FEATURE FOCUS: Tomorrow's Coal Systems

old king coal

It generates more than half the electricity in the U.S., and so much is lying in the ground. The trick is to use it without killing all the fish in Canada.

Critics will say that tomorrow's coal systems ought to be cold. They will point to the dangers of mercury emissions, to the hazards of handling more than 100 million short tons of coal waste every year, to the devastation of acid rain.

Others consider how much coal lies under the ground. There's more of it than any other fossil fuel. And forecasters for energy predict that fossil fuels—the hydrocarbon legacy of dinosaurs and primeval forests—will drive the economies of the planet for the next generation or two.

The U.S. Energy Information Administration estimates that coal generates 34 percent of the world's electricity today and will still account for more than 30 percent in 2020.

The backers of coal say that systems can be—and must be—developed to make coal more efficient to burn and less troublesome to the biosphere. According to the EIA, the United States relied on coal for more than 51 percent of its electric power last year. Meanwhile, China, so populous and such a go-getter, needs energy to support its sprouting industry and is sitting on 12 percent of the world's coal reserves. Only the U.S. and Russia have more.

And no country anywhere is willingly going to turn off its lights. Instead, it will use what it has to keep them on—and to keep its industries going and to maintain order.

Tampa Electric's Polk Power Station incorporates a gasifier to feed a combined-cycle unit. It's one of the two IGCC plants operating in the U.S.

Clean coal has been one of the major goals of the National Energy Technology Laboratory for some time. In the past few months, the program has been given renewed impetus by the White House.

In response to President Bush's national energy policy, the U.S. Department of Energy, which operates the lab, in March put out a solicitation for clean coal proposals. It offered to go 50-50 with industrial partners on projects that would proceed from definition through demonstration. The solicitation said that the government would spend as much as $400 million on various projects.

Areas of interest include a reduction in carbon and other emissions, including mercury, which is only now coming under regulatory scrutiny in the United States. The DOE is also considering proposals under such themes as combined heat and power, gasification, process control, and improvements in steam turbines.

According to the solicitation, qualifying projects have to specify coal for three-quarters of their fuel energy input. The application deadline was the first of this month, and the acceptance list will come out in January.

The United States is also a supporter of the International Energy Agency and is one of the member countries that support IEA Coal Research, a program based in London. Several European member countries also are involved, as are Canada, Japan, and the European Council. IEA Coal Research bills itself as "the world's foremost provider of information on efficient coal supply and use."

The Electric Power Research Institute, a research organization partly backed by the power industry, announced its Global Coal Initiative two years ago. When it did so, the group predicted that research could make integrated gasification combined-cycle and pressurized fluidized-bed combustion competitive with natural gas on a cost-of-electricity basis sometime between 2010 and 2020.

Slow to Catch Fire

So far, there have been few takers of advanced coal systems. The DOE and IEA Coal Research maintain Web sites that discuss clean coal technologies. They include two high-profile methods of cleaner combustion—gasification and circulating fluidized beds. The ideas aren't new, but they have yet to catch on in a big way.

The plan for a gasification plant feeding a combined-cycle generating station is still in the demonstration stage in the United States. Although the process squeezes more efficiency out of coal and scores points for cleaner air and corporate goodwill, prospective buyers have yet to form a line around the block.

Tom Sarkus, coal power projects division director at the National Energy Technology Laboratory in Pittsburgh, pointed out that there are just two IGCC units generating electricity commercially in the United States: Tampa Electric operates one integrated gasification combined-cycle unit at its Polk Power Station, 40 miles from Tampa, and Global Energy Inc. runs a gasifier that feeds a turbine owned by Cinergy at the Wabash River plant near Terre Haute, Ind.

Phil Amick, vice president for commercial development at Global Energy Inc., called it "the cleanest coal-fired plant in the world." Amick was project manager when the Wabash River plant was repowered.

JEA's Northside plant in Jacksonville, Fla., is adding two 300-MW circulating fluidized-bed boilers, the largest that Foster Wheeler has delivered.

The repowering project changed a pulverized coal-fired unit generating about 90 megawatts into a more efficient 262-MW unit. It wasn't cheap. According to the DOE, the project, which repowered one unit at the plant, cost just over $438 million. Four other units at the plant burn pulverized coal.

Published numbers for IGCC claim 99 percent removal of sulfur from flue gas, and efficiencies of 40 percent. The current best for pulverized coal boilers is about 38 percent. The older Wabash River unit replaced by the repowering had a nominal efficiency of 33 percent.

