Battlefield and other emergency medics are sometimes confronted with more casualties than they can treat. Survival of the greatest number is their goal. What they have learned to do is to divide their patients into three groups:
- Those who will live even without immediate treatment. These are watched but left for later or evacuated for treatment elsewhere.
- Those who cannot be saved. These are left untreated.
- Those who can be saved, but only with immediate treatment. Attention is focused on these patients.
The concept of triage is useful beyond the medical context; in particular, it can be usefully applied to government policy-making. Energy technologies can be divided into similar groups:
- Technologies which will succeed with little or no assistance. These are best left alone.
- Technologies which are either failures or cannot succeed without permanent subsidies. These should be dropped.
- Technologies which are
The former should receive research; incentives and subsidies can push the latter over the hump.
- long-term or speculative or
- ready for prime time but need to build manufacturing volume to get their costs down.
Examples of technologies in each of these categories:
- No assistance or mild regulatory relief: petroleum, coal, conventional natural gas, coal-bed methane, off-grid solar PV, nuclear.
- Will never work without subsidies: fuel ethanol from grain, biodiesel from virgin oils.
- Speculative or long-term: fusion, hydrogen, OTEC, central solar PV, solar chimneys.
- Almost ready for prime time, but can use a push: wind power, distributed peaking solar PV, plug-in hybrid vehicles.
The energy bill which just headed for the President's desk makes serious mistakes in all of the above categories. For instance:
- Conventional fossil fuel producers, already raking in profits, got big subsidies. This is a complete waste of money.
- Ethanol from corn, which some still claim is energy-negative and even whose advocates admit yields perhaps a quarter of its gross production as actual net energy profit, also kept huge subsidies and received mandates for increased use.
- Technologies such as plug-in hybrids, which have the potential to replace perhaps half of all motor-fuel consumption with electricity, were shoehorned into the bill at the last minute and got token support of a few tens of millions of dollars.
- Measures which would have pushed wind across the experience curve to make it cheaper than coal power (a "renewable portfolio standard") were defeated outright.
I have seen no reports on the amount of money for photovoltaic R&D, biological photosynthetic hydrogen, battery technology, zinc-air battery demonstration projects, artificial photosynthesis, or any of the other possibilities out there; I suspect that they have made no news because they are trivial or even zero. Some of these are almost ready for production, some demand research money because of their potential, all have attracted next to no attention. We're not going to feel the pain from these omissions for a while any more than CARB's refusal to pump GO-HEV's in 1990 was felt before the turn of the century, but feel it we will.
In medical terms, this energy bill throws expert trauma teams at patients in the best of health and cadavers already cold while patients with great prospects for recovery but also great need are left bleeding in the halls. It's especially ironic that the US Senate is currently headed by a surgeon.
All the attention in the nation appears to be on hydrogen as the ideal medium for energy in a renewable economy. It has a lot going for it, in particular the fact that it can be produced from nothing more than water and energy. But this comes at a high (and hidden) price, especially for production from renewable energy; it is far from obvious that the use of hydrogen is worth the additional costs. The consequence is that we should downgrade hydrogen research, and cease deployment efforts immediately.
Hydrogen is certainly a wonderful molecule. It's the lightest element and has a very high energy/mass ratio. It's also the foundation of many chemical synthesis processes, both artificial and natural; when plants make sugar, they begin by splitting a water molecule to make hydrogen. There are even some ways to persuade plants to yield hydrogen directly. And when hydrogen is required, nothing else will do. You need hydrogen to make ammonia (for nitrogen fertilizer) or synthesize hydrocarbons.
We can learn a lot from plants (biomimicry has yielded a lot of good concepts), but there are limits to how far this can go and still be useful. It's one thing to borrow inventions and techniques from nature when they are well-suited to the task at hand, and quite another thing to cut the engineering problem to fit the Procrustean bed of a biological prototype. I intend to show that the "hydrogen economy", and particularly the hydrogen fuel-cell car, is a poor way to accomplish this.
The efficiency of any system has to be considered in context. Grass is perhaps 1% efficient converting sunlight to biomass? That's bad, isn't it? Not compared to the efficiency of forests. I understand that an acre of woodlot captures energy at an average rate of something like 500 watts. By way of contrast, you can average 500 watts by taking the rather small fraction of a 1/5 acre lot covered by the roof of the house standing on it and covering it with PV.
