Engineering: Heat and Mass Balances Around Extruder Preconditioners II
In this column, Levine continues his discussion of the heat and mass balances that describe the performance of extruder preconditioners and explores factors that impact performance. One factor affecting preconditioner heat balance is heat loss and the influence of preconditioner size. The approximate steam and water rates required to reach the same temperature and product moisture for preconditioners with different capacities vary. The ratio of steam required to water decreases as the flow rate increases. Another very important item is steam quality (i.e., purity of vapor). A lack of steam quality (i.e., condensates [water] in the vapor) can have a dramatic effect on temperature. Factors that have smaller impacts include addition of hot water, which results in higher temperatures and reduced steam requirements, and increasing or decreasing the level of gelatinization or denaturation. All of these heat and mass balance calculations described can be reversed to obtain the final temperature of a product at a fixed steam to water ratio.