The Oil Drum

Today I would like to describe the events that take place when a company chooses to surface mine coal from under the earth. Of all aspects of mining this is, perhaps, the most controversial, in part because of the large surface disruption that often occurs during the time that it is happening. This post will try, however, to just describe the process, without using any of the emotive words that usually surround this topic.

For those wondering what this is, on many weekends I post a small technical talk, which tries in a relatively simple way to explain some aspect of fossil energy extraction. I will direct you to earlier talks at the bottom end of this one. For those that are more knowledgeable I recognize that I am often simplifying considerably, however, by knowing some of the basics it may be possible to achieve a better understanding.

This becomes particularly true when one talks about coal mining, since there is often discussion on these pages about the relative investments in energy in a process, relative to the amount of energy recovered. Part of that evaluation involves the nature and structure of coal as it is mined and treated, and I will go into more depth on that subject next time.

It is relevant here, since it is one of the bases of judgment as to how a seam of coal is mined. If you remember, I had suggested that you might think that coal is found as being similar to a layer of cream in a cake. Separated by the layer of rock above, and more rock below, the coal itself is a relatively even thickness of material that can stretch for miles. However you should note the word "relatively" in that description, and look at the rock layers in a road cut the next time that you drive through one. You will see variations in the layer at the top and bottom all along the length. Also the layers do not have to be flat, geological movements may have tilted the seams until they are at angles all the way up to vertical. (The coal is the Urals is often highly angled, as are some of the seams in Washington State).