Effect of thickness of liquid layer on instability of absorption

The Marangoni instability in the non-steady-state absorption of a gas by a liquid layer with a finite thickness is considered. The critical time of reaching the unstable convective regime as a function of the physical characteristics of the process and the thickness of the liquid layer is studied. The dependence of the critical Marangoni number on the Lewis number is obtained numerically.     

Prediction of ash fusion temperature from ash composition for some New Zealand coals

Three improved techniques are presented for predicting the fusibility temperatures of coal ash from ash composition for particular coalfields. The first uses ternary equilibrium phase diagrams where the vertices are percent base, percent fluxing acidic oxides and percent non-fluxing acidic oxides. For reducing conditions FeO is a base, but for oxidizing conditions Fe₂O₃ is a non-fluxing acid. Plots of ash fusibility results on these diagrams show the range of behaviour of a particular coal and where low temperatures occur. They can be used to predict behaviour of fresh samples. The second method uses multiple regression equations above and below the minimum in the ash fusion temperature-percent base plot (usually 38% base), using as predictors, percent base (B), B², and acid flux and base flux factors F_A, F_B (or their logarithms). The third technique, the most accurate, uses stepwise regression, again on split observations above and below the minimum in the ash fusion temperature-percent base plot. With 40 parameters it is possible to identify the significant ash fusion parameters present for each ash fusion measurement in each coalfield. Two sets of observations which included measurements of borate (B₂O₃) showed that it caused a significant but negligible reduction in ash fusion temperature.     

Effect of cathode catalyst layer thickness on methanol cross-over in a DMFC

The effects of cathode catalyst layer (CCL) thickness on the detrimental effect of methanol cross-over in a direct methanol fuel cell (DMFC) under various operating conditions are studied. Three membrane electrode assemblies (MEAs) with different CCL thicknesses but identical catalyst loading and identical anode catalyst layer are used. The results show that, when a thicker CCL, approximately twice the thickness of the base case, is used, the fuel cell performance increases significantly. The increase in performance with a thicker CCL is attributed to the oxidation of the methanol crossed-over in part of the catalyst layer and leaving the rest of the catalyst layer free from methanol contamination, leading to mitigations of the effects of mixed potentials. The results of electrochemical impedance spectroscopy (EIS) show that the charge transfer resistance for the fuel cell with twice the thickness of CCL is 30% lower compared to that for the base case, indicating that the active catalyst area available for oxygen reduction reaction (ORR) is indeed greater. The results of the electrochemical active surface areas (ECA) show that without methanol contamination, the ECA of the thicker CCL is actually lower, indicating that the better performance and the lower charge transfer resistance are not caused by a higher original ECA, but a higher active area for ORR. A much thicker CCL, about 5 times of that for the base case, is also used and the cell performance is also higher than that for the base case. The experimental results show that there exists an optimum cathode catalyst layer thickness and the thickness of cathode catalyst layer has a significant effect on DMFC performance.     

合理配煤入洗获取最大效益的探讨

汾西矿业集团公司为适应市场需求,合理利用资源,需对各矿各煤层不同灰分、不同硫分的煤进行配比入洗,以调整产品结构,合理利用现有资源,提高煤矿的经济效益;提出了三种可行的配煤入洗方案,并分析比较了各方案的经济效益。     

Effect of cation-exchange layer thickness on electrochemical and transport characteristics of bipolar membranes

To study the effect of cation-exchange layer thickness on the electrochemical and transport characteristics of bipolar membranes (BPM), asymmetric BPM with varied cation-exchange layer thickness (of 10, 30, 50 and 70 μm) were investigated. High influence of BPM monopolar layers thickness on its selectivity had been shown. This fact is non-trivial in relation to monopolar ion-exchange membranes as their selectivity does not depend on their thickness. At the same time, increase or decrease in the thickness of BPM monopolar layers can increase products purity or, on the contrary, combine ion transport and pH shift functions.     

