Crack Propagation and Remaining Life Assessment of Coke Drums Due to Thermal Stresses

Coke drums are subjected to cyclic thermal stresses, thus their operational life is much shorter than other pressure equipment in oil refineries. It is known through surveys that one of major typical location of failure in coke drums is the shell-to-skirt junction. The main objective is to simulate crack propagation and to develop a remaining life assessment method for shell-to-skirt junction with crack. Operational temperatures and strains on a coke drum have been measured for 100 cycles. The selected operational temperatures will be applied as thermal boundary conditions in analyses. The crack propagation is then simulated to assess the remaining life.     

THERMOELASTO-PLASTIC STRESSES AND THERMAL DISTORTIONS IN A BRAKE DRUM

Most analyses of thermal stresses generated in a brake drum are studies within either an elastic or a plastic region with constant yield strength. As a matter of fact, however, a severe brake application will create a thermal environment on the friction surface with an excessively high surface temperature. At a high temperature, the degradation of yield strength of a drum material may become significant and an important factor to be taken into account in the analysis. This article deals with the thermoelasto-plastic stresses and the thermal distortions produced in a brake drum during a severe braking condition, taking account of the temperature dependence of the yield strength of a drum material. It is found that high compressive thermoelastoplastic stresses are created during a brake application but eventually residual tensile stresses are developed in the vicinity of the rubbing surface in the course of cooling. These residual tensile stresses are strongly presumed to be one of the significant factors causing the heat crack in a brake drum. In addition, the thermal distortions of the drum suggest a loss of the contact area between the drum fictional surface and the brake shoe linings during braking.     

VOC and PAH characterization of petroleum coke at maximum thermal decomposition temperature

In steel industry, hard coal is proceeded in coke ovens to produce metallurgical coke. In this process, some additives such as petroleum coke (petcoke) are used for optimizing operational cost. For the determination of addition ratio of petcoke, it is important not to disrupt coke quality, especially with respect to coke reactivity index and coke strength after reaction, while another important point is emission quality. In this study, petcoke gas (PCG) emitted from the thermal decomposition of petcoke at the maximum thermal decomposition temperature is characterized for volatile organic compounds (VOCs) and polyaromatic hydrocarbons (PAHs) and the results are assessed in comparison to the coke oven gas (COG). First, the petcoke sample is heated for gasification by using thermal gravimetric analyzer-DTA device. The gas in the temperature range of 490–510°C, where the highest gasification acceleration occurs, is taken from the funnel and transferred to GC-MS device by using a headspace gas sampler unit. The total VOC concentration in PCG and COG is found to be 121.76 ppm and 5,774.76 ppm, respectively, while the total PAH concentrations are 0.625 and 0.495 ppm, respectively. The results show that using petcoke in coal blend seems to be a more environment-friendly process with respect to a significant decrease in VOC emissions.     

延迟焦化装置弹丸焦形成机理探讨

关于弹丸焦形成机理的研究,国内外起步都比较晚,目前关于其深层的机理研究并不多。就国内而言,大多来源于炼油企业的生产报道,实验室研究较少,未形成成熟的理论体系。根据弹丸焦的形态及物性,提出了弹丸焦气相成核的动态过程,认为形成弹丸焦的本质原因是塔内气速过大,造成气相中焦粒(或前驱物)浓度过大,且停留时间过长。气相中的焦粒经融合、摩擦等过程后,最终形成弹丸焦。根据此机理,可以很好地统一解释各种影响弹丸焦形成的因素。该理论认为,塔内气速为原料性质、操作条件等因素的综合函数,是弹丸焦形成的关键因素之一。通过该机理,可以很好地解释弹丸焦生成过程中各种现象及其影响因素。塔内气速是弹丸焦生成的一个综合判据,它是原料性质、操作条件的函数。如果能够结合装置工况、原料性质等因素,通过流体动力学计算,拟合出弹丸焦生成的临界气速,可以对装置操作起到实质性的指导作用。     

Elastic–plastic behaviours of pressurised tubes under cyclic thermal stresses with temperature gradients

Elastic–plastic behaviours of pressurised tubes under cyclic thermal stresses are investigated, incorporating temperature (and resulting the yield strength) gradient through the tube thickness. Based on analytical investigations, explicit equations for various stress regimes representing elastic–plastic behaviours are obtained. In the limiting case of no temperature (and yield strength) gradient through the thickness, proposed equations recover those for the well-known Bree diagram. The proposed results are then validated against the results from full-cyclic elastic–plastic finite element analysis.     

