EGEE 101
Energy and the Environment

Buy a Cleaner Coal

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Reducing S02 by Buying Cleaner Coal

Coal quality is very variable, which is one reason that we take the measurements of proximate, ultimate analysis along with calorific value. Shown in the graph below is the acceptable line for emissions of 1.2 pounds of sulfur dioxide per million BTU of chemical input. If you purchase a coal below the green line and you have an efficient utility (normal efficiency should be >35%) then you will not have to spend money on cleaning the coal or installing a scrubber. As in the case of our crude oil, the quality of our coal is decreasing because we have consumed much of the cleaner coals. Many of our coal regions are not under the green line and so a sulfur reduction strategy is necessary to ensure compliance with the Clean Air Act. One of the easiest methods of reducing the sulfur dioxide emissions is to buy the cleaner (and thus more expensive) coal from another coal seam.

Line graph.  Percent Sulfur by weight vs Calorific Value.  See caption hyperlink for details.
We have discussed coal quality measures before. Here is why S content and calorific value are very important for emissions. By increasing the calorific value (selecting another coal with a similar S content but higher calorific value), or selecting a lower S content coal (but with the similar calorific value) we can reduce the SO2 emissions. Of course, we could always use other energy sources (renewable, nuclear), or capture the SO2 in a scrubber.
Credit: USGS

Unlike most coal properties, the S content (from the ultimate analysis) has very little to do with rank. Anthracite does have a low S content because the high temperatures necessary for anthracite creation would have been sufficient to remove the S as H2S. However, increasing in rank has very little to do with S content, rather you need to go back millions of years and look to see where the sea shore was. Seawater infiltration into the existing coal seam was responsible for much of the enhanced S content of some coals. Fortunately for the Western states, their coal was not exposed and they tend to have the cleaner (lower S) coals. So as Wyoming coal has a lower S content there was a massive switch to this cleaner coal.

Graph showing the rise of low-S coal production and the decline of higher S coal fields.
The high S content of the Since this figure above was produced there was a more significant drop in coal production as shown earlier in the course.Northern Appalachian region, uneconomic mining conditions (room and pillar underground mining), the Clean Air Act, and the closing of many underground mines because of coal depletion contributed to the reduction of the percentage that our region contributed to the total US coal production. Increases in productivity (Longwall mining) enabled the total tonnage to remain about the same for the 1990's to 2000. The major increase was the purchasing of much lower S coal (slightly lower calorific value) from the strip-mining operations in the West (Wyoming and Montana). 
Credit: USGS

Coal use is declining in the U.S. as we use more natural gas for electricity generation and industries also move towards natural gas. A smaller contribution comes from more wind power generation.

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Recall that I have indicated that the economy has a role to play in our emissions of pollutants. During the recession, there was much less industrial activity and less coal was consumed, and pollution emissions dropped accordingly.
Credit: eia