Well I'm on a roll so why not. As explained to me recently, yes, absolutely
1 inlet well, 8 inch diameter, steel encased. Goes down 500metres through rock and non fractured overburden/ strata. Hits a coal seam - lets say its 12 metres thick, and it turns 90 degrees and runs for another 50 metres through the seam, then turns up and comes back up out of the ground, that is the outlet well. Same 8 inch pipe connected.
At the bottom they encase part of that in concrete I believe. Anyway, they drop a jiffy firelighter down to the bottom of the outlet well and the coal eventually ignites, speed of which depending on how damp it is I imagine. They then blow in air through the inlet well head to get the burn going heat it up and it is off to the races, self heating. Not burning but heating, like the BBQ beads do. It then burns backwards along the pipeline away from the outlet well pipe back towards the inlet downpipe, if that makes sense.
The coal releases Synthesis Gas* which comes out the outlet well. If they want more gas flow, they increase oxygen to get the burn harder and faster, and maintain pressure. Out comes the gas. I understand that the size each chasm eventually grows to about is about 25m x 12m x seam thickness. So small swimming pool size. They don't want it to be too big because it runs the risk of roof collapse.
So out of that comes x million cf of gas in a day. More oxygen and pressure = more gas, less = less gas.
Once that cavern has used all the coal and you have some ash left but otherwise a cavity, you stop the flow of oxygen and cap the well, maybe flush some water in, and it will burn out
Lets say for example their testing shows they can dial up and flow 3 million cf a day from one seam, if they want 30 million, they know they just need to run 10 inlet, outlet pipes - possible even through the same seam but ensure each are far enough apart so that the 2 cavities don't burn the pillars and walls between them to retain the roof structures.
Synth gas is the type of gas that is required to make fertiliser. It is not pipeline gas, they would need to do some conversion to make tis gas pipeline ready. Why they say they are likely to go fertiliser is because everyone else has to buy methane/pipeline gas at market prices, then spend $3 extra to turn it into syngas, and then make the fertiliser. I believe they get their syngas out of the ground for about $1
What I don't know but would like to, can the carbon they produce be bottled up top and then injected back into the cavity?
I have heard them say they have enough coal there for 30 years of constant flow. If they get a 2400pj Reserve that's suggesting they think they can produce 80 pj a year. Yes, I know. Soon enough people will have done some math on this
Anecdotal, DYOR, (sincerely) happy to be corrected
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