Insights into pyrolysis and catalytic co-pyrolysis upgrading of biomass and waste rubber seed oil to promote the formation of aromatics hydrocarbon

To solve the problem of low aromatic hydrocarbon yield and selectivity in biomass catalytic pyrolysis, we used added oxygen-containing hydrogen supplier of rubber seed oil (RSO) with a higher hydrogen-to-carbon ratio to investigate the thermal decomposition behaviors, kinetic and production distribution of biomass, cellulose and RSO with the weight ratio of 1:2 using thermogravimetric analyzer (TGA) for kinetic analysis and fixed bed reactor with the feed composition of 1.2 g: 0.4 mL/min (Biomass to RSO) for product distribution in non-catalytic and catalytic co-pyrolysis over a HZSM-5 catalyst. The results show that there was a positive synergistic interaction between biomass and RSO according to the difference in weight loss, which could decrease the formation of solid coke at the end of experiment. The addition of the HZSM-5 catalyst can markedly increase the reaction activity, accelerate the reaction rate, and the reaction Ea, leading to a substantial increase in the conversion rate; furthermore, the residual carbon content will decrease, and the activations of Cellulose + RSO + Catalyst and Biomass + RSO + Catalyst are only 50.80 kJ/mol and 62.36 kJ/mol, respectively. The kinetic analysis showed that adding a catalyst did not change the decomposition mechanism. Co-pyrolysis of biomass and RSO could effectively improve the yield and selectivity of aromatics, when the pyrolysis temperature and catalytic temperature were 550 °C and 500 °C, respectively, the mass space velocity of RSO was 0.4 mL/min, the reaction time was 30min, the yields of benzene, toluene, xylene and ethyl benzene (BTXE) were up to 78.77%, and the selectivity of benzene, toluene and xylene was much better. Finally, the coke yield was substantially lower.     

THERMAL STRESSES IN PARTIALLY ABSORBING FLAT PLATE DUE TO SUDDEN INTERRUPTION OF STEADY-STATE ASYMMETRIC RADIATION,I: CONVECTIVE COOLING AT REAR SURFACE

An analysis is presented of the thermal stresses in a partially absorbing flat plate due to sudden interruption of steady-state asymmetric thermal radiation on the front face with convection cooling at the rear face. Maximum transient tensile stresses occur in the rear surface and are almost independent of the heat transfer coefficient, h. For optical thicknesses of ≥ 0.5 μa, the maximum tensile stress initially rises to reach a peak and then decreases with time. In contrast, for thicknesses ≤ 0.5 μa, the stresses decrease monotonically. It is shown that a plot of nondimensional stress as a function of nondimensional time for a given value of pa and h does not result in a universal plot from which thermal stresses can be obtained for any value of plate thickness.     

Transient Response of a Clamped Slab under Pressure and Thermal Loads

The transient response of clamped thin slab under pressure and thermal loads is investigated through analytical and finite difference approaches. Due to the linear-elastic nature of the analysis, the superposition principle is implemented to treat each load individually and to obtain its corresponding response. The analysis introduced a new parameter, the pressure-temperature coupling term, in the mechanical stress solution. It is found that both mechanical and thermal stresses are of the same order of magnitude for coupling term values between 1000 and 10000 Pa/°C, the thermal stresses dominate for coupling term less than 1000 Pa/°C, and the mechanical stresses dominate otherwise.     

