Influence of raw material moisture on the synthesis of black tea production process

Abstract

Tea industry is one of the main activities in the northeast of Argentina. It presents some particularities respect of tea production in other regions of the world, mainly in the high level of automation in tea shoots harvesting. Besides, the factory configurations in terms of the equipment used in tea production are different and it is not clear if they are efficient or not. The objective of this work is to study the effects of the moisture in the raw material (tea shoots) in the optimal design of a tea manufacturing plant not only in the investment but also in the operation costs. A superstructure that includes all the equipment involved in black tea manufacturing is proposed and a Generalized Disjunctive Programming model (GDP) is formulated to find the optimal flow sheet to produce black tea minimizing investment and operation cost, considering different wet contents in the tea shoots. A comparison was also made among the optimal plant and typical factories configurations to analyze their performance. From the results obtained can be observed that if the moisture of raw material is below of 4.5 kg of water per kg of dry matter the optimal plant configuration does not change; above this value more investment is needed to extract the extra water content. A similar conclusion can be obtained from the analysis of the operation costs. The optimal configuration is formed by conventional preservation chambers, continuous withering belts, Rotorvane crusher, continuous fermenting machines and fluid bed dryers. Comparing other typical configurations against the optimal one, the operative unit cost is about 20%–60% greater.