Abstract: A process and an apparatus is disclosed for drying sludge or other materials, more specifically, sewage sludge, in which a mixture of base material and wet material is introduced to a drier and passing hot gas or hot air passed over the mixture. The process and apparatus by regulating the feed rate of the wet material (wet sludge) in relation to the exit temperature of the hot gas or hot air from the drier. In embodiments, the feed rate of material is adjusted to maintain a substantially constant temperature of the gas.

Abstract: A method of operating a milling installation to regulate the fineness of the milled product, in which the milled product emerges from the output side of a mill, e.g. a ball-type tube mill, and material to be milled is introduced at the opposite side of the mill. According to the invention, the mass output rate dm/dt or m of the product is continuously or discontinuously measured and this measurement is used to control the rate of mass output at the output side of the mill so that the output rate is held substantially constant. The invention is applicable to a through-flow (continuous open-circuit) mill in which a fresh starting material is continuously introduced into the mill and to the circulating system (continuous closed-circuit mill) in which the output of the mill is delivered to a classifier which separates the fine product from a coarse component which is recycled to the mill.

Abstract: A centrifuge for sifting granular material, ranging in particle size from a few microns to several hundred microns, for example, comprises an upwardly concave frustoconical disk rotatable about a horizontal axis and provided with a similarly shaped cover defining therewith a narrow annular gap of outwardly converging radial cross-section. Air, or some other gaseous or liquid fluid, is axially introduced from above into that gap together with the granular material to be centrifuged, the fluid stream imparting to the smaller particles an added acceleration making the velocities of all particles substantially equal at the disk periphery.