Integrated gasification combined cycle (IGCC) power plants are believed to be the type of power plants that will predominately be used to add to our electrical power supply, replace our aging coal power plants and out increasingly expensive natural gas power plants. (Wabash River, IN IGCC plant shown above) The process offers options to eliminate greenhouse gases, produce hydrogen and/or produce liquid fuels.
The process used by IGCC plants can be broken down into five broad steps:
- the coal is gasified to produce a synthetic gas (syngas)
- the pollutants are removed from the syngas, then electricity is generated using a combined cycle, consisting of the following three steps:
- a gas turbine-generator burns the syngas
- heat from the gasification and the exhaust heat from the gas turbine are used to create steam
- the steam is used to power a steam turbine-generator.
The potential for carbon dioxide sequestration makes IGCC technology even more appealing and environmentally responsible. If desired hydrogen can be separated from the syngas stream. A more complex, but even more economical option is to generate Fischer-Tropsch liquid fuels from a portion of the syngas.
The following are the characteristics of an IGCC plant:
- SOx, NOx and particulate emissions are much lower in IGCC plants than from a modern coal plant. Its VOC emissions and mercury emissions are comparable.
- IGCC plants emit approximately 20% less CO2 emissions than a modern coal plant.
- IGCC plants use 20-40% less water than a modern coal plant.
- IGCC plants operate at higher efficiencies than conventional coal fired power plants thus requiring less fuel and producing less emissions. Current efficiency is 42% with efficiencies as high as 60% expected in the very near future using a high efficiency turbines and some other process improvements.
- Costs for electricity, without CO2 capture, is about 20% higher than in a modern coal plant. Electricity costs are 40% lower than from a natural gas IGCC plant with natural gas at $6.50 per MMbtu.
- CO2 can be captured from an IGCC plant much more easily that from a conventional coal plant at an an additional cost increase of 25-30% for capture and sequestration, without transportation charges.
- IGCC offers the possibility to capture the hydrogen that is part of the syngas stream, in an economic manner.
A simplified flow diagram (courtesy Energy Northwest) for an IGCC process is shown below:
Coal and/or petroleum coke is pulverized and fed into the gasifier along with oxygen that is produced in an on site air separation unit. The combination of heat, pressure, and steam breaks down the feedstock and creates chemical reactions that produce hydrogen (H2) carbon monoxide (CO) and synthesis gas, or syngas. Feedstock minerals become an inert, glassy slag product used in road beds, landfill cover, and other applications.
The syngas is cooled producing syngas and high pressure steam. Sulfur and mercury are removed from the syngas. Elemental sulfur is recovered as a marketable commodity. CO2 is removed either as vent gas or captured for sequestration. If hydrogen is to be recovered it is also separated and recovered at this point. The syngas then goes to the gas turbine where it is burned to drive the turbine and generate power. The nitrogen, from the air separation unit, is expanded through the turbine to increase power production and reduce NOx emissions. The steam from gasification is combined with steam produced in the gas turbine heat recovery unit and fed to the steam turbine-generator.
1) Moving Bed Gasifiers (dry ash) 2)Fluidized Bed Gasifiers and 3)Entrained Bed Gasifiers
In a presentation by EPRI, single stage entrained gasifiers (Shell/Prenflo, E-gas, GE (formerly Texaco), KBR, Mitsubishi, Noell/GSP, Eagle, Boeing Rocketdyne, etc) were found to have the best features.
- At high operating pressures and in the quench mode they are best for high CO2 capture.
- They are the least expensive way of putting in the moisture needed for the Shift reaction.
- They produce the least CH4 and are best for producing syngas for Fischer-Tropsch synthesis.
- They use dry coal feed
- Cooled refractory liner extends refractory life.
- Eliminates high maintenance carbon scrubber.
- Continuous slag removal.
See EPRI presentation for more details.
CONTINUING R & D
DOE is continuing research on gasification projects in several areas aimed at reducing emissions, reducing capital cost and increasing process efficiency.
Turbines with higher efficiencies and operating temperatures are being developed. When the Energy Department started its advanced turbine systems program in the early 1990s, the best turbines available had efficiencies of only 50 percent. Today, efficient systems typically operate in the 57- to 58-percent efficiency range. The efficiency is important because each percentage point gain can mean as much as $20 million in reduced operating costs over the life of a typical gas-fired combined-cycle plant. Turbines with efficiencies as high as 60% operating at 2600 F have been developed and tested in natural gas combined cycle applications. The Mesaba IGCC project hopes to use a 60% efficiency turbines in its plant. Both GE and Siemans Westinghouse are participating in this program.
