The Ergosphere
Friday, December 23, 2005

What can you do with 1.3 billion tons?

There's an estimated 1.3 billion tons of unused (waste) biomass produced in the USA every year.  <Dr. Evil voice> 1.3 billion tons. </Dr. Evil voice>  Sounds like a lot, doesn't it?  Should be a great energy supply, right?

Maybe, maybe not.  It depends how it is used.

The buzz today is all about cellulosic ethanol.  Ethanol is touted because it is miscible with gasoline and can be used by some vehicles in concentrations up to 85% (E-85).  There is a large agribusiness lobby behind ethanol, which claims it as the route to energy independence.  Is it?

Iogen is a biotech company which makes enzymes for the hydrolysis of cellulose to sugars; these sugars are then available for yeasts to ferment into ethanol.  Iogen claims a net yield of 330 liters (87 gallons) of ethanol per dry ton of biomass.  This is an energy efficiency of roughly 48%; the balance of the energy is in lignin which is not converted to sugars (and typically burned to distill the ethanol) or used by the yeast for their own metabolism.

A gallon of ethanol has energy equivalent to roughly 2/3 of a gallon of gasoline, so Iogen's process turns a ton of biomass (roughly 15.2 million BTU) to the equivalent of about 58 gallons of gasoline (about 7.3 million BTU).  1.3 billion tons of biomass would yield 75 billion gallons-equivalent, about 54% of US gasoline consumption or about 38% of total US motor fuel consumption last year.  Due to other uses of petroleum, it represents an even smaller fraction of total demand.

This is clearly not going to get us to independence; even with complete use of the entire 1.3 billion tons, losing about a quarter of petroleum supply would put us right back where we are now.  But are there other ways to use this biomass surplus which would get us there?


Someone I won't name has been bugging me to write about direct-carbon fuel cells (DCFC's).  These things are lab test articles and not ready for production, but they are remarkable nevertheless.  The efficiency of any energy conversion machine is limited by the increase in entropy during its operation; entropy can only be carried away as waste heat, and so limits the possible conversion of chemical energy to electricity.  DCFC's convert oxygen and carbon directly to carbon dioxide, which has approximately the same entropy as the reactants.  Their theoretical efficiency is accordingly very high, and researchers claim 80% at practical current densities (100 mA/cm2).

It's easier to convert biomass to carbon than to ethanol; the production of charcoal is older than recorded history.  Simple processes can convert biomass to 28-30% of its dry weight of charcoal, of which perhaps 25% of the original mass is carbon.  1.3 billion tons could produce 325 million tons of carbon, plus pyrolysis products.  How far could we get with that?

A mole of carbon burns to yield 93960 calories of energy; that's 7830 calories/gram, or 32.8 kJ/g.  A ton of biomass at 16 GJ converted to charcoal yields about 8.2 GJ of carbon as charcoal (51%) and the balance (49%) as chemical energy and heat in the pyrolysis gases.  The carbonization of 1.3 billion (metric) tons of biomass would produce 1.02e19 joules (9.7 quadrillion BTU) of energy in addition to the charcoal.  This is 1.6 times as much as all the natural gas burned for electricity in 2004; if it could be converted to electricity at 45% efficiency, it would make 4.4 quads of electricity, or an average power of 145 GW.  That's more than 30% of total US electric consumption in 2004.  Alternative possibilities include conversion of the pyrolysis gas to syngas followed by F-T synthesis to produce liquid fuels and other products.  As a SWAG, perhaps 15% of the pyrolyzed mass might be converted to hydrocarbons; that would come to 146 million tons, roughly 42 billion gallons (1 billion barrels) of liquid at the density of diesel fuel.  A half-ton of hydrocarbon per capita should meet US needs for plastics and other chemicals.

1.3 billion tons of biomass converted to carbon at 25% efficiency yields 325 million tons (325 teragrams) of carbon.  At 7830 calories/gram, this represents 2.54e18 calories (1.06e19 J, 10.1 quadrillion BTU) of energy.  At an efficiency of 80%, DCFC's could convert this to roughly 8 quads of electricity.  This is an average power of 267 GW.  But what's that compared to motor fuel demand?

