The temperature in this stage is 280-400 ℃. In this stage, the wood material accelerates pyrolysis and generates a large number of decomposition products. The produced liquid product contains a large amount of acetic acid, methanol, and wood tar. The carbon dioxide content in the produced gas product gradually decreases, while the flammable gases such as methane and ethylene gradually increase.
This stage emits a lot of reaction heat, so it is also called the exothermic reaction stage.