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A lot of these recent biofuels companies are looking at gasification now(cracking at ~+1000 degrees F).
But how can gasification be more energy efficient than simple distillation(at ~212 degrees F)?
OTH, you can make pretty much whatever you want and it would be relatively carbon neutral and would not use up (as much ) fossil fuel as gasoline. So it's certainly not a terrible idea.
The problem for plain ol' distillation is the enzymes are still to expensive (and fossil fuels still too cheap).
What cellulosic ethanol needs is cheaper enzymes and molecular sieves to separate water from alcohol or cars that can run with more water mixed in the alcohol than IC engines can(ethanol fuel cells).
As I understand things, an internal combustion engine with an Otto cycle can run on 180 proof ethanol. That's 90% ethanol, 10% water. The reason that pure ethanol is needed to make E10 or E85 is that the water in low purity ethanol prevents mixing of the gasoline with the ethanol. There are problems with E85 when water absorbed from the air causes the ethanol to separate from the E85 mix and drop to the bottom of the tank. This might not be a big problem once the fuel is put into a car, but makes shipping and storing the mixture rather difficult and pure ethanol can not be shipped thru a pipeline.
The reason the 15% gasoline is needed in the E85 mixture is to be able to start the engine, especially when doing so under cold conditions. Another solution to this part of the problem would be to use two tanks, one for gasoline and the other for low purity ethanol. Start the engine on gasoline and run that way until warm, then switch to the ethanol tank. With today's computer controlled injection systems and oxygen sensor feedback, this approach should be relatively simple to accomplish. On shutdown, the engine could switch back to gasoline for a brief period to clear the ethanol from the injectors. With cars set to run this way, many small time producers could use local resources to produce low grade 180 to 190 proof fuel ethanol, using heat from local sources, such as wood or solar energy. Of course, the big time oil companies would not like this prospect one bit, as they could not control the marketing and distribution of the ethanol.
E. Swanson
Black_Dog -
Your idea of having a duel fuel system has some precedent with an interesting bit of trivia.
During the 1910s and 1920s mechanical tractors were just starting to make major inroads into US farming practice. At that time, in rural areas kerosene was quite readily available and reasonably inexpensive. Gasoline, however, was not so easy to get and was much more expensive, so some of the early tractors ran a crude Otto cycle engine on kerosene.
But the kerosene first had to be vaporized, and this was accomplished by means of a heat exchanger in contact with the exhaust manifold. These tractors had a single fuel tank separated into two compartments by an internal partition. One side held kerosene and the other gasoline. You started the engine on gasoline and ran it on gasoline until it warmed up and then turned a valve to switch it over to kerosene.
These kerosene-fueled tractors made a distinctive popping sound, and so the farmers nicknamed the early John Deere tractor "Johnny Popper."
I think PHEV cars are the best because you have two fuel options. I think we'll be finding out that having diverse sources of power are a good thing.
The problem with this "solution" (other than the fact that a lot of ethanol is burned) is that it doesn't take advantage of the octane boosting power of ethanol very well. If you're going to keep wet ethanol in a separate tank why not just inject it when you need the octane--according to this:
http://www.autobloggreen.com/2006/10/25/mit-researchers-developing-an-on...
Only about 5% ethanol is required, overall, which, IMO, is the limit we should impose on ourselves in this ridiculous "food-to-fuel" frenzy we are embarking upon. Driving up food costs for those least able to afford it to satisfy and SUV's does strike me as immoral. Feed a Hummer--starve 10 children to death.
But, I digress--a similar trick was used in aircraft during WWII using (smaller amounts of ) pure water when extra power/range was need. (Lugging the engine, gave you the extra range, but also needed a fuel mixture with high anti-knock characteristics).
The popping sound that's heard when kerosene is fed into a gasoline engine is knock or ping--very detrimental to an engine. (next post)
Thanks for the link, HvyOilGuy, but you missed the point entirely. Were running out of oil, remember?
The proposed use of a separate fuel tank was to enable the use of "wet" ethanol during most of the operation of the engine. The octane boost for gasoline, which one would expect from E10, was not the reason. I was suggesting another approach to that presently being used, that is, a mixture of 85% ethanol with 15% gasoline, called E85.
As for water injection, I am well aware of its use as an octane booster and there have been various systems marketed which provide this for cars. The newer ones appear to be quite sophisticated. I bought one years ago, thinking to try it on a high compression (13:1) engine project I built back in the 1980's. The injector system is still sitting in the box in my attic. If I ever get around to fixing my Ford SHO's blown head gasket, I may install the device to the engine, since the Yamaha engine in the SHO was designed for high octane fuel, even though it will run on regular. The knock sensor probably cuts the spark advance to allow operation.
As I recall from my college IC engines course, the use of water injection on WW II aircraft piston engines was intended to allow higher supercharge boost, which gave higher effective compression ratios, thus more power and better efficiency.
E. Swanson
Actually, it's you who is missing the point, IMO. We shouldn't be trying to replace fuels we are consuming that are now (or soon will be) in decline on a Btu per Btu basis, especially with ethanol for which the external costs outweigh the benefits, which seem to accrue to the few. We need to move on to a new transportation paradigm that relies less and less on the private automobile.
That being said, if the "blending value" of ethanol to boost compression ratio and efficiency for the entire fuel system, is sufficienly high, it would justify the production of a certain amount to attain this benefit. I think the article states that it does, but only up to about 5% of the total.
When ethanol is used in excess of this amount, it no longer yields the benefit that the first incremet did--it basically behaves as E85 does now--which hasn't been received all that favorably by the motoring public.
Once you reach the point where more ethanol doesn't provide any special boost, you have reached the practical limit, IMO.
I apologize that the link I gave wasn't particularly informative, since part of the system also involves the use of a supercharger, in addition to the ethanol injection. Maybe this one is a little better, but still just a "news" story.
www.technologyreview.com/Energy/18304/
The other day, Robert brought up another point - oxidizers simply aren't needed on all cars built for the US market after 1994, which adjust their combustion mixture automatically if they encounter different combustability rather than needing it normalized to certain proportions. Ethanol was a great replacement for other environmentally unsound oxidizers, but it's largely an anachronism in 2008.
edit: Remind me to click the links before responding.
Looks interesting. I'd seen it before, but never quite distinguished the technology from others. It looks like it heavily overlaps with hybrid technology, though. Nice for cheapish sportscars and motorcycles for a higher power:weight ratio than hybrids, but electric start:stop driving, wheelhub motor 4WD, and plug-in ability are more attractive in mainstream vehicles IMO.
Sounds similar to the diesel / veggie oil duality. You can run a diesel engine on No. 1 etrodiesel (-40C), No. 2 petrodiesel(-10C), biodiesel(-10 to 10C), or veggie oil(20C to 45C) equally well, but the fuel all gels below a certain temperature(given) and clogs the fuel line. You need to heat it until the fuel temperature is above its cloud point, so everything remains fully dissolved & viscous. So people use No. 1 petrodiesel to start the engine (and use the coolant system to heat the tank), and then switch over. Analogous systems exist for extreme cold weather and fuel additive tanks.
When you distill fermented ethanol out of water, you have to heat the entire mass of water (say 10 times the mass of the water) up to close to the boiling point, plus put the ethanol-water mixture (azeotrope) through a phase change. When you pyrolyze biomass, you're just heating the dried biomass directly - no water to heat, and no phase change to go through.
Bingo. I started to write exactly the same thing until I scanned down and saw your answer.
But how much biomass(wood=6000 BTU per pound) do you need to make a
a pound of ethanol?
For distillation you have to put the 10% ethanol/water azeotrope thru the phase change with a heat of vaporization of about 11000 BTUs per pound of ethanol (~1000 BTU/10%).
A biomass gasifier(75% efficient?), typically produces
a 500 BTU per cubic foot synthesis gas. To make a pound of methanol would take 34 SCF of synthesis gas based on coal gasification(biomass would be worse). So 500 x 34/.75 divide by 6000 would mean that 3.78 pounds of wood make 1 pound of methanol which has 2/3 the heating value of a pound of ethanol. So 5.6 pounds of wood(3.78/.66), 33600 BTUs would make 1 pound of ethanol.
