NOVELTY - The method (200) involves introducing biomass to a reactor feed chamber (202). A low oxygen gas is made to flow into the reactor feed chamber to purge the reactor feed chamber and biomass of oxygen. The purged biomass is delivered to a reactor (206). The biomass is thermally converted in the reactor. The low oxygen gas i.e. inert gas, is supplied. The biomass producing vapor and char is thermally converted (208). The vapor is separated from the char and heat transfer medium. The char in a combustion unit is combusted and the low oxygen gas is formed.    USE - Method for thermally converting biomass. Uses include but are not limited to an ignin, plant part, fruit, vegetable, plant processing waste, wood chip, chaff, grain, grass and corn.    ADVANTAGE - The method enables improving thermal conversion of biomass under conditions in which oxygen levels are controlled at selected levels. The method enables eliminating or inhibiting the introduction of oxygen through the biomass inlet, instrument purge inlets and/or heat transfer medium inlet through the use of oxygen-free or low oxygen purge gases. The method enables allowing each instrument inlet to be in communication with a purge gas header via a purge line, so that the purge gas can be made to flow through the purge line and instrument inlets and into or over the instruments to dislodge any heat transfer medium or char or prevent lodging of any heat transfer medium or char, and maintain proper instrument operation. The method enables efficiently converting biomass into pyrolysis oil with minimized loss in the yield of pyrolysis oil.    DETAILED DESCRIPTION - The low oxygen gas includes carbon oxides and nitrogen. An INDEPENDENT CLAIM is also included for an apparatus for thermally converting biomass.    DESCRIPTION OF DRAWING(S) - The drawing shows a flowchart of a method for thermally converting biomass that includes purging the biomass feed with an oxygen-free or low oxygen gas.    Method for thermally converting biomass (200)    Step for introducing biomass to reactor feed chamber (202)    Step for purging biomass with low oxygen gas (204)    Step for delivering purged biomass to reactor (206)    Step for thermally converting biomass producing vapor and char (208)