The numbers of IGCC plants have been growing, but not rapidly. A few IGCC plants have been set up out-
side the United States, for instance in Buggenum in the Netherlands and in Puertollano, Spain.

Meanwhile, Global Energy, through a unit called Kentucky Pioneer Energy, is working with the DOE on another IGCC project planned for Trapp, Ky. Besides the combination of gas and steam turbines to generate electricity, the plan would divert some of the gas to a molten carbonate fuel cell.

The gasifier in Kentucky will be able to handle a feed of lump fuel. The Wabash River unit requires that fuel be prepared as a slurry.

Perhaps as a sign of its confidence in the technology, Global Energy is already making plans to open a commercial IGCC plant on its own. In May, a subsidiary, Lima Energy Co., got the go-ahead from the Ohio Power Siting Board for an IGCC plant in the city of Lima. The 580-MW plant is expected to cost $500 million. The DOE is not involved in that plant.

Cooler Burn, Less NO_x

The fluidized bed hasn't been a runaway best-seller either.
Don Bonk, NETL's product manager for advanced combustion technologies, said there are perhaps 400 fluidized beds operating worldwide. About 130 of them are in the United States, which has a fleet of approximately 1,100 coal-fired generating units.

There is a large-scale CFB project nearly complete right now, Sarkus said. JEA, the former Jacksonville Electric Authority, is repowering its Northside generating station with two circulating fluidized bed boilers, each rated at nearly 300 MW.

The boilers were made by Foster Wheeler. According to Harlan Trammell, a Foster Wheeler regional vice president whose area includes Florida, they are the largest CFB boilers that the company has ever delivered.

The DOE is participating in Unit 2, which will undergo tests using coal, according to Joey Duncan, JEA's project manager. Duncan said among the benefits of CFB boilers is that they burn fuel at lower temperatures and produce less nitrogen oxide than hotter boilers do.

"There's churning hellfire and brimstone going on," Duncan said, but the coal burns in the 1,500s Fahrenheit. A conventional boiler will reach temperatures of 2,000°F or higher. The biggest NO_x output with coal is at combustion temperatures above 1,600°F, Duncan said.

The boiler's contents are 95 to 97 percent limestone and ash, and only 3 to 5 percent fuel at any time, he added. The limestone draws sulfur from the coal. A dry scrubber and a polishing scrubber further reduce pollutants downstream.

According to Bill Goodrich, lead mechanical engineer for the repowering project, the boilers have "the best heat rate I've seen in a CFB." He said circulating fluidized bed boilers are usually slightly less efficient than pulverized coal boilers, but in this case, he expects each boiler to be comparable to a PC unit, at 37 or 38 percent efficiency.

The boilers are in the process of coming on line. "Both units are producing power that is out on the grid, but I wouldn't say they're in commercial service yet," Goodrich said. Unit 2 this month will be in its final testing stages. Unit 1, which is lagging behind Unit 2, will be "halfway between preliminary and final," Goodrich said.

Other features of the plant are a continuous ship unloader that will unload 60,000 tons of fuel in about 52 hours, and two fuel storage domes 400 feet across and 140 high, able to hold 60,000 tons each.

Unit 1 of the Polk plant burns syngas, which can be derived from coal, pet coke, or other fuels. The gasifier is the large tower in the background, surrounded by white sheet metal at the top.

The capture of sulfur and reduction of NO_x address a problem that crosses borders. Less than 20 years ago, smokestack emissions from power plants in the midwestern United States were blamed for the acid rain that was killing off lakes and threatening ecosystems in Canada.

Much of the corrective response took the form of flue gas scrubbers and other capture devices. According to Sarkus, that technology today is fitted on only about a quarter of the coal-burning plants in the United States.

Even so, he added, coal is burning cleaner. Since 1970, when the Clean Air Act really kicked in, coal plant SO₂ emissions declined by 11 million tons a year, or 35 percent. Coal use has doubled in that time.

Sarkus suggested that many plants running without flue gas controls or scrubbers are burning coals that contain less sulfur and other pollutants to begin with.

Joan Masterton, director of the science assessment and integration branch of Environment Canada in Toronto, said that industry has responded well to the problem of emissions. "Emissions have been drastically reduced, and that's very good, but there's still a way to go," she said.

Although emissions are down, Canadian researchers have not seen corresponding diminishing effects. The causes will have to be researched. "It is a more complex system than we originally thought," Masterton said.

