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An Extended Conversation with POET

Today (July 17th) I spent some time on the phone with POET‘s VP of Science and Technology Dr. Mark Stowers. (I was invited up for a visit, but I couldn’t swing that just now). Dr. Stowers is in charge of company R&D, which includes corn and cellulose to ethanol, as well as the investigation of novel processes for utilizing waste to power their facilities.

Joining us on the call was Matt Merritt, POET’s Media Relations Specialist. We covered a lot of ground on the call. Along with the environmental impact, key interests of mine in assessing fuels of any kind are the energy inputs – what kind, how much – and the related topic of logistics. I probed the energy inputs in some depth, as I consider that critical when considering long-term commercial feasibility.

First a bit of background on POET. They are the largest ethanol producer in the world, producing more than 1.5 billion gallons of ethanol each year from 26 production facilities across the country (each with its own nuances, I was told). They recently started up a 20,000 gal/yr pilot-scale cellulosic ethanol plant, which uses corn cobs as feedstock. Plans are to commercialize the process in 2011. They have named this effort Project Liberty.

My questions and Mark’s answers below are paraphrased, but as I told them if they spot anything that I got wrong they can notify me and I will correct it. The format below includes questions, answers, and comments from me. Where the comment was part of the interview, it will appear as a prelude to a question or a comment in the follow-up as “RR: Comment…. Mark’s answers will appear as “MS: Comments…” To distinguish from additional comments I might interject, I will indicate those with [RR: Comment…]

I first voiced my skepticism that cellulosic could ever make a huge impact, due to logistical issues and energy requirements. That was going to be a major thrust of the interview, but I started off with a related comment/question.

RR: Conditions in Texas have been really dry. [RR: See this story on the current drought in Texas.] We have had over a week with temperatures exceeding 100 degrees each day. There are a number of corn fields near my house, and the fields appear to be dead. How are conditions up north?

MS: Actually this will probably be one of the best years ever. We got rain when we needed it. Corn grew 6 inches overnight recently. In Sioux Falls right now the temperature is 70 degrees.

RR: OK, let’s move on to your process. Can you start by walking me through your cellulosic ethanol process?

MS: Our cellulosic process is based on corn cobs. We have harvested 25,000 acres over the past couple of years. We are currently still trying to work out harvesting and storage. The yield of cobs is 0.65 tons/acre, and we can collect them commingled with grain with a modified combine. Or we can collect them with stover coming out of the back of the combine. The bulk density for cobs is higher than for stover, and that makes them easier to separate. We store at the farm field edge currently and can collect over the following 6-9 months. We make sure sufficient stover is left on the field for erosion control and nutrition. We are focused on cobs because the bulk density for cobs is better than for stover, and cobs have 16% more carbohydrates than the stover. We believe that there is a nationwide potential for 5 billion gallons of ethanol if all cobs are collected and converted.

RR: OK, I am going to walk through some numbers here. As you may know, I have been skeptical about the potential of cellulosic ethanol to scale very well. I feel that there are niches in which it will work, but I don’t think it works well as a large scale solution.

As you mentioned, average cob yields are 0.65 bone dry tons (1300 pounds) per acre. I have a reference that says the heating value of cobs is about 7900 BTU/lb [RR: Mark agreed that this was correct]. So the total BTU value of the cobs on an acre is about 10 million BTUs/acre, which is also the energy content of 135 gallons of ethanol (ethanol has a heating value of 76,000 BTU/gal). That would seem to be an upper limit on a hypothetical perfect conversion process that could capture 100% of the BTUs. But of course enzymatic processes are not going to convert lignin, and there will be some inefficiencies. My guess is that you probably need 20 pounds or more of cobs to produce a gallon of ethanol (as opposed to 10 pounds for a perfect conversion process), putting the actual yield at around 65 gallons per acre. I saw someone (not POET) who recently claimed cellulosic from corn cobs would increase per acre yields by about 110 gallons per acre, but based on the BTU value I don’t think that’s possible.

MS: Yes, I think that 110 gal/acre number looks too high. The 20 pound number you came up with looks approximately correct. We can get 85 to 100 gallons per ton with our process but operate mostly in the high eighties and low nineties at present. We are drying and burning the lignin for fuel, but in addition to the cellulose we are also converting the hemicellulose to ethanol.

