延长裂解炉运行周期问题探讨

分析了中国石化广州分公司乙烯装置裂解炉运行周期的现状，阐述了裂解原料、工艺操作和设备维护等各方面因素对裂解炉运行周期的影响，提出了延长裂解炉运行周期的对策。     

Determining particle-size distributions from chord length measurements for different particle morphologies

A recently proposed model to determine particle-size distributions (PSDs) from chord length measurements has been applied to different particle morphologies, namely compact, platelet- and rod-shaped particles. To study these systems, chord length distributions (CLDs) were measured at varying particle size and solids concentration for each compound and were subsequently utilized to determine the system-specific parameters. Each model was successfully applied to its respective compound such that the experimental PSDs and model predictions were in good agreement. Moreover, the effect of other variables such as agitation rate and solvent composition was investigated and found to be negligible for the specific systems tested. Finally, potential model optimizations of the general model construct have been studied. Two variants of the CLD compression step, namely principal component analysis and a geometric model have been considered as surrogate models. However, neither of these approaches yielded superior results than the previously proposed approach.     

双探头传感器可燃气体报警器的设计

针对目前国内常用的可燃气体报警器的检测原理及结构设计的现状,结合可燃气体报警器在检定周期内存在安全隐患及缺陷的弊端,详细分析了催化燃烧型、双波长红外型传感器的原理和应用环境的优势,最终将两种传感器的优势相融合,提出双探头传感器可燃气体报警器的设计方案。该方案结合了催化燃烧型、双波长红外型两种传感器的优点,既可以检测出所有可燃气体,又可以检测出含硫、硅、磷等元素的气体,避免了双探头传感器因其中一个传感器失灵而引起的报警器失效,大大提高了安全系数。     

Estimation of particle size distributions from focused beam reflectance measurements based on an optical model

A popular in situ particle characterization technique, which can be applied without dilution, is the focused beam reflectance measurement (FBRM^®). The FBRM probe measures a chord length distribution (CLD) which is different from a particle size distribution (PSD). In order to compare results obtained by an FBRM probe with other measurement technologies such as laser diffraction, it is necessary to reconstruct the PSD from a measured CLD. For this reconstruction a measurement model and an inversion procedure are required. Most FBRM models presented in the literature assume that an FBRM records a geometric chord which can be deduced from a two-dimensional projection of the particle silhouette. In previous work [Kail, N., Briesen, H., Marquardt, W., 2008. Analysis of FBRM measurements by means of a 3D optical model. Powder Technology 185 (3), 211-222] it has been demonstrated that FBRM data show significant deviations from this geometric model. Consequently, an estimation of a PSD using such a geometric FBRM model will fail. A novel FBRM model is developed in this work. This model imitates the chord discrimination algorithm used in a Lasentec D600L FBRM system and takes the intensity profile of the laser beam and the optical aperture of the probe into account. The model is ideally suited for the estimation of a PSD from a measured CLD using a sequential, linear inversion routine, as proposed in this work. The novel FBRM model and the inversion procedure are evaluated using small, mono-disperse polystyrene beads, large ion-exchanger beads, and α-lactose-monohydrate particles. The applicability of the FBRM for PSD measurements is discussed on the basis of these results.     

Hidden Markov model based approach for diagnosing cause of alarm signals

When a fault occurs in a process, it slowly propagates within the system and affects the measurements triggering a sequence of alarms in the control room. The operators are required to diagnose the cause of alarms and take necessary corrective measures. The idea of representing the alarm sequence as the fault propagation path and using the propagation path to diagnose the fault is explored. A diagnoser based on hidden Markov model is built to identify the cause of the alarm signals. The proposed approach is applied to an industrial case study: Tennessee Eastman process. The results show that the proposed approach is successful in determining the probable cause of alarms generated with high accuracy. The model was able to identify the cause accurately, even when tested with short alarm sub-sequences. This allows for early identification of faults, providing more time to the operator to restore the system to normal operation.     

