Evolution of volatile cloud in pulverized coal combustion with high-speed digital inline holographic visualization Fuel (IF 4.908) Pub Date : 2018-12-13 Xiaodan Lin, Yingchun Wu, Chenyue Wu, Longchao Yao, Xuecheng Wu, Linghong Chen, Kefa Cen
The coal devolatilization plays a significant role in the combustion of pulverized coal particles. The evolution of volatile cloud during devolatilization of pulverized coal particles (105–125 μm) is studied in a high-temperature flat-flame burner by combining high-speed photography with high-speed digital inline holography (DIH). By the high-speed holographic visualization, the evolution of volatile cloud of pulverized coal from volatile release to soot aggregation generation can be divided into four stages. Effects of coal type on volatile cloud evolution are investigated using three different coals, i.e., Shanxi bituminous coal, Ximeng lignite and Yinni lignite. The results show that both the Shanxi bituminous coal and Ximeng lignite produce soot aggregation during devolatilization, which is rarely observed for Yinni lignite. Moreover, Shanxi bituminous coal has a higher potential in soot cluster formation for its higher coal rank than Ximeng lignite. The high-speed reconstructed image sequences are analyzed to measure the velocity slip between the parent particle and volatile cloud. Compared with Shanxi bituminous coal, Ximeng lignite exhibits a larger slip velocity. This work also demonstrates that high-speed DIH has the powerful capacity of directly observing the evolution of volatile cloud, and helps to gain a deep understanding of pulverized coal combustion.
The stage evolution characteristics of gas transport during mine gas extraction: Its application in borehole layout for improving gas production Fuel (IF 4.908) Pub Date : 2018-12-13 Leilei Si, Zenghua Li, Yongliang Yang, Ruiting Gao
Diffusion and seepage play a significant role in the mine gas extraction, while their influence degree is dynamic with the change of time or location, showing a notable dynamic stage characteristic. Therefore, it is significant to master the conversion node of gas transport for improving the gas production. However, it is difficult to determine the conversion node and master controlling roles during mine gas extraction due to the lack of judgment index. In this work, a dual-porosity model was constructed to describe the gas transport in coal seam. Then, a transfer coefficient ratio between gas diffusion and gas seepage was used to define as the conversion node. Furthermore, our model was validated by comparing with the previous model, showing that our model can better describe the evolution of gas pressure under different stress conditions. The influence of stress, initial permeability and initial diffusion coefficient on the conversion node were investigated. Results showed that the initial permeability shows the most notable influence on the conversion node, followed by the stress. The initial diffusion coefficient has the relatively complex effect on the conversion node depending on the specific reservoir conditions. Finally, the transfer coefficient ratio was used to determine the best distance of boreholes for improving the gas production. The research results are important for CBM and mine gas extraction.
Combustion of straight algae oil in a swirl-stabilized burner using a novel twin-fluid injector Fuel (IF 4.908) Pub Date : 2018-12-13 Oladapo S. Akinyemi, Lulin Jiang, Rafael Hernandez, Carl McIntyre, Williams Holmes
The current study investigates the combustion performance of straight algae oil (AO) in a 7-kW lab-scale gas turbine burner enabled by a novel twin-fluid injector, named Swirl-burst (SB) injector. The chemical structure (fatty acid profile), the physical, and chemical properties of AO are acquired to understand the combustibility of the oil as a potential biofuel. Effects of equivalence ratio (ER) and atomizing air to liquid mass ratio (ALR) across the injector on the global combustion characteristics are investigated at a constant heat release rate for the oil. The features of interest include visual flame images, product gas temperature, emissions of carbon monoxide (CO), and nitrogen oxides (NOx) at the combustor exit. Results show that mono-unsaturated fatty acid is predominant in the composition of the oil, suggesting possibly short ignition delay. AO has a heating value comparable to that of diesel but with a high kinematic viscosity (approximately 16 times more viscous than diesel). Clean combustion highly depends on fine sprays that lead to fast fuel pre-vaporization, thorough fuel-air mixing, and thus clean premixed combustion. Conventional injectors such as air blast (AB) atomizers cannot finely atomize viscous oils for clean combustion due to the low viscosity tolerance. Fortunately, with the SB injection, clean, complete, and lean-premixed combustion of straight AO has been successfully achieved without fuel preheating at most of the investigated cases, reasonably reflecting the fine atomization capability of the SB injector even for the viscous oil. The blue flames, overlapping temperature profiles, and low emissions of CO and NOx consistently show the clean lean-premixed AO flames. Stable and clean flames are obtained at ERs of 0.60–0.75 (with the optimum ER identified at 0.65, in terms of flame stability and low emissions), and a blow-out limit at the ER of about 0.55. At the ER of 0.65, clean and lean-premixed flames are also acquired for all the tested ALRs (2.0–5.0). Increase in ALR varies the SAA and spray behavior of the SB injection as well as the aerodynamic interaction between fuel and oxidizer. The increasing ALR results in dominantly blue flames and decrease in CO and NOx concentrations, less than 10 ppm at ALRs > 2.5, due to finer atomization and better fuel-air mixing at the higher ALRs, and thus enhanced premixed combustion. Overall, clean and stable lean-premixed combustion of straight AO is achieved without fuel preheating using the novel SB injector despite the high fuel viscosity. The SB injection potentially enables AO itself as a cost-effective and near-zero-emission biofuel.
Raman spectroscopic study of chemical structure and thermal maturity of vitrinite from a suite of Australia coals Fuel (IF 4.908) Pub Date : 2018-12-13 Yulong Zhang, Zhongsheng Li
The deconvolution and resolution of overlapping bands in the Raman spectra of a suite of coals studied by curve-fitting methods has improved our understanding of the main structural changes in naturally matured coals. Even though much work on deconvolution of Raman spectra has been done, the systematic evolution of chemical structures is not well established. In this study we used a suite of 28 coal samples from Australia with vitrinite reflectance ranging from 0.38 to 3.52%. The micro-Raman spectra of vitrinite macerals from selected coals were acquired using a custom-made Raman spectrometer and supplemented by other Raman spectra previously acquired under the same experimental conditions. In the spectral deconvolution procedure, the second derivative curve-fitting method was used to determine the number of peaks and peak positions of the Raman spectra. Each band was tentatively assigned to a corresponding chemical structure by references to the interpreted major structural changes likely to have taken place during coalification. These parameters included PD (the position of D band), RBS (the distance between G band and D band), FWHMG (full width at half maximum of G band), IG/IGL (the intensity ratio of G band and GL band), and AR/b (the ratio of Raman integrated area and the slope of the spectral background). All of these Raman parameters are found to have a very good correlation with Ro% with R2 higher than 0.90. While five simple equations have been proposed and may be used to estimate thermal maturity of coals, two equations (Eq. (4) for Ro% from 0.38 to 1.5 and Eq. (5) for Ro% from 1.5 to 3.52) are best suitable to predict thermal maturity of coals with the most accuracy.
The influence of mixing ratio of low carbon mixed alcohols on knock combustion of spark ignition engines Fuel (IF 4.908) Pub Date : 2018-12-13 Hongqing Feng, Hongdong Zhang, Jianan Wei, Bowen Li, Di Wang
Alcohol fuels, owing to the characteristics of oxygen-containing and high octane number, are considered as one potential alternative fuel additive in spark ignition (SI) engines. In this paper, the ethanol and n-butanol are blended with gasoline to form the new low-carbon mixed alcohols-gasoline blended fuels. The effect of different mixing proportions of ethanol and n-butanol in gasoline on knock combustion and fuel economy of SI engine was studied by experiment and simulation. The results showed that with the increase of n-butanol ratio, brake specific fuel consumption (BSFC) increase, but knock index (KI) and knock intensity decrease. Moreover, crank angle delays under the same knocking condition when the engine fueled with E5-Bx and B5-Ey fuel, and the crank angle is delayed more significantly with the increase of engine speed. In addition, when the ethanol and n-butanol are blended as the same proportion in gasoline (i.e. x = y), the KI and knock intensity of E5-Bx fuel is lower than that of B5-Ey, which indicates that the B5-Ey fuel has better antiknock property. But the BSFC of B5-Ey is slightly greater than that of E5-Bx under the same operating condition, that is, the B5-Ey fuel has higher fuel consumption.
Influence of pH and grain size on physicochemical properties of biochar and released humic substances Fuel (IF 4.908) Pub Date : 2018-12-13 Marta Cybulak, Zofia Sokołowska, Patrycja Boguta, Agnieszka Tomczyk
The main goal of this study was to investigate the influence of pH and grain size of biochar on its physicochemical properties and on the quantity and quality of humic substances released from biochar. The studies were conducted on 5 biochar fractions and on the mixture of all fractions. Influence of grain size on physicochemical properties of biochar was characterized by analyzing changes in total carbon content, ash, density, total surface charge, average adsorption energy, specific surface area, content of functional groups and FTIR spectra. The effect of pH and grain size of biochar on releasing organic compounds were examined at pH of the extraction solution: 3, 5, 7 and 9 by analyzing aqueous extracts for changes in organic carbon content and for variation of humification degree coefficients. The results showed the grain size affected physicochemical properties of investigated material. The fraction <0.5 mm was characterized by the highest density, ash, content of functional groups and the lowest carbon content. Increasing grain diameter corresponded with decrease in average adsorption energy and with increase in the specific surface area. Only grain size, not pH of the solution, revealed clear effect on the quantity and quality of humic substances released from biochar.
Ultrasonic parameter measurement as a means of assessing the quality of biodiesel production Fuel (IF 4.908) Pub Date : 2018-12-12 Raphaela M. Baêsso, Rodrigo P.B. Costa-Felix, Piero Miloro, Bajram Zeqiri
Whilst fossil fuels have been an industrial driver for many decades, environmental concerns related to global warming have driven the development of alternative energy sources, such as the generation of biodiesel from vegetable oils. For a biodiesel to be commercialised, it must meets property and quality requirements from International Standards. Most of these checks must be performed off-line, with significant costs in terms of shutdown time and testing. On the other hand, ultrasound measurement can provide an in-line monitoring tool to assess the advance of transesterification. Although this was highlighted in previous works, hitherto this has not been the subject of a detailed metrological approach to define the uncertainty associated with ultrasound techniques applied to biodiesel and related liquids. This paper presents such research and addresses measurement of two ultrasound parameters, Speed of Sound (SoS) and attenuation coefficient (Att), and their capability of assessing macroscopic characteristics of the biodiesel. The liquids tested were pure edible oils (vegetable, corn, and sunflower), castor oil, pure biodiesel (B100), as well as blends of biodiesel with common contaminants or by-products related to biodiesel transesterification. Details of the biodiesel manufactured were varied, using different stirring speeds of rotation (200 rpm and 550 rpm), temperatures (40 °C and 50 °C), and KOH catalyst concentrations (0.2% and 1.5%). Contaminants added to pure biodiesel were methanol (0.10% and 0.20%), glycerol (0.10% and 0.15%) and triglyceride (2%). The acoustic characteristics of these liquids were determined relative to water using a broadband through-transmission substitution method covering the frequency range 1–20 MHz. Normalized error analysis has been applied to assess the equivalence of experimental results, as well as to discriminate the detection sensitivity of the technique. From the measurements, all edible oils showed equivalent experimental values for SoS and Att over the usable frequency band 2 MHz to 18 MHz. In contrast, biodiesel produced from sunflower and different reaction routes led to SoS and Att which were statistically different over the same frequency range, reflecting the ability of ultrasound to monitor low-level contamination of different blends. Finally, the paper concludes that ultrasound shows promise as a means of assessing biodiesel quality and purity with sensitivity sufficient to discern contaminants in a proportion as low as 0.1% in mass for Att measurements.
