Pre-pressing devices with self-cleaning screws are essential for thick, stiff materials that cannot be sucked in by themselves. To achieve a high volumetric efficiency, the material is kneaded in the hopper by screws, then mixed and pressed into conveying cylinders. This makes it possible to feed solid, earth-moist and visually almost dry materials into the feed pump. The KLEIN feed screws have been specially developed to introduce additional heat (up to 450 kW) into the biomass to conserve resources and protect the environment. This results in a high potential for energy savings.