As oil and gas resources are projected to decline any time now, attention is increasingly focussed on coal as the principal fossil energy source in the longer term. It has further been proposed that synthetic oil can be manufactured from coal, e.g. using Fischer-Tropsch technology or other methods of coal liquefaction, as I have described in previous postings ("Gasoline from Coal"; "Coal may lead to 'Limitless Oil'"). How much coal there is actually present in the Earth is anyone's guess, but it is only the extractable coal that is of any significance. For example, 3,000 billion tonnes (3 trillion tonnes) have been discovered off the coast of Norway, but that cannot be readily exhumed from its undersea location. Indeed, I have seen estimates of almost 10 trillion tonnes of coal as a world resource, but 1.2 trillion tonnes (or a bit less) as a reserve, from which 5,540 million tonnes of coal were produced in 2004. This quantity rises year on year according to rising demand, particularly in China and India to fuel a gigantic and unparalleled phase of industrialisation. China puts on-stream a new coal-fired power station every week, each of which is about the equivalent of 4 typical U.K. power stations in its output.
Coal is one of the dirtiest of fuels. I have written previously "Coal and Dust" on the troubles of the Chinese coal industry, both in terms of the number of miners killed (about 50 times as many!) compared with the number killed in the U.S. during the production of an equivalent amount of coal, and the worrisome levels of pollution, and according health problems that it brings. This is a consequence of the enormous quantities of ash, and flue gases containing pollutants, notably arsenic compounds and sulphur dioxide. It is possible to first clean the emissions before they are released, but this of course adds cost to the whole enterprise. It is not widely realised that almost 50% of the energy used to mine coal in fact comes from oil. As I have pointed out, it takes energy to produce energy, but oil to produce coal is one vital component in the energy balance sheet, especially when coal is spoken of as a precursor to a synthetic substitute for scarce naturally abundant oil.
I shall assume that there are 1.2 trillion tonnes of coal that can be extracted with relative efficacy. This suggests there are 1.2 x 10*12/5.54 x 10*9 = 217 years worth left in the ground, ignoring any growth in demand. Now that is the amount available to satisfy current damnds for coal as a fuel mainly for direct heating and electricity generation. So what about conversion of coal to synthetic oil by various methods of coal liquefaction? The world burns 84 million barrels of oil per day, which x 365 days = 30,660 million barrels in a year. One barrel contains 159 litres (I had worked this out at 163.7 litres from Imperial Measures, but this is the oil industry figure). The density of crude oil varies enormously, and is highest according to the various levels of oxygen and sulphur compounds it contains, the "sweet" light crude being principally pure hydrocarbons, which have the lowest densities.
However, it is assumed as an oil industry figure that there are 7.3 barrels per tonne of crude oil, which implies a mean density for crude oil of 862 kilograms per cubic metre (for reference, one cubic metre of water weighs 1,000 kilograms). We would therefore estimate the mass of oil consumed worldwide as: 30,660 x 10*6/7.3 = 4,200 million tonnes, which is not far from the B.P. figure for the year 2004 of 3,770 million tonnes. Using Fischer Tropsch chemistry, 1.5 barrels of synthetic oil is obtained per tonne of coal, which amounts to 1.5/7.3 = 0.205 tonnes, or a 20% yield. However, there are Chinese coal liquefaction plants that claim production of 0.33 tonnes of oil per tonne of coal and so I shall hedge on the side of optimism and use this conversion instead. Hence, to produce all of our 3,770 million tonnes of oil synthetically from coal, we would need 3,770 million x 3 = 11,310 million tonnes of coal plus the 5,540 million tonnes currently used, i.e. we would need to roughly treble our coal production to meet this total demand, on top of the fuel required to actually run the processes themselves, whereupon the world coal reserve would run out in a little over 70 years.
Probably this is not at all realistic, and if we used half the currently produced coal (5,540 million tonnes) for oil synthesis = 2,770 million tonnes, that would give 2,770/3 = 923 million tonnes of oil or 24% of current demand. Interestingly, this amounts to about 20 million barrels a day, which is coincidentally the requirements of the U.S. alone, although I doubt the rest of the world would be prepared to give it all to them!