System simulation and experimental verification: Biomass-based integrated gasification combined cycle (BIGCC) coupling with chemical looping gasification (CLG) for power generation Fuel (IF 4.908) Pub Date : 2018-12-12 Huijun Ge, Haifeng Zhang, Wanjun Guo, Tao Song, Laihong Shen
Biomass-based integrated gasification combined cycle (BIGCC) is a power generation technology to convert biomass fuel to electricity. In view of biomass gasification characteristic, chemical looping gasification (CLG) is an innovative biomass utilization technology. Due to the presence of metal oxygen carrier materials in CLG process, syngas yield can be increased and tar catalytic cracking is occurred. In this paper, a new system integrating BIGCC with CLG is designed for power generation and the simulation of the whole process, including biomass gasification, gas cleaning, heat recovery steam generator (HRSG) and gas/steam turbine, are carried out with Aspen Plus software. At first, in order to ensure the model accuracy, the experiments in a 25 kWth reactor of interconnected fluidized beds are conducted and the experiment results are compared with the simulated results from the designed model. It is verified that the designed biomass gasification model, especially kinetic model and equilibrium model, is accurate with the change of gasification temperature and steam-to-biomass (S/B) ratio, which enhances the reliability of the whole CLG-BIGCC system. The CLG-BIGCC system exhibits a better plant performance, where power efficiency is higher than the ones in the existing BIGCC demonstration plants. The sensitivity analysis on the CLG-BIGCC system is also discussed. Results indicate that optimal gasification temperature is 860 °C and most suitable S/B ratio was 1.0. Besides, five optimization schemes about CLG-BIGCC with nitrogen reinjection are proposed and investigated.
Intrinsic relationship between Langmuir sorption volume and pressure for coal: Experimental and thermodynamic modeling study Fuel (IF 4.908) Pub Date : 2018-12-12 Yun Yang, Shimin Liu, Wei Zhao, Liang Wang
Gas adsorption volume has long been recognized as an important parameter for coalbed methane (CBM) resource assessment as it determines the overall gas capacity of coal. As the industrial standard practice, Langmuir volume (VL) is used to describe the gas adsorption volume. Another important parameter, Langmuir pressure (PL), is typically overlooked because it does not directly relate to the resource estimation. However, PL defines the slope of the adsorption isotherm and the ability of a well to attain the critical desorption pressure in a significant reservoir volume, which is critical to plan the initial water depletion rate for a CBM well. Qualitatively, both VL and PL are related to the fractal pore structure of coal, but the intrinsic relationships among fractal pore structure, VL, and PL are not well studied and quantified due to the complex pore structure of coal. In this study, a series of experiments were conducted to measure the fractal dimensions of coal and their relationship to methane adsorption capacity. The thermodynamic model of the gas adsorption on heterogonous surfaces was revisited, and the theoretical models that correlate the fractal dimensions with the Langmuir constants were proposed. Applying the fractal theory, adsorption capacity ( V L ) is proportional to a power function of specific surface area and fractal dimension, and the slope of the regression line contains information on the molecular size of the adsorbed gas. We also found that P L is linearly correlated with sorption capacity, which is defined as a power function of total adsorption capacity ( V L ) and a heterogeneity factor (ν). This implies that PL is not independent of VL, instead, a positive correlation between V L and P L has been noted elsewhere (e.g., Pashin ). In the Black Warrior Basin, Langmuir volume is positively related to coal rank (Pashin, 2010; Kim, 1977) [1,2], and Langmuir pressure is inversely related to coal rank. It was also found that P L is negatively correlated with adsorption capacity and fractal dimension. A complex surface corresponds to a more energetic system, which results in an increase in the number of available adsorption sites and adsorption potential, which raises the value of V L and reduces the value of P L .
Effect of reflux digestion time on MoO3/ZrO2 catalyst for sulfur-resistant CO methanation Fuel (IF 4.908) Pub Date : 2018-12-12 Jia Gu, Zhong Xin, Miao Tao, Yuhao Lv, Wenli Gao, Qian Si
A series of ZrO2 supports were treated by ammonia solution with different reflux digestion time, and loaded 25 wt% MoO3 for sulfur-resistant CO methanation reaction by incipient-wetness impregnation method. The MoO3/ZrO2 catalysts were also characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), infrared spectra of adsorbed pyridine (Py-IR). Compared to the undigested ZrO2, ZrO2 with reflux digestion in ammonia solution could achieve more oxygen vacancies, less Lewis acidic sites, smaller crystalline MoO3 and more amount of active sites. Generally, when the support reflux digested in ammonia solution exceed 12 h, the CO conversion of digested catalysts Mo/A-ZrO2-xh reached 60%, while the CO conversion of undigested catalysts was just 36% at the same reaction condition.
Experimental study on soot formation, evolution and characteristics of diffusion ethylene/air flames in ψ-shaped mesoscale combustors Fuel (IF 4.908) Pub Date : 2018-12-12 Mingfei Chen, Dong Liu, Yaoyao Ying, Kai Lei, Minye Luo, Guannan Liu, Rui Zhang, Bo Jiang
Soot formation, evolution and characteristics of diffusion ethylene/air flames in ψ-shaped mesoscale combustors of two different diameters with the variations of excess air ratio and flow rate were experimentally investigated. The variation in nanostructure and oxidation reactivity of soot was compared based on the results of high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Results demonstrated that with an increasing excess air ratio and flow rate, the unventilated flames with bifurcated shapes were observed in both types of combustors due to the deteriorated mixing process in large flow velocity. Different effects on characteristics of soot from two combustors with the same variation of flow rate were found. For the variation in ethylene flow rate of 60–100 ml/min at excess air ratio of 0.5, the oxidation reactivity of soot from the combustor with d = 4 mm first decreased and then slightly increased, while it decreased all the time as for the soot from the combustor with d = 6 mm. Moreover, the significant distinctions in soot nanostructure due to the scale effect were observed. The soot from the combustor with d = 4 mm exhibited the partial amorphous structure aggregated by a large amount of PAHs with high reactivity. Whereas among the soot from the combustor with d = 6 mm, a typical fullerene-like structure which represented the simultaneous existence of PAHs and graphitic parts was found. The soot graphitization degree and production increased notably with the enlargement of combustor size because the higher combustion temperature and longer residence time were simultaneously obtained, which both were beneficial to soot formation and growth rate. Significantly, the lower combustion efficiency was obtained in the combustor of d = 6 mm than 4 mm at α = 0.5 because of the larger soot production and more existence of unburned gas. But the higher combustion efficiency was found for the 6 mm than 4 mm at α = 1 in the case of almost no soot generation, which was due to the longer residence time.
Effects analysis on the gasification kinetic characteristics of food waste in supercritical water Fuel (IF 4.908) Pub Date : 2018-12-11 Jingwei Chen, Yi Fan, Jiaqiang E, Wen Cao, Feng Zhang, Jinke Gong, Guanlin Liu, Wenwen Xu
The gasification kinetic characteristics of food waste (FW) gasification by supercritical water (SCW) were investigated by examining the SCW gasification (SCWG) of FW in a quartz tube reactor, and the experimental results were investigated by using a series of kinetic models. The experimental results show that the carbon gasification efficiency increases with reaction temperature at the same residence time, and reactivity increases sharply at the early stage of gasification and then decreases with reaction time. The simulation results show that all the classical kinetic models underestimate the experimental results, similar to the models used in previous work on coal gasification by SCW. The underestimation of the models results from the catalytic effect of alkaline earth metals (AAEMs), which can notably increase the active sites of gasification reaction without changing the gasification kinetic mechanism. To solve the above problem, the catalytical effect to describe the kinetic behavior of the SCWG of FW is considered and a semiempirical modified random pore model (MRPM) is developed based on the RPM model. The simulation results of the MRP models are close to experimental findings, indicating that MRP model can be used to predict the entire process of SCWG under different conditions without dividing gasification into different stages of reaction. The MRP model can also be used for the prediction of SCWG of coal, biomass, and organic wastes and is crucial to reactor optimization and scaling up.
Improving biodiesel monoglyceride determination by ASTM method D6584-17 Fuel (IF 4.908) Pub Date : 2018-12-11 Teresa L. Alleman, Earl D. Christensen, Bryan R. Moser
Biodiesels produced from commercial and non-traditional feedstocks were analyzed by ASTM D6584-17 for monoglyceride (monoacylglycerol, or MG) content. It was found that D6584-17 as currently written may not accurately determine MGs from conventional feedstocks due to significant differences in retention time using modern instrumentation. For biodiesel from non-traditional feedstocks, D6584-17 did not sufficiently account for MGs containing fatty acids outside of C16 and C18 species. This led to under- and over-reporting of MGs, as critical components were not accurately measured. Improvements to the method were made through a three-step process. First, a standard mixture of MGs was run to determine the retention time of individual MGs that could be present in the samples from C10 to C24. An additional analysis for the fatty acid methyl ester (FAME) profile was used to determine the major MG species present in the biodiesel samples, using the assumption that the MG profile was proportional to the FAME profile. The biodiesel samples were analyzed by D6584-17, and the MGs were identified using retention time matching, based on the major species expected from measuring the FAME profile. By combining these two methods, the accuracy of MG determination by D6584-17 was improved for biodiesels prepared from all feedstocks.
A new model of emulsion flow in porous media for conformance control Fuel (IF 4.908) Pub Date : 2018-12-11 Long Yu, Boxin Ding, Mingzhe Dong, Qi Jiang
Emulsion flow in porous media is of paramount importance to the use of emulsions in the conformance control and enhanced oil recovery processes. In this paper, a new theoretical model, incorporating physical properties of porous media, physicochemical properties of the emulsion system, injection strategy, and the interactions between porous media and emulsion, was developed to quantitatively describe flow behaviors of emulsions in porous media. The resistance factor of an emulsion when transported in porous media was first derived through a-two phase flow method. The strong interaction between emulsion droplets and porous media was characterized by the capillary resistance force in the model. A non-uniform capillary model which considers size differences of the pore-body and pore-throat in porous media was proposed to represent the complicated real porous media. By analyzing the adsorption and plugging properties of different emulsion droplets in the non-uniform capillary model, the capillary resistance force was finally determined. To describe emulsion flow in the subsequent water flooding process after emulsion injection, an emulsion dilution factor was introduced into the model. A set of experimental data of emulsion flow in sandpacks was used to validate the reliability of the newly proposed model. The validation results show that by appropriately choosing coefficients, the simulated results are in good agreement with experimental values, with a maximum average absolute error less than 10%, and the developed theoretical flow model can be used to describe emulsion flow behavior in porous media.
