Zhezi Zhang

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.

A NUMERICAL MODELING STUDY OF IGNITION OF SINGLE COAL PARTICLES UNDER MICROGRAVITY CONDITIONS

The ignition characteristics of single coal particles under microgravity conditions were investigated by means of numerical modeling, considering the effects of particle size, ambient temperature, and oxygen concentration as well as intraparticle thermal conduction. The predicted particle surface temperature and flame displacement agreed well with the experimental data observed under microgravity. It was revealed that when the coal particle size was greater than 100 µm, the intraparticle temperature distribution becomes significant. The primary ignition mechanism was heterogeneous for smaller particles but homogeneous for larger particles. The transition diameter for the ignition mechanism to switch from heterogeneous to homogeneous was found to depend on the ambient temperature, O2 concentration, and whether the intraparticle thermal conduction was considered or not. At a relatively low ambient temperature of 1123 K in air, the predicted transition diameter changed from 800 µm to 600 µm when intraparticle thermal conduction was considered. However, at 1500 K, the intraparticle thermal conduction had little effect on the ignition temperature and the transition diameter predicted was about 700 µm. It was shown that homogeneous ignition occurred when O2 concentration was low while heterogeneous ignition occurred when O2 concentration was high. It was also shown that the homogeneous ignition temperature was slightly lower than the heterogeneous ignition temperature. At high O2 concentrations, the predicted ignition temperature and ignition delay decreased with increasing O2 concentration, consistent with the literature findings, including those from the authors own previous studies. However, at low O2 concentrations, the predicted ignition temperature and ignition delay were less variant. The discrepancies of the predicted transition diameters for the isothermal particles and those with intraparticle thermal conduction considered were attributed to the heating rate and the influence of volatile matter release.

Interactions of coal gangue and pine sawdust during combustion of their blends studied using differential thermogravimetric analysis

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 behaviour of the blends. The interactions decreased with decreasing the coal gangue ratio in the blend, oxygen concentration and heating rate.

Effect of Ashing Temperature on the Physicochemical Properties of Zhundong Lignite Ashes Prepared in a Muffle Furnace

The effect of the ashing temperature on the physicochemical properties of ashes from Zhundong lignite was investigated. The ash samples were prepared in a muffle furnace in air at ashing temperatures ranging from 550 to 1200 °C and were then subjected to a series of analysis including the yield and chemical compositions of the ash, ash mineralogy and morphology, and ash sintering temperature. It was found that these physicochemical properties of the ash varied significantly with the ashing temperature. Firstly, the ash yield was significantly decreased with increasing the ashing temperature. Secondly, the ash chemical compositions were found to be rich in Ca, S, Mg, Na and K at 550 °C, and the fates of these contents varied significantly with increasing the ashing temperature. Furthermore, XRD results showed that Ca-bearing and Na-bearing minerals such as anhydrite, calcite, halite and sodium calcium silicate were identified at 550 °C. As the ashing temperature increased, complex mineral reactions including the vaporisation of halite, the decomposition of calcite and anhydrite, and the formation of yeelimite and calcite silicate occurred. SEM observations showed that the ash particles collected at 550 °C were fine discrete powdery particles. However, sintered particles with progressively developed strengths and increasing sizes were observed with increasing the ashing temperature, and fused large particles were observed at 1200 °C. In addition, the sintering temperature of the ash increased significantly with increasing the ashing temperature due to the formation of the refractory minerals and the decrease in the contents of Na, Cl, K and S, etc. Moreover, the sintering temperature of the ash was lower than the corresponding ashing temperature other than that at 550 °C, which explained the difference in ash morphology at different ashing temperatures.

