A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A R C H 2 0 2 3 2 1 is achieved throughout the entire process. New particles are continuously being conveyed over the heating element so that the heating surface remains optimally utilized at all times. In addition, the design of the heating surface ensures optimum heat transfer to the product. By mixing the material in this way, temperatures do not get too high or too low. All parameters can be precisely controlled throughout the process, which is a critical factor for product quality. In addition, homogeneous mixing leads to significant gains in efficiency. The core components of these systems are horizontal contact dryers that can be run either in batch or continuous operation. Inmany cases, multiple steps such as mixing, evaporation, and reaction can be performed by a single machine. A few examples of where contact dryers are used in calcination and pyrolysis are discussed below. APPLICATION EXAMPLES Calcination: High mineral content and efficient vacuum operation. Calcination describes a wide range of processes in which input materials such as minerals or metals are modified under thermal treatment. Minerals that contain different amounts of hydrate are often heated with the goal of splitting off physically bound water. Gases and water vapor are also released during the process. For one calcination process at a customer’s facility, BHS adapted a continuous horizontal dryer for intense heat transfer and precise material conveyance. Special high-temperature sluices for input and output streams ensure efficient, high-temperature operation, while vapors are cleared of dust using hot gas filters. Since the dryer went into service, it has been operating at a throughput rate of more than one metric ton per hour. Pyrolysis and gasification. Pyrolysis refers to the thermal cracking of materials in an oxygen-free environment. It is used in many industrial processes with the aim of recovering and recycling gases or oils. As a thermochemical conversion process, gasification goes beyond pyrolysis. Two examples of this include the conversion of biomass into gases or ash and the conversion of plastics to a gaseous state. Further examples involving pyrolysis are discussed below. Silicon carbide production. The horizontal dryer has proved particularly advantageous in a newly patented process that enables production of high-purity cubic silicon carbide in large quantities. This silicon carbide can be used in a variety of specialty applications involving semiconductor circuits, sensors, and hydrogen generation. Several process steps can be combined in one high-temperature machine that serves as a mixer, vacuum dryer, and pyrolysis reactor. The horizontal reactor is first charged with different aqueous input solutions. These solutions contain the silicon content and various additives. After preparation of a homogeneous mixture, the aqueous input solution is evaporated. This is carried out under vacuum at temperatures well below 200°F. The product is then heated. Starting at roughly 350°F degrees, several chemical processes take place including oxidation, caramelization, and partial pyrolysis. The product undergoes strong toughening phases, The horizontal dryer makes it possible to work with sticky, viscous materials in pyrolysis applications. In-house testing center for new applications at BHS-Sonthofen.
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