Investigation of electrical properties with medium and heavy Brazilian crude oils by electrochemical impedance spectroscopy Fuel (IF 4.908) Pub Date : 2018-12-10 John W.S. Rocha, Maristela A. Vicente, Breno N. Melo, Maria de Lourdes S.P. Marques, Regina C.L. Guimarães, Cristina M.S. Sad, Eustáquio V.R. Castro, Maria F.P. Santos
Petroleum and petroleum products characterization are vital for decision-making in the oil industry. Electrical properties have been used for quality, safety control, indirect characterization and investigation of some physicochemical properties of petroleum and by-products. In this study, a heavy and a medium oil, labeled as alpha and beta, respectively, their distillation products and water-in-oil (W/O) emulsions were characterized by impedance spectroscopy to obtain electrical conductivity and dielectric constant at 30 and 50 °C. The results were used to propose one among many ways in which electrical properties can be used to predict other non-electrical physical properties in the field. We obtained kerosene cut (KC), diesel cut (diesel) and atmospheric residue (RAT) after distillation of the oils. The blends KC/oil, diesel/oil and KC/RAT were synthesized to investigate the effect of viscosity increase and addition of polar compounds to the conductivity and dielectric constant of these cuts. We synthesized W/O emulsions containing 10, 30 and 50% w/w of saline water. The Nyquist diagrams for the oil samples, cuts and blends presented only a single semicircle. For emulsions, two semicircles were observed, one attributed to the oil phase and the other to the emulsion phase. It was observed that an increase in temperature was followed by an increase in electrical conductivity and a decrease in dielectric constant for all samples. The highest values of electrical conductivity and dielectric constant were observed for the alpha oil, which has higher viscosity and polar compounds than beta oil. For KC, diesel and RAT cuts, it was observed that electrical conductivity decreases and the dielectric constant increases for higher boiling range cuts (KC < diesel < RAT). Concerning the blends, incorporation of oil or RAT into the KC or diesel was followed by an increase in electrical conductivity up to a maximum at a concentration of 25% w/w oil or RAT, then the conductivity drops. It was observed that the dielectric constant increases linearly with the addition of oil or RAT and that it can be used to infer the viscosity of these blends by plotting ln (kinematic viscosity) as a function of dielectric constant. Water incorporation to the oils was followed by a decrease in electrical conductivity and a linear increase in the dielectric constant for both oils. This last result implies that one can predict emulsions viscosity by using the dielectric constant results of these emulsions.
Experimental investigations of wall jet droplet impact on spray impingement fuel film formation Fuel (IF 4.908) Pub Date : 2018-12-10 Hujie Pan, Di Xiao, David Hung, Min Xu, Xuesong Li
The understanding of fuel spray impingement phenomenon and its impact of film formation on wall are significant for engine related applications, such as emission reduction and lubrication improvement, etc. However, the impingement phenomenon of the airborne droplets in the wall jet moving parallel to the wall has not been fully understood yet, especially for the fact that negligible amount of fuel film is formed underneath the wall jet. In this experimental research, various laser diagnostic techniques, including laser-induced fluorescence, Mie scattering, phase Doppler interferometry, and particle imaging velocimetry were utilized to capture both macroscopic and microscopic behavior of the spray impingement process. It was found that droplets in the spray with a high tangential velocity may be governed by the lift force induced by the boundary layer near the plate, gliding away without impinging the wall and forming wall film. Based on the observations, a modified impingement criterion is proposed to incorporate such gliding effects to improve the current understanding of droplet-wall interactions.
Effect of residual air bubbles on diesel spray structure at the start of injection Fuel (IF 4.908) Pub Date : 2018-12-10 M. Ghiji, L. Goldsworthy, V. Garaniya, P.A. Brandner, P. Hield, V. Novozhilov, K. Moinuddin, P. Joseph
Experimental and numerical analyses of the effect of residual air bubbles in a single-hole high-pressure diesel injector nozzle are presented. Detailed information on spray structures and dynamics near nozzle exit at the Start of Injection (SOI) is described. Experimental measurements are performed using a laser-based backlit imaging technique through a long distance microscope by injecting diesel fuel into a constant volume high-pressure spray chamber. Numerical investigation of, in and near-nozzle fluid dynamics is conducted in an Eulerian framework using a Volume of Fluid (VOF) interface capturing technique integrated with Large Eddy Simulation (LES) turbulence modelling. The present flow setup includes residual air bubbles remaining from a previous injection event, in-nozzle turbulence with no-slip wall conditions. Experimental images show a toroidal starting vortex near the nozzle exit suggesting a partially filled nozzle; transparency in the emerging jet demonstrates the presence of air trapped inside the nozzle liquid from the previous injection event. The numerical model provides insight into the influence of residual air bubbles on the spray morphology and dynamics of the emerging jet at the SOI. A mathematical code is developed to replicate the backlit imaging approach with the numerical results. The virtual images demonstrate a transparent liquid jet emerging into the pressurized chamber gas showing improved agreement with experimental images. The inclusion of air bubbles in the nozzle liquid prior to injection in the numerical model also yields improved agreement in the penetration velocity profile of the jet. These results explain how inclusion of residual air bubbles inside the nozzle liquid affects the physics of the penetrating jet at the SOI. The air bubbles inclusion also provides an explanation for the transparency of the emerging jet, rough interfacial surfaces, and enhanced necking behind the jet tip captured at the SOI.
Recent advances of surfactant-stabilized N2/CO2 foams in enhanced oil recovery Fuel (IF 4.908) Pub Date : 2018-12-11 Lin Sun, Baojun Bai, Bing Wei, Wanfen Pu, Peng Wei, Daibo Li, Changyong Zhang
Foam has been applied in enhanced oil recovery (EOR) for more than sixty years. The surfactant-stabilized N2/CO2 foams are two of the most widely used foams in foam EOR processes, and numerous oil reservoirs could potentially benefit from them. This paper comprehensively reviews the development of these foams over the past decade. We focused on the promising surfactant formulas and their corresponding mechanisms under different reservoir conditions, especially harsh conditions. The most recent studies have shown that low interfacial tension foaming surfactants are efficient in fractured/tight reservoirs, while CO2-switchable surfactants are well suited to CO2 foam in carbonate reservoirs with high temperatures. Pure surfactants and mixed surfactants that combine anions and cations contain superior foam properties. The surfactant aggregates, such as vesicles and wormlike micelles, could distinctly enhance the foam stability. However, the adsorption of the mixed surfactants on reservoir rocks and the temperature sensitivity of the complex structures should be given particular consideration. The phase behaviors involved in foam EOR processes are vital and much more complicated than those in other EOR processes. Thus, a better knowledge of the phase behaviors could further improve foam EOR performance. The results of this paper provide clues to N2/CO2 foam EOR design and also promote the development of harsh reservoirs.
Impact of gasoline direct injection fuel injector hole geometry on spray characteristics under flash boiling and ambient conditions Fuel (IF 4.908) Pub Date : 2018-12-11 Changzhao Jiang, Matthew C. Parker, Jerome Helie, Adrian Spencer, Colin P. Garner, Graham Wigley
The effect of injector nozzle design on the Gasoline Direct Injection (GDI) fuel spray characteristics under atmospheric and flash boiling conditions was investigated using Phase Doppler Anemometry (PDA) measurements. To understand the impact of hole diameter and conicity, experiments were conducted on two bespoke 3-hole injectors in a pressure and temperature controlled constant volume chamber and in the open air. The measurements were taken radially outward from the injector axis to the outer extent of the plume at distances of 15 mm, 25 mm and 40 mm from the injector tip. Observations of the influence of surrounding gas and temperature conditions and hole design on the injector spray performance were made. Under non-flash boiling conditions, it was found that the injection pressure dictates the length of the spray penetration before collapse occurs, with an increase in pressure resulting in an increase in this length. Comparison of mean velocity and droplet diameter data are also made to understand the performance under flash boiling conditions. Results show that, under flash boiling conditions, the droplet velocity significantly increases while the droplet size reduces. More importantly, it is found that the impact of the flash boiling environment on sprays of different hole geometries is different. Some hole designs offer more resistance against spray collapse. It was found that the mid-sized of the three hole diameters tested here was found to produce a spray that more readily collapsed than that of the smaller or larger hole diameters. In addition, it was found that under flash boiling conditions, the convergent hole had a greater propensity to exhibit spray collapse.
A comparative applicability study of model-fitting and model-free kinetic analysis approaches to non-isothermal pyrolysis of coal and agricultural residues Fuel (IF 4.908) Pub Date : 2018-12-11 Asma Ashraf, Hamed Sattar, Shahid Munir
Comparative applicability of model-fitting and model-free kinetic methods to pyrolysis of two coals and four agricultural residues was analyzed by using two models from each class of methods. The two model-fitting methods were Arrhenius and Coats-Redfern while Friedman and Vyazovkin were selected from the model-free category. According to kinetic analysis by all four models, the fuels could be arranged in following order of activation energy, CC > DC > SD > RH > FS > CH. The two model-fitting methods exhibited different kinetic parameters (E and reaction mechanism). All fuels were found to have a third order reaction mechanism (F3) by using Arrhenius model. In the case of Coats-Redfern model, the CC and RH displayed 3-dimensional diffusion mechanism (D3) whereas CH, SD and FS exhibited third order reaction mechanism (F3). DC was found to decompose according to 2-dimensional diffusion mechanism (D2). The percentage difference between the values of activation energy found from the Arrhenius and Coats-Redfern models was in the range of 6.24–21.64%. The percentage difference between the values of activation energy from two isoconversional models was not more than 3.29% for coals and 4.91% for agricultural residues in the fractional conversion range of 0.1–0.7. Isoconversional models were found to be more reliable and accurate for estimation of non-isothermal kinetics for pyrolysis of solid fuels compared with model-fitting methods.
Investigation of gas slippage effect and matrix compaction effect on shale gas production evaluation and hydraulic fracturing design based on experiment and reservoir simulation Fuel (IF 4.908) Pub Date : 2018-12-10 Courtney Rubin, Mehrdad Zamirian, Ali Takbiri-Borujeni, Ming Gu
Recent core-lab study of Marcellus Shale illustrated that effect of gas slippage and matrix compaction are significant on gas production because of substantial reservoir pressure depletion, especially during the late time of gas production. However, the impact of gas slippage and matrix compaction on gas recovery evaluation and hydraulic fracturing design is still not clearly understood and systematically investigated. Additionally, such impact varies with production time and completion/production circumstances. Therefore, it is critical to develop a laboratory-modeling based approach that properly characterizes the two permeability effects and evaluates their impact on well production evaluation and hydraulic fracturing design. In this study, a comprehensive parametric study is conducted by running reservoir simulations using empirical permeability correlations developed from core-lab tests under different confining stress and pore pressure conditions. Simulations of different case scenarios are run in two contrast groups. One group considers the effect of gas slippage and matrix compaction on gas production and the other group ignores the two effects. By comparing the simulated gas production, critical conductivity, and proppant pumping amount/cost of the two contrast groups, a better understanding of the effect of gas slippage and geomechanics on shale gas well performance and hydraulic fracturing design can be developed for operators. The results show that ignoring the two permeability effect in reservoir simulation leads to an overestimation of gas production evaluation, which is up to 11% for Marcellus Shale. It also leads to an over-design of proppant pumping amount, resulting in early staging, screening-out, and excessive pumping cost. Calculations further show that, an average of over 2 million dollars can be wasted for fracturing a single horizontal well in Marcellus Shale if excluding the two effect from a fracturing design. The two effects are more significant for lower BHP, longer hydraulic fracture, and larger stage spacing conditions.
