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 Advanced Coal-Fueled Power Generation

Coal currently accounts for more than half of the electricity generated in the United States, and is also the dominant fuel source for power production in rapidly-growing countries such as China and India. Because coal is such an important resource in so many major economies, the development and deployment of affordable, efficient new coal technologies that produce less CO2 is key to meeting targets for reducing CO2 in coal-dependent countries.

As a fuel, "coal" spans a diverse range of characteristics, with quality characteristics such as Btu content, sulfur, ash, varying widely among sources. Because of this, and because of different needs among consumers and different requirements for emission controls, there is not a single universal "best" system for using coal. All of the coal-using technologies are seeing technological improvements, enhancing their ability to remain competitive under shifting market and regulatory conditions.

Pulverized Coal (PC) Technologies

Most plants today use pulverized coal (PC) technology, in which the coal is finely ground, mixed with air, and blown into a boiler for efficient combustion. High-pressure steam produced in the boiler passes through a steam turbine, which drives an electric generator. The pressure and temperature of the steam produced in the boiler are often used as shorthand to characterize the design features of PC plants.

Currently, the majority of coal-fired boilers in the United States are subcritical, where the pressure and temperature are below the critical point of water. Subcritical plants are well established and relatively easy to control, with overall energy conversion efficiencies in the range of about 30% to almost 40% (calculated using the higher heating value of the coal).

Higher efficiencies can be achieved by increasing steam temperature and pressure to supercritical conditions. Some 400 supercritical (SC) coal-fired power plants are currently operating around the world, including a large fleet in the United States. To prevent premature wear, supercritical plants require careful control of water chemistry and metal temperatures, but today they are just as reliable as subcritical plants. 

To gain further efficiency, so-called ultra-supercritical (USC) plant designs have been introduced in Europe and Asia and are now being developed for the United States as well. Steam temperatures in initial USC units will be about 1100°F (600°C), with the goal for future designs being 1400°F (760°C) or higher, which translates to an energy conversion efficiency of approximately 50%. As USC plant designs cross the 1250°F (670°C) threshold, they will require more-expensive, nickel-based alloys for high-temperature components. A sustained commitment to materials technology development is needed to produce these advanced alloys, address field fabrication and repair issues, gain approval from industry standards organizations and insurers, and optimize plant designs for their use.

Fluidized-Bed Combustion (FBC) systems

Developmental advances are also under way for another direct combustion technology. Fluidized-bed combustion (FBC) systems are already being selected for new generation capacity, especially where inexpensive, hard-to-burn fuels such as lignite and solid waste are available.

Advanced fluidized-bed combustion (FBC) technology offers a viable power generation option for the post-2000 time frame.  Commercial FBC units operate at competitive efficiencies, cost less than today's units, and have NOx and SO2 emissions below levels mandated by Federal standards. 

FBC systems fit into essentially two major groups, atmospheric systems (FBC) and pressurized systems (PFBC), and two minor subgroups, bubbling or circulating fluidized bed. However, technology advancements have created several variations, including:

Integrated Gasification Combined Cycle (IGCC)

Integrated gasification combine cycle (IGCC) technology is a new method of using coal to produce electricity, heat, and possibly other products. Compared to conventional pulverized coal-fired systems, IGCC offers potentially greater efficiency and lower emissions. Additionally, the IGCC process is inherently better suited to the capture and storage of CO2, should those emissions also need control.

The heart of gasification-based systems is the gasifier that converts hydrocarbon feedstock into gaseous components by applying heat under pressure in the presence of steam. A gasifier differs from a combustor in that the amount of air or oxygen available inside the gasifier is carefully controlled so that only a relatively small portion of the fuel burns completely. This “partial oxidation” process provides the heat. Rather than burning, most of the carbon-containing feedstock is chemically broken apart by the gasifier's heat and pressure, setting into motion chemical reactions that produce “syngas.” Syngas is primarily hydrogen, carbon monoxide and other gaseous constituents, the proportions of which can vary depending upon the conditions in the gasifier and the type of feedstock.

The hot raw syngas is cooled and purified by technologies that are commonly used in natural gas purification and oil refining. The generated syngas is then used in one or a combination of many product applications – syngas for gaseous fuels, liquid fuels, chemicals, and/or power generation. The traditional market for gasification has been synthesis gas production as an intermediate step in the production of important chemicals, such as ammonia for fertilizer. Application of gasification in other markets is emerging due to market changes associated with improved gas turbines, deregulation of electric power generation, and stringent environmental mandates.

