasification, Combustion Research Facility website. Internet: http://www.ca.sandia.gov/crf/research/combustionProcesses/coalResearch.php. 18. Discussion on Coal Gasification (IGCC), Recovered Energy website. Internet: http://www.recoveredenergy.com/d_igcc.html. 19. Clean Coal Technologies, Australian Coal Association website. Internet: http://www.australiancoal.com.au/cleantech.htm. 20. Coal Gasification for future Power Generation, Fluent website. Internet: http://www.fluent.com/about/news/newsletters/04v13i2/s8.htm.
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End Notes 1
Coal Reserves, BP website. Internet: http://www.bp.com/genericarticle.do?categoryId=113&contentId=2014980. 2 Natural Resources of Alberta website. Internet: http://www.iclei.org/EFACTS/COAL.HTM. 3 National Energy Board (2003). “Canada’s Energy Future Scenarios for Supply and Demand to 2025”, Calgary, AB, pg. 72. 4 Natural Resources of Alberta website. Internet: http://www.iclei.org/EFACTS/COAL3.GIF. 5 Union of Concerned Scientists Citizens and Scientists for Environmental Solutions website. Internet: www.ucsusa.org/clean_energy/renewable_energy/page.cfm?pageID=60. 6 BP Statistical World Review of Energy 2004, BP website. Internet: www.bp.com/statisticalreview2004. 7 US Department of Energy Office Fossil Energy website. Internet: http://www.fe.doe.gov/programs/powersystems/gasification/howgasificationworks.html. 8 US Department of Energy Office Fossil Energy website. Internet: http://www.netl.doe.gov/cctc/factsheets/tampa/tampaedemo.html. 9 US Department of Energy Office Fossil Energy website. Internet: http://www.netl.doe.gov/cctc/factsheets/wabsh/wabashrdemo.html. 10 US Department of Energy Office Fossil Energy website. Internet: http://www.fe.doe.gov/programs/powersystems/gasification/index.html. 11 US Department of Energy Office Fossil Energy website. Internet: http://www.netl.doe.gov/cctc/factsheets/pinon/pinondemo.html. 12 US Department of Energy Office Fossil Energy website. Internet: http://www.fe.doe.gov/programs/powersystems/gasification/index.html. 13 Energy Development in China presentation, United Nations Framework Convention on Climate Change website. Internet: http://unfccc.int/files/meetings/workshops/other_meetings/application/vnd.mspowerpoint/yang.ppt.
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