Rapid fabrication of KTa0.75Nb0.25/g-C3N4 composite via microwave heating for efficient photocatalytic H2 evolution Fuel (IF 4.908) Pub Date : 2018-12-10 Zhiqiang Chen, Pengfei Chen, Pingxing Xing, Xin Hu, Hongjun Lin, Leihong Zhao, Ying Wu, Yiming He
A novel KTa0.75Nb0.25O3 (KTN)/g-C3N4 composite photocatalyst was fabricated through microwave heating for realizing the efficient photocatalytic H2 evolution. The energy-efficient preparation method allowed g-C3N4 to be formed in-situ on KTN surface in thirty five minutes. The binary constitution of the KTN/g-C3N4 composite was verified by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) experiments. UV–visible diffuse reflection spectroscopy (DRS) experiments suggested that the photoabsorption performance was increased after the introduction of KTN. N2-adsorption analysis indicated that the addition of KTN slightly increased the surface area of g-C3N4. Photoluminescence (PL) spectroscopy, electrochemical impedance spectroscopy (EIS) and transient photocurrent response (PC) analyses confirmed that the KTN/g-C3N4 composite displayed longer lifetime of photoexcited charge carriers than g-C3N4, owing to the suitable band potentials and the close contact of KTN and g-C3N4. This property was believed to the key characteristic of the composite, which led to its excellent photocatalytic performance. Under simulated sunlight irradiation, the optimal KTN/g-C3N4 catalyst presented a photocatalytic H2-generation rate of 1673 μmol·g−1·h−1, 2.5 and 2.4 times higher than that of KTN and pure g-C3N4, respectively. Under visible light irradiation, the value was determined to be 86.2 μmol·g−1·h−1, which achieved 9.3 times that of g-C3N4.
Fuel adhesion characteristics under non-evaporation and evaporation conditions: Part 1-effect of injection pressure Fuel (IF 4.908) Pub Date : 2018-12-10 Hongliang Luo, Keiya Nishida, Youichi Ogata, Wu Zhang, Tatsuya Fujikawa
Spray-wall impingement has been proved unavoidable in direct-injection spark-ignition (DISI) engines, which affects the fuel-air formation as well as combustion and exhaust emissions, making it difficult to meet the regulation of particle number (PN) in the future standards. In this study, the characteristics of fuel adhesion injected by a mini-sac gasoline injector with a single hole were investigated in a constant high-pressure chamber. The fuel spray and adhesion were measured via Mie scattering and refractive index matching (RIM) methods, respectively. The effect of injection pressure on the spray-wall interaction under room and high temperature condition were tested. The results showed that under room temperature, the injection pressure promotes better atomization, resulting in longer spray tip penetration, larger impinging spray height, and more fuel adhesion on the wall. However, when evaporation occurs, higher injection pressure favors the fuel evaporation due to the small droplets size, leading to shorter spray tip penetration, smaller impinging spray height, and less fuel adhesion on the wall. Moreover, under non-evaporation condition, high injection pressure has less effect on the uniformity of the fuel adhesion on the wall, while under evaporation condition, it improves the uniformity of the fuel adhesion. Owing to the different mechanisms of the fuel adhesion formation in the primary impingement (Region I) and secondary impingement (Region II) regions, injection pressure has more influence on the fuel adhesion in Region I, especially under evaporation condition.
H2 production by the water splitting reaction using photocatalysts derived from calcined ZnAl LDH Fuel (IF 4.908) Pub Date : 2018-12-08 M. Suárez-Quezada, G. Romero-Ortiz, J.E. Samaniego-Benítez, V. Suárez, A. Mantilla
Photocatalysts based on calcined ZnAl layered double hydroxides were obtained by coprecipitation and the subsequent thermal treatments at different temperatures. The calcined materials were characterized and its photocatalytic behavior was evaluated in the water splitting reaction in presence of UV irradiation. According to the XRD analysis, there was detected the presence of Zn as hexagonal ZnO in all the samples, as well as Al forming ZnAl2O4 and Zn6Al2O9, depending on the temperature of calcination employed. H2 yield was higher as the annealing temperature was increased due to the formation of the heterojunctions of ZnO with the Zn6Al2O9 and ZnAl2O4 oxides, reaching the maximum value in the sample annealed at 600 °C. Some decay in the activity was observed in the sample calcined at 700 °C, probably due to the higher recombination rate of the photogenerated charge carriers in that heterojunction in comparison with that obtained at 600 °C.
The link between the kinetics of gas hydrate formation and surface ion distribution in the low salt concentration regime Fuel (IF 4.908) Pub Date : 2018-12-08 Fariba Asadi, Majid Ejtemaei, Greg Birkett, Debra J. Searles, Anh V. Nguyen
Inorganic salts can thermodynamically inhibit gas hydrate formation. However, some inorganic salts at low concentration can act as a kinetic hydrate promoter. The mechanism of kinetic hydrate promotion in the presence of low concentration of inorganic salts is still unknown. This paper presents an experimental study into methane hydrate formation in an impeller-agitated vessel in the presence of sodium halides and alkali metal chlorides at low concentrations. It is shown that alkali metal chlorides and sodium halides at low concentration can reduce the induction time and kinetically promote gas hydrate formation. It has been proposed that bubbles form inside the agitated vessel as a result of the gas pocket break-up. Simulated gas pocket break-up studies show a smaller gas bubble formation in the salts solution with low concentrations in comparison with in the pure water. The small bubbles formation leads to an increase in the gas-water interface area and gas hold-up of the vessel. Consequently, there will be an increase in the mass transfer for gas hydration formation. In addition, the strength of hydrogen bonds at the gas/water interface affect the gas dissolution rate into the aqueous phase. Ions that have more affinity for the interface order water molecules weakly and improve the gas hydrate formation. Bubbles zeta potential measurements also confirm the ion-specific effect of the applied salts at the gas-water interface. Ultimately, gas-water interfacial area and ion-specific effect play critical roles in the gas hydrate formation.
The effect of densification with alkali hydroxides on brown coal self-heating behaviour and physico-chemical properties Fuel (IF 4.908) Pub Date : 2018-12-08 Mohammad Reza Parsa, Alan L. Chaffee
Victorian Morwell coal’s physico-chemical properties were modified through densification with Ca(OH)2, KOH, NH4OH and NaOH, in order to compare the effects of varying alkali metals addition on self-heating behaviour. The wire basket results showed that densification of brown coal with alkali hydroxides increased the critical ignition temperature in the order Ca(OH)2 < KOH < NaOH relative to densified sample with NH4OH and without additive. The surface area and pore volume of all coal products densified with alkalis reduced. In addition, results showed that the size and charge of the exchanged cations play an important role in their interaction with coal oxygen functional groups, the extent of cross-linking network and consequently on the reduction of surface area of densified products with alkalis. Thermogravimetric analysis (TGA) results demonstrated a decrease in the proportion of the mass loss occurring at lower temperatures, and a shift to higher temperature in the main oxidation/decomposition stages, consistent with increasing the critical ignition temperature. Fourier transform infrared spectroscopy (FTIR) results suggested a catalytic role for cations (K > NH4 > Na > Ca) in the formation of quinones during kneading of brown coal under alkaline conditions. The results revealed that the addition of alkalis to brown coal at basic pH improves the oxidation tolerance of the carboxylic/carboxylate groups and also enhances the polymerization and aromatization reactions during the thermal oxidation of coal, generating aromatic ether and/or ketone substituted polymers with higher thermal stability toward oxidation. Using NaCl as additive, at coal’s natural acidic pH, resulted in a very brittle densified product, with higher macro and mesopore volumes than the coal densified prepared without additive. However, the Tcr value increased, probably due to its lower micropore volume.
A numerical study on the impact of chemical modeling on simulating methane-air detonations Fuel (IF 4.908) Pub Date : 2018-12-08 L.F. Gutiérrez Marcantoni, J. Tamagno, S. Elaskar
This article presents a study concerning the influence of chemical kinetic models on the generation and evolution of methane-air planar detonations. The open source solver rhoCentralRfFoam is applied to perform all numerical simulations. Four chemical kinetic models are considered. Two of them are highly simplified (with, at most, one global chemical reaction and two simple steps), while the other two involve 19 and 53 species, with 57 and 325 chemical reactions, respectively. Insights are provided into methane-air planar detonation waves and the development conditions under which they may or may not become self-sustained. Numerical results showed that regardless of how much time the detonation remains overdriven, without the adequate support it shall always decay to a Chapman-Jouguet (CJ) steady-state value. However, the CJ state may not stand on its own and may continue to decay until the reacting zone decouples from the leading blast. This sort of detonation failure is described and discussed.
Emission reduction of particulate matter from the combustion of biochar via thermal pre-treatment of torrefaction, slow pyrolysis or hydrothermal carbonisation and its co-combustion with pulverized coal Fuel (IF 4.908) Pub Date : 2018-12-08 Wenyu Wang, Chang Wen, Changkang Li, Meng Wang, Xiaomin Li, Ying Zhou, Xun Gong
Emission reduction of PM10 (of an aerodynamic diameter of 10 μm or less) was investigated via the combustion of biochar pre-treated from straw by torrefaction at 300 °C (T-300), slow pyrolysis at 500 °C (S-500), or hydrothermal carbonisation at 240 °C (H-240), and their co-combustion with Ping Ding Shan (PDS) bituminous coal in a drop tube furnace at 1400 °C. The generated PM10 was collected by a Dekati low pressure impactor (DLPI) sample system, and its mass/chemical composition was characterised. During single combustion of the straw and its pre-treated biochar, the emission amount of PM0.3 (aerodynamic diameter of ≤0.3 μm) from the biochar was linearly affected by the release of Cl during various pre-treatments and the formed KCl release into the gas phase during combustion. The emission of PM1-10 still changed linearly, mainly because of the increased ash content after pre-treatment. Co-combustion of biomass fuels and PDS coal presents an obvious reduction in PM10 emission, particularly PM0.3. The higher Cl content in biomass fuels is also linearly correlated with a greater reduction in PM0.3 emission. Aluminosilicates in coal, e.g. kaolinite, are responsible for the capture of gaseous species from biofuels and the subsequent coalescence of sticky minerals, reducing PM0.3 and PM1-10 emissions following co-combustion.
