Dongke Zhang

Effects of moisture and coal blending on Hardgrove Grindability Index of Western Australian coal

Abstract Investigations into the effects of moisture and coal blending on Hardgrove Grindability Index (HGI) were carried out on Collie coal of Western Australia. Experiments were conducted in a standard Hardgrove apparatus on four individual Premier seam coals (namely P2, P3, P4 and Hebe) and several blends (namely Hebe/P2, Hebe/P3, Hebe/P4, Hebe/P2/P4) prepared at various blending ratios. The experiments comprised of 5 days of air-drying followed by oven drying. Among the coal seams tested, Hebe showed the highest HGI (58) whereas P4 was the lowest (47). HGI was found to correlate well with residual moisture, with correlation coefficients ranging from 0.5 to 0.9 depending on the type of coal seam or blend. In contrast, moisture measurements on the samples loaded into the HGI apparatus (size 0.600 to 1.180 mm), referred to as the “coarse fraction” showed erratic trends with HGI. The experimental results suggest that no relationship exist between the coarse fraction moisture and HGI. Measured HGI values of binary and ternary blends were found to correspond well with the weighted average values of HGI within ±2 HGI units. This effect was confirmed by a further investigation with a range of 11 binary (P3/Hebe) blends of various proportions.

Conversion of hexose into 5-hydroxymethylfurfural in imidazolium ionic liquids with and without a catalyst.

Conversion of fructose and glucose into 5-hydroxymethylfurfural (HMF) was investigated in various imidazolium ionic liquids, including 1-butyl-3-methylimidazolium chloride (BmimCl), 1-hexyl-3-methylimidazolium chloride (HmimCl), 1-octyl-3-methylimidazolium chloride (OmimCl), 1-benzyl-3-methylimidazolium chloride (BemimCl), 1-Butyl-2,3-dimethylimidazolium chloride (BdmimCl), and 1-butyl-3-methylimidazolium p-toluenesulfonate (BmimPS). The acidic C-2 hydrogen of imidazolium cations was shown to play a major role in the dehydration of fructose in the absence of a catalyst, such as sulfuric acid or CrCl(3). Both the alkyl groups of imidazolium cations and the type of anions affected the reactivity of the carbohydrates. Although, except BmimCl and BemimCl, other four ionic liquids could only achieve not more than 25% HMF yields without an additional catalyst, 60-80% HMF yields were achieved in HmimCl, BdmimCl, and BmimPS in the presence of sulfuric acid or CrCl(3) in sufficient quantities.

Thermal stability and kinetics of decomposition of ammonium nitrate in the presence of pyrite.

The interaction between ammonium nitrate based industrial explosives and pyrite-rich minerals in mining operations can lead to the occurrence of spontaneous explosion of the explosives. In an effort to provide a scientific basis for safe applications of industrial explosives in reactive mining grounds containing pyrite, ammonium nitrate decomposition, with and without the presence of pyrite, was studied using a simultaneous Differential Scanning Calorimetry and Thermogravimetric Analyser (DSC-TGA) and a gas-sealed isothermal reactor, respectively. The activation energy and the pre-exponential factor of ammonium nitrate decomposition were determined to be 102.6 kJ mol(-1) and 4.55 x 10(7)s(-1) without the presence of pyrite and 101.8 kJ mol(-1) and 2.57 x 10(9)s(-1) with the presence of pyrite. The kinetics of ammonium nitrate decomposition was then used to calculate the critical temperatures for ammonium nitrate decomposition with and without the presence of pyrite, based on the Frank-Kamenetskii model of thermal explosion. It was shown that the presence of pyrite reduces the temperature for, and accelerates the rate of, decomposition of ammonium nitrate. It was further shown that pyrite can significantly reduce the critical temperature of ammonium nitrate decomposition, causing undesired premature detonation of the explosives. The critical temperature also decreases with increasing diameter of the blast holes charged with the explosive. The concept of using the critical temperature as indication of the thermal stability of the explosives to evaluate the risk of spontaneous explosion was verified in the gas-sealed isothermal reactor experiments.