New aspects of unsaturated polyester resin synthesis. Part I: modelling and simulation of reactant sequence length distributions in stepwise polymerization

The quantification of the relationship between physical properties of polymeric products and the sequence distribution of comonomer units in a polymer chain is not an easy task. In this work, detailed consideration is given to the sequence lengths and sequence length distributions to be expected in unsaturated polyesters formed by the reaction of maleic anhydride, phthalic anhydride and a diol, a reaction which gives rise to the low molecular weight precursors used in unsaturated polyester resins. Monte Carlo methods are used to explore the effects of rate constants, reactant stoichiometry and extent of reaction on the microstructure of the chain. Attention is also given to structural asymmetry of the diol component and the influence of the dynamics of the ring opening of the anhydride coreactants on the products. The approach is generic and can be readily adapted for any copolymerization which proceeds by a stepwise kinetic mechanism. © 2003 Society of Chemical Industry     

Monomer sequence length distributions of hard segments of linear segmented poly(urethane–urea)s 1: chromatographic study

An attempt was made to determine, by the chromatographic method, monomer sequence length distributions of the hard segments in segmented poly(urethane–urea)s (PURs) synthesised in a two-step process: (1) a prepolymer formation reaction of an excess of methylenebis(4-phenylisocyanate) (MDI) with poly(tetramethyleneoxide) (PTMO) and (2) a polymerisation reaction of the prepolymer containing unreacted MDI with ethylenediamine, giving PUR. The monomer sequence length of the hard segment was found to become longer and its distribution to broaden as the initial concentration ratio of MDI to PTMO increased. This result is attributable to an increase of the concentration ratio of the unreacted MDI to the prepolymer, leading to gelation of the polymer solution. By comparing the chromatographic results with the theoretical data calculated in the simple case of the equal reactivity of the reactants in the prepolymerisation and polymerisation reactions, respectively, the existence of unequal reactivities of the reactants in both reactions, is predicted.     

Effect of fiber length distribution on gas holdup in a cocurrent air-water-fiber bubble column

An experimental investigation is reported on the effect of fiber length distribution on gas holdup in a cocurrent air-water-fiber bubble column. Different combinations of 1 and 3 mm Rayon fibers are used to simulate different fiber length distributions. At a constant total fiber mass fraction, gas holdup generally decreases with increasing mass fraction of the 3 mm Rayon fiber while other conditions remain constant. Crowding factors estimated using four different methods (N_c=N_c,A, , N_c,L, and N_c,M) and the parameters and are tested on their performance to quantify the overall effects of fiber mass fraction and fiber length and its distribution on gas holdup. and provide the best characterization of the fiber effects on gas holdup in the cocurrent air-water-fiber bubble column. The crowding factor estimated using the model-based average fiber length (N_c,M) also provides a good characterization and is better than the other crowding factor definitions.     

Influence of fibre length and filler particle size on pore structure and mechanical strength of filler‐containing paper

Test sheets were prepared by incorporating softwood pulp with silica filler, PW‐5 (diameter 4.5 μm) or PW‐20 (15 μm). Length‐weighted averages of fibre were 2.5 (uncut fibre) and 1.25 mm (short‐cut fibre). Pore sizes less than 150 urn were measured by mercury porosimeter. Sheets of short‐cut fibres and mixed with uncut fibres at ratio of 3:1 or 1:3 had larger pore volumes than others tested. When filler content increased, the total pore volume increased for PW‐20 sheets, but it did not for PW‐5 sheets with short‐cut fibres. Tensile index and folding endurance were very much affected by fibre length. Contact number on a fibre was calculated by computer simulation, and it had a linear relation with tensile index of sheet.     

基于结构胶种类及搭接长度变化的胶接接头剪切强度及应力测试分析

通过对3种类型(双组分丙烯酸酯结构胶、双组分环氧树脂结构胶、单组分环氧树脂结构胶)共9款结构胶的搭接长度–剪切强度曲线测试及回归方程拟合,获得搭接长度–剪切应力曲线并对比分析曲线差异,基于结构胶种类及参数提出匹配不同搭接长度的选胶建议。结果表明:对此3种类型的结构胶单搭接满黏结接头,随搭接长度延长,平均剪切强度减小;低模量胶的搭接长度–剪切强度曲线形态与高模量胶的相反,前者为由缓降转为陡降,后者为由陡降转为缓降最后稳定;单组分环氧树脂结构胶适用于承受静载结构;用于承受动载的接头,建议选用双组分结构胶,搭接长度30mm以下选用丙烯酸酯型,搭接长度30mm以上选用环氧树脂型。     

Effect of maturation on the bulk viscosity and molecular chain length of cuplump natural rubber

The effects of the maturation and storage of naturally coagulated latex, generally termed cuplumps, on some bulk rheological properties and on parameters characterizing the macromolecular chain length were investigated for natural rubbers of different clonal typologies. The sensitivity of the clonal material to the degradative effects of cuplump maturation increased with the level of tree energetic metabolism, with the most metabolically active plant materials (e.g., PB 235) being most sensitive, whereas the less active clone PB 217 was less sensitive. A definite relationship evolves between Hevea tree metabolism and the stability of the structure of the biosynthesized rubber. The results presented here highlight at a macromolecular level the effects of maturation previously demonstrated on bulk processing parameters. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 703–708, 2002     

