Clean Coal

Here are two classic statements said to be the first and second greatest lies of all time:

• I'm from the government and I'm here to help you
• The check is in the mail.

The term 'Clean Coal' has a really good chance of displacing one of these!

In reality, there is no such thing as clean coal. If you look at generating electricity from coal, ignoring all of the intermediate steps, the equation looks like this:

C (i.e. carbon from coal) + O2 (Oxygen) --> CO2 (carbon dioxide) + energy

There isn't any way of changing this fundamental process although it can be made a bit more efficient so that we get a more useful energy from a give amount of coal. If we are to refrain from adding to the CO2 in the atmosphere, we must separate it from the stack gases and, somehow, sequester it for a very long time.

Some have talked about using coal to generate hydrogen for use in [clean] fuel cells. Unfortunately, the equation looks much the same although there are a couple of intermediate steps to show. One way is this:

C (needs to be red hot) + H2O (steam) --> CO (carbon monoxide) + H2 (hydrogen) + energy.

Some of the energy is lost in the process.

This product used to be called town gas and was used in the UK and other countries for heating and cooking. It was also a very efficient product for committing suicide: just put your head in the oven and turn on the gas.

For fuel cell use, the CO and H2 must be separated which consumes energy and then:

2 H2 + O2 --> 2 H2O + energy

There is also a bit more energy available by burning the carbon monoxide:

2 CO + O2 --> 2 CO2 + energy

So we start with carbon and water (steam) and end up with carbon dioxide, water and energy - just like burning coal to make electricity. The carbon dioxide must still be removed and sequestered which is hard to do and expensive.

We could skip the town gas step and make hydrogen from water. Generate electricity by burning coal, then use a technique known as electrolysis. Unfortunately, electrolysis is pretty inefficient. The process goes like this:

2 H2O + a lot of energy --> 2 H2 + O2

and using our fuel cell again:

2 H2 + O2 --> 2 H2O + energy.

As if the inefficiencies (and the need to sequester CO2) were not enough, we are faced with the problem that coal does not consist of pure carbon. The main pollutant is sulphur which, when burned, produces SO2. In the atmosphere SO2 is the main component of acid rain. The second problem is that, at the temperatures found when burning coal, nitrogen in the air burns providing a little additional energy (good) and oxides of nitrogen ( really bad) which contribute to acid rain and smog.

There are well established, and relatively economical, methods for extracting sulphur and nitrogen oxides from the power plant exhaust but safe disposal of these materials must still be accomplished. In the USA, pollution resulting from emission of oxides of nitrogen and sulphur is reasonably well controlled. Not so in many third world countries.

It is possible that coal can be cleaned up - at a price - but the technology for CO2 sequestration still needs much development.

Given the current situation, the best thing is to remember that there is no such thing as clean coal. Then beware those who use misleading words to advance an agenda that is unlikely to be in the interests of all of us.