We would then need other sources mainly for electricity generation to substitute for the missing half of the coal production taken from the market to make oil from, maybe nuclear, and some renewable resources.
Now, coal is not evenly distributed, and all such sums depend in reality on actual levels of availability and extraction. The majority endowed regions in the world are the U.S., former U.S.S.R., Australia, China and India. Once upon a time the U.K. was a major coal producer and exporter, producing anywhere up to 300 million tonnes per year, but this has fallen as oil and natural gas have been adopted. Now the latter is running out, attention is once again turned to our old friend "coal". However, we have only 220 million tonnes or so left in readily accessible deposits. With the industrial strife of the coal mining industry in the 1980's (and in the 1970's too), and the final closure of many of the mines, it is not a simple matter to just start-up production again. True, the mines that were sealed-shut, spitefully with concrete by Margaret Thatcher's government, could be blasted open again, but meanwhile they have flooded severely, and it is a difficult matter to pump-out so much water and render the workings safe enough that they can be mined once more.
In 2005, we used 62 million tonnes of coal. Of that, 20 million tonnes (around 50:50 from deep mines and from surface mines) were produced in the U.K., while the rest was imported mainly from Europe. Clearly we cannot be self-sufficient in coal, and at best we have 220/62 = 3.55 years worth on these shores!
Even if we turned it all into oil, we'd have 220/3 = 73 million tonnes of oil, which is about one year's worth in total, for transportation and for industry including supply of oil as a chemical feedstock for manufacturing processes. If we provided all of our 62 million tonnes of coal from the home base, that would leave us with a capacity to produce (220 - 62)/3 = 53 million tonnes of oil, which is less even that our present annual demand to fuel transportation of 57 million tonnes. In short, we need to rely on coal imports...
Even at status quo levels of production (20 million tonnes per year), we still only have enough of our own coal to last 220/20 = 11 years.
So, we are in fact worse-off in terms of coal than we are in oil and gas, both of which the U.K. is now also a net importer of. It is proposed there are more (but harder to get) coal reserves in and off Scotland and under the North Sea, perhaps 1,500 million tonnes altogether. So, if we made all our oil from coal and provided that and all other demands for coal from U.K. reserves, we would need 220 + 60 = 280 million tonnes a year, so that's 1,500 million/280 million = 5.37 years worth. Even at this optimistic level of accounting, we are inexorably enmeshed in the European/world coal/oil/gas/uranium "mix" that we depend upon to provide our energy, and will never be self-sufficient in fossil fuels as some have voiced, using coal. There just isn't enough of the stuff left, as we have been digging it up for years, and selling most of it. I suspect we will experience cuts in electricity supply, as the rest of Europe did last week, before not too long. The nations with clout will be those with ample resources "at home" or accessible to them, and they are the U.S., Russia, China, India, Australia and Eastern Europe, increasingly part of the European Union, in consequence of the recent Enlargement policy. The EU, including the U.K., will need to maintain good cooperation with President Putin, since between them, Europe and "Russia" hold around 40% of the Earth's coal!
Friday, November 10, 2006
Shall Coal be Crowned King?
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4 comments:
Hi Chris,
Interesting post. I've been reading up on coal and its uses recently and consequently have a few observations/questions.
Chris: "Indeed, I have seen estimates of almost 10 trillion tonnes of coal as a world resource, but 1.2 trillion tonnes (or a bit less) as a reserve"
The figure of about a trillion tonnes increases dramatically if the price of coal increases. For example, U.S. reserves go up from about 250 million to 450 million if you assume a higher price.
Currently, known reserves of coal are so large (R/P in centuries) that exploration for new sources is low. In the long term the amount of recoverable coal may well be closer to the 10 trillion figure.
Chris: "It is not widely realised that almost 50% of the energy used to mine coal in fact comes from oil."
But is this necessarily so? Britain was mining 100 million tonnes or more of coal every year in the late 19th century. Was it really using large amounts of oil to do this? Furthermore, would it not be possible to replace the currently used oil with electricity from other sources or synthetic fuel from biomass or the coal itself?