[RR: OK, so 85 gallons per ton is equal to 55 gal/acre, and 100 is 65 gal/acre – which is the number I had worked out. Incidentally, I think the difference between a skeptic and a cornucopian is that the skeptic will look at that range and say “OK, realistically speaking they probably get 85 gallons/ton on a good day, and they think they can push it to 100 gallons if they continue to push the envelope.” The latter will claim matter-of-factly that yields are at least 100 gallons/ton.]

RR: OK, I did not know you were converting the hemicellulose. What is the percentage of cellulose and lignin in the cobs?

MS: The cellulose plus hemicellulose is upwards of 60%. Lignin is about 15%.

RR: One of the keys to success for a cellulosic ethanol process is to increase the concentration of ethanol in the crude product. Historically this has been in the 3-4% range for cellulosic ethanol, and I don’t believe that will be commercially practical. The energy required to purify a solution in that range would be comparable to the energy contained in the ethanol. [RR: Of course with waste heat or very cheap BTUs, you might be OK to do it anyway]. So can you discuss the sorts of ethanol concentrations you are getting?

MS: First of all, I agree with your comments on ethanol in the 3-4% range. While we have not released information on our cellulosic ethanol titers, they are lower than those for corn ethanol. On the other hand we have some of the highest corn ethanol titers in the business; we can achieve greater than a 20% ethanol solution from corn. But we are better than the 4-5% range for our cellulosic process. Also, there is sufficient energy in the solid waste stream and the liquid stream to provide more than enough energy to power our cellulosic process.

RR: Don’t you have problems with the enzyme activity diminishing at higher ethanol concentrations?

MS: We do not see enzyme activity as a rate limiting step with respect to ethanol tolerance.

RR: Beyond the energy required to process the cellulosic ethanol, there is the fuel required to gather and transport the corn cobs. Along those lines, one of my readers wondered about the radius to the plant in which the logistics are still economical. His comment was that he heard that shipping costs for cobs are twice as costly as the grain because they are so bulky.

MS: We can go out to a 25-35 mile radius; about the same as corn.

[RR: I suspect if you did the analysis for cobs by themselves, collecting cobs and transporting them from 35 miles away might not be worth the fuel value of the subsequent ethanol produced.]

RR: Do you have a feel for how many BTUs is required to produce a BTU of cellulosic ethanol?

MS: We have some idea of those numbers, but haven’t released them. [RR: I think he said they are waiting for more results from their pilot plant, and they are working on getting better numbers.]

RR: Another question from a reader: “Will they contract with producers and what will the terms be?” I think I know the answer to this, because I read an article yesterday in which Poet spokesman Nathan Schock said that this hasn’t been fully determined. [RR: Here is the article: Iowa plants to offer farmers cash for corn cobs.]

MS: Nathan was correct; we have contracted with some farmers for fall harvest but we don’t know where the economic sweet spot for everyone involved is going to be.

RR: I would think you would hold those numbers close anyway, or all farmers will be holding out for the highest published price.

MS: Yes, that is a key point.

RR: (I asked if another reason for focusing on cobs over stover was related to concerns about soil depletion. I also incorporated another question from a reader): “Ask POET what they think of cellulosic from corn stover. They seem to say that stover has too many collection and handling problems (dirty, low density, etc), and that is one reason they are concentrating on cobs only. Many others assume corn stover will be the primary source of cellulosic feedstock.”

MS: We don’t have to leave all stover in the field necessarily over soil depletion issues; we have just chosen to focus on cobs. How much one can remove depends on soil type, location, and tillage practice. Cobs take those variables away.

RR: Is your ethanol purification compatible with existing corn ethanol infrastructure? I would think that with a higher water concentration you could go into your corn ethanol distillation system, just at a lower feed location.

MS: A cellulosic plant will be a bolt on to an existing corn ethanol plant. But we will have a better efficiency if we don’t intermingle the streams with corn ethanol because we don’t want to get things like lignin in our corn ethanol distillation train. So it is better to have separate distillation trains. The infrastructure will be more of what you see in common (utilities, logistics in and out, etc.).

RR: Why not just use the cobs to produce steam for the corn ethanol process? Have you done comparative studies on that?

