Solar thermal energy for supplemental heat to process tea in Sri Lanka

Abstract

In tea processing, the subprocesses of withering and drying require thermal energy for dehydration of tea leaves. At present, the Sri Lankan tea industry depends mostly on imported fossil fuels for its thermal energy needs. The economic pressure has forced the industry to investigate energy alternatives. In this study solar thermal energy, heat recovery from the fluidized-bed dryers, and a combination of solar system with heat recovery were analyzed. The $bar{phi}$, f-chart general design method was used to design solar systems to match thermal energy needs in tea processing. The analysis was extended to the f-chart economic analysis to select economically optimum systems. On the basis of highest life cycle savings, flat plate solar collector area and storage tank were sized. Results showed that solar thermal systems require a high investment, but can provide 42, 52, and 63 percent of the energy needs for high, mid and low tea growing regions respectively. Combination of solar thermal systems with heat recovery from a fluidized-bed dryer decreases the amount of energy required by another 7 to 12 percent yet requires only a small increase in investment. Heat recovery systems alone are attractive in economic terms since the required investment is very small compared to solar systems and significant savings are achieved. Comparison of the fraction of loads predicted by using the $bar{phi}$, f-chart method agreed with limited experimental tests of a solar collector with water thermal storage and heat exchanger. An analysis of dynamic behavior of solar thermal system applications is suggested since the unique characteristics of tea processing may vary from the basic assumptions made in developing the $bar{phi}$, f-chart design method. Simulation techniques can be used to avoid expensive experiments.