US gasoline consumption in 2004 was up to 139 billion gallons; at 126,000 BTU/gallon, this comes to 17.5 quads of raw energy.  But gasoline vehicles are inefficient; at 16% efficiency, only 2.8 quads of this gets to the wheels.  Diesel vehicles are better.  The 60 billion gallons of distillate oil consumed in 2004 contained 8.7 quads at 145,000 BTU/gallon; converted to work at 35% efficiency, it would deliver 3.0 quads to the wheels.  The total of 5.8 quads is about 73% of the energy available from the carbon, allowing a surplus for other uses.

The one liability is that the DCFC cycle cannot use energy from sources other than biomass; if productivity runs low, there's the potential for a crisis.  This is why I still like the thermal zinc process (driven by solar or any other heat source).  Its direct path is not as efficient as the DCFC system (93960 calories of carbon yields 84670 calories of zinc, which produces 52500 calories of electricity - about 56% throughput to the DCFC's 80%) but it produces more net energy (via the carbon monoxide, the output from a mole of carbon includes another 68330 calories of chemical energy), more useful byproducts, and zinc can also be regenerated using electricity from any source.  Zinc also allows nearly complete carbon capture even when the energy is used in mobile applications.

So, what CAN you do with 1.3 billion tons?  The answer, I think, is "enough."

Further reading:  Direct Carbon Conversion Workshop presentations.

"Unused" means "left to rot on the surface".  I understand that soil tilth isn't changed much by matter left on top (it decomposes too quickly); it is influenced much more by the deep roots left 8 inches or so below the surface, which are not disturbed by combines.
The most interestinf part of the carbon cell is that people think they can mass product it cheaply. It is very nice to get a more efficient engine, but to get a cheaper and more efficient one, this is incredible.

But you are a bit too fast when you put ethanol out. When produced the right way, one can get a lot of fuel with a reasonable amount of biomass. Brazil got very far this way, if you want an example.
Marcos, look again at the ultimate recoverable energy using the ethanol route.  Calculate how much biomass it would take to replace the US's petroleum consumption using ethanol.

Now consider what you would need to get that much biomass.  Tell me what other land uses you would replace to make fuel, and how much you would take.
Fascinating stuff, EP. How does the pyrolysis part of the process scale? Can you have pyrolyzers small enough, and geographically scattered enough that you don't get whacked by transport costs for bulky and widely dispersed biomass? Can it be done cleanly? If the process is high emission, it will be hell to site. Are pyrolysis products a decent feedstock? (for making plastic, e.g.) My gut feeling is that they're pretty gnarly, but I haven't researched it. I guess anything's possible with enough chemistry applied to it, but what's it cost?
"How does the pyrolysis part of the process scale?"

Pyrolysis definitely works at a small scale, but I'll bet that the equipment to do synthesis with the pyrolysis gas needs to be much bigger.

"Can it be done cleanly?"

The researchers seem to think so.

"Are pyrolysis products a decent feedstock? (for making plastic, e.g.)"

If coal (which yields some mighty nasty stuff as coal tar) can be made into clean syngas, I have no doubt that biomass pyro-gas can be too.
Using google, I was able to discover that the cannae average productivity at Bazil is 57ton/ha, and that each ton have the net energy sorplus of 1.2gal of diesel (that is the only figure I found).
You said that the US uses 139e9gal (how much is to run cars?) of gas per year (1gal diesel = 1.12gal gas), so would need 1.7e9ha of canae. Yes, you are right, it is not viable.
" As far as I know Lignin is impervious to yeast."

Even cellulose is impervious to yeast.  There are obviously organisms which can degrade lignin, because it decays in nature; however, that's marginally relevant to the energy balance of biomass-to-ethanol.

"Wrong Wrong Wrong: Heating value is only valuable for comparison for heating. Heat production is a by-product of ICE operation not the main event which is mechanical energy."

You're telling me that the same engine can run at 50% greater thermal efficiency burning ethanol than burning gasoline?  The same engine in the same vehicle?  On alternate tanks of fuel?

I question that claim, especially since you've cited nothing to support it.

Even if true, it would only allow ethanol to displace slightly more than half of total US gasoline consumption and about 36% of total motor fuel demand.  That's nowhere close to eliminating oil imports, let alone replacing our decreasing domestic production.

