June 01, 2012

Researchers studying coal-to-synthetic gas process

by Tim Crosby

CARBONDALE, Ill -- In the evolving business of coal gasification, the holy grail of efficiency lies in two words: pressure and temperature. Creating those two unnatural conditions -- high pressure and high temperature -- are the leading costs in turning the energy-dense solid substance into a cleaner, more efficient and versatile synthetic gas.

Coal gasification, typically, is a bit of a cook’s recipe in most cases.  Depending on the type of coal and its content, engineers must subject it to certain amounts of heat, pressure and catalysts in order to convert it to so-called syn-gas.  Syn-gas, in turn, can be burned in gas turbines to make electricity or converted to liquid fuels such as gasoline, diesel or jet fuel.

Researchers at Southern Illinois University Carbondale, however, are looking closely at the main ingredient in this mixture -- coal -- and how manipulating its wide-ranging mineral content might help engineers more readily convert it to gas.

Tomasz Wiltowski, professor of mechanical engineering and energy processes, is leading an effort funded by a state economic development grant to find ways to actually prepare coal for gasification. If successful, such processes would likely lower the energy needed to subject the coal to the higher pressures and temperatures needed to make the switch.

Along with its combustible, organic energy-producing content, coal also contains many other minerals and metal oxides that do not burn.  Such impurities become the fly ash and bottom ash left over when coal is burned.  Iron, magnetite, aluminum, titanium and others can make up a small percentage of the coal.

The researchers are working on approaches that could turn this situation to a gasification advantage in two ways.  First, by simply removing some of the impurities before gasification, the process should become more efficient.  Secondly, if some of those impurities can be manipulated and transformed to act as catalysts that speed up the gasification, the result should again be higher efficiency.

“We are taking coal samples and preparing them for gasification by looking at those other minerals and such as catalysts that can speed up the process, resulting in using less energy to gasify the coal,” said Wiltowski, who also serves as director of the University’s Coal Extraction and Utilization Research Center.  “We are looking at in effect breaking the coal into pieces and saying ‘OK, this piece may work for gasification, we’ll leave it in.  But this may not, let’s take it out.’

“Also, when you’re supplying the heat for gasification you are also heating the material in the coal that is useless in that process.  So we’re not only looking at the rate of gasification, the speed, but also at ways to make it lower temperatures, lower pressures, which translates into dollars,” he said.

Working along with Sue Rimmer, professor of geology, and Manoj Mohanty, professor of mining and mineral resources engineering, Wiltowski’s research is funded by a $140,000 grant from the state Department of Commerce and Economic Opportunity.  The group has worked for the last year experimenting with the concept and creating seed data that they hope will translate into a much larger U.S. Department of Energy grant next year that will take it to the next level.

The researchers are looking at variety of coal approaches.  “We have samples where we remove 10, 20, 50 percent of minerals in a selective way, leaving those that we believe may help,” he said.  “Some of them help, some of them inhibit. We have some nice data that is very promising.”

Working at both the SIU Carbondale campus and at the Illinois Coal Development Park in Carterville, Wiltowski said if they are successful the research would not only lead to better efficiency in gasification but could provide a starting point for finding ways to gasify both coal and biomass together.  Such a process would hold much promise both in terms of renewable energy abundance and lessened environmental impacts.

One component that is very common to coal -- and that is near and dear to Wiltowski’s heart -- is iron.  In its various forms, iron can make up to 20 percent of the coal’s mineral content.

“I always say I fall in love with iron,” Wiltowski said. “It’s very cheap, and it’s practically everywhere and it’s one of the main components of the coal mineral matter.  And I believe it could be a catalyst for gasification in certain forms.  If you can find way to manipulate the iron to make this work, bingo, it’s the best way to go.”

While iron makes up a large portion of the coal’s mineral content, there are many others that make up 1 percent or less of that content.  But those are not escaping the researchers’ gaze either.  The group is looking at ways that gasification plants might create the conditions that would cause such minerals to diffuse into the surface of the coal, in a way that simulates the preparation of the catalytic process currently used in such plants.

“So this is something we’re exploring that really isn’t widely done,” Wiltowski said.