In integrated gasification combined-cycle (IGCC) systems, the syngas is cleaned of its hydrogen sulfide, ammonia and particulate matter and is burned as fuel in a combustion turbine (much like natural gas is burned in a turbine). The combustion turbine drives an electric generator. Hot air from the combustion turbine is channeled back to the gasifier or the air separation unit, while exhaust heat from the combustion turbine is recovered and used to boil water, creating steam for a steam turbine-generator.

The use of these two types of turbines - a combustion turbine and a steam turbine - in combination, known as a “combined cycle,” is one reason why gasification-based power systems can achieve unprecedented power generation efficiencies. Currently, gasification-based systems can operate at around 45 percent efficiencies; in the future, these systems may be able to achieve efficiencies approaching 60 percent. (A conventional coal-based boiler plant, by contrast, employs only a steam turbine-generator and is typically limited to 33-38 percent efficiencies.)

Utilities and power generators are investing their own money and resources in the development of these and other clean coal technologies. For example, integrated gasification combined-cycle (IGCC) technology shows promise in producing electricity with ultra-low pollution levels. Two electric utilities – Tampa Electric and Duke Energy – currently operate small IGCC plants. AEP, Duke Energy Indiana, and Southern Company have announced plans to build additional IGCC plants.

The economics of IGCC technologies demonstrated so far in the United States are less favorable for lower-rank coals such as subbituminous or lignite that predominate the resource in certain regions, as the technologies currently work best using the higher-rank bituminous coal typical of many commercially mined coal depos­its east of the Mississippi River. Design changes or success with the advanced, dry-feed compact gasification systems now under development by DOE and industry partners may eventually make IGCC more economical for low-rank fuels.

Oxy-combustion

More recently, oxy-combustion — the burning of pulverized coal in pure oxygen separated from air — has emerged as a potential combustion option for the future. Oxy-fuel combustion is being developed for both turbine power cycles and for pulverized coal plants.  Pulverized coal oxy-fuel combustion burns fossil fuels in a mixture of recirculated flue gas and oxygen, rather than in air. The resultant flue gas has a high CO2 concentration, mixed with water vapor, particulates, residual oxygen, and SO2. This alternative is attracting increased attention because the high-concentration CO2 stream would be more amenable to separation for long­term storage.

An optimized oxy-combustion power plant will have ultra-low emissions. Oxy-fuel power cycles can use coal syngas containing both CO and H 2 for combustion in a turbine cycle. Temperatures are controlled by recycled water (or CO2) in a complete power system. Advances in systems that can properly manage oxygen combustion and CO2 recycling and purification will require additional development work before full-scale demonstration, and new methods of oxygen production may be needed to make oxy-combustion technology economical.
 

FutureGen

FutureGen is an initiative to build a first-of-its-kind coal-fueled, near-zero emissions power plant. The plant, to be located in Mattoon, Illinois, will establish the technical and economic feasibility of producing electricity from coal (the lowest cost and most abundant domestic energy resource), while capturing and sequestering the carbon dioxide generated in the process. The initiative will be a government/industry partnership to pursue an innovative "showcase" project focused on the design, construction and operation of a technically cutting-edge power plant that is intended to eliminate environmental concerns associated with coal utilization.

The project will employ coal gasification technology integrated with combined cycle electricity generation and the sequestration of carbon dioxide emissions. The project will be supported by DOE’s ongoing coal research program, which will also be the principal source of technology for the prototype. The project will be led by the FutureGen Industrial Alliance, Inc., a non-profit industrial consortium representing the coal and power industries, with the project results being shared among all participants, and industry as a whole.

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AES Corporation has started the construction of a $46-million emissions-reduction project at its AES Greenridge coal-based plant in New York, which will extend the life of the plant by more than 20 years. AES’s IPL subsidiary will soon complete a 10-year, $600-million multi-pollutant reduction initiative to lessen the impact of the utility’s coal-based plants on the environment while maintaining competitive rates.

AES Eastern Energy, a subsidiary of AES Corporation, and Praxair Inc. plan to research and demonstrate improved CO2 capture technologies for new and existing electric generation facilities in New York. They will focus on opportunities to create capture-ready technology designs for new generation plants and low-cost retrofit options for existing generation facilities, including oxyfuel combustion of coal.

CoalFleet for Tomorrow was launched in November 2004. This initiative seeks to accelerate the deployment and commercialization of clean and efficient advanced coal power systems, thereby preserving coal as a vital component in the electric generation mix. More than 50 organizations — including various types of power generators, suppliers, engineering firms, DOE, and other U.S. and international organizations — are participating in this program. CoalFleet is tackling the technical, economic, and institutional challenges of making advanced coal power plants a prudent investment option in both the short- and long-term, while taking into account the potential for future CO2 emissions regulations.
http://www.epriweb.com/public/000000000001014845.pdf

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Clean Energy Systems, Inc., "Kimberlina: A zero-emissions demonstration plant" (June 2007)
http://www.cleanenergysystems.com/news/june_07.html

Clean Energy Systems Inc. (CES) has developed a zero-emissions power generation technology by integrating a component proven in the aerospace industry with conventional power plant equipment. Its most distinctive element (the third box from the left) is an oxy-combustor, similar to one used in rocket engines, that generates steam by burning a clean, gaseous fuel in the presence of gaseous oxygen and water. The clean fuel is prepared by processing a conventional fossil fuel such as coal-derived syngas, refinery residues, biomass or biodigester gas, or natural or landfill gas.

Electric Power Research Institute, “Coal-Based Generation at the Crossroads”, EPRI Journal (Summer 2005)
http://mydocs.epri.com/docs/CorporateDocuments/EPRI_Journal/2005-Summer/1012149_CoalBasedGeneration.pdf

Offering clean electricity generation from an abundant fuel, advanced coal technolo­gies seem tailor-made for a power industry facing ever-tighter environmental regula­tions. But committing to new approaches — and the inevitably higher cost of first-of-a-kind units — is always a difficult business proposition. To help break through the final barriers to market acceptance, EPRI is leading an industry-driven initiative to speed the deploy­ment of new clean coal plants and support the development of next-generation designs.

Electric Power Research Institute, “CoalFleet for Tomorrow"
http://www.epriweb.com/public/000000000001014845.pdf

CoalFleet for Tomorrow ("CoalFleet") is an industry-led, broad-based collaborative research program founded with the goal of making a portfolio of advanced coal technologies more accessible and affordable for power producers and society. Key to achieving this goal is the near-term deployment of advanced coal power systems to resolve the technical, economic, and institutional challenges facing advanced coal technologies through real-world experience (i.e., learning by doing). The result will be a self-sustaining commercial marketplace offering prudent investment options capable of satisfying society's energy demands and environmental concerns both in the short term and over the long term.

Electric Power Research Institute, “66 CoalFleet for Tomorrow - Future Coal Generation Options”
http://mydocs.epri.com/docs/Portfolio/PDF/2007_P066.pdf

EPRI and the electricity industry are accelerating research in coal generation technology. The long-term vision of this investment is a new fleet of highly efficient, low-emission, moderate-cost, and flexible coal-fueled power plants. The enormous potential payoff of this acceleration in R&D—on the order of $300 billion to $1.3 trillion—would primarily accrue to the power-consuming public in terms of abundant power from this economic fuel, a cleaner environment, and improved national and economic security. Working toward this vision of cleaner, cost-effective, and high performance coal power generation, EPRI's program is  evaluating new coal generation technologies (such as gasification combined-cycle and ultra supercritical steam cycle plants, fluidized-bed combustion, and co-production of power, heat, and chemicals), and promoting promising options to commercialization.

Electric Power Research Institute, “Generation Technologies For a Carbon-Constrained World”, EPRI Journal (Summer 2006)
http://my.epri.com/portal/server.pt?space=CommunityPage&cached=true&parentname=
CommunityPage&parentid=0&in_hi_userid=234&control=SetCommunity&CommunityID=260&PageID=486

Planning future generation investments can be difficult in the context of today’s high fuel costs and regulatory uncertainties. Of particular concern are sharp changes in the price of natural gas and the possibility of future mandatory limits on the atmospheric release of CO2. Research on advanced coal, nuclear, natural gas, and renewable energy technologies promises to substantially increase the deployment of low- and non-carbon-emitting generation options over the next two decades. Prudent power providers are likely to invest in a number of these advanced technologies, weighing the advantages and risks of each option to build a strategically balanced generation portfolio.

FutureGen Alliance, "Clean Energy Starts Here - FutureGen"
http://www.futuregenalliance.org/

FutureGen is a public-private partnership to design, build, and operate the world's first coal-fueled, near-zero emissions power plant, at an estimated net project cost of US $1.5 billion. The commercial-scale plant will prove the technical and economic feasibility of producing low-cost electricity and hydrogen from coal while nearly eliminating emissions. It will also support testing and commercialization of technologies focused on generating clean power, capturing and permanently storing carbon dioxide, and producing hydrogen. In the process, FutureGen will create unique opportunities for scientific exploration, education, and stakeholder engagement.

Nexant, Inc.,  "The Environmental Footprints and Costs of Coal-Based Integrated Gasification Combined Cycle and Pulverized Coal Technologies" (prepared for the U.S. Environmental Protection Agency, EPA-430/R-06-006, July 2006)
http://www.epa.gov/air/caaac/coaltech/2007_01_epaigcc.pdf

This EPA Report provides information on the environmental impacts and costs of IGCC technology relative to conventional pulverized coal (PC) technologies. The technical report concludes the following:
1. IGCC thermal performance (efficiency and heat rate) is significantly better than current generation pulverized coal technologies in the US;
2. Future generation, ultra-supercritical pulverized coal technologies may match or exceed current IGCC thermal performance;
3. IGCC results in better environmental performance, including lower air emissions of criteria pollutants, lower water usage, and lower solid waste generation requiring landfilling, than conventional PC plants;
4. IGCC has a potential advantage in capturing and sequestrating CO2 at lower costs; and;
5. IGCC has higher capital costs than conventional PC plants.

O'Keefe, Luke. F., et al.,  "A Single IGCC Design for Variable CO2 Capture" (2001)
http://www.berr.gov.uk/files/file22061.pdf

This 10-page paper by engineers from Texaco Power and Gasification, Jacobs Engineering, and GE Power Systems examines using a 900 MW IGCC powerplant configured to remove 75% of the feed carbon and CO2 precombustion. Carbon is removed from the fuel at relatively high concentration, allowing coal to be used as a fuel with low CO2 emissions. The flow scheme is designed such that the power plant can be built and operated without CO2 removal, and then later upgraded to low CO2 emissions at minimal additional cost.

Perrin Quarles Associates, Inc., “Review of Potential Efficiency Improvements at Coal-Fired Power Plants” (prepared for the Clean Air Markets Division, U.S. Environmental Protection Agency, April 17, 2001)
http://www.cier.umd.edu/RGGI/documents/Stakeholder%20Comments/Data_coaleff_epa_2001.pdf

This study reviews available data on potential and actual efficiency improvements at coal-fired utilities. The objective was to identify heat rate reductions or efficiency improvements that have taken place due to either optimization efforts at existing utility boilers or due to the use of newer advanced technologies for coal combustion.

SFA Pacific, Inc., “Gasification – Worldwide Use and Acceptance” (prepared for U.S. Department of Energy, Office of Fossil Energy, National Energy Technology Laboratory, and the Gasification Technologies Council, January 2000)
http://www.netl.doe.gov/publications/brochures/pdfs/SFAgasifi.pdf

A database was developed to collect and organize information on specific facilities where gasification technology is employed. The database was compiled based on information on gasification technologies and projects available from nonproprietary public reference sources.

U.S. Department of Energy, National Energy Technology Laboratory, “Clean Coal Power Initiative: Bibliography"
http://www.netl.doe.gov/technologies/coalpower/cctc/ccpi/bibliography/ccpi_bibliography.html

The CCPI bibliography page provides access to all project-specific information as well as general program information. The links are grouped by Demonstration Project Documents, Program and General Documents, and related information on a wide array of topics that are related to the general category of clean coal.

U.S. Department of Energy, National Energy Technology Laboratory, “Fluidized-Bed Combustion Program"
http://www.fossil.energy.gov/programs/powersystems/combustion/Fluidbed_prog031.pdf

Research being conducted in several FBC subprograms is demonstrating advanced features of FBC and developing the technology base to lower capital and production costs.  Thrusts include simplification of FBC systems and components, incorporation of alternative feed and withdrawal systems, and incorporation of advanced subsystems and steam cycles.

