A benchmark assessment of residues: comparison of Athabasca bitumen with conventional and heavy crudes

Compared to benchmark crude oils, bitumen does not respond well to conventional upgrading processes. In order to improve our understanding of this problem, we compare the chemical and physical properties of fractions from super critical fluid extraction of bitumen pitch with the corresponding fractions of residua from Venezuelan heavy oil, a Saudi Arabian light crude and a Chinese Daqing conventional crude.Relatively minor differences in chemical structure were observed between the corresponding residua fractions from Athabasca bitumen, Venezuelan heavy oil and Saudi Arabian light crude. Only the Chinese Daqing showed significant variance; this sample is much more aliphatic and has greater geometrical dimensions than the corresponding samples from the other residua.The end-cut from Athabasca bitumen pitch contained ultra-fine solids together with much higher levels of nickel, vanadium and nitrogen than the conventional crude end-cuts. These components are among the most intractable in upgrading and could be responsible for the problems encountered in bitumen upgrading, especially by catalytic processes.     

热等离子体裂解煤制乙炔下行反应器的研究进展

从反应器的工艺开发角度探讨了热等离子体裂解煤制乙炔下行反应器的研发进程,分析了热等离子体裂解煤制乙炔的快速连串反应特点,对比了下行及上行两种不同类型反应器对能耗及乙炔收率的影响,评述了下行床传递性能的显著优点,进而从超短接触反应、高乙炔收率与流体动力学角度出发指出了热等离子体下行床的集成工艺是裂解煤制乙炔工艺的合理选择。最后提出了制约该工艺实际连续生产的严重结焦难点与解决的方法。     

碳氢燃料热裂解与引发裂解换热对比实验

通过流动管反应器对碳氢燃料RP-3在超临界条件下的热裂解及引发裂解进行了实验,对两种条件下的燃料吸热能力及传热特性进行了对比分析,并对裂解产物进行了采样分析。结果表明,引发裂解降低了燃料的裂解起始温度,在一定温度区间内提高了燃料的裂解率,从而有效提高了燃料热沉,在相同热通量条件下,降低了燃料温度,并降低了加热段壁面温度。对流换热受化学反应及物性变化的影响,燃料裂解吸热可增强换热,而大量气态产物的生成会降低换热,因此,裂解反应的增强不一定增强换热。     

Kinetics of the thermo-oxidative and thermal cracking reactions of Athabasca bitumen

The thermo-oxidative and thermal cracking reactions of Athabasca bitumen were examined qualitatively and quantitatively using differential thermal analysis (DTA). Reaction kinetics of low temperature oxidation (LTO) and high temperature cracking (HTC) were determined. The rate of the LTO reaction was found to be first order with respect to oxygen concentration. The activation energy and the Arrhenius pre-exponential factor were 64 MJ kg^?1 mol^?1 and 10^5.4 s^?1, respectively. The effects of atmosphere, pressure, heating rate and support material on the thermal reactions of bitumen were studied. In general, it was found that partial pressures of oxygen > 10% O₂ favoured exothermic oxidation reactions. High pressure increased the rates of LTO and HTC as well as the exothermicity of these reactions. A major contribution of this study to thermal in-situ processes is that heating rate can be used effectively to control the extent of low temperature oxidation and hence fuel availability during in-situ combustion. Low linear heating rates (2.8 °C min^?1) favoured low temperature oxidative addition and fission reactions. The reaction products readily formed coke and combusted upon heating. High linear heating rates (24.5 °C min ^?1) led to rapid oxidation reactions in the high temperature zone; the high temperature and the energy released during oxidation appeared to promote combustion. Finally, when sand was used as the support material there appeared to be a catalytic effect in both LTO and HTC reactions.     

