The Continuing Carbon Sequestration Conundrum

17 Aug

Carbon sequestration, the technology of burying carbon dioxide from coal-fired plants, appears to increase other pollutants, states a recent report from this week’s Science News.

Unfortunately this is not all that surprising given that each new technology for dealing with pollution, when examined as a whole, has additional energy costs associated with the sequestration process that has to be accounted for in detail.

With worldwide energy demands expected to increase more than 50% by the year 2030, the net costs of power generation and the subsequent costs associated with sequestering the resulting carbon dioxide pollutants will be prohibitive by default unless or until power can be “generated” or “captured” via clean sources such as wind or solar, rendering the sequestration issue null.

Ultimately, the near term answer to the question of how to meet our power hungry needs will have to deal primarily with the idea of conservation of energy first, and then clean generation second.

Power plant emissions that cause acid rain, water pollution and destruction of the ozone layer may actually be made worse by capturing the CO2 and pumping it deep underground, a new study reported online and in an upcoming International Journal of Greenhouse Gas Control suggests.

This increase of other emissions is largely because collecting and burying CO2 — a process called carbon sequestration — requires additional energy, new equipment and new chemical reactions at the plants. And using current technology, meeting all of these requirements releases extra pollutants.

“Other studies mostly just look at one aspect, the carbon capture,” says study coauthor Joris Koornneef, an environmental scientist at Utrecht University in the Netherlands. “This is a first step in trying to quantify the [environmental] trade-offs.”

Captured CO2 must be compressed to about 100 times atmospheric pressure (which takes energy), transported to a suitable underground reservoir (which takes energy) and pumped into the ground (which takes energy). A coal-fired power plant that sequesters its CO2 must burn about 30 percent more coal than conventional plants to cover these energy needs. And that extra coal must first be mined (which has environmental effects) and transported to the plant (which takes fuel) — the list goes on and on.

Even with this extra burden, a CO2-burying plant emits between 71 and 78 percent less CO2 than a normal coal-fired plant for each unit of usable electricity produced, Koornneef and his colleagues report. But when the researchers factored in all the “cradle to grave” pollution of a CO2-burying plant, emissions of acid rain-causing gases like nitrogen oxides and sulfur oxides were up to 40 percent greater than the total cradle-to-grave emissions of a modern plant that doesn’t capture its CO2.

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Posted by on August 17, 2008 in Science News



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