"The discussion of fuel cells is an interesting sideshow with no merit. Fuel cells make electricity at fairly low efficiency from highly valuable liquid fuels or they require massive amounts of coal/nuclear power to make hydrogen. The materials materials needed to convert to a fuel cell based transportation system, such as copper for electric motors and platinum for cells, are non-renewable, energy intensive and limited in supply compared to tried and true cast iron for ICE.s"

Funny, my calculations show that ethanol is the sideshow with no merit.  Further, it's obvious that you did not read the links on direct-carbon fuel cells (which need neither liquid fuels nor platinum nor hydrogen) and paid no attention to the calculations in the main post.  Last, there is already plenty of material used in modern vehicles (copper and aluminum) which is also suitable for high-current wiring; in the future, Buckytube wires (6 times as conductive as copper) could replace both of them.  (The 100 ppm of post-industrial CO2 in the atmosphere means there's about 270 grams of excess carbon above each and every square meter of Earth's surface; we're not about to run out of carbon.)

You score a zero on your homework.

"Alcohol fuel production in Brazil uses virtually no fossil fuels at all! The process energy comes from burning a fraction of the cellulose left over. In India, none of the 200 plus alcohol fuel plants there burn any electricity since the process energy comes from making methane from process by-products."

That's very nice for them.  It's also irrelevant to the issue of meeting US demands with US supplies (unless you want to postulate a radical change of lifestyle).  Marcos did that calculation right before you, but you appear to have been too hasty to have read his work either.

"There is far more than enough land to produce all the fuel we need for vehicles even if we didn't do our damndest to reduce our consumption"

Even with 1.3 billion tons you can't even get halfway there; anything beyond that requires changes in land use from something else to fuel crops.  While that might be desirable, you can't take it for granted; people have more than just one priority.

" Sugar cane yields are now topping 1000 gallons of alcohol per acre using no chemical fertilizer, just the liquid and ash by-products from the alcohol plants being returned to the field."

Very little land in the USA is suitable for growing cane, and cane is both non-native and one of the more polluting crops we grow.  Regardless, fermentation is a lossy process and the internal combustion engine is lossier yet.  Direct-carbon fuel cells and zinc-air fuel cells can produce a great deal more energy at the end per unit of biomass.  You may not like that, but the facts are against you.
I think it is useful to think about this question from the opposite direction. Instead of wondering if there is enough waste to supplant petroleum dependence, how about considering the cost of the biomass waste (agricultural, forestry, and urban) as it is and what positive thing can we do with it that would reduce our dependence on fossil fuel.

For instance, farmers have a problem with disposing rice straw to the point where it is no longer financially even breakeven to grow rice in some states that have outlawed burning it. Disposal of autofluff is a big waste problem throughout the country. MSW have relied on landfills for its disposal - and I would say we are beyond "peak land" for the availability of alternative landfill sites given NIMBYism and the expense of trucking it to remote locations (which doesn't deal with the real problem anyway). So what can we do with all this biomass that is economically feasible?

You mentioned cellulosic ethanol. According to Wikipedia there are two methods for its production - enzymatic hydrolysis you mentioned and it is very expensive and not very efficient - nor is it applicable to most biomass feedstock.

Syngas fermentation you did not mention. You can gasify 75-85% of all unrecycled waste (agricultural, forestry, and urban) into syngas which can then be fermented into ethanol using bioconversion processes - anerobic bacteria ingesting the gas and expelling ethanol and water.

So - you are not only reducing waste volume by 75-85% but you are co-generating clean electricity (from the heat of the process) and producing renewable liquid fuel to blend or replace gasoline.

You also did not mention the emissions data related to any of the processes you mention - a HUGE issue. I refer you to Argonne National Laboratory and U. of Riverside/CE-CERT for comparative data.

Could waste and biomass conversion supplant all of fossil fuel dependence? Who cares so long as it reduces the waste problem and provides a clean technology for renewable fuel.
"Instead of wondering if there is enough waste to supplant petroleum dependence, how about considering ... what positive thing can we do with it that would reduce our dependence on fossil fuel."

The standard for that is much lower.  Suppose you could make one gallon of ethanol per ton; that's 1.3 billion gallons/year, about 1% of gasoline consumption.

Sure, that's something.  It's also so trivial that it's barely worth doing (a 0.3 MPG increase in CAFE would do more), and it offers no prospect of a sustainable energy cycle.

