Australia is in the grip of the most severe drought on record. The nation are warned that unless heavy rains come soon to break the unprecedented dry-spell, it might prove necessary to cut water supplies for food production. The Murray-Darling basin in south-eastern Australia produces 40% of the continent's agriculture and is supplied by two rivers, which are now so low that soon there will only be enough water available for drinking, not for irrigation. It is thought that the reason for the drought is climate-change, and the government are blamed for not acting sooner. John Howard, the Australian Prime Minister, has said that unless there is a significant rainfall during the next six to eight weeks, irrigation will be prevented in the main farming area, with the consequence that crops such as rice, cotton and grapes (for wine) will fail, while citrus, olive and almond trees will die, as will livestock.
In 2002 - 2003, drought halved wheat production in Australia. Mr Howard said: "It's a grim situation, and there is no point pretending to Australia otherwise. We must all hope and pray there is rain." The causes of the present drought are believed to be complex, but few scientists doubt that climate change is part of the problem, which is making Australia hotter and drier. With pastures reduced to dust, some farmers have resorted to selling-off their livestock at rock-bottom prices, or they try to keep them going on feed that is now massively expensive. The suicide rate among rural communities has soared, as indeed it did in the UK, when our farming industry was hit by BSE and then foot-and-mouth disease.
Australians enjoy one of the best standards of living, and have the highest per capita greenhouse gas emissions in the world. Average temperatures in Australia have increased by 0.7 degrees C over the past 100 years, and most of that during the last 50 years. 80% of the population live on the eastern seaboard or the coastal perimeters of the continent. 50% of all Australia's CO2 emissions arise from burning coal, which as noted in an earlier posting, is very abundant there. The Great Barrier Reef is suffering from rising sea-temperatures, and 60% of it was bleached in 2002. At 2,575 and 2,739 kilometers in length, respectively, the river Murray and its tributary, the Darling, provide 84% of all water used for irrigating farmland; however, there will soon be just enough for essential supplies. Australia is also beset by forest-fires which consume large areas of land. The south-eastern region is especially prone to them and the hot, arid climate there will be worsened by the current drought.
The death toll of wildlife is significant when the fires strike, particularly in the eucalyptus forests, where the flammable vapours from them fuel intense firestorms, and wombats, koalas and many of Australia's other unique indigenous creatures are greatly at risk from this kind of fire. Environmentalists refer to the rising number of El Nino events which bring drought, and blame them on global warming. Until only recently, Mr Howard and his minsters remained skeptical about the issue of global warming and climate change, and he refused to meet Al Gore during a recent visit he made there to promote his documentary, An Inconvenient Truth. He was also less than sanguine about "The Stern Report", published in the UK by the economist Sir Nicholas Stern, which contains the warning that large arable areas of Australia would be rendered barren if global temperatures increased by an average of four degrees C.
George Bush has said that "the jury is out" on the link between human-produced CO2 emissions and global warming, despite the consensus of world scientists that there is no doubt they are connected. Mr Howard has responded to the view of his citizens' opinion, and recently announced the intention to ban inefficient light bulbs, with the view to cut Australia's CO2 emissions. It is a serious business and I wonder whether there will be a massive re-immigration of Australians who are originally of British and European stock back to these countries. Almost certainly, populations will follow climate change, moving to warmer, cooler or wetter lands in order to survive.
Related Reading.
Kathy Marks, "The Epic Drought", writing in The Independent, April 20th, p.2-3.
Monday, April 23, 2007
Friday, April 20, 2007
Carbon-Trading, the Ozone Layer and Frying Fish.
While the developed nations have all but banned manufacture of CFC's (chlorofluorocarbons) and related compounds, in the interests of trying to preserve the ozone layer, they are paying billions to countries like India and China to produce them. The problem is a loophole in the Kyoto Protocol which allows industrialised nations to meet their own greenhouse gas emissions by paying for cheaper emission reducing projects in developing nations. The Clean Development Mechanism (CDM) means that for every tonne of carbon saved (or its equivalent, denoted CO2e), one "carbon credit" is earned. Nearly half of all CDM credits have been issued for destroying HFC-23 (trifluoromethane), which is 11,700 times more potent as a greenhouse gas than CO2, and is produced during the manufacture of HCFC-22 (chlorodifluoromethane), which is widely employed as a refrigerant. The situation is very opportune for China and India, since they hold most of the developing world's facilities for manufacturing refrigerants, and foreign investors are prepared to pay up to 15 Euro for each CO2e credit - a lot less than it would cost to reduce emissions in Europe or the US!
In a recent paper published in Nature, it was estimated by Michael Wara, who is both a lawyer and an authority on CDM, the total cost of destroying HFC-23 via carbon credits is 4.7 billion Euro, whereas the actual cost to do it is more like 100 million Euro. He points out that this isn't merely an expensive loophole, it also discourages more desirable CDM projects based around biomass or wind-power, and might engender an incentive for companies in the developing nations to expand production of refrigerants for the simple purpose of destroying by-products from HFC-23 production.
So, how is the "ozone hole" these days? You may recall that the whole business of ceasing to manufacture CFC's and indeed of destroying existing stockpiles was to do with the fact that these volatile compounds survive transport through the troposphere, to reach the stratosphere where the ozone is, and there they are photolysed in a series of chemical reactions that result in decomposition of the ozone layer. This is also sometimes called the ozone-shield, in emphasis that ozone absorbs harmful UV radiation (UV-A and UV-B), and helps to protect life on earth from its harmful effects, e.g. causing skin-cancer. A well-documented "hole" has appeared in the ozone layer, most dramatically over Antarctica and worryingly over Europe too.
Earth systems are complex, and it is probably misleading to consider any aspect in isolation from the highly interconnected whole. There is no better example of a holistic system at work than the Earth and its climate. (A philosophical overview of this has been espoused in the novel Jagged Environment, by Chris James). Indeed, it is now thought that marine and freshwater systems might be placed at risk by the increasing levels of UV now reaching the Earth' surface. Aquatic ecosystems constitute more than half the biomass of the planet and are hence an essential component of the biosphere. According to a report by the United Nations, marine organisms may be killed-off by the UV, especially in the polar regions above where the ozone layer is thinnest, and such a diminution in marine organisms, e.g. phytoplankton, may reduce the capacity of the oceans to soak-up CO2 from the atmosphere.
