Technical and Business Evaluation of Geothermal Dryhouse for Coffee in Kamojang, West Java, Indonesia

Abstract

The coffee farmers in Kamojang still currently rely on conventional drying method using direct sun radiation. However, the cold ambient temperature and fluctuative weather in Kamojang brings challenges to this method. Therefore, PT PGE Area Kamojang built a trial geothermal dryhouse with a heating pipe connected to a blowdown on the existing geothermal steam pipeline as the heat source. In this study, the existing geothermal dryhouse is evaluated from the technical and business aspects. The technical evaluation studies the thermal performance of the heating pipe to calculate the dryhouse heating load, the required heating pipe length, the effect of heating pipe operation on the dryhouse temperature, and the suggested technical improvements. Meanwhile, the business evaluation studies qualitatively about the relationship between the potential farmer profit enhancement and the possible coffee-drying duration reduction from previously 2-3 weeks to 1-2 weeks by substituting conventional drying method with the use of geothermal dryhouse. Aside from that, it was expected to retain the coffee’s pleasant flavor and not have any sulfur odor problems. The technical evaluation is performed using analytical and experimental methods. The analytical results show that the required heating load is 10.94 kW and the heat transfer rate per unit length of the heating pipe is 0.2618 kW/m. Hence, the required heating pipe length is 41.79 m. The Subsequently, the heating pipe was tested operational three times on 16 – 18 January, 27 April – 4 May, and 31 May – 5 June 2023. On Trial 1, the heating pipe performance was not optimal due to condensate built-up inside the heating pipe. Therefore, steam traps were installed to reduce the condensate built-up. On Trial 2, the heating pipe performance was better, which was indicated by the higher and stable dryhouse temperature during the night. Hence on Trial 3, the technical improvement involving rearrangement of steam trap and bypass valve considerably improved the heating pipe performance. It reaches the design temperature and being maintained above 40°C for a maximum of 50°C longer than it did previously. The business evaluation expects a significant profit enhancement for the farmers if the drying duration could be cut into 1-2 weeks using the geothermal dryhouse.