Energy efficiency and economic analysis of a biochar production system

Abstract

This research presents an analysis of the energy efficiency and economics of a biochar production system. Three biomass types were studied: corncobs, rice husks, and longan husks. They were available in large amounts in the northern region of Thailand. The biochar production process can help solve such problems. The product from the process is carbon- rich biochar. The system consisted of two essential parts. The central part constituted five kilns with a 200-liter capacity each and a re-burning kiln heat exchanger with 80 cm of width and 173 cm of height. A 3.8 cm diameter spiral pipe inside the heat exchanger transported a working fluid from a 100-liter storage tank into the system for heat exchange. The byproduct was a hot working fluid that could be used for a drying system. The main product obtained from the system was biochar. It could be suitable for soil improvement in order to increase agricultural productivity. Tests were performed with a volume of biomass 200 liters, moisture content ≤15%w.b., fuel weight 144 kg (60 kg for biochar kilns and 84 kg for the re-burning kiln), fuel feeding every 15 min, and working fluid flow rate of 5 liters/min, respectively. In batch production, high-quality biochar was obtained from corncobs, rice husks, and longan husks at 76.0±2.0, 65.5±2.8, and 85.5±1.8 kg, respectively. It was found that the energy efficiency of the biochar production system from corncobs, rice husks, and longan husks were 49.75±0.93%, 31.52±0.78%, and 46.97±1.04%, respectively. Economic analysis found that the minimum payback period was obtained for longan husks, followed by corncobs, and rice husks, respectively.