I have noted previously, "Carbon in the Sky" (6-1-07), that since 1950 the amount of CO2 emitted into the atmosphere from burning fossil-fuels appears to have exceeded the planet's ability to absorb it by an average of 40%, or around 2 ppm per year. That excess seems to be increasing, probably in consequence of steadily increasing levels of emissions but also destruction of the world's forests and the phytoplankton - "green lawns" - of the oceans. Phytoplankton is thought to absorb more than half the CO2 that is taken-up from the atmosphere by the plant kingdom altogether through photosynthesis, and hence is responsible for over 50% of the atmosphere's oxygen. The fear is, of course, that an increase in atmospheric CO2 might lead to more dramatic global warming.
It is interesting that although there appears to be no direct link between "global warming" and the "ozone layer", there are indirect connections. Here, through the interactive ozone-hole/UV/phytoplankton/CO2 system, and that while rising CO2 levels cause the troposphere to warm, they cause the stratosphere to cool, leading to more cloud formation upon the surfaces of which more ozone is decomposed, we have a perfect (deadly!) "feedback mechanism". The interconnected processes of the Earth "systems" indeed constitute an intricate and delicate mechanism, and we tamper with it at our peril.
Related Reading.
Jagged Environment, by Chris James. http://www.jepublications.co.uk/ This is described as: "A discussion on the origins of life and the relative impact of humankind on the environment". Personally, I found it interesting from a philosophical point of view, whether I agree with the "science" or not! "
Chemistry World, April 2007, Vol. 4, No. 4, p.8/p.32.
D.P.Hader et al., Photochem. Photobiol. Sci., 2007, 6, p.267.
M.Wara, Nature, 2007, 445, p.595.
In a recent paper published in Nature, it was estimated by Michael Wara, who is both a lawyer and an authority on CDM, the total cost of destroying HFC-23 via carbon credits is 4.7 billion Euro, whereas the actual cost to do it is more like 100 million Euro. He points out that this isn't merely an expensive loophole, it also discourages more desirable CDM projects based around biomass or wind-power, and might engender an incentive for companies in the developing nations to expand production of refrigerants for the simple purpose of destroying by-products from HFC-23 production.
So, how is the "ozone hole" these days? You may recall that the whole business of ceasing to manufacture CFC's and indeed of destroying existing stockpiles was to do with the fact that these volatile compounds survive transport through the troposphere, to reach the stratosphere where the ozone is, and there they are photolysed in a series of chemical reactions that result in decomposition of the ozone layer. This is also sometimes called the ozone-shield, in emphasis that ozone absorbs harmful UV radiation (UV-A and UV-B), and helps to protect life on earth from its harmful effects, e.g. causing skin-cancer. A well-documented "hole" has appeared in the ozone layer, most dramatically over Antarctica and worryingly over Europe too.
Earth systems are complex, and it is probably misleading to consider any aspect in isolation from the highly interconnected whole. There is no better example of a holistic system at work than the Earth and its climate. (A philosophical overview of this has been espoused in the novel Jagged Environment, by Chris James). Indeed, it is now thought that marine and freshwater systems might be placed at risk by the increasing levels of UV now reaching the Earth' surface. Aquatic ecosystems constitute more than half the biomass of the planet and are hence an essential component of the biosphere. According to a report by the United Nations, marine organisms may be killed-off by the UV, especially in the polar regions above where the ozone layer is thinnest, and such a diminution in marine organisms, e.g. phytoplankton, may reduce the capacity of the oceans to soak-up CO2 from the atmosphere.
I have noted previously, "Carbon in the Sky" (6-1-07), that since 1950 the amount of CO2 emitted into the atmosphere from burning fossil-fuels appears to have exceeded the planet's ability to absorb it by an average of 40%, or around 2 ppm per year. That excess seems to be increasing, probably in consequence of steadily increasing levels of emissions but also destruction of the world's forests and the phytoplankton - "green lawns" - of the oceans. Phytoplankton is thought to absorb more than half the CO2 that is taken-up from the atmosphere by the plant kingdom altogether through photosynthesis, and hence is responsible for over 50% of the atmosphere's oxygen. The fear is, of course, that an increase in atmospheric CO2 might lead to more dramatic global warming.
It is interesting that although there appears to be no direct link between "global warming" and the "ozone layer", there are indirect connections. Here, through the interactive ozone-hole/UV/phytoplankton/CO2 system, and that while rising CO2 levels cause the troposphere to warm, they cause the stratosphere to cool, leading to more cloud formation upon the surfaces of which more ozone is decomposed, we have a perfect (deadly!) "feedback mechanism". The interconnected processes of the Earth "systems" indeed constitute an intricate and delicate mechanism, and we tamper with it at our peril.
Related Reading.
Jagged Environment, by Chris James. http://www.jepublications.co.uk/ This is described as: "A discussion on the origins of life and the relative impact of humankind on the environment". Personally, I found it interesting from a philosophical point of view, whether I agree with the "science" or not! "
Chemistry World, April 2007, Vol. 4, No. 4, p.8/p.32.
D.P.Hader et al., Photochem. Photobiol. Sci., 2007, 6, p.267.
M.Wara, Nature, 2007, 445, p.595.
Wednesday, April 18, 2007
All About Oil.
Specifically, supplies of the cheap "sweet" light crude oil, on which the economy of the modern world is based, are set to decline. Exactly when this will occur is the matter of debate, but my own prediction is that within 10 years fuel will begin to run short. A society that is unable to travel easily will inevitably fragment into small communities, and that might work out fine - it is the transitional powering down to a lower energy economy which worries me, since it might amount to serious civil disorder and strife. At worst anarchy! If we look around, we see plastics, synthetic fibres, and all of them made from oil, in addition to its vital importance as a fuel. It is ironic that when petroleum was first encountered in quantity, particularly in the United States, the material was regarded as rather a nuisance.
In Pennsylvania, wells were sunk to extract brine (salt-water) which was allowed to evaporate in salt-pans, for salt production. Often, however, the brine was found to be contaminated with petroleum. Generally the oil was skimmed-off and thrown away, usually onto fields, but so the story goes, in one area where there was rather a lot of petroleum coming-up with the brine, the "salt-miners" began to throw it into a canal. One day, a boy threw a lighted branch into the canal, whereupon the entire waterway erupted into flame, so the locals got the idea that petroleum might be useful after all. It was marketed as a replacement for whale-oil used in lamps, and also as a medicine. In the latter aspect, "rock-oil" as it became known was applied externally to burns and internally for conditions ranging from tuberculosis to its application as a laxative.
