Vapors from the digester contain turpentine and 85% of it is released during the relief cycle. Recovery of this volatile organic compound (VOC) is undertaken for environmental reasons, to lessen effluent treatment of condensate, to utilize turpentine as a fuel source, or to sell it as a by-product to chemical processors.
Two vessels in a typical recovery system require level control of the turpentine/ water interface: the decanter, or separator, and the storage tank. The National Fire Protection Association (NFPA) rates turpentine as a "severe fire hazard." For this reason, the decanter is contained in a dyked area, storage tanks are sometimes located below ground, and controls must be rated explosion-proof.