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The present work examines the impact of the dimensionality of single-particle models (SPMs) for the pyrolysis of thermally thick biomass particles. It builds up comprehensive one- and three-dimensional SPMs and assesses their performances to gain a systematic understanding of the accuracy of predicted results, predictive capability, and computational costs. Cylindrical wheat straw pellets with an average size of 10 mm length and 7 mm diameter were studied on their pyrolysis performances at temperatures ranged from 200 to 700 °C. It investigates the correlation between the inner heating rate of the particle and the resulting irregular porosity distribution in the pyrolyzed particle. The predictions of the models are in good agreement with the experimental measurement, and they show that the predicted char yield is not sensitive to the model dimensionality; however, the rate of mass loss and the char porosity are sensitive to the model dimensionality. Additionally, the three-dimensional SPM is found to be compatible with a wider range of biomass types. The model captures a higher heating rate at the surface and at the center of the particle compared to the region in between. This is linked to an uneven porosity distribution in the pyrolyzed particle, which is higher at the surface and at the center of the particle. While the three-dimensional SPM provides a small improvement in the prediction of the temperature profile compared to the one-dimensional model but offers additional details (e.g., temperature distribution, heating rate, and porosity distribution inside the particle); it requires significantly greater computational times, which might not be justifiable in many situations.

A mathematical model for the operation of a thermal lance is developed and validated, with the focus on its heat transfer and kinetics behavior. It has been found that there is a "window"of combustion rates in which the thermal lance can operate, which is mainly dictated by the oxygen partial pressure. The particular value of the combustion rate can be set by adjusting the flow rate of the oxygen supply, which is practically done by manipulating the oxygen supply pressure. An open issue is the lack of experimental kinetics data for thermal lance combustion.

Understanding of the release mechanism of potassium from biomass is crucial to address the detrimental ash-related issues that are suffered widely in biomass boilers. However, currently available experimental methods only allow the analysis of the overall amount of potassium release; the profiles of released potassium species are still unknown. This study develops a new two-step kinetic model, which integrates the potassium release along with biomass devolatilisation and the reactions of potassium species in the environment of near real biomass combustion. The model enables the quantification of potassium species released from biomass during combustion over a broad range of temperatures. The modelling results indicate that the majority forms of released potassium are KOH and KCl, their amounts could reach as high as 2.6 × 10−5 mol/g biomass and 4.3 × 10−5 mol/g biomass, respectively. With the temperature increasing up to 1400 K, K2SO4 suddenly becomes the third significant potassium species with an amount of 1.8 × 10−5 mol/g biomass. Intermediate species are greatly involved in the release of potassium, at the initial stage, KCl and KOH are very likely to be homogeneously combined as (KCl)2 and (KOH)2; while KO and KO2 are two most important intermediate species that involved in the potassium transitions throughout the biomass combustion process. Those intermediate species, however, show a significant effect on the formations of KCl and KOH, but less on the formation of K2SO4. The developed model is capable to forecast the potassium release from various types of biomass feedstocks, thus promoting solutions that can effectively address alkali-related biomass combustion challenges.

Analytic relations are developed that directly link visually observable features of differential thermogravimetric (DTG) curves (e.g., peak temperature, height, width, skewness and conversion at the peak) to the parameters of chemical reaction kinetics models (e.g., activation energy and prefactor), which can be used to study the thermal decomposition of solid fuels. General expressions suitable for any reaction model are provided, as well as explicit expressions for nth order reactions with a rate constant given by the Arrhenius equation. This approach is illustrated for the pyrolysis of biomass, where it is found to provide a rapid and accurate estimate of the relative contributions of cellulose, hemicellulose, and lignin to the volatile yield, as well as their kinetic parameters. The method offers a simple way to obtain the model reaction kinetics parameters from thermogravimetric data and saves computing time by providing sensible initial values and bounds of the fit parameters.

Ignition behaviour of biomass is an essential knowledge for plant design and process control of biomass combustion. Understanding of ignition characteristics of its main chemical components, i.e. cellulose, hemicellulose, lignin and their mixtures will allow the further investigation of ignition behaviour of a wider range of biomass feedstock. This paper experimentally investigates the influences of interactions among cellulose, hemicellulose and lignin on the ignition behaviour of biomass by thermogravimetric analysis. Thermal properties of an artificial biomass, consisting of a mixture of the three components will be studied and compared to that of natural biomass in atmospheres of air and nitrogen in terms of their ignition behaviour. The results showed that the identified ignition temperatures of cellulose, hemicellulose and lignin are 410 °C, 370 °C and 405 °C, respectively. It has been found that the influence of their interactions on the ignition behaviour of mixtures is insignificant, indicating that the ignition behaviour of various biomass feedstock could be predicted with high accuracy if the mass fractions of cellulose, hemicellulose and lignin are known. While the deficiencies of the determined mutual interactions would be further improved by the analytical results of the activation energies of cellulose, hemicellulose, lignin, their mixtures as well as natural and artificial biomass in air conditions.