The first commercial oil-well was sunk in Pennsylvania in 1859, and yielded an initial 25 barrels a day, but this had fallen to just 15 barrels a day within a year, making the point that oil-wells have a finite supply - i.e. they run-out eventually. Henry Ford, of the "Model-T Ford", the first car to be produced on an assembly-line, thought the world supplies of petroleum were actually highly limited and so the "Model-T" was originally designed to run on ethanol. Interestingly, Rudolph Diesel, in his original patent for the "Diesel Engine" intended the device to run on coal dust or vegetable oils. A couple of his prototype engines did explode when fired with coal-dust, however.
The car industry expanded hugely and more petroleum was discovered all the time, so it became the fuel of choice. World War I resulted in a massive growth in the number of vehicles run on oil-based fuels, worldwide, and all powers began to realise that securing adequate supplies of oil was key to ensuring their economic prosperity. Lawrence of Arabia (T.E.Lawrence, who wrote the novel, "Seven Pillars of Wisdom", describing his experience) led the Arab revolt against the Ottoman empire, in the Eastern flank of WWI. We are familiar with the fighting in France particularly during WWI, but there was also a war being fought in the east, some historians say to secure oil supplies for the Europeans. Sadly, some of the soldiers who survived Galipoli were sent off to fight in the Somme. This led to an effective partitioning of what was "Arabia" and the creation of Iraq, Saudi and the other Arab states. I wonder what future historians will conclude about the true purpose of current military action by The West in Iraq and Afghanistan (and God forbid, Iran).
More oil-wells continued to be sunk (especially in the US) and the peak in the number of oil deposits found - "Peak Discovery" - occurred in 1930. A man called M. King Hubbert (the "M" stood for "Marion", so perhaps that's why he chose "King" as his first name), a very famous geophysicist, predicted mathematically that the peak in oil production - "Peak Oil" - would come 40 years after peak discovery. This proved to be spot-on for US oil production, which peaked around 1970, and now the US needs to import 2/3 of the oil it consumes, much of it from the Middle East, but mostly from Canada. Altogether, the US uses one quarter of the entire world's output of oil, and demand rises inexorably there and increasingly so in other countries like China and India, to fuel their unprecedented economic expansion. It is predicted that by 2020, China will match the US in terms of its thirst for oil, but by then half the remaining oil will have gone, and it is almost certain that production of natural petroleum will be well down by then. Hence, if this "target" is to be met, much of it will need to derive from synthetic oil, e.g. as produced from tar sands or from coal-liquefaction.
World oil production is around 84 million barrels a day, or just over 30 billion barrels per year. However, the amount of oil in the ground is finite, and believed to amount to around one trillion (one thousand billion) barrels. Hence, if we could extract all of it at 30 billion barrels a year, there is enough for about 30 years or so. If demand grows we simply get through the stuff faster. There are also suspicions that e.g. Saudi may have revised its reserves optimistically upward, and so there may be less oil in the ground that was thought. Indeed, it is debatable just how much oil can be extracted from an oil-well. An oil-well is not like a water-well: that is to say that you can't simply drain it to bottom with a bucket. Some wells yield only 5% of the oil they contain, though 30% is more usual, especially with enhanced recovery methods.
The amount of oil recovered depends on the precise geology of the well, i.e. if the rock is highly fractured then its permeability may be impaired. Hence, the rate and volume of oil that can flow out of it is reduced. It is speculated that the enhanced recovery methods used in Saudi to meet world demand may have damaged the rock and so less oil will ultimately be recovered from its oil-fields. Only one well out of every hundred sunk produces a major source of oil, and consequently oil exploration is very expensive and laborious. World oil discovery peaked in 1965 and no "elephant" (giant) field has been discovered since 1980. If Hubbert is right about the 40 year "lag" between peak discovery and peak production, we can expect oil production to peak around now.
Mathematically, according to the Hubbert analysis, the point at which Peak Oil is reached corresponds to when half the oil has been used-up. It is estimated that the world has got through a little over about 1 trillion barrels since 1859, and so if there are one trillion barrels left, that would fit with Peak Oil being with us now. The upshot is that the cheap light crude oil , which is most easily refined, is running out. The remainder is a dirtier, heavier oil that takes more energy to purify and process. The EROEI (Energy Returned On Energy Invested) is about 8 for light crude (it was 100 in the days of the original "gushers"!) but can be as low as 3 for heavy oil and that extracted from cracking bitumen in shales and oil-sands.
Burning oil also contributes CO2 to the atmosphere, which many believe is causing global warming and climate-change, so finding a substitute for oil is imperative on grounds both of its looming short supply and curbing CO2 emissions. Obviously, as oil runs-out, we will be emitting less CO2 - it's just that we may not have much of a civilization left without finding an alternative source of fuel to run it! Since hydrogen is a complete non-starter (as I describe in the immediately previous article) and biofuels are unlikely be produced in a quantity to match 30 billion barrels of petroleum per year, that alternative "fuel" will be mostly a re-localisation of society - "The Global Village" will be a matter for future historians to discuss. We can expect a return of local farms and horses and carts! Fuel will be too precious to waste on personal cars, but reserved for tractors and lorries.
Related Reading.
http://en.wikipedia.org/wiki/Petroleum
In Pennsylvania, wells were sunk to extract brine (salt-water) which was allowed to evaporate in salt-pans, for salt production. Often, however, the brine was found to be contaminated with petroleum. Generally the oil was skimmed-off and thrown away, usually onto fields, but so the story goes, in one area where there was rather a lot of petroleum coming-up with the brine, the "salt-miners" began to throw it into a canal. One day, a boy threw a lighted branch into the canal, whereupon the entire waterway erupted into flame, so the locals got the idea that petroleum might be useful after all. It was marketed as a replacement for whale-oil used in lamps, and also as a medicine. In the latter aspect, "rock-oil" as it became known was applied externally to burns and internally for conditions ranging from tuberculosis to its application as a laxative.
The first commercial oil-well was sunk in Pennsylvania in 1859, and yielded an initial 25 barrels a day, but this had fallen to just 15 barrels a day within a year, making the point that oil-wells have a finite supply - i.e. they run-out eventually. Henry Ford, of the "Model-T Ford", the first car to be produced on an assembly-line, thought the world supplies of petroleum were actually highly limited and so the "Model-T" was originally designed to run on ethanol. Interestingly, Rudolph Diesel, in his original patent for the "Diesel Engine" intended the device to run on coal dust or vegetable oils. A couple of his prototype engines did explode when fired with coal-dust, however.
