A greener way to get electricity from natural gas

Dec 03, 2009 by David L. Chandler
Graphic: Christine Daniloff

(PhysOrg.com) -- A new type of natural-gas electric power plant proposed by MIT researchers could provide electricity with zero carbon dioxide emissions to the atmosphere, at costs comparable to or less than conventional natural-gas plants, and even to coal-burning plants. But that can only come about if and when a price is set on the emission of carbon dioxide and other greenhouse gases — a step the U.S. Congress and other governments are considering as a way to halt climate change.

In findings recently published online in the Journal of Power Sources, postdoctoral associate Thomas Adams and Paul I. Barton, the Lammot du Pont Professor of Chemical Engineering, propose a system that uses solid-oxide fuel cells, which can produce power from fuel without burning it. The system would not require any new technology, but would rather combine existing components, or ones that are already well under development, in a novel configuration (for which they have applied for a patent). The system would also have the advantage of running on natural gas, a relatively plentiful fuel source — proven global reserves of natural gas are expected to last about 60 years at current consumption rates — that is considered more environmentally friendly than coal or oil. (Present natural-gas power plants produce an average of 1,135 pounds of for every megawatt-hour of electricity produced — half to one-third the emissions from coal plants, depending on the type of coal.)

Natural gas already accounts for 22 percent of all U.S. , and that percentage is likely to rise in coming years if carbon prices are put into effect. For these and other reasons, a system that can produce electricity from natural gas at a competitive price with zero could prove to be an attractive alternative to conventional power plants that use fossil fuels.

The system proposed by Adams and Barton would not emit into the air any carbon dioxide or other gases believed responsible for global warming, but would instead produce a stream of mostly pure carbon dioxide. This stream could be harnessed and stored underground relatively easily, a process known as carbon capture and sequestration (CCS). One additional advantage of the proposed system is that, unlike a conventional natural gas plant with CCS that would consume significant amounts of water, the fuel-cell based system actually produces clean water that could easily be treated to provide potable water as a side benefit, Adams says.

Although no full-scale plants using such systems have yet been built, the basic principles have been demonstrated in a number of smaller units including a 250-kilowatt plant, and prototype megawatt-scale plants are planned for completion around 2012. Actual utility-scale power plants would likely be on the order of 500 megawatts, Adams says. And because fuel cells, unlike conventional turbine-based generators, are inherently modular, once the system has been proved at small size it can easily be scaled up. “You don’t need one large unit,” Adams explains. “You can do hundreds or thousands of small ones, run in parallel.”

Adams says practical application of such systems is “not very far away at all,” and could probably be ready for commercialization within a few years. “This is near-horizon technology,” he says.

Costs and benefits

Adams and Barton, with funding from the BP-MIT Conversion Research Program, used computer simulations to analyze the relative costs and performance of this system versus other existing or proposed generating systems, including natural gas or coal-powered systems incorporating carbon capture technologies.

Combined-cycle natural gas plants — the most efficient type of fossil-fuel power plants in use today — could be retrofitted with a carbon-capture system to reduce the output of greenhouse gases by 90 percent. But the MIT researchers’ study found that their proposed system could eliminate virtually 100 percent of these emissions, at a comparable cost for the electricity produced, and with even a higher efficiency (in terms of the amount of electricity produced from a given amount of fuel). Jack Brouwer, associate director of the National Fuel Cell Research Center at the University of California, Irvine, says that the high efficiency and the carbon separation capabilities of solid-oxide fuel cell technology “are indeed impressive.”

Absent any price for carbon emissions, Adams says, when it comes to generating electricity “the cheapest fuel will always be pulverized coal.” But as soon as there is some form of carbon pricing — which attempts to take into account the true price exacted on the environment by emissions — “ours is the lowest price option,” he says, as long as the pricing is more than about $15 per metric ton of emitted carbon dioxide. Such a pricing mechanism would be put in place, for example, by the Waxman-Markey “American Clean Energy and Security Act” that was passed by the U.S. House of Representatives in July, through its “cap and trade” provisions. (A corresponding bill has not yet reached the floor of the U.S. Senate.) If the program becomes law, the actual price per ton of carbon would vary, being determined through the free market.

CCS is considered the only practical way of meeting reduced emissions targets under a cap-and-trade program, because alternatives to the use of fossil fuels are not far enough advanced to be able to quickly replace them at reasonable cost. CCS involves separating out the carbon dioxide from other gases in the plant’s exhaust, and then injecting them into deep geological formations (for example, in depleted oil wells) to keep them from going into the atmosphere. Most approaches to capturing the carbon dioxide emissions from a fossil-fuel power plant require the use of a chemical solvent that absorbs the carbon dioxide from a mixture of gases — a process that is inherently inefficient and adds significantly to the cost of the power produced. Adams and Barton’s system eliminates this inefficient separation step.