By gasification you get about 54 gallons of ethanol per ton of biomass. By distillation of corn ethanol you get about 150 gallons a ton.
If distillation makes me boil a lot of water, gasification makes you burn/gasify a lot of wood.
Not the same thing. Roughly half of the gasified biomass becomes fuel [1], while the energy used in distillation doesn't add to the caloric value of the product.
[1] At 17.4 GJ/dry ton of biomass and perhaps 78000 BTU/gallon of ethanol, Syntec's figure of 105 gallons/ton is equivalent to ~50% efficiency. This does not include any useful energy yield from the high-temperature gases of the gasifier. It's possible to do far better than the end-to-end efficiency of Syntec ethanol to combustion engine, but Syntec is far better than biological processes which require distillation of relatively weak ethanol solutions.
If I use Syntec and your number above I get an energy loss of 78000 BTU per gallon; 17.4GJ/ton=16.5MMBTU/ton x 50%/105 gal=78,000 BTU per gal.
Shapouri(1995) gives 37000 BTU per gal of thermal input to dry mill distillery plus we also get 18 pounds of DDGS( animal feed) per bushel ( so corn ethanol does make some food!).
http://www.ethanol-gec.org/corn_eth.htm
I made a math mistake 2000 x 2.8/56=100 gallons per ton, not 150.
But Broin has increased the productivity to 3 gpt.
http://tiny.cc/ot7mN
I'm happy that Syntec is getting close to corn ethanol, but just as some think the carbohydrate path to ethanol is limited, I think the thermochemical approach is inherently limited as well. But good luck to Syntec, I'd love to see 113 gpt cellulosic ethanol.
Shapouri(1995) gives 37000 BTU per gal of thermal input to dry mill distillery
That's just for the distillation step. Total energy inputs are almost twice that. They do calculate a BTU credit back for DDGS, but even after that the energy inputs into corn ethanol come out to be around 60,000 BTUs. Not counting DDGS, the energy inputs are actually around 70,000 BTUs.
Let's go back to basics:
To make ethanol, you have to ferment simple carbohydrates - dissolve them in water and let microbes go at them. Some of the energy will be used by the microbes producing heat and other products, but some will end up in ethanol.
Then, you're left with a 10% ethanol, 85% water, 5% other stuff (the "other stuff" scales up the dirtier you make the carbohydrates).
Ethanol really likes water. It really doesn't like to be separated from water - above a certain point(191 proof), it's even impossible to separate it from water via evaporation (it forms something called an azeotrope). Distillation works on the principle that the ethanol has a slightly lower boiling point than the water, and so the ethanol evaporates first (though of course, this is mixed with steam from the just-below-boiling water), and then is condensed. Usually, you have to repeat this several times to get high-purity ethanol. Everyday water is one of the best coolants around, because the hydrogen bonds involved have such a fantastically high specific heat capacity - it takes a lot of energy to boil water. It is this process that is so energy intensive. Keeping things at the required only 80 degrees celsius or so makes secondary energy recovery difficult (and any attempts at that slow down the distillation process, which relies on cold copper to condensate the ethanol out).
Gasification is an entirely different process based on pyrolysis, which is done entirely chemically - it doesn't rely on living things, just hydrocarbon inputs.
Gasification is very Deep Alchemy, but it doesn't require that you separate the result from 10 cubic meters of water (repeated three or four times to achieve high purity, so let's say 40 cubic meters of water) for every cubic meter of fuel you produce. For comparison, a high-level gigawatt nuclear reactor with a once-through fuel cycle (which are currently being blamed by Georgians for the amount of water being taken out of Lake Lanier) only evaporates about a cubic meter of water per second.
Now, most of that energy isn't wasted absolutely (or the ROI would be close to zero rather than close to 1), but every conversion involves losses, and keeping part of the container at 80C while having part of the container cooled takes a lot of energy.