Analytical Models of Thermal-Stress Induced Phenomena in Isotropic Multi-Particle-Matrix System

The paper presents four topics dealing with phenomena induced by elastic thermal stresses acting in an isotropic multi-particle-matrix system to represent a model system applicable to real multi-phase materials of a precipitation-matrix type. The isotropic multi-particle-matrix system consists of periodically distributed spherical particles in an infinite matrix to be imaginarily divided into cubic cells containing a central spherical particle. Formulae for the thermal stresses to be investigated within the cubic cell represents functions of the particle volume fraction v and the particle radius R. The thermal stresses originate during a cooling process as a consequence of the difference α _m  ? α _p in the thermal expansion coefficients α _m and α _p of the matrix and the particle, respectively. Additionally, such temperature range is considered within which the multi-particle-matrix system exhibits elastic deformations regarding the yield stress and the particle-matrix boundary adhesion strength. Analytical fracture mechanics to represent the first topic of this paper results from the determination of a curve integral of the thermal-stress induced elastic energy density. The curve elastic energy density results in the determination of the critical particle radii R _pc and R _mc as reasons of the crack initiation in the spherical particle and the matrix for α _m  ? α _p  < 0 and α _m  ? α _p  > 0, respectively. Consequently, the crack propagation to follow the crack initiation is a consequence of the particle radius R > R _qc (q = p, m). Finally, a shape of the crack in a plane perpendicular to the direction of the crack propagation in the particle (q = p) and the matrix (q = p) is described by the function f _q related to the ideal-brittle components. With regard to the crack initiation, the analytical determination of the radius R _qc is considered for any multi-phase materials of a precipitation-matrix type. With regard to the crack propagation, the analytical determination of the function f _q along with an analysis concerning the crack dimension and directions of the crack propagation is considered for ceramic multi-phase materials which are generally assumed to be ideal-brittle. The thermal stresses induce resistance against compressive or tensile mechanical loading for α _m  ? α _p  > 0 or α _m  ? α _p  < 0, respectively. The analytical determination of the resistance results from the elastic energy gradient to represent the second topic of this paper. Derived by two equivalent mathematical techniques, the gradient within the cubic cell is defined as a surface integral of the thermal-stress induced elastic energy density. Consequently the ‘surface’ elastic energy density results in the analytical determination of the system strengthening to represent the third topic of this paper. Representing the fourth topic of this paper, an analytical model of stresses originating in isotropic crystalline lattices are derived. The stresses in the lattices are a consequence of the presence of a central substitutive atom. Additionally, elastic energy, induced by the substitute atom and accumulated in the lattices, is also derived. Finally, readers can substitute numerical values of parameters of real multi-phase materials into the presented formulae.     

Quasi-Static Thermal Stresses Due to Heat Generation in a Thin Hollow Circular Disk

The present paper deals with the determination of displacement and thermal stresses in a thin hollow circular disk defined by a ≤ r ≤ b due to internal heat generation within it. Time dependent heat flux Q(t) is applied at the outer circular boundary (r = b), whereas inner circular boundary (r = a) is at zero heat flux. Also, initially the circular disk is at arbitrary temperature F(r). The governing heat conduction equation has been solved by the method of integral transform technique. The radial stress function σ_rr is zero at inner and outer circular boundaries (r = a and r = b). The results are obtained in a series form in terms of Bessel's functions. The results for displacement and stresses have been computed numerically and illustrated graphically.     

延迟焦化装置混合渣油加工方案及调整措施

2008年,为了提高经济效益,中国石油辽阳石化公司炼油厂160×104t/a延迟焦化装置在加工俄罗斯渣油的基础上,开始混炼委内瑞拉渣油。初步加工方案为:俄罗斯渣油与委内瑞拉渣油的混炼比例为3:2;加热炉辐射段出口温度F101A为493℃,F101C为491℃;循环比为0.25;焦炭塔操作压力为0.2MPa左右;采用"两炉四塔"进行生产,单炉辐射段进料量为72～76t/h。为了防治弹丸焦,对运行参数进行了调整:将混炼比例由3:2调整为4:1;将加热炉出口温度降低1℃;及时调整辐射炉管的注水量,保证焦炭塔空塔线速度不大于0.15m/s。经过调整,延迟焦化装置石油焦产率增加了3.46个百分点,石油焦质量达到SH0527—1992《延迟石油焦(生焦)》3B标准的要求,柴油馏程和硫含量达到下游加氢精制装置对原料的要求,装置运行工况良好,各项工艺参数运行稳定。     