MS: We are doing that today as well. We are using other renewable biomass to fuel a solid fuel boiler at Chancellor, South Dakota. This is a 100 million gal/yr facility. We are also using landfill gas in a multi-purpose boiler.

RR: What is the quality of the methane from your digestor? Do you have to clean it up?

MS: We have two applications for our biogas. One is for overall energy, and the other is fuel for the dryers. We are just finishing up our 3rd month of operation. The boiler that we have developed can handle the biogas that is produced.

RR: How many engineers are working on Project Liberty?

MS: Between the lab and pilot plant, we probably have 25 scientists and engineers.

RR: Is your pilot unit fully integrated? Is the pilot process fully connected?

MS: We are completely integrated from cob collection through ethanol production and recycle streams. We have a 24/7 operation with 4,000 data points collected. The pilot plant has been running since about Nov 18, 2008.

RR: One of the things that I strongly believe is that if the corn ethanol industry is ever going to break free from endless subsidies, you have to get the fossil fuels out of the process to the greatest possible extent. The sugarcane ethanol producers are more immune to the ups and downs of fossil fuel prices because of the large role bagasse plays in providing fuel for their process. So it feels like you are headed down the right path here, even though natural gas prices aren’t exactly a pressing concern for ethanol producers right now.

However, it might be that you have enough waste energy to fuel your process, but most of the BTUs are used up in the conversion, leaving very little ethanol. So in a case like that the question becomes, “Are you left with a small net amount of ethanol, or a very small net amount of ethanol?”

[RR: For example, if you had one BTU of biomass, and consumed 0.9 BTUs to produce 0.1 BTU of liquid fuel, you could say that you have gotten the fossil fuel inputs out, but you have produced very little fuel and were very inefficient with the utilization of the BTUs. In that case you could ask if there might have been a better use for that BTU of biomass.]

MS: The energy from our waste streams should be sufficient to power the 25 million gal/yr cellulosic plant and nearly power the 50 million gal/yr starch plant next door.

[RR: To me this was the most significant statement he made during the interview. If an added benefit is that you are also powering your corn ethanol plant with the energy produced from the cellulosic process, you have a very powerful synergy. But I admit that I have a bit of a hard time with this one. I would like to really dig into the energy balance, because it doesn’t seem to me like there are enough BTUs. If I go back to my analysis of 10 million BTUs/acre available from the cobs and you back out 65 gallons of ethanol produced from the cobs, that would only leave you with about 5 million BTUs per acre to power both a cellulosic plant and a corn ethanol plant. If I make a couple of reasonable assumptions, it looks to me like they are assuming only 30,000 BTUs of energy input per gallon of ethanol production. This seems on the low side, but is perhaps reasonable when the ethanol yields from the cobs are on the low end of the range – leaving >30,0000 BTUs/gal for running the process.]

RR: When you are out front with a technology, there are always risk factors. What are some of the risk factors that you have identified that might keep you from meeting your goals?

MS: First is the absence of a market for cellulosic ethanol. The blend wall from E10 really limits the cellulosic market.

RR: OK, that’s market risk. How about technical risk?

MS: We must have farmers and equipment manufacturers engaged; we need a solution in which both sides can make money. We need programs early on to help biomass collectors overcome the risk. How many cobs can you get in a truck? The logistics become important. There is also the issue of inventory management. The annual supply of cobs for a 25 million gal/yr cellulosic plant would require a silo the size of the Empire State Building. We need to decentralize this, and we need as high a throughput into the reactor as possible.

RR: Gentlemen, that’s about all the questions I have, although I will probably come up with 10 more when I am writing this up.

MS: Feel free to contact us for any followups.

RR: Thanks guys. Appreciate you taking the time.


July 17, 2009 - Posted by | biogas, biomass, cellulosic ethanol, POET


  1. "[RR: To me this was the most significant statement he made during the interview. If an added benefit is that you are also powering your corn ethanol plant with the energy produced from the cellulosic process, you have a very powerful synergy.]"If true, that would indeed be a major breakthrough, and they should book their tickets for Stockholm to get their Nobel Medals.

