an indirect heat exchange relationship with volatile compound free u201c clean u201d liquid to heat the water above its boiling point or flash point to produce clean volatile compound free odor free steam the clean liquid is fed via line 21 it may typically be evaporator condensate demineralized water boiler feed water or clean enough water fraction the clean steam produced in the reboiler has substantially less noncondensable gases than steam produced by direct black liquor flashing the clean steam in line 2 is preferably used for pretreating wood chips with steam e g in the chip bin 10 when used to treat chips since the steam does not introduce volatile compounds to the presteaming process the load of the volatile compounds which must be collected and treated by a mill 39 s ncg system is reduced the flash vapor from the black liquor flash tank 15 contains volatile compounds such as sulfur compounds these compounds are passed to a foul condensate and to a concentrated noncondensable gas cncg stream which are generated in the reboiler the foul condensate is sent from the reboiler via line 19 to the evaporator plant where it is treated in a way known per se the cncg stream is led via line 20 to a condenser e g digester 5 a auxiliary condenser not shown the potential advantages of the system and method disclosed herein include a mill wide heat economy will improve as the dry solid.