Lab manager, University of Western Australia
Utilisation of biomass by means of pyrolysis has received great interests for the production and use of biofuels. Biomass consists of three major components, namely, cellulose, hemicellulose and lignin and their contents vary from feedstock to feedstock. Understanding the pyrolysis behavior of each component and their interactions holds a key to understanding the complex biomass pyrolysis process. This study was aimed to compare the pyrolysis characteristics of cellulose from various biomass resources. Cellulose samples isolated from selected raw biomass materials, namely, pine wood and wheat straw, in addition to a pure cellulose sample acquired from Sigma Aldrich as a reference, were used in this study. The raw biomass sample was first milled to a particle size fraction of < 310 μm and treated using Soxhlet extraction in a 2:1 (v/v) toluene/ethanol solvent to remove wax. Lignin was then removed by treating the de-waxed sample in a 1M NaClO2 solution at 343K until the product became white. Finally, hemicellulose was leached out by soaking the de-lignified sample in a 6 wt % KOH solution at room temperature overnight and then at the same concentration at 353K for 2 h. Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometer (XRD) were applied to characterise the surface functional groups and the crystallinity of the cellulose samples. The pyrolysis experiments were performed using a thermogravimetric analyser (TGA) in nitrogen at 10Kmin-1 heating rate from room temperature to the final temperature of 823K. The FTIR and XRD results indicated that cellulose can be successfully isolated from the raw biomass samples via the chemical treatment used. The cellulose isolated from both pine wood and wheat straw showed similar pyrolysis characteristics but differed significantly from the reference cellulose. The DTG curves of cellulose samples isolated showed characteristic peaks at 600 and 608K, ca 5-13K lower than that of the reference cellulose and exhibited a large flat shoulder in the temperature range of 475 – 575K. It was identified that the cellulose samples isolated from selected biomass had lower crystallinity and smaller crystallite compared to the reference cellulose, which in turn, impacted on their pyrolysis behavior.
Abstract: The interactions between coal gangue and pine sawdust during the combustion process were studied using thermogravimetric analysis. The effect of the blending ratio, oxygen concentration and heating rate on the weight loss (TG) and differential thermogravimetric (TGA) profiles was examined. The TG and DTG curves of the blends were not additives of those of the individual materials, suggesting that interactions between coal gangue and pine sawdust had occurred during the combustion, especially in the temperature range of 400-600 °C. Kinetic analysis confirmed that the combustion of coal gangue, pine sawdust and their blends was chemical reaction controlled. Further analysis revealed that the interactions between coal gangue and pine sawdust were primarily due to thermal effects rather than structural changes, with the thermal inertia of coal gangue dominating over the behavior of the blends. The interactions decreased with decreasing the coal gangue ratio in the blend, oxygen concentration and heating rate.
Pub.: 30 Apr '16, Pinned: 27 Jul '17
Abstract: The ignition and combustion behaviour of single droplets of biochar-glycerol-water slurry fuels was experimentally investigated. A pine sawdust biochar with a median particle size (D50) of approximately 12 µm was used. The slurry fuels with a constant biochar loading of 42wt% and glycerol/water ratios varying from 0 to 0.5 by weight were prepared. A single droplet of a slurry fuel with diameter ranging from 0.5 mm to 2.0 mm was suspended on a silicon carbide fibre and burned in air at 1023 K in an electrically heated tube furnace. The ignition and combustion processes of the droplets were recorded using a colour CCD camera. The ignition delay time, burnout time and burning rate based on the d2 law were determined. It was found that all the slurry fuels exhibited heterogeneous ignition of biochar residue (agglomerate) following water and glycerol evaporation. The addition of glycerol significantly reduced ignition delay time, shortened burnout time and increased burning rate of the droplets. This effect was enhanced with increasing glycerol/water ratio in the slurry fuels. It was also found that the glycerol was not completely evaporated before ignition and the remaining glycerol burned concurrently with the biochar on or near the agglomerate surface. The combustion of agglomerate after ignition was controlled by external oxygen diffusion to the outer layer of the agglomerate under the conditions tested.
Pub.: 25 Jul '16, Pinned: 27 Jul '17
Abstract: A kinetic modeling study of the effect of iron on the ignition and combustion characteristics of diesel, modeled as n-heptane, in compression ignition engines was carried out using CHEMKIN PRO. The ignition was simulated using the SENKIN code, and combustion was modeled using the OPPDIF code. The kinetic models incorporated n-heptane mechanisms involving 159 species and 1540 reactions and iron reaction mechanisms of 7 iron species and 46 reactions. It was found that small amounts of iron in the fuel significantly reduced the ignition delay time. The ignition delay time decreased with an increasing iron concentration. A reaction pathway analysis showed that the ignition was promoted as a result of an early injection of the OH radicals. It was also showed that the addition of iron increased the peak flame temperature of n-heptane in the counter-flow diffusion flame and reduced the maximum mole fractions of H and O in the peak flame region as a result of the catalytic recombination cycles involving FeO, Fe(OH)2, and FeOH. The reaction rates of H + O2 ⇔ O + OH and CO + OH ⇔ CO2 + H in the peak flame region were found to increase, which is considered to be responsible for the increased peak flame temperature.
Pub.: 02 Dec '16, Pinned: 27 Jul '17
Abstract: The ignition and combustion characteristics of Zhundong lignite (ZDL), with and without washing to remove different forms of inherent sodium, were investigated. Water washed (ZDL-WW) and acid washed (ZDL-AW) samples were prepared by soaking the raw lignite (ZDL-Raw) in ultrapure water and 0.5 M hydrochloric acid (HCl), respectively, at 60 °C for 24 h. A single particle of a ZDL sample, ca 2.5 mm in diameter, was suspended on a silicon carbide fibre (142 µm) tip and burned in air at 1123 K in a furnace. The time-resolved ignition and combustion behaviours of the single particles were observed with the aid of combined use of a shortwave infrared camera, a CCD camera, which enabled the determination of the ignition mechanism, ignition time, burnout time and burning rate. A flame emission spectrometer was used to identify the presence of sodium in the flame. The ignition of all ZDL samples followed the joint hetero-homogeneous mechanism in the present work. Upon the homogeneous ignition, ZDL-Raw exhibited a soot free yellowish translucent flame while ZDL-WW and ZDL-AW showed sooty flames. The ignition time followed the order of ZDL-Raw>ZDL-WW>ZDL-AW while the burning rate followed the opposite order. These observations were attributed to the catalytic effect of sodium in the lignite whose amount was varied due to the water and acid washing. Sodium ions were detected in the flame of ZDL with and without washing and the intensity of sodium signal also followed the order of ZDL-Raw>ZDL-WW>ZDL-AW. It is believed that sodium ions released in the flame promoted catalytic cracking of large tar fragments and oxidation of soot precursors.
Pub.: 30 Sep '16, Pinned: 27 Jul '17