Development and Sustainability Assessment of a Fish-drying Kiln: Eco-thermodynamic Insights

The demand for sustainable and viable drying technologies has risen continuously in response to the growing energy costs and emerging environmental decline. The study designed and evaluated the operational efficiency of a counter-flow heat recovery fish drying kiln at a uniform temperature (55 $^\circ$C), varying air velocities (1.0, 1.5, and 2.0m/s), and batch sizes (15, 20, and 25kg) of catfish using an eco-thermodynamic approach embodying energy, exergy, environmental, and economic assessments. The findings indicate that heat transfer was greatly improved with higher air speeds and batch sizes, which also reduced charcoal consumption from 22.18kg to 18.85kg and shortened the drying duration from 330 to 180 minutes. The drying rate varied between 0.041 $\leq \mathcal{X}_d \leq$ 0.083kg/min, with a rehydration ratio of 1.71 $\leq \zeta_R \leq$ 1.74 and shrinkage of 20 $\leq \phi_s \leq$ 30.54$%$ ($\pm$ 2.25$%$). Specific energy utilization dropped from 42.88 $\times$ 10$^3$ to 21.87$\times$10$^3$ kJ/kg, and exergy efficiency increased from 42.88 $\leq \eta_{ex} \leq$ 49.75$%$ ($\pm$ 0.48$%$). The sustainability index and improvement potential were obtained as 1.68 and 457.48MJ, respectively. Environmental assessment enhanced as carbon credits rose to ₦532.33 and CO$_2$ emissions dropped from 62.77 kg to 53.35 kg/cycle. The kiln exhibited unique economic feasibility, as evidenced by the reduction in drying costs from ₦26.13 to ₦15.68/kg, and an increase in yearly savings from ₦3.88 million to ₦6.86 million. The benefit-cost ratio rose from 1.98 to 3.59, and the payback time was shortened to 0.27 years. These findings support the kiln’s potential as an inexpensive, ecologically friendly, and thermally productive solution for drying fish products. Future research directions were proposed.