The Study of Molecular Modeling for Heavy Oil Thermal Cracking

The tighter specifications for refining products have gradually led refineries to focus on the molecular modeling of petroleum processing. In this work, a systematic methodology is presented for the molecular modeling of heavy oil thermal cracking (HOTC). This research which is based on a microscopic understanding provides a basis to achieve better design, management, optimization, and control of HOTC. The molecular information of HOTC product streams is represented in the form of a MTHS (molecular type homologous series) matrix. From consideration of the complexity of structural isomers in heavy petroleum fractions, the heavy molecules in a homologous series are grouped to reduce the dimension of the MTHS matrix. Transformation correlations are developed to capture the molecular properties of each homologous series in the MTHS matrix and to interrelate the molecular composition and bulk properties of the product streams. The HOTC process model was built on the basis of the molecular representation provided by the MTHS matrix and the transformation correlations. Two case studies are illustrated for validation of the proposed model and methodology.     

New path in the thermal cracking of triacylglycerols (canola and soybean oil)

Triacylglycerols (TGs) are naturally occurring oils abundant in many crops. A series of batch uncatalyzed thermal decomposition experiments were performed using canola and soybean oils to explore pathways of TG cracking. A detailed gas chromatographic protocol based on mass spectrometric identification and flame ionization quantification was applied to the organic liquid product generated upon cracking. Reaction conditions were identified that resulted in a novel organic liquid product (OLP) composition compared to previously reported work. Under these conditions (temperatures within a 420-440 °C range) a new route for TG thermolysis was discovered in which cracking reactions of original TG-bound fatty acids were nearly complete and led to the formation of 15-25 wt.% C₂-C₁₀ linear saturated monocarboxylic acids and ca. 30% linear alkanes. Less than 2 wt.% C₁₆-C₁₈ fatty acids which were originally present in the feedstocks as glycerol triesters were found in the OLP. These reactions appear to be kinetically controlled due to abundant hydrogen formation. This route provides a significant enrichment of low-MW compounds in the OLP (65-70 wt.% being <C₁₁) and thus may be considered as a new option for the production of replacement products for petroleum-based fuels and chemicals.     

Modeling mass transport and microbial activity in stratified biofilms

The most recent mathematical models of microbial activity in heterogeneous biofilms are based on cellular automata. The main weakness of these models is that to obtain numerical solutions the operator must specify the rules governing microbial cell behaviour in the biofilm, and these rules are difficult to establish experimentally. To avoid this difficulty, we have used an alternative approach, discretizing biofilms into layers, to include the effects of biofilm heterogeneity on biofilm activity. This procedure conceptually converts heterogeneous biofilms into a stack of stratified layers of various densities, activities, and diffusivities, and can include some effects of biofilm heterogeneity, e.g vertical distribution of biofilm density, activity, and effective diffusivity. We present this model and selected examples of computational procedures illustrating it. We found that the activity of homogeneous biofilms can be lower, higher, or equal to the activity of stratified biofilms; since homogeneous biofilms do not exist, their properties have to be assumed. As expected, the model predicts that the growth-limiting nutrient penetrates deeper into stratified biofilms than it does into homogeneous biofilms.     

Speciation and thermal transformation of sulfur forms in high-sulfur coal and its utilization in coal-blending coking process:A review

The utilization of high-sulfur coal is becoming more urgent due to the excessive utilization of low-sulfur,high-quality coal resources, and sulfur removal from high-sulfur coal is the most important issue. This paper reviews the speciation, forms and distribution of sulfur in coal, the sulfur removal from raw coal,the thermal transformation of sulfur during coal pyrolysis, and the sulfur regulation during coal-blending coking of high organic-sulfur coals. It was suggested that the proper characterization of sulfur in coal cannot be obtained only by either chemical method or instrumental characterization, which raises the need of a combination of current or newly adopted characterization methods. Different from the removal of inorganic sulfur from coal, the organic sulfur can only be partly removed by chemical technologies;and the coal structure and property, particularly high-sulfur coking coals which have caking ability,may be altered and affected by the pretreatment processes. Based on the interactions among the sulfur radicals, sulfur-containing and hydrogen-containing fragments during coal pyrolysis and the reactions with minerals or nascent char, regulating the sulfur transformation behavior in the process of thermal conversion is the most effective way to utilize high organic-sulfur coals in the coke-making industry.An in-situ regulation approach of sulfur transformation during coal-blending coking has been suggested.That is, the high volatile coals with an appropriate releasing temperature range of CH_4 overlapping well with that of H2 S from high organic-sulfur coals is blended with high organic-sulfur coals, and the C–S/C–C bonds in some sulfur forms are catalytically broken and immediately hydrogenated by the hydrogencontaining radicals generated from high volatile coals. Wherein, the effect of mass transfer on sulfur regulation during the coking process should be considered for the larger-scale coking tests through optimizing the ratios of different coals in the coal blend.     

