System and process for refining lignocellulosic biomass material

A system (1) for refining lignocellulosic biomass material (A) comprising a presteaming bin (2)， a dewatering device (3)， a preheater (4)， a defibrator (9) comprising at least one refining zone (14) wherein steam is generated during refining of said biomass material so that a pressure peak occurs， a blow pipe (19)， and a first steam flow path (D) arranged to convey steam from said refining zone to said presteaming bin (2). The system further comprises a second steam flow path (E) arranged to convey steam from said refining zone to said presteaming bin， wherein said first and second steam flow paths are connected to the refining zone on opposite sides of the pressure peak in a biomass material transport direction， and wherein said first and second steam flow paths are separate from said blow pipe. The invention also relates to a process for refining lignocellulosic biomass material.