NOVELTY - Discharge device for discharging pretreated biomass from higher to lower pressure, the discharge device in the orientation intended for use, comprises a vessel having an opening to a high pressure region at the top, and configured to be connected with a pressurized biomass pretreatment device; one or more inlet openings situated along the sides of the vessels through which water or liquid may be added; and an orifice or valve at a lower part of the vessel, the orifice or valve being configured to eject pretreated biomass, optionally into a pipeline.    USE - The device or apparatus is useful for transferring a pretreated biomass from higher to lower pressures or for discharging biomass from higher to lower pressure; for suppressing loss of C5-saccharides, such as xylan species, from biomass into an aqueous phase during the transfer; for suppressing formation and transfer of furfural into the liquid phase; and for limiting adverse effects of deposition of re-solidified lignin (all claimed).    ADVANTAGE - The significantly reduced concentration of furfural in the liquid traces of the fibrous lignocellulosic biomass implies a highly beneficial effect in terms of improved yields of target fermentation substances in downstream further processing of the biomass. By including a mechanical agitation unit, the problems associated with such clogging are eliminated because the mechanical agitation unit will upon impact with such lumps comminute these lumps to smaller particles having sizes which do not pose a problem in relation to clogging. By providing the drive unit, such as an electric motor, outside the interior of the vessel, any maintenance may be easily performed. Further, as the drive unit may constitute delicate equipment, more protection to this equipment is provided outside the vessel, compared to inside the vessel. Sealing provides sufficient separation between the interior and the exterior of the vessel. As the biomass intended for processing with the device may be very viscous and comprises elongated material such as straws and the like which may be intertwined, the vessel allows the biomass to enter the interior in a safe and efficient way without any risk of obstructing the opening at the top. The free falling of the biomass between each cylinder of the hydrothermal pretreatment reactor provides for mixing the biomass and thus a better heat transfer and a more homogeneous heating.    DETAILED DESCRIPTION - Discharge device for discharging pretreated biomass from higher to lower pressure, the discharge device in the orientation intended for use, comprises a vessel having an opening to a high pressure region at the top, and configured to be connected with a pressurized biomass pretreatment device; one or more inlet openings situated along the sides of the vessels through which water or liquid may be added; and an orifice or valve at a lower part of the vessel, the orifice or valve being configured to eject pretreated biomass, optionally into a pipeline. The discharge device also comprises mechanical agitation unit comprising an agitation element arranged in the interior of the vessel at a lower part of the vessel, and being configured to provide agitation of a content of the vessel, where the agitation unit being adapted to withstand a pressure in the interior of a the vessel of 10 bar or more. INDEPENDENT CLAIMS are included for:    (1) an apparatus comprising the discharge device in combination with a hydrothermal pretreatment reactor; where the hydrothermal pretreatment reactor comprising a cylinder being essentially horizontally arranged and having an inlet for biomass at a first axial end and an outlet for biomass at a second axial end, opposite to the first end; where the cylinder comprises in its interior a rotatable auger screw, the auger screw being configured for conveyance of biomass from the first axial end to the second axial end; where the cylinder furthermore comprises one or more inlets for steam and/or water; where the outlet for hydrothermally pretreated biomass at a second axial end of the cylinder being connected to the opening arranged at the top of the vessel of the discharge device; and    (2) a method for discharging biomass from higher to lower pressure which involves: (i) loading pretreated biomass originating from a higher pressure environment into an upper end of a vessel so as to obtain in the vessel a lower aqueous slurry comprising biomass and an upper gaseous fraction; (ii) performing a mechanical agitation of the aqueous slurry in the lower part of the vessel by unit of a mechanical agitation element arranged in the interior of the vessel; (iii) supplying a stream of aqueous liquid into the vessel; and (iv) unloading aqueous slurry comprising pretreated biomass from a lower part of the vessel.