(449b) Investigation of the Effect of Wet Flue Gas on Torrefaction of Corn Residues Pellets in a Fixed Bed Reactor

Fossil fuel power plants are major emitters of greenhouse gases. In the past few years, emphasis is on producing clean energy. Accordingly, torrefactionof waste biomass has gained momentum as it improves the higher heating value (HHV) equal to and sometimes above that of coal. The advantage of torrefaction is that, torrefied biomass could be co-fired with coal, thereby lowering greenhouse gas emissions and global warming. The utilization of wet flue gas for torrefaction of biomass pellets is of practical significance and increases, affordability and environmental sustainability, if compared to employing pure inert gas from compressed gas cylinders.

This work was carried out to experimentally investigate the effect of wet flue gas on the torrefaction of corn biomass. The experiment were conducted on pressed corn residue pellets in a fixed bed reactor. Parameters investigated were temperature, oxygen content, heating rate, and residence time. Wet flue gas simulated by steam (0-21% v/v), carbon dioxide (12% v/v), oxygen (4% v/v) and balance with nitrogen as reactive gas was applied. It was observed that at a temperature of 260 °C under inert conditions with a heating rate of 10 °C/min and residence times between 10 and 40 min, the best torrefied biomass with properties comparable to those of coal was achieved. The effects of varying residence time and steam concentration in the reactive gas on the product distribution of torrefied biomass (i.e. gas, liquid, and torrefied pellets yields) were studied. The changes in the surface structures of torrefied pellets were evaluated by Raman spectroscopy and scanning electron microscope. In order to gain insight into the decomposition mechanism of torrefaction, mass spectrometry was employed to analyze the components of gas products. The residence time and steam concentration in the wet flue gas were found to have significant effect on product properties and yields. Compared to inert conditions, torrefied liquid yield doubled with the addition of steam to the simulated wet flue gas, and gas yield increased by four times at high steam concentrations. The concentrations of torrefied gaseous products carbon monoxide, methane, carbon dioxide, and hydrogen were found to be proportional to the inlet steam concentration in the reactive gas. Moreover, higher steam concentrations increased the reaction rate and caused most sugars in hemicellulose and some sugars in lignin to be converted to a graphene structure, and provided more porosity of the torrefied pellets. The graphene structure of carbon in torrefied pellets was discovered by Raman spectroscopy. At the outset, it could be concluded that wet flue gas is useful and has practical relevance for torrefaction of corn residue pellets. Further, the mechanism of torrefaction with wet flue gas clarified that elements of gas products and steam accelerates decomposition of hemicellulose and lignin, and cause more porosity.