NOVELTY - The apparatus has a loading device situated within a loading chamber (1). An L-shaped sluice chamber (3) has an upper vertical component (3a) and a lower component (3b) in communication with loading chamber and vertical reactor inlet (6) respectively. A sluice inlet piston valve (5a) axially displaced across vertical component, seals opening from loading chamber into vertical component. A sluice outlet piston valve (5b) axially displaced across vertical reactor inlet or outlet, seals opening from lower component into reactor inlet.    USE - Apparatus for loading particulate matter such as biomass feedstock into pressurized reactor for producing bioethanol in pulp and paper industry.    ADVANTAGE - The sluice chamber has a horizontal unloading segment fitted with an additional device for force-unloading to provide resistance to sudden pressure changes so that the operational safety is increased and a safety chimney is ensured. The compression of biomass by the loading and unloading device creates low-density plugs that effectively seal against pressures intermediate between atmospheric and reactor pressure. The loading device, unloading device and the piston valves are actuated by hydraulic cylinders, reliable and readily scalable to large sizes. The electric driven actuators have improved energy efficiency and simple structure. The actuators are self-locking so that the safety related to the hydraulic cylinders is improved. Since the sluice chamber can be loaded or unloaded at bar difference pressure, the pump cycle time is reduced and the throughput efficiency is improved.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) method for loading biomass feedstock into pressurized reactor;    (2) apparatus for removing pretreated biomass hydrothermal reactor; and    (3) method for removing pretreated biomass hydrothermal reactor.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the apparatus for loading particulate matter.    Loading chamber (1)    L-shaped sluice chamber (3)    Vertical component (3a)    Lower component (3b)    Sluice inlet piston valve (5a)    Sluice outlet piston valve (5b)    Vertical reactor inlet (6)