Relative efficiency is important for many things: what's better at getting energy from where it is to where you want it to go. This is where hydrogen falls down. Worse, it hurts exactly where most people would expect that a "clean" energy source would do the best: carrying renewable energy from source to end use. Hydrogen is far more efficient (and thus cheaper) at carrying energy from fossil fuels than renewable sources like wind and solar.
When comparing different approaches, there's nothing like an example. Suppose that we've got two sources of energy, coal and wind. The goal is to power a car. We have two options for using coal: gasify and convert to hydrogen, or burn and generate electricity to charge batteries. We have similar options for wind: generate electricity and either electrolyze water to hydrogen or charge batteries.
The theoretical efficiency of proton-exchange membrane (PEM) electrolyzers is quite high, about 85%. Unfortunately this efficiency is only achieved at low power levels and PEM systems cost too much to use them to make trivial amounts of product. Quoted efficiencies for real systems are in the range of 65% to 75%. Let's use 75% for now.
Fuel cells are the essential part of the hydrogen economy. According to the Rocky Mountain Institute
, PEM fuel cells have efficiencies ranging from 35% to 60%. Let's use 60%.
Coal can be used to make either electricity or hydrogen; IGCC powerplants make large amounts of hydrogen as part of their syngas. The quoted efficiency of the gasifier at the Wabash River powerplant is 76%. The composition of the combustible (non-nitrogen, non-CO2) syngas is described as being 37% hydrogen, with most of the rest being carbon monoxide; unfortunately, I cannot unequivocally determine whether this is by volume (mol %) or by mass. The conversion of carbon monoxide to hydrogen via the water-gas shift loses energy, but without a clear distinction between the two cases it is impossible to calculate how much. If the product syngas is 37% hydrogen by mass, the losses in conversion to pure hydrogen will be relatively small; for the sake of argument, let us assume that they are zero. Let's also assume that the efficiency of electric generation from coal is 40%.
Last, let's assume that the efficiency of batteries is 90%.
There are four possible routes for energy depending on the source and the storage option:
coal -> electricity -> batteries -> motor
coal -> hydrogen -> fuel cell -> motor
wind -> electricity -> electrolyzer -> hydrogen -> fuel cell -> motor
wind -> electricity -> batteries -> motor
Each path has a different efficiency (ignoring losses in transmission, compression, etc):
| coal -> electricity -> batteries -> motor || 40%*90% = 36% |
| coal -> hydrogen -> fuel cell -> motor || 76%*60% = 45.6% |
| wind -> electricity -> electrolyzer -> hydrogen -> fuel cell -> motor || 75%*60% = 45% |
| wind -> electricity -> batteries -> motor || 90% |
Interesting things become apparent in this comparison:
- When hydrogen is used as the medium, coal and wind have roughly the same end-to-end efficiency.
- If electricity is used as the medium, coal loses about 20% compared to hydrogen.
- If electricity is used as the medium, wind GAINS 100% compared to hydrogen!
In short, hydrogen fuel for vehicles is moderately advantageous for fossil energy sources, but it applies a 50% penalty to renewable sources such as wind (also solar and hydro). This handicap is completely artificial, and comes on top of hydrogen's very poor storage density and high cost of hydrogen fuel cells.
There you have it: hydrogen isn't the way to a renewable future, it's just a boondoggle.
Labels: hydrogen, renewable energy
Note 15-October-2006: If you came here via a Google search for "ethanol lobby", you probably want to read this concise summary of the issue before digging through this post. You can always come back later.
This is annoying. I've got two posts being editted (one on hydrogen, one to continue the analysis of the possibilities of a zinc economy) and distractions keep getting in the way. Fortunately, I'm getting a post out of this one.
Recently, a mail from a very sincere but not terribly logical ethanol advocate was forwarded to me by James at Alternative Energy Blog
. I picked apart some of the questionable claims and did a short analysis which showed that bio-fuels cannot possibly replace petroleum (quoted directly from my mail, lightly reformatted for the web):
Yes, you can derive energy from waste. No, you cannot use this
to replace more than a small fraction of coal, oil and natural gas.
To the extent that the waste contains energy derived from fossil
fuels, the net benefit is even smaller.
