We would need an area of land more than twice the size of the U.K. to grow enough sugar-crops to replace our current demand for liquid petroleum fuels by bio-hydrogen, and hence the concept is utterly preposterous. As I stressed in a previous posting "The Hydrogen Economy - How Economic is it?" substituting hydrogen for hydrocarbons (oil) to fuel our nation's current transportation requirements is a task of such considerable magnitude that it probably will never be accomplished. I made my arguments in terms of the MW (Mega-Watt) generating capacity that would be required in simplistic terms of energy conversion, ignoring details of the losses that are inevitably incurred in converting one form of energy to another, an irrefutable consequence of the Second Law of Thermodynamics. When such losses are factored-in, the demand on generating supply becomes even worse than the 61 Sizewell B capacity reactors or the 180,000 2 MW wind turbines that would be needed, respectively, to produce sufficient hydrogen from the electrolysis of water to replace the equivalent of 54.2 million tonnes of oil that fuel internal combustion engines each year in the U.K. alone; 12 million tonnes of it being burnt by the aviation industry. In all likelihood, we would need nearer 120 new Sizewell B's or 360,000 2 MW turbines, allowing for a 50% loss: 70% loss in the electrolysis step and another 70% in the "combustion" of hydrogen in fuel cells, the overall conversion from "tank to wheel".
This leaves us with the question: are there any alternative - ideally sustainable, renewable - sources, that might generate the quantities of hydrogen required to meet this task? One potential source is "Bio-hydrogen", as made from fermenting sugar, and quite a sizeable number of academic research groups are drawing considerable research funding for projects that purport to develop methods that will lead to the production of hydrogen from renewable sources - essentially from the fermentation of sugar into hydrogen, CO2 and acetic acid (vinegar). This may be expressed by the shorthand equation:
C6H12O6 (glucose) --> 2C2H4O2 + 2CO2 + 4H2.
It is instantly apparent that one CO2 molecule is produced for every two hydrogen molecules (H2) and so, but it is assumed that the growth of next-year's sugar-crop will consume this amount of CO2 and, ignoring the additional CO2 emissions produced from its cultivation/harvesting/processing etc., the process may be thought of as "carbon neutral", to coin a phrase. Crop cultivation to make "biofuels" is not neutral in fact, but is thought to consume about 20-40% of the total CO2 produced in production/combustion of the fuel. Notwithstanding, if the glucose is formed from fermenting crops that are grown on our own shores, there remains the appeal of security of supply. The overriding criteria, however, are exactly how much hydrogen would we need to produce and what level of resource - arable land, fermentation vessels etc. - might this mean. I will concentrate on the basic aspect of hydrogen production, in the form of a simple calculation. In the following, a term such as 10*6 means "ten raised to the power six", i.e. one million; put another way, it is the number one written with six noughts after it.
The U.K. uses 54 million tonnes of oil to supply its transportation = 54 x 10*6 x 42 x 10*9 = 2.268 x 10*18 Joules of energy.
The heat of combustion of hydrogen = 285.83 kJ/mole, and so we would require 7.93 x 10*12 moles of H2 = 1.78 x 10*14 litres of H2 = 1.78 x 10*11 m*3 (cubic metres) of H2.
Assuming 100% efficiency, by the conversion of glucose according to the reaction:
C6H12O6 + 2H2O --> 2C2H4O2 + 2CO2 + 4H2, 0.5 m*3 of H2 would be produced per Kg of sugar. However, the process becomes thermodynamically less favourable as the H2 concentration increases, which must therefore be continuously flushed from the digester.
The process is not so simple, in fact, and the following reaction also occurs:
C6H12O6 --> C4H8O2 (butyric acid) + 2CO2 = 2H2, which is clearly less effective in terms of its hydrogen yield. It is also far worse in terms of CO2 production (now four times that produced from natural gas reforming). Experimentally, it is found that the latter reaction competes with the ideal one to the extent of about 3:1 and a maximum yield of 0.18 m*3 of H2 is obtained per Kg of sugar, not 0.5 m*3. It may be deduced that overall, the process is occurring with 60% efficiency.
Now, back to the scale of H2 production. As noted, we need to make 1.78 x 10*11 m*3 of it, which according to the above, would require 9.88 x 10*8 tonnes of sugar. Under favourable circumstances, it is possible to produce 19.1 tonnes of sugar (sucrose; I am assuming that this can be converted quantitatively to glucose) and so the cultivation would demand 51,727,749 hectares, or about 520,000 km*2. This is just for the U.K., and is in fact just over twice the entire land area of mainland Britain, to grow it.
Just for fun, let's work out what the total digester volume would be. To ferment 1 Kg of glucose requires 154 litres (about 34 gallons), given typical concentrations under which the process is most efficient. So, we need 154 x 9.88 x 10*11 Kg = 1.52 x 10*14 litres = 1.52 x 10*11 m*3 = 152 cubic kilometers. This would have to be fresh-water, so it couldn't simply be withdrawn from the sea. I note that the entire volume of fresh water available in the U.K. is reckoned to be 2,465 m*3 per person per year, which for a population of 60 million, amounts to 148 km*3, and so even if we used the nation's entire supply of freshwater for this purpose alone, we still couldn't entirely fill our bio-hydrogen fermenting digesters.
There would also be lake-sized quantities of butyric acid (essence of sweat) and acetic acid (raw vinegar acid) to cope with, around 300 million tonnes and 120 million tonnes of each, respectively, which is more than enough to fill Lake Windermere... and all this would have to be done each and every year for the U.K. alone. It just doesn't add-up, and neither do many other putative technologies to replace the world's declining oil supply, as we shall see in these postings.
I am updating this (16-12-07), as I am recently aware that the idea of biomass to liquids conversion is being taken seriously in Europe. In effect, plant material is converted to syngas (a mixture of H2 + CO), and then to liquid hydrocarbon fuels using Fischer-Tropsch catalysis, similar to that used for some forms of coal-liquefaction. This is probably the only way that significant amounts of fuel from petroleum can be replaced. It also means that the hydrogen is used to make combustible liquid fuels and therefore we don't need the huge number of PEM fuel-cells that the "Hydrogen economy" as commonly referred to would require; a genuine problem since there is insufficient platinum available to make enough of them to run 600 million vehicles.
[There are other research-stage approaches to use enzymes to break-down lignocellulose from wood and other plant material into sugars that can be fermented into ethanol]. It is predicted that this will be functional on a wide-scale by 2020. We shall see, but just using sugar and fermentation looks like a nonstarter! I hope this does work, as the world will be pretty short of oil by then... at any reasonable price, that is!
Related Reading.
"Creating value from renewable materials. A strategy for non-food crops and uses. Two year report." Defra, November 2006.
11 comments:
what about the metabolic engineering of certain stains already able to ferment sugars to produce hydrogen? ie if the stoichiometric production is incresed per mol of glucose (or other carbon source cinsumed) Also why are people giving pletny of money towards biohydrogen projects when Im sure others as bright as yourself would have come to the same conclusions from energy calculations? or maybe you are the first person in the world to give your hypothesis?
"Strains" to improve hydrogen yields? O.k. but even if you got twice as much, it changes nothing in terms of the overall chances of replacing gasoline for H2!
Why is it being funded - and H2 generally for that matter? Good question. Perhaps some of the reason in academic careers, research grants - let's face it any excuse will do to "get a grant"!
You'd better ask those other "clever people" hadn't you?
No, I'm not the first person to show calculations that fail to support the "hydrogen economy". There are loads of web pages about the subject.
The essential difference seems to be that "dissenters" show numbers and "supporters" don't. In my opinion we are not going to replace oil with hydrogen, and that means people having to give-up their cars because petrol will be too expensive as the oil runs-short.
Nobody much thinks that the fossil fuel era is on the way out, and there is really no way to replace that huge amount of oil used, and certainly not within the next 10 years by when oil supplies will be down to probably 85% of current world production.