Sulfonic acid functionalized hydrophobic mesoporous biochar: Design, preparation and acid-catalytic properties Fuel (IF 4.908) Pub Date : 2018-12-08 Yao Zhong, Qiang Deng, Peixin Zhang, Jun Wang, Rong Wang, Zheling Zeng, Shuguang Deng
Sulfonic acid functional strong acidic catalysts are largely used in various chemical reactions. However, in many reactions with water as product, the catalytic activity and selectivity are unsatisfactory, because hydrophilic acid sites of SO3H would suffer from acidity decreasing and some hydrolysis side reactions would occur via water adsorption. Herein, a novel hydrophobic arenesulfonic acid functionalized biochar was successfully prepared for the first time by one-pot diazo reduction method of biochar with amino-arenesulfonic acid (such as, 4-aminbenzenesulfonic acid, 4-amino-1-naphthalenesulfonic acid, 8-amino-1-naphthalenesulfonic acid, 4-amino-3-hydroxy-1-naphthalenesulphonic acid). It has a large specific surface area of 200–400 m2/g, a hydrophobic network with water contact angle higher than 120° and a higher concentration of sulfonic acid over 1.0 mmol/g. Moreover, the hydrophobicity-oleophilicity and acidity are increased with the arene length and grafting amount of arenesulfonic acid. In the esterification reaction of fatty acid with methanol as well as the transesterification reaction of glycerol trioleate with methanol for the production of biodiesel, the sulfonated biochar shows a higher conversion of 96.7% for esterification and 86.3% for transesterification compared with amberlyst-15 (86.7%, 39.9%) and traditional sulfonation biochar-SO3H (27.4%, 32.6%). In the alkylation reaction of 2-methylfuran with cyclopentanone for the production of high-density biofuel, its catalytic efficiency with target product yield of 76.1% is higher than that of amberlyst-15 (50.2%) and traditional sulfonation biochar-SO3H (13.2%), because of its hydrophobicity and strong acidity. Furthermore, the catalyst is stable and shows an excellent cycle performance after 6 runs. The successful preparation of hydrophobic biochar-based acidic catalysts not only provides a new way for high-value utilization of biochar, but also eliminates the negative effect of water on many catalytic reactions.
Effects of the N, O, and S heteroatoms on the adsorption and desorption of asphaltenes on silica surface: A molecular dynamics simulation Fuel (IF 4.908) Pub Date : 2018-12-08 Yun Bai, Hong Sui, Xiaoyan Liu, Lin He, Xingang Li, Esben Thormann
The adsorption and desorption of asphaltene on silica surface is highly dependent on the heteroatoms present in its structure. Herein, some model asphaltene molecules with different heteroatoms (i.e., N, O, S) at different positions (in the aromatic cores, in the middle and termination of alkane side chains) are selected as the adsorbates to investigate their adsorption and desorption behaviors on silica surface through molecular dynamics (MD) simulation. Results reveal that the characteristic adsorption configuration of asphaltenes is ascribed to the competition between the asphaltene-silica interaction and π–π stacking interaction among the asphaltene polyaromatic rings. The presence of heteroatoms is found to be able to strengthen the interactions between asphaltenes and silica, depending on their type and location. For example, the terminal polar groups, especially the carboxyl (COOH), exhibit the greatest contribution to the electrostatic interaction (increasing from −81 to −727 kJ/mol). The S atoms are also found to increase the van der Waals interaction energies by 25%. According to the equilibrium desorption conformation and density profile, the presence of heteroatoms is found to significantly hinder the desorption of asphaltenes from silica due to the enhanced polar interactions. The impeded desorption is also confirmed by the slower detachment of asphaltenes based on the time-dependent interaction energies and center of mass (COM) distances analysis. Additionally, the terminal polar groups lead to extraordinary desorption properties of asphaltenes. It is observed that the strong asphaltene-silica and asphaltene-water interactions coexist in these systems due to the high polarity and hydrophilicity of the terminal polar groups.
Experimental investigation of nitrogen addition effect on combustion characteristics of buoyant turbulent diffusion flame Fuel (IF 4.908) Pub Date : 2018-12-07 Yubo Bi, Jian Chen, Xiao Chen, Shouxiang Lu, Changhai Li
Experimental study was carried out on the combustion characteristics of buoyant turbulent diffusion propane flame with fuel volume fraction ranging from 0.2 to 1.0 by nitrogen addition. The combustion characteristics reported include total flame length, flame diameter, soot free length fraction (SFLF), axial temperature distribution, maximum axial temperature and flame radiation fraction. Results show that the total flame length and flame diameter are insensitive to nitrogen addition. Soot free length fraction was found to be proportional to (1+S)1S-0.5fv,fuel-1. The axial temperature near the burner decreases while increases at higher height with nitrogen addition. The maximum axial temperature increases at first then decreases with nitrogen addition. The different trends in axial temperature characteristics are brought by two competitive effects between cooling effect and declined radiative heat loss due to nitrogen addition. The flame radiation fraction decreases with nitrogen addition due to soot reduction and is found to be proportional to (1+S)-0.25S0.125fv,fuel0.25 based on theoretical analysis and experimental results. The correlation result is compared to the previous data indicating good applicability.
The mechanism of Pd, K co-doping on Mg–Al hydrotalcite for simultaneous removal of diesel soot and NOx in SO2-containing atmosphere Fuel (IF 4.908) Pub Date : 2018-12-07 Li Yang, Chen Zhang, Xinqian Shu, Tao Yue, Sujian Wang, Zengshe Deng
A Pd/K/MgAlO mixed oxide was obtained by coprecipitation. The effect of Pd, K co-doping on the structure and catalytic activity of the Mg–Al hydrotalcite in a high concentration of SO2 atmosphere was characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), Temperature-programmed reduction (H2-TPR), and the transient response method. Studied the reaction mechanism and action mechanism of the doped K and Pd with the polluted gas in the catalytic, and calculated the kinetic parameters of the catalytic reaction. Our results show that potassium was highly dispersed on the surface of Mg–Al hydrotalcite and that incorporating potassium into the catalyst resulted in smaller grains than those of the original catalyst. After potassium doping K, K+ cations substituted protons of the weakly basic OH on MgAlO to form Mg(Al)-O-K., and the formation of this new basic valence bond conducive to the combustion of diesel soot. The ignition temperature of soot decreased from 380 to 217 °C. Moreover, modification of this Mg–Al hydrotalcite catalyst with potassium and palladium significantly reduces the activation energy of the reaction which form CO2 and N2 and benefit the combustion of soot and removal of NOx.
A fractal approach to fully-couple coal deformation and gas flow Fuel (IF 4.908) Pub Date : 2018-12-07 Guannan Liu, Jishan Liu, Liu Liu, Dayu Ye, Feng Gao
Although the impact of matrix microstructures on the evolution of coal permeability is significant, this impact has not been included in the analysis of coupled multiple processes during the extraction of coal seam gas. Previous studies normally investigate the relation between microstructures and coal porosity or permeability through imaging characterization techniques. In this study, we developed a fractal permeability model that defines coal permeability as a function of effective stress. In this model, coal microstructure is characterized by three fractal parameters: (1) fractal dimension of pore size; (2) fractal dimension of throat tortuosity; and (3) maximum pore size. These fractal dimensions may evolve with the effective stress through porosity. We applied this fractal permeability model to fully couple coal deformation and gas flow. Model results illustrate the significant differences between the fractal approach and the classical cubic model between permeability and porosity. When the porosity remains unchanged, the permeability calculated by the classical cubic model remains as a constant. However, the fractal permeability changes due to different microstructural parameters. These results show that the macroscopic permeability of coal is directly proportional to the fractal dimension and the maximum pore size, and is inversely proportional to the fractal dimension of the throat tortuosity. These characteristics cannot be captured by the classical cubic porosity-permeability model.
Effects of doping Mg2+ on the pore structure of MIL-101 and its adsorption selectivity for CH4/N2 gas mixtures Fuel (IF 4.908) Pub Date : 2018-12-07 Qingzhao Li, Chuangchuang Yuan, Guiyun Zhang, Junfeng Liu, Yuannan Zheng
In this paper, one kind of porous materials had been prepared by doping Mg2+ on MIL-101 materials using hydrothermal method. Based on the low-pressure nitrogen adsorption (LPNA), X-Ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM) and High-pressure methane adsorption (HPMA) analyzer, the characteristics of new materials and its adsorption selectivity had been measured and analyzed systematically. Results show that doped Mg2+ would greatly increase the specific surface areas of MIL-101 by 58.2% at the most. Moreover, the pore structure of MIL-101 @ Mg2+ materials tend to be uniform. Compared with MIL-101 parental material, the single crystal size would be decreased by 100–200 nm. From XRD and TEM results, it can be concluded that the chemical skeleton structure of MIL-101 @ Mg2+ series materials are greatly similar with that of parental MIL-101 and not be destroyed by doping Mg2+. Doping Mg2+ increases the adsorption capacity of CH4 and N2 at different level because doping proper amount of Mg2+ restrains the generation of H bond, which has a positive effect on methane gas adsorption. Based on the maximum adsorption capacity and the hysteresis of adsorption and desorption curves, it can be concluded that the optimal Mg2+ doping amount is determined of 12.8%. And, according to the theory of Ideal Adsorbed Solution Theory (IAST), the separation coefficient of CH4/N2 selective adsorption also indicates that MILemail@example.com% Mg2+ presents the largest adsorption separation coefficient and highest separation potentials.
Lean ignition and blow-off behaviour of butyl butyrate and ethanol blends in a gas turbine combustor Fuel (IF 4.908) Pub Date : 2018-12-07 Zhichao Zhang, Longfei Chen, Yiji Lu, Anthony Paul Roskilly, Xiaoli Yu, Andrew Smallbone, Yaodong Wang
This paper reports the experimental study on lean ignition (LI) and lean blow-off (LB) behaviour of butyl butyrate-based biofuels in a gas turbine combustor. The butyl butyrate-based biofuels were formulated (butyl butyrate–ethanol blends with the volume percentage of ethanol 0, 10%, 30%, 50% respectively, named BE-0, BE-10, BE-30, BE-50). The aviation kerosene RP-3 was also tested as a reference fuel. A combustor of an aero-engine was fabricated to conduct experiments on these fuels. The statistic method Design of Experiments (DoE) was employed to correlate LI and LB with fuel properties and operating conditions, and then analyse the significance of these experimental variables. The results indicated that all test biofuels had lower equivalence ratio of LI than RP-3, but the LB between RP-3 and the biofuels of high ethanol fraction (30% and 50%) had no appreciable difference at low air flow rate. The results also demonstrated that fuels with high ethanol fractions tended to ignite and blow off the flame at higher equivalence ratios. Meanwhile, the equivalence ratio of both LI and LB decreased at high inlet air flow rate for all the test fuels. RP-3 could combust under a larger range of air conditions yet its stability was more sensitive to air flow rate than test biofuels. Two predictive equations of LI and LB were obtained via Design of Experiments (DoE) and demonstrated that the lower heating value (LHV) of fuels, air pressure drop in the combustor, fuel pressure and inlet air pressure of the combustor were the main factors influencing LI and LB.
Progressive crude oil distillation: An energy-efficient alternative to conventional distillation process Fuel (IF 4.908) Pub Date : 2018-12-05 Shankar Nalinakshan, V. Sivasubramanian, Vineesh Ravi, Aneesh Vasudevan, M.S. Ramya Sankar, K. Arunachalam
Distillation, the major process in crude oil refineries as of now. In this work we focused the attention to energy saving with respect to an industrial crude oil distillation unit. An alternative to the conventional crude oil distillation model present in the Bharat Petroleum Corporation, Kochi Refinery is proposed and simulated. The theoretical predictions as well as the simulated results indicate that the Progressive crude oil distillation reduces the utility burden as well as increase the extraction of more valuable light components. The simulation was carried out using Aspen HYSYS V8.8.2. Different crudes are taken into account and their properties and amount of distillate are analyzed. The optimization is done in an easy manner rather than the conventional mathematical method, together with the advanced process control tools; make it profitable in the operation in real time.
