Producing biofuels from a fast-growing grass delivers vast savings of carbon dioxide emissions compared with petrol, a large-scale study has suggested. US researchers also found that switchgrass-derived ethanol produced 540% more energy than was required to manufacture the fuel.
One acre (0.4 hectares) of the grassland could, on average, deliver 320 barrels of bioethanol, they added.
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It should be pointed out that this ethanol process doesn't just depend on one source for raw material.
This cellulose method can use any plant material, not just switchgrass.
Corn and wheat can be redirected back to food production where it belongs; but the corn stalks and wheat straw can be used for ethanol.
Wood chips and saw dust is another source. The list goes on...
I don't know how the BBC arrived at a figure of 320 barrels per acre for the yield of ethanol from switch grass.
Using the numbers provided in the PNAS paper I get a yield of approximately 6 barrels per acre (3000 litres per hectare is quoted in the paper).
The paper can be found at:
http://www.pnas.org/cgi/content/abstract/0704767105v1
(download the abstract then click on "Full Text (PDF)"
There has been much hype, both in the US and in Canada, regarding the production of ethanol using ligno-cellulose substrates. However, in my opinion, the technology is still unproven and the economics seems to be way too high, suggesting vast subsidies.
There are two main technological differences in producing ethanol from starch and lingo-cellulose. Starch from grains is readily hydrolysed using enzymes or mild acid. The amount of pre-treatment required is minor (short term heating).
However, with ligno-cellulose, there has to be an energy intensive step to separate the lignin from the cellulose. This is exactly the process used in preparing wood pulp for paper making. It requires a combination of mechanical, chemical and thermal processes. It is very expensive. Secondly, the hydrolysis step has not been fully optimized. There are essentially two methods, enzymatic and mild acid. The Canadian approach has always been the use of enzymes and Iogen (based in Ottawa) has spent literally tens of millions of dollars (probably close to 100 now) trying to improve the economics of enzymatic treatment. Others are investigating the use of acid, in fact, most of the plants at the planning stages elsewhere in the world plan to use acid. Conditions have to be carefully controlled to minimize production of non-fermentable sugars and compounds that could be toxic to the yeast.
Why do I say that the pre-treatment is expensive? Well the process is very similar to manufacture of wood pulp. The price of pulp varies quite considerably but ranges between $500 and $1000. At $500 per ton pulp mills close down and at $1000 they make a profit.
Will manufacture of “pulp” from switchgrass or wood to use as a substrate for ethanol production be any cheaper? I doubt it since we are probably talking similar scale of plants. Even at $500 per ton of “pulp” that works out to about $1500 per ton of ethanol for substrate costs (assuming 1 ton of “pulp” will give you about 0.33 tons of ethanol). This works out to a raw material cost of $1.20 per litre. Add in all the other costs (including some return to the farmer) and you have very expensive ethanol.
I think that it would be much better to burn the switch grass or other lingo-cellulose material and produce electricity. Unfortunately, governments have a “liquid fuels” plan but not a “total energy” plan.
Ian Forrester
The Ottawa company that you mention is the one that went to Bali with the official delegation.
More generally, it would be nice if we could get people thinking about a "total energy plan," as you put it. No single solution is going to solve every aspect of this crisis, and this is a perfect example.
Fern Mackenzie
1) Electrifying everything we can is good.
2) Burning biomass with carbon sequestration is good, since it actually draws down CO2. Without sequestration, I'd guess wind and solar are better.
3) But, with Peak Oil here (or soon), as conventional oil gets really expensive, [and we know what happens if we go all-out on oil sands, shale oil, and coal-to-liquid], it's not obvious to me that we can electrify everything, even in the food chain alone. Yes, we can have:
- small/medium electric tractors
- more electrified train lines
- small/medium electric trucks
But one really has to study transport networks and population distributions in North America to see that a lot of food necessarily travels a ways (I'm ignoring the silly things that go on, those will disappear.) Half of the USA's fruit and veggies is grown here in California, and I guarantee that we don't eat it all.
4) Anyway, there seems to me to be an irreducible kernel of transport fuel that needs to be grown. [I don't know how much]. It's certainly the end of current air travel otherwise, but shipping is problematical as well, and like it or not, N. America uses a lot of trucks.
I've yet to see plausible proposals for electrifying big tractors, combines, Class 8 trucks, etc... and even hybrids don't help some of them much. Most car use can be done with electric or hybrid, but cars have different usage patterns than cargo-carrying trucks.
Maybe we get to hydrogen, but I'd guess that needs a lot of excess electricity, and some other breakthroughs.
Can anyone point to a good study that addresses these issues?
I think that Ian's point is that electrifying as much as possible - both from using fuels (like switchgrass) to produce electricity rather than biofuels, and electrifying functions as much as possible (e.g. PHEV's) instead of today's gas/electric hybrids - is the way to go.
I am not sure the EROEI's for, say, switchgrass to electricity vs. switchgrass to liquid fuel, but I would suspect that the payback is favourable.
You are quite correct that oil is uniquely valuable as a transport fuel. I think you are also "with Hansen" in accepting that we are likely going to burn up all the oil and the challenge is stopping us from burning all the coal. So I think that one of the cornerstones of this is trying to use alternatives as much as possible to generate electricity and to convert functions to electricity as much as possible, so that we can reserve conventional oil for "higher order" applications like large tranport vehicles, etc., petrochemicals, etc.
Any of the major "liquid" initiatives - ethanol, coal-to-liquids, oil sands, etc. - typically come with lousy EROEI's and a host of other net relative emission problems...
John, way back when the first fuel crisis hit (the 70's) I got some govt contract money to look at ways farmers could use their own crops as a substrate for bio-fuels. There were a number of projects on the go, I had a project on looking at better ways to recover butanol (it is a better fuel and is miscible with diesel). The farm scale ethanol was almost a fait accompli when the Govt got cold feet. They were worried that farmers would start selling their ethanol as hooch thus they mandated that all systems had to include a fool proof way to automatically denature the alcohol as it was produced. Thus a rather simple (and cheap) process was converted into a highly technical (and expensive) process which was no longer viable. The price of oil dropping to $8 per barrel didn't help.
There are other things that can be done with agricultural wastes and switch grass. At the same time as I worked on the butanol recovery process I developed a thermo-chemical process for converting the dry waste into a hydrocarbon miscible product. One of the by products is char which can be burned, buried to sequester carbon in a stable form or can be used to generate hydrogen.
Thus there are a number of ways to get to liquid fuels on the farm. Unfortunately, most governments seem to only think about ethanol. Of course it is a great vote getter (farming communities) and a great way to attract money into political pockets (most companies involved now are large international companies who get the ears of government if they line their pockets).
My model for ethanol production would include the following and should be run by a coop of farmers and local businesses:
1 - locally produced grain
2 - associated feedlot to use the by products
3 - biogas from the manure, used in part of supply energy for the ethanol plant
4 - supplemental energy by burning straw and other dry waste
For those worried about methane from cattle, feed lot cattle produce far less methane than cattle fed hay or grazing on grass.
Ian Forrester
Yes, these are sensible things. [I grew up on a small farm that had been in the family since ~1840, i.e., we reused everything we could. I forked a lot of manure, etc.]
My only real disagreement is that grains have generally been bred for thousands of years for food yield, and we need to go all-out to tweak things like switchgrass, miscanthus, etc, as fuel crops, or even better really make algae biodiesel work well.
I.e.., I'm happy to reuse wastes in any possible way, but sometimes having two crops, each engineered differently, will work better. Again, the goal is to figure out the right way to handle whatever transport fuel is really needed after we've done all the rest, and do it before the oil is gone, and before the pressure comes for CTL, etc. In any case, I was pleased to see:
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2004/05/14/BAGJG6LG3R15.DTL
Of course, given the impending demise in the next few decades of cheap natural-gas-based fertilizer, that manure remains valuable. I suspect there will be a lot of GM to try to get yields up with less fertilizer and water...
Dont forget about decreasing soil quality as well. The industrial intensive farming method has led to serious loss of topsoil through erosion and organic matter loss. So even maintaining yields with decreasing soil quality in general will need to be considered.
A little different spin on your story title, but hopeful nonetheless...
'Plantstones' could help lock away carbon
07 January 2008
From New Scientist Print Edition. Rachel Nowak Melbourne
One way to cut greenhouse gas levels in the atmosphere may be to exploit a particular talent some plants have of locking away carbon. All we need to do is choose the right strains of crops to grow, and they will sequester carbon for us for millennia.
That's the idea of two agricultural scientists in Australia, who say the trick is to grow grasses such as wheat and sorghum, which lock up large amounts of carbon in so-called plantstones, also known as phytoliths.
http://environment.newscientist.com/channel/earth/mg19726374.800-plantstones-could-help-lock-away-carbon.html
Although, by my calculations, if we are dumping ~ 100 million tons of CO2 emissions into the atmosphere daily, we would have to cover the entire planet, including the seas, with this stuff to even just keep up! Still, lots of promising little solutions add up...
A low-energy, low-environmental impact method of removing CO2 from ambient air would be a wild card that could change so much, although I have not seen anything promising on the scales required...
... I thought phytoliths were silica-based plant cell structures.