Posted on 06/13/2006 5:34:38 AM PDT by aculeus
Sulfur causes costly problems for high-temperature fuel cells. Tufts U. researchers may have found an answer.
High-temperature fuel cells promise clean, efficient energy in quantities large enough to power cities. But, so far, they've been too expensive for widespread use. One major problem is the sulfur in fossil fuels, such as coal, oil, and natural gas, which contaminates the hydrogen gas that runs the cells. The sulfur attacks and degrades a part of the fuel cell called the anode, reducing power production -- and eventually shutting down the cell.
Now chemical engineers at Tufts University in Medford MA, led by Maria Flytzani-Stephanopoulos, have found a way to continuously remove sulfur from incoming hydrogen before it feeds these cells. The work could be a significant step in making high-temperature fuel cells practical.
[For images of this new fuel-cell technology, click here.]
Low-temperature fuel cells have already found uses in laptops and buses, for example. But these fuel cells produce relatively little power. In contrast, high-temperature solid oxide fuel cells (SOFCs) could generate enough power to supply cities. And their heat can be channeled into other uses: for heating buildings or turning steam turbines to produce more power.
Lanny Schmidt, professor of chemical engineering and materials science at the University of Minnesota, says many operational issues have kept more powerful fuel cells off the market, including long startup times and parts wearing out under high heat. But, he says, sulfur is "one of the major problems." Schmidt predicts that researchers will overcome these obstacles in the next few years, and, if successful, SOFCs "may become the fuel cell of choice." He says that Flytzani-Stephanopoulos has "an innovative, clever new way to remove sulfur."
For low-temperature fuel cells (such as proton-exchange membranes), engineers have addressed the sulfur problem using a series of processing steps. They remove most of the sulfur from fossil fuels by refining the liquid fuel, and then use a reformer and materials called "sorbents." In the reformer, the fossil fuel is heated with air and water to make a hydrogen-rich gas. The sorbents then soak up hydrogen sulfide, so that the gas reaching the fuel cell is sulfur-free. But common sorbents, such as zinc oxide, would degrade in high-temperature fuel cells, which operate at 600 to 1,000 degrees Celsius.
The Tufts group has designed the first sorbent system for high-temperature fuel cells. First, they use new materials: rare earth oxides, known to be stable and able to absorb hydrogen sulfide at high temperatures. And, instead of filtering gas through a thick sorbent bed, they pass it over the surface of a thin sorbent layer. Flytzani-Stephanopoulos calls the new design a "simple" solution to the sulfur problem.
Rare earth oxides are inexpensive and easy to obtain. The system could be added to a SOFC using two small boxes -- one for fresh sorbents, the other for spent ones. Sulfur-free gases generated by the fuel cell would sweep the spent sorbents clean, allowing the same sorbents to be used over and over. "You don't need valves or pumps," she says, because all gases would diffuse naturally through the system. She adds that her sorbents could also outperform those used for in low-temperature fuel cells.
The Tufts research is funded by the Army Research Laboratory, which wants to use SOFCs as backup power for tanks and trucks. Since these vehicles run on fuel oil that's rich in sulfur, they would need effective sorbents.
Copyright Technology Review 2006.
Yet another step toward one of the solutions.
Energy in the future is going to come from a basket much greater than today. Fuel cells are one of a number of promosing technologies that will be developed.
The sooner the we stop buying oil from the Middle East the better. Slightly higher costs for energy will be paid off in greater independence and security. The only people who will lose are the oil men in and around the White House.
It should be part of the war on terror. It would be a role that everyone could play. Sadly that type of leadership isn't there.
SOFC are relatively "old hat" in the fuel cell business. The biggest advantage is that they run at sufficiently high temperatures to act as their own "reformers". But they have other problems. One of the biggest is that the solid-oxide (basically a ceramic) is very prone to "thermal shock", so they have to be brought up to operating temperature (and shut down from operation) VERY SLOWLY AND EVENLY. So they will be good for "baseline load" type applications, but not much use for "peaking" type uses.
ping
I'm not sure what you are suggesting here. Please clarify the proposal if there is one.
Are you implying that this might increase our independence because most domestic supplies are high-sulfur?
No, I was thinking that having a mix of fuels from nuclear to coal to wind, solar and biomass will increase our US independence on oil from the Middle East. That is because the US has all of those things in abundance, but an ever shriking amount of oil.
Homework time...
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"but not much use for "peaking" type uses."
Like driving?
"wind...That is because the US has all of those things in abundance,"
An abundance of wind right here, I'm afraid. By the way, I believe we have centuries worth of coal in the ground in the US.
It is true and so do the Indians, Chinese and Australians. Just have to figure out a way to use the energy stored there without destroying the local, regional or global environment.
Even if you don't think that humans are playing a role in climate change, SOX is real.
Even if the doubling of CO2 concentration over the last 200 years doesn't concern you, if it doubles again, there is no way to know what happens.
Thus if there are cheap ways to gasify coal and also sequester the carbon than it is great. Ultiamtely it may prove cheaper to use other sources of energy.
>Energy in the future is going to come from a basket much greater than today
The magic word is Tokamak
Aus is #2 in the world for Uranium... Nuclear power is the direction they should take... instead of just selling the UO...
Australia is supposed to have the most uranium of the countries, with Canada second.
World Uranium Mining
July 2005
http://www.world-nuclear.org/info/inf23.htm
Canada produces the largest share of uranium from mines (29% of world supply from mines), followed by Australia (21%).
"but an ever shriking amount of oil."
That's a total lie!
California alone has hundreds of years of oil but environmentalists and high taxes keep it trapped in the ground.
How is that a lie. Oil is a fossil fuel. Thus, there is no more of it being produced in a time-frame that is relevant to us. Therefore, when you burn it, the amount left shrinks.
Moreover, the figures say that the earth probably had about 6 trillion barrels of oil. We have used about 1 trillion. Of that 6 trillion about 2 trillion are easily recoverable i.e. cheap.
As we finish up with the second trillion over the next 15-20 years we will either have to come up with new technologies for recovering the more difficult stuff, or switch to alternatives that are cheaper.
As far as California having "hundred of years" of oil, you just made that up. Hundreds of years for whom? The US? Calfornia? Your Ford explorer?
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