Operational optimization of crude oil distillation systems using artificial neural networks

A new methodology for optimizing heat-integrated crude oil distillation systems is proposed in this work. The new procedure considers an artificial neural networks (ANN) model for representing the distillation column. Models of the distillation column and the associated existing heat exchanger network are incorporated in an optimization framework to systematically determine the operating conditions that improve the overall process economics. Of particular interest is the problem of optimizing the net value of the products obtained from the column by increasing the yield of higher-value products at the expense of less valuable products, while taking into account feasibility of the distillation specifications, heat recovery, energy and equipment constraints. A two-stage procedure is applied to first optimize the column operating conditions based on minimum utility requirements. In the second stage the heat exchanger network is designed.     

A methodology for the graphical determination of operating conditions of chromatographic sequences incorporating the trade‐offs between purity and yield

Multiple‐step chromatography sequences are necessary in biopharmaceutical downstream processing to achieve the desired levels of purity for products such as therapeutic proteins. Traditional methods of process design deal with each step individually, but this can result in a sequence that does not achieve best overall performance. This paper proposes a graphical methodology for the identification of operating conditions for a two‐step chromatography sequence. The method uses windows of operation to incorporate the trade‐offs between yield, purity and productivity. A tie‐line procedure is developed that separates the window of operation for the first chromatographic step into two zones. One zone contains those operating conditions that combine to produce a material which can be purified successfully by the second step to produce a product that meets the desired specifications. The second zone consists of operating conditions which will not yield a material that can be adequately purified by a second chromatographic stage to yield a product of the predetermined specifications. The methodology is valuable in that it helps in achieving the rapid design of a two‐step chromatography sequence, and aids in choosing the optimum operating conditions for the first step that are highly dependent upon the operation and specifications of the second chromatographic step. Simulations carried out using a software package based on the general rate model depict the construction and use of the method applied to a sequence of ion exchange and hydrophobic interaction chromatography separating a three‐component protein mixture. Copyright © 2006 Society of Chemical Industry     

Discrete-time contraction constrained nonlinear model predictive control using graph-based geodesic computation

Modern chemical processes need to operate around time-varying operating conditions to optimize plant economy, in response to dynamic supply chains (e.g., time-varying specifications of product and energy costs). As such, the process control system needs to handle a wide range of operating conditions whilst optimizing system performance and ensuring stability during transitions. This article presents a reference-flexible nonlinear model predictive control approach using contraction based constraints. Firstly, a contraction condition that ensures convergence to any feasible state trajectories or setpoints is constructed. This condition is then imposed as a constraint on the optimization problem for model predictive control with a general (typically economic) cost function, utilizing Riemannian weighted graphs and shortest path techniques. The result is a reference flexible and fast optimal controller that can trade-off between the rate of target trajectory convergence and economic benefit (away from the desired process objective). The proposed approach is illustrated by a simulation study on a CSTR control problem.     

Material specification and the availability and life of desalination equipment in both Saudi Arabia and the Arabian Gulf

The author describes operational experience with various materials of construction in both low temperature polyphosphate treated evaporators and also in high temperature evaporators using acid treatment