Like a weathervane turning to shifting winds, power generators are seeking the next source of low-cost fuel to fire powerplants. Hemmed in by demands of regulators, environmentalists and communities, powerplant owners once again are looking at the nation’s most abundant and inexpensive fuel–coal–while mitigating its well-known toxic emissions.

"Many feel ‘clean coal’ is an oxymoron and emissions will increase," said Gary Stiegel, gasification technology manager at the Pittsburgh-based National Energy Technology Laboratory, addressing a well-attended symposium on coal gasification in Pittsburgh June 2. But gasification–a venerable technology first developed in the 19th century–has demonstrated that emissions of sulfur dioxide, nitrogen oxides, volatile organic compounds, particulates and even mercury can be removed from the synthesis gas before combustion. The resulting emissions are far below those from conventional pulverized-coal (PC) boilers and most compare well with those of supercritical PC (SCPC) boilers. Click here to view chart

High temperature and pressure in a slagging gasifier convert carbon in feedstock to synthesis gas, or syngas, which is primarily a mixture of carbon monoxide and hydrogen, explained Charles McConnell, president of the Gasification Technologies Council, Arlington, Va. The controlled, oxygen-starved atmosphere in the process avoids creation of undesirable combustion byproducts.

A World Gasification Survey in 2004 conducted by SFA Pacific Inc., Mountain View, Calif., for the Dept. of Energy, tallied 117 operating gasification plants worldwide. Twenty are in the U.S., but only four are producing electricity. Most also produce chemicals from the syngas.

The Wabash River Coal Gasification Repowering Project, Terre Haute, Ind., co-owned by SG Solutions LLC and Cinergy Corp., was a 100-MW PC plant repowered to 262 MW integrated gasification combined-cycle (IGCC) in 1995. It is fueled by coal and petroleum coke. A large commercial demonstration project with DOE funding, its operating record has been spotty, and it just resumed operation after being shut down in 2004 "for commercial reasons" during a change in ownership, said Phil Amick, technology director for ConocoPhillips, the IGCC unit’s operator.

Tampa Electric Co. owns the country’s only other electric-utility IGCC plant. Since 1996, its Polk Power Station has operated a 260-MW IGCC unit, also built in part with DOE funds. Lloyd Webb, senior consulting engineer for the plant, said the overall reliability of the combined-cycle unit is better than coal units and he maintained that gasifier reliability can be increased by incorporating the lessons learned from test units in the design of the next generation of plants.

High prices for natural gas and oil are driving interest in IGCC. Last December, assuming an index value of 1.0 for the coal-petcoke blend, the relative cost of coal alone was 1.5, natural gas 4.4 and oil 5.9, McConnell said.

Also driving the interest are demand for cleaner fuels while keeping coal in the mix and expectations of more stringent emissions regulation, including mercury and carbon-dioxide capture. IGCC generates almost as much CO2 as a conventional PC plant, but it is in a concentrated stream that is easily captured, several speakers said.

Several attendees asked about the cost of constructing IGCC. Webb cited an Electric Power Research Institute estimate of $1,200 to $1,300 per kW, higher than for a natural gas combined cycle, but comparable to a PC unit with selective catalytic reduction equipment and a scrubber. ConocoPhillips’ Amick said a greenfield plant might run about $1,500 per kW.

Perhaps one of the surest signs that IGCC is maturing is the formation of three different teams to develop IGCC plants, and announcements by two major coal-burning utilities of plans to build IGCC plants.

Fluor and ConocoPhillips last year were first out of the gate, announcing an alliance in May 2004 "to facilitate the development, design and construction of new projects utilizing ConocoPhillips’ E-Gas Technology." GE Energy and Bechtel in October formed an alliance to develop an IGCC "reference plant," a standardized design that can be built with minimal customization. Cinergy Corp., Cincinnati, quickly signed up the team to study the feasibility of an IGCC plant in Indiana. Black & Veatch, Uhde and Shell in November also formed an alliance to pursue IGCC opportunities.

Daniel Duellman, manager of mechanical systems engineering for American Electric Power, says AEP is "studying IGCC" and has identified three possible sites in West Virginia, Ohio and Kentucky. But of the three IGCC alliances, GE-Bechtel "is the only one spending money," he notes.

While no new construction is guaranteed a pass from the environmental community, John Thompson, advocacy coordinator for the Clean Air Task Force, Carbondale, Ill., spoke up to endorse IGCC "as an answer to global warming." He noted that 70,000 MW of new coal-fired generation capacity is under development, compared with almost none five years ago. "This is part of a worldwide trend," he asserted, noting that coal-fired power is growing in India and China as well as in the U.S. "In the last 18 months, IGCC interest has really grown," he said. "It now represents half of all new coal plants proposed in the Midwest." He added, "I think there’s a real opportunity if we do this right to build IGCC plants without a lot of environmental opposition."