Development of a Controlled System for Trough Withering to Reduce the Cost of Black Tea Processing in Sri Lankan Tea Industry

Abstract

A control system was developed for trough withering to reduce the cost of manufacture in tea withering by optimizing the electrical energy consumption. Withering is the largest electrical energy consumer among the other unit operations of black tea processing. Sri Lanka consumes approximately 135 GWh electrical energy, annually for the process of withering. In this study, the electrical energy consumption was optimized by controlling the fan speed using a variable speed drive (VSD) coupled with the fan motor. A software program, incorporating a mathematical model developed previously for simulating the withering process was used to determine the fan speed. The Raspberry Pi 3 model B was used to run the mathematical model using the software programme to actuate the variable speed drive for controlling the mass flow rate, and the withering air temperature. The results, showed that the specific electricity consumption was 0.17 to 0.18 kWh.kg-1of made tea with the control system and it was 0.27 to 0.35 kWh.kg-1 of made tea without the control system. The electrical energy was saved by 0.13 kW.kg -1of made tea with the control system during the withering process. The annual estimated electrical energy saving is about 19.5 GWh, if the 50 % of tea factories are adapted this control system and the mount of saving in cost is around Rs. 250 million.

Keywords: Raspberry Pi 3 model B, Tea Withering