The Energy Department is working with its private sector partners to develop a new, potentially low-cost configuration for a future gasifier. Called the "transport reactor," the gasifier is an advanced circulating fluidized-bed reactor.
Production of oxygen with cyrogenic air separation plants adds a considerable parasitic load to the process. A much lower cost alternative being explored is to use new innovations in ceramic membranes to separate oxygen from the air at elevated temperatures.
An especially important goal of the Energy Department's coal gasification program is to develop inexpensive membranes that can selectively remove hydrogen from syngas so that it can be used as a fuel for future fuel cells or refineries, or perhaps one day as a substitute for gasoline in a hydrogen-powered automobile.
Future concepts that incorporate a fuel cell or fuel cell-gas turbine hybrid could achieve efficiencies nearly twice today's typical coal combustion plants.
The summer 2005 issue of Clean Coal Today, p8, has an article updating current sequestration methods being investigated in the US. The following is a brief summary:
- The Weyburn enhanced oil recovery test being conducted in Saskatchewan, Canada is the longest running program, being started in 2001. It is estimated that half the CO2 injected will remain sequestered.
- In the Frio, TX saline formation project 1,600 tons of CO2 was injected, in October of 2004 and various types of measuring tools are being evaluated as well as movement of the plume, which has stabilized much as predicted.
- Coalbed methane recovery has been combined with CO2 sequestration in some field projects. In a seven year project with CONSOl Energy R&D in Marshall County WV, both methane recovery and sequestration in an unmineable coal seam are being investigated. The project is currently in the pre-injection phase with over 26,000 tons of CO2 to be injected over a one year period. Another similar project is being undertaken in the San Juan Basin, New Mexico.
According to a study by Foster Wheeler the cost of electricity from IGCC plants is increased 25%-30% to $.056 to $0.063 per kWh if sequestration of the CO2 is added.
According to US Coal, American Energy Review 2005, Gasification plants come at a high price tag. They have typically cost US$1.2m to US$1.6m per megawatt of capacity compared to US$1m per megawatt for a conventional coal plant and US$550,000 per megawatt for natural gas plants. Not surprisingly, IGCC plants in the US have been constructed with financial support from the DOE. High prices for natural gas have made natural gas plants unattractive and some are idle. DOE has several projects to decrease emissions, hopefully at lower costs. Higher standards for emissions controls on new plants are shifting the tradeoffs towards IGCC because of its inherently lower emissions
DOE DEMONSTRATION PROGRAM
Kentucky Pioneer Energy, Trapp, KY - 580 MWe (gross) Project to demonstrate and assess the reliability, availability, and maintainability of a utility-scale IGCC system using a high-sulfur bituminous coal and refuse derived fuel (RDF) blend in four British Gas Lurgi (BGL) oxygen-blown, fixed-bed, slagging gasifier. Projected efficiency of a commercial unit 42.5%. Project started 12/94, projected completion 12/07.
Tampa Electric Company, Tampa, FL - . The objective of this plant was to demonstrate IGCC technology in a greenfield commercial electric utility application at the 250-MWe size using an entrained-flow, oxygen-blown Texaco gasifier with full heat recovery and conventional cold-gas cleanup. A GE MS 7001FA advanced gas turbine, with nitrogen injection for power augmentation and NOx control, generates 192 MWe. A steam turbine uses steam produced by cooling the syngas and superheated with the gas turbine exhaust gases in the heat recovery steam generator to produce an additional 123 MWe. The air separation unit consumes 55 MW and auxiliaries require 10 MW, resulting in 250 MWe net power to the grid. Project started 11/91, project completed 12/02.
Pinion Pine IGCC Project, Reno, NV - 107 MWe (gross) To demonstrate air-blown, pressurized, fluidized-bed IGCC technology incorporating hot gas cleanup to evaluate a low-Btu gas combustion turbine; and to assess long-term reliability, availability, maintainability, and environmental performance at a scale sufficient to determine commercial potential. Project started 8/92, project completed 10/01.
