Friday, February 16, 2007

Electricity from Coal... and Oil too!

The prospect if making crude oil synthetically appears increasingly attractive as the natural reserves of it become depleted. Synthetic crude oil is not of the same chemical composition as the material that is extracted from oil-wells, but it is essentially hydrocarbon in nature and can be turned into fuel for cars, planes and other methods of transport. It can also be processed into a useful feedstock for industry e.g. in the manufacture of plastics and synthetic fibres to underpin the commerce of the world and clothe its societies. Hydrocarbons can be produced from syngas, which is a mixture of carbon monoxide (CO) and hydrogen (H2) formed from some carbon-rich source such as natural gas or coal, by reacting it with steam at elevated temperatures usually aided by the presence of a catalyst. Since natural gas production is predicted to peak in only a decade or so after oil, any attempt to build a hydrocarbon economy based on gas is likely to prove of only short-term benefit, and the obvious carbon source is coal, since there is sufficient to be had for hundreds of years. The technology is tested and proven too, since the company Sasol satisfies most of South Africa's oil demand by coal-liquefaction, as it has for many years. The coal is converted to CO + H2 and this is converted to hydrocarbons using the Fischer-Tropsch process. As a matter of fact, it was this technology that kept Hitler's invasion and military programme going throughout WWII, in the face of initial scepticism that Germany's war-effort would be short-lived because the country had insufficient natural fuel resources to keep it going, and supplies from the Middle East were cut-off by the Allied navies. I have seen various estimates of how much oil can be produced per tonne of coal, ranging from 0.2 to 0.33 tonnes of it. Put another way, to make a tonne of synthetic crude takes anywhere between 3 and 5 tonnes of coal. In the form of a fine powder, coal is also used to fire power stations to produce electricity, and about 30% of that in the U.K. is made from coal, a figure that has increased since the North Sea gas reserves began to decline significantly. There is still plenty of gas in the North sea, but our nation's demand for it has now outstripped what can be supplied from there, hence we are now importing more gas from Norway and from other regions of the world.
There is a technology that combines the production of electricity with oil synthesis from coal, which is called Integrated Gasification Combined Cycle (IGCC). The difference between an IGCC plant and a conventional one is that instead of burning the coal powder in a furnace as normal coal-fired power plants do, the coal is converted into syngas and it is this that is burned in a turbine - hence it is another form of-gas-fired plant. There are many potential advantages to IGCC plants: for a start they are at least 10% more efficient in terms of their thermal energy (heat) output than are conventional plants, they use 40% less water (an important point as pressure on water increases, especially in countries like China), produce around half as much ash and solid waste, and are almost as clean as natural gas-fired plants in terms of their environmental emissions. Some of the gas can also be drawn-off e.g. to make synthetic fertilisers or synthetic oil, which is my interest here.
Right, let's look at some figures. There has been a study made of a similar technology by the U.S. DOE, which concluded the following statistics (I am grateful to McCrab for alerting me to this work, some few months back, but I am looking at it with renewed interest since my calculations of biofuels indicate them to be severely lacking as a substitute for conventional oil). This is for a single plant:

Coal consumed per day: 9,266 tons
Liquid hydrocarbons: 12,377 barrels per day
Electric power: 676 MW
Thermal Efficiency: 52.6%

So, nearly 53% of the coal's energy is being turned into something useful as opposed to just 33% extracted into electricity by a conventional coal-fired power plant. The electric power produced in this case study comes from the excess syngas which is burnt in an IGCC turbine at high efficiency, and so the same amount of coal can produce both electricity and liquid hydrocarbons. I shall try to do the math on this, but first of all we have the inevitable matter of "units" to consider. the U.S. ton (short ton) is not the same as the British (long) or the metric ton (tonne). As a scientist not a nationalist, I shall use the (metric) tonne, which is 1,000 kilograms. The U.S. ton is based on there being 100 pounds to the hundredweight, rather than 112 pounds as we assume over here. Hence 1 tonne = 1.1023 U.S. ton. (and about 0.98 British tons).

In 2005, 409 TWh of electricity were generated in the U.K. from all sources. This implies an average annual generating capacity of: 409 x 10*12 Wh/8760 h = 4.67 x 10*10 W. Hence, at a capacity of 676 MW, this could be met by 4.67 x 10*10/676 x 10*6 = 69 plants.

The coal consumed is 9,266 tons (8,406 tonnes) per day = 3,068,212 tonnes per year. And to run 69 plants = 3,068,212 x 69 = 212 million tonnes of coal per year.

Each plant yields 12,377 barrels per day of liquids x 365 = 4,517,605 barrels per year x 69 plants = 311,714,745/7.3 barrels per tonne = 42,700,650 tonnes per year.

We can compare this with the 73 million tonnes of oil used for everything, 57 million tonnes used for all transport and 44 million tonnes for road transportation annually in the U.K.

O.K., so if we made all our electricity from coal to gas to liquid processing, we have also met 55%, 75% and 97% respectively of the demand cited. These are meant merely as figures for thought, and I do not think it is feasible to introduce 69 new plants of this technology in short order. The road transport requirement could be cut to one third by using hybrid "Prius" vehicles, and so a mere 23 plants could provide that, and if we opened 2-3 of them per year we would be at capacity within a decade. We would of course need to dig the coal infrastructure to fuel them. Personally, I think that it is more important to use this "gasification" technology to provide feedstocks for industry and to make some fertilisers for agriculture. We are still going to need to provide food in as self-sustained a fashion as is possible. So, if we made half our electricity from coal, we could simultaneously provide 21 million tonnes of synthetic oil per year. 50% of our road transportation fuel equals 7.5 million tonnes of oil (if burned in hybrids) leaving 13 million tonnes of oil (or its CO + H2 equivalent) for industry and agriculture. However, there are many issues concerning pollution and CO2 emissions to be addressed if we are to take this path. If we installed 3-4 such plants per year beginning now, we would be able to meet this capacity within a decade, by when I predict that world oil will be in significantly restricted supply, and whence placing us in a relatively secure position in terms of energy based on an annual requirement of just over 100 million tonnes of coal.

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