[referencing Going negative] I was talking about biomass as a source of CARBON, with most of the energy coming via a more direct route (from sunlight). You could have proven this to yourself with a little arithmetic, which would have shown that 600 million tons of biomass per year is nowhere near enough to replace US use of petroleum.
Let's work it out just for show. Let's assume that all the biomass is carbohydrate, with a general formula of CH2O. If you converted the full 600 million tons to hydrocarbons by magical removal of the oxygen without adding more energy or losing any of the rest (impossible, but assume it for the sake of argument) this 600 million tons of biomass would make about 280 million tons/yr of syn-oil, or about 770 thousand tons per day. Figuring this as short tons and the density of the syn-oil at 0.8, that makes 873 thousand cubic meters of syn-oil per day or 5.5 million barrels. (Remember, this is with a process of impossible efficiency.)
US oil consumption is approximately 20 million barrels/day, and then there's natural gas and coal. Even if you could manage this feat of removing oxygen from biomass and converting the carbon and hydrogen to syn-oil without losing any of it, you'd only replace about 27% of US petroleum consumption. You wouldn't even cut imports in half, and you wouldn't displace anything else.
What you missed ... is that you can get a lot more out of the resource using a couple of levers to multiply the benefits from the inputs. In my blog example, the two levers are:
- Ethanol as currently made (from corn) is a loser.
- Biomass sources are insufficient to replace petroleum directly.
- Waste biomass can be a useful source of supplemental fuel and other chemicals, but most energy has to come from something else.
- The biggest advantages come from leveraging new energy sources and boosting efficiency, which can be done in very un-obvious ways.
Combine those two multipliers, and you go from a replacement for 27% of US crude use to replacing ALL motor fuel (roughly equal to US oil imports) and something like half of the coal-fired electricity too.
[correspondent notes that THERE's a surprise is very down on ethanol and asks if I was being sarcastic in one piece or the other]
I was being completely serious both times. The devil really and truly is in the details, and you've got to know your chemistry and physics to avoid getting completely lost. The laws of physics and thermodynamics are uncompromising and will break any attack you can throw at them without yielding, but you can sometimes find paths of lesser resistance which go around them like jiu-jitsu. "Nature, to be commanded, must be obeyed."
The problem with current corn-growser subsidy programs, excuse me, alcohol fuel programs, is that they attack Nature head-on. This is why they need something like 3 BTU of fossil fuel inputs to get 4 BTU of alcohol out. Don't you agree that such wastefulness really is worthless?
- Using carbon from biomass to make a *solar* process much more efficient. Much of the new energy comes from the sunlight, not the carbon feed. (At least, that's what the Swiss are claiming they've done.)
- Getting the energy *out* in the form of metallic zinc, which can be used in a zinc-air battery instead of a combustion engine. The Zn-air battery is far more efficient than an engine and yields much more useful energy out per unit of input. It's like getting a new type of car engine that's 80% efficient instead of 20%.
Apparently not. The response was a list of enterprises making fuel ethanol, and their annual production. I replied that they were probably in it for the subsidy money. This attracted a fairly long and marginally literate screed, from which I shall paraphrase the author's remarks to avoid quoting without permission.
[subsidies are not to get people to make alcohol]
They aren't? There's a 52 cent/gallon federal subsidy for ethanol used in gasohol (5.2 cents/gallon tax charged to 100% gasoline but not 90% gasoline/10% ethanol). Subsidies to the growers are in addition to subsidies for the fuel blenders.
[correspondent knows because correspondent is a farmer]
I was going to go into your reply to my analysis and ask you why you had no rebuttal to the facts I cited - facts which prove that what you desire is IMPOSSIBLE - but you just explained everything in 4 words:
"I am a farmer"
That shows where your interests are. It is actually BETTER FOR YOU if ethanol cannot fully satisfy demand, because this means that you can never wind up with the oversupply problem that exists now.
Here, I'll prove it. Look at the 2004 USDA harvest figures for corn:
I summed up the state by state figures and came up with 11.8 billion bushels total harvest. At a conversion rate of 2.66 gallons per bushel (per http://www.ethanol-gec.org/corn_eth.htm), you would only get 31.4 billion gallons if *all* of it was converted to ethanol.