U.S. Department of Energy, National Energy Technology Laboratory, “Combustion - Fluidized-Bed Combustion Repower: FBC Repowering Project Overview”
http://www.netl.doe.gov/technologies/coalpower/Combustion/FBC/APFBC/APFBCprojects.html

This is the overview page for discussions of the projects in CHIPPS, PFBC, GFBCC, and APFBC repowering series.  These projects detail how existing power plants can be improved using advanced combustion technologies.  The present PFBC, GFBCC, and APFBC repowering efforts are described in a series of 14 volumes.

U.S. Department of Energy, National Energy Technology Laboratory, “Oxy-Fuel Combustion"
http://www.netl.doe.gov/publications/factsheets/rd/R&D127.pdf

The overall objective of this project is to assist in improving and validating modeling tools for designing and improving oxy-combustion systems for new plants and retrofitting existing power plants. The result of this project will be that NETL has the capability to analyze retrofit and new oxy-combustion plants, to predict performance, and to recommend measures to improve performance.
 

U.S. Department of Energy, National Energy Technology Laboratory, “Piñon Pine IGCC Power Project: A DOE Assessment” (DOE/NETL-2003/1183, December 2002)
http://www.netl.doe.gov/technologies/coalpower/cctc/resources/pdfs/pinon/PinonPineR2.pdf

The goal of the DOE’s Clean Coal Technology (CCT) program is to furnish the energy marketplace with a number of advanced, more efficient, and environmentally responsible coal utilization technologies through demonstration projects. This document serves as a DOE post-project assessment (PPA) of the Piñon Pine IGCC Power Project, selected in Round IV of the CCT Demonstration program.

U.S. Department of Energy, National Energy Technology Laboratory, “Wabash River Coal Gasification Repowering Project: A DOE Assessment” (DOE/NETL-2002/1164, January 2002)
http://www.netl.doe.gov/technologies/coalpower/cctc/resources/pdfs/wabsh/netl1164.pdf

DOE’s Clean Coal Technology (CCT) Program seeks to furnish the energy marketplace with more efficient and environmentally benign coal utilization technologies through demonstration projects. This document is a post-project assessment (PPA) of one of the demonstration projects selected in Round IV of the CCT Program, the Wabash River Coal Gasification Repowering (WRCGR) Project.

U.S. Department of Energy, Office of Fossil Energy, “Combustion - Fluidized-Bed Combustion Repower”
http://www.netl.doe.gov/technologies/coalpower/Combustion/FBC/APFBC/APFBCprojects.html

This is the overview page for discussions of the projects in CHIPPS, PFBC, GFBCC, and APFBC repowering series.  These projects detail how existing power plants can be improved using advanced combustion technologies. 

U.S. Department of Energy, Office of Fossil Energy, “FutureGen Clean Coal Projects”
http://www.fossil.energy.gov/programs/powersystems/futuregen/index.html

FutureGen Clean Coal Projects is an initiative to equip multiple new clean coal power plants with advanced carbon capture and storage (CCS) technology.  On February 27, 2003, the federal government announced FutureGen, a $1 billion initiative to create a coal-based power plant focused on demonstrating a revolutionary clean coal technology that would produce hydrogen and electricity and mitigate greenhouse gas emissions. FutureGen's restructured approach proposes federal funding to demonstrate cutting-edge CCS technology at multiple commercial-scale integrated gasification combined-cycle (IGCC) coal power plants. It includes engagement with the international community which will remain integral to advancing CCS technology on a global scale.

U.S. Department of Energy, Office of Fossil Energy, “How Gasification Power Plants Work”
http://www.fossil.energy.gov/programs/powersystems/gasification/howgasificationworks.html

The heart of gasification-based systems is the gasifier. A gasifier converts hydrocarbon feedstock into gaseous components by applying heat under pressure in the presence of steam. This fact sheet provides diagrams and explanations for an overview on the gasification and combined cycle processes.

U.S. Department of Energy, Office of Fossil Energy, “Secretary Chu Announces Agreement on FutureGen Project in Mattoon, Illinois,” Fossil Energy Techline, June 12, 2009
http://www.fossil.energy.gov/news/techlines/2009/09037-DOE_Announces_FutureGen_Agreement.html

U.S. Secretary of Energy Steven Chu today announced an agreement with the FutureGen Alliance that advances the construction of the first commercial scale, fully integrated, carbon capture and sequestration project in the country in Mattoon, Illinois. Under the terms of the provisional agreement between the Department of Energy and the FutureGen Alliance, the Department will issue a Record of Decision on the project by the middle of July, with the following activities to be pursued from the end of July 2009 through early 2010.

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