Influence of asphaltenes on coke formation during the thermal cracking of different Brazilian distillation residues

This research was conducted to allow the investigation on the influence of asphaltenes on coke formation, during the thermal cracking of atmospheric distillation residues, using thermogravimetry. Asphaltenes of five refinery atmospheric distillation residues, of different API gravity Brazilian crude oils, were isolated by the IP143 methodology. The original samples and the same samples, after asphaltenes extraction, were analyzed by thermogravimetry. It was observed that the heavier the sample, the higher was the contribution of the asphaltenes to the coke formation. The extracted asphaltenes were analyzed under the same TG conditions of the atmospheric distillation residues and all asphaltenes appeared to form approximately the same amount of carbonaceous residue after the thermal cracking. Heavier and lighter atmospheric distillation residues were doped with 10%, 20% and 30% amount of asphaltenes and, again, the higher the asphaltenes amount, the higher would be the carbonaceous material formation. The same tendency was observed for both doped samples.     

Modeling and simulation of heat and mass transfer during drying of solids with hemispherical shell geometry

A heat and mass transfer model was proposed to describe the moisture and temperature evolution during drying of solid products with hemispherical shell geometry (HSG). The dimensionless form of the model was numerically solved for both several drying conditions and values of a geometrical factor related with the inner radius of the HSG to obtain their moisture and temperature profiles. In addition, average drying kinetics were calculated from the volume integration of local moisture values. A theoretical and numerical approach was used to develop a mass transfer analogy between the proposed HSG and a simpler flat slab-shaped product. These analogies provide simple mathematical expressions for drying process simulation and estimation of diffusion coefficients in solids with the proposed geometry, and may be applicable to other mass and heat transfer operations. Furthermore, the presented procedure may be used to develop similar expressions in other non-traditional or dissection geometries.     

Investigation of kinetics and cracked oil structural changes in thermal cracking of Iranian vacuum residues

Two vacuum residues obtained from Iranian Tehran and Bandar Abbas refineries (T-VR and B-VR) were thermally cracked under various operating conditions (soak time and temperature). The yield distribution of the products and the alteration of the physical properties of the liquid products were evaluated in terms of a change in the operating conditions or the feedstock. It was found that, especially, at higher severities, T-VR tends to give higher yields of liquid product and a lower yield of residual product in comparison with B-VR. The average viscosity, density, refractive index, and molecular weight increased and the H/C ratio decreased upon raising temperature for the cracked oils obtained from both of the feedstocks. The integrals derived in quantitative NMR experiments are suggested to be used as a basis for calculation of paraffinic, olefinic, naphthenic, and aromatic portions of a hydrocarbon sample. The effects of temperature, residence time, and feed type on the composition of the cracked oils are thoroughly investigated on the basis of detailed carbon and proton spectra. A three-lump kinetic model is presented to determine the yields of gas, liquid, and (semi)solid in the upgrading process at hand. The unconvertible portion of the solid is proposed to represent coke or fouling tendency for the residue feedstocks.     

