Burning coal in place or in-situ gasification
Posted by Heading Out on March 5, 2006 - 1:01am
The Chinese government has authorized an underground coal-gasification project in Lineng of Shandong Province recently. This is a model project combining in-sit-coal gasification and gas-fired power generation., as well as being of interest to the British, the Australians and ourselves, to name but a few.
This is another in the weekend technical talks that pop-up at frequent intervals on this site, It fits in with a series on coal technology that is listed at the end of the post, and more particularly is related to other ways of generating fuel from coal other than just burning it in a boiler to generate steam. As with a number of ideas that are getting more discussion (such as the injection of carbon dioxide back into the ground, and the use of pulverized coal in diesel engines) it is not particularly new, but since it is now getting more attention, the post will attempt, in a relatively simple manner, to explain what it is all about. For those more knowledgeable please do comment, as should those who find the explanation not totally clear.
Which brings up the first point, which is that coal can, on its own, catch fire. The old pit heaps that dotted the landscape around mines were made up of old coal waste, including a fair amount of un-recovered coal. When they were later reclaimed it was often found that the tips had caught fire and burned the clay into a red-brick-like material. This self-ignition is known as spontaneous combustion and occurs because
Coal reacts with atmospheric oxygen even at ambient temperatures and this reaction is exothermic. If the heat liberated during the process is allowed to accumulate, the rate of the above reaction increases exponentially and there is a further rise in temperature. When this temperature reaches the ignition temperature of coal, the coal starts to burn and the phenomena is described as spontaneous combustion.Coal oxidation can occur in coal storage and, as I mentioned, undergound.The temperature at which the coal oxidation reaction becomes self sustaining and at which spontaneous combustion occurs varies generally depending on the type (nature and rank) of coal and surrounding conditions of heat dissipation. In poor quality coal and where the heat retention is high the coal and carbonacous material may start burning at temperatures as low as 30-40° C.
The fires are not always spontaneous, perhaps the most famous is the Centralia fire where the coal seam outcropped at the surface, where it ignited, and the fire then moved underground and beneath the town of Centralia, PA. Despite vast amounts of effort, money and time, the fires are still burning.
Which brings me to the second point. For a fire to continue to burn it has to have fuel (the coal) and air (oxygen). If the fire is totally cut-off all the air is consumed and the fire goes out. But if there are cracks through which air can reach the fire, then it will continue to burn. Thus, in Centralia, for example, as the coal burned in and under the town, it removed part of the rock holding the town where it was. The ground would then collapse into the burned out cavity, and a crack would run up to the surface along the edge of the opening, allowing air to flow back down to the fire and continue the progression. Having been once involved in fighting such an event, it is very difficult to tell where the fire front is, and the coal does not burn in a vertical front, but in a very jagged pattern, depending on air flow and relative composition of the different layers of the coal. The air generally flows through the cleat pictured here.
Having proved that coal seams can burn in place, we still have to work out how to make that useful. Short of running water pipes down, and using the steam that comes out for power surely there has to be a better way of getting the energy, and there is.
In the post last week I described how the old gas-from-coal plants worked in the UK to produce town gas. Simply put by heating the coal, and passing air and steam across it, one can generate "producer gas' and "The final composition of producer gas is about 12% hydrogen, 25% carbon monoxide, 7% carbon dioxide, and 56% nitrogen; the nitrogen comes from the air used in the producer gas reaction." So that if we can get the water and air to the coal fire underground in the right quantities then we can generate a gas that we can extract and it can be used as an energy source.
Sounds easy, right? It turns out that it is not quite that simple. Again from the DTI report on the Chinese work (pdf file)
Underground coal gasification (UCG) experiments have been carried out in many coal mining countries and industrial scale production has been achieved in the former Soviet Union. More than 15Mt of coal has been gasified by UCG and in excess of 50 billion m3 of gas has been produced from UCG projects around the world. Despite research and many trials in different countries, no truly commercially viable UCG project has yet been demonstrated. However, various technologies are now available which could change this situation. A shallow seam, commercial power generation project is currently under development in Australia.The problems relate to a number of issues, but let me concentrate on two.
