Design of model based controller for air temperature control in tea leaf withering process

Abstract

Good tea manufacturing process actually starts with proper plucking of shoot, handling of leaf, Withering, Fermenting and Blending. Withering of tea leaves is the first and foremost step in the process of tea manufacturing after plucking the leaves. After plucking it is necessary to separate the shoots and hence the leaves in the trough needs to be broken up to separate every shoot from each other as this is must for even withers. The tea leaves are dried to arrest enzymic reaction as well as oxidation and also to remove moisture from the leaf and to produce a stable product with good keeping quality. Application of hot air during withering reduces the moisture content in the leaf. This process of drying tea leaves to reduce moisture content is done by blowing hot air of temperature 60 o C to 80 o C for 6 hours to 10 hours and the moisture content is reduced to 65% initially. Then further processing like fermentation and drying of leaves to ultimate 3% moisture level is done in successive stages to obtain the end product. Maintaining the temperature of the air blown in the troughs is critical and monitoring the temperature continuously is challenging. Hence this paper proposes a remote monitoring and control system for air temperature via Ethernet.