Thursday, August 09, 2007

Energy-generation: Fossil fuels.

(Ed. note: Since this is mostly general information stuff, I'm relying exclusively on Wikipedia. While they're not great on specialist topics, they're as good as any encyclopaedia on general ones. Also note, though, that this introduces an American bias in data discussed. I'm not aware of any reason to be concerned about that, though.)

Oil, coal, natural gas and other fossil fuels (including oil shale, which seems to me to combine the worst characteristics of coal and oil) are converted into electricity by approximately the same process. They're burned to produce heat; the heat is used to boil water and convert it to steam; the steam is channelled via a series of pipes to drive turbines; and the turbines are attached to generators, which convert the mechanical energy of the turbine's motion into electrical energy. There may also be a series of turbines attached to further generators, which are driven by waste gases and heat/steam.

All these plants, thus, share the same construction and maintenance costs. They also all use water in the boilers which, although it is recycled after being converted into steam, must be replenished due to minor steam leaks in the boiler system. It's also worth noting that all fossil fuel plants consume energy. For one, once the steam has recondensed, it has to be pumped back into the boiler for re-use. Figuring out a dollar amount for this class of input costs is, apparently, impossible. I've been Googling for the better part of an hour and have come up with zip in terms of costs of construction or maintenance costs for fossil fuel plants in either the US or Canada.

Fuel costs are variable. In terms of actual purchase price, according to the World Bank (.pdf), coal cost about $47.62/metric ton in 2005, $49.09/metric ton in 2006, and $57.32/metric ton in 2007. (Just to make my life easier, I'm assuming these and all other costs of fossil fuels fully internalize the economic costs associated with mining. Otherwise, I'd be doing this for months.) In terms of externalized costs, coal mining produces greenhouse gases and can impact on water-flow in mined regions. Coal can also introduce toxic chemicals into water, but mines are required by law to monitor and control this problem. By law, future coal mining sites must provide reclamation plans (i.e., plans for returning the land to a safe and usable state); but there is no such law for older mines, as far as I can tell. Once coal is mined, it must be transported to the plant and unloaded (apparently a more lengthy process than other fuels, given that it won't flow, unlike oil or gas). It must also be (mechanically) pulverized to a fine powder before it can be successfully burned.

Crude oil, according to the same World Bank .pdf, cost $53.39/barrel in 2005, $64.29/barrel in 2006, and $63.38/barrel in 2007. Petroleum extraction appears to be less environmentally costly than coal extraction. (Although, interestingly, Wikipedia notes there are several methods currently in use -- and others being developed -- for transforming coal into an oil substitute.) Costs associated with using fuel oil rather than coal are for me hard to determine, given that natural gas appears to be the preferred alternative to coal, as far as fossil fuels go. So, with that in mind, turning to natural gas....

According to that World Bank .pdf, natural gas cost $8.92/million BTUs in 2005, $6.72/million BTUs in 2006, and $7.20/million BTUs in 2007. (One million BTUs is equivalent to 1 gigajoule and, according to this, thus 278 kW-h.) Natural gas must be processed before it can be burned in a fossil fuel plant. "Raw" natural gas is a combination of various hydrocarbon gases, some of which (e.g., ethane, propane, butane) can be sold commercially once extracted. Sulfur can also be extracted for use. Others (e.g., carbon dioxide) are considered waste and incinerated once extracted. Transportation of natural gas is also problematic, as it must be compressed or liquefied in order to be transported on carriers, adding to the cost. Alternately, it can be piped from its source, but this can be impractical over long distances. Natural gas is generally found in naturally-occurring gas fields, but can be produced by treating coal and from biological material. The latter is still largely in development.

In terms of output, all these plants are a significant source of air pollution. Coal plants are the worst offenders here, but no fossil fuel -- not even natural gas -- is exempt. Burning coal produces several toxic gases which have to be removed through, for example, limestone wet slurry in exhaust stacks. Burning coal also produces ash which, if removed with filters, can (sometimes) be recycled for other purposes (such as manufacturing concrete). It is also possible to combine the emitted gases with water, and use the result to drive a gas turbine. Fossil fuels can also contain trace amounts of radioactive and toxic metals, and this is not an insignificant problem, given the volumes consumed by fossil fuel plants. All fossil fuel plants emit carbon dioxide and there is no known way to deal with it. Of course, CO2 is known to contribute to global warming. So-called "clean coal" plants would have to eliminate all these emissions and, as yet, the process is theoretical. Clean coal technologies may also be cost-prohibitive. Natural gas produces less of these pollutants, in part because it has been purified through processing, in part because it contains less carbon and thus releases less CO2 when burned. It is still, however, polluting.

In terms of energy production, fossil fuel plants vary depending on technologies used. Efficiency for coal can be as low as 35% (i.e., 65% of energy produced lost to the environment in the form of heat) or as high as 50% (if steam is superheated). (It is, in principle, possible to convert coal into a gaseous form that could be used in a fuel cell, which would drive efficiency, possibly, as high as 85%. These cells are currently still in development, and thus I'll cover them in a later installment.) Coal contains about 6.67 kW-h of energy per kilogram. Using the efficiency numbers above, this works out to about 2.3 to 3.3 kW-h per kg of coal produced by coal plants. Using the 2007 cost above, given that a metric ton is equivalent to 1,000 kg, 1 kg of coal costs $0.04762, or about 5¢. So, 1 kW-h of electricity produced by coal costs between 2¢ and 1.5¢ (at most and least inefficient, respectively). (I know that's just counting the fuel costs, but I can't find numbers for the other costs. So, it's a conservative estimated cost.) Unfortunately, I can't calculate the energy production for natural gas, as the data don't appear to be easily available. However, given the 2007 cost of natural gas above, and the conversion of 278 kW-h equalling 1 gigajoule, it follows that natural gas costs about 3¢ per kW-h.

In terms of jobs sustained, a little over 100,000 miners work in coal mines in the US. Coal mining is the second-most dangerous occupation in the US, in terms of worker injuries and fatalities. Comparable figures are, again, not readily available for natural gas.

So, surveying the fossil fuels, it seems they have two main advantages. They're (currently) not too expensive to extract, and the plant technology is not terribly complicated. Thus, I would expect fossil fuel plants to be the cheapest power plants, in terms of construction, maintenance and operating costs. (Of course, the latter is a bit of a guess, as I can't find the data.) They have two disadvantages, though. They produce a lot of pollutants, primarily into the air, and they're finite resources. Overall, it seems that natural gas is the best of the three possibilities, given that it is less polluting, not obviously less productive, and only marginally more expensive. (Without efficiency numbers, it's hard to estimate the costs.) It's a slight advantage, though, from my perspective. So, I'll take it that none of the fossil fuels is clearly superior to the others.

Next week: hydroelectric, nuclear fission, and wind power.


1 comment:

Hallq said...

Hey, you think you could link back to the philosophy blogroll announcement post, even if you don't use the thing at your site?