Separation and characterization of bitumen from Athabasca oil sand

Separation and chemical analysis was investigated using bitumen samples from Athabasca oil sand in Alberta. Fractionation according to solubility and polarity has been used to separate bitumen into its fractions. The solvent de-asphaltening was performed by n-pentane solvent (solubility fractionation), and the polarity fractionation using Fuller’s earth allows maltene to separate into SARA components (saturates, aromatics, resins and asphaltenes). The SARA components are analyzed comprehensively using elemental analysis (EA), Fourier-transformed infrared (FTIR), ultraviolet-visible spectroscopy (UV-vis), high performance chromatography (HPLC) and thermogravimetric analysis (TGA). EA (C, H, N, S), heavy metals (Ni, V) concentrations, FT-IR and UV-vis tests provided the explanation of chemical composition. From IR spectra, maltene and saturates/aromatics (sat/aro) contained more aliphatic compounds than resin or asphaltene. Also, IR spectrum of sat/aro was similar to crude oil and VGO (vacuum gas oil). Different UV signal data clearly indicates the contribution of aromatic constituents in the fractions. Using optimized analysis conditions of HPLC, we successfully separated the peaks for bitumen and its fractions. The characteristic peak pattern of SARA (saturates, aromatics, resins, asphaltenes) fractions was observed, and also the peak pattern of sat/aro was similar to that of crude oil and VGO. However, TGA results revealed that thermal behavior for sat/aro was similar to that of crude oil but different from that of VGO. Also, from the comparison between decomposition temperature of TGA and boiling point, their correspondence was found.     

Two-dimensional numerical simulations of Marangoni-Bénard instabilities during liquid-liquid mass transfer in a vertical gap

Two-dimensional (2D) simulations of isothermal liquid-liquid mass transfer subject to surface tension- and buoyancy-driven hydrodynamic instabilities have been carried out. Simulation is based on the numerical solution of 2D equations of momentum and mass transport, using a combination of finite difference and finite volume methods. Two different cases have been considered: (1) buoyancy stable mass transfer, only surface tension-driven convection occurs; (2) surface tension-driven instability superseeded by buoyant convection. The faster attenuation of mass transfer coefficients in buoyancy stable situations is attributed to the merging of convection cells leading to a reduction in the number of renewal zones along the interface. Concentration profiles next to the interface reveal the diffusional nature of the mass transfer in the immediate interfacial neighbourhood.     

Addition methods of sulfur and sulfur/phosphorus-based compounds on coking behavior during thermal cracking of naphtha

Using naphtha as raw material for cracking, the effects of adding sulfides and sulfur/phosphorus compounds on the coking behavior of thermal cracking were investigated. The morphologies and structures of the pretreated HP40 alloy specimen and coke deposits were characterized by Raman spectroscopy, XRD, SEM and XPS. The results showed that the addition of phosphide into the sulfide additives led to the change in the structure of coke deposits under the condition of continuous addition of additives into the feed. The method with continuous addition of sulfur/phosphorus-based compounds showed excellent anti-coking properties. The surface pretreatment with sulfur or sulfur/phosphorus-based compounds made the increase of Fe content in the oxide film on the specimen. So anti-coking effect was limited when the pretreatment method was applied. The coking inhibition property of the application of surface pretreatment with sulfide/phosphide followed by continuous addition of sulfur/phosphorus-based compounds were similar to that of the application of continuous addition of sulfur/phosphorus-based compounds in the feed. However, the combination method showed the better anti-coking effect during the initial cracking process. All the addition methods led to the increased amounts of amorphous coke in the coke layer and the decreased graphitization degree of cokes. The results of the low H/C ratios showed the highly condensed structure of the coke deposits during thermal cracking process. The addition of sulfur and sulfur/phosphorus-based compounds could influence the dehydrogenation reaction to some extent during the coke formation by reducing catalytic coking.     

