an apparatus , system , and method for subjecting biomass to pyrolysis to extract energy products using a pyrolysis unit comprising generally concentric chambers including a combustion chamber and at least one pyrolysis chamber . each chamber is in communication with an adjacent chamber such that a directed , generally - deoxygenated heated gas stream passes through the combustion chamber to each of the pyrolysis chambers in turn . additionally , each pair of adjacent chambers shares a heat - conducting wall , further promoting heat transfer throughout the unit . a heat source , which can be a burn enclosure configured as part of the pyrolysis unit , produces the heated gas stream . biomass introduced into the pyrolysis unit is pyrolysized by the gas stream , resulting in exhaust containing non - condensing gases , bio - oil vapor , and entrained char . the exhaust is directed from the pyrolysis unit to other parts of the system where the bio - oil and char can be separated from the exhaust and collected .