Ashes to Grout

Emissions controls—the capture of particulate matter and SO₂ scrubbing—have developed a revenue stream for many power plants.

A report issued last May by the U.S. Geological Survey tabulates the production and use of coal combustion byproducts from 1966 through 2000. In the first year, the only products that show up are fly ash and bottom ash, totaling almost 23 million metric tonnes. About an eighth of that, some 2.8 megatonnes, found a market.

As of two years ago, the field had expanded. Boiler slag and flue gas desulfurization products had broken into the charts a few years earlier. The two new categories and a considerable increase in coal consumption boosted the total of potentially recyclable byproducts to 98.2 megatonnes. Some 28.6 megatonnes, or 30 percent of it, wound up in places as diverse as concrete floors, bowling balls, and peanut fields.

A larger share of a bigger total is recycled, but that still leaves 70 million metric tonnes a year of slag, ash, and sulfur-laced limestone headed for landfills. It is Bob Patton's job to help reduce the waste.

Patton is a project manager in the environmental projects division of the National Energy Technology Laboratory in Pittsburgh. His work focuses on matching the leftovers of coal fires to places where they can serve a need or, as he put it, "to turn a waste product into a useful, money-making product."

Flue gas desulfurization creates raw materials for gypsum wallboard, for instance. Bottom ash becomes the cinders that are spread on icy roads. Slag will do the same job, but needs to be ground to size first. Ash and slag may even be used to fill the caverns of old mines to stop ground subsidence.

Global Energy operates the gasifier that fuels a Cinergy power plant on the Wabash River in Indiana. Global Energy is planning to build IGCC plants in Kentucky and Ohio.

The most common use for any coal combustion by-product is in concrete or grout, where fine fly ash replaces some of the cement. According to Patton, western fly ashes are particularly cement-like and, on average, can replace 15 to 20 percent of the cement in concrete.

Out of 57 million metric tonnes of fly ash produced in the United States each year, 17.6 million tonnes are recycled. About half of that is used in place of cement in grout, concrete, and other hard-setting materials.

The fine ash has other uses, too. Fly ash can sweeten acid soils and lighten dense earth. Adding fly ash can also stabilize soils to support construction.

Ebonite International Inc., a manufacturer in Hopkinsville, Ky., uses fly ash as ballast to adjust the heft of its bowling balls, which can be as much as 40 percent fly ash by weight.

Great River Energy, based in Elk River, Minn., produces at least 450,000 tons a year of marketable ash at its Coal Creek station. Right now, the company sells 320,000 tons and hopes that it will be selling all the ash by the end of 2004, according to Al Christianson, project coordinator for business services at the plant in Underwood, N.D.

The total ash output at the 1,200-MW Coal Creek plant is about 500,000 tons a year. Some ash is lost during start-ups when oil is burned to support coal combustion, he said. The company ships the ash through terminals in Minneapolis, Denver, and Fargo, N.D. Sales of ash represented a profit of about $3 million last year, Christianson said.

The marketing of Great River's ash is handled by ISG Resources, a Salt Lake City company that specializes in building materials that contain coal combustion byproducts. John Ward, ISG's vice president of marketing, said the company sells its ash-containing products across the country and receives fly ash from 110 power plants.

One of the company's products, Swiftcrete, is a rapid-setting concrete and asphalt repair material. The U.S. Army used it to repair runways in Afghanistan.

ISG Resources also sells PeanutMaker, a high-calcium fertilizer. The company said the product has been used on more than 60,000 acres of peanut crops. Ward said it helps soil to retain water.

Refining Emissions

According to Sarkus at NETL, there has been a progression in emissions controls for the past half-century. The 1950s and '60s focused on smog and particulates. The next decade shifted to SO₂. The '90s saw a tightening of NO_x emissions. Now, Sarkus said, the list is headed by fine particulates under 3 micrometers and by mercury.

It was less than two years ago that the U.S. Environmental Protection Agency recognized a "plausible link" between power plant emissions of mercury and human health. The link arises when people eat fish that have eaten other fish that have swallowed the stuff.

Mercury can cause people serious illness and can even kill. It is especially hazardous to unborn children, so preg-nant women are often warned to curb their intake of freshwater fish in certain regions.

In December 2000, the agency decided it should look into regulating mercury emissions. The EPA right now has a deadline of December 15 this year by which it must publish proposed rules, and then has to wrap them up in final form exactly one year later.

