From: Pablo, Triple Pundit, More from this Affiliate
Published November 12, 2007 08:20 AM

AskPablo: What's up with "Clean Coal" and Carbon Capture and Sequestration?

Many people have asked me about the feasibility of "clean coal" paired with carbon capture and sequestration (CCS) as a genuine option for a more sustainable future. In a previous article I wrote about coal-fired power plants (see AskPablo: Coal-Fired Power Plants) so I won't beat that dead horse too much. However, I will discuss coal-to-liquids as well as the feasibility of CCS.

Some politicians will have you believe that coal-to-liquids is a viable and sustainable alternative to our dependence on oil-based fuels. Whether or not these politicians are from coal-rich states, or which party they belong to I will leave up for you to explore.Here is how a liquid fuel is made from coal:

The coal is extracted from the ground via mines or mountain top removalThe coal is transportedThe syngas is converted into liquid hydrocarbons using the Fischer-Tropsch processThe liquid hydrocarbons can be further converted into gasoline or diesel.

Unfortunately this process also results in significant quantities of CO2, which could be recovered. Similarly "clean coal," which refers to the gasification and removal of sulfur dioxide and other impurities before combustion in a power plant, yields a great deal of CO2 that is more economically recoverable than standard coal power plant flue gas.

But what to do with all that CO2? We all know that the atmosphere has had just about enough of it... Well, you may have heard of a process called carbon capture and sequestration (CCS), which involved pressurizing the CO2 and pumping it into geologically favorable areas underground. CCS can reduce the carbon dioxide emissions of a coal fired power plant by 80-90%, making the "clean coal" red herring strangely plausible. But if that sounds too good to be true, it probably is, right? The energy required to capture, compress, and pump the CO2 into the ground would increase the fuel needs of the plant by 10-40%. With oil prices approaching $100/barrel last week (and probably reaching it this week) the growing cost of fuels might make this economically infeasible in the minds of most politicians and energy company executives. The problem here is that there is a certain (and rising) price on energy, yet an uncertain price on the climate.

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So is all lost when it comes to CCS? Perhaps not. The Massachusetts based company General Compression has developed a system for dispatchable wind power, that is, a way to store wind energy for later use. What does this have to do with CCS? Well, their idea is to use compressors, rather than generators in each windmill, to pressurize air that can be stored in underground caverns or pressure vessels to later power a centrally located generator. If the words "compressor" and "underground" stood out to you then you are starting to follow me.

The idea is that you could co-locate a "clean coal" or coal-to-liquids facility with a wind farm. Rather than having the windmill compressors pressurize air they could pressurize the captured waste CO2 and pump it into the ground. It just so happens that a lot of the big coal-burning states have abundant supplies of wind. Does this make CCS more economically feasible in the face of growing energy costs? It still depends greatly on how much we value the stability of our climate but it does provide a renewable alternative...

Pablo Päster

Sustainability Engineer

www.AskPablo.org

 

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