Comparison of Heat Transfer from Flue Gas Waste Heat in a Charcoal Kiln Using Heat Transfer Oil in a Helical Tube Heat Exchanger

This paper presents an approach that utilizes waste heat from the exhaust of Biomass Cookstoves (BCS), which is dominantly used for food grilling in tropical Asian countries, Thailand's fish grilling stoves were used as a case study. The study involves designing and comparing computationally the exergy quantities from four types of spiral heat exchangers— (H01, H02, H03, and H04) - using Computational Fluid Dynamics (CFD) within a flow rate range of 0.5-2.5 l/min with heat transfer oil as the working fluid. Subsequently, the economic feasibility was analyzed using the Net Present Value (NPV) and Internal Rate of Return (IRR) methods, and the carbon dioxide emissions to the atmosphere were evaluated across four helical coil configurations, C01, C02, C03, and C04. The results from the CFD analysis under specified conditions demonstrate that the helical heat exchanger can reclaim up to 2900W of exergy from BCS exhaust, which is transferred to water used by coffee machines for commercial use. This system can reduce electricity consumption for water heating by 38.48%, equating to a cost savings of 22,311.81 THB (621.50 USD) per year, with a maximum NPV of 20,195.49 THB (562.55 USD). The investment in upgrading BCS can be recouped within 4.6 years. On the environmental conservation front, using waste heat from BCS exhaust can also reduce carbon dioxide emissions to the atmosphere by up to 3,606.04 kg CO2e per year per stove. The findings from this analysis can help restaurant operators make informed decisions on investing in BCS improvements and aligning business operations with environmental conservation efforts.