Application of incomplete similarity theory for estimating maximum shear layer thickness of granular flows in rotating drums

Granular flow in a rotating drum provides a convenient system for investigating mixing, segregation and general properties of granular materials. This study is concerned with the maximum thickness of the flowing surface layer observed at the rolling regime. A scaling relation is first derived with the consideration of incomplete similarity associated with the drum-particle size ratio and the Froude number. Calibration is then carried out with published laboratory data, which were collected for the case of rotating drums half-filled with glass beads. The scaling relation is also compared with other kinds of datasets, showing good agreement and possibilities of the proposed approach to be further extended to more complex cases.     

Correlation relations between mineralogical components in ash from Kaa-Khem coals

Regression analysis was used to study correlation relations between the mineral components of coals. Regularities in the variability of the concentrations of individual ash-forming elements with changing ash contents of coals and changing seam depth were found. The X-ray diffraction characteristics of coal ashes and the qualitative composition of their mineralogical components are presented.     

Structural-chemical modeling of transition of coals to the plastic state

The structural-chemical simulation of the formation of plastic state during the thermal treatment (pyrolysis, coking) of coals is based on allowance for intermolecular interactions in the organic matter. The feasibility of transition of coals to the plastic state is determined by the ratio between the onset plastic state (softening) and runaway degradation temperatures, values that depend on the petrographic composition and the degree of metamorphism of coals and the distribution of structural and chemical characteristics of organic matter.     

煤红外快速热解过程中床层对二次反应的影响

针对煤快速热解研究中样品添加量少(mg级)、焦油收集难等问题,本研究利用压片法制备微薄厚度(mm级)的煤层,并采用红外加热装置考察大添加量(g级)、微薄煤层的快速热解特性。对比堆积煤样和不同煤压片厚度(1.5~3 mm)与个数(1~2)的压片煤样热解特性发现,压片煤层热解过程的二次反应受到明显抑制,焦油产率急剧增加,在1000℃时达9.96%,为格金分析的1.5倍,实现油气产量的同步增长。模拟蒸馏分析发现,堆积状态下焦油以沥青质为主,而微薄煤层制焦油含大量轻油、酚油、萘油、洗油和蒽油。GC-MS和FTIR分析表明,随煤层厚度和个数的减少,焦油组分和含量提高,芳香烃类和含氧官能团吸收增加,进一步验证煤快速热解过程中煤层厚度对焦油产率和品质的影响,揭示在二次反应充分抑制下煤高温热解的初级反应特性。     

几种高灰熔点煤用于气流床气化性能的探讨

分析了几种高灰熔点煤应用于气流床气化炉时存在的问题,提出了添加助溶剂降低灰熔点的方法,讨论了添加助溶剂后对气化性能的影响,总结了针对灰熔点过高时气流床气化的解决方案。     

Effect of blending on liquefaction of coals

After solvent extraction of Taiheiyo, Miike and Balmer coals using wash oil under nitrogen atmosphere at 370 °C for 30 min, the extraction yield is always within the additivity law. Further studies used Yallourn, Soyakoishi, Taiheiyo, Horonai, Miike, Shin Yubari, Balmer coals and their blends which were hydrogenated in tetralin, wash oil or creosote oil, with or without catalyst, at 400–450 °C under 10 or 3 MPa of initial hydrogen pressure. When hydrogen is available, the additivity law exists for blended coals, but when the hydrogen supply is deficient, the experimental conversion of blended coals is always lower than calculated conversions. This may be due to the faster consumption of the hydrogen by more reactive coals and thus the less reactive coals were unable to react with hydrogen.     

高硅铝煤灰熔融流动特性的调控研究进展

在对添加剂(钙基、镁基、铁基)、生物质(K、Na)、配煤三种调控方法讨论的基础上,对煤灰流动温度的变化规律进行了分析,并从低温共熔、成键机理和吉布斯自由能角度论述了流动温度降低的机制。最后对预测煤灰流动温度的方法(最小二乘法、多元线性回归分析)进行了归纳。为添加剂、生物质和配煤调控高硅铝煤的灰熔融流动特性提供指导,从而促进高硅铝煤的高效洁净转化。     

