Kinetics of the thermal decomposition of biomass and the influence of alkali metals on these kinetics

The thermal degradation of biomass has received extensive consideration due to its central role in biomass combustion. Biomass decomposition is also a major step in fast pyrolysis and other thermal processing methods involved in the production of chemicals. Detailed understanding of the kinetics of biomass decomposition is vital for reactor kinetics and combustion processes modeling. Analysis methods were studied to determine which method is best suited for reliable kinetic parameter extraction based TGA derived data, kinetics most applicable to industrial applications were explored. This paper then goes on to develop a preliminary expression (involving only SRC Willow and only potassium) directly linking biomass degradation kinetics to the inherent alkali metal content. The Senum-Yang, the Murray and White, and the reaction rate constant methods all yield apparent first-order kinetics that give excellent predictions of pyrolysis under slow heating rate conditions. For higher heating rates, as encountered under flash pyrolysis conditions, kinetics expressions with high E and A values typically give more sensible predictions of conversion. A Langmuir-Hinshelwood relation can be applied to describe the catalytic effect of potassium on biomass pyrolysis. The maximum reaction rate constant of 3.26 x 10-3 (s-1) and the potassium saturation constant of 0.56 (wt%) can be accurately used to derive the pyrolysis reaction rate at 300 °C of any willow sample with a known potassium concentration. A leveling off of the catalytic effect is seen with regard to potassium concentration and the apparent first-order reaction rate at ca. 4.5 wt%.</p

Assessment of the self-ignition characteristics of both torrefied and untreated biomass fuels

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Commodity fuels from biomass through pre-treatment and torrefaction: effects of mineral content on torrefied fuel characteristics and quality

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Behavior and role of alkali metals in biomass combustion

This paper details fundamental work on alkali metals (sodium, potassium, and cesium) to determine if group chemistry has an effect upon the catalytic process observed in SRC Willow thermal degradation, thereby gaining mechanistic insight into the process. Work detailing both pyrolysis and combustion (TGA), and combustion under flame conditions is presented. DTG profiles and first order reaction kinetics comparing the pyrolysis and combustion of the three alkali metal impregnated, raw, and demineralized samples revealed a strong and similar catalytic effect that all three alkali metals have on these reactions. Combustion under flame conditions again showed a stark contrast between the strongly catalyzed degradation of samples with alkali metal presence, and the uncatalyzed degradation of mineral-free samples. As with the low heating rate results, at flame conditions, no observable difference between samples impregnated with varous group 1 metals is noted. These findings imply that a similar thermal degredation mechanisim is followed when this woody biomass contains any alkali metals.</p

Assessment of the self-ignition characteristics of raw and processed biomass fuels

This paper is concerned with the self-ignition characteristics of untreated and torrefied biomass fuels and two coals. Using thermogravimetry in air, first order reaction kinetics at low temperature were derived, and the point of ignition and the maximum weight loss in air measured. In oxygen, data was obtained for the characteristic ignition temperature. Self–ignition temperatures and ignition delays were measured for two untreated and two torrefied biomass fuels for a number of different basket sizes using the European standard test method of spontaneous combustion.</p

Combustion characteristics of chars from raw and torrefied willow

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Combustion of two imported biomass feedstocks for co-firing in the UK

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