Influences of phosphorus on ash fusion characteristics of coal and its regulation mechanism Fuel (IF 4.908) Pub Date : 2018-12-06 Fenghai Li, Hongli Fan, Xiaochuan Wang, Tao Wang, Yitian Fang
A large quantity of livestock manure and sewage sludges produced annually in China, and the co-gasification with coal provides a promising way for these clean and large-scale utilization. The livestock manure and sewage sludges generally contain high phosphorus content. To explore the influences of phosphorus on the fusion temperatures (AFTs) of different coals and their mechanisms, the ash fusion variation behaviours of high aluminum Shajuzi coal (SJZ) and high calcium Zhundong coal (ZD) or Yimi coal (YM)) with different mass ratio phosphorus pentoxides (P2O5) were investigated by an AFT tester, x-ray diffraction, and FactSage software. The P2O5 addition could change the AFTs of three coals effectively, however the changing trend was different due to the difference in their ash-composition. With increasing P2O5 mass ratio, low melting point (MP) berlinite formation and high MP mullite content decrease resulted in decreases in the AFTs of SJZ mixture; while high MP calcium phosphates formation led to the AFTs of ZD or YM mixture increase. At high temperature the silicon in silicate or silicaluminate in ash compositions was gradually substituted by phosphorus with increasing P2O5 mass ratio and transformed into different MP phosphates because the ionic potential of P5+ (147 nm−1) was higher than that of Si4+ (95 nm−1), which resulted in different variation behaviours in the AFTs of mixture.
Experimental measurement and analytical estimation of methane absorption in shale kerogen Fuel (IF 4.908) Pub Date : 2018-12-05 Yu Pang, Yuanyuan Tian, Mohamed Y. Soliman, Yinghao Shen
Gas storage in shale (organic-rich mudstone) consists of three different states: free gas in pores and natural fractures; adsorbed gas on organic and inorganic pore walls; and absorbed gas into organic matter (kerogen). Since it is difficult to differentiate absorbed gas from adsorbed gas, most current studies combine the adsorbed gas with absorbed gas and call the combination as gas sorption. In this study, a conceptual model of gas sorption is proposed to account for the contributions from adsorption and absorption to gas storage in shale, respectively. Methane sorption capacity of Barnett and Eagle Ford shale core samples is measured by magnetic suspension sorption system. Regression analysis is performed on the measured data by Simplified Local-Density model coupled with modified Peng-Robinson Equation of State (SLD-PR). Absolute sorption capacity of these two shale core samples is estimated based on the density profile of SLD-PR model. Additionally, the absorbed gas, which is regarded as the gas molecules dissolving/diffusing into the bulk of solid kerogen, is distinguished from the adsorbed gas through interpreting the results of gas expansion measurements using Fick’s law of diffusion. Moreover, methane diffusion coefficients for the two shale core samples are determined, which range from 10−22 m2/s to 10−21 m2/s. The percentage of absorbed gas accounting for total sorbed gas increases with pore pressure. When the pore pressure increases, more gas molecules attempt to adsorb on the surface of kerogen and create a larger gas concentration gradient for gas diffusing into the kerogen. The gas molecules, which adsorb on the pore walls of kerogen and then diffuse into the solid lattice of kerogen, may lead to the swelling of kerogen and thus reduce the pore width for free gas transportation. Therefore, the accurate prediction of the gas absorption capacity of kerogen is significant to understand gas storage mechanism and characterize original gas in place (OGIP) in shale gas reservoirs.
Elucidation of reaction pathways of nitrogenous species by hydrothermal liquefaction process of model compounds Fuel (IF 4.908) Pub Date : 2018-12-04 Aisha Matayeva, Daniele Bianchi, Stefano Chiaberge, Fabrizio Cavani, Francesco Basile
The reaction pathway of nitrogen containing compounds under hydrothermal liquefaction (HTL) conditions was investigated by using amino acids as protein model compounds. The effect of organic acids and alkaline catalysts was also investigated by determining the structure and the partition of nitrogen containing species between the resulting solid, aqueous and bio-oil phases. Representative results showed that operating in a water-acetic acid (95/5% v/v) binary solvent system resulted in a dramatic improvement in carbon recovery in the oil phase due to the transformation of water soluble hydrophilic products into oil soluble derivatives by acylation of the amino moiety. The conclusions of this study provide a useful tool to improve the HTL process applied to nitrogen rich biomass, such as the organic fraction of urban waste, sewage sludge, and aquatic biomass (microalgae).
Crude oil/water emulsion separation using graphene oxide and amine-modified graphene oxide particles Fuel (IF 4.908) Pub Date : 2018-12-04 S. Nathalia Contreras Ortiz, Rafael Cabanzo, Enrique Mejía-Ospino
Graphene oxide (GO) nanosheets have been experimentally proved to be a highly efficiency, rapid and universal demulsifier to break up the crude-in-water emulsion. The alkylamine functionalization of graphene oxide is well known as a way to turn graphene oxide highly affine with organic solvents. In the present work an amphiphilic material, graphene oxide functionalized by amino groups were prepared by Hummer’s modified method. We introduced it as a versatile demulsifier to break up crude-in-water emulsions. The amphiphilic material was characterized by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction (XRD) and emission scanning electron microscope (SEM). The efficient demulsifier to break up crude-in-water emulsion was proved in synthetic emulsion using Colombian crude oil with different concentration. Demulsification tests indicated that graphene oxide amine-modified (GO-A) could separate the crude-in-water emulsion in a short time. Demulsification performance of amphiphilic material was made using the bottle test and evaluated by UV–Vis absorption spectroscopy to measure the final grease concentration after GO-A treatment.
The influence of CO2 saturation time on the coal gas flow: Fractured bituminous coal Fuel (IF 4.908) Pub Date : 2018-12-04 Xiaogang Zhang, Ranjith Pathegama Gamage, M.S.A. Perera, A. Haque, A.S. Ranathunga
The permeability reduction due to the coal matrix swelling induced by the adsorption of CO2 is the major concern during enhanced coalbed methane recovery (ECBM) as well as CO2 sequestration in coal reservoir. Many problems arise in the context of this process regarding the coal permeability variations, and very few studies have been made with consideration of long-term CO2 saturations on gas flow behaviour alterations. The main objective of this study is therefore to examine the influence of both subcritical and supercritical CO2 flooding durations on N2 and CO2 permeability variation of naturally fractured low volatile bituminous coal under various tri-axial conditions. Five CO2 flooding durations, up to 65 h, both subcritical (6 MPa) and supercritical (14, 20 MPa), were introduced to the sample under three confinements, respectively. Results show that for 11 MPa and 17 MPa confining environment, most permeability reduction occurs during the first CO2 flooding process, and supercritical CO2 flooding causes significant higher N2 permeability reduction (from 14.38% to 50.18%) than subcritical CO2 (from 4.11% to 11.25%). The permeability reduction rate decreases with time but this reduction continues even after a total of 153 h flooding. Longer permeability reduction process is observed upon supercritical CO2 adsorption due to the much higher viscosity of supercritical CO2. Under deep underground condition (>1 km), CO2 exhibits a N2-like flow behaviour because of the dominant poroelastic effect. The influence of CO2 flooding on permeability alterations has been significantly compromised with much smaller permeability reduction after 20 MPa CO2 flooding compared with 14 MPa CO2 flooding (7.33% and 38.75% for 7 MPa CO2 injection pressure, respectively), along with no apparent permeability reduction for the further CO2 flooding scenarios.
HDT of the model diesel feed over Ir-modified Zr-SBA-15 catalysts Fuel (IF 4.908) Pub Date : 2018-12-04 Verónica A. Valles, Yanika Sa-ngasaeng, María L. Martínez, Siriporn Jongpatiwut, Andrea R. Beltramone
Iridium catalyst using different zirconium modified-SBA-15 supports were tested in the HDT of tetralin and typical sulfur and nitrogen compounds present in diesel feed. The zirconium modified-SBA-15 supports were synthesized by sol-gel method using two sources of zirconium, zirconyl chloride and zirconium (IV) propoxide. Regarding XRD, N2 adsorption isotherms and TEM, we obtained better textural and structural properties using the alkoxide, especially when lactic acid was added in order to decrease the hydrolysis rate of zirconium propoxide. In addition, XPS and DRUV-Vis demonstrated that zirconium was incorporated mainly as tetrahedral Zr4+ species NH3-TPD showed that higher acidity is observed when tetrahedral Zr4+ species are present. Iridium dispersion was determined by TEM and H2-chemisorption and reducibility by XPS and TPR. Among the catalysts prepared, the catalyst synthesized using zirconium propoxide and lactic acid presented the highest dispersion, lowest cluster size and lowest reduction temperature. Consequently, this was the most active catalyst for the hydrogenation of tetralin, the HDN of indole and quinoline and the HDS of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). The presence of Zr+4 had a remarkable effect on the dispersion and reducibility capacity of the iridium actives species. In addition, the presence of moderate acidity in this material gives the best catalyst for HDN and HDS in the studied conditions. The inhibition effect of the sulfur and nitrogen compounds over tetralin hydrogenation was studied using individual feeds and a mixture feed. We observe that 4,6-DMDBT and quinoline were the most refractory compounds and they showed the highest inhibition effect. Tetralin hydrogenation was stronger inhibited when using the mixture feed compared with the individual feeds. This can be explained in terms of the competition between the different compounds that retard the rate of hydrogenation of tetralin. However, a high conversion of tetralin was achieved even when 300 ppm of S or N was added. The most active catalyst synthesized by direct synthesis using propoxide and lactic acid was stable after several catalytic cycles making this material as potential catalyst for HDT reaction at mild conditions.
Investigation on the physicochemical structure and gasification reactivity of nascent pyrolysis and gasification char prepared in the entrained flow reactor Fuel (IF 4.908) Pub Date : 2018-12-04 Hongyu Zhao, Yuhuan Li, Qiang Song, Shucheng Liu, Jie Yan, Xiaohua Wang, Qingxiang Ma, Xinqian Shu
The structure of nascent pyrolysis and gasification char during lignite pyrolysis and gasification changes due to the product branching which holds the key to unveil these mechanisms, but it is notoriously difficult to find the relationship among the reaction time, structural evolution and gasification reactivity of the nascent char. Here, we investigate the changes in the structure of nascent char during lignite pyrolysis and gasification in the entrained flow reactor under N2 and CO2, respectively. Subsequently, we determine the selective consumption of small aromatic rings and rapid formation of oxygen-containing functional groups. In the initialization phase of gasification reaction, the condensation polymerization between the aromatic rings in char increases, which might result in the rapid decrease of the ratio of aromatic rings and aromatics with not less than 6 rings. The formation temperature of char is responsible for the char stability and the path of gasification reaction. The sensitivity to temperature of the nascent gasification char decreased in the process of non-isothermal gasification. Simultaneously, gasification kinetic parameters shows that the effect of popplycyclic reaction of benzene rings in nascent pyrolysis char due to the changes of chemical structure, which is more intense than that of structure changes of nascent gasification char.