The car industry expanded hugely and more petroleum was discovered all the time, so it became the fuel of choice. World War I resulted in a massive growth in the number of vehicles run on oil-based fuels, worldwide, and all powers began to realise that securing adequate supplies of oil was key to ensuring their economic prosperity. Lawrence of Arabia (T.E.Lawrence, who wrote the novel, "Seven Pillars of Wisdom", describing his experience) led the Arab revolt against the Ottoman empire, in the Eastern flank of WWI. We are familiar with the fighting in France particularly during WWI, but there was also a war being fought in the east, some historians say to secure oil supplies for the Europeans. Sadly, some of the soldiers who survived Galipoli were sent off to fight in the Somme. This led to an effective partitioning of what was "Arabia" and the creation of Iraq, Saudi and the other Arab states. I wonder what future historians will conclude about the true purpose of current military action by The West in Iraq and Afghanistan (and God forbid, Iran).
More oil-wells continued to be sunk (especially in the US) and the peak in the number of oil deposits found - "Peak Discovery" - occurred in 1930. A man called M. King Hubbert (the "M" stood for "Marion", so perhaps that's why he chose "King" as his first name), a very famous geophysicist, predicted mathematically that the peak in oil production - "Peak Oil" - would come 40 years after peak discovery. This proved to be spot-on for US oil production, which peaked around 1970, and now the US needs to import 2/3 of the oil it consumes, much of it from the Middle East, but mostly from Canada. Altogether, the US uses one quarter of the entire world's output of oil, and demand rises inexorably there and increasingly so in other countries like China and India, to fuel their unprecedented economic expansion. It is predicted that by 2020, China will match the US in terms of its thirst for oil, but by then half the remaining oil will have gone, and it is almost certain that production of natural petroleum will be well down by then. Hence, if this "target" is to be met, much of it will need to derive from synthetic oil, e.g. as produced from tar sands or from coal-liquefaction.
World oil production is around 84 million barrels a day, or just over 30 billion barrels per year. However, the amount of oil in the ground is finite, and believed to amount to around one trillion (one thousand billion) barrels. Hence, if we could extract all of it at 30 billion barrels a year, there is enough for about 30 years or so. If demand grows we simply get through the stuff faster. There are also suspicions that e.g. Saudi may have revised its reserves optimistically upward, and so there may be less oil in the ground that was thought. Indeed, it is debatable just how much oil can be extracted from an oil-well. An oil-well is not like a water-well: that is to say that you can't simply drain it to bottom with a bucket. Some wells yield only 5% of the oil they contain, though 30% is more usual, especially with enhanced recovery methods.
The amount of oil recovered depends on the precise geology of the well, i.e. if the rock is highly fractured then its permeability may be impaired. Hence, the rate and volume of oil that can flow out of it is reduced. It is speculated that the enhanced recovery methods used in Saudi to meet world demand may have damaged the rock and so less oil will ultimately be recovered from its oil-fields. Only one well out of every hundred sunk produces a major source of oil, and consequently oil exploration is very expensive and laborious. World oil discovery peaked in 1965 and no "elephant" (giant) field has been discovered since 1980. If Hubbert is right about the 40 year "lag" between peak discovery and peak production, we can expect oil production to peak around now.
Mathematically, according to the Hubbert analysis, the point at which Peak Oil is reached corresponds to when half the oil has been used-up. It is estimated that the world has got through a little over about 1 trillion barrels since 1859, and so if there are one trillion barrels left, that would fit with Peak Oil being with us now. The upshot is that the cheap light crude oil , which is most easily refined, is running out. The remainder is a dirtier, heavier oil that takes more energy to purify and process. The EROEI (Energy Returned On Energy Invested) is about 8 for light crude (it was 100 in the days of the original "gushers"!) but can be as low as 3 for heavy oil and that extracted from cracking bitumen in shales and oil-sands.
Burning oil also contributes CO2 to the atmosphere, which many believe is causing global warming and climate-change, so finding a substitute for oil is imperative on grounds both of its looming short supply and curbing CO2 emissions. Obviously, as oil runs-out, we will be emitting less CO2 - it's just that we may not have much of a civilization left without finding an alternative source of fuel to run it! Since hydrogen is a complete non-starter (as I describe in the immediately previous article) and biofuels are unlikely be produced in a quantity to match 30 billion barrels of petroleum per year, that alternative "fuel" will be mostly a re-localisation of society - "The Global Village" will be a matter for future historians to discuss. We can expect a return of local farms and horses and carts! Fuel will be too precious to waste on personal cars, but reserved for tractors and lorries.
Related Reading.
http://en.wikipedia.org/wiki/Petroleum
Monday, April 16, 2007
"Does a Hydrogen Economy Add-up?"
Last week I gave a lecture at a "Cafe' Scientifique" meeting in the charming city of Salisbury - famous for its cathedral - with the title "Does a Hydrogen Economy Add-up?". This is indeed a good question, especially considering the enormous investment of funds sunk into creating a putative "Hydrogen Economy", within which the world is supposed to run most of its transportation on hydrogen "fuel". I have placed the word "fuel" in inverted commas because hydrogen is not in fact a fuel at all, but an energy carrier. This means that hydrogen cannot be simply dug out of the ground, like oil, gas and coal, but it must be artificially synthesised, in general using gas, oil or coal either as a chemical feedstock or a fuel or both. Since the second law of Thermodynamics amounts to the fact that processes whereby one form of energy is transformed into another are never 100% efficient, turning natural gas into hydrogen by "steam-reforming" is less cost effective in terns of energy than simply burning the gas (principally methane) itself, and leads overall to more CO2 being emitted, which rather flies in the face of hydrogen as the ultimate "green fuel".
On paper and said quickly, hydrogen sounds like the perfect solution to all our fossil-fuel related environmental problems. You simply mix it with oxygen (air) in a fuel cell, and this generates electricity to power a "green car". The only product is pure water, which simply drips out of the exhaust-pipe. However, as just noted, if the hydrogen has to be made from natural gas the overall process is anything but "green". It can also be made by steam-reforming coal, but as the following equations show, twice as much CO2 is emitted in the latter case per unit of hydrogen produced:
CH4 + 2H2O ---> CO2 + 4H2
C (coal) + 2H2O ---> CO2 + 2H2.