Analytical pyrolysis as a tool for the study of plastic coals

The technique of analytical pyrolysis has been used to characterize 40 similar mid-rank western Kentucky coals of widely differing ASTM Gieseler plasticity. Certain pyrolysis/g.c. variables were shown to correlate well with both ASTM Gieseler and isothermal plasticity. Highly plastic coals were shown to exhibit certain characteristic peaks in the 450 °C pyrogram which were absent in the pyrogram of the non-plastic coals. Two coals, representing the two extremes in plasticity, were selected for further study. After extraction with solvents such as DMF the characteristic peaks were absent in the 450 °C pyrogram of the extraction residue of the highly plastic coal. These peaks were also shown to decrease with increasing severity of air oxidation of the plastic coal. This technique appears to be a useful tool for the analysis of mid-rank plastic coals and supports the view that the substances contained in the bitumen fraction of these coals are involved in the development of the plastic state.     

单种煤煤岩参数对焦炭质量的影响规律

通过研究各单种煤的镜质组平均最大反射率R0max及分析单种煤40kg小焦炉试验所得焦炭气孔结构,得到焦炭气孔结构参数的回归方程及其影响规律,可用于指导配煤炼焦。     

Effect of coke shrinkage and plastic layer deformation on gas pressure in a coke oven

A plausible mechanism is provided for the generation of internal gas pressure (IGP) in the plastic layer of a coke charge, by relating the formation of low permeability at the outer edges of the plastic layer to the deformability of the plastic material. The amount of lateral shrinkage post-resolidification is shown to be important in constraining the deformation of the plastic material, and hence the generation of low permeability to gas flow. The mechanism provides a natural explanation for permeability variation in the plastic layer, as well as for the linkage between IGP/coking pressure generation and pushing difficulties.     

Effect of a thin plastic adhesive layer on the stress singularities in a bi-material wedge

Geometric singularities for perfect bond constitute a fairly well explored area in linear elasticity. In this paper, an effect of a thin plastic adhesive layer on the singular stress field at the interface corner of a glued bi-material wedge is studied within a simple model. Following the conventional one-dimensional analysis of bonded joints, the adhesive layer is treated as a layer of displacement discontinuity between two materials. A new characteristic equation for the determination of the characteristics of the singular stress field is derived based on the classical works of Williams and Bogy. The new characteristic equation is studied for certain particular composites and angles, which commonly occur due to joining dissimilar materials. The focus of this paper is the problem associated with elimination of the singular stress field, with the goal of providing an approach for designing singular-free adhesive joints.     

Mineralogy of ash of some American coals: variations with temperature and source

Ten samples of mineral-matter residue were obtained by the radio-frequency low-temperature ashing of subbituminous and bituminous coals. The low-temperature ash samples were then heated progressively from 400 °C to 1400 °C at 100 °C intervals. Mineral phases present at each temperature interval were determined by X-ray diffraction analyses. The minerals originally present in the coals (quartz, kaolinite, illite, pyrite, calcite, gypsum, dolomite, and sphalerite) were all altered to higher temperature phases. Several of these phases, including kaolinite, metakaolinite, mullite, anhydrite, and anorthite, were found only in limited temperature ranges. Therefore the temperature of formation of the ashes in which they occur may be determined. Mineralogical differences were observed between coal samples from the Rocky Mountain Province, the Illinois Basin, and the Appalachians; and as a result of these mineralogical differences, different high-temperature phases resulted as the samples were heated. However, regional generalizations cannot be made until a greater number of samples have been studied.     

Effect of air-oxidation on the pore-structure of coals and cokes or chars obtained from oxidized coals

Seven kinds of coals (C, 77.8–89.8 wt% daf) were oxidized with air at 150 °C for 1, 5 and 10 h. The oxidized coals were heat-treated at various temperatures between 300 and 1500 °C with intervals of 50 or 100°C. The pore-structure of the oxidized coals and the cokes or chars obtained from the oxidized coals was compared with those of parent coals and their cokes or chars. True densities were measured in methanol and straight-chain hexane and pore volumes were determined by the Dubinin-Polanyi procedure. For the coals, the methanol-density increased with extent of oxidation; the hexane-density increased at first, but then decreased and again increased in the course of the oxidation. The air-oxidation of coals has a marked and controlling effect on the development of the pore-structure of cokes and chars in the course of the carbonization.