Chris: "We would then need other sources mainly for electricity generation to substitute for the missing half of the coal production taken from the market to make oil from, maybe nuclear, and some renewable resources."
Your analysis ignores the fact that electricity is/can be a byproduct of the coal-to-liquids process. A U.S. DOE study into coal gasification with liquid co-production gave figures for a typical plant based on current technology:
Coal consumed per day: 9.266 tons
Liquid hydrocarbons: 12,377 bpd
Electric power: 676 MW
Thermal Efficiency: 52.6%
Most coal fired power stations in operation in the U.S.(and in the world) are pulverised coal burners operating at 33% efficiency. The electric power produced in the case study is from the excess syngas which is burnt in a combined cycle gas turbine at high efficiency. Thus, the same amount of coal can produce both power and liquid fuels.
Lets assume all current U.S. coal plants were replaced with the case study plant. At present, the U.S. has 320GW of coal fired capacity that produce 1,900 TWh of electricity each year. The case study plant would produce 5.92 TWh of electricity each year, meaning 321 would need to be built to match current production. In providing this electricity the plants would also produce 1.45 billion barrels of oil per year. This comes to almost 20% of the U.S. oil demand and requires 1.085 billion tons of coal. Currently, about 900 million tons is used for electricity generation in the U.S. of about 1.1 billion tons mined each year. Thus producing a fifth of their oil supply would only need an increase of around 18% in coal production.
A similar analysis can be done for Britain, showing that we can provide our current coal generated electricity and about 15% of our oil demand with the case study plants, using around 65 million tonnes (a 15 million tonne increase on that used for power generation and thus a 19% increase in our use of coal overall).
Like IGCC's, these plants make it easier to seperate the CO2 produced and could be utilised with carbon sequestration. Also, efficiencies of IGCC's and other combined cycle plants are predicted to hit 60% or more, making them even more viable.
I realise that 15-20% is not the 100% of oil demand you use in your calculations, Chris. But even the most pessimistic peak oil predictions still gives us as much oil being produced from conventional sources in 2050 as in 1970. Liquids from coal and gas as well as cellulosic ethanol, algal biodiesel and unconventional oil (sands, shale) will all help mitigate the effects of peak oil while we make the much needed transfer to hybrids, PHEVs and finally fully electric vehicles.
Chris: "However, we have only 220 million tonnes or so left in readily accessible deposits"
"It is proposed there are more (but harder to get) coal reserves in and off Scotland and under the North Sea, perhaps 1,500 million tonnes altogether."
In 1991, British coal reported that there was 190 billion tonnes of coal in place (in seams over 0.6 metres thick and less than 1 200 metres deep), of which 45 billion tonnes was accessible with current technology. Only around 1 billion tonnes of this was in the reserves of existing mines at that time.
So what happened to all that coal? Was it mined? Stolen by pixies? The answer is that the cheapness of imported coal and natural gas made most of Britain's coal resource uneconomic to mine. In the event of peak oil/gas, however, it is reasonable to assume that increased demand for coal would raise the price, potentially making Britain's deep coal once more economic.
Technology may also allow the exploitation of this resource. Underground coal gasification (UCG) is still in its infancy and could be used to access vast amounts of coal untouchable by modern mining techniques. The DTI gives a figure of 17 billion tonnes of on land, deep seam coal suitable for UCG, with a similar figure possible but unverified. These figures do not include the far larger resource under the North Sea.
In conclusion, known and likely reserves of coal are sufficient to last for centuries and further exploration and technological advancement may increase this substantially. The pertinent question is not "will coal run out?", but whether it will be used cleanly or not.
Hi Martin,
you've raised some very central points here (in your two postings), and I thank you for that. I think the most important fact is there is actually far more coal available than I have accounted for in my calculations. That much, I find reassuring as the small U.K. reserve particularly appeared to me depressingly low! So, it is a matter of resource vs reserve, and as you say, more coal will be found as the price goes up. For instance, the former USSR has 6 trillion tonnes and China 1 trillion, though not in mine company holdings as yet. So, 10 trillion tonnes worldwide doesn't sound ridiculous, does it? Quite right, the pixies didn't nick that 190 billion tonnes of coal from the British (I have found an article confimring what you say), and 45 billion tonnes could apparently be got using conventional technology. So, by simple arithmetic, we can supply all our coal and oil from coal for about 200 years. It does mean intriducing a huge new mining infrastructure and if that is intended, surely "they" whoever, ought to be getting on with it. I will post another article with more of these details and some new (more optimistic) figures.