    Comment by Wendell Mercantile | July 17, 2009

  2. "The annual supply of cobs for a 25 million gal/yr cellulosic plant would require a silo the size of the Empire State Building."Wow! Building a silo that large would represent a significant amount of embodied energy. And think of the energy demands to just move the corn cobs around between the silo and the plant.Something I didn't hear him mention is the need to dry the corn cobs before siloing them. (One of the problems with stover is the potential for spontaneous combustion if stored damp or wet.)Also how do you keep the insects and vermin out? Not many neighbors would appreciate a massive storage silo that becomes a breeding point for insects and vermin."We make sure sufficient stover is left on the field for erosion control and nutrition." Glad to hear that is on their radar screen. Too many cellulosic proposals want to strip all stover from the field."We need programs early on to help biomass collectors overcome the risk. How many cobs can you get in a truck?" One solution would be to bring in the corn from the field still on the cob, and shell the corn at the plant diverting the cobs into to a separate processing stream.

    Comment by Wendell Mercantile | July 17, 2009

  3. Good Interview, Robert. The energy for transporting the cobs should be pretty easy to figure (as long as you know the weight/volume of corn cobs, that is.)Just farting around, if you could get ten tons of cobs on a semi, and figuring 100 gallons/ton that would be 1,000 gallons/ethanol/load. Figuring 15 gallons/round trip (60 miles) that would be about 2 million btus of diesel, or 2,000 btus diesel/gallon of ethanol. +/- something, or other, of course. 🙂

    Comment by rufus | July 17, 2009

  4. If true, that would indeed be a major breakthrough, and they should book their tickets for Stockholm to get their Nobel Medals.Check out my updated comments in the article. I am having a hard time with those numbers. This is when I would like to get in there and dig through their data. :-)RR

    Comment by Robert Rapier | July 18, 2009

  5. They say they get 85 – 110 gallons per ton of cob – why the large spread? Is 110 really possible at commercial scale, 24/7/365, or is it more likely to be 85 or less (many papers suggest with current technologies, 60 gallons / ton may be closer to reality at commercial scale). Current corn ethanol only gets about 95 gal / ton – can cellulosic really outperform corn starch? POET indicates 0.65 ton of cobs per acre, but I assume that is at harvest and does not include any waste / deterioration that might occur during storage, assume that might be 5% or so? The referenced article on cob costs says that POET will offer between $30-60/ton. If it's $60 ton, and maybe 70 gal/ton at scale, and if CBoT ethanol price is $1.60 gal (equivalent to $2.40 gas), seems like it would be hard to make a profit given the expected high capex and operating costs? I guess they would need to rely on the $1 per gallon fed subsidy for cellulosic gallons? Iowa has a bunch of coal fired power plants, and I have to think it would be easier,and probably a more efficient/economical way to reduce GHG, to burn all the cobs in IA in a month or two after harvest rather than trying to store them for 6-9 months and then try to make ethanol from them.

    Comment by Anonymous | July 18, 2009

  6. The 110 was my typo, now corrected. He said the upper end was 100, which I wonder about given my quick analysis of BTU content. Again, I would love to dig into their data.RR

    Comment by Robert Rapier | July 18, 2009

  7. Very interesting. Nice questions and frank answers. You must be really enjoying your new job.

    Comment by takchess | July 18, 2009

  8. Can anyone identify any cellulosic ethanol company that has understated its anticipated performance (cost, timing, yield etc)? I think POET is probably a bit better than most, but am I wrong to be suspicious of their stated claims? Maybe they can make a profit from cobs, and I wish them well, but isn't it impossible to know if cellulosic from cobs will be viable until there is 2 years or so of operating experience of their commercial scale plant? Also, isn't POET a good example of how long it takes to try to scale up new fuel technologies? DoE selected them as one of the 6 best hopes for cellulosic in the US in Feb2007 (2 of those 6 are no longer active) and promised them ~$80 million towards a commercial facility. 2.5 years later and they are still 6-9 months away from construction?? Did they say what their capex will be for their ~20 mgy plant, and if they have the rest of the funding lined up for it? Or are they planning on getting even more federal funds from the DoE stimulus package that has $700 mil for biofuels (those decisions to be made late this year)?

