Zigong drillers solved wood shortage by burning gas from same wells

Unlike coastal salt makers who could rely on sun to evaporate seawater, Zigong's brine came from wells drilled far inland, so every drop had to be boiled off over a fire, and Sichuan's salt industry had been consuming wood at industrial scale for two thousand years by the time forests within reach of the wellheads began to run out. The obvious response was to economize on the fuel itself: spreading brine on tree branches in the sun to pre-concentrate it before boiling, and routing several boiling pans off a single chimney to reuse residual heat.

Drillers pushing their percussion wells deeper in search of richer brine had been striking pockets of flammable gas in the rock below the brine layer since at least the 16th century — at first a hazard to route around or vent off, since a well only a few hundred meters deep rarely produced enough of it to matter. It took centuries of incremental advances in bamboo-cable drilling technology before wells could reliably reach the 700-800 meter Triassic formation where gas and brine occurred together in commercially useful quantity.

Drilled deeper to hit gas, then used a Kang Pen drum to separate gas from brine in the same well, piping gas to boil brine, so fuel scaled with the resource it boiled.

Deeper wells hit gas-bearing rock, providing fuel at the source.

Kang Pen drum separated gas and brine from one well, avoiding extra wells.

Bamboo pipelines delivered gas directly to pans, cutting hauling costs.

Fuel supply scaled with brine output, so growth didn't worsen scarcity.

When an input gets scarce, check if your process already produces a byproduct that can replace it, then invest to capture it.

By 1821 natural gas fueled roughly a tenth of Zigong's evaporating pans, with the rest still burning wood or charcoal; by 1857 gas had overtaken wood as the more common fuel. Zigong grew into what became known as China's Salt Capital, with annual production around 150,000 tons by the 1850s; over the industry's full history it drilled an estimated 130,000 brine and gas wells and produced a cumulative 30 billion cubic meters of natural gas, transported through hundreds of kilometers of bamboo pipeline — some of it still in operation as late as the 1950s.