The most optimistic technologies (which still need to become fully developed) appear to be making biodiesel from algae, possible cellulosic ethanol (or butanol?) routes, or old fashioned coal-liquefaction. Not hydrogen. But still, matching the amount of oil used will be an enormous undertaking.
I wish it were otherwise.
Oh dear, it's always a shame when someone who doesn't know what he's talking about gets involved. It's not really worth the effort in dismantling all the apparently ever well thought through calculations, but just a couple of decimations will do: 1kg of glucose in 154 litres? err don't think so, more like 15.4 litres? Are not acetate and butyrate useful chemicals? An idiot would form a lake with them, more sensible people would use them for feedstocks for other processes - Hold on a minute, they can be used to fed further fermentations to yield more hydrogen. How much I hear you ask, well I think you can increase the four moles to 12!
Hello "Anonymous"!
Yes it is shameful when someone who doesn't know what he's talking about speaks up! So hello again.
Do criticise my calculations if you wish (or can?). Even if I am "out" by a factor of ten (BTW look at the Research literature for concentrations etc. which is where my "volume" value comes from), the amount of water needed to fill these as yet un-engineered reactors is stupendous (as indeed is the engineering itself), in order to match, by hydrogen, the energy equivalent of the petroleum that we currently use and is running-out. It's as simple as that.
However, concentrations change nothing about the "lake-full" of butyric and acetic acid that will be produced. Yes there is research-stage work that shows hydrogen can be extracted from these materials, but nothing as yet on an industrial scale. All such processes - fermentation or thermal - produce methane and CO2 as well, which would be a further issue to contend with.
In any case, the "sugar" value is not sweetened either: irrespective of concentration, to match our current fuel quantity we still need to grow the amount that I indicate, and that is far more than the area of arable land in the country. Do you not get the point?
I am a trained chemist and what other calculations would you have me provide than "apparently ever so well thought through" ones...?
I have also worked-out the energy value of those by-products of acetic and butyric acid, which you will find in a posting made shortly after the article of our present discussion.
Also, I have handled acetic acid, butyric acid and hydrogen and they are not nice materials... believe me. We would not want an economy based around them.
BTW you're not an academic getting research funding for this are you?
Who are you, exactly, Mr/Dr (even "Professor" at one of the "new" universities?) Anonymous?
If you wish for a serious discussion about this or any other subject you are welcome to contact me, but spare me your sarcasm.
Hi, have you ever heard of the following three things:
1. gasification?
2. carbon capture and sequestration?
3. biomass trade in tankers and bulk carriers which is very efficient.
You can read a good introduction to the efficiency of biohydrogen production here:
http://www.bio-wasserstoff.de/pdf/Brussels2007_slides.pdf
You can then also read about why bio-hydrogen is both the most efficient and cleantest of over 25 hydrogen production pathways, here:
http://ies.jrc.cec.eu.int/wtw.html
You can produce biohydrogen very efficiently from gasified wood (or any type of biomass for that matter; imported if necessary).
You then obtain H2 with the lowest emissions of more than 25 production pathways and the highest energy balance.
You can go even further and sequester the CO2 under ground. The result is decarbonized energy, also known as carbon negative biohydrogen which delivers 'negative emissions' energy.
That is, when you use this energy, you actually take CO2 out of the atmosphere. You are not carbon neutral like renewables (solar, wind, etc....) which merely prevent new emissions. No, instead you clean up the atmosphere, which other renewables can't.
Anyway, you still have quite a lot to study. That much is clear.
Hi Johnny!
Do see my response on the other article re. biohydrogen that you passed-by.
It's all wonderful... all that you say, but do you really think we can put a completely new system in place for sugar production (which would involve turning over much of the world's agriculture for that purpose), handling and distributing the hydrogen, making the fuel cells without platinum to convert 600 million vehicles to run on it and so on?
And by the way, what sources of energy do we use to power all of this? Oil, gas, coal?
I am emphasising scale here. Do you simply not understand just how much oil the world gets through and what would be accordingly involved in substituting all that is underpinned by it, using hydrogen?
If this were a serious proposition, why didn't we do it 30 years ago when OPEC artificially hiked-up the price of oil? The reason was that cheap oil came back onto the markets thus removing the incentive to find alternatives. In certain respects it is a shame that we weren't forced to find them then, as we now face a geological problem regarding oil supplies, rather than a relatively simple political issue.
However, in view of the engineering problems involved on such a massive scale, I doubt that hydrogen would have been the answer. The most promising idea I have come across is to grow algae to make diesel and use this as a conventional liquid fuel.
Any thoughts on that?
If my critic is right and we can simply buy all that sugar in from elsewhere, how much arable land would it take to grow enough sugar to run the world's transportation on biohydrogen made from it? Roughly 30% of the Earth's surface is land and around one tenth of that is arable. This makes a grand total of 14.9 million square kilometres. We may deduce that to grow sufficient sugar from cane or beet would require 34.4 million km^2 of arable land to substitute for the entire world's oil requirement to fuel transport (clearly not feasible) and more than half of it, or 8.8 million km^2 just to keep the U.S. mobile. Unfeasible though these numbers are per se, they must be further regarded against recent estimates that the Earth can only support about 3 billion people, or half the present human population, in the absence of fertilizers etc. and a system of modern agriculture based on oil and natural gas. It should be noted too, that this population is predicted to rise to around 9 billion by 2050, but how can it, when many producing wells of oil and gas will be running out by then?
You need to get out more mate and get a life. Its amazing how you have sourced all of that data. Maybe you need to go and find yourself and girlfriend or soemthing?
You're not dealing with an amateur here, "mate". Look me up on the web. My knowledge derives from my former profession as a research scientist. Now I am a writer and a businessman.
A girlfriend? I think my wife might object to that! What about your own sad, uninformed little life. You probably won't have a job when the oil runs out or welfare payments ... oh and all those credit card debts!
It's notable that there has been no serious scientific criticism of this article. Just carping and "I don't like what you say", but no contradicting numbers or facts. This speaks volumes about the likelihood of a "hydrogen economy" happening before oil begins to run out.
I have read through your blogs Chris and they are very interesting indeed. Though a question that I must ask is that do you ever get anything incorrect? Is there any form of biofuel technology that you do champion or see the potential use of?
I think you should be a government advisor with the breadth of knowledge you have.
Hi!
I have a reasonable and broad background in science and I try to answer some of these questions from first principles. Am I ever incorrect? Well, that's why I show my workings, to give the reader the chance to point out anything that's wrong.
In this article, I am mainly emphasising the sheer question of scale in the quantity of liquid fuel the world uses: 84 million barrels a day or 30 billion barrels a year, of crude oil.
Before I started writing this blog, I hadn't really understood this, and I think most people don't and when it is pointed out some simply fall into denial.
I find some of the conclusions that have materialised from my musings pretty uncomfortable and I think there are difficult times ahead although I don't subscribe to the idea of some kind of immediate return to the "stone age".
Neither do I think that many proposed technologies can be brought-in fast enough, or on a sufficient scale, to replace oil as its supplies begin to wane (within 10 years certainly).
On the basis of the amount of fuel that might in principle be generated per hectare, growing algae to make diesel seems the most promising, although this is an untested technology on the grand scale, as are most others.
I like the idea of biomass to liquids but there are many technical difficulties here too. I attended a meeting in Oxford a while back where a speaker reckoned we could expect commercial BTL by 2020. However, this is not certain, but what is almost indisputable is that world crude oil production will have fallen considerably by then.
If BTL is possible, it means that the present contest between growing crops for food production or for fuel production is avoided, as it must be to feed a rising global population. The difficulty in feeding the latter number as fossil resources dwindle is the most uncomfortable aspect I have found yet.
In the end, this is just my view, but as I say, I do try to base it on hard numbers, rather than being bamboozled by hydrogen-salesmen and taking what is written on websites written by people with vested interests as gospel!
Chris.
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