Cyclic variations on LPG and gasoline-fuelled lean burn SI engine

Lean operation is an attractive operational condition; it is known as one of the methods to increase thermal efficiency, and to decrease exhaust emissions and fuel consumption. However, as the mixture leans, cyclic variations increase. Cyclic variations are usually attributed to the result of random fluctuations, excess air ratio and flow field due to the turbulent nature of the flow in the cylinder that limits the range of operating conditions of the spark ignition engine. Gaseous fuels as clean, economical and abundant fuels can improve the lean operating limits and decrease the cyclic variations. Therefore, the purpose of this research is to investigate the use of liquefied petroleum gas (LPG) as a fuel for spark ignition engine in terms of lean operation, and focuses on the cyclic variations and exhaust emissions. The results of this study showed that use of LPG decreased the coefficient of variation in the indicated mean effective pressure, and emission.     

THERMAL STRESSES IN ISOTROPIC CELL-DIVIDED PARTICLE-MATRIX SYSTEM: SPHERICAL ANDCUBIC CELLS

Thermal stresses are studied in an isotropic particle-matrix system of homogeneously distributed spherical particles in an infinite matrix. The isotropic particle-matrix system is divided into cells containing the central spherical particle embedded in the matrix and is of dimensions equal to an interparticle distance. The cell surface is assumed to be acted on by nonzero stresses derived by a criterion of a minimum of the cell elastic energy of the thermal stresses. The thermal stresses originate during a cooling process as a consequence of the difference in thermal expansion coefficients between the matrix and the particle. The formulae for the thermal stresses acting in the isotropic cell-divided particle-matrix system for the ratio of a spherical particle volume to a cell volume v_p = 0 reduce to those for the isotropic particle-matrix system of one spherical particle embedded in an infinite matrix. The thermal stresses are derived for spherical and cubic cells, depending on the spherical particle distribution.     

某舰主锅炉筒身内壁裂缝起因分析

本文介绍某舰中修时发现锅炉汽水联箱水部筒壁及锅炉汽筒产生裂缝情况。分析了产生这种情况的原因,主要是由腐蚀性疲劳和腐蚀性热应力所致。并对此提出一些合理化建议,供有关人员参考。     

An integrated thermal and mechanical investigation of molten-salt thermocline energy storage

Thermal ratcheting is a critical phenomenon associated with the cyclic operation of dual-medium thermocline tanks in solar energy applications. Although thermal ratcheting poses a serious impediment to thermocline operation, this failure mode in dual-medium thermocline tanks is not yet well understood. To study the potential for the occurrence of ratcheting, a comprehensive model of a thermocline tank that includes both the heterogeneous filler region as well as the composite tank wall is formulated. The filler region consists of a rock bed with interstitial molten salt, while the tank wall is composed of a steel shell with two layers of insulation (firebrick and ceramic). The model accounts separately for the rock and molten-salt regions in view of their different thermal properties. Various heat loss conditions are applied at the external tank surface to evaluate the effect of energy losses to the surroundings. Hoop stresses, which are governed by the magnitude of temperature fluctuations, are determined through both a detailed finite-element analysis and simple strain relations. The two methods are found to yield almost identical results. Temperature fluctuations are damped by heat losses to the surroundings, leading to a reduction in hoop stresses with increased heat losses. Failure is prevented when the peak hoop stress is less than the material yield strength of the steel shell. To avoid ratcheting without incurring excessive energy loss, insulation between the steel shell and the filler region should be maximized.     

Spatially Resolved Measurements of Thermal Stresses by Picosecond Time-Domain Probe Beam Deflection

Measurements of thermally induced strains with micron-scale lateral spatial resolution, picosecond time resolution, and sub-picometer vertical sensitivity are achieved using a newly developed experimental method, time-domain probe beam defection (TD-PBD). TD-PBD is a pump-probe optical technique that combines an ultrafast laser oscillator as the light source, high frequency (10 MHz) modulation of the pump beam, and a wide range of time delays (0–4 ns) between the pump and probe. Deflections of the probe beam are measured by a position sensitive detector and an rf lockin amplifier. The beam-deflection data are analyzed using a detailed model of heat transport and thermally generated stresses and strains. Comparisons between the model and the data enable quantitative measurements of the coefficient of thermal expansion with a spatial resolution of 4 µm.     