    Comment by OxyMaven | July 18, 2009

  9. "On the other hand we have some of the highest corn ethanol titers in the business; we can achieve greater than a 20% ethanol solution from corn. But we are better than the 4-5% range for our cellulosic process."RR,Thanks for taking the time to conduct this interview and publically share. Poet: Thanks for wading into this level of debate with some direct answers.I'd like to ask for additional clarification on the quotes above regarding ethanol titers. 20% etoh volumes in the beer porriage would be double what most scientists could achieve with their yeasty biobugs munching away. Thanks.Rodney

    Comment by Anonymous | July 18, 2009

  10. Some great comments. Thanks for taking time to get engaged. Let me respond to a couple of questions. First off — tickets aren't booked for Stockholm – cellulosic ethanol is a real challenge, but I don't think that hard work and passion for renewable fuels qualifies for the Nobel Prize. Let's reduce our dependence on foreign oil. With regard to cob storage, the Empire State Building is a way to visulaize the amount of cobs needed in a year. We will be storing cobs on farms and other locations off site and will draw on our needs for feedstock like what we do with corn today (and you can get and need to get more cobs on the truck than that said in one of the comments). A second question related to ethanol titers — we do get more than 20% and the other dry mill ethanol producers probably 17%. Our process is different — we don't cook the starch which allows better fermentation conditions with 8-12% less energy.

    Comment by Mark Stowers, POET | July 18, 2009

  11. Well, goody; but, how much more? 15 Tons? 20 Tons? I'm sure the weight of corn cobs isn't considered "proprietary" knowledge.Are you still hoping to be able to get your costs down to $2.00/gal?

    Comment by rufus | July 18, 2009

  12. “The blend wall from E10 really limits the cellulosic market.” This tells me all I need to know as a practicing engineer in energy production industry. BZ to POET and the rest of the ethanol industry for allowing me to use more renewable energy. The overarching criteria for the energy production industry is to provide energy where and when our customers need it. Customers will use more renewables if it easier to use.The enemy of good is perfect. If Mark Stowers would be so kind as to explain the economics and engineering aspect of switching to biomass a fuel. For example, can fluidized bed boilers using PRB coal be switched to corn cobs?

    Comment by Kit P | July 18, 2009

  13. I wish POET every success. But with the emergence of an epic, global glut in natural gas, I am more dubious about the need for "extreme ethanol," or biofuels in North America.I admire the incredible skill, inventiveness and tenacity of the ethanol crowd. If they can stand on their own two feet in the marketplace, then I will salute them as well.

    Comment by Benny "Boom, No Doom" Cole | July 18, 2009

  14. Trying to get a handle on how much they could generate here's the upperlimit.If they will only collect cobs from 35 miles away, the plant will be limited as follows using their numbers. Assuming all land in a 35 mile radius produced only corn, then the maxium plant capacity would be 160 million gallons (assuming .65 tons per acre and 20 lb of cob per gallon).(.65 ton/acre * 2,500,000 acres*2000lb/ton / 20 ton/gal = 160 million gallons.)To me that sounds like quite a bit of alcohol. We'll see if they can build a plant anywhere near that.

    Comment by SamG | July 19, 2009

  15. So Mark if you're a poet how come nothing rhymes?

    Comment by robert | July 19, 2009

  16. Robert, He is a poetAlthough you don't know it He is working to see Corn Ethanol at 2.0 EROEI efficentcy

    Comment by Anonymous | July 19, 2009

  17. "First off — tickets aren't booked for Stockholm – cellulosic ethanol is a real challenge, but I don't think that hard work and passion for renewable fuels qualifies for the Nobel Prize."Mr. Stowers,Ah, but it would. Being able to power yourself with no external energy inputs would essentially mean a reversal of the Laws of Thermodynamics.In anybody's book that would qualify for a Nobel Medal.

    Comment by Wendell Mercantile | July 19, 2009

  18. The "External" inputs are sun, and microbe.

    Comment by rufus | July 19, 2009

  19. Iowa has a bunch of coal fired power plants, and I have to think it would be easier,and probably a more efficient/economical way to reduce GHG, to burn all the cobs in IA in a month or two after harvestDirect burning sounds like a good idea, but it probably would take less than 2 weeks. Or, if all the corn cobs produced from current corn crop in the USA were burnt, it would be about 4% of annual coal consumption in the US.

