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Using Steam from Nuclear Power Plants for Ethanol Production

22 March 2007

Nucetoh
Nuclear reactors and ethanol plants in the Corn Belt. Click to enlarge.

Researchers and engineers at Oak Ridge National Laboratory and the US Department of Energy are suggesting using the steam from existing nuclear power plants in the Corn Belt to reduce the costs of producing ethanol from corn and other biomass.

While current corn-to-ethanol plants provide the near-term market for nuclear steam, future cellulose-to-ethanol plants represent a much larger and longer-term market for nuclear steam. The ethanol market could require hundreds of gigawatts of thermal energy and thus may become the dominant cogeneration market for nuclear heat, according to the authors of a paper on the topic to be presented at the upcoming International Conference on Non-Electrical Applications of Nuclear Power.

The cost of low-pressure steam from nuclear power plants is less than that of natural gas, which is now used to make steam in corn-to-ethanol plants. The use of steam from nuclear power plants reduces greenhouse gases compared with the generation of steam from fossil fuels. Last, in cellulose-to-ethanol plants the liquid fuel produced per unit of biomass can be substantially increased if the ethanol plants also have the capability to convert lignin to liquid fuels. Lignin is the primary non-sugar-based component in cellulosic biomass that can not be converted to ethanol. It is planned to use this lignin as boiler fuel in these ethanol plants; however, if there are other sources of steam it may be feasible to also convert the lignin to liquid fuels and thus increase the yield of liquid fuels per unit of cellulosic biomass. In several decades, this market may become the largest market for cogeneration of steam from nuclear electric power.

—from “Fuel Ethanol Production Using Nuclear-Plant Steam”

Although the concept of using steam from nuclear power plants in ethanol production is not new, up until recently the economics and the scale of ethanol production were not particularly compelling.

From a lifecycle perspective, the greenhouse gas releases from consuming fossil fuels—from growing the corn through the conventional production of ethanol—are only about 20% less than from the alternative of producing gasoline from crude oil with an equivalent energy value, according to the authors.

If nuclear energy is used to support ethanol production, however, fossil fuel inputs can be dramatically reduced. The conversion of corn to ethanol primarily requires low-quality, low-cost steam—something nuclear power plants are very good at producing. Using low-quality steam from nuclear power plants in the corn-to-ethanol production process would reduce fossil fuel inputs and the resultant greenhouse gas emissions for the entire process of growing the corn and converting it to ethanol by almost half.

Steam provided by the reactor would be condensed at the ethanol plant, and warm water would be returned to the nuclear power plant. Almost all of the heat required by the production process could come from condensing the steam. Modern steam systems would allow more than a mile of separation between the reactor and the ethanol plant.

Based on the price of electricity, the cost of low temperature steam from a nuclear power plant is about half the cost of steam from natural gas.

(A hat-tip to Charles!)

Resources:

March 22, 2007 in Cellulosic ethanol, Ethanol, Nuclear | Permalink | Comments (18) | TrackBack (0)

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Comments

Wouldnt this be an interesting way to use Sterling engines to produce power as well?

Seems that this would make corn ethanol and the nuke power plants alike more energy efficient.

Those cooling towers have always bugged me...surely somebody could use all the almost "free" hot water they could handle.

Every caloric power plant produces low-grade waste heat, not just nuclear ones. Typically, pressure after the turbine set is well below atmospheric, though. To deliver steam at pressures a little above atmospheric, you have to bleed steam from the system prior to the last turbine stage(s), which reducees the thermodynamic efficiency of electricity generation a little.

Still, co-generation of low-grade steam and hot water is an excellent way to increase overall thermodynamic efficiency (e.g. district heating and cooling via absorption chillers). The main problem is usually a lack of nearby consumers of low-grade heat. Without those, the infrastructure required to transport it is not economically viable.

Using low-grade heat to help dry and otherwise process biomass into automotive fuels (e.g. ethanol) sounds like a good idea but there are a few catches. First, the biorefinery must be located in close physical proximity to the power plant, a constraint that increases the cost and energy required for feedstock transport in many (not all) cases. The biorefinery would also have to operate very reliably such that it can accept steam 24/7.

Second, the corn ethanol boom in the US is already causing competition in the food market, especially in Mexico. Reducing production costs via co-generation schemes will merely exacerbate this competition until and unless industrial-scale production of cellulosic ethanol gets off the ground.

Third, if you use cellulosic feedstocks rather than starchy kernels, you not only have to figure out how to co-ferment glucose and xylose. You also have to find a use for the 1/3 of dry biomass that is lignin, a natural glue that only certain fungi can digest. Current cellulosic ethanol technology assumes this by-product will be burnt to produce the low-grade steam required for feedstock pre-processing and enzymatic breakdown.

Converting lignin to ethanol fuel would require adding a lot of hydrogen to it - which I expect the nuclear industry would quite like to deliver by way of electrolysis. Lignin can also be converted to fuel via gasification and F-T or MTG processes. The argument put forward here is that this BTL route may be economically viable iff a fraction of the steam required were purchased from a co-generation plant. Note that F-T and MTG are exothermic processes, so some steam would still be produced within the biorefinery.

My $0.02: Low-grade steam from co-generation might be an attractive proposition if and when cellulosic ethanol becomes an industrial-scale reality. While legacy nuclear power stations are a possible source of such steam, significant retrofit infrastructure would be required. Other sources of low-grade steam should also be considered, especially in favor of new reactor construction.

Another possibility would be small dedicated reactors producing just low grade steam. This would enable the plant to avoid including turbines and generators, which are a significant part of the cost of a nuclear electric generating plant.

Rafael,

I think that biomass that contains virtually no lignin would be preferred anyway for cellulosic ethanol. Without the lignin the enzymatic degradation of the cellulose should be easier, and grasses and corn stover contain very little lignin and can be selected to contain even less.

RS-

Good analysis. Transporting the corn or mash to the reactor would involve massive transport. This might offset any gains made in using the rejected heat. It might be better to use an ORC on the final stage at the plant and use solar thermal for the ethanol.

The entire point is the nuke reactors already are there in those areas anyway so pitting the ethanol plants right next to them is a win.

Wintermane -

Siting a biorefinery close to a power plant just so you can get cheap steam makes no sense if you then have to transport the corn feedstock much further.

The map shows that only a small number of reactors are candidates for this, e.g. those in Minnesota, South Dakota and Illinois. The resources provided articulate this in more detail.

Ethanol refineries elsewhere in the corn belt might benefit from a similar arrangement with local legacy gas- or coal-fired power plants.

Paul,

Using nukes for just low grade steam would not be economic. Nuclear plants are expensive gadgets, even a small one. (The liscensing and operating costs are pretty much the same for a 100MW plant and a 1600MW plant.)

The beauty of this scheme is that the low grade steam is already there and of little value to the nuclear power plant. Using the steam for bioreactors, hot greenhouses or desalination is a good benefit.

Want to bet that the DOE authors have never been at a commercial nuke plant? While providing 150# steam is not a technical problem, who needs the hassle of a small income that creates more truck traffic and media attention when some solar panels provide a good photo op.

A better idea is a gasifier running on all the NRC paper generated.

I understand the attraction of better utilizing heat from sources that do not release CO2, but the whole idea of renewables is we can burn them without contributing to an increase in the CO2 because the replacement fuel will remove approximately the same amount of C02 during its growth cycle. Therefore we should be able to get the heat from the process from the process or something is rotten in Denmark.

See Headwaters and Great River Energy partnership story on this website. Looks like they already thought of this, only it is a coal plant.

"Green Car Congress...for sustainable mobility."

Presumably sustainable does not mean infinite. I would guess it means for a long time, because it is efficient and balanced.

There are those that would say that the supply of uranium will last a long time, but somehow I do not consider it "sustainable".

It is unlikely that we will run out of fissionable material before the sun stops working. Therefore, renewable energy is also not sustainable.

A more practical question, is it maintainable? Hydroelectric and geothermal are two examples of renewable energy energy that are worth maintaining. Same with nukes. So far, wind and solar have yet to prove that they can be maintained.

In five years we could have enough data on ethanol production, we can determine if ethanol plants could be built next to a new nuke.

The sun will last millions of years, I do not know of anyone saying that we have millions of years of uranium available.

I do not know of anyone saying that we have millions of years of uranium available.

Well, you do now.

Used in breeder reactors, we do have millions of years of uranium remaining, even at much higher rates of energy production. Breeders are so effective at fully using the energy in the element that essentially all the uranium in the Earth's crust could eventually be exploited (and also the thorium, which is several times as abundant).

The fission energy derivable (with breeding) from an average piece of crustal rock, per unit mass, has something like 20 times the combustion energy of the same mass of coal.

I wonder when can we not bother those countries that sell fuel, and just take care of ourselves in supplying our cars with whatever available uranium we could get. I have strong feeling that I will not regret to pay tax more in supporting the uranium research and production, rather then pay those countries for ever. It just like when I must pay credit card interest. After I paid them all, men, men, how good I feel, eventhough It took guts to pay them all. Ruth

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