Post by engineerpoet on Aug 21, 2019 1:15:38 GMT 9.5
Oxygen provides the oxidizer supply for what amounts to in-situ gasification. This was worked on with coal but apparently didn't work too well. Now that the emphasis is on H2 rather than heavier hydrocarbons it may be getting a new lease on life.
The YouTube video linked at GCC doesn't show anything about down-hole separation or carbon capture. Once that stuff is brought to the surface it's going to be far cheaper to dump the CO2 than put it back where it came from.
Oxygen provides the oxidizer supply for what amounts to in-situ gasification. This was worked on with coal but apparently didn't work too well.
In the 1970s the British (Coal Board?) performed a series of tests of underground gasification of coal. They used compressed air, trying to extract producer gas. That would have been H2, CO, N2. However what they were getting out was more than 90% N2, with variable proportions of other gases. The surprise was that more CH4 was coming out than H2 or CO. (There is such a reaction (the Sabatier reaction) but it requires a catalyst.) It seems that an oxidising atmosphere in the cavity was preferentially burning what little flammable gas emerged from the heated face of the wet coal, rather than forming a reducing atmosphere in the coal itself. As the burnt cavity collapsed, fractures travelling into the body of the coal released its associated methane. Of all the various oxidation and pyrolysis products, most dissolved in the pressurised water while only methane and a little hydrogen were flushed out by the nitrogen.
Resorting to injecting oxygen instead of air would produce a hotter, pyrolysing fire, and a richer gas extracted, but it would be leaving behind a criminal mess of nasty chemicals to leach out upwards into the groundwater and atmosphere. Not least of those would be the much greater mass of CO2 created than CH4 recovered.
Zarimba goes into corn ethanol as if it's the only possible biofuel. It's true that both the US and Europe use biofuels as ways to increase demand for grains and seed oils and support crop prices, but biofuels do not require foodstuffs and many crops generate large amounts of "residues" which are inedible to humans but still contain lots of fixed carbon. As I've covered from the work of Frank Shu, lignocellulose can be thermally cracked into solid carbon plus a gas rich in combustibles including hydrogen and methane. This hydrogen can be separated and used to make ammonia. The methane is usable as CNG (perhaps with added hydrogen to increase the flame speed) and carbon can be sequestered or used as fuel.
The amount of residues and other wastes comes to at least hundreds of millions of dry tons per year in the USA alone. If my numbers are right, that's more than enough to provide for the needs which cannot be served by electric power IF it is used properly. Unfortunately, every single scheme I've seen touted so far does it wrong. Almost like failure was the intent.
Post by engineerpoet on Sept 2, 2019 11:52:41 GMT 9.5
I suspect the problem is that almost everyone is trying to make ethanol to meet "biofuel" mandates, when methanol and dimethyl ether are much simpler and cheaper to make. Range Fuels had this exact problem; they started off making MeOH but had difficulty graduating to EtOH.
"Advanced biofuels 'not yet viable', industry study warns"
If photosynthesis could have provided more energy than coal, the Industrial Revolution would have started and continued in the large forested areas of Russia and Canada. Land that could sustainably grow biofuels could more profitably grow food for a hungry world.
The article is interesting in that it says that EU lawmakers say that crop based biofuels should be limited to a maximum of 7% of transport fuels. A maximum! These guys know what agricultural land should be used for.
However it does encourage "recycled carbon fuels". I only wish that it was referring to "recycled carbon" with the energy for hydrogenation supplied from a more sustainable noncarbon energy source.
How much better would that be if hydrogen cracking were used instead!
Carbon starts serious reactions with CO2 and water at around 900 C. You probably don't want to use straight hydrogen as you'd get mostly methane, and methane requires strong measures to turn it into anything heavier.
Agriculture efficiently polymerises carbon
Not all that efficiently; IIUC it's in the single digits.
My point is that nuclear is far more efficient than photosynthesis at producing chemical energy (in the form of H2), but the polymerisation of carbon atoms (as cellulose and lignin to convert into hydrocarbon fuels) is more efficiently done by photosynthesis.
We are talking here about thermal/hydrogen cracking of an existing polymer – lignocellulose which is just dried vegetation. Roughly speaking, lignin and cellulose are polymers of [HCOH], so the first interaction with hydrogen is to replace some of the OH with H. However some of the oxygens are links in the polymer chain (Wikipedia says that cellulose is a polymer of [C6H10O5], linked by one of the oxygens). With rising temperature, that link begins to break open: R-O-R' -> RH + R'OH.
Perhaps a chemist visitor to this site could advise us all how much oxygen we could replace with hydrogen, and how the length of the fragments could be controlled. But as far as I can see, given copious hydrogen, the production of liquid hydrocarbon fuels from biomass and hydrogen would be a fairly routine matter for modern fuel refineries.
However some of the oxygens are links in the polymer chain (Wikipedia says that cellulose is a polymer of [C6H10O5], linked by one of the oxygens). With rising temperature, that link begins to break open: R-O-R' -> RH + R'OH.
Lignin is much more difficult to break apart, and it is resistant to enzymes as well. However, sufficient heat will crack lignin too.
Perhaps a chemist visitor to this site could advise us all how much oxygen we could replace
How about "all of it"? That's what Fischer-Tropsch synthesis does: it uses hydrogen to de-oxygenate carbon monoxide and create hydrocarbon chains.
F-T is energy inefficient (turns a lot of chemical energy into waste heat) and doesn't make the best use of the limited carbon either. From what I've calculated, the best room-temperature liquid we can make is methanol. It not only retains more of the chemical energy of syngas than any other liquid we could make, it can be cracked back to syngas using engine waste heat and the added chemical energy recycled straight back to the fuel supply. If it wasn't toxic we would be using it for darn near everything. Blasted alcohol dehydrogenase.
Er, now let me get this straight. You know a much, much better way to convert biomass into multi-carbon molecules for liquid fuels.
I know a better way to convert biomass to syngas (and I need to get back to work on my patent application). What you do with it is up to you.
However, the best you can achieve is C1H3OH ?
Go ahead, work the numbers yourself. You can always throw extra hydrogen at something, but you're not going to get any more energy in your product than is inherent in the molecule and you have to go up to C5 hydrocarbons before you get room-temperature liquids. Further, if you're limited by the amount of carbon you can get, you want to optimize energy per mol carbon rather than any other number.
Heat of combustion of pentane is 3509 kJ/mol; heat of combustion of MeOH is 726 kJ/mol (source). The MeOH yields more energy per carbon atom. IIUC MeOH is also more efficient in a piston engine because its flame speed is higher so it turns more of its heat of combustion into work.
Post by Roger Clifton on Sept 3, 2019 23:43:40 GMT 9.5
Aircraft don't carry so-many moles of fuel, they carry so-many kilograms of fuel. In joules per kilogram, pentane trumps methanol by a mile. Clearly, aircraft do need liquid fuel made up of multi-carbon molecules. That's liquid, not syngas.
EP, your commenting is mischievous. I think your intention in giving smart-ass answers is to provoke angry replies with incomplete science, so that you can make merry with someone who had taken you seriously.
Aircraft don't carry so-many moles of fuel, they carry so-many kilograms of fuel.
Aircraft are a special case, and some are volume-limited rather than weight-limited (think cruise missiles). There are special carbon-dense hydrocarbon mixes just for them. So yes, for those you would make hydrocarbons.
In joules per kilogram, pentane trumps methanol by a mile. Clearly, aircraft do need liquid fuel made up of multi-carbon molecules.
Not deliberately so. I have to be close-mouthed about my IP until the applications are filed, and some things that I take for granted are not known to others. I can't tell what those things are until the discussion stumbles over them. Would you have me expound about everything I've learned all the time? Totally impractical as well as boring.
In this windy piece we learn that according to the Rocky Mountain Institute it is now less expensive to use wind, solar and unspecified storage than to build and operate a new CCGT. Further, the projection is that the so-called renewables option will be priced below existing natural gas equipment.
I don't agree with some points. For example, pumped hydro schemes are hard to come by. For another, nuclear power plants have several virtues and more should be built. Nonetheless, a decent summary.
I beg to differ. The author is quite deliberately wrong about a number of things. To wit:
Overbuild renewable generation
Since the scalable "renewables" are massively unreliable, no feasible overbuild is going to get rid of periods of shortage. Unless combined with massive amounts of storage (far in excess of the 20 TWh of vehicle batteries he postulates) this is mostly going to increase spillage.
Build a fair amount of hydro storage
PHS is wasteful of real estate and requires particular geography. The author's prescription for existing dams shows that he is ignorant; most dams are already operated as peaking plants, with quite low capacity factors. There are also minimum and maximum flow requirements imposed by ecological considerations.
Shut down coal and gas generation aggressively
The gas-rich USA is already doing this for coal, but the addition of more and more unreliables means a locked-in demand for natural gas.
Mechanical carbon capture and sequestration is a mostly dead end
The debut of the Allam cycle power plant will change this, and good thing because we'll need it for biomass capture of carbon with sequestration.
Nuclear power is too slow to build and too expensive
That's because people like him have made it so.
The author's deliberately wrong prescription shows that he is part of the "false fire brigade" which claims to be putting out the fire but instead lets it burn. Given that he's writing for Cleantechnica, which is a front for the gas industry, this should be no surprise.
I'll just mention 3 localities that I know something about; ones with significant natural gas usage in generating electricity. The first is South Australia. Despite the interties to Victoria, South Australia is on its own in keeping the air conditioners running. There is enough wind power and solar power for ordinary days. But on the hottest days the wind turbines do not contribute much; South Australia turns to its natural gas and even diesel generators. On two days last summer running this equipment cost the South Australians about Au$430 per person per day for electricity.
The second is ERCOT Texas where natural gas is embarrassing plentiful. So naturally the wind turbines are backed up, megawatt by megawatt with natural gas generators. This past summer the wholesale price of electricity was frequently over $2000/MWh and went to the limit of $9000/MWh. While the wholesale price is usually quite low it is enough so that the nuclear power plants can compete in that energy only market.
The third is California. In northern California recently 3 CCGTs have been mothballed. In southern California LADPW is going to turn off and not replace 2 old CCGTs. There is a proposal to develop pumped hydro at Hoover Dam.