Illinois Coal, part 3

At the mouth

Sequestration will inevitably bump up the cost of electricity, although DOE hopes to hold FutureGen to only a 10 percent increase over a nonsequestered system. But improving mining productivity can help make both IGCC systems and sequestration more feasible economically. Mining engineering professor Chugh, for example, is overseeing several projects with the overall goal of cutting the cost of a ton of coal by 20 percent or more.

The Midwest, Chugh's data indicate, will see about a 10 percent increase in demand for power over the next five years. Chugh worked as a DOE intern in summer 2004 to study the potential for meeting that demand with gasification technology. The chief roadblock for companies, he says, is "the capital costs requirement and the uncertainty of economic feasibility," given that a 1,000-megawatt IGCC plant would cost at least $1.5 billion to build.

Chugh's solution is to offset costs by using a mine-mouth approach. That means siting coal preparation plants and power plants adjacent to mines to avoid having to ship the coal. (Shipping coal by rail costs about 4 cents per ton per mile, which adds up fast.) By using mine-mouth facilities, IGCC is economically feasible in the Midwest, Chugh's analyses show. "It helps a bundle," he says. "It helps enough."

The mine-mouth concept also can come into play with new combustion plants using the best pollution-control technologies. Such plants are expensive propositions too. The more that companies can bring down the cost of a ton of coal, the more they can justify the capital outlay for building a state-of-the-art facility.

Chugh and Bane Kroeger, an assistant professor of mining and mineral resources engineering, are using a $250,000 grant from the Illinois Clean Coal Review Board to demonstrate the technical and economic feasibility of the mine-mouth approach at a pilot-scale coal industrial park. Three sites in central Illinois are being considered. Because building a small power plant for the demonstration isn't an economical option for industry partners, the park will burn the coal using a modified fluidized bed combustion unit and run an ethanol plant with the resulting steam.

The combustion unit will use limestone to capture sulfur dioxide. Combustion waste and waste from fine coal cleaning will be used for construction in and around the mine. With DOE funding, Chugh and his team have successfully tested support pillars made of this material.

"Every new mine should look at the mine-mouth approach," Chugh says.

"We want zero or near-zero solid waste discharge from the mine, and we want to squeeze every Btu we can out of the coal we're producing."

Waste not, want not

Another way to increase productivity while helping the environment is to reduce the amount of waste material mixed in with the coal coming out of the mine, which can account for up to 35 percent of the yield. Preparation plants remove as much of that extraneous material as possible, but it's an imperfect process.

The problem is that continuous miners, the big machines that bite out the coal at the mine face, don't just hit the coal seam. They also bite into a bit of the rock strata above and below, and that material gets mixed in with the coal. The phenomenon is called "out-of-seam dilution." For safety reasons these machines are controlled remotely, from 20 to 25 feet away, so the operators can't see when the machinery is getting out of the seam.

"We're the only ones in the world who have done a systematic study of out-of-seam dilution and its impact on coal production costs," says Chugh. "We found that it can increase the cost of producing coal by 20 to 25 percent. Most people in the industry don't realize that. Out-of-seam dilution also affects coal quality--it adds big-time to the amount of trace elements in the air."

Chugh worked with Viper Mine, in Elkhart, Ill., to develop a pilot training program to help operators reduce out-of-seam dilution. "We thought from some earlier work we did that we could reduce it by 3 inches," he says. "We've achieved 1 inch, and the rest will require developing a device by which the operator can control the height of the mining head, so he knows if it is starting to contact the roof or the ceiling [i.e., pulling in material from outside the coal seam]. That's the next step, and we're already working on it."

The machinery in underground mines creates a lot of fine coal particles at the mining face that get mixed in with the coarse coal. Another way to reduce waste and increase mining efficiency is to clean, dewater, and use this fine coal (generally defined as less than 1 millimeter in diameter) instead of discarding it. Over the years, SIUC and other researchers have tested and refined various fine-coal cleaning and dewatering technologies for their suitability for Illinois coal. But nearly half of the preparation plants in Illinois have yet to adopt such systems.

In fact, Illinois plants are disposing of about 1 million tons of fine coal in slurry ponds every year, says Manoj Mohanty, an assistant professor of mining and mineral resources engineering. If only half of this "waste" coal were recovered--cleaned and dewatered to make it suitable for burning--the Illinois coal industry could generate an extra $10 million per year. That would enable companies to cut the selling price of Illinois coal and still maintain profits.

The systems used at preparation plants to clean coarse coal of extraneous mineral matter don't work efficiently for fine coal, which must be separated out. Within the fine-coal range, many plants further separate out particles 150 microns or bigger, which can be cleaned using conventional technologies. But coal particles smaller than 150 microns--much finer than the finest sand--can't be handled by most plants and get discarded.

