dollar a gallon gasoline

Demand for petroleum products is growing while existing fields are declining. If it is not already here, peak oil is not far off.

One way of engineering, especially for very large markets, is "design to cost."

What would it take to make dollar a gallon, possibly carbon neutral, synthetic gasoline?

Why gasoline?

Hydrogen and gasoline can be thought of as energy storage media, like batteries but much higher performance. In the case of current gasoline the energy was stored in the hydrocarbons a long time ago. Unlike batteries, most of the reacting chemical (oxygen) comes from the air.

Hydrogen is widely considered a future fuel. It has serious drawback in that it either has to be stored liquid or under high pressure, or absorbed as in hydrides. All of these are low density.

The hydrocarbons that make up gasoline, diesel, jet fuel, etc. are energy dense liquids at normal temperatures and pressures. There is a vast technology base and infrastructure behind them.

As we run out of hydrocarbons (peak oil) some other primary energy source will have to replace oil. But if we have such an energy source, we can make hydrocarbons. All it takes is vast amounts of low cost energy.

Making synthetic hydrocarbons

Sasol's Fischer-Tropsch processes provides [1] two ways to do this. It costs a few dollars a barrel if you have low cost syngas. Syngas is carbon monoxide and hydrogen.

Old landfills could be mined for the carbon and fed into plasma gasifiers to make syngas. [2] More carbon could come from coal, biomass or even separating CO2 from air and reducing it to carbon monoxide with hydrogen. The water gas reaction, H2O + C--> H2 + CO makes syngas. It's endothermic at 131 kj/mol, about 11 kj/g or 11 mj/kg. A kWh is 3.6 mj so the reaction uses 3 kWh/kg of carbon or 3 MWh/t.

Idled coal fired power plants could be rebuilt as coal to oil syngas plants and the resultant synthetic oil pumped into the nearest crude oil pipeline or the sysgas could be pumped into a re purposed gas pipeline (the hydrogen content makes this a bit questionable, but until displaced with natural gas in the 1950s, syngas with its carbon monoxide was used in homes.)

Fischer-Tropsch process needs twice that much H2, 2H2 + C0 --> (CH2)x + H2O. Making electrolytic hydrogen takes about 48 kWh/kg or 48 MWh/t. One sixth of a ton of hydrogen would take 8 MWh for a total of 11 MWh/t of input carbon. This would result in 14/12th of a ton of oil or about 9.4 MWh/t of oil. At a penny a kWh, a MWh is $10. So the energy feed would be $94/ton of oil or $16 per bbl. Processing 100 tons of carbon an hour, it would draw 1100 MW and produce 700 bbl/hour or 16,800 bbl/day

An alternative is C + H2 --> (CH2)x where a ton of carbon and 1/6th ton of H2 are reacted. This takes 8 MWh/t of carbon, 6.9 MWh/ton of oil, or $11.4 per bbl.

These are worse case numbers since coal has some hydrogen.

Cost

Coal ranges from $15/ton to $150/ton. Figured at $60/ton of carbon, synthetic oil would cost about $25/bbl for energy and carbon plus the capital charge for the synthetic oil plants.

Fischer-Tropsch process converts syngas to a mix of hydrocarbons. The most recent example at Qatar cost $30,000 per bbl/day (note 1) for a refinery being fed natural gas. A modified power plant heating coal electrically is less complicated and while it could turn out local diesel, it would probably just put the whole output into a crude oil pipeline. If the power plant conversion even cost $30,000/bbl/day the capital cost would under $10/bbl (ten year write off at $3000/year, 300+ days/year.) So before making a profit on the oil, this coal to oil converted power plant makes synthetic oil for $35 a barrel. Fed to existing refineries, the gasoline fraction from $35/bbl oil would be about a dollar a gallon.

This process has to clean out all the sulfur out before the syngas goes into the reactor or the sulphur poisons the catalyst. The plants don't produce any carbon dioxide at the plant, it's all released from trains, aircraft, ships, trucks, farming tractors and personal transport. Eventually the plants will have to make do with biomass (turning all the carbon into liquid fuels), take carbon from limestone or even pull C02 from the air.

(note 1) "Sasol's first international joint venture, a factory in Qatar that turns natural gas into liquid fuel, cost $1 billion, or about $30,000 per barrel of capacity. According to Sasol CEO Pat Davies, that's twice as much as a more conventional oil refinery costs. "

Coal ranges from $15/ton to $150/ton. Figured at $60/ton, synthetic oil would cost about $25/bbl for energy an materials plus the capital charge for the synthetic oil plants. At a capital charge of $10, a synthetic oil plant could cost up to $36,000 per barrel of capacity per day. (Ten year write off, ten dollars per day, 360 days/year.

If all 1.3 billion tons of coal per year the US burns were made into oil, the rate would about 120,000 t/hr of carbon or about 20 million barrels of synthetic oil per day, equal to consumption without considering domestic production. The conversion plants would draw 1300 GW. That's less 3 years of power sat production and twenty six 5 GW power sats and rectennas.

If you can buy penny a kWh electricity, then on an industrial scale you can expect to make dollar a gallon synthetic gasoline.

Electricity, even in industrial quantities, is at least five times too expensive for this and we want *renewable* which makes solar the energy source of choice. Can we get solar power into this price range?

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