An alternative means to producing hydrogen is by water electrolysis, but this immediately begs the question of how to make the necessary electricity to do this? A recent analysis by Ulf Bossel has indicated that it would take around one 1 GW power station to produce enough hydrogen to run 20 - 30 filling stations, assuming that the hydrogen will be made in situ, in order to obviate the considerable problems that would be incurred in providing an extensive transportation network of pipelines or a fleet of tankers to move huge amounts of either compressed or liquefied hydrogen around the country from central generating facilities. In the UK there are around 3,000 filling stations ("garages" as we tend to call them over here), which implies that around 100 - 150 new 1 GW power stations would need to be built. If these were coal or gas-fired, that would add considerably to our national CO2 emissions. Indeed, the nation's average amount of electricity generated is around 40 GW (out of a maximum generating capacity of close to 69 GW), around 80% of which is created by burning gas or coal (50% of it comes from coal now). So, as a rough estimate we would increase our CO2 emissions by a factor of three or four from the electricity industry - or about a 50% increase in terms of overall energy, since electricity only accounts for about one quarter of the UK's total "energy".
One alternative is to use nuclear power, an option that is being considered seriously. However, this would mean installing 100 or so new nuclear power stations, and that is on top of replacing the 30 existing ones when they come to the end of their working life in 2024. We need to remember too, that time is fast running out for oil, which is close to the peak of production beyond which world supplies of crude oil will inexorably fall. It appears likely that any new technology will need to be on-stream within 10 - 15 years, in order to take up the slack in oil based fuel. Hence, it appears salient to ask just how quickly could these new nuclear power stations be brought on-line? For the sake of argument, would 5 per year be a reasonable estimate? If so, it would take 20 -30 years to install the lot, by which time oil (and especially the "sweet", light crude) will be long gone.
It is also probably worth noting that there is only one factory in the world (in France) that can produce the necessary new generation of reactors, and it makes 2 per year - in total! So, that would need to be stepped-up considerably. Another important question is how much nuclear fuel does the world have? Current reserves of uranium amount to about 3 million tonnes, and we get through about 75,000 tonnes of it per year (that's the whole world). Ignoring the fact that about 10,000 tonnes of it currently come from recycled nuclear warheads - although all the US, the UK and Russia are revamping their nuclear arsenals, so that supply might well fall - a simple sum suggests that there are 3,000,000/75,000 = 40 years worth. If we install more nuclear generating capacity, we simply get through the stuff faster than we would otherwise, and probably in just a few years if all the world switched-over to hydrogen. I have noted before that there is probably plenty of uranium to be had if people went looking for it hard enough, and especially in low grade deposits. For example, soil contains on average 2.7 parts per million of uranium, and there are extensive deposits of rocks with 10 - 20 ppm of uranium which could be mined with an estimated EROEI of 15 - 30. However, it takes gas and oil to mine, mill and process uranium ores and so these resources might fail first, irrespective of any theoretically comforting EROEI values.
The only feasible means to producing the electricity for hydrogen generation is from renewables, e.g. wind-power. Now, let's assume the best estimate - the lower end of the scale - of 100 GW worth of generating power; that's 100,000 MW. If we used 2 MW turbines, which we need to multiply by a suitable capacity factor, say 0.2, then that means each one delivers an average of 0.4 MW, and we would need 250,000 of them. They would probably need to be placed off-shore, around the coast of the UK mainland. Assuming that the coastal perimeter is 2,560 km, that means if the turbines were placed at the recommended separation of 0.5 km (any closer and each turbine interferes with the wind flow to the next and reduces its efficiency) , a single band around the main island would be occupied by 5,120 turbines. Hence the full band would need to be 250,000/5,120 = 49 turbines deep, stretching to a width of about 25 km. If the French did the same thing, there would be considerable overlap between the English and French wind farms especially in the English Channel, and surely a considerable obstruction to shipping! Agreed, many of them could be placed further up in the North Sea, but they would suffer considerable buffeting there from the elements, which is a great potential problem for off-shore wind farms since it imposes limitations on their durability and indeed "sustainability". The North Sea in particular is notoriously rough.
Another question is how quickly might the turbines be installed? 10 a week, say? 500 a year? Then that would take 500 years to install the lot. 100 a week? 50 years - and oil will be long-gone by then!
The other problem rests with the use of hydrogen itself. It is intended that it will be "burned" in fuel-cells, which use 50 - 100 grammes of platinum in each as the working electrode. Platinum is a very rare metal, and currently 150 tonnes of new platinum are produced each year, 40% of which is used in catalytic converters, and coincidentally is almost exactly the amount used to make jewelry. Since current demand for platinum already outstrips its supply, we would need to produce more "new" platinum. For the sake of argument, let's suppose another 150 tonnes could be made per year (and there is no reason to be sure it could) - double the present quantity. Therefore, 150 tonnes x 1000 kg x 1000 g/50 g = 3 million.
So, 3 million new fuel-cell powered vehicles might be brought on-stream per year, a figure which can be compared with around 700 million vehicles worldwide. Hence, 45 million could be available in 15 years (about 6% of the current total) when at least half of all the remaining oil will be used up. 90 million might have been produced (about 13%) in 30 years by when the conventional oil will certainly have all gone - to all intents and purposes at any rate - and we will be making it from tar sands and coal-liquefaction instead!
How would you store the hydrogen in vehicles? One way is as a compressed gas in a steel tank at 5,000 psi (pounds per square inch pressure) - that's just over 300 atmospheres - but the tank would weigh-in at 65x the weight of the hydrogen it contained. For a car containing 20 kilograms of hydrogen (which is the energy equivalent of 20 US gallons of gasoline), the tank would weigh about 1.3 tonnes, which is about twice the weight of the car itself. The tank would need to be fabricated in the form of a sphere about 5 feet in diameter - not so conveniently located in a car, unlike a normal "gas-tank" which can be made to fit unused space. This baby would be pretty evident! Tanks could be made lighter and wrapped with carbon fibre, which would get the weight down to about 200 kg, but they offer poor crash-resistance (particularly the connections, even if the tank itself survives), and so the car would become a mobile bomb.