This situation will change, Mohanty hopes, with new technologies he has tested. With funding from the ICCI, he and Bane Kroeger first tested a new type of screening equipment, originally developed in South Africa, at the Knight Hawk Coal Company's Creek Paum mine near Ava, Ill. The equipment, called a Pansep Screen, "does an excellent job" separating out that sub-150-micron fraction, Mohanty says. Then, with a second ICCI grant, he added and successfully demonstrated two new pieces of technology at Creek Paum that can process coal this size: a cleaning system developed in Germany, and a dewatering system developed in South Africa.

The first system, called a G-Cell, uses a froth of water bubbles to carry coal particles away from heavier impurities. It also uses centrifugal gravity forces to spin out some of the hardest-to-remove impurities: sulfur-laden pyrite particles. Mohanty was interested in the G-Cell over other possible cleaning technologies because its ability to reduce pyrite is a good choice for high-sulfur Illinois coal. The equipment had been tested on a pilot scale in Europe but hadn't been evaluated yet in the United States.

The dewatering system, called a Steel Belt Filter, combines two conventional dewatering technologies. It first removes some of the water using a vacuum filter. Then, to squeeze out as much of the remaining water as possible, it feeds the concentrated slurry between two steel mesh belts moving in opposite directions.

Mohanty's goal was to optimize these technologies for the types of coal found in Illinois. They're more efficient and economical than current technologies, he says, and thus should be more attractive to Illinois plants. They could be adopted in the near term. What's more, he says, they also could be used to recover fine coal from existing slurry ponds.

With a grant from DOE, Mohanty and his team also recently tested equipment at an earlier stage of development that he designed himself. His invention ultimately could replace two steps in processing fine coal--size separation and cleaning--with one step. It can clean all coal particles below the 1 millimeter threshold with no further separation required.

The invention, called an EG (for enhanced gravity) Float Cell, "is the first of its kind to do that job efficiently," Mohanty says. SIUC, which will file a patent application on the invention, has already found an industry partner to commercialize it.

Keep on Truckin'

Finally, mining productivity also relies on keeping the machinery running. And little things can gum up the works.

Take dust. It's a health hazard for miners, and the government limits the amount of fine dust (the most dangerous kind) to 2 milligrams per cubic meter of mine air. Often, productivity levels must be lowered to keep mines in compliance.

Scrubbers mounted on continuous miners function something like wet vacs, sucking in air and spraying it with water to wet and filter out dust particles. Chugh recently partnered with Joy Mining Machinery to improve scrubber design. With dust under better control, productivity can stay higher, bringing down the cost per ton of coal. One coal company has already ordered new scrubbers based on the SIUC/Joy design.

Chugh and his team are also working with industry to redesign and test two different haulage systems to improve the efficiency of transporting coal from the mine face. Continuous miners scoop the coal onto a belt that carries it back to haulage cars. When cars are changed out, the machine must stop running for up to a minute. That sounds negligible, but think again.

"Continuous miners produce 16 tons per minute," says Chugh. "If you can gain even 10 minutes of extra productivity over an 8-hour day, that's an extra 160 tons--which is 2 to 3 percent of the mine's output. That's pretty substantial."

Bane Kroeger tests the mine roof prop he designed

One of the haulage systems being redesigned is a modification of what's currently in use; the other is a revival and adaptation of an older design from the 1970s. The goal is achieving near-continuous haulage.

In another project that will increase efficiency, Ohio-based Excel Mining Systems Inc. recently licensed a type of steel roof support invented by Kroeger to replace wooden and other steel props in longwall mining. Kroeger's telescoping props can be installed in less than two minutes by a miner working alone. They also are safer than current steel props, some of which can't bear the weight of the mine roof until workers have finished tightening the bolts. The new props, which will be on the market within the next few months, have an adjustable, telescoping design to fit roofs of varying heights and can support a roof as the prop is being jacked into place.

"We're at the cutting edge of new mining systems development," Chugh says. These new systems can help pave the way to adopt IGCC technology by making coal production more economical, but they also can help existing operations. And many of them reduce pollution and waste.

Companies anticipating tougher air pollution standards that will necessitate scrubbers on all combustion plants--even those burning western coal--are already planning to open several new underground mines in Illinois. Others would like to take a renewed look at Illinois coal, Chugh says.

The saying may be "black as coal," but the future of Illinois coal is looking greener.

For more information about SIUC's coal research program, contact John Mead, director, Coal Research Center, at (618) 536-5521 or jmead@siu.edu.

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