Viscosity effect on the pressure swirl atomization of an alternative aviation fuel Fuel (IF 4.908) Pub Date : 2018-12-04 Reza Alidoost Dafsari, Hyung Ju Lee, Jeongsik Han, Dong-Chang Park, Jeekeun Lee
Atomization characteristics with viscosity have motivated a number of works to investigate the flow behavior with temperature variation. An experimental study on the atomization characteristics of an aviation fuel was performed to investigate the effects of fuel temperature and its physical properties on the atomization quality and spray structure. A pressure-swirl-type atomizer as a wide-range-applicable nozzle in industrial field and gas turbine combustors was employed to inject the aviation fuel into a gaseous medium. The experiments were conducted by optical diagnostic methods, namely, phase Doppler particle analyzer (PDPA) to measure droplet size and velocity and particle image visualization to capture spray structure. Changes in physical properties of the fuel altered the spray structure, droplet distribution, and atomization quality, which apparently are effective in combustion efficiency and combustion products. Spray development was mapped with the effective parameters from the unstable to fully developed stage. It was also found that decreasing the fuel temperature degrades atomization quality, decreases spray angle and velocity component values, and generates a lower number of fine droplets. Pursuing the effects of injection pressure and temperature on the atomization characteristics led to correlations for predicting spray angle and mean SMD. The findings contribute well to the literature and clarify the atomization process with temperature variation.
Experimental and computer simulation studies of dehydration on microporous adsorbent of natural gas used as motor fuel Fuel (IF 4.908) Pub Date : 2018-12-04 M.R. Petryk, A. Khimich, M.M. Petryk, J. Fraissard
An experimental and theoretical study of the dehydration of natural gas using microporous silica beds for motor fuel technology in extreme winter climates is described. Analytical solutions to the problem of non-isothermal adsorption and desorption are based on Heaviside’s operational method and Laplace integral transform, but the development of calculations is quite original. Experimental and modeling distributions of moisture and temperatures of gas at the inlet and outlet of the silica beds for each adsorption – desorption phase at different times are presented. The distribution of moisture within the beds for the full dehydration – regeneration cycle is determined.
Fully-resolved simulations of coal particle combustion using a detailed multi-step approach for heterogeneous kinetics Fuel (IF 4.908) Pub Date : 2018-12-03 G.L. Tufano, O.T. Stein, A. Kronenburg, G. Gentile, A. Stagni, A. Frassoldati, T. Faravelli, A.M. Kempf, M. Vascellari, C. Hasse
Fully-resolved simulations of the heating, ignition, volatile flame combustion and char conversion of single coal particles in convective gas environments are conducted and compared to experimental data (Molina and Shaddix, 2007). This work extends a previous computational study (Tufano et al., 2016) by adding a significant level of model fidelity and generality, in particular with regard to the particle interior description and heterogeneous kinetics. The model considers the elemental analysis of the given coal and interpolates its properties by linear superposition of a set of reference coals. The improved model description alleviates previously made assumptions of single-step pyrolysis, fixed volatile composition and simplified particle interior properties, and it allows for the consideration of char conversion. The results show that the burning behavior is affected by the oxygen concentration, i.e. for enhanced oxygen levels ignition occurs in a single step, whereas decreasing the oxygen content leads to a two-stage ignition process. Char conversion becomes dominant once the volatiles have been depleted, but also causes noticeable deviations of temperature, released mass, and overall particle conversion during devolatilization already, indicating an overlap of the two stages of coal conversion which are usually considered to be consecutive. The complex pyrolysis model leads to non-monotonous profiles of the combustion quantities which introduce a minor dependency of the ignition delay time on its definition. Regardless of the chosen extraction method, the simulations capture the measured values of very well.
Effect of biodiesel, biodiesel binary blends, hydrogenated biodiesel and injection parameters on NOx and soot emissions in a turbocharged diesel engine Fuel (IF 4.908) Pub Date : 2018-12-03 Sundararajan Rajkumar, Jeyaseelan Thangaraja
Recent research works show that the biodiesel is one of the most promising renewable and sustainable fuels for diesel engines because it is biodegradable, oxygenated, sulphur free and renewable in nature. The major issue in using the biodiesel fuel is the increase in oxides of nitrogen emission compared to that of fossil diesel which is coined as Biodiesel-NOx penalty. Hence, it is attractive to focus on the parameters that mitigate the NOx emission for enhancing the usage of sustainable biodiesel fuels. Therefore, this paper presents comprehensive experimental investigation and multi-zone phenomenological model for analyzing the combustion and emission characteristics of biodiesel fuels. The test fuels include the baseline diesel, karanja, coconut biodiesel, binary blends of karanja, coconut and hydrogenated karanja samples. The model results are validated with the experimental results at a wide range of speed and load conditions. The model predictions are observed to be matching well with the measured data with a maximum prediction error of 7% and 18% for NO and soot emissions respectively. The parametric investigations in terms of experiments and validated model to study the effect of start of injection, fuel formulation and blends of biodiesel fuels on the emission characteristics of biodiesel fuels demonstrate that biodiesel-NOx penalty could be alleviated by restoring the start of injection of biodiesel fuel to that of diesel and through fuel formulation technique. While, the binary blends of karanja and coconut does not significantly alter the emission characteristics at lower speed, it shows a beneficial effect on NO emission at higher speeds.
Effect of molecular size of lignin on the formation of aromatic hydrocarbon during zeolite catalyzed pyrolysis Fuel (IF 4.908) Pub Date : 2018-12-03 Jae-Young Kim, Joon Weon Choi
Three lignin fractions with different molecular size (Fraction 3 > Fraction 2 > Fraction 1) were prepared by sequential solvent fractionation of soda lignin. These were structurally investigated by several analytical techniques, such as GPC, 31P-NMR, 2D-HSQC-NMR, and TGA. They revealed that F1 was the smallest and the most thermally labile lignin fraction. Pyrolyzing lignin fractions at 600 °C with zeolite Y produced aromatic hydrocarbons (benzene, toluene, xylenes, and naphthalenes) with several types of monomeric phenols. Total pyrolysis product yields were the highest for F1, followed by F2 and F3. Additionally, aromatic hydrocarbons formation was inversely proportional to molecular size and abundantly produced with F1 (35.0 mg/g). They gradually increased in all fractions as the pyrolysis temperature increased (up to 800 °C). The transformation behaviors of functional groups were also investigated by using lignin model compounds. Lignin fractions prepared in this study had not only molecular size but also different phenolic hydroxyl (Phe-OH) content which would play a deleterious role in aromatic hydrocarbon formation during zeolite-catalyzed pyrolysis. Therefore, we prepared methylated lignin from each fraction (Methylated fraction 1, 2, and 3) and these were also pyrolyzed under same condition to investigate the independent effect of molecular size.
Comprehensive study of structure model, pyrolysis and liquefaction behaviour of Heidaigou lignite and its liquefied oil Fuel (IF 4.908) Pub Date : 2018-12-03 Hualin Lin, Jun Lian, Yeping Liu, Yuan Xue, Song Yan, Sheng Han, Wei Wei
An integrated study involving structure model, pyrolysis and liquefaction behaviour of Heidaigou lignite (HL) and its liquefied oil was carried out to have an in-depth and comprehensive understanding of lignite and its direct liquefaction behaviour. Detailed information on HL was obtained using a molecular structural model constructed on the basis of ultimate analysis combined with solid-state 13C nuclear magnetic resonance (NMR), X-ray photoelectron spectrometer (XPS) and X-ray diffraction (XRD) studies. The HL model has few aromatic ring structures, which are composed of naphthalene, benzene, pyridine and pyrrole. The aromatic structures are linked by the aliphatic chains, and the carbon content in each chain is not less than three. Pyrolysis is the basis of liquefaction; as such, the pyrolysis behaviour of HL was investigated by TG/DTG. Results show that the maximum weight loss rate is about 425 °C. At below 500 °C, some Cal–Cal and Cal–Car broke, but Car–Car did not. The effects of time and temperature on the liquefaction behaviour of HL were investigated in a PARR-stirred high-pressure reactor. The liquefaction took a certain amount of time. With increasing temperature, the coal conversion rate and oil yield remained stable or increased slowly. The optimal time and temperature for liquefaction of HL are 40 min and 440 °C, and the maximum oil yield and HL conversion rate reach 56.68% and 89.79%, respectively. In addition, the optimal temperature of liquefaction (440 °C) is slightly higher than that of the maximum weight loss rate (425 °C). The composition of aromatics in the liquefied oil was determined using column chromatography and GC–MS. Most of the aromatics are tetraline, naphthalene and its derivatives and monocyclic benzenes. Agreements and consistency exist between the HL model, pyrolysis and aromatics in the liquefied oil.
Transformation of Ammonia Fiber Expansion (AFEX) corn stover lignin into microbial lipids by Rhodococcus opacus Fuel (IF 4.908) Pub Date : 2018-12-03 Zening Wang, Ning Li, Xuejun Pan
The lignin from AFEX-pretreated corn stover and lignin model compounds were evaluated as the sole carbon source for microbial lipid production by Rhodococcus opacus NRRL B-3311. R. opacus NRRL B-3311 could grow on the AFEX-lignin without pretreatment and accumulate lipids up to 32 mg/L in 72 h with consuming 20% of the total lignin. The lipid produced from lignin had a similar fatty acid compositional profile to those of vegetable oil. Based on the metabolism analysis, R. opacus NRRL B-3311 could depolymerize AFEX-lignin and catabolize the aromatic compounds derived from the lignin. Study using aromatic model compounds found that R. opacus NRRL B-3311 preferably utilized 4-hydroxybenzoic acid as the sole carbon source over glucose, while it could not grow on p-coumaric acid or vanillin.
Experimental investigation into the influence of the oxygen concentration on a pulverized coal swirl flame in oxy-fuel atmosphere Fuel (IF 4.908) Pub Date : 2018-12-01 Johannes Hees, Diego Zabrodiec, Anna Massmeyer, Oliver Hatzfeld, Reinhold Kneer
One of the significant advantages of oxy-fuel combustion is the added degree of freedom, given by the possibility of choosing the O2 partial pressure in the oxidizer within a reasonable range, allowing the operation of such combustion systems to be fine-tuned for higher efficiency. However, the influence of the O2 content in the oxidizer on flame structure and characteristic parameters (e.g.: flame temperature, chemical composition) is not fully understood. Therefore investigations were carried out to unveil these effects in a coal flame. For this purpose a swirl burner specifically designed for oxy-fuel combustion was utilized in a pilot scale test furnace (40 kWth). Thereby concentration of oxygen in the oxidizer was varied between 23 and 33 vol% while keeping the total volume flows (inlet velocities) constant. To investigate flame structures, a narrow-band radiation signal was captured using a CCD-camera with an image intensifier and an optical filter. Besides the flame structure, local particle temperatures and gas compositions were examined. The local gas composition was analyzed using an oil-tempered suction probe connected to an FTIR- (Fourier-Transform-Infrared-) spectrometer. Additionally, particle temperatures were estimated from analysis of emitted radiation in the visible part of the spectrum. It was found that the flame structure remains the same for all flames. However the O2 concentration (stoichiometry) influences the local intensity of the combustion. Further, differences in the local gas composition are observed and maximum particle temperatures were found to increase linearly with increasing O2 content in the oxidizer.
Oxidation of ammonia by iron, manganese and nickel oxides – Implications on NOx formation in chemical-looping combustion Fuel (IF 4.908) Pub Date : 2018-12-01 Fredrik Normann, Andrea Oliver Wismer, Christoph R. Müller, Henrik Leion
We report an experimental evaluation of NH3 oxidation over three types of oxygen carrier materials under conditions relevant for chemical-looping combustion. The active metal and the oxidation state of the oxygen carrier is crucial to NO formation from NH3. Although, the carriers tested were equally efficient in terms of CO oxidation they differed from 0 to 6000 ppm of NO in the off-gas. The nickel based carrier produced the lowest amounts of NO and the manganese based the most. The sensitivity to the oxidation state also differed between the materials. The results stress that NO formation should be consider in the choice of oxygen carrier material as well as in the design of chemical looping-combustion systems.