In the initial concept, it was proposed that two wells could be drilled from the surface to the coal seam. In one early US test of this idea, in Hannah WY, the seam was relatively close to the surface, and for the first test the wells were set 75 ft apart. After reaching the seam, it was intended that the connecting passage between the injection well and the extraction well would be created by starting a small fire at the bottom of the seam, at the first producing well, and then by blowing air down the injection well have the fire work back to that well along the cleats through which the air was passing. By restricting the flow it was intended that the passage would be small, and run along the bottom of the seam. Then, once a passage existed, more air and steam could be fed into the injection well, increasing the size of the fire, and creating the producer gas that could be extracted from the production well.
Unfortunately the fire would not "behave" and over-burned the coal, rather than burning in the lower section, and did not otherwise go as planned. The conclusion was that this passage had to be artificially created first. The need for a long hole in the coal requires a directional drilling tool, and in the 1970's when the earlier trials were made, those were not available, particularly ones that could turn ninety degrees within the 140 ft from the surface to the seam. One had to be invented (and was). Thus in recent experiments the UK planners have looked at directional drilling from the surface to the coal, as a way of creating the initial passage, and providing paths for the air and steam to the fire and for the producer gas to come out.
(Source UK Coal
Two different approaches are being looked at in China, one of which works by creating panels in existing mines from adjacent cross-cuts, while the second uses a pair of directionally drilled holes with the fire to be initiated between them. Although as I mentioned from the work done in the US, getting that initial connection may be rather difficult and long-term control of fire location gets to be rather tricky.
(Derived from the DTI report).
This is a part of a series of talks that has, most recently, dealt with coal mining.
Gas and gasoline from coal
As usual any concerns, corrections, or questions, should be addressed in comments.
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Oil was put here on earth to tempt man into sin. Coal was put here to punish him for for giving in to temptation. Coal is the direction that's going to taken, no matter the negative consequences. Woe betide us.
Any methods that lessen the impact on GHG has to be supported, with the planet weighted down by so many humans wanting to live like those in California. What will be adopted into new equipment to keep coal-fired plants relatively clean will be vital over the next ten years.
We have a lot of coal in North America. Not so much in Europe, China, or Japan.
Can you (or anyone else) point me to a source for understanding current and projected numbers of coal utilities?
Thanks.
Yes I can. Christian Science Monitor ran the article and it can be seen at:
http://www.rense.com/general61/jyoto.htm
EIA coal link
Top 3 energy demand nations in world are in the top 4 of coal reserves? Ominous...
Increasingly, I see the battle of the next few decades being between peak oil and climate change and the tradeoffs therein.
Your point about trade offs is right on.
The scary thing too is that the USA is talking about 120 new power plants and we have two, a whole two, that are synfuel, under construction (there may be one completed . . . ?) and apparently they are small plants at that.
We have a local Supervisor race underway, and Diablo Canyon nuclear power plant is in my backyard. One of the candidates wants to stop nuke power and talks about building thousands of PV systems on homes in our county. Wonderful idea, but the solar industry right now is having supply problems. And a whole six silicon plants for PVs under construction around the world as of last fall. Anyone have better figures on this?
That is what is striking to me. Good ideas not being executed at any required scale to make an immediate difference.
For example Australia is cock-a-hoop over coal exports to China and has effectively emasculated the greenhouse watchdog agency and climate scientists. The government's chief science advisor took a second job as a coal industry lobbyist. I live in an area that was all hydro with some NG peak load but is now connected to high emissions lignite burning plants.
I long for the day somebody who loses out to global warming will sue the coal barons.
Happened in the time of Socrates: Many Athenians were suing many of their fellow citizens others over most everything, and hence the sophists (old Greek name for shyster-lawyer) thrived and multiplied. Happened again near the end of the Roman republic. The more things change, the more they stay the same. Athenian democracy self-destructed, and the Roman Republic, after civil war, became the Roman Empire. The proliferation of lawsuits is both a symptom and cause of terminal decline.