    Comment by bc | July 19, 2009

  20. "Direct burning sounds like a good idea, but it probably would take less than 2 weeks."There is not much heat value in corn cobs and stover. Interestingly, back in the pioneer days, farmers on the high plains would rarely bother to go into the fields to collect stover and cobs to burn in their stoves and fireplaces, because the effort to collect it didn't justify the return.They preferred to hitch up a team and wagon and go many miles to the nearest stand of trees — even cottonwoods — to bring back firewood.They would burn the residue from the corn crop and twisted wheat and oat stalks in only the most dire situations when there was no other alternative.

    Comment by Wendell Mercantile | July 20, 2009

  21. Rufus said ~ "The "External" inputs are sun, and microbe."Then why do corn farmers o to the trouble of using synthetic nitrogen fertilizer made from natural gas feedstock?If you think the Sun and microbes are the only source of external energy in corn ethanol, try throwing a handful of seed corn on your driveway next April. Make sure it gets plenty of Sun, even water it if you want to, and then tell me what you get along about October.

    Comment by Wendell Mercantile | July 20, 2009

  22. All I meant, Wendell, is that there are enough external inputs from Sun, and microbes that the laws of thermodynamics aren't being violated.

    Comment by rufus | July 20, 2009

  23. Rufus, do you post at The Oil Drum as kdolliso?

    Comment by Anonymous | July 20, 2009

  24. I'm contributing my BOTE estimate of the cob requirement. 25 million gallons at 85gal per ton is 294,100 ton/year. The ESB has an average floor area of 26,900ft2 and is 1224 tall to the roof. That's 32.9^6 ft3 holding 294,100 ton = 110ft3/ton of cob. Say a semi is 6082ft3 = 54 ton or 109,000lb per truckload (about the limit of GVW, no?). At 54 ton/truck, that's 5450 truckloads per year or 15 truck loads per day. But corn doesn't grow year round.Is the plant is sized to run year round at a steady throughput, more or less? Or does it operate seasonally?

    Comment by Bryan | July 21, 2009

  25. Aren't these the folks that were going to use corn fiber in addition to cobs? Is that where they got higher gallon yields per acre? Their own website refences 40% of feedstock being fiberhttp://www.poetenergy.com/news/showRelease.asp?id=86

    Comment by Southernbob | July 21, 2009

  26. Thanks again for your interest in POET's cellulosic ethanol process. We probably should have emphasized that we are still in our pilot stage of development. We have accomplished a lot, but have much more to solve. Having a pilot plant affords one the opportunity to explore and define aspects like energy balances, which we are continuing to develop. With regard to SamG's calculations — those are on target — first plants are likely to be much smaller — 25 million gallons per year and adjacent or integral to existing corn ethanol plants to take advantage of the existing farmer network and plant infrastructure. Bryan – we will run year round like our corn to ethanol plants and drawn down cob inventory on a regular basis. Southerbob – we are looking at corn fiber, which is a good substrate for cellulosic ethanol. Corn fiber compositionally is more complex with higher amounts of arabinose which current microorganisms find difficult to ferment to ethanol.

    Comment by Mark Stowers, POET | July 21, 2009

  27. There is no surplus biomass, on earth. That's the bottom line. And it really doesn't matter what the alchemical process is. If we just grant that the maximum efficient process to extract liquid energy from biomass is available, you are then left with the cruel reality: thin quantities of energy from the biomass, and, at scale one quickly realizes that there is no surplus biomass.One piece of this 5000 piece puzzle that I have learned, is that all the engineers at the biofuel companies want to keep the focus on the transformative process. Not actual market or real world application.It was a good piece (as always). I expect POET to go bankrupt like all the rest.

    Comment by www.gregor.us | July 23, 2009

  28. "There is no surplus biomass, on earth. That's the bottom line."Well, there is a surplus. (At least for now.) It's the millions of years of biomass that slowly accumulated and was transformed into oil, coal, and natural gas.The problem is we are using that "surplus" more rapidly than the natural– but slow–process of turning biomass into oil can replenish. In fact in only a little more than a 100 years or so, we will have used up millions of years worth of energy stored in that "surplus" biomass.

    Comment by Wendell Mercantile | July 27, 2009

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