硫化物和硫/磷化合物的添加方式对石脑油热裂解结焦影响的研究

以石脑油为裂解原料,考察了硫化物和硫/磷化合物的添加方式对热裂解结焦行为的影响。采用Raman光谱、XRD、SEM和XPS等检测手段表征了HP40试样的氧化层和焦炭的形貌与结构。结果表明,原料连续注入硫化物条件下,磷化物的加入使得焦炭结构改变,显示出优异的抗结焦效果。硫化物和硫/磷化合物预处理导致氧化层中Fe含量升高,抑制结焦效果有限。硫/磷预处理与原料连续注入硫/磷化合物联合方式与原料连续注入硫/磷化合物方式的抗结焦效果接近,但前者在初期的抑制效果更明显。所有添加方式都会引起结焦层中无定形焦炭含量升高,焦炭的石墨化程度降低。热裂解焦炭缩合程度较高,硫化物和硫/磷化合物减少了催化结焦的生成,在一定程度上提高了焦层中氢含量。     

CFD modeling of pervaporative mass transfer in the boundary layer

Modeling mass transfer in the liquid boundary layer accounting for concentration polarization in pervaporation (PV) is particularly challenging since there is no practical way of experimentally determining solute concentration at the membrane surface. We have developed a computational fluid dynamics (CFD) approach to describe not only velocity distribution but also concentration profile in the liquid boundary layer of a slit membrane channel. The satisfactoriness of the numerical methodology used in CFD for obtaining concentration profiles were verified using a classic diffusion problem with its known analytical solution. The overall mass transfer coefficients from the numerical study were also compared with those from the experiment.     

Simulation of thermal shock cracking in ceramics using bond-based peridynamics and FEM

The effects of moderate intensity ‘hot’ or ‘cold’ shock in brittle solids have been extensively studied, while much less is known about thermal shock response during large temperature variations. In this study, a combined finite element – peridynamics numerical procedure is proposed for the simulation of cracking in ceramic materials, undergoing severe thermal shock. Initially, Finite Element nonlinear heat transfer analysis is conducted. The effects of surface convection and radiation heat exchange are also included. Subsequently, the interpolated temperature field is used to formulate a varying temperature induced action for a bond-based peridynamics model. The present model, which is weakly coupled, is found to reproduce accurately previous numerical and experimental results regarding the case of a ‘cold’ shock. Through several numerical experiments it is established that ‘cold’ and ‘hot’ shock conditions give rise to different failure modes and that large temperature variations lead to intensified damage evolution.     

Well-developed mass transfer in axial flows through randomly packed fiber bundles with constant wall flux

An analysis of the effects of fiber packing on mass transfer coefficients for axial fluid flow through fiber bundles with uniform wall flux in the well-developed limit is presented. The finite element method is used to solve the governing momentum and conservation of mass equations. The effective mass transfer coefficient depends strongly on fiber packing. Randomly packed fiber bundles have much lower mass transfer coefficients than regularly packed fiber bundles. Mass transfer rates are controlled by the lowest fiber packing regions through which most of the flow occurs.     

基于迁移学习的裂解炉产率建模

乙烯裂解炉通常以石油分馏产品为原料,并在高温条件下使长链分子的烃断裂成各种短链的气态烃和少量液态烃,从而获得乙烯、丙烯等烯烃及其他产品.建立这些主要产品的产率模型对裂解炉的先进控制、操作优化等任务在理论和实际上都具有重要意义.尽管在不同裂解原料、不同炉型的裂解炉状况下产品收率均存在差异,但由于裂解炉运行具有半连续性、周期性特征,裂解温度、停留时间及烃分压等因素对裂解产率的影响具有共性,因此为减小建模过程中典型样本采集等成本,有效利用历史数据提高建模精度,有效利用这些不同运行过程中存在的相似性,辅以迁移学习算法实现不同工况下裂解产率的快速建模.相比较以前的研究,此建模方法在少量新数据的情况下充分挖掘了历史数据中包含的信息.最后,以某乙烯厂为研究实例进行裂解产率建模,结果显示能够获得较好的产率预测精度,验证了该建模方法的有效性.     

提高催化裂化装置掺渣量时存在的问题与对策

阐述了某催化裂化装置的设计特点。分析了装置设备结焦原因及对策 ,对提高催化裂化装置掺渣量提出了相关建议和改进措施