Hmmm, this makes me wonder how much of the carbon petrified wood retains and if there isn't some method where the process might be accelerated (without a lot of energy input, a quick google shows you can do it rapidly using a heated chamber but that's going to be counterproductive and require an absurd amount of energy).

Although, maybe you could use concentrated solar or even geothermal for the heating part. Hell, you could probably make it profitable selling the petrified wood for use in construction (mantles, counter tops, tile). If it retains a decent amount of the carbon.