"Syngas fermentation you did not mention. You can gasify 75-85% of all unrecycled waste (agricultural, forestry, and urban) into syngas which can then be fermented into ethanol using bioconversion processes - anerobic bacteria ingesting the gas and expelling ethanol and water."

I've seen those claims, and I'm skeptical.  Enzyme hydrolysis and fermentation is about 48% efficient (87 gallons/ton).  I'm having trouble finding the reference, but I've seen a claim of either 110 or 140 gallons/ton for the gasification/fermentation cycle (61% or 77% efficiency respectively), plus electric generation.  You still have to do the distillation step, with all the losses there.  I don't see how this works.

I've also searched for information on the Clostridium pathway from syngas to ethanol.  I didn't find any papers which described experiments which worked smoothly even at the laboratory scale.  This is not to say it hasn't been done, but at this point I say "show me".

"You also did not mention the emissions data related to any of the processes you mention - a HUGE issue."

The zinc-air fuel cell is emissions-free.  The DCFC can be sealed on the fuel side.  The conversion of biomass to charcoal makes tars and such, but it's pretty much the same as the first step in syngas fermentation; you could even add air to break down heavy tars and feed the results to a fermenter.  The charcoal would yield much more energy in a DCFC than ethanol could make in an engine.

"Could waste and biomass conversion supplant all of fossil fuel dependence? Who cares...."

I do.  If we can get all the way there, there's no reason to settle for a tenth, or even half.
According to what I've been able to find, sugar beets yield roughly 20 tons/acre and are about 16.7% dry matter by weight.

That's about 3.3 tons of dry matter per acre, which is very unimpressive compared to Miscanthus, switchgrass or willow shrubs.  The one reason to use sugar beets is to avoid the expense of enzymes for cellulose hydrolysis, though I suspect that the lower yields and higher cultivation costs would offset that.  When someone breeds a yeast which makes its own cellulase, even that argument will be out the window.

Perhaps I'm wrong.  Show me the data (like you didn't for that Saab).
Popfuel, it seems that there are a lot about fuel cells that you don't know. Fuel cell is simply a name for a battery where the reactors are not inside it, but pupped into it all the time.
That means that you can build one with any kind of chemical reaction that outputs energy, not only with Hydrogen and oxygen. It also means that your generator is not restricted by the Carnot cycle's efficiency, but it is possible to get something near 100% efficient.
Also, the platinun cataliser is used only on the hydrogen fuel cells, and, even there, it have cheaper replacements.
About the ethanol, I made the calculations up there, it is not viable to get everything that is needed from canae and other traditional cultures. those numbers put at a new light the recent rise on the price of this fuel at Brazil.
But with alternative cultures, it may be possible to run the world on ethanol. Eichornia crassipes is a plant (angimnosperm) that lives on polluted waters, and helps cleanning it. It produces 150+ ton/ha of almost all cellulosis. With 87 gal of ethanol by ton, 16e6 ha of it can produce the energy equivalent of those 139e9 gal of gas. It is worth notice that this plant spreads very well at the south at the US.
Of course, there may not be 16e6 ha of polluted water out there to produce it, but it could be possible to produce a significant amount of fuel this way. And if this plant can yeld a so large amount of cellulosis, other cultures may do the same.
I asked the VP Marketing of BRI Energy what a rough number for conversion of a ton of waste to ethanol using syngas fermentation is. His answer:

"It depends upon the BTU content of the material being processed.

In very rough numbers, I would say between 70 and 85 gallons per dry ton for such materials as MSW, animal wastes, sewage sludge, agricultural residues, etc., and between 160 and 180 gallons per ton for such high BTU materials as coal, used tires or plastics."

Feedstocks can be blended which would affect yield.

Another efficiency factor is - where does the feedstock reside? Shipping sugar fermented ethanol from the Midwest doesn't make much sense for California, although the state imports 99% of the ethanol it uses. However, California could produce all of its needs for ethanol from the ample waste that is generated here. We could even "mine" landfills for feedstock.
poopfuel:  You don't have a cite for the Saab, and your link has a statement but zero supporting data for the economy claim.  I realize that alcohol will burn lean without knocking and allow greater economy, but you've not provided any evidence that this can be done while meeting NOx emissions limits.  The standard flex-fuel car runs at stoichiometric and will have an economy penalty for greater ethanol fractions.