Coupled modeling of combustion and hydrodynamics for a coal-fired supercritical boiler Fuel (IF 4.908) Pub Date : 2018-12-01 Tang Chen, Yan-jun Zhang, Meng-ran Liao, Wei-zong Wang
Computational fluid dynamics (CFD) model of coal combustion is coupled with the one-dimensional hydrodynamic model of supercritical steam, and applied in the simulation of the superheater. The convective heat exchangers are neglected. Complex tube arrangements can be modeled with the aid of AutoCAD, and therefore the simulation could offer detailed information on heat exchangers. It is found that the outlet steam temperature of the tube is very sensitive to the variation of ash deposit temperature. Therefore it is not reasonable to use decoupled method for predicting the energy flux transported to the steam. The outlet steam temperature of a row of tubes is compared with the running data from the power plant. The simulation result fits well with running data. Nevertheless, one can impose an average steam temperature plus 50 K as the tube outside surface temperature; then calculates the temperature of the ash deposit according to the thermal resistance of ash deposit and energy flux. The result from this “simplified” coupled method is very close to fully coupled method.
Structural characterization of sulfur-containing aromatic compounds in heavy oils by FT-ICR mass spectrometry with a narrow isolation window Fuel (IF 4.908) Pub Date : 2018-12-01 Ling Liu, Chunxia Song, Songbai Tian, Qundan Zhang, Xinheng Cai, Yingrong Liu, Zelong Liu, Wei Wang
Detailed structural information on sulfur-containing aromatic compounds in heavy oils is valuable for the petroleum industry. In this work, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) combined with collision-induced dissociation (CID) was applied to study the structures of sulfur-containing aromatic compounds in vacuum gas oil (VGO) and vacuum residue (VR). The parent ions of the sulfur-containing model compounds and high-sulfur heavy oils were isolated by the quadrupole in FT-ICR MS with a narrow isolation window of 1 Da. For most of the sulfur-containing model compounds, removal of S atoms was achieved in the collision voltage range 10–30 V. On the other hand, the removal of S atoms from the sulfur-containing compounds in heavy oils was restrained by optimization of the collision voltage. The structures of VGO and VR were also studied by CID FT-ICR MS with a narrow isolation window at the optimal collision voltages. The results suggested that naphtheno-aromatic sulfur-containing compounds were components of heavy oils and that the structural diversity of the heavy oils increased significantly with an increase in molecular weight.
Partitioning of trace elements in coal combustion products: A comparative study of different applications in China Fuel (IF 4.908) Pub Date : 2018-11-30 Guanyi Chen, Yunan Sun, Qin Wang, Beibei Yan, Zhanjun Cheng, Wenchao Ma
The partitioning of twelve trace elements (Be, V, Cr, Mn, Ni, Cu, Zn, As, Se, Cd, Hg and Pb) in combustion products were carried out in this work. Samples of raw coal (RC), bottom ash (BA), fly ash (FA) were collected from China power plants and heating stations. The relative enrichment factors (RE) were calculated, and the influences of temperature, boiler types, coal type and characteristics of trace elements were discussed. The results indicate that only As, Se, Cd, Pb are strongly depended on temperature between 700 °C and 830 °C. As, Se, Hg have low REs in both BA and FA in three kinds of boiler, whereas Cr, Zn, Pb have low REs only in BA. Mass balance suggests that trace elements can be classified into four groups based on their volatility. The results of this study were based on China's actual power plants and heating stations, and the data could be used as a reference to the selection of coal, boiler type and operate temperature.
Cetane number prediction of waste cooking oil-derived biodiesel prior to transesterification reaction using near infrared spectroscopy Fuel (IF 4.908) Pub Date : 2018-11-29 Juan Francisco García-Martín, Francisco Javier Alés-Álvarez, María del Carmen López-Barrera, Irene Martín-Domínguez, Paloma Álvarez-Mateos
Fifty waste cooking oils (WCOs) were transesterified with methanol (1:8 WCO:methanol molar ratio) at 60 °C for 60 min using NaOH as catalyst (1% wt.). Fatty acid methyl ester (FAME) composition of the resulting biodiesels was analysed by gas chromatography, and near infrared (NIR) spectra of these biodiesels and those of the starting WCOs were acquired. Biodiesel cetane number was then calculated from both FAME composition and from biodiesel NIR spectra, this last technique using the former one as reference data. Because of transesterification does not modify fatty acid distribution of the starting WCO, and the similarity between biodiesel and WCO NIR spectra, biodiesel cetane number was successfully predicted from WCO NIR spectra, achieving RPD (ratio of performance to deviation) of 3.83. Therefore, biodiesel cetane number (and, as consequence, any other biodiesel property related to FAME composition) can be predicted by NIR spectroscopy before performing the transesterification reaction, which allows beforehand selecting the most suitable substrates for biodiesel production.
Surface tension, light absorbance, and effective viscosity of single droplets of water-emulsified n-decane, n-dodecane, and n-hexadecane Fuel (IF 4.908) Pub Date : 2018-11-29 Gyu Min Jang, Nam Il Kim
Water-emulsified liquid fuels have been used occasionally in combustion systems to control flame temperature and NOx emission. Atomization characteristics are important for efficient combustion of emulsified fuels, and they are affected by the mechanical properties of the emulsion. The dynamic behavior of an emulsion droplet is affected by the micro-droplets dispersed within the emulsion, and the actual properties of the emulsion are of interest. Recently, a new dynamic method using a pulse laser was developed based on the Taylor’s analogy breakup model. In this study, surface tension, light absorbance, and viscosity were evaluated for two emulsified fuels (n-decane and n-hexadecane), and their results compared with those of n-dodecane from the previous study. Three independent ordinary methods and the dynamic method were employed to measure the emulsion properties. Actual light energy absorbance, more reliable surface tension, and effective viscosity of emulsion could be predicted through the dynamic method. Finally, a simple empirical equation was suggested for the prediction of the effective viscosity of emulsion. The applicability of the proposed dynamic method was verified conclusively, and the most effective properties of single emulsion droplets were determined.
Development of a decoupling physical-chemical surrogate (DPCS) model for simulation of the spray and combustion of multi-component biodiesel fuels Fuel (IF 4.908) Pub Date : 2018-11-29 Pengfei Wang, Ming Jia, Yanzhi Zhang, Guangfu Xu, Yachao Chang, Zhen Xu
A decoupling physical–chemical surrogate (DPCS) model was established for simulation of the spray and combustion characteristics of multi-component biodiesel fuels. In the DPCS model, the physical and chemical properties of biodiesel fuels are described separately. For the case study of soybean methyl ester (SME), the physical properties are represented based on the five primary components, i.e., methyl palmitate, methyl stearate, methyl oleate, methyl linoleate, and methyl linoleate. Meanwhile, the chemical kinetics of SME are described by a skeletal reaction mechanism composed of methyl decanoate, methyl 5-decenoate, and n-decane. Furthermore, an improved quasi-dimensional multi-component vaporization model was applied to predict the fuel vaporization process. To validate the DPCS model, the predictions from the present model and the previous models are compared with the experimental data, including the liquid penetration in a constant-volume bomb and the combustion and emission characteristics in a premixed charge compression ignition (PCCI) engine. The results indicate that the predictions of the DPCS model agree better with the measurements than the previous models considering only the single-component physical and/or single-component chemical properties of SME on the spray, ignition, and combustion behaviors. It is found that the ignition delay and heat release rate of PCCI combustion are dominated by the evaporation rate of SME and the fuel-reactivity stratification within the cylinder. By considering the multi-component properties of SME, the combustion and emission characteristics can be satisfactorily reproduced by the DPCS model. Meanwhile, the computational time can be well controlled due to the simplification of the physical and chemical surrogate sub-models.
Eulerian-Lagrangian simulation of pulverized biomass jet using spheroidal particle approximation Fuel (IF 4.908) Pub Date : 2018-11-29 Ning Guo, Tian Li, Lihao Zhao, Terese Løvås
Pulverized biomass has great potential to replace coal in many industrial systems such as suspension-firing furnaces and entrained-flow gasifiers. The shape of pulverized biomass deviates significantly from the quasi-spherical coal particle, however, it is common to simulate pulverized biomass particles as spheres as most biomass models are developed based on coal models. With the aim of obtaining a more realistic simulation of pulverized biomass, this work extends the treatment of pulverized biomass to spheroids. A spheroid model that accounts for spheroidal particle drag force and torque was implemented into an Eulerian-Lagrange computational fluid dynamic solver. Comprehensive verifications and validations were performed by comparing with experiments and direct numerical simulations. Furthermore, non-reactive simulations of a lab-scale entrained flow gasifier were carried out using a conventional spherical particle model, a simplified non-sphere model, and the implemented detailed spheroidal particle model. By studying the simulation results of particle and fluid velocities in axial, radial and tangential directions, differences were observed when comparing the sphere model, the simplified non-sphere model, and the spheroid model. The spheroid model shows that particle orientation, which is ignored in the sphere model and the simplified non-sphere model, plays a role in the behavior of the particle dynamics. It was also found that, under such conditions, the spheroid model, compared to the sphere model, yields a more dispersed distribution regarding the particle residence time and local concentration. These non-reactive simulation results imply that shortcomings may exist in the common practice of simulating conversion of pulverized biomass in which the sphere model or the simplified non-sphere model is applied.
Towards oxy-steam combustion: The effect of increasing the steam concentration on coal reactivity Fuel (IF 4.908) Pub Date : 2018-11-29 Cristina Dueso, M. Carmen Mayoral, J. Manuel Andrés, Ana I. Escudero, Luis I. Díez
Oxy-steam combustion and devolatilization performance of three different coals (anthracite, blend of bituminous coals and low-rank coal) was studied in a thermobalance with a water vapour furnace under variable steam concentrations (0, 20, 40 and 70 vol% H2O) in N2 and CO2. Two oxygen concentrations were used during the combustion tests (20 and 30 vol%). Devolatilization behaviour was similar under N2 and CO2 atmosphere and increasing steam concentration did not affect significantly the observed reactivity and the reaction temperature range. Replacing CO2 with 20 vol% H2O during combustion tests produced a decrease in ignition and burnout temperatures. When H2O content increased to 40 and 70 vol%, this effect was only found with high-rank anthracite. Maximum mass loss rates for the low-rank coal with high volatile content were up to four times higher than with the other two coals. During direct oxidation experiments, DTG curves of anthracite and the coal blend showed a double peak, corresponding to devolatilization and oxidation reactions. This allowed determining independent kinetic parameters (Ea and A) for both stages. An only DTG peak was detected with the low-rank coal since devolatilization and oxidation reactions took place simultaneously owing to its high reactivity. Devolatilization and oxidation kinetics followed a first-order reaction using the Coats-Redfern integral method. Significant differences were not observed between the activation energies of the three coals when comparing conventional (N2), oxy-fuel (CO2) and oxy-steam conditions (70 vol% H2O in CO2), although Ea values were higher for the devolatilization stage than for the oxidation process.
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