Wabash River Coal Gasification Repowering Project, Terre Haute, IN - The 262 Mwe (net) project was to demonstrate utility repowering with a Destec, now ConocoPhillips E-Gas, two-stage, pressurized, oxygen-blown, entrained-flow IGCC system, including advancements in the technology relevant to the use of high-sulfur bituminous coal; and to assess long-term reliability, availability, and maintainability of the system at a fully commercial scale. The power block consists of a single 192-MWe General Electric MS7001FA (Frame 7FA) gas turbine, a Foster Wheeler single-drum heat-recovery steam generator with reheat, and a 1952 vintage Westinghouse reheat steam turbine. Project started 7/92 completed 9/00
ISAB Energy IGCC plant, Priolo, Sicily (Italy) - The 512MW power plant was designed by Foster Wheeler who formed a consortium with Snamprogetti which won the contract in early 1996. The power units came into operation in the first half of 1999, shortly before the process units. Asphalt from a nearby refinery is used for feedstock. The plant uses two Texaco (now GE) quench type gasifers to convert asphalt to syngas. The combined cycle has two Siemens gas turbines, with two heat recovery steam generators and two condensing steam turbines. Two similar plants to the ISAB venture are located at Falconara Marittima (on the Italian Adriatic coast) and at Sarlux in Sardinia. The 548MWe Sarlux plant, with three gasifiers, started producing electricity in September 2000, is the worlds largest IGCC plant.
Elcogas IGCC Power Plant, Puertollano, Spain - The 335 MWe (ISO) demonstration plant has been designed to use a 50/50 mixture of high ash local coal and petroleum coke from a nearby refinery. Gasification is based upon the PRENFLO system, which is a PRessurized ENtrained-FLOw gasifier with dry feeding. The power block consists of a 200 MWe (ISO) Siemens model V94.3 gas turbine, a three-pressure level and IP steam reheating heat recovery steam generator, designed by Babcock, and able to additionally superheat the steam generated through raw gas cooling in the gasification and a two casing reheat steam turbine designed by Siemens that delivers roughly 135 MWe. The plant achieves a 47% efficiency.
The Nippon Oil Corporation Refinery 342 MWe plant went on line in mid 2003. The worlds newest IGCC plant uses asphalt residue as feed. It uses a Texaco (now GE) reheat cycle, triple pressure, vertical gas flow, natural circulating type gasifier and Mitsubishi Heavy industries gas and steam turbines. The plant is located Negishi, Yokohama, Japan and started operation June, 30, 2003.
The William Alexander plant has been operating in Buggenum, Netherlands since 1994. The plant has a capacity of 253 MWe using a shell gasifier and Siemans turbines.
Gilberton Coal-to-Clean Fuels and Power Project - This demonstration plant to be completed in 2009 - The objective of this project is to design, construct, and demonstrate the first clean coal power facility in the United States using coal waste gasification as the basis for clean power, thermal energy, and clean liquid fuels production. The Gilberton plant will gasify the coal wastes (anthracite culm) to produce a synthesis gas of hydrogen and carbon monoxide. Electric power and steam will be produced, and then a portion of the synthesis gas will be converted into synthetic hydrocarbon liquids via a catalytic chemical process known as FT synthesis.
Mesaba Energy Project - A 531 MWe demonstration plant, being developed by Excelsior Energy, the owner operator, and ConocoPhillips. The plant will demonstrate significant performance, efficiency and emission improvements over previous IGCC plants. The plant will have three 50% (one spare) ConocoPhillips E-Gas gasifiers that will supply syngas to two combustion turbine-generators. The waste heat from these turbines goes to two heat recovery boilers that create the steam for a single steam turbine-generator.
ConocoPhillips’ E-Gas Technology was selected because of the technology’s impressive performance in achieving across-the-board low emissions at Indiana’s Wabash River plant, and the company’s eight years of experience with gasification technology. The project will demonstrate a full slurry quench (FSQ) two-stage gasification configuration that will increase overall plant thermal efficiency, as well as cold gas efficiency. Full slurry quench will be achieved by increasing the coal slurry feed to the second stage of the gasifier to the point where only slurry will be used to quench the syngas, thereby eliminating the thermal loss associated with water used to cool the syngas in existing IGCC configurations. Full slurry quench further improves efficiency by increasing the fuel feed to the second stage where no additional oxygen or combustion will be needed to add to syngas output.
The Mesaba Energy Project will be the first coal power plant in the United States to achieve greater than 90 percent mercury control. Mesaba will demonstrate long-term (30-day rolling average) criteria pollutant emission rates for SOx, NOx, mercury and particulate matter that will redefine what is considered best available control technology for coal-fueled electric power generating plants. Mesaba can also be retrofitted for carbon dioxide capture in the event that greenhouse gas emission reductions are imposed by future regulations.
