Pyrolysis is entirely endothermic - it requires applying heat to biomass. Pyrolysis yields a vapor that will combust in the presence of oxygen and release energy.
The energy released in the combustion of pyrolysis products can be used to drive further pyrolysis. A "Top Lit Updraft Gasifier" is a simple apparatus to achieve this.
Capturing the heat from pyrolysis in this way does however convert the pyrolysis vapor from hydrocarbon into combustion byproducts, namely C02. This company claims to be condensing all of these hydrocarbons, not combusting them.
For a nice and understandable example of pure pyrolysis without combustion, there is this project [0] wherein an airtight vessel is loaded with biomass, heat/energy is applied with electrical resistive heating elements. The pyrolysis occurs and the resulting vapors are captured and stored as a low pressure vapor for later use in cooking or powering internal combustion engine.