When lawyers run things such as corporations or governments, they generally fall apart. Why is this? Well, Plato thought it was obvious: Lawyers accept money to make the weaker argument appear the stronger. Thus they corrupt their souls and destroy the young by their example, and they also destroy any form of decent government.
Not all lawyers are bad. I personally know two who are honest and competent, and I have heard that there is one other of this kind in Minnesota;-)
Show me an oil company, a coal company, a university or an airline or a government run by lawyers, and I'll show you an organization in serious trouble.
What I object to is government of the lawyers, by the lawyers and for the lawyers.
Compare, for example, the U.S. and Japan. The U.S. has--what? 2 million lawyers? Very rapid rate of growth in enrollment in law schools . . . . true?
Now look at Japan. Hardly any lawyers, a few tens of thousands. Guess what:
1. Japanese live longer than Americans.
2. Japanese have far more leisure than Americans because they retire younger and have far fewer women in the work force.
3. Japanese have far less drug addiction, depression and other diseases rampant in U.S.
4. Japanese have a high and positive saving rate. U.S. has a negative saving rate.
5. GM and Ford are headed to bankruptcy; Honda and Toyota flourish.
6. Do we begin to see a pattern here? I am not blaming everything on lawyers, although after viewing the "Bleak House" series on PBS and rereading the novel by Dickens I am tempted to do so. As Socrates and Plato realized, the proliferation of sophists (i.e. lawyers) is as much a symptom as a cause of decay.
Note that never in their gloomiest nightmares did our Founding Fathers envision a rule by lawyers. They thought the lessons of history were so clear that we could not be stupid enough to fall into that trap.
Well, they were wrong.
1. Generally you are honest and
2. You can think quantitatively.
Alas, you are few.
And the organization currently in the greatest trouble is the US federal government.
Now, is it any coincidence that by far and away more members of Congress come from a legal background than probably all other professions combined?
Of course we need a legal system. Without the enforcement of contracts and property rights all meaningful commerce would stop. But when legal warfare in and of itself becomes a common and accepted means of generating wealth, then I agee that is a sign of real trouble.
By current definition, a lawsuit adds to the GDP (just as 10-car accident does), but does it really add to the general welfare?
1. Suing our doctors, because they have not kept us in perfect health.
2. Getting a divorce once a year.
3. Suing our parents, because they screwed us up.
4. Suing our children, because they do not support us in the style to which we would like to become accustomed.
5. Suing our lawyers, because they did not get us the settlements we wanted in #1. through #4.
Thus you see the future of economic growth . . . .
Wish I were kidding about this.
O.K., then let's get back on topic, which as I recall was the burning of coal in situ...as opposed to burning it in a powerplant, or extracting coal bed methane (CBM) or extracting it to be used in a coal to liquids (CTL) plant, or in a CTG (Coal to gas) plant, or in first CTG and the the gas to liqiufy and make fertilizer....are we starting to get a picture here....most current estimates give the reserves of reasonably extractable coal to be around 100 years worth, AT CURRENT RATES OF CONSUMPTION.
In a recent analysis I found on this issue, it was projected that if we endorsed a major coal to liquids conversion program, that number would come down by half...and if we went further and tried to do in situ burning, and coal to liquids combined..(??), well then it would be a race to see if we could make it a three way race to depletion between crude oil, natural gas and coal within three decades. We are like the kid who is given the dollar and then has three places to spend it...so he wants to spend the dollar three times!
Coal is now in a comparable situation to the one natural gas was in back in the early 1970's...when we were told we had an easy century worth left...of course, no one accounted for Dr. Hubbert's idea that the second half, only 50 years out, would be much harder to extract than the first half, and no one realized we would more than double our consumption, meaning that peak extraction was MUCH closer at hand than expected...more like 30 years than the "century's worth of clean gas" that had been expected. Note the big difference between coal and gas...gas is relatively clean. The coal CO2 output could be catastrophic unless this issue is resolved.
So if all these plans were to work at full utilization, we would have bought a few short years, (and who can imagine where the infrastructure, technicians and manpower will come from for all this) before coal started getting harder and harder to get to and use (leave aside the real risk of uncontrolled flame front and fires that cannot be controlled or stopped, thus wasting more coal, which would be no fun to mine the old fashioned way with fire and gases still loose in the mine...) we end up with a CO2 blast into the atmosphere for a couple of decades, and then the smoldering smoke from fires burning for another (??) what, half century...and we would have bought maybe a decade or two worth of power, at incredible cost....picture it, it would look lke Dante's inferno with columns of black smoke rising from the abandoned mines, choking gases and abandoned mines....quiet a legacy we are leaving to the grandbabies ain't it?
Go to offshore coal, like the giant North Sea coal bed that has been discovered, and mix in filthy sea water with ash and muck being swept around the North Atlantic, and remnent uncontrolled fires below the ground that is below the sea, and the picture just get's prettier and prettier don't it?
Thank you for your thoughtful response.
If a major utility said today that it was planning to build a nuke, I would not take even odds that it would get up and running before 2012, if that, or if ever.
No, I fear that we are going to claw and scratch at each other till the stern of the Titanic finally slips below the waves. Technology is hardly the limiting factor in our ability to survive. WE are the limiting factor in our ability to survive.
I am looking for more definitive info on what our current best technology is, generating GTL, CTL, in-situ or otherwise and sequestering the carbon - how much of an EROI hit is it?
So one last great pollution blow out and we expire, unless a huge climate shift does us first.
From Bleak House to Bleak Planet - time to drag out the Dickens.
If we go with oxygen-blown IGCC, the cleanup yields less CO2 in two ways:
- Total thermal efficiency is higher, so less coal is needed per kWh; a 20% boost in thermal efficiency (from 10200 BTU/kWh to 8500) cuts emissions about 17%.
- Roughly half of the carbon is converted to CO2 in the gasifier, and it can be removed from the fuel gas along with the hydrogen sulfide. Co-capture is deemed cheaper than separate capture, and both gases can be sequestered together. Co-sequestration would cut carbon emissions roughly 58%.
We'll only be stuck in your dilemma if we allow more powdered-coal fired atmospheric boilers to be built. Given the stakes, we should not grant any more construction permits for them and implement stiff taxes on their emissions to get them replaced and retired ASAP.- The producer gas way: blow with air and steam continuously, get low BTU gas (~100-150 BTU/cf).
- The water gas way: blow with air and then steam on a cycle, get ~300-400 BTU/cf. (You can still buy small units in Europe).
- The modern gasifier way, blow with air and oxygen continously, get 300-400 BTU/cf gas. (There are a few air-blown Lurgi gasifiers). Only good way if you want to make methane later.
You need an oxygen plant for number 3. Lots of additional capital and a power requirement. IIRC, most of the tests were done with continuous air, but on a large scale you probably end up with 2 or 3.12% hydrogen, 25% carbon monoxide, 7% carbon dioxide, and 56% nitrogen
How well does this burn? Doesn't it have a pretty high inert content? Caution - I sucked at chem!
I've had some experience with in situ bioremediation of hazardous waste sites from my environmental consulting days. In that technique one tries to contact the subsurface contaminated soil and/or groundwater with an aqueous stream saturated with air and containing small amount of nutrients. The purpose is to stimulate the endigenous soil bacteria to chomp away on the organic contaminants. The stream is often recirculated. Even though the technique has advanced quite a bit, it is inherently tricky, for it is very difficult to tell what is really going on 'down there'. One often doesn't know if one is coming or going.
And I guess one has the same sort of problem with in situ coal gasification. It must be a constant battle to keep the whole thing under control and to maintain the conditions that are conducive to efficient gasification. Keeping the combustion front where you want it must be exceedingly difficult.
I was wondering whether there has there been any work done on trying to gasify the coal by means other than lighting an undergound fire? Just thinking out loud: but what about electrical resistance heating? Or ciculating a superheated non-oxidizing gas such as very hot CO2 or nitrogen?