Engineering: Heat and Mass Balances Around Extruder Preconditioners I
The majority of commercial extruders use preconditioners prior to feeding raw materials into an extruder for completion of cooking and expansion. The primary role of the preconditioner is to preblend, preheat, and partially cook the ingredients entering the extruder. The targets are the final moisture and temperature of the preconditioned product, in addition to other variables. Preconditioning results in a lower mechanical energy input requirement for the extruder, which can improve quality and will increase the capacity of and reduce wear on the extruder. The reduction in the mechanical energy requirement comes primarily from the injection of steam, which upon condensation provides moisture in the product. Some additional energy input can be obtained by feeding hot water into the preconditioner, but the effect of this heat input is small compared with the heat input obtained from condensing steam. This column describes the mass and energy requirements of this process.