Total US motor gasoline consumption in 2003 was 134 billion gallons. (http://www.eia.doe.gov/emeu/aer/txt/ptb0513c.html). And given that each gallon of ethanol requires roughly 3/4 of a gallon-equivalent of fossil fuel (including about about 0.44 gallon-equivalent of natural gas, according to http://www.cvec.com/general_manager.htm), the net gain is perhaps 8 billion gallons-worth. That's a lousy 6%.
In short: farmers will NEVER solve this problem, because it is PHYSICALLY IMPOSSIBLE. Worse, farmers DO NOT WANT THE PROBLEM SOLVED because if supply catches up with demand they wind up with the same unprofitable crop prices they have now.
Conclusion: FARMERS BENEFIT FROM PUSHING A "SOLUTION" THAT CANNOT WORK.
[correspondent know what farmers are and are not getting paid for]
I know what fixes your personal problem as a farmer. I know that this will never fix the problems faced by the nation as a whole.
[correspondent includes article titled "Claims that Ethanol has a Negative Energy Balance are Outrageous"]
So what? Even if ethanol from corn required NO fuel for planting, tillage
and harvest, NO fertilizer and NO distilling, it would STILL never come
close to replacing petroleum. And you want it that way.
That's it, folks. The ethanol lobby is as foul a pile of money-grubbing liars as has ever graced Tammany Hall or the the oil-for-palaces office at the UN. They are not even trying to solve America's energy problems, they are trying to make certain that the problem is never solved so that they can benefit from a demand that their scheme can never sate. You can confront them with facts, and they will ignore them and continue to push programs which benefit only themselves with the lie that this is good for the nation.
These people disgust me.
THERE's a surprise
Labels: ethanol, ethanol lobby
Blogger has a new trick.
The old tricks were annoying enough:
- Not allowing more than trivial HTML in blog responses (the least they could do is come up to the bar set by Slashdot, with lists and such).
- The posting Preview doesn't work according to your Blogger posting settings, only the defaults.
- Allowing blog owners to try to force comments into popup windows. (Why not give readers the option of how they want to see comments? Say, with a configuration cookie?)
- The "clear=both" HTML crud they shove into every post, which pushes post text below the sidebar in my template.
- Having no useful responses to bug reports about any of the above.
Now they've got a new one that just appeared today. I tried to log in today to enter a new post, and I was told that my browser was rejecting cookies.
I'd had a browser crash the previous day, and wondered if it had left some setting in a funky state. Nope, all cookies from Blogger were being accepted. Problem with previous cookies in an inconsistent state? I deleted them all and still could not log in.
Why? It worked perfectly well before. Was it too hard to just leave it alone? Blogger, what kind of thoughtlessless lets you trade your coding convenience off against my data security?
I expect I'll never get an answer to that.
UPDATE 19-Aug-2005: Here's a good time to say DAMN BLOGGER. I tried to post a new entry, and it claimed "Blog not found". Then it got worse: the "back" button returned to a BLANK entry, and the recover feature DID NOT WORK! It returned only a partial post, which took half an hour to reconstruct. (Talk about gross incompetence; you can go back in comment entry without losing anything, but not post entry! This is the last time I compose in their text window.)
If this doesn't stop post haste, The Ergosphere is gonna be outta here.
Question for the readers: Would the usefulness of The Ergosphere be improved if I added Technorati tags to posts?
Interesting things have been happening over the last few years. While the petroleum-dependent world chugs along doing business as usual despite the market for crude, the alternatives come quietly down in price and up in practicality. Once the price curves cross, the situation is unstable; petroleum would still hold dominance due to the installed base, but this position would be vulnerable as users who convert lower the barriers for the rest. As I commented on another blog:
Zinc fuel cells are already being tested in city buses; if many cities adopt them, they would function as nuclei from which a "zinc economy" could spread organically. I haven't tried to crunch numbers on the details, but I suspect that farm equipment might be able to use zinc-air FC's also; any farmer who has energy from wind or the like could regenerate his own zinc and cut petroleum out of the budget. That would turn farms into nuclei too.
Or, as seems more likely, a transport authority or a few farms or other enterprises in an area might spin off such work into a separate service business. Metropolitan Metal Fuel would start out servicing just the city buses under contract, but might find it attractive to add fleets of delivery trucks and even private vehicles. Once you have Jake's Truck & Auto Service and Zinc out among the cornfields, it seems likely that Jake would welcome transient business.
