Economic analysis and drying kinetics of a geothermal-assisted solar dryer for tomato paste drying

The economic value of many fruit and vegetables is often linked to the ability to preserve such natural products. In the case of tomatoes, the manufacture of 1 kg of powder or concentrate requires the evaporation of about 16 kg water kg^-1 dry matter. In the present work, the effectiveness and economic analysis of solar drying systems for drying of tomato paste with and without geothermal water heat exchanger (GWHE) were studied.

The GWHE integration significantly increased the recorded drying temperature up to 53.41 °C, with an improvement of 11.5 °C compared to the conventional dryer. Moreover, the drying temperature inside the drying chamber exceeded ambient temperature after sunset and at night by 30.8 °C. GWHE ensured a continuous drying process, while drying time was 22 consecutive hours, compared to the basic dryer with 18 h in 3 days. Effective moisture diffusivity was found to be 1.617 × 10^-9 and 1.202 × 10^-9  m²  s^-1 for hybrid and basic drying systems, respectively, using the slope. Three methods were used to perform economic analysis. The cumulative present worth of savings, at 23 382.6 USD, is much higher than the capital cost of the hybrid dryer, at 467 USD. The payback period is quite acceptable, at 2.21 years as compared to dryer lifetime of 15 years. Therefore, the hybrid dryer will dry tomato paste without additional charges for 12.79 years and is recommended for a large-scale tomato paste dryer.

The hybrid system with GWHE ensures a continuous drying process during night-time, in addition to reduced drying time. The economic study revealed a high feasibility for the hybrid dryer, with a short payback period. © 2021 Society of Chemical Industry.