True, in the good old days of British coal, say back in the late 1800's, oil was not used as the extractive energy source. Then, they used coal to drive pumps, pit-cages, and surface machinery. Down below it was pit ponies, men (a few women) and children... until the law was changed so they had to be at least 12 years old before they could send them down. I suppose we could always send the little buggers down again, if times got hard enough? Seriously though, there is no mandatory need for oil to mine coal, I agree. Sure, we could now divert electricity made from other sources as you say, or indeed use the coal itself since there is plenty of it (in principle).
Right, I agree about the efficiency of coal fired plants, energy "out" is about a third. Some of the new integrated clean coal(gasification) systems reckon they can get up to 50%, but they are technically a lot more complex. and expensive to install ($1500 per kilowatt of generating capacity is a figure I have seen), which implies about $1.5 billion for a 1 GW plant? That sounds a lot.
Your sums certainly look convincing, and the only obstacle I see to introducing an integrated infrastructure as you say, is initial outlay costs. Providing 15 - 20% of oil that we don't have to import would be a hell of a lot, and has everything to recommend it!
You say that the most pessimistic predictions are that there will be as much "conventional" oil produced in 2050 as in 1970? I would like to believe that, but I don't understand where it comes from. What I mean is that we are burning somewhere over 30 billion barrels of oil every year. O.K., I see that 2010 (about now) is half-way between 1970 and 2050, so on a Hubbert symmetric "bell-curve" what you say sounds reasonable. But, there is increasingly less of the light crude that is most easily got and used. If there is one trillion barrels left in the ground we will have used that up by 2050: 30 billion x 40 > 1 trillion? So, unless there is more or more can readily be extracted from some other source, still keeping to an acceptable EROEI, supply will begin to dwindle before then. Personally, I hope there is a lot more than that down there, and the "pixies" you refrred to can go on dancing forever, but I doubt it. However, producing 20% of our oil from coal and if we got cracking to do so ASAP, would certainly ease our slide down the steep side of the peak.
Hi Chris,
Thanks for your reply. The reference to pixies was more in whimsy than sarcasm (honest). :)
The sheer volume of coal that could be exploited is always a welcome antidote to those who claim peak oil will mean a die-off of billions. If we aren't prepared then peak oil may well mean economic hardship, but I find it hard to lend much credence to the idea that it'll force us into a new agrarian age.
As I wrote at the end of my last post, the question is whether this coal will be used cleanly or will lead to a runaway greenhouse effect. I find it profoundly depressing when I read that 72% of planned coal stations in the U.S. will be of the conventional pulverised coal type. Hopefully, developments at the state level and the election of a Democratic congress may change these plans by forcing power companies to plan for a future of carbon taxes/trading.
In the medium term super/ultracritical and IGCC coal plants may allow us to use coal much more efficiently and cleanly as well as for dual use production of liquid fuels. In the longer term carbon sequestration and plants of truly mind boggling efficiency may be feasible. If you have the time, Chris, google Integrated Plasma Gasification and Fuel Cell (IPFC). This technology gasifies a wide range of fuels (biomass, coal, petroleum, natural gas, domestic waste) to produce hydrogen for use in solid oxide fuel cells (with a bottoming rankine cycle) and molten carbonate for use in direct carbon fuel cells. The efficiency for this combination of techologies is reckoned to be in the 70-90% range! A further benefit is a pure stream of CO2 ready for sequestration.
In my comments on your blog, Chris, I've tried to give a sense of the inefficient way in which we use energy in the times of plenty that currently reign. In my view constriction of supply will be the mother of invention that leads us to a far more efficient and sustainable future. A truly excellent recent post at The Oildrum illustrates this far better than any of my posts.
As always, enjoying the blog.
Martin
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