Is CO2 Sequestration the Answer?

, Ph.D.

Power plants contribute about 40% of the carbon dioxide (CO2) that is released to the atmosphere in the United States, about 60% world-wide. With permits on tap for about another 150 in the United States alone, millions of addition tons of CO2 would be released if built. The common theme presented is that the CO2 would be sequestered in the new plants and not to worry.

Recently I attended an American Chemical Society meeting at USC where research was reported there on converting coal to supplant oil for all applications and rid us of our reliance on imported oil. I asked a colleague what would happen to the CO2. 'It would be sequestered,' he replied.

How?

They are dreaming.

So I decided to investigate. The task to sequester the enormous amounts generated is gigantic and would be very expensive. Would the money and time be better spent elsewhere? The current concentration in the air of CO2 is 383 ppm (parts per million), up from the pre-industrial level of 273 ppm. The goal is to keep the concentration below 550 ppm where climate scientists predict catastrophic changes in the earth's ecosystem. Recent measurements indicate that the rate of CO2 increase has accelerated.

There are some studies ongoing and the following is what is known or at least well estimated. Several thousand tons of CO2 have been pumped underground for years by oil companies to release more oil from deposits. There are 3,000 miles of C02 pipelines in the U.S. Preliminary studies estimate that global geologic reservoirs could potentially hold 9.5 trillion metric tons, more than 300 times greater than all of the anthropogenic C02 vented annually from all sources world wide.

The volume of the CO2 is huge. If only 60% of the CO2 from coal fired plants in the United States, were captured and compressed to a liquid, the volume would be equal the annual oil consumption of 7.3 billion barrels. To make a meaningful impact we would need thousands of plants practicing CCS (carbon capture and sequestration) operating around the world. Present calculations indicate that to capture, compress and sequester the CO2 would take 40% of a plants energy output. The plants would have to be located near a geological reservoir which may then require rail for the coal and other infrastructure. The CO2 would have to be moved by pipeline and injected. This would amount to a major change in the way the world gets it energy.

Of the many approaches considered for CCS, three remain. One is by using amines to capture the CO2 from the exhaust stream; another is by using pure oxygen to burn the coal to get nearly pure CO2 and the third by converting the coal to CO2 and hydrogen. Integrated coal gasification combined cycle (IGCC) plants are favored for their higher efficiencies and ease pf CO2 capture. Of the few demonstration IGCC plants in operation, none use CCS. The feasibility is unproven.

Of the many ideas proposed, only three sequestration geological formations are considered currently. The formations under consideration are deep saline sandstone formations, basalt, and in depleted oil and gas reservoirs. All still have their problems but are being currently investigated by Department of Energy's (DOE) National Energy Technology Laboratory. What is to be learned is massive if this approach is to be utilized. In the first case, we do not know how long the carbon will remain sequestered, what reaction the pressurized CO2 will undergo with its surroundings and above all, the costs. Basalts are prone to fractures, so leakage may be difficult to assess. Depleted wells may even be more leak-prone since any field may have hundreds to a few thousand wells that have not been efficiently capped and their records lost.

It could be decades before we get reliable answers to any of these questions. Can we wait that long?

Presently, the Department of Energy is spending $100 million a year on this problem. Great Britain has launched a comparatively sized effort and even China has obtained a World Trade Bank loan to study CCS. In the U.S. the massive coal industry regards this as survival and will push hard for an order of magnitude increase in budget. In fairness, gas-fired plants could also benefit from CCS and indeed, should we eventually find renewable waste as a suitable fuel for power generation, CCS would be a greater benefit. After all CCS with coal or any fossil fuel only tries to minimize the increase of CO2 released to the atmosphere but it would actually withdraw the pollutant from air when used with renewable fuels.

For natural gas fired plants, DOE has started Future-Gen which is slated to use CCS and should proceed. But is difficult to see any reason for building more coal fired plants until CCS has been validated as to cost and effectiveness. Alternatively, CCS might be used to equip current coal plants. In fact, Kansas just has refused a permit for a new coal fired plant because it used the Supreme Court ruling that CO2 is a pollutant. Also, many states as well as California have moved to have a Renewable Portfolio Standard i.e., a requirement that a minimum amount of future generation of energy come from renewables. This minimum is 20% or more in the near future. It is also difficult to see the need for more coal plants or imported liquefied natural gas. The research and development funds might be more effectively used to develop these renewables. Thus, as we develop our global warming mitigation scenarios, we then have the right to ask, indeed insist, that the developing countries follow suit. Together we can save the planet.