IGCC power plants will soon join utility fleets where they will be called on to dispatch and perform head-to-head with pulverized coal units.
By Steve Blankinship, Associate Editor
Within the next few years, utility-scale power plants using integrated gasification combined cycle (IGCC) technology will be built and fully integrated into utility fleets. Standardized IGCC plant designs incorporating knowledge acquired over decades of operation at industrial facilities worldwide, and more recently honed to utility power requirements at two demonstration plants in the United States, will allow IGCC to take this big step.
IGCC has been in commercial use for decades at industrial facilities worldwide. Globally, more than 100 sites use gasified coal to operate a variety of chemical manufacturing and refining processes. More than a dozen locations produce power. In an IGCC plant, coal is converted to synthesis gas (syngas), which is then fired in a combustion turbine (CT) to produce electricity. Exhaust heat from the CT is sent to a heat recovery steam generator (HRSG) where steam is produced to spin a steam turbine.
Because gasification allows the use of both a combustion turbine and a steam turbine in the power production process, an IGCC power plant can achieve an operating efficiency of about 45 percent, compared to pulverized coal (PC) plants, which operate at efficiencies ranging from about 33 to 40 percent. Particulate matter, sulfur, nitrogen and mercury are removed from the gasified coal prior to combustion instead of from boiler exhaust gases post-combustion as in a PC plant.
Two IGCC power plants currently operate in the United States, both as “demonstration” plants that dispatch to the grid. The 260 MW Wabash River Repowering Project operated by Global Energy Inc. and built on ConocoPhillip’s E-Gas Technology went into service in 1995 in Terre Haute, Ind.
Since in went into operation, Wabash has gasified more than 3.3 million tons of petcoke, reducing more than 60 million Btu of cyngas and generating more than 9 million MWh of power.
TECO Energy’s 250 MW Polk Unit 1 IGCC unit near Tampa, Fla. began commercial operation in 1996 using the Chevron Texaco gasification technology later purchased by GE and using a GE power block based upon the 7FA gas turbine. To date Polk has gasified more than 4.8 million tons of feedstock composed of coal, petcoke and biomass and generated 12.5 million MWh on syngas. The unit, which is typically base-loaded, boasts the lowest incremental cost on the TECO system. Mark Hornick, general manager of TECO’s Polk Station, reports the IGCC has operated at a 72 percent syngas capacity factor, a 78 percent syngas equivalent availability and has had a 96 percent unit equivalent availability with backup fuel.
The first full-scale IGCC utility plants likely will be built by Duke Energy Indiana at its Edwardsport plant site, and by AEP at two sites in its service area. Sites under consideration are located in Ohio, West Virginia and Kentucky. Both utilities plan to build 630 MW plants based upon a standardized design developed by the IGCC alliance formed by Bechtel and GE.
The GE reference plant is a 2 X 2 X 1 configuration consisting of two power trains, each producing more than 300 MW. The plant based on the GE reference design will have two gas turbine generators, two gasification and syngas treatment systems and two HRSGs that feed to a single reheat turbine generator. Overall plant availability is engineered to achieve 85 percent availability using syngas. That availability includes both planned and forced outages.
The same GE reference plant design will be used at Duke’s Edwardsport site. Vectren Energy is participating in preliminary engineering work as a potential co-owner. If regulatory approvals are received – which appears likely – construction could begin late in 2007 with commercial operation expected in 2011.
The history of the reference design to be used by Duke Energy and AEP goes back to the 1980s, when Bechtel and GE collaborated with the U.S. government to develop the Cool Water IGCC demonstration project in Daggett, Calif. Cool Water successfully demonstrated many of the key technical features that allowed IGCC to be scaled up to commercial size. Among them were coal feed at high pressures, safety systems for fuel and oxygen control, performance of high purity air separation units, slag removal and cooling at pressure and sulfur removal and recovery.
