Abstract
Biomass is a promising energy source due to its abundant, carbon-fixing, and carbon-neutral properties. Torrefaction can be employed to improve the properties of biomass in an oxygen-free or nitrogen atmosphere. This study investigates the product yields and the solid product characteristics from corncob waste torrefaction at the temperatures of 250 °C and 300 °C for 1 h. Nitrogen, carbon dioxide, and a gas mixture of air and carbon dioxide are employed as the carrier gases. The solid product characteristics approach those of coal at the higher temperature, regardless of what the carrier gases are. The fixed carbon, higher heating value, and solid and energy yields using carbon dioxide as a carrier gas at 300 °C are close to those using nitrogen. The product safety and storage properties before and after torrefaction are revealed by the measurements of ignition temperature and hygroscopicity. A higher torrefaction temperature leads to a higher ignition temperature of treated biomass, except using the mixture of air and carbon dioxide as the carrier gas. Carbon dioxide is a better carrier gas than nitrogen for biomass torrefaction, from the storage and transportation points of view.
Highlights
With increasing global energy demand and deteriorating atmospheric greenhouse effects, biomass has become a promising energy source due to its abundance, carbon-fixing, and carbon-neutral properties [1,2,3]
The product yields and characteristics of corncob waste torrefied at the temperatures of 250 °C and 300 °C using N2, CO2, and the gas mixture of air and CO2 as the carrier gases have been investigated
The results suggest that the role played by temperature on the performance of torrefaction is more than that of the carrier gas, and a higher torrefaction temperature makes the properties of solid products approach those of coal
Summary
With increasing global energy demand and deteriorating atmospheric greenhouse effects, biomass has become a promising energy source due to its abundance, carbon-fixing, and carbon-neutral properties [1,2,3]. The applications of raw biomass in industry are limited because of its high hygroscopicity and moisture content, as well as its low volume and energy density [4,5,6,7]. Torrefaction is a process to keep biomass in an oxygen-free or nitrogen atmosphere at temperatures between 200 °C and 300 °C for several minutes to several hours. This pretreatment process has received a great deal of attention in recent years [8,9,10,11,12]. Torrefaction imposes additional costs because of nitrogen separation from air to maintain the biomass in an oxygen-free environment
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