In any case, compressing the hydrogen takes about 20% of the energy that might be recovered from it. Another possibility is to store it as liquid hydrogen; however, hydrogen is extremely difficult to liquefy, since it boils at -253 degrees C (20 degrees above absolute zero), and the process takes 40% of the energy that the hydrogen actually contains! Hydrogen could be piped around from central generating stations, but these pipes would need to be very big since hydrogen contains only around one third the energy of an equal volume of natural gas, and a lot of energy would be required to move the gas down the pipeline.
Hydrogen is a marvelous "escape artist" too. It can get through the minutest of cracks and can even diffuse through solid steel. It also makes metals brittle over time and so cracks would keep appearing in the pipes etc. requiring constant maintenance, and very likely leading to fires and explosions. If on the other hand the hydrogen were employed in liquid form, because of the risk of explosion (very cold liquid suddenly becoming a gas at room temperature leading to a huge pressure increase) the system would need to be open, so that the gas could be vented. Consequently, there would be multi-story car-parks full of cars potentially venting hydrogen into the air. Since hydrogen has the greatest explosive range of any gas (any mixture containing between about 14% and 75% of hydrogen in air will explode) regular catastrophes could be expected.
Another problem is that the oxygen is drawn into the fuel-cell in terms of air, which contains nitrogen oxides and sulphur compounds etc. which are well known to poison (inactivate) catalysts and so the fuel-cell would probably not work for too long (a few months maybe) before needing to be replaced. I could go on at far greater length about why the "hydrogen economy" in its present generation of design will never work, but probably I have made my point by now. I am not saying there will never be any use for hydrogen, for example in stand-alone applications, for "storing" energy in remote locations generated from solar-power say, hydrogen could be just the job. But on the scale required to replace petroleum based transportation at an equivalent of 20 billion barrels of oil per year (from a toal of 30 billion recovered in total) the whole idea is a complete non-starter.
Ulf Bossel also points out that three times the efficiency could be gained in storing electricity as electrons rather than as hydrogen, which would require a considerable installation in effective "battery" technology to run electric cars. This would mean that only one third of the new generating capacity is needed! [It's crazy really, the "hydrogen option" means taking electricity from a power station, using it to make hydrogen and then recombining the hydrogen with oxygen from air to make electricity again!]. There is still a pressure on resources in this option too, and probably there is not enough lithium in known reserves (or even resources) to implement the full transformation to 700 million vehicles using lithium or lithium ion batteries. You would need an awful lot of batteries. If half the world's nickel production were turned over to making nickel-cadmium batteries instead (5 million tonnes annually) we could bring around 10 million vehicles onto the roads per year, arriving at 20% of current numbers in 15 years. Either way, transportation will be curbed considerably, forcing us to live in small communities...
Related Reading.
Ulf Bossel, Proceedings of the IEEE, Vol. 94, No. 10, 2006, pages 1826 - 1837.
On paper and said quickly, hydrogen sounds like the perfect solution to all our fossil-fuel related environmental problems. You simply mix it with oxygen (air) in a fuel cell, and this generates electricity to power a "green car". The only product is pure water, which simply drips out of the exhaust-pipe. However, as just noted, if the hydrogen has to be made from natural gas the overall process is anything but "green". It can also be made by steam-reforming coal, but as the following equations show, twice as much CO2 is emitted in the latter case per unit of hydrogen produced:
CH4 + 2H2O ---> CO2 + 4H2
C (coal) + 2H2O ---> CO2 + 2H2.
An alternative means to producing hydrogen is by water electrolysis, but this immediately begs the question of how to make the necessary electricity to do this? A recent analysis by Ulf Bossel has indicated that it would take around one 1 GW power station to produce enough hydrogen to run 20 - 30 filling stations, assuming that the hydrogen will be made in situ, in order to obviate the considerable problems that would be incurred in providing an extensive transportation network of pipelines or a fleet of tankers to move huge amounts of either compressed or liquefied hydrogen around the country from central generating facilities. In the UK there are around 3,000 filling stations ("garages" as we tend to call them over here), which implies that around 100 - 150 new 1 GW power stations would need to be built. If these were coal or gas-fired, that would add considerably to our national CO2 emissions. Indeed, the nation's average amount of electricity generated is around 40 GW (out of a maximum generating capacity of close to 69 GW), around 80% of which is created by burning gas or coal (50% of it comes from coal now). So, as a rough estimate we would increase our CO2 emissions by a factor of three or four from the electricity industry - or about a 50% increase in terms of overall energy, since electricity only accounts for about one quarter of the UK's total "energy".
One alternative is to use nuclear power, an option that is being considered seriously. However, this would mean installing 100 or so new nuclear power stations, and that is on top of replacing the 30 existing ones when they come to the end of their working life in 2024. We need to remember too, that time is fast running out for oil, which is close to the peak of production beyond which world supplies of crude oil will inexorably fall. It appears likely that any new technology will need to be on-stream within 10 - 15 years, in order to take up the slack in oil based fuel. Hence, it appears salient to ask just how quickly could these new nuclear power stations be brought on-line? For the sake of argument, would 5 per year be a reasonable estimate? If so, it would take 20 -30 years to install the lot, by which time oil (and especially the "sweet", light crude) will be long gone.
It is also probably worth noting that there is only one factory in the world (in France) that can produce the necessary new generation of reactors, and it makes 2 per year - in total! So, that would need to be stepped-up considerably. Another important question is how much nuclear fuel does the world have? Current reserves of uranium amount to about 3 million tonnes, and we get through about 75,000 tonnes of it per year (that's the whole world). Ignoring the fact that about 10,000 tonnes of it currently come from recycled nuclear warheads - although all the US, the UK and Russia are revamping their nuclear arsenals, so that supply might well fall - a simple sum suggests that there are 3,000,000/75,000 = 40 years worth. If we install more nuclear generating capacity, we simply get through the stuff faster than we would otherwise, and probably in just a few years if all the world switched-over to hydrogen. I have noted before that there is probably plenty of uranium to be had if people went looking for it hard enough, and especially in low grade deposits. For example, soil contains on average 2.7 parts per million of uranium, and there are extensive deposits of rocks with 10 - 20 ppm of uranium which could be mined with an estimated EROEI of 15 - 30. However, it takes gas and oil to mine, mill and process uranium ores and so these resources might fail first, irrespective of any theoretically comforting EROEI values.
