Assessing the Importance of Pyrolysis Process Conditions and Feedstock Type on the Combustion Performance of Agricultural-Residue-Derived Chars

Abstract

The combustion performance of chars derived from vine shoots, wheat straw, and corn stover was investigated to assess the influence of both the biomass precursor and pyrolysis operating conditions. Chars were produced through slow pyrolysis at different peak temperatures (350 and 500 °C), pressures (0.1 and 0.5 MPa), and residence times of the vapor phase (50 and 150 s). From the thermogravimetric curves obtained under air, the combustion performance index ( S ) was calculated for each char. Apparent kinetics were also estimated using the Coats–Redfern method and assuming an F3/2 reaction model. Results show that the combustion patterns of chars were more influenced by the type of feedstock than by the pyrolysis conditions. Corn stover appeared to be the most interesting feedstock in order to produce chars with tuned reactivity. Results from partial least-squares (PLS) regression revealed that the most important factors affecting S were the contents of potassium (negative effect) and cellulose (positive effect) in the original biomass.

Burning Dynamics of Straw Chars under the Conditions of Thermal Analysis

“…The thermal conditions of char formation do not affect the qualitative features of the curves. As already reported, 11,12 they always present a first zone of moderate rates at low temperatures (char devolatilization), followed by the occurrence of the actual oxidation (burning) reactions. However, these take place with different qualitative features for the samples originated from wood or straws.…”

“…A review, published more than 10 years ago, puts into evidence that pyrolysis conditions and substrate properties are the key issues for the oxidation and gasification rates of biomass chars. As for the oxidation process, studies carried out afterward have contributed in clarifying these aspects, confirming the important role played by the pyrolysis temperature, heating rate and pressure, the macrocomponent content and nature, the microstructure, and mainly the content and composition of inorganics. − Despite significant advancements, − the improved understanding of these effects has not yet been fully incorporated into intrinsic kinetics of general validity, that is, capable of describing, through the kinetic parameters, the variability of char reactivity. Kinetics is needed for coupling with the description of transport phenomena aimed at the development of predictive models of practical systems for gasification and combustion …”

Influence of Feedstock and Final Pyrolysis Temperature on Breaking Strength and Dust Production of Wood-Derived Biochars

“…These particle sizes were used in order to following a cutting practice that could be carried out under field conditions in a reasonable way. In addition, these particle sizes could enhance the carbonization efficiency of the pyrolysis process [47].…”

“…Van Soest method was adopted to determine the biomass constituents (lignin, cellulose, hemicellulose and extractives) [49]. The complete description of this procedure is available in previous publications [47,50].…”

“…Proximate, elemental and XRF analyses were carried out following the aforementioned methodology. The specific surface area (S BET ) was determined using a gas sorption analyzer through the measurements of CO 2 adsorption isotherms at 0 • C. The detailed procedure for S BET determination and pore volume (volume total-V total and ultramicropore-V ultra ) is available in a previous publication [47].…”