Mesaba will demonstrate a 5% increase in plant efficiency compared to first generation IGCC plants consuming similar fuel types.
The site has two rail lines and a dedicated port on Lake Superior, providing attractive fuel transportation options for the facility. The plant located in Hoyt lake, MN is scheduled to begin operation in 2010.
Southern/Orlando, Orlando Utilities Commission and Kellogg Brown will construct a 285 MW airblown KBR IGCC plant based on the transport gasifier at Orlando's Utilities Commission's Stanton Energy Center in Orange County, FL. The technology to be used is based on the transport gasifier that Southern Company, DOE and others have been developing at the Power Systems Development Facility near Wilsonville, Ala. The transport gasifier offers a simpler, more robust method for generating energy from coal than other available alternatives. It is unique among coal gasification technologies in that it is cost-effective when handling low rank coal, as well as coals with high moisture or high ash content. These coals make up half the proven U.S. and worldwide reserves. Total cost of the project is $557 million of which DOE will contribute $235 million. Expected date for operation is early 2010.
Future Gen is an initiative to build the world's first coal based integrated sequestration and hydrogen production research power plant. The $1 billion dollar project is intended to create the world's first zero-emissions fossil fuel plant. The 275 MW (net equivalent output) will produces both electricity and hydrogen as output and sequesters one milion metric tones of carbon dioxide per year. The project will take at least ten years to complete. To prove sequestration technology it must be tested and validated at a large scale and with real-world conditions.
In the private sector the following plants are in various stages of development:
- American Electric Power (AEP) has announced that it will build two 600 MW IGCC plants which they will need by 2010. Bechtel and GE will to do a preliminary design. The preliminary cost estimate is $1 billion. Three sites are under consideration, but is believed that at least one of the plants will be located in West Virginia.
- Cinergy/PSI (being acquired by Duke Energy) announced on 9/22/05 that they plan to negotiate with the GE/Bechtel alliance to start the preliminary engineering and design of a 600 MW IGCC plant. Preliminary analysis has estimated the cost at $900 million. Several sites are under consideration in Indiana with the targeted site being at PSI's 160 MW Edwardsport coal-fired generating station near Vincennes.
- Energy Northwest is pursuing permitting and possible construction of a 600 MW IGCC plant in western Washington. They have selected ConocoPhillips’ E-Gas Technology for use in the solid fuel gasification process. The plant would consist of two 300 MW trains. Cost is expected to be between $900 and $950 million. Site selection has been narrowed down to one site and negotiations for a lease are proceeding. Construction could begin in 2006 with operation in 2011.
- Tondu Corporation is planning a 550 MW IGCC plat at Crossroads Power Plant In St Joseph County, IN. The proposed IGCC plants will use the same technology and design of the Shell Buggenum IGCC plant in the Netherlands. Cost is estimated at $1 billion.
GE Energy has aligned with Bechtel, ConocoPhilips has aligned with Flour and Shell/Krupp Uhde has aligned with Black and Veatch to offer complete IGCC gasifier, turbine and engineering/construction packages.
"A Program Plan for FutureGen", DOE Report to Congress, 03/04
American Energy Review 2005, US Coal
Elcogas IGCC power plant, Puertollano, Spain
Excelsior Energy website
"Field Tests Validate Geosequestration", Clean Coal Today newsletter, summer 2005
"CO2 capture in Coal-Based IGCC Plants" , IEA Greenhouse Gas R & D Program, Foster Wheeler Italiana SpA, 2004
"Gasification & IGCC - Design Issues & Opportunities and design issues", Neville Holt, EPRI, Presented at the GCEP Coal Workshop, Provo, Utah, March 15-16/05
"Getting to Clean Coal", Chemical and Engineering News, 2/23/04
"How to Clean Coal", onearth magazine, Fall 2005
IGCC, Energy Northwest website
ISAB Energy IGCC plant, Prioli, Italy
Kentucky Pioneer Energy LLC, Trapp KY
Mesaba Energy Project, DOE Project facts, 5/05
Pinion Pine IGCC Power Project, Reno, NV - Final Report
Sarlux IGCC power plant, Sarroc, Italy
Tampa Electric Company, Mulberry, FL - Final Report
Wabash River Coal Gasification Repowering Project, West Terre Haute, IN - Final Report