Wabash River and Polk followed in 1995 and 1996, respectively. The Polk design uses GE’s full-scale gasifier and syngas cooler design-plus and validated the performance of GE’s F class turbine on syngas. It also validated integrating the air separation unit nitrogen stream to control NOx emissions, along with a number of other features. TECO has operated Polk on a variety of coals as well as coal and petcoke mixtures. Wabash uses a ConocoPhillips’ E-Gas gasification block feeding a GE power block.
The focus of GE’s reference plant design was environmental performance, capital cost and cost of electricity. GE and Bechtel set emission targets for the IGCC that approach those of gas-fired combined cycle plants. The partners also assumed that a 600 MW supercritical PC plant in the Ohio Valley would cost $1,200/kW at a brownfield site and $1,460/kW at a greenfield site. And although it is generally assumed an IGCC plant will cost 20 to 25 percent more than a comparable supercritical unit, the alliance’s launch plants are targeted at a capital cost premium around 10 percent above that of a comparably-sized state-of-the art supercritical. This capital cost reduction would be achieved through optimized gasification and power island integration, plus reduced engineering, material and construction costs based on replicating the alliance reference plant design. The facility will remove more than 90 percent of the mercury and the HRSGs will allow for the addition of selective catalytic reduction for enhanced NOx removal if needed.
The GE reference plant’s two gasifiers are designed to gasify about 5,000 tons of bituminous coal each day to fully load two GE Frame 7FB gas turbines configured to combust syngas.
“The design is expected to achieve efficiencies ranging from 38.5 percent to 40 percent depending on the feedstock used,” says Edward Lowe, general manager of gasification for GE Energy. The 630 MW net output for the GE design matches typical coal plant capacity additions in the U.S. while utilizing economies of scale and providing the ability to replicate to applications as large as 1,200 MW.
The plant is designed to turn down to 50 percent of net power output while operating both gasifiers. With one gasifier operating, the plant can turn down to about 30 percent. In the first scenario, as grid demand decreases both CTs are initially turned down together along with both gasifier trains. At a point determined by site-specific analysis, one CT can be shut down, leaving the other operating at almost full load with both gasifiers operating in a turndown condition.
“This operating philosophy provides an economical strategy to operate the plant during off-peak hours and then ramp back up to full capacity as demand increases,” says Robert Rigdon, director of IGCC commercialization for GE Energy. Individual 7FBs can be turned down to a limit of 60 percent of design capacity while staying in emissions compliance.
AEP’s fuel use plan for its IGCCs is flexible, says Monty Jasper, director of new generation development projects for AEP. It accommodates current fuel supplies and offers some additional diversity. “That envelope will let us burn low fusion temperature Appalachian coals, higher chloride coals out of the Illinois Basin and let us blend petcoke, too,” he says. “So we’ll be diversifying our fuel mix beyond what is consumed by the existing AEP fleet.”
Jasper says that in addition to what AEP routinely uses, its IGCC plants will let it use fuels that that do well in an IGCC but make “really poor boiler fuels.”
Right Place, Right Time
If there was ever an ideal spot to locate one of the first utility-scale commercial IGCC plants, Edwardsport, Ind., could be it. Located on the White River in the southwestern part of the state, Edwardsport has been a coal-fired power site since 1918. Support for building an IGCC is overwhelmingly positive, and includes Indiana Governor Mitch Daniels, state legislators, customers and the general public. Duke CEO Jim Rogers has long viewed Edwardsport as an ideal place to build a state-of-the-art IGCC. Indiana legislators passed a law providing an investment tax credit worth about $75 million to the project with a condition that it burn Indiana coal exclusively. Local governments added incentives totaling another $116 million.
Edwardsport is not large enough to support a similarly-sized pulverized coal plant requiring electrostatic precipitators, fabric filter systems, scrubbers and a coal yard. The existing plant running about 20 percent of the time emits around 11,000 tons of SO2, NOx and particulate a year, says Dennis Zupan, the man responsible for IGCC projects at Duke Energy. “If it ran 100 percent of the time, the new plant would produce about 2,900 tons. We expect to run it about 85 percent of the time.”