The effect of inherent and added inorganic matter on low-temperature oxidation reaction of coal

Abstract The influence of inherent and added inorganic matter on low-temperature oxidation reactions of coal and the effectiveness of the additives to affect the oxidation reactions are examined in this paper. A Victorian brown coal was selected for this study. Samples of the raw coal, water-washed coal, and acid-washed coal were prepared. The acid-washed coal was also doped with seven additives, respectively, by both wet-mixing (5% wt.) and ion-exchanging with the additives. Each of the samples was then tested in a wire-mesh reactor to determine its critical ambient temperature, above which thermal runaway occurred. The critical ambient temperatures of the acid-washed and water-washed coals were higher than that of the raw coal, indicating that the inherent inorganic matter in the coal catalysed low-temperature oxidation. Of the seven additives used, Cu(Ac) 2 , KAc, and NaAc were found to promote the oxidation reaction, while NaCl, CaCl 2 , and Mg(Ac) 2 inhibit the reaction. Ca(Ac) 2 showed a very little effect. Furthermore, it was observed that the promotion effects of Cu(Ac) 2 and KAc were stronger when they were ion-exchanged into the coal, while the inhibition effect of Ca(Ac) 2 was stronger when it was wet-mixed with the coal. Low-temperature oxidation kinetics of various samples were also estimated and compared. Scanning Electron Microscope (SEM) and Energy Dispersive X-ray (EDX) quantitative analysis of the samples respectively wet-mixed and ion-exchanged with Cu(Ac) 2 indicated that the pore volume of the ion-exchanged sample was greater than that of wet-mixed sample, and the amount of copper ion absorbed in the ion-exchanged coal particle was higher and more uniformly distributed in the coal matrix than that in the wet-mixed coal particle.

Copper and zinc adsorption by softwood and hardwood biochars under elevated sulphate-induced salinity and acidic pH conditions.

Biochar adsorption may lower concentrations of soluble metals in pore water of sulphidic Cu/Pb-Zn mine tailings. Unlike soil, high levels of salinity and soluble cations are present in tailing pore water, which may affect biochar adsorption of metals from solution. In the present study, removal of soluble copper (Cu) and zinc (Zn) ions by soft- (pine) and hard-wood (jarrah) biochars pyrolysed at high temperature (about 700 °C) was evaluated under typical ranges of pH and salinity conditions resembling those in pore water of sulphidic tailings, prior to their direct application into the tailings. Surface alkalinity, cation exchange capacity, and negative surface charge of biochars affected Cu and Zn adsorption capacities. Quantitative comparisons were provided by fitting the adsorption equilibrium data with either the homogeneous or heterogeneous surface adsorption models (i.e. Langmuir and Freundlich, respectively). Accordingly, the jarrah biochar showed higher Cu and Zn adsorption capacity (Qmax=4.39 and 2.31 mg/g, respectively) than the softwood pine biochar (Qmax=1.47 and 1.00 mg/g). Copper and Zn adsorption by the biochars was favoured by high pH conditions under which they carried more negative charges and Cu and Zn ions were predicted undergoing hydrolysis and polymerization. Within the tested range, salinity had relatively weak effects on the adsorption, which perhaps influenced the surface charge and induced competition for negative charged sites between Na(+) and exchangeable Ca(2+) and/or heavy metal ions. Large amounts of waste wood/timber at many mine sites present a cost-effective opportunity to produce biochars for remediation of sulphidic tailings and seepage water.

Behaviour of inorganic constituents and ash characteristics during fluidised-bed combustion of several Australian low-rank coals

Abstract Behaviour of inorganic constituents during fluidised-bed combustion of several Australian low-rank coals was studied using a laboratory-scale spouted-bed combustion system. Coals from Victoria (Loy Yang and Morwell) and South Australia (Lochiel and Bowmans) were chosen for the present study. Characteristics of ash buildup on bed material and bed defluidisation were compared for the coals tested at temperatures between 800°C and 900°C. Samples of ash-coated bed particles and fly ash withdrawn from the system were subjected to various analytical techniques including chemical analysis, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Experimental results indicated that the coal type has a significant effect on the ash characteristics and buildup on bed material particles. Coals with high contents of sodium and sulphur have resulted in the formation of low-melting-point compounds (viz. alkali sulphates) in the ash coating on bed material particle surfaces, rendering them more sticky at fluidised-bed temperatures. This led to increased ash buildup on bed material particle surfaces with such low-rank coals. In contrast, for coals with low sodium and sulphur contents, the combustion lasted for longer periods without any particle agglomeration and defluidisation. The varying content of sodium and sulphur in these coals were identified to be responsible for the different ash buildup and defluidisation behaviour observed.