Co-Carbonization of Two Anthracites with a Fat Coal or Two Pitches

The blends of two anthracite powders (YQ and JC) with a fat coal (C4) or a petroleum pitch (PP) or a coal tar pitch (CTP) in different proportions were co-carbonized at 3°C/min up to 1000°C in an experimental 1 Kg coke oven. Coke yield, coke particulate size, coke micro-strength and coke cracking strength were measured respectively. Coke optical textures were watched under a microscope. The results show that as anthracite proportion increases, coke yields of all blends improve; > 0.8 mm lump coke yields of blends with CTP or PP decline slightly, blends with C4 drop heavily; coke micro-strengths do not change sharply, and coke cracking strength of blends with C4 or PP decrease more than blends with CTP. C4 produces fine-grained mosaics, and two anthracites are mainly fusinite and fragments, PP is coarse-grained mosaics, and CTP is chiefly flow or domain textures. Independent optical textures were observed in cokes. There exist evident borders between the two contact optical textures which were produced by different components, and a few phenomena that domain or flow textures penetrating into fusinite appeared in the blends. It seems that CTP is the best adhesives for blending with anthracites for producing high quality cokes.     

Hydrogen from glycerol steam reforming with a platinum catalyst supported on a SiO2-C composite

This work studies 2 wt% Pt catalysts. The support is a SiO₂-C composite whose main features are a high specific surface due to its mesoporosity, a higher thermal stability than the C support, and the absence of surface acid sites which could promote the dehydration reactions that produce coke precursors. The Pt/SiO₂-C catalyst has very small metallic particles (d_va = 1.37 nm) that favor the CC bond cleavage reactions which allow obtaining total gas conversion at 450 °C. With this catalyst, it is possible to obtain high yields to H₂, between 4 and 5, which indicates that the active sites promote the WGS reaction, even with glycerol concentrations of 30 and 50%. Pt/SiO₂-C is a very stable catalyst since it loses only 10% of its initial activity after 66 h on stream and is resistant to sintering and coke deposition.     

Formation of white etching cracks at manganese sulfide (MnS) inclusions in bearing steel due to hammering impact loading

Wind turbine gearbox bearings (WTGBs) are failing prematurely, leading to increased operational costs of wind energy. Bearing failure by white structure flaking (WSF) and axial cracking may both be caused by the propagation of white etching cracks (WECs) and have been observed to cause premature failures; however, their damage mechanism is currently not well understood. Crack initiation has been found to occur at subsurface material defects in bearing steel, which may develop into WECs. One hypothesis for WEC formation at these defects, such as non‐metallic inclusions, is that repetitive impact loading of a rolling element on a bearing raceway, due to torque reversals and transient loading during operation, leads to high numbers of stress‐concentrating load cycles at defects that exceed the material yield strength. In this study, a number of tests were carried out using a reciprocating hammer‐type impact rig. Tests were designed to induce subsurface yielding at stress concentrating manganese sulfide (MnS) inclusions. The effects of increasing surface contact stress and number of impact cycles, with and without surface traction, were investigated. Damage adjacent to MnS inclusions, similar to that observed in a failed WTGB raceway, was recreated on bearing steel test specimens. It has been found that increasing the subsurface equivalent stresses and the number of impact cycles both led to increased damage levels. Damage was observed at subsurface equivalent stresses of above 2.48 GPa after at least 50,000 impact cycles. WECs were recreated during tests that applied surface traction for 1,000,000 impacts. Copyright © 2016 John Wiley & Sons, Ltd.     

Plane Thermal Stresses in a Functionally Graded Plate Subjected to a Partial Heating

This paper presents plane thermal stresses in a functionally graded plate (FGP) subjected to a partial heating. The heat conductivity, Young's modulus and the coefficient of the linear thermal expansion are expressed by exponential functions of the position. The analytical solution for the FGP with two-dimensional temperature distribution is obtained by use of the stress function method. General solution of the governing equation of the stress function is derived in the functionally graded materials (FGMs). The numerical calculations are carried out for ZrO₂/Ti-6 Al-4 V and ZrO₂{/} stainless (SUS304) functionally graded plates, when the ceramic surface is partially heated. The numerical results are shown in figures for two cases. Even though the FGM, suitable selection of the compositional materials does not produce thermal stresses in the FGP.