by Tanada » Fri 28 Mar 2014, 06:23:22
My younger brother worked for a while in a Gasification plant in Indiana. They didn't use an underground system, they put petcoke and hazardous chemical waste in a retort and broke them down by burning in pure oxygen, then fed the resulting Carbon Monoxide and Hydrogen through catalysts to make synthetic diesel fuel in a variation of the Haber-Bosch process. I suppose underground coal gasification would work the same way, average coal in America is 50-50 Carbon to Hydrogen chemically so burning it in Oxygen would give you Carbon Dioxide and Water Vapor for low temperatures and Carbon Monoxide mixed with Hydrogen gas for high temperatures. By controlling the Oxygen flow in and gas draw out the production well you could control the temperature of the burning. Injecting steam would be the same basic process many cities used to produce 'water gas' before 'natural gas' became so easily available.
Early last century many cities used the 'water gas' process where they would alternate blowing air through a combustion chamber of burning coal/coke with blowing steam through the embers once the fire was hot enough. The air gasses would be routed to boil water to make the steam, then out exhaust stacks during the burning phase, and the output from the steam would be a mixture of Carbon Monoxide and Hydrogen gas that would be put through the city gas network. They had to cycle back and forth between the two phases because breaking Water Vapor and Carbon down into Carbon Monoxide and Hydrogen is endothermic, it robs heat from the white hot coal/coke bed. By injecting pure oxygen along with the steam this is avoided and the process is continuous, but getting the oxygen to do this is an energy cost.
I used to think we would go back to using 'water gas' because natural gas supplies were shrinking in lock step with oil, but fracking and shale gas are a cheaper alternative so I no longer expect that to happen. A country like China that has a lot of uneconomic coal seams and not a lot of Natural Gas potential on the other hand might use underground gasification to produce ample 'water gas' to do all sorts of things, both as chemical feed stocks and as fuel.
I should be able to change a diaper, plan an invasion, butcher a hog, design a building, write, balance accounts, build a wall, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, pitch manure, program a computer, cook, fight efficiently, die gallantly. Specialization is for insects.