Coal exists in vast amounts in the earth's crust, and it represents an enormous energy resource. However, climate change considerations dictate that we must not emit CO2 into the atmosphere. That would be irresponsible, as we all most of us know. The burning of coal for energy, however, produces about 3.6 tons of CO2 for every ton of carbon burned. (The coal ash and other toxic valuable minerals such as mercury, sulfur and arsenic are important byproducts, but alas, not commercially recoverable as yet.) Coal is the worst fossil fuel with regard to climate change. It produces more CO2 per unit of energy recovered than either petroleum or natural gas. So, sequestering the CO2 it produces should be a very high priority.
Below the fold, I will describe a foolproof method for storing every ounce of this CO2 permanently and effectively. Believe me, you will be impressed.
First of all, let's consider the problems of storing CO2 in deep injection sites. The first problem is that the storage volume needed is roughly 10 times the volume of the coal burned to produce the CO2. In fact, 73% of the CO2 (by weight) is oxygen. Does it make sense to bury oxygen to improve our atmosphere? More on this later.
Deep injection sites, by their very nature, are much hotter than sites near the surface. In fact, their temperature is well above the critical temperature of CO2. This means that what we are trying to do is to store supercritical CO2 at high temperatures and pressures. Now, supercritical CO2 doesn't blow up or anything like that, but like any other fluid under pressure (It shares some properties of both liquids and gases), it tends flow toward areas of lower pressure, like our atmosphere. It is a pretty good solvent, meaning that it is difficult to contain indefinitely.
Moreover, pushing all that CO2 into deep injection sites takes energy. I won't go into the math, but trust me on this one, it's true. Add to this the energy expended digging the stuff out of the ground, transporting and processing it, and dumping processing the ash, and the net energy recovered diminishes some more. And I won't even mention black lung.
Given the fact that the supercritical CO2 will eventually find its way to the surface, storing greater and greater amounts of CO2 underground is a dubious solution at best. Naturally, the power company that generated it would be responsible for maintaining these sites in perpetuity. As the inevitable leaks develop, these power companies would be obligated to apply the appropriate measures for hundreds of years many millenia eons a long time to come. Let's hope they never declare bankruptcy, because that would leave the rest of us holding the bag.
I must confess that this scenario doesn't inspire a great deal of confidence, and I have an innovative solution. It's so breathtakingly simple that I wonder why nobody has yet thought of it. Here's what we should do:
First of all, burying all that oxygen doesn't make sense. If we separate the oxygen from the carbon (an endothermic process), we can just release the oxygen to the atmosphere where it won't do any harm. Or, heck, we could just breathe it. Hospitals would pay good money for it, not to mention steel mills and welding supply stores. Moreover, the remainder, the pure carbon itself, would be much easier to store. It happens that it could be converted to a rock-like glossy black substance simply by subjecting it to heat and pressure. This would have another advantage: it wouldn't exert many atmospheres of pressure like supercritical CO2 does, simplifying greatly the storage problem. We could just dump these lumps of carbon into played-out coal mines where they could be stored indefinitely at practically no cost or risk. When you think about it, this is a brilliant solution. I am so proud of myself for thinking of this.
Excuse me, but I have to get to work on my Nobel prize acceptance speech.