Temperature distribution and properties of biochar from a two-heating-stage kiln

Abstract

This study was about biochar production from agricultural waste by calcination and pyrolysis in a concentric cylindrical kiln. Three biomass types were studied: corn cob, rice husks, and longan peels. The kiln was of 50-L capacity and was externally heated by a 15 kW electric heater. Two heating modes of operation were tested, one with a single heating stage and the other with two heating stages. Temperature distribution inside the kiln was found to be better controlled than traditional biomass charcoal kilns. From the production process, the corncob biochar yield from the two- stage was higher than the single-stage kiln. At the same time, biochar yields of rice husk and longan peel decreased from 45. 0 to 43. 3% and 43. 3 to 38. 3% from the single- stage to two- stage mode, respectively. The pH value of the corncob biochar was decreased from 8. 08 by the single- stage to 7. 33 by the two- stage. In contrast, rice husk and longan peel biochars increased from 6.96 to 7.34 and 8.76 to 8.96, respectively. The electrical conductivity of corn cobs, rice husk, and longan peel biochar was increased when the operation was switched from the single-stage to the two-stage.