Hand-waving will get you far among believers, but if you aim to solve problems in the real world you have to show how you'll handle real-world complications.  You haven't done that; you're not even close.

Neither have you supported your claim regarding sugar beets.  Where are the yield figures which would support that much productivity?  How many farmers are getting that?  Your failure to support your claims with pertinent data makes me question your accuracy; keep it up, and I'll have to question your truthfulness.  Especially when you're writing to mislead:

"2000 pounds of cellulose converts to more than 1000 pounds of alcohol."

Even if true, very misleading:  biomass is a lot less than 100% cellulose.
"Neither Corn nor Soybeans are the largest US crop by weight. Grass clippings are and they are nearly pure cellulose.

Figures on the web are all over the map, but I've seen no claim for total yard waste (more than just grass clippings) which is over 30 million tons/yr (example).  Other sources are far greater; there is about 200 million tons of excess corn stover alone.

The actual 2004 maize harvest was 11.8 billion bushels, which is 330 million short tons at 56 lb/bu.

It appears we cannot trust anything you write.  Either you don't check your facts, or you just don't care what's true.
Last, poopfuel writes:

"Note too that the carbon fuel cell uses coal as fuel. Co2 problems here?
And where will you get renewable carbon?

Scott:  That's far more realistic (and in line with what I thought I remembered from the last go-ground with this concept).  "Agricultural wastes" is probably equivalent to biomass in general, so it appears that the ethanol conversion efficiency is a bit below Iogen's claims (87 gal/ton).  That's more like what I would expect given the nature of the bio-processing and the ancillary output.

Does BRI have figures on the web that they're willing to stand behind?  I've been over their site and found nothing pertinent.

There are many technologies which appear to be able to process ag wastes into useful substances.  For instance, fast pyrolysis could convert all that rice straw into bio-oil, char and gas.  The gas heats the process, the char is either used for heat or a carbon-sequestering soil amendment, and the bio-oil could be used as a natural gas substitute in powerplants (perhaps a bigger deal for California than anything petroleum-related).

What concerns me is that we not get locked into a system which commandeers all the available resource but won't let us get very far toward sustainability.  I fear that ethanol will do that, by harnessing us to the internal combustion engine.  DCFC's won't, and alternative fuels for stationary powerplants probably won't.
Wait 6 months so that we can pay to see if you've actually got facts to back your claims?  After your sorry showing here, I won't be waiting.
I don't have any figures more definitive than what I have told you although I am assured that Dr. Gaddy tends to understate yield. The chicken or egg concept applies here - their numbers are based on pilot plant data to help secure investment on a full scale installation - they expect groundbreaking next quarter.

My focus at BioConversion Blog has been on supporting California AB 1090 which is a linchpin piece of legislation that could open the doors for investment in waste conversion technologies in CA. Crucial first committee vote is scheduled for January 9.

In general, I support ethanol because it (and flex-fuel vehicles) exist. And, as you pointed out, ethanol is miscible with gasoline. For me the key to any broad acceptance of any renewable is infrastructure. I also like the idea of weaning a wary public off fossil fuels by providing them with a price competitive alternatives at the pump (like they have in Brazil). Change will be glacial and gradual.

I am told that the BRI process can also be used to produce hydrogen from biomass.
Regarding poopfuel's economy claim for the Saab:

I went digging and found a press release which states that fuel cost declines 15% when burning an ethanol mix which costs 25% less per unit volume.  This indicates that the vehicle burns 13% more fuel by volume when running on E-85, or 98% as much ethanol as gasoline plus another 15% gasoline.

Efficiency does appear to go up (the fuel has only about 80% of the energy of the displaced gasoline), but it's not the 50% leap he implies.
My research reveals that the MPG for ethanol is almost always lower for E85 than gasoline with lower blends of ethanol.

Check out This has a handy chart/calculator for comparing not only MPG for city and hwy but also annual fuel cost (with user customizable gas prices), GHG in tons/yr., and EPA air pollution score for each 2006 model of FFV.

But let the market decide which is more economical. Two things are certain - 1) fossil fuel prices will make renewable fuel prices more affordable by comparison and 2) competition between gas and ethanol prices will keep each in check.
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