Procedure for conveyer-belt dryer sizing using dehydration-rate curves

Abstract

The aim of this dissertation is to provide an understanding of the drying phenomena associated with the drying of a selected extruded maize product. Mathematical modelling of drying is complicated and in many cases inaccurate due to the assumption of constants used in the mathematical models. These constants vary for each product and are determined by the nature of the product being dried. Using the assumed values for designing a dryer can lead to energy losses and a decrease in product quality. Current literature does not provide sufficient data regarding the drying process of extruded maize products. This can lead to faulty and inefficient drying procedures. In the drying industry, products for commercial use need to adhere to strict regulations regarding the moisture content of the food. By failing to comply with these regulations, companies can face legal implications. On the other hand, decreasing the moisture content of the product too much increases the amount of raw material needed to make up the desired weight specified on the packaging. This causes the profit margins to decrease, since the company is using more expensive raw product than cheaper water. In addition, current literature does not provide adequate data regarding the effects of the process parameters involved, for this reason the influence of selected operating parameters will have to be investigated. To achieve this, drying tests were performed. Tests were conducted through batch samples inserted into a drying chamber. Through accurately logging selected variables, the influence of the process parameters were investigated. The results of these tests can be used to determine the actual moisture content of the product at a certain time. As a result of this, the product can be dried up to the selected moisture content and no extra moisture is removed. In addition, these results provide data on the quality of the product after drying. These results can also be used to optimize the energy consumption of the system. From the tests performed, conclusions are reached regarding the selected process parameters as well as the calculated residence time. Considering the abovementioned results, a preliminary sizing design with the chosen parameters is provided.