The only feasible means to producing the electricity for hydrogen generation is from renewables, e.g. wind-power. Now, let's assume the best estimate - the lower end of the scale - of 100 GW worth of generating power; that's 100,000 MW. If we used 2 MW turbines, which we need to multiply by a suitable capacity factor, say 0.2, then that means each one delivers an average of 0.4 MW, and we would need 250,000 of them. They would probably need to be placed off-shore, around the coast of the UK mainland. Assuming that the coastal perimeter is 2,560 km, that means if the turbines were placed at the recommended separation of 0.5 km (any closer and each turbine interferes with the wind flow to the next and reduces its efficiency) , a single band around the main island would be occupied by 5,120 turbines. Hence the full band would need to be 250,000/5,120 = 49 turbines deep, stretching to a width of about 25 km. If the French did the same thing, there would be considerable overlap between the English and French wind farms especially in the English Channel, and surely a considerable obstruction to shipping! Agreed, many of them could be placed further up in the North Sea, but they would suffer considerable buffeting there from the elements, which is a great potential problem for off-shore wind farms since it imposes limitations on their durability and indeed "sustainability". The North Sea in particular is notoriously rough.
Another question is how quickly might the turbines be installed? 10 a week, say? 500 a year? Then that would take 500 years to install the lot. 100 a week? 50 years - and oil will be long-gone by then!
The other problem rests with the use of hydrogen itself. It is intended that it will be "burned" in fuel-cells, which use 50 - 100 grammes of platinum in each as the working electrode. Platinum is a very rare metal, and currently 150 tonnes of new platinum are produced each year, 40% of which is used in catalytic converters, and coincidentally is almost exactly the amount used to make jewelry. Since current demand for platinum already outstrips its supply, we would need to produce more "new" platinum. For the sake of argument, let's suppose another 150 tonnes could be made per year (and there is no reason to be sure it could) - double the present quantity. Therefore, 150 tonnes x 1000 kg x 1000 g/50 g = 3 million.
So, 3 million new fuel-cell powered vehicles might be brought on-stream per year, a figure which can be compared with around 700 million vehicles worldwide. Hence, 45 million could be available in 15 years (about 6% of the current total) when at least half of all the remaining oil will be used up. 90 million might have been produced (about 13%) in 30 years by when the conventional oil will certainly have all gone - to all intents and purposes at any rate - and we will be making it from tar sands and coal-liquefaction instead!
How would you store the hydrogen in vehicles? One way is as a compressed gas in a steel tank at 5,000 psi (pounds per square inch pressure) - that's just over 300 atmospheres - but the tank would weigh-in at 65x the weight of the hydrogen it contained. For a car containing 20 kilograms of hydrogen (which is the energy equivalent of 20 US gallons of gasoline), the tank would weigh about 1.3 tonnes, which is about twice the weight of the car itself. The tank would need to be fabricated in the form of a sphere about 5 feet in diameter - not so conveniently located in a car, unlike a normal "gas-tank" which can be made to fit unused space. This baby would be pretty evident! Tanks could be made lighter and wrapped with carbon fibre, which would get the weight down to about 200 kg, but they offer poor crash-resistance (particularly the connections, even if the tank itself survives), and so the car would become a mobile bomb.
In any case, compressing the hydrogen takes about 20% of the energy that might be recovered from it. Another possibility is to store it as liquid hydrogen; however, hydrogen is extremely difficult to liquefy, since it boils at -253 degrees C (20 degrees above absolute zero), and the process takes 40% of the energy that the hydrogen actually contains! Hydrogen could be piped around from central generating stations, but these pipes would need to be very big since hydrogen contains only around one third the energy of an equal volume of natural gas, and a lot of energy would be required to move the gas down the pipeline.
Hydrogen is a marvelous "escape artist" too. It can get through the minutest of cracks and can even diffuse through solid steel. It also makes metals brittle over time and so cracks would keep appearing in the pipes etc. requiring constant maintenance, and very likely leading to fires and explosions. If on the other hand the hydrogen were employed in liquid form, because of the risk of explosion (very cold liquid suddenly becoming a gas at room temperature leading to a huge pressure increase) the system would need to be open, so that the gas could be vented. Consequently, there would be multi-story car-parks full of cars potentially venting hydrogen into the air. Since hydrogen has the greatest explosive range of any gas (any mixture containing between about 14% and 75% of hydrogen in air will explode) regular catastrophes could be expected.
Another problem is that the oxygen is drawn into the fuel-cell in terms of air, which contains nitrogen oxides and sulphur compounds etc. which are well known to poison (inactivate) catalysts and so the fuel-cell would probably not work for too long (a few months maybe) before needing to be replaced. I could go on at far greater length about why the "hydrogen economy" in its present generation of design will never work, but probably I have made my point by now. I am not saying there will never be any use for hydrogen, for example in stand-alone applications, for "storing" energy in remote locations generated from solar-power say, hydrogen could be just the job. But on the scale required to replace petroleum based transportation at an equivalent of 20 billion barrels of oil per year (from a toal of 30 billion recovered in total) the whole idea is a complete non-starter.
Ulf Bossel also points out that three times the efficiency could be gained in storing electricity as electrons rather than as hydrogen, which would require a considerable installation in effective "battery" technology to run electric cars. This would mean that only one third of the new generating capacity is needed! [It's crazy really, the "hydrogen option" means taking electricity from a power station, using it to make hydrogen and then recombining the hydrogen with oxygen from air to make electricity again!]. There is still a pressure on resources in this option too, and probably there is not enough lithium in known reserves (or even resources) to implement the full transformation to 700 million vehicles using lithium or lithium ion batteries. You would need an awful lot of batteries. If half the world's nickel production were turned over to making nickel-cadmium batteries instead (5 million tonnes annually) we could bring around 10 million vehicles onto the roads per year, arriving at 20% of current numbers in 15 years. Either way, transportation will be curbed considerably, forcing us to live in small communities...
Related Reading.
Ulf Bossel, Proceedings of the IEEE, Vol. 94, No. 10, 2006, pages 1826 - 1837.
Saturday, April 14, 2007
Peak Coal by 2025?
For the first time I heard on the news this morning mention of "a shortage of crude oil". This was in a soundbite about how UK petrol (gasoline) prices may well hit one pound (about 2 US dollars) a litre. By US standards that probably sounds pretty expensive, at about 7 or 8 dollars a gallon! We hear much about climate change and the need to curb our CO2 emissions, but the nub of the matter is probably the limited amount of oil there is in the ground, and how securely that might be supplied in the future. If indeed, crude oil supplies are set to fall shortly - they will at some stage in any case - we can manufacture synthetic oil from coal, using the Fischer Tropsch process, where the coal is first converted into a gas ( a mixture of carbon monoxide and hydrogen CO + H2) and this passed over a heated metal (iron or nickel) catalyst, which turns it into a mixture of hydrocarbons.
