"gasoline more expensive."
I thought up something that could get your gas down to a dollar a gallon,
maybe less. Uses coal and a little electricity from solar.
Any big renewable project has to make some liquid hydrocarbon fuels,
they are just too useful. So I have watched synthetic fuel production
for a long time. Recently it dawned on me that intermittent renewable
energy might be useful.
H2O + C H2 + CO (H = +131 kJ/mol)
The water gas shift reaction would let you run up the hydrogen at the
expense of the CO. This would halve the carbon without substantially
changing the energy content of the gas, (Making diesel or gasoline
takes twice as much hydrogen as CO.)
https://en.wikipedia.org/wiki/...
The first reaction is endothermic, so heat must be continually added to
maintain the reaction. (Wikipedia)
Carbon is 12 gm/mol. 83 mol/kg and a kg would soak up 10900 kJ. A
metric ton of carbon evaporated in steam would need 10900000 kJ or
3.03 MW hours.
This would produce 1/6th of a ton of hydrogen with a combustion energy
content of 50 MWh=/ton, about 8.3 MWh. CO combustion is 10.1 MJ/kg. We
have 2800 kg or about 7.85 MWh. So we make about 16 MWh of gas from a
ton of coal and 3 MWh of renewable electric power. Most of the energy
in the gas is from the coal.
It’s an interesting way to use intermittent power though. From this
point, the gas can be stored for winter, burned in combustion turbines
or made into gasoline or diesel.
To solve the CO2 buildup we would still need to do air capture, but
that has to be done anyway.
From a data point on coal cost.
The cost of 16 MWh of gas is $20/ton of coal, 3 MWh of solar power
plus the capital cost of the plant. Since there is no storage
involved, I am going to assume a cost of 2 cents per kWh or $20/MWh
(that may be optimistic, but the cost of PV is close to 1 cent per kWh
in the Mideast). Thus a ton of vaporized coal would cost $80. Following
a ton of coal through the process, half of it would come out as CO2 increasing
the hydrogen. Half a ton of carbon and 1/6th of that in hydrogen would show
up in the product. At 7.3 bb/s per ton, 583 kg gives 4.25 bbl. The raw materials
and energy cost would $18.80/bbl or about 44 cents per gallon.
That leaves a lot of room for the capital cost of submerged arc gasifiers.
It's a method to bootstrap intermittent solar and coal into diesel fuel or gasoline.