Stick a chunk of lignite in your home microwave and you’ll find that it doesn’t even warm up: coal is transparent to microwave radiation. But you might also notice that when you’re done, your lump of “brown coal” is sitting in a little puddle of water. Electromagnetic radiation in the microwave spectrum causes polarized molecules in water to build up thermal energy due to dielectric heating. Water that’s trapped within the coal begins to expand as it nears the boiling point and will actually create cracks in the coal to force its way out.
Admittedly, this property lacks an obvious household application. But for thermal power producers, who burn hundreds of thousands of tonnes of coal per day, this method of drying their feedstock could revolutionize the industry and turn billions of tonnes of relatively worthless, low-rank coal into a ready and saleable product.
Money can be made and saved if low-rank lignite can be used as a replacement for bituminous coal or anthracite, which, when extracted and burned, has negative impacts for the landscape and environment.
That’s the promise of a Vancouver venture-capital start-up called MicroCoal Technologies Inc. Originally led by a small team of entrepreneurs with a background in the Polish thermal coal industry, MicroCoal fixed upon the idea of microwave drying coal in mid-2000.By 2012, it had a functioning test facility operating at the Hazen Research facility in Golden, Colo. It’s an innovative vertical processor: you drop lignite in the top of a chute, microwave it on the way down, vacuum off the water and collect the dry coal on a conveyor at the bottom. “So, we know it works at eight tonnes a day,” says MicroCoal CEO Lawrence Seigel. “The question is whether we can make it work in the thousands of tonnes.”
MicroCoal is on track to find out. It is currently partnering with the company PT Wajiya Tri Utama to build a processor attached to a thermal power plant on Kalimantan, the Indonesian portion of the island of Borneo. The plant, which is set to open this October, is designed to dry 190,000 tonnes of lignite a year. By removing 10 percent of the lignite’s moisture, MicroCoal believes it can increase the calorific count of the lignite from 8,000 British thermal units per pound to 9,000 BTU, turning an almost useless fuel into a cheap, efficient and slightly cleaner thermal plant feedstock. And if they can prove the process works, Seigel says, the company expects to be fending off inquiries from thousands of thermal power plants the world over.
MicroCoal’s technology stems from one of those eureka moments in science. In the 1940s, Percy Lebaron Spencer, a self-trained electrical engineer with a serendipitous sweet tooth and a fortuitous attention to detail, was leading the combat radar program for the United States defence contractor Raytheon. The company was building magnetrons that generate the microwave radio signals that are the core mechanism of radar. One day, Spencer was standing too close to one such machine when he realized that the candy bar in his pocket was melting. He started experimenting with other foodstuffs and, in 1945, Raytheon filed the first patent for a microwave cooking oven — paying Spencer the customary $2 gratuity that it gave to all its inventors at the time.
The challenge of “wet” coal pretty much demanded another, similar innovation. The easiest and cheapest coal to access in the world supply is lignite, the youngest version of a fossil fuel that has not fully metamorphosed into high-rank bituminous coal or anthracite. Those older coals tend to be buried deeper in the ground, whereas lignite is usually near the surface.
Unfortunately, lignite also tends to have a high content of both moisture and non-organic matter such as sand and soil. Howard Herzog, a senior research engineer at the Massachusetts Institute of Technology (MIT) Energy Initiative, says that a useful synonym for lignite is “dirt” — uneconomic even for low-value applications such as the firing of thermal power plants. Angela Waterman, vice-president of Environmental and Technical Affairs at the Mining Association of British Columbia, adds that her province ships virtually no lignite; the transportation costs are prohibitive because of the high earth and water content. Thus, lignite is sometimes referred to as “stranded coal,” destined to stay where it is, even in the current competitive market.
MicroCoal’s proprietary microwave process utilizes technology that reduces inherent moisture in low-rank coal prior to combustion. This helps reduce costs and inefficiencies as well as greenhouse gases and other pollutants. Photo credit: Microcoal technologies
For obvious reasons researchers, coal and power companies have been trying all manner of methods for drying out low-rank coal. In thermal power plants, the simplest method is to build an oversized boiler, counting on the heat to vapourize the water and then ignite the coal. But the process is inefficient, expensive and dangerous because wet coal is more explosive. Another common method is to use off-peak waste heat to dry coal before sending it into the boiler. But MicroCoal director Slawomir Smulewicz says that most heat-drying processes warm the coal to near its 455 C ignition temperature; you wind up using almost as much energy to dry the coal as you gain from its ultimate combustion. A microwave-based drying process, on the other hand, separates coal and water, rather than heating both till the moisture evaporates. With the MicroCoal process, temperatures never rise above 100 C, so microwave drying can be four to 12 times more energy efficient, Smulewicz says.
Smulewicz adds that the microwave process has beneficial environmental impacts, although the extent of the benefit is a matter of argument even within the company. First, while microwaves are transparent to organic sulphur, they act to excite pyrite and other contaminants, which tend to separate and be washed away with the water that is being vacuumed off in the MicroCoal process. The term is always relative, but Smulewicz describes the result as “clean coal.”
As a side benefit, the watery effluent from this process contains a certain amount of coal dust — effectively activated charcoal — so the pollutants precipitate out, leaving water that is clean enough for use after a simple and relatively inexpensive filtration. This can be a huge advantage in a place like Indonesia, where clean, fresh water is in short supply. If you are removing, say, 10 percent of the moisture from the feedstock for a 1,000 megawatt power plant, which burns three million tonnes of thermal coal per year, you wind up with 300,000 tonnes of available water. That’s enough to satisfy the power plant’s steam and cooling demands. Because the microwave-treated feedstock has a perfectly consistent moisture content, it’s also easier to adjust the thermal plant’s boiler for an optimally clean burn, which increases depletion of the nitric oxides that are another problematic component of coal plant emissions, Smulewicz says.
A complication of this preparatory microwaving and water vacuuming is the energy consumed. Unlike waste heat, microwaves are a very high-quality energy source. But by marrying its processor to a functioning thermal power plant, MicroCoal is also able to harvest “waste” energy to run its operation. Thermal generating stations are huge heat factories. During the day when power demands peak, operators run the boilers at maximum capacity, producing steam, which is then used to drive massive turbines, capable of generating electricity almost at the flick of a switch. Come night, however, when demand subsides, operators disconnect the turbines, but they can’t just douse the flame or they’d be days getting the plant restarted. So they wind up venting a huge amount of waste heat straight up the chimney. MicroCoal plans to use that otherwise-wasted resource, continuing to generate enough electricity to dry and store enough coal to fill the following day’s demand.
Seigel is blunt about the importance of this first commercial application. He also acknowledges that they are likely to run into significant challenges in a large-scale facility that didn’t crop up in the small test plant in Colorado. But, he says, there are thousands of thermal plants around the globe and more than 20 percent of the world’s 850 billion tonnes of known coal resources are in the form of cheap, available and mostly stranded lignite. There’s money to be made — and money to be saved — if lignite can be used as a replacement for bituminous coal or anthracite.
There is, of course, the added complication that a huge additional supply of cheap and accessible coal will also increase the climate change threat attendant to the burning of CO2; coal fired power plants are already the biggest point sources of CO2 pollution in the United States and are a fast-growing source in China and around the world. MicroCoal claims its process can also reduce CO2, but only by a small amount (for every two percent reduction in moisture content, there is a one percent reduction in CO2 emissions). The ultimate solution to that emission problem would be full-bore carbon capture and sequestration.
The only current example of a thermal-plant carbon capture project is about to come on line in Saskatchewan with the integrated carbon capture and storage (ICCS) demonstration project at Unit 3 of SaskPower’s Boundary Dam generating station near Estevan. Coming in at $1.355 billion — nine percent over budget — it will be the world’s first commercial-scale, post-combustion, carbon capture of coal. The scrubbers are designed to trap a million tonnes of CO2 a year, which will then be sent through 100 kilometres of pipelines and pumped into underground reservoirs to enhance oil recovery. Sulphur dioxide will also be captured and sold. SNC Lavalin and Cansolv Technologies Ltd. are overseeing engineering and construction.
SaskPower reports that it is fielding inquiries from coal plants around the world about the technology but MIT’s Herzog notes that there is no real incentive for coal or power producers to use this process: “No matter how successful we are [in refining CCS], it will always be cheaper to emit CO2 than to store it. But sooner or later, we’re going to have to deal with climate change, and when we do, this technology will be important.”