Interactions during CO₂ Co-gasification of Biomass and Coal Chars Obtained from Fast Pyrolysis in a Drop Tube Furnace

Abstract

This work investigated the co-gasification of biomass and coal chars obtained from fast pyrolysis (1000 °C, ∼104 °C s–1) in a drop tube furnace. Olive residue and Soma lignite were fast-pyrolyzed in a drop tube furnace, and different char blends were prepared for co-gasification at different temperatures (800, 900, 950, and 1000 °C) in a thermogravimetric analyzer. The chars obtained from the drop tube furnace were analyzed for their chemical and mineral composition, morphology, surface area, and particle size distribution. Three distinct blends of olive residue and Soma lignite chars were prepared in the (biomass-coal) ratios of 50–50, 25–75, and 10–90. Three kinetic models were fitted to the (co)­gasification profiles: the volumetric model, the grain model, and the random pore model. The results showed that fast pyrolysis strongly affected the morphology and surface area of the chars, which were not the decisive factors influencing the gasification behavior. Biochar displayed the presence of K in an active form (K2Ca­(CO3)2 and KCl), which had a catalytic effect on the gasification. Synergies during the co-gasification were observed for ratios of biochar above 25%, whereas the 10–90 blend showed a similar gasification behavior to that of the lignite char. The results strongly suggested the existence of a threshold for K/Al and K/Si in the char blend for which synergies can be observed, which coincided with the 25OR-75SL blend, specifically, K/Al = 0.7 and K/Si = 0.4.

Special Issue in Memory of Professor Mário Costa

“…CO 2 and H 2 O influence the formation of char N to NO in different ways, and the ash-forming matter contributes to the differences in the NO release rates. Kazanç et al investigate the co-gasification of biomass and coal chars obtained from fast pyrolysis (1000 °C and ∼104 °C s –1 ) in a drop tube furnace. The results strongly suggest the existence of a threshold for K/Al and K/Si in the char blend, for which synergies can be observed.…”

Evolution of Char Properties during Rapid Pyrolysis of Woody Biomass Particles under Pulverized Fuel Conditions

“…Biomass contains abundant inorganic species, so that the release and transformation of these inorganic species during rapid pyrolysis play key roles in ash deposition/fouling/corrosion issues associated with biomass combustion. − Many previous studies were carried out at temperatures of ≤1100 °C, using wire-mesh reactors, − thermogravimetric analyzers, , quartz/fixed bed reactors, − or other indirect methods to quantify the release/retention of inorganic species. , The combustion temperature in PF boilers is typically significantly higher than 1100 °C for optimum char burnout . Therefore, in the laboratory, rapid pyrolysis of solid fuels under conditions pertinent to PF conditions is often carried out in drop-tube furnaces (DTFs) for achieving rapid heating and high pyrolysis temperatures (>1100 °C). , A major weakness of the past studies using DTFs is that those studies rely on the ash tracer method to determine the char yield, with the assumption that the ash or ash species used as the tracer is conserved during the thermochemical process . Because part of ash species would have been released in the gaseous phase under the reaction conditions particularly at a high temperature, this assumption has been long suspected to be invalid .…”

“…26 Therefore, in the laboratory, rapid pyrolysis of solid fuels under conditions pertinent to PF conditions is often carried out in drop-tube furnaces (DTFs) for achieving rapid heating and high pyrolysis temperatures (>1100 °C). 27,28 A major weakness of the past studies using DTFs is that those studies rely on the ash tracer method to determine the char yield, with the assumption that the ash or ash species used as the tracer is conserved during the thermochemical process. 29 Because part of ash species would have been released in the gaseous phase under the reaction conditions particularly at a high temperature, this assumption has been long suspected to be invalid.…”

On the combustion parameters of coal, biomass and iron, burning either as isolated particles or in groups of particles

“…However, the effects of fast pyrolysis of biomass particles under high temperatures on the shape and size of biomass particles are quite different. Upon undergoing devolatilization at high heating rates and high temperatures biomass particles have been observed, in this laboratory and elsewhere, to undergo plastic deformation, and in many cases spherodize and form highly porous and ceno-spheric, ceno-elliptic, or ceno-cylindrical particles [134,[137][138][139][140][141]. These phenomena are particularly pronounced and more uniformly observed in the case of torrefied biomass particles [138].…”