An economic environment poised for a cost-driven technological shift is not unlike a super-cooled liquid. The colder it gets (the greater the economic advantage from changing over), the more likely it is that a crystal will form (some users will jump). The new crystal has surfaces which allow more liquid to freeze on them (users nearby can take advantage of the investments made for the previous users). As the crystal grows (more users switch), the surface area available for new freezing increases (more users find their barriers to switching are lowered).
This is a model with a recipe for action. If you are a researcher at an agricultural college, see if you can't get a grant to test zinc fuel cells as power for farm equipment. If you have a municipal transit service which operates buses, try to get Electric Fuel
to run a test there. When the results are finally ready for prime time, buy them.
Each step forward lowers the resistance for the next step. If you want the phase of the energy economy to change, do what you can to super-cool it.
Related posts: Zinc: Miracle metal?
I don't run Windows at home. My work is done exclusively in Linux. Normally I savor the freedom from BSOD's and malware, and I accept the need to kill and restart Mozilla every couple of days when its memory leaks cause it to thrash and die. Such problems are small and easily worked around. But I've come across something which is an airtight roadblock in the way of what I need to do.
I've been working on a document with a number of images in it, which are coming from a CD-R. A couple of the images are oriented at right angles to the way they need to be displayed. No problem, right? Just fire up the Gimp and go to town. Version 1.2.3 is right here; should take about ten minutes, right?
That was several days ago, and I'm still stuck.
First, let me mention that the authors of the Gimp seem to like to insert half of obvious operation sets and leave out the other half. There is a "flip" to swap an image left to right, but no top-bottom flip. This is a strange omission. I had to invert an image which was upside down, and I had to dig for quite some time before I found a tool which would let me manipulate the vertical dimension as well as the horizontal. That was wasted time.
Second, the authors seem to have no talent for nomenclature. The rotation tool isn't called "rotate", it's hidden in something called "transform" beneath "transform tools". Once you find this tool, it allows you to specify a rotation angle; you can watch a grid representing the image rotate on the screen as you move the slider. It took some digging and trial-and-error to find it, but find it I did. Okay, that's what I need.
Only it isn't. The operation does not rotate the entire image; it rotates a part which fits within the shape of the original image boundary, which is not rotated! If the image is not square and the rotation is not 180 degrees, the parts which no longer fit the old boundary are chopped off.
I thought that maybe, just maybe, making my image square would let me rotate it 90 degrees without losing anything. I dug a bit more and found a canvas-size control. Unfortunately, expanding the canvas does not help. First, the Gimp won't allow me to take my rectangular canvas and make it square; for reasons unknown to me it insists on growing both margins when I've specified only one. (Why? That's completely illogical, and there is not a hint of explanation.) Second, rotating within the larger canvas produces the same uncommanded and undesired cropping of the image. There's a perfectly good cropping tool. I figured it out in about 10 seconds. I will get the image cropped exactly how I want it when the time comes. Why do these authors make me go through hell to find a way to not
crop something when I don't
And whose idea was it to not make a tool go away
when the user clicks the "close" button on its pop-up? Once you have that rotation tool up, you have to find a creative and very un-intuitive way to get rid of it again without using it. Didn't anyone test this?
The help is useless. Nobody ever thought to describe the theory behind these operations so that a user would have some clue as to where to look for the tools to accomplish a particular end. The entire manual is devoid of insights of this kind.
So here I am, several days of delay and frustration later, no closer to getting one simple but essential transformation done to this image than I was when I started. The value of my lost time is rapidly approaching the cost of Windows and Office. And open-source advocates wonder why people still buy Microsoft? Look no further.
Postscript: Okay, the way you do it is to not
change the canvas size, but to stretch the display window with the mouse and then select the transform tool. For some reason it displays a different dialogue with fixed rotation angles and without the sliders - a dialogue that I cannot find again. I found this completely by accident; the help was as utterly useless in this as in everything else thus far.
Second postscript: Whatever I did to find that fortuitous useful menu, I cannot find it again. I am back to "only-rotates-with-the-unwanted-cropping" mode.
Third postscript: Okay, I think I have it. The window has to be smaller
than the displayed image; only then will the Gimp allow one to do the obvious and desired thing.
Fourth postscript: It is not trivial to get the desired menu to come up. The Gimp can apparently get stuck in a state where only the rotation-tool-that-crops-without-asking is accessible; I was very lucky to find the right tool at all, and I can't get to it now. Even closing and restarting the program doesn't fix the problem, because state information seems to be saved between runs (bad news when the state is broken).
