If you have kept up with the conversation – which has continued following the initial post – you will see exactly what my issues are. First, you can’t make any sort of reasonable plant estimate based on lab scale experiments. You are probably aware of this. You can’t reasonably extrapolate mass and energy balances from a few hundred gallons a year in a lab (their current pilot scale) to a hundred million gallons a year.

Regarding the selectivity issues, most (alcohol) gasification processes do result in mixed alcohols (or at least have significant by-products). Coskata indicated to me – and I reported it in my followup – that their microbes produce no byproduct alcohols. This was your only legitimate criticism, but I had already reported that in my follow-up. This will simplify the purification step, but they also indicated that the alcohol coming off the fermenter is at 3 or 4% ethanol. If you have access to HYSYS, run a separation at that level of ethanol and see how much net energy is lost due to the BTUs required for removing water.

To conclude, I actually hope they deliver on their claims. For that matter, I would help them in any way that I could. I have long been on the record that I think gasification is the future. I just see some areas that warrant a good investigation.

RR

Thanks for the response. First, thanks for catching my typo: instead of $356 per daily barrel, I meant $356k per daily barrel. The discrepancy between this number and the chart on your blog post, like I mentioned, was about twofold.

Second, I fail to see how your caveat that the “graphic is for full-sized plants” explains away my objection on your use of the $9.6 million number.

Third, your comparison of “pilot to pilot” is still not a fair comparison. The GTL pilot plant you mentioned was 400 bbl/d of capacity. The Coskata pilot is only 2.6 bbl/d. See the equation in my earlier comment? If we use that to scale down the GTL pilot to 2.6 bbl/d in size, the cost per daily barrel of the hypothetical super-small GTL plant would be $1.4 million. That’s still much lower than Coskata’s pilot, but not nearly as low as your comparison would (mis)lead one to believe.

You seem to reject the idea that plant costs do not scale directly with capacity. Although I recognize that the 0.6 value for the scaling exponent is not universal, it is surely closer to the truth than the 1.0 you implicitly assume.

Fourth, you have not responded to my criticism of your claims about selectivity vs. methanol.

Further, I have to presume the Curt didn’t actually read the post, since he is confused about a quote and states that I didn’t note a huge inconsistency. Yet that post states “Caveats are that the graphic is for full-sized plants, and the numbers are a couple of years old.” So the very issue that Curt is complaining about was addressed in the post. Curt is taking exception to something that he has misinterpreted in one case and overlooked in another.

The issue in focus in the original post was how far out of the stratosphere the numbers were for their pilot plant – and I gave a specific example of another pilot plant (GTL). When comparing pilot to pilot, the numbers were $9.6 million to $188,000 – and the $188,000 plant didn’t go to commercialization because it was too expensive. It is known that the $9.6 million will fall as the process scales (Curt seems to believe this would be a revelation to me, despite the fact that I have actually been closely involved in the scale up of facilities), but the point was that they wouldn’t fall enough (based on the $25 million which Coskata now says includes things other than the plant) to be competitive.

So, I am left to conclude that Curt thought the quality was bad because of his misinterpretations of what I ‘really meant’ instead of what I actually wrote.

Cheers, RR

First: A well-known approximation to chemical engineers is that costs scale as the 0.6 power of the capacity.

In equation terms, where C is cost and P is capacity: (C_big / C_pilot) = (P_big / P_pilot)^0.6.

If we accept the 0.6 as gospel for a second, that would give a extrapolated cost for a 150 MMgal / yr plant of $356 per daily barrel, not $9.6 million. That’s still ~2x higher than EIA Annual Energy Outlook 2006’s estimate for biomass-to-liquids capital costs. I’m confused why R. Rapier would quote both the $9.6 million number and the EIA number in the SAME POST, without noting the huge inconsistency.

Second, the correlation is known to be inaccurate when making giant extrapolations. Our extrapolation here is indeed gigantic, by at least a factor of 3000 or so. A lot will depend on what the right value for the exponent turns out to be. For example, changing it from 0.6 to 0.55 reduces the capital cost by a third. Raising it to 0.65 makes the costs surge. But whatever the exponent might be, we know for sure that it won’t even be close to 1.0, which is what Rapier assumed.

Third: Rapier says: One final thing I would point out is that the selectivity of these processes generally favors methanol over ethanol. They may be able to push the selectivity toward ethanol, but they will almost certainly end up producing mixed alcohols that will have to undergo purification to ethanol.

This is ridiculous, as the selectivity for ethanol relative to methanol of the bacteria Coskata plans to use is virtually infinite. Bacterial metabolism is not the same as Fischer-Tropsch (no relation to me).