That means the IGCC will run four times as many hours and produce almost four times as much power each hour it runs, while producing less than 25 percent of the emissions of the 160 MW unit built at the site in the 1940s. Furthermore, the White River does not have enough water to support a large PC plant. But the IGCC’s demand for water is low enough that the company plans to use collector wells without tapping the river for make-up water, says Zupan.
Siemens, which has been building combined cycle plants in the U.S. since the 1960s, is combining its combined-cycle design experience to offer a 630 MW IGCC reference power plant design. The power block is based on its proven SGT6-5,000 F combustion turbine. To date, the company has more than 320,000 hours of gas turbine operating experience on low-Btu fuels including IGCC applications in the United States and Europe, and has supplied a range of products from gas turbines to compression solutions and plant controls for many of today’s IGCC plants.
Siemens is working with ConocoPhillips on some of its current project opportunities. The base configuration of the Siemens reference power block supports all requirements of ConocPhillips’ E-Gas coal gasification process and allows for potential operation on various compositions of syngas derived from an array of feedstocks supported by the E-Gas technology. The E-Gas technology has been used to process millions of tons of sub-bituminous and bituminous coal and petcoke. The oxygen blown, slurry fed gasifier has two stages of gasification and incorporates proprietary slag removal, char recycle and syngas cooling schemes.
The gasification island design in the reference design aimed at existing project opportunities is an advancement over the Wabash River design by improving plant efficiency to allow an overall plant availability of 85 percent. In addition, the power block supports the ability to incorporate selective catalytic reduction for NOx control as well as the ability to support (with some modification of the power block) carbon capture and sequestration modifications to the gasification island.
“The Siemens IGCC reference plant philosophy results in fixed spatial configurations and establishes a firm basis for determining bulk material quantities and constructor scope definition,” says Gerald Feller, Ph.D., of Siemens. “ Pre-designed option modules provide means to accommodate varying site and project requirements with minimal impact to the base plant modules.” The result, he says, is a design package that can be repeated from project to project while maintaining the flexibility necessary to meet customer and project-specific needs.
Siemens 630 MW IGCC Reference Plant. Illustration courtesy of Siemens
He adds that modularization and replication improve the ability to respond quickly to customer requests for proposals and with a high degree of confidence that the designs are optimal.
“Siemens has always employed a highly adaptable modular approach to plant designs,” he says. “The high level of detail available during the early development stage of the project provides an added degree of confidence in capital cost estimates, O&M cost estimates, and implementation schedules.”
He says the permitting process is also expedited due to the availability of firm design information early in the project. “These factors ease concerns often expressed by lending institutions providing financing on independent power producer and co-generation projects thus helping to expedite financial closing.” Siemens employs an approach that takes full advantage of available integration opportunities between the gasification systems, air separation unit and the power block.
Earlier this year, Siemens acquired the Coal Gasification Business of the Swiss Sustec-Group, thus expanding its power plant business with products and solutions for converting coal to electricity. The acquisition comprises the German firm Future Energy GmbH, and as a 50 percent stake in a Chinese joint venture with the Shenhua Ningxia Coal Group. With the acquisition, Siemens plans to accelerate development and testing of the next gasifier generation. In addition to its ability to gasify a wide range of coals, the Sustec-Group process, known as GSP entrained flow gasification, can also use biomass, petcoke and refinery residues as feedstocks.
AEP will need at least two new baseload plants in its seven-state eastern operating area and is proposing that the two IGCC plants it wants to build be that new baseload capacity. In April, Ohio utility regulators issued an order allowing recovery from AEP customers of pre-construction costs, including the front-end engineering and design study, for its proposed IGCC in Ohio. That keeps the project on schedule for commercial operation by 2010. AEP is also awaiting cost-recovery approval from West Virginia regulators. Duke Energy Indiana filed an integrated resource plan with state regulators in June indicating that the Edwardsport IGCC represents a least-cost scenario for meeting baseload needs. Duke now expects to file for a certificate of public convenience and necessity in the third quarter of this year.