We drill own to the geothermal water. I comes up as 270oC steam, with CO2 and SO2 in. We pass over the hot end of a Carnot heat pump, and heat the gas up to 380oC. We pass into a large, thermally insulated vessel, and we get the Sabatier reaction.
We take out the SO2 using a very weak alkaline – CO2 does not react with.
1 CO2+3H2Os->(CH4+2O2-E)+(He+O+E2) for once, not really interested in the Molecular Nuclear Fusion – except as a heat source.
So we lead out the CH4, He and O2 onto the cold end of the Carnot heat pump – where is dumps the heat. CH4 is a heavy gas, He and O2 light – so we separate them from the H2O and unreacted CO2 using semipermeable membranes.
So we get the gas mixture at 98oC. And we can't use iron – we have to use copper tubes. Until we get the CH2 and O2 separated. With welding, He is worth more than gold, weight for weight.
We pass the CH4 down a series of titanium honeycomb, and get out light fuel oil. A mixture of diesel and petrol. So we refine this carbo 0 gas: it takes as much CO2 out of the air to form, as it releases when burnt. Diesel C12H26, petrol C16H34
So no need for Fossil Fuels. An inexhaustible source of He – and even O2! Which itself has high commercial value. Texas can export oil to the world again. Who needs fracking?
When we vent the superheated water, we drive a small turbine – after we have passed through a Dyson dry cleaner – to remove the gold dust. Before the reactor vessel, we vent down to 1 atmosphere.