On the suitability of thermogravimetric balances for the study of biomass pyrolysis

Abstract

In fixed-bed pyrolysis reactors, the stacking of sample particles often leads to higher yields of solid pyrolysis products (chars) than are obtained from other types of reactors. This phenomenon is particularly emphasised in thermogravimetric (TG) balances, which unlike many fixed-bed reactors, do not sweep gas through the stationary bed of pyrolysing sample.Gas is swept through the sample bed to reduce the residence time of tar vapours in close proximity to chars, which affects the extent to which these vapours will condense onto the surface of chars and repolymerise, thus increasing char yield. Depth of the sample bed affects this residence time, and thus affects char yield. In this work, the sensitivity of typical analyses of biomass thermogravimetry to variations in bed depth have been assessed. Results of these analyses, including product distributions, proximate compositions, and kinetic predictions, carried out on microcrystalline cellulose and birch wood hydrochar samples produced at temperatures ranging from 160 to 280 °C, have been shown to be sensitive to variations in bed depth, and it has been demonstrated that this sensitivity is amplified at higher heating rates and temperatures. Thus, when a single sample mass is used for any of these typical TG analyses, as is common in published literature, the results are not fundamental properties of the material tested but rather a product of the exact experimental design employed. Future work is needed to identify reactor and experimental design guidelines to minimise this sensitivity in fixed-bed reactors.

Identifying Synergistic Effects between Biomass Components during Pyrolysis and Pointers Concerning Experiment Design

“…The data in Figure were acquired at a peak temperature of 300 °C and show the effect of sample mass on mass loss in a TG balance. In previous work, similar trends have been reported for cellulose at 325 and 450 °C, in addition to 300 °C. , …”

“…In previous work, similar trends have been reported for cellulose at 325 and 450 °C, in addition to 300 °C. 14,15 As explained elsewhere, 14−16 one basic drawback of TG balances is the fact that sample particles are stacked together on the sample pan. Figure 1 presents data showing that mass loss during pyrolysis experiments may be altered by changing the initial mass of sample charged to the pan.…”

Study of the Molecular Structure and Elemental Mercury Adsorption Mechanism of Biomass Char

“…Based on the pyrolysis characteristics, pore structure (as shown in Table ), and surface chemical properties (as shown in Figure ), the pyrolysis evolution process of biomass was obtained. In addition, due to the existence of numerous parallel first-order reactions in the biomass pyrolysis process, obviously different complex reaction stages were constituted, and the chemical reaction rate changed accordingly. To accurately obtain the pyrolysis characteristics and mechanism, the kinetic parameters of different pyrolysis stages were studied using the distributed activation energy model (calculated by eq ).…”

Tagasaste, leucaena and paulownia: three industrial crops for energy and hemicelluloses production

“…TGA data can be processed in different ways to estimate kinetic parameters, but are usually handled with model-free fitting techniques. In fact, determining kinetic parameters for combustion reactions by model-based fitting is a difficult task [ 71 , 72 ] and better done with isoconversional methods (e.g., model-free methods such as those based on single-step kinetics). Specially, prominent among such methods are the Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods.…”