Tom Feeley, product manager for environmental and water resources at NETL, is one of the people working to develop a practical means of mercury control. He said he doesn't have it yet.

Wet scrubbers designed to remove sulfur dioxide from coal flue gases also can remove as much as 80 percent of the mercury, if it's oxidized. And there's the catch. Lignite and Powder River Basin coals tend to have a lower concentration of oxidized mercury and more elemental mercury, and the elemental form is difficult to capture, Feeley said.

One method being tested is an injection of activated carbon into the flue gas. The carbon absorbs the mercury, but there can be additional costs as a result of the treatment.

We Energies, which used to be Wisconsin Electric Power Co., hosted a carbon-injection test at its Pleasant Prairie plant. The test involved one-quarter of the precipitator on one unit, according to Dave Michaud, the company's principal environmental scientist.

"We did not sell any of the fly ash from that part of the precipitator during testing," he said. As it turns out, carbon can make fly ash unsuitable for mixing into concrete.

Carbon, especially activated carbon, inhibits the formation of small bubbles in concrete. The bubbles, which provide space for water droplets to expand and contract, let concrete survive freeze and thaw cycles.

Injectors put activated carbon into the flue gas stream to remove mercury. ADA Environmental Solutions has tested the system at various plants.

Fly ash of Powder River Basin coal has about 0.4 percent carbon content and is equivalent by itself to lower-grade Portland 2 cement, Michaud said. The same ash with perhaps 0.5 percent activated carbon will fail cement-criteria tests.

One test of ash is to add drops of a surfactant, a soluble compound that affects the surface tension of liquids, into a mixture containing fly ash. After each drop, the mixture is shaken. The number of drops it takes until a consistent head forms on the surface is the foam index.

Good fly ash has an index of about 15, Michaud said. The contract limit is 25 drops. Ash with 1 percent activated carbon can have an index of 72. The usual limit for carbon is 3 percent.
ADA Environmental Solutions, a supplier of coal-cleaning technology in Littleton, Colo., conducted the test at Pleasant Prairie and another at a plant owned by Southern Co.

Larry Monroe, Southern's program manager for pollution control research, said the test involved half of Unit 3 at the company's E.C. Gaston plant in Wilsonville, Ala., between January and April last year. The unit has a capacity of 270 MW.

Gaston has a baghouse to remove remaining particulates from flue gas after it leaves the precipitator. The test injected activated carbon after the precipitator and used the baghouse to catch the particles, according to Jean Bustard, executive vice president of ADA-ES.

Tests at Gaston included a 10-day continuous run that removed about 80 percent of the mercury from the flue gas. Bustard and Monroe agreed that more could have been removed, but carbon injection was limited by the capacity of the baghouse.

Bustard said ADA-ES is currently testing the activated carbon system at a plant in Massachusetts. In that setup, carbon enters the exhaust stream after the main precipitator and in front of an electrostatic precipitator.

Technology for Diversity

There's no doubt that coal's image is tainted. Out of hundreds of proposals for new power plants in the United States, coal projects can be numbered in tens.

Natural gas has become the fuel of choice for power generation. Consider one of the crown jewels of clean coal, the Polk Power Station in Florida. While Unit 1 at Polk burns gas made from coal, Units 2 and 3 burn natural gas.

Coal, on the other hand, is often seen as the fuel of diversity. Or one of them, at least. There are also hydro, wind, solar, petroleum, and nuclear—some more important than others. Biomass is another option, whether it is banana plantation waste, chips from the lumber mill, or municipal trash, either burned straight or gasified.

Diversity of fuels has become a given for a sustainable energy supply, for political and economic reasons. Clean coal technologies play into that drive for diversity not only by curbing the environmental risk of an available resource, but also because the gasifier and the CFB can handle fuels besides coal.

Duncan of JEA said the new CFB boilers being tested at Jacksonville can handle coal or petroleum coke, or even as much as 22 percent biomass. He said the company will test coal under the DOE program, but the current plan is to run both boilers primarily on coke. Unit 1 is burning 70 percent petroleum coke and 30 percent coal.

The Polk station is testing different fuel sources, a spokesman said, and has tried pet coke among them.

Amick said that Global Energy has repowered the Wabash River gasifier with pet coke with no change in plant hardware. He said the switch was made for economic reasons.

New sources in Venezuela, which has South America's motherlode of petroleum, have come onto the market and competition is driving down coke prices.

"We got a good deal on petroleum coke," he said.

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