One of the critiques most often leveled against proposals for fuel-cell is that the technology has high initial costs compared to conventional combustion technologies. But the new study found that once carbon pricing is in effect, even if the cost of fuel cells remains more than double that targeted by the U.S. Department of Energy for 2010, the solid-oxide fuel cell system would be the cheapest option available in terms of lifecycle costs of electricity produced, even though the up-front capital costs could be three to four times greater than for natural gas or coal combustion systems.

In fact, the system’s predicted efficiency is so high that it beats the lifecycle cost of a combined-cycle plant, even without carbon pricing. And the study shows that a very low level of carbon tax, on the order of $5 to $10 per ton, would make this technology cheaper than coal plants, which are currently the lowest cost option for electricity generation.

More information: dx.doi.org/10.1016/j.jpowsour.2009.10.046

Provided by Massachusetts Institute of Technology (news : web)

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User comments : 9

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Loodt
2.5 / 5 (13) Dec 03, 2009
Why tax carbon dioxide, the product of clean, full and efficient combustion? Carbon dioxide is plant food!
christian_physicist
3 / 5 (12) Dec 03, 2009
That first paragraph boggled my mind. I got all excited that the technology would be cheaper than coal... but then I read "if and when a price is set on the emission of carbon dioxide." Well, shoot. With the right subsidies/punishments, you can make whatever you want the cheapest option, but it doesn't really mean anything.

It looks like belief in CO2 as bogeyman-in-chief may be on the way out anyways, or at least certainty in the supposed imminence of catastrophic AGW is, after what the climategate emails reveal coupled with the statements of other researchers. Although with so much money invested in the hypothesis, people are going to have to be dragged away kicking and screaming.
winthrom
3.3 / 5 (6) Dec 03, 2009
CO2 becomes plant food when solar energy is used to run chlorophyll reactors built into plant cells. These reactors are only a few % efficient. The depletion of plant habitat to support the ever increasing numbers of humans, with an ever increasing standard of living, is part of the equation that shows greenhouse gasses are now, and will continue, increasing. Human activity considers natural plant habitats [rain forests, natural forests, etc.] as exploitable resources that may be destroyed and replaced with cattle grazing grass, grass lawn, suburban housing, sprawling highway systems, etc.
A preferred solution is described in the article above: collect and sequester the offending CO2. An idealized solution is converting CO2 to useful chemicals using man-made solar power. CO2 converts via processes such as described in:
http://www.physor...219.html
CO2 converts to Sodium Formate an Acid as described in:
http://www.mantra...ion.html
fed005
3.7 / 5 (3) Dec 03, 2009
CO2 aside, what would be the cost comparison without carbon pricing if coal ash is declared a toxic waste, and waste water from coal plants is regulated for heavy metals?
kasen
3 / 5 (2) Dec 03, 2009
I don't know if there is one whole paragraph that deals with the actual new technology proposed here, solid-oxide fuel cells. The "greener way" turns out to be increased taxes and government control. Well, money is green, after all.

Am I the only one who feels that this CCS idea is kinda like stuffing the trash under the carpet? Also, it sounds like a pretty good excuse to keep using fossil fuels. Heck, Big Oil have probably started digging big ol' holes in the ground already. Wait, they've actually been doing that for a while, haven't they? This should really conflict AGW zealots.
nkalanaga
1 / 5 (1) Dec 03, 2009
Coal ash also exceeds government radiation standards, and should be regulated as low-level nuclear waste. At least one Oak Ridge study concluded that, using breeder reactors, the uranium and thorium in coal as could produce more electricity than was produced by burning the original coal. Even without the other heavy metals and toxic chemicals coal ash is nasty stuff.
freethinking
1 / 5 (1) Dec 03, 2009
nkalanaga,

do you have reference using coal ash to produce electricty.

nkalanaga
3.7 / 5 (3) Dec 03, 2009
No, but I have the paper at home. At one time it was available as a .pdf file. The paper wasn't about actually about using it as nuclear fuel, but simply said that the amount of fissionable material in it would produce that much energy if it was refined. Coal ash itself is useless as a nuclear fuel, or much of anything else, although it has been used as filler in concrete and as granules on asphalt shingles. I can't find that one online now, but here is one with some numbers.

http://www.physic...Su03.pdf

“A coal plant releases about 74 pounds of uranium-235 each year, enough for two or more nuclear bombs.” (D. R. Francis, “Energy study gives black marks to coal, boost to nukes,” The
Christian Science Monitor, 29 May 2001.)"

And with the U-238 and thorium, there is a lot more usable energy there.
Shootist
1 / 5 (1) Dec 06, 2009
"(PhysOrg.com) -- A new type of natural-gas electric power plant proposed by MIT researchers could provide electricity with zero carbon dioxide emissions to the atmosphere, at costs comparable to or less than conventional natural-gas plants, and even to coal-burning plants. But that can only come about if and when a price is set on the emission of carbon dioxide and other greenhouse gases — a step the U.S. Congress and other governments are considering as a way to halt climate change."

Thrice damned communists.