基于浓度/速度场测量的吸收过程液相传质系数

针对矩形流道内气、液流体的并流吸收传质过程,分别应用实时激光全息干涉术和激光多普勒速度仪对不同气、液流速下液相内近界面浓度分布与速度分布进行了实验观测.结果表明,边界层内浓度分布呈指数下降,流速越大梯度越陡,且速度边界层厚度要大于浓度边界层厚度.建立了通过物料衡算求算液相传质系数的方法.得到了不同条件下平均液相传质系数,并与Whiteman’s双膜理论的计算结果进行了比较.     

基于模型预测残差和目标函数的MPC实时性能监控

模型预测控制的性能受多种因素的影响,现有的模型质量评价指标没有考虑外界干扰的变化,反映系统整体性能时不够全面。针对上述问题,现结合两个指标:基于模型预测控制目标函数的历史性能指标和基于模型预测残差的协方差指标对系统性能进行实时监控。其中,历史性能指标用以评价系统的整体性能,协方差指标反映模型失配和干扰变化的影响。根据两个指标对不同性能影响因素的不同表现和性能恶化后对干扰新息的重新辨识结果,对系统性能下降的原因进行初步诊断,缩小性能下降源的范围,并通过Wood-berry塔实验验证了该方法的有效性。     

Analytical and numerical simulations of depolymerization based on discrete model: A chain-end scission scenario

Depolymerization by chain-end scission enables ideally full recovery of monomers, which is considered as a promising route for polymer recycling. Despite attractive experimental achievements, insightful depolymerization kinetic modeling study is capable of providing information for better understanding polymer degradation process and reactor design in polymer industry. Herein, an improved analytical solution for depolymerization by chain-end scission is derived and validated by numerical exact solution. The strength of the as-derived analytical solution lies on its capability of capturing depolymerization kinetics of polymers with large degrees of polymerization and different initial distributions (e.g., Gamma, monodisperse, Poisson, Flory-Schulz, exponential, and log-normal distributions). Additionally, the changes in average properties of polymer are accessed by using a hybrid method based on the method of moment (MoM) and the improved analytical solution considering dimers in chain-end scission process for the first time. Finally, kinetic insights into depolymerization of self-immolative polymers are also gained by the MoM-based model in parallel with two sets of experimental data. This work offers simulation protocols for a profound understanding of depolymerization kinetics and inspecting molecular properties during depolymerization.     

基于多元统计方法的过程单元缓变故障识别

在实际化工生产过程中存在一些缓变故障,在发生的初期过程偏离正常工况的程度较少,且受生产数据噪声的影响,不易被传统过程监测方法及时发现。本文针对缓变故障的特点,提出了一种基于偏最小二乘法-主元分析法(PLS-PCA)的过程监测方法。首先利用偏最小二乘法(PLS)回归提取出各变量之间的关系,通过获取变量实测值与回归预测值之间的误差,以放大装置运行状态与预设状态之间的偏差,在此基础上建立基于主元分析法(PCA)的过程监测模型,实现了对缓变故障的早期识别。该过程监测模型被应用在某制氢装置预转化反应器上,结果表明该方法对缓变故障具有较好的早期识别效果,能够比工程师提前13h,比基于传统PCA的过程监测模型提前8h。     

Data-driven optimal operation of the industrial methanol to olefin process based on relevance vector machine

Methanol to olefin(MTO) technology provides the opportunity to produce olefins from nonpetroleum sources such as coal, biomass and natural gas. More than 20 commercial MTO plants have been put into operation. Till now, contributions on optimal operation of industrial MTO plants from a process systems engineering perspective are rare. Based on relevance vector machine(RVM), a data-driven framework for optimal operation of the industrial MTO process is established to fully utilize the plentiful industrial data sets. RVM correlates the yield distribution prediction of main products and the operation conditions.These correlations then serve as the constraints for the multi-objective optimization model to pursue the optimal operation of the plant. Nondominated sorting genetic algorithm Ⅱ is used to solve the optimization problem. Comprehensive tests demonstrate that the ethylene yield is effectively improved based on the proposed framework. Since RVM does provide the distribution prediction instead of point estimation, the established model is expected to provide guidance for actual production operations under uncertainty.