A Preliminary High-Pressure Thermogravimetric Study of Combustion Reactivity of a Collie Coal Char

The effect of pressure(up to 20 bar)on the reactivity of a char(150–160 μm) produced from Western Australian Collie coal has been studied using a high-pressure thermogravimetric analyser (HP TGA). The pressure demonstrated a positive effect in enhancing char combustion reactivities.Kinetic parameters have been determined from the experimental data.The apparent reaction order was found to be approximately 0.7 and the apparent activation energies were 91.0 kJ/mol at atmospheric pressure and 1.5 kJ/mol at an elevated pressure(10 bar),indicating a shift in the control regimes of the reaction at elevated pressures.The lumped effect of the sample size, bulk diffusion,interparticle and intraparticle diffusion at the elevated pressures played an important role in reducing the mass transfer during the HP-TGA experimentation.Thus the activation energy calculated at elevated pressures may not represent the intrinsic activation energy of the char particles but the apparent values of the bulk of the samples.

Contrasting the Pyrolysis Behavior of Selected Biomass and the Effect of Lignin

This study was aimed at comparing the pyrolysis behavior of several selected biomass samples, namely, pine wood, poplar wood, wheat straw, and sugarcane bagasse, with a particular attention to the effect of lignin. Raw samples were first treated using Soxhlet solvent extraction with a 2:1 (v/v) mixture of toluene/ethanol to remove wax. Lignin was then removed by soaking the dewaxed samples in a 1.0 M sodium chlorite solution at 343 K till the solids became white. Fourier transform infrared (FTIR) spectroscopy analysis was applied to characterize the surface functional groups of the samples. The morphology of the samples before and after delignification treatment was analyzed using scanning electron microscope (SEM). The pyrolysis behavior of the raw and treated biomass samples was studied using a thermogravimetric analyzer (TGA) operating in nitrogen at a constant heating rate of 10 K min−1 from room temperature to the final temperature 823 K. The FTIR and SEM results indicated that lignin can be successfully removed from the raw biomass via the chemical treatment used. As expected, the pyrolysis behavior differed significantly among the various raw biomass samples. However, the pyrolysis behavior of the delignified samples showed almost identical thermal behavior although the temperature associated with the maximum rate of pyrolysis was shifted to a lower temperature regime by ca. 50 K. This suggests that the presence of lignin significantly affected the biomass pyrolysis behavior. Thus, the pyrolysis behavior of the biomass cannot be predicted simply from the individual components without considering their interactions.

An experimental study of the rheological properties and stability characteristics of biochar–algae–water slurry fuels

ABSTRACT An innovative technology to integrate the utilization of biochar and algae in the form of slurry fuel for power generation was conceptualized. This study aimed to understand the rheological properties and stability characteristics of biochar–algae–water (BAW) slurry fuels. The BAW slurries were prepared by mixing pine sawdust biochar and Chlorella vulgaris in different proportions first and then dispersing the mixtures in deionized water. The BAW slurries showed shear-thinning flow behavior, which became more apparent as the algae proportion in the solid increased. The slurries displayed better stability at higher algae proportion due to increased water uptake capacity and enhanced flocculation.

An Experimental Investigation into the Effect of Soap on Ignition and Combustion Characteristics of Single Droplets of Glycerol

ABSTRACT The effect of soap on the ignition and combustion characteristics of single droplets of glycerol was studied experimentally. Soap was added into a pure glycerol, both as by-products of biodiesel manufacturing, at concentrations of 1 wt% to 5 wt%. A single droplet of glycerol with and without soap addition was suspended on the tip of a silicon carbide fiber and exposed to air at 1023 K in an electrically heated tube furnace. The ignition and combustion behavior of the droplet was recorded using a CCD camera and the ignition delay time, burnout time, and burning rate were then estimated. A flame emission spectrometer was used to identify the presence of sodium in the flame. It was found that combustion of the glycerol droplets with soap addition occurred in a two-stage manner: (1) the first stage where glycerol preferentially was evaporated and burned and (2) the second stage where soap was evaporated and burned. This resembled that of bi-component droplets with vastly different volatilities. The addition of soap in the glycerol slightly reduced the ignition delay time and shortened burnout time of the droplets. The burning rate of glycerol was greater with increasing soap content in glycerol. Sodium ions were detected to present in the flame of glycerol droplets with soap additions. The release of sodium ions into the flame promoted the combustion rate of the fuel vapor.