It was indeed this technology that kept Hitler's armies operating throughout World war II, to the consternation of the Allied forces who believed that Germany would run out of fuel within months, once their navies had cut-off supplies of oil from the US and the Middle East. By example, coal might come to our aid in the peaceful context of augmenting dwindling supplies of crude oil as we slide down the declining side of Hubbert's Peak following the advent of Peak Oil. However, some researchers have concluded that "Peak Coal" will hit the world by the year 2025.
Clearly if we begin using coal on the large scale to make oil, we will run out of the resource sooner than otherwise; coincidentally, "Peak Gas" is thought to arrive around 2025 (give or take half a decade), and hence if the Peak Coal prediction proves true (and much of the crude oil long gone by then), we will be in quite a pickle, unless we manage to abate our inexorable thirst for energy!
I was my understanding that world reserves of hard (anthracitic) coal amounted to 10 trillion tonnes, although I have seen some downwardly revised estimates of four trillion tonnes or so. The reality is that accurate data for coal reserves are scant and poor, and so a precise final figure is somewhat nebulous. However, it appears that the reserves and resources of coal have been overestimated on the global scale, and both quantities have been downsized during the past two decades from their previous values. According to the logic of classifying reserves (which are defined as being proven and recoverable) and resources (which is an umbrella term for all proven, inferred, assumed and even speculative amounts), over time advances in production and exploration methods allow some of the resources to be reclassified into reserves. 85% of coal reserves are concentrated in six countries, which are, in order of decreasing quantity of their reserves: US, Russia, India, China, Australia and South Africa.
The US holds a massive 30% of the world reserves and is the second largest global producer. China, albeit with far less coal than the US is way ahead as the world's number one producer, since it pays around 80% of its colossal and burgeoning energy bill from coal. Indeed, just 15% of Chinese coal is exported while the remaining 85% is burned at home. However, the US have passed their peak in producing high quality (anthracitic, i.e. 90% carbon) coal which hit in 1990. This potential shortfall has more than been compensated in terms of volume by production of sub-bituminous coal from Wyoming, and according to the stated reserves there, this can be maintained for another 10 - 15 years. It should be noted that sub-bituminous coal has a lower energy yield than hard coal, and so in terms of energy, US coal production in fact peaked 5 years ago.
It is thought that coal production may yet increase over the next 10 to 15 years by around 30%, mainly from Australia, China, South Africa and the former Soviet Union countries, in particular, Russia, Ukraine and Kazakhstan. World coal production will then reach a plateau (of unknown duration) and then eventually decline. The best estimate for world "Peak Coal" is around 2025, assuming production rates of 30% above current. Potential reductions in coal use for reasons of trying to avert climate change caused by anthropogenic CO2 emissions and global warming might push the peak further into the future - but probably not much further (10 years maximum, say?). It is the actual quantities of coal that will prove available for extraction that are the key issue, however, as indeed is true of all reserves of fossil fuels - including oil and gas.
Related Reading.
http://energybulletin.net/print.php?id=28287
"Coal Reserves and Future Production" (PDF) - link available in above article.
It was indeed this technology that kept Hitler's armies operating throughout World war II, to the consternation of the Allied forces who believed that Germany would run out of fuel within months, once their navies had cut-off supplies of oil from the US and the Middle East. By example, coal might come to our aid in the peaceful context of augmenting dwindling supplies of crude oil as we slide down the declining side of Hubbert's Peak following the advent of Peak Oil. However, some researchers have concluded that "Peak Coal" will hit the world by the year 2025.
Clearly if we begin using coal on the large scale to make oil, we will run out of the resource sooner than otherwise; coincidentally, "Peak Gas" is thought to arrive around 2025 (give or take half a decade), and hence if the Peak Coal prediction proves true (and much of the crude oil long gone by then), we will be in quite a pickle, unless we manage to abate our inexorable thirst for energy!
I was my understanding that world reserves of hard (anthracitic) coal amounted to 10 trillion tonnes, although I have seen some downwardly revised estimates of four trillion tonnes or so. The reality is that accurate data for coal reserves are scant and poor, and so a precise final figure is somewhat nebulous. However, it appears that the reserves and resources of coal have been overestimated on the global scale, and both quantities have been downsized during the past two decades from their previous values. According to the logic of classifying reserves (which are defined as being proven and recoverable) and resources (which is an umbrella term for all proven, inferred, assumed and even speculative amounts), over time advances in production and exploration methods allow some of the resources to be reclassified into reserves. 85% of coal reserves are concentrated in six countries, which are, in order of decreasing quantity of their reserves: US, Russia, India, China, Australia and South Africa.
The US holds a massive 30% of the world reserves and is the second largest global producer. China, albeit with far less coal than the US is way ahead as the world's number one producer, since it pays around 80% of its colossal and burgeoning energy bill from coal. Indeed, just 15% of Chinese coal is exported while the remaining 85% is burned at home. However, the US have passed their peak in producing high quality (anthracitic, i.e. 90% carbon) coal which hit in 1990. This potential shortfall has more than been compensated in terms of volume by production of sub-bituminous coal from Wyoming, and according to the stated reserves there, this can be maintained for another 10 - 15 years. It should be noted that sub-bituminous coal has a lower energy yield than hard coal, and so in terms of energy, US coal production in fact peaked 5 years ago.
It is thought that coal production may yet increase over the next 10 to 15 years by around 30%, mainly from Australia, China, South Africa and the former Soviet Union countries, in particular, Russia, Ukraine and Kazakhstan. World coal production will then reach a plateau (of unknown duration) and then eventually decline. The best estimate for world "Peak Coal" is around 2025, assuming production rates of 30% above current. Potential reductions in coal use for reasons of trying to avert climate change caused by anthropogenic CO2 emissions and global warming might push the peak further into the future - but probably not much further (10 years maximum, say?). It is the actual quantities of coal that will prove available for extraction that are the key issue, however, as indeed is true of all reserves of fossil fuels - including oil and gas.
Related Reading.
http://energybulletin.net/print.php?id=28287
"Coal Reserves and Future Production" (PDF) - link available in above article.
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