What clean coal is:
Historically, “clean coal” referred to any method of reducing the environmental impact of coal-based electricity. Today, clean coal refers specifically to containing the carbon dioxide (CO2) emissions in tanks underground, also known as carbon sequestration. Separating out the carbon dioxide from other waste is not simple! Carbon dioxide sequestration is not simple! The carbon dioxide needs to be separated out from other waste before it can be sequestered. Carbon can be separated out before or after burning.* Pre-combustion separation is basically cleaning the coal. Before burning, the coal is cooled to separate out nitrogen and sulfur. Cooling the coal is very energy intensive. (Ha! we need to burn more coal in order for us to clean the coal we’re burning!) When this clean coal burns, it only gives off CO2 and water. Post-combustion separation is basically cleaning the emissions. The smoke is dissovled in a solvent and then different parts are separated out of the solution one at a time. Currently the chemicals needed for the dissolving and separating are very expensive. This method is also pretty energy intensive. The separated out CO2 is then pumped to underground storage tanks. This stored CO2 would be kept underground indefinitely.
How clean coal makes electricity:
As I explained last week, coal is burned to heat water into steam which spins a turbine. Clean coal works the same way, but the coal (pre-combustion) or emissions (post-combustion) are cleaned.
How much of our current electricity is produced by clean coal:
Coal power currently accounts for half of the U.S. electricity production. Essentially none of it is “clean coal”.
Potential energy supply:
According the the EIA, the US currently has 19.2 billion short tons of easily accessible coal. The EIA estimates that these reserves will last about 200 years. It is difficult to say how much total coal there is since it is underground and some of it has yet to be discovered. Total coal estimates in the US are 4 trillion short tons.
- [Source: U.S. Energy Information Administration, U.S. Coal Reserves 2011, November 2012]
With carbon sequestration technology, all of this coal could be burned as clean coal.
Materials and how we get them:
We mine coal, which provides jobs (yeah!) and environmental problems (boo!). For clean coal, we need massive amounts of pipeline and pumps to move the CO2 through from power plants to in-ground tanks. Additionally, we need tanks for storage and the space for the tanks underground. And those tanks would need to be fitted with leak detection to ensure that the CO2 wasn’t getting out.
Waste produced and how we deal with it:
The stuff that we clean out of the coal or emissions (sulfur, nitrogen, and particulates) can be used in industrial processes. The used solvents and the waste from their production and the production of pipes and tanks would be a new kind of waste we would need to deal with.
Cost:
Estimates vary for how much carbon sequestration costs, but the short answer is tens of billions of dollars per year in the U.S.. A coal power plant in Mississippi is being built to showcase clean coal technology, and the cost of building the plant equipped to sequester CO2 is nearing $5 billion. For comparison, the cost of a regular coal burning power plant is around $1 billion. According to the EPA, first generation carbon capture technology used in coal-powered electricity production would increase the cost of electricity by 70-80%.
Challenges:
The biggest challenge of clean coal aside from the cost to convert our power plants, is that there is so much unknown about long term storage of CO2. Can we make tanks that don’t leak? Will storing it below ground have negative impacts on structural integrity of the ground? What happens if there is an earthquake? However, clean coal is an opportunity for America to lead the world in green tech. Many developing countries – notably China and India – use coal power. If we worked with them towards clean coal, there would be a huge impact on carbon emissions. Whew. I know this is a complicated one. You’re a champ if you made it through. Goes to show, solving our energy needs is not going to be easy. *Alternatively, the coal can be gasified. Burning gas is much more efficient than burning straight coal, but the process of gasifying coal is complicated, expensive, and currently only being accomplished in small scale amounts.
… For an introduction on sources of electricity, look here. For an explanation of how we make electricity, look here. Oh, hey, Building Earth has a facebook page now. Keep up to date on posts and other interesting green news by liking us!