Fifth postscript: The correct state is extremely difficult to recover. Even removing the .gimp-1.2 directory and re-installing does not allow the correct menu to come up.
It is wrong
to hide simple, obvious, essential operations behind what amounts to magical incantations. It was weird, undocumented, counterintuitive state-dependent crap like this which turned me off so thoroughly to Microsoft stuff. The last thing I need is the same grief under Linux.
It takes hard work to obfuscate things this well, work that could have added something useful. The authors of the Gimp ought to be ashamed of themselves for releasing this. Are there any folks with UI design expertise out there? If these problems haven't been corrected yet, this project is ripe for a fork.
One concept near and dear to environmentalists is restoration. Seeding of native species and regular burning is re-establishing the tallgrass prairies, rendered nearly extinct by the plow; Lake Erie provides excellent fishing; wolves once again roam Yellowstone. Restoration does not just relate to nature; it also extends to human activities. Organic farming in particular is intended to be a restorative, adding humus to depleted soils and re-establishing biological cycles broken by agrichemicals.
Restoration has been applied to many things, but so far there has been one major (and global) exception: the atmosphere. Not that air hasn't been the subject of cleanup and protection efforts; far from it. The first controlled pollutants included sulfur, oxides of nitrogen, carbon monoxide, non-methane hydrocarbons and mercury. The Montreal Protocol added ozone-depleting chemicals to this list, limiting the production and controlling the handling of halocarbons. The Kyoto Protocol in turn attempted to regulate greenhouse gases, though its lack of comprehensive coverage and assent make it unlikely to succeed.
Human activities and the atmosphere
The various efforts and treaties aimed at the air have thus far limited their goals to stopping undesirable emissions. None have yet been aimed at restoration, removing unnatural and unwanted constitutents from the air to return it to its historical state. The rather obvious question is, why not? One reason is that it's a mighty big job. The atmosphere weighs roughly a ton per square foot of Earth's surface, about 5.3*1015
tons total; changing the composition by one part per million (by mass) means fiddling with 5.3 billion tons of material. However you cut it, that's not something you do for a weekend project.
On the other hand, it is something we do whether we want to or not. This is an intractable problem at the moment because the energy systems which run industrial civilization are built around the removal of carbonaceous fuels from the earth, burning them, and exhausting the combustion products to the atmosphere. It's going to be difficult to change this, save for a minority of current technologies; the expense of capturing carbon from them (save for a few processes like IGCC fuel-gas scrubbers) will be large, and will have no other payoffs.
What could we do?
Anyone who's been reading this blog for very long knows I like to do what if's. Since I'd hate to disappoint anyone on that account... what if our major energy systems either did not use carbon at all, or were easily and cheaply set up to be carbon negative
? That would certainly be a huge accomplishment; it would represent a capability for tuning the CO2
content of the atmosphere to our specifications.
It also appears to be possible. The thermochemical zinc process
, which converts carbon and zinc oxide to carbon monoxide and metal, is so far as I know unique in that it accepts biomass as a carbon source and releases it without any contamination from e.g. nitrogen. This pure carbon monoxide can be burned in a gas turbine, but it could also be used to run a solid-oxide fuel cell
and kept nitrogen-free. The product stream of pure carbon dioxide would be disposal-ready.
In principle, almost anything could be used as a carbon source; given the heats of reaction of zinc vs. other things, it appears best that this material be free of oxygen. Carbon char from anaerobic pyrolysis of biomass or MSW would probably do. This would not retain all the carbon of the input material, but the pyrolytic gas could be used as fuel along with the off-gas from zinc reduction. For the sake of carbon sequestration, the exact route of the carbon through the process is irrelevant so long as it is captured.
High-temperature processes favor simpler molecular products. If the biomass is considered to be carbohydrate with a general formula of (CH2
, the possible decompositions into simple molecules would include these:
O + Δ --> C + H2
O + Δ --> CO + H2
O + Δ --> CH4
For this purpose, the reaction conditions would be adjusted to yield as much carbon char as possible. It may also be possible to use methane and heavier hydrocarbons as carbon sources; they would react to CO and H2 in the reduction step. Water in any form is undesirable. The need to purify and dry the off-gas may make it too expensive to use as a reducing agent, in which case only the char would be used in that role.
