# Clean coal **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [July 9, 2010, 2:06pm UTC](https://boards.straightdope.com/t/clean-coal/546095 "2010-07-09T14:06:23Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [July 9, 2010, 2:06pm UTC](https://boards.straightdope.com/t/clean-coal/546095/1 "2010-07-09T14:06:23Z")
From column: > **[Is “clean coal” really clean?](https://www.straightdope.com/21344041/is-clean-coal-really-clean)** > [@](#): > > Mercury will be captured in a bed of activated carbon, What is “activated carbon”, and how is it different than, say, coal? > [@](#): > > But that could be optimistic. A recent paper (Ehlig-Economides and Economides, 2010) claims actual underground storage capacity could be less than a hundredth of what scientists now assume. If so, U.S. coal power plants over a 30-year period would require underground storage almost three and a half times the size of Texas. Should this be confirmed, our global-warming life rope just broke. I’m not sure I follow. If we have less space than we think we do, then it will take space three and a half times the size of Texas? But not if we have the space we think we have? Something is poorly stated in that paragraph. ---
**Author:** ![Ed\_Zotti](https://avatars.discourse-cdn.com/v4/letter/e/fbc32d/32.png) [@Ed\_Zotti](https://boards.straightdope.com/u/Ed_Zotti)\ **Post date:** [July 9, 2010, 2:22pm UTC](https://boards.straightdope.com/t/clean-coal/546095/2 "2010-07-09T14:22:29Z")
Storage capacity per unit of volume. ---
**Author:** ![Strassia](https://avatars.discourse-cdn.com/v4/letter/s/e8c25b/32.png) [@Strassia](https://boards.straightdope.com/u/Strassia)\ **Post date:** [July 9, 2010, 3:08pm UTC](https://boards.straightdope.com/t/clean-coal/546095/3 "2010-07-09T15:08:01Z")
> [@Irishman](#): > > From column: > [Is “clean coal” really clean? - The Straight Dope](http://www.straightdope.com/columns/read/2946/is-clean-coal-really-clean) > > What is “activated carbon”, and how is it different than, say, coal? Google is your friend. [Activated carbon](http://en.wikipedia.org/wiki/Activated_carbon) is the stuff used in water filters. It has high surface area and tends trap certain chemicals and elements within its porous structure. > [@](#): > > I’m not sure I follow. If we have less space than we think we do, then it will take space three and a half times the size of Texas? But not if we have the space we think we have? > > Something is poorly stated in that paragraph. Basically, old estimates mean that the U.S. has enough capacity for 2000 years worth. New estimate, we would fill Texas up in 30 years. Meaning that we would fill the whole U.S. in 423 years, or only as fifth as long. ---
**Author:** ![palindromemordnilap](https://avatars.discourse-cdn.com/v4/letter/p/db5fbb/32.png) [@palindromemordnilap](https://boards.straightdope.com/u/palindromemordnilap)\ **Post date:** [July 9, 2010, 3:58pm UTC](https://boards.straightdope.com/t/clean-coal/546095/4 "2010-07-09T15:58:51Z")
The Texas thing still confuses me too. I assume in discussing underground storage we are talking cubic feet, but “the size of Texas” sounds like square feet. Asked another way, we would need storage capacity the width and breadth of Texas, but to what depth? Anyway, thanks for the explanation, Cecil. This is one of those topics where everyone who knows the facts is driven by an agenda, so research on the topic leads to arguments based on one of two irreconcilable sets of facts. Perfect for Cecil’s penetrating mind. ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [July 9, 2010, 4:55pm UTC](https://boards.straightdope.com/t/clean-coal/546095/5 "2010-07-09T16:55:57Z")
> [@Irishman](#): > > I’m not sure I follow. If we have less space than we think we do, then it will take space three and a half times the size of Texas? But not if we have the space we think we have? > > Something is poorly stated in that paragraph. What it means is that those authors made a calculation for the typical amount of CO2 which could be safely stored in porous rock/aquifers per square foot, and then extrapolated this to determine a total land area. They originally assumed they would need to store 3 million tons of CO2 per year at the density and pressure which they calculated (in this case, 1,000 psi over ambient underground pressure), and what Cecil did was multiply the area which they said was required for their single 3M ton example by the ratio of the tons of CO2 from US coal plants per year (1,946M), so we get: (1,946 tons CO2/year / 3 tons CO2/year) \* 1,371 square miles to store 3M tons CO2 = 889,322 square miles. Texas has 268,581 square miles, so we have a ratio of 3.31 : 1. FTR, the authors assumed 100 feet of usable aquifer depth for storage on average. ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [July 9, 2010, 4:59pm UTC](https://boards.straightdope.com/t/clean-coal/546095/6 "2010-07-09T16:59:22Z")
…I’ll also add there is a lot of uncertainty and controversy regarding the potential underground storage capacity of huge amounts of CO2. There is a lot which is unknown, and I personally, from my research in the field, would not be surprised by any estimate which had error bands of -90%/+1000% when one tries to assess the potential storage in an entire country the size of the US. It’s one of those things which we’re going to have to find out by some hard knocks, IMO. ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [July 9, 2010, 6:09pm UTC](https://boards.straightdope.com/t/clean-coal/546095/7 "2010-07-09T18:09:22Z")
**Una Persson** said: > [@](#): > > What it means is that those authors made a calculation for the typical amount of CO2 which could be safely stored in porous rock/aquifers per square foot, This is what bugged me. I knew it was something like that, but gas is something stored in volume, not area. So there is an invisible assumption about the storage per area being consistent across the surface of the Earth. I doubt that is true. ---
**Author:** ![Ed\_Zotti](https://avatars.discourse-cdn.com/v4/letter/e/fbc32d/32.png) [@Ed\_Zotti](https://boards.straightdope.com/u/Ed_Zotti)\ **Post date:** [July 10, 2010, 4:41am UTC](https://boards.straightdope.com/t/clean-coal/546095/8 "2010-07-10T04:41:08Z")
> [@Irishman](#): > > \*\*This is what bugged me. I knew it was something like that, but gas is something stored in volume, not area. So there is an invisible assumption about the storage per area being consistent across the surface of the Earth. I doubt that is true. Did some editing of the last graf; see if it’s clearer now. Questioning all the assumptions is a column for another day. -Ed ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [July 13, 2010, 7:43pm UTC](https://boards.straightdope.com/t/clean-coal/546095/9 "2010-07-13T19:43:26Z")
Wordinage much betterer. Thankanators.