Thread: Carbon Pollution? A Summary

Originally Posted by Lotz-A-Landies

The problem with this scenario is that most of our current coal fired power stations are above ground and a long way away from unproductive coal seams. ....

Not as hard as you might think - for example, in the Sydney basin, there are two distinct sets of coal measures. Both are pretty much continuous across the basin (roughly from the Hunter to Wollongong and west to Lithgow, bordered in the east by the continental margin a few tens of kilometres out to sea. The coal is (economically) mineable only round the edges - were you aware that there used to be a coal mine at Balmain? This was put out of business by the construction of a rail bridge across the Hawkesbury - 100 miles horizontal haulage was cheaper than one mile vertically! All of these coal measures are accessible by drilling using well established (oilfield) techniques, and could be used for underground gasification.

Similarly, virtually all of Bass Strait is underlain by thick coal measures, and the same applies to the majority of the great Artesian and Bowen basins. Australia literally has no shortage of coal, and even readily and economically mineable coal is not likely to be in short supply for hundreds of years even at the present rate of increase of mining.

However, I remain unconvinced that underground gasification involves less CO2 emissions than mining the coal and burning it in a power station. It is a simple matter of looking at the energy balance - if you burn it, you use (at least potentially) all the available energy from oxidation of the coal. If you use underground gasification, part of the energy is lost in this process, and this is reflected in the fact that a major product of the gasification is CO - oxidation of which provides less energy than you would get if you oxidised the carbon in a power plant, but the end amount of CO2 is the same as if you had done that. The only CO2 saving I can see is that which is generated by the actual mining and transport of the coal - and I would have to be convinced that this saving is greater than the energy wasted underground in the gasification.

John

Originally Posted by JDNSW

Not as hard as you might think - for example, in the Sydney basin, there are two distinct sets of coal measures. Both are pretty much continuous across the basin (roughly from the Hunter to Wollongong and west to Lithgow, bordered in the east by the continental margin a few tens of kilometres out to sea. The coal is (economically) mineable only round the edges - were you aware that there used to be a coal mine at Balmain? This was put out of business by the construction of a rail bridge across the Hawkesbury - Wasn't the Balmain coal mine finally closed only when the Balmain Power Station closed, and that closed because it was too old to be economically viable against new stations like Liddel in the Hunter Valley.
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However, I remain unconvinced that underground gasification involves less CO2 emissions than mining the coal and burning it in a power station.
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The only CO2 saving I can see is that which is generated by the actual mining and transport of the coal - and I would have to be convinced that this saving is greater than the energy wasted underground in the gasification.

John

About current power stations being a long way from uneconomic coal seams, relates to the fact that most of the main base load stations are actually supplied by open cut mines and often supplied by conveyer belt.

Has the CO2 content of our atmosphere increased since the industrial revolution ??

Originally Posted by clean32

Has the CO2 content of our atmosphere increased since the industrial revolution ??

Yes (not that they had accurate measures of Global CO2 at the begining of the industrial revolution, however from ice core samples taken at the poles there has been an increase in CO2 levels in the last few centuries. Is that a factor of increased industrial production of CO2 or a reduction of carbon sinks like forrests, I don't know.)

Originally Posted by Lotz-A-Landies

About current power stations being a long way from uneconomic coal seams, relates to the fact that most of the main base load stations are actually supplied by open cut mines and often supplied by conveyer belt.

The Balmain coal mine was closed in 1931, as soon as coal could be shipped to the power station more economically than the mine could supply. Contrary to my earlier post, I have now looked it up and this was not when the bridge was built, but much later. The power station lasted into the 1970s.

Since the 1950s at least, power station location in NSW and most other places has been dictated by the availability of coal and water, preferably both. It is significant that they are mostly in the general Newcastle or Lithgow area, although the power stations around Lithgow are having water supply problems at present. As you say, the main power stations are in fact often within conveyor belt distance of open cut mines (but some of these belts are kilometres long).

But getting back to the original point, the Balmain mine was not closed because the coal ran out - there is still plenty there. A test bore from the bottom of the shaft confirmed the predicted presence of the lower coal measures. Also of interest is that the short Wikipedia article mentions two fatal gas explosions at the mine, neither during normal mining, but suggesting substantial gas reserves.

John

Originally Posted by Lotz-A-Landies

Yes (not that they had accurate measures of Global CO2 at the begining of the industrial revolution, however from ice core samples taken at the poles there has been an increase in CO2 levels in the last few centuries. Is that a factor of increased industrial production of CO2 or a reduction of carbon sinks like forrests, I don't know.)

is there any period in history that had the same levals of CO2 as we have now ?

Originally Posted by clean32

is there any period in history that had the same levals of CO2 as we have now ?

Air bubbles trapped in the ice cores provide a record of past atmospheric composition. Ice core records prove that current levels of carbon dioxide and methane, both important greenhouse gases, are higher than any previous level in the past 400,000 years. (Photograph courtesy U.S. National Ice Core Laboratory) Paleoclimatology: The Ice Core Record : Feature Articles

Originally Posted by Lotz-A-Landies

Air bubbles trapped in the ice cores provide a record of past atmospheric composition. Ice core records prove that current levels of carbon dioxide and methane, both important greenhouse gases, are higher than any previous level in the past 400,000 years. (Photograph courtesy U.S. National Ice Core Laboratory) Paleoclimatology: The Ice Core Record : Feature Articles

400,000 years being about 0.00002% (if my mental arithmetic got the decimal in the right place) of the time since oxygen largely replaced carbon dioxide in the earth's atmosphere in the Archaeozoic. Before that the atmosphere was mostly nitrogen and carbon dioxide - the change was due to oxygen pollution by photosynthetic organisms, setting the stage for animal life.

Worth noting that the ice core record only goes back to the start of the current ice age, as through most of the earth's history there have been no ice caps and hence no ice record.

John