Sep
4
The Fuel That Won’t Go Away
September 4, 2008 | 2 Comments
That’s how the CO2, environmental, and global warming people see it. It simply is to good to ignore. Vast amounts of carbon, solid as a rock to nearly soft as wood, coal is as easily handled as any fuel. It’s concentrated with some hydrogen so it burns readily and hot and can be used for myriad purposes. Great stuff for energy. But it would be best used in moderation.
Coal in Hand
Coal is born in the soil so it brings with it all the stuff that concentrates while the coal was forming. The minerals of note are usually mercury, expelled into the air by volcanoes to settle in or washed in by water, and sulfur in much the same way.
The down side is that coal is the weakest fossil fuel for hydrogen content. All the petroleum fuels have larger proportions so making them liquid in the first instance and handy in a much different way. But when it comes to carbon, the main player in energy handling by any sensible description – coal is king.
The future from what we saw yesterday is in gasification of coal then on to other processes to make other fuel products. Its gasification that we’ll look at today.
For the most part gasification is a vessel fed the coal, sometimes water and air. Under intense heat and pressure the coal comes apart into carbon monoxide (the air is to get the oxygen part) and hydrogen. What’s left is the ashes or slag, the mineral part that can be used for building roads and constructing other things. The stuff that won’t settle out into the ash or slag are things like mercury, sulfur products and the ammonia that forms from the nitrogen in the air. These things are cleaned with well-known technology leaving hot, ready to process syngas as the hydrogen and carbon monoxide is now described.
Gasification to liquid fuels is an expensive investment. This spring the highly respected Oil and Gas Journal (March 24, 2008, GTL, CTL Finding Roles in Global Energy Supply) revealed that Sasol of South Africa has between $67 and $82 in each barrel of fuel. Granted the fuel products are comparable to refined petroleum such as diesel, but the price would be close to $2.00 a gallon. That works good when coal is still low cost and oil is a high price. But the plants, as well known as the design and engineering is, are still quite complex and expensive. The National Academies suggested in 2005 that building coal gasification would be $25,000 per barrel. But the current budgets exceed $120,000 per barrel of capacity as with the American Clean Coal Fuel project. It will take a very long time to amortize that amount off the books.
The investment issue will likely see economizing over additional projects. It also explains why these projects are headed to high-density fuels in the middle distillate range like diesel and jet fuel. Airplanes, heavy equipment in mining and construction, farm equipment and other high power uses need high-density fuels. At low loads, such as personal transportation, with a few hours of operation time, would be better served when coal is turned directly into electricity where the efficiency would be three times higher even when charged into a vehicle.
The financial problem is only exacerbated by the carbon capture and sequestration of the approximately 3/4s of the carbon that cannot be hydrogenated by the coal fuel stream to a liquid fuel. That might seem to be an insurmountable problem, but to some algae people the CO2 flow would be a bonanza. The question coming is at what price for the CO2 flow.
That brings us to the old/new innovation of gasification in the coal bed without mining it at all. The history begins with the idea first floated by Sir William Siemens in 1868, then to a UK experiment beginning in 1912 that fell incomplete during WWI. The USSR began research in the 1930s and got to industrial scale in the 1950s and 1960s, but cheap abundant natural gas killed the effort. Uzbekistan still keeps its unit running, though. The Europeans took up underground gasification again in the late 1940s focusing on shallow deposits in narrow seams. Cheap oil and natural gas in the 1960s killed that off, too. The US used Soviet experience beginning in 1972, the Europeans restarted in 1989 to mixed results. But Australia tried again in 1999 to 2003 and should have a commercial startup imminently. China is said to have 16 trials underway.
What keeps the underground technology “back” is the facts of the lessons learned. The coal has to be deep, at least 300 feet and much better deeper than 1000 feet. Seams must be thick enough, more than 15 feet. No water can be nearby. The proportion of ash cannot be over 60%. That thins the applicable locations to only 600 of 847,488 million tons, less than 0.1%. Most coal is going to be dug up and processed at the surface.
In the other hand are the CO and CO2 issues. Fossil fuels are dauntingly effective at sequestering carbon. About 12 billion metric tons of CO2 comes from annual coal use of about 5 billion metric tons. (Gee, sequestered a lot of O2 doesn’t it?) So you liquefy the CO2 cooled to 32 degrees F and pressurize it to 2940 psi for storing it and you still have more than 11 cubic kilometers (A bit more than six tenths of a miles per side each) of cold high-pressure plant food. Which would make quite a lot of algae very happy indeed.
Gasification can be quite efficient, burn the syngas to propel a generator, use the remaining heat to make steam for another generator and whatever CO left over can be run through a catalytic converter to make CO2 releasing even more heat. By then you have a lot of plant food available for adding hydrogen and making liquid fuel. Should the integration of gasification and combining heat uses and the processes to making a plant food at the end be engineering and financially viable the overall efficiency of coal would be much higher. That might reduce the need for so much being dug out in the first place. But when can the algae industry afford to buy CO2? Maybe a bug to just make methane would be more viable.
A Sharp Hat Tip to Al Fin for prodding a deeper look. Thanks Al.
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