Discussion on Torrefaction Parameters for Making the Refuse-Derived Fuels by Response Surface Methodology

Abstract

The torrefaction process is one of the mild pyrolysisor the low-temperature carbonization, which is a thermochemical conversion in which biomass is heated in an inert or nitrogen atmosphere, and the temperature ranges from 200°C to 300°C. It is considered to be an effective pretreatment method to make solid fuels. This study utilizes low-temperature carbonization technology to improve the combustion efficiency of solid-derived fuel (RDF-5) made from biomass. In this experiment, a tubular furnace was used to feed nitrogen gas for 15 min, and four raw materials of pennisetum, rice straw, wood chips and Camellia seed cakes were fed. The analysis was carried out, and the effects of temperature and residence time on the calorific value, energy yield and energy density of the four raw materials were explored using response surface methodology (RSM). It can be seen from the experimental results that among the four raw materials, the carbon content and calorific value of Camellia seed cakes are the highest. Elemental analysis showed that the proportions of nitrogen and sulfur in these four raw materials are very low. These four substances were understood to be suitable to be refuse-derived fuels (RDF-5). Comparing the calorific value of the four kinds of biomass after torrefaction process, the calorific value of pennisetum, Camellia seed cakes, wood chips and rice straw increased by 42.5%, 38.7%, 52.7%, and 18.6%, respectively. These findings revealed that the higher temperature and the longer residence time, the smaller energy yield and the higher energy density.