Effect of biochar addition on hydrogen and methane production in two-phase anaerobic digestion of aqueous carbohydrates food waste

Effect of biochar addition on hydrogen and methane production in two-phase anaerobic digestion of aqueous carbohydrates was studied using bench-scale bioreactors. The cultures with biochar additions were placed in 100ml reactors and incubated at 35°C and pH 5 for hydrogen production. The residual cultures were then used for methane production, incubated at 35°C and pH 7. Daily yields of hydrogen and methane and weekly yield of volatile fatty acids (VFA) were measured. The hydrogen and methane production potentials, rate and lag phases of the two phases were analysed using the Gompertz model. The results showed that biochar addition increased the maximum production rates of hydrogen by 32.5% and methane 41.6%, improved hydrogen yield by 31.0% and methane 10.0%, and shortened the lag phases in the two phases by 36.0% and 41.0%, respectively. Biochar addition also enhanced VFA generation during hydrogen production and VFA degradation in methane production.

Inhibition of Arabidopsis chloroplast β-amylase BAM3 by maltotriose suggests a mechanism for the control of transitory leaf starch mobilisation

Starch breakdown in leaves at night is tightly matched to the duration of the dark period, but the mechanism by which this regulation is achieved is unknown. In Arabidopsis chloroplasts, β-amylase BAM3 hydrolyses transitory starch, producing maltose and residual maltotriose. The aim of the current research was to investigate the regulatory and kinetic properties of BAM3. The BAM3 protein was expressed in Escherichia coli and first assayed using a model substrate. Enzyme activity was stimulated by treatment with dithiothreitol and was increased 40% by 2–10 μM Ca2+ but did not require Mg2+. In order to investigate substrate specificity and possible regulatory effects of glucans, we developed a GC-MS method to assay reaction products. BAM3 readily hydrolysed maltohexaose with a Km of 1.7 mM and Kcat of 4300 s-1 but activity was 3.4-fold lower with maltopentaose and was negligible with maltotetraose. With maltohexaose or amylopectin as substrates and using [UL-13C12]maltose in an isotopic dilution method, we discovered that BAM3 activity is inhibited by maltotriose at physiological (mM) concentrations, but not by maltose. In contrast, the extracellular β-amylase of barley is only weakly inhibited by maltotriose. Our results may explain the impaired starch breakdown in maltotriose-accumulating mutants such as dpe1 which lacks the chloroplast disproportionating enzyme (DPE1) metabolising maltotriose to glucose. We hypothesise that the rate of starch breakdown in leaves can be regulated by inhibition of BAM3 by maltotriose, the concentration of which is determined by DPE, which is in turn influenced by the stromal concentration of glucose. Since the plastid glucose transporter pGlcT catalyses facilitated diffusion between stroma and cytosol, changes in consumption of glucose in the cytosol are expected to lead to concomitant changes in plastid glucose and maltotriose, and hence compensatory changes in BAM3 activity.

Effect of coal blending on particle agglomeration and defluidisation during spouted-bed combustion of low-rank coals

The possibility of blending coals to alleviate particle agglomeration and bed defluidisation during fluidised-bed combustion (FBC) of several low-rank coals was exploited. A laboratory scale spouted bed combustor was employed to fire coal blends from two lignites with a sub-bituminous coal at ratios of 50:50 and 90:10, at temperatures ranging 800°C. Experiments showed significant improvements in FBC operation with the coal blends compared to the raw lignites. No particle agglomeration and bed defluidisation were evident after 15 h of operation with the blends at 800°C. Chemical analyses indicated that the formation of low temperature eutectics was suppressed by calcium aluminosilicate phases from the sub-bituminous coal, rendering the surface of ash-coated particles dry and less sticky. This was identified as the key mechanism for the control of particle agglomeration and bed defluidisation in FBC, which led to extended combustion operation with the coal blends.

The role of carbon surface chemistry in N2O conversion to N2 over Ni catalyst supported on activated carbon

The effect of acidic treatments on N2O reduction over Ni catalysts supported on activated carbon was systematically studied. The catalysts were characterized by N-2 adsorption, mass titration, temperature-programmed desorption (TPD), and X-ray photoelectron spectrometry (XPS). It is found that surface chemistry plays an important role in N2O-carbon reaction catalyzed by Ni catalyst. HNO3 treatment produces more active acidic surface groups such as carboxyl and lactone, resulting in a more uniform catalyst dispersion and higher catalytic activity. However, HCl treatment decreases active acidic groups and increases the inactive groups, playing an opposite role in the catalyst dispersion and catalytic activity. A thorough discussion of the mechanism of the N2O catalytic reduction is made based upon results from isothermal reactions, temperature-programmed reactions (TPR) and characterization of catalysts. The effect of acidic treatment on pore structure is also discussed