Both the pyrolysis off-gas and the zinc-reduction off-gas have considerable energy content. After scrubbing, all the gas might be suitable for SOFC fuel. The efficiency of conversion of the gas to electricity could reach 60%, or perhaps 70% if a steam-turbine bottoming cycle can be used.
The hypothetical solar-zinc plant in "miracle metal"
consumed 308 tons of carbon per day; if supplied as carbohydrate, this would be 770 dry tons of biomass. Configured as an all-electric plant and ignoring the efficiency gains from fuel cells, its output would be 3570 MWh/day or 149 MW average, yielding a biomass feed rate of 5.18 tons/day/MW.
Possible sources of biomass include corn stover, wheat and rice straw, waste wood and the organic fraction of MSW
. While it's easy to get figures for per-acre yields of grain, the production of byproduct materials is not so widely published. Biomass crops are another matter. Switchgrass has been studied as a crop for both livestock fodder and energy production, with published yields ranging from 7 to 14.7 dry tons/acre/year.
Assuming 10 tons/acre/year as a reasonable value and 30 million acres planted to switchgrass, the total annual yield would be 300 million dry tons/year (of which 120 million tons would be carbon). If crop byproducts yielded a similar amount of stalks, cobs and straw, the total annual yield would be 600 million dry tons biomass (240 million tons carbon). At a biomass consumption rate of 5.18 tons/day/MW for the solar-zinc plants, this would supply the carbon demand for 317 gigawatts of power production and sequester 0.24 billion tons of carbon (0.88 billion tons CO2
) per year. Total US power consumption averages about 440 GW, so this system could satisfy about 72% of current US electric demand. (That figure surprised me - it's pretty much the total electric demand supplied by fossil fuels.) If used to supply energy for vehicles it could satisfy about 1.8 times the US's current demand of roughly 180 GW, rendering the entire US road transportation system carbon-negative and allowing plenty of room for expansion.
If this system was used to replace all combustion-supplied electricity and all other energy consumption went carbon-neutral, US use alone could reduce atmospheric CO2
concentrations by about 0.16 ppm/year by mass (about 0.11 ppm by volume). If we assume the entire world uses the same system and world electric consumption is 4 times US consumption, the impact becomes 0.64 ppm/year (0.44 ppmv). Increasing world electric production from thermochemical zinc plants also increases the potential atmospheric CO2
reductions. Use of metallic zinc as vehicle fuel would increase the rate of CO2
reduction if it was recycled via the thermochemical pathway with sequestration, and would be carbon-neutral if it was reduced electrolytically using energy from solar, wind or nuclear.
Thermochemical reduction of zinc oxide to metal using biomass as the carbon source captures atmospheric carbon and can convert it to a stream ready for permanent disposal. Possible biomass sources include biomass crops, byproducts from food crops, forestry waste and post-consumer waste materials. At a biomass consumption rate of 600 million dry tons per year, the system would supply roughly 317 gigawatts. This would supply 72% of US electric needs or 1.8 times US transportation energy needs, while sequestering 880 million tons of carbon dioxide every year. World-wide use of biomass-fed thermochemical zinc systems could reduce atmospheric concentrations of carbon dioxide by about 0.44 parts per million (by volume) per year; acting alone, such systems could restore the global atmospheric CO2
concentration to its pre-industrial level in about 225 years. Expansion of thermochemical zinc systems and their biomass feeds to allow increased electric production would hasten this process. Both the effluent CO2
stream and the stored CO2
could be returned to the atmosphere at any time should that be desirable. This spells the end of air pollution and human control of global warming.
Restore the atmosphere? Engineer the climate? If we want to, we can
Related items: Zinc: Miracle metal?
Researchers (including neither of the usual suspects, Pimentel and Patzek) have concluded that fuel ethanol is not worth the impacts of producing more of it, in either the United States or Brazil (!). Article: Physorg
They produce an estimate of the energy payback from ethanol in the USA in the expected range: about a 10% gain over the inputs. This isn't anything like the return required to be worthwhile.
If we are really, really
lucky, sanity just might prevail in the House-Senate conference committee handling the energy bill, and they'll get rid of all the ethanol subsidies and mandates. And maybe monkeys will fly out of my butt.
Labels: ethanol, ethanol mirage