A great many hours? Days? I've had a small 1lb tank I've used for odd jobs (plumbing, lighting the woodstove, weed-torch, and yes, incinerating a chip or two) for literally years, and it doesn't seem like I've even used a measurable amount of fuel (consider that you can run a gas grill nonstop for a few hours on one cylinder).
That said, I noticed two things about trying to do chips with a torch...
Small RAM chips work great - The torch makes enough heat and a big enough flame that they flare up quickly, all the nasty fumes they make get burned away, and you have no cloud of toxic fumes hovering around you for hours. Trying to do a large chip like a northbridge, however - That gets ugly. The torch can't quite heat enough of it at a time, so the parts you don't have the flame on will spew fumes (I don't know about you, but it seems like once I get the smell of burning chip on me, I can't get rid of it no matter what I do).
More importantly, I think the Patnor process necessarily takes time, not just heat. With the RAM chip I did, I kept it cherry for about five minutes, flipped it over, and did another 3 or so minutes on that side. It looked beautiful, a nice uniform white ash. Then I crushed it, and although it did crush pretty easily, I found that only the outer half millimeter or so had turned to ash. The inside remained thoroughly black and fairly resilient.
I'll stick with the patient roasting on a campfire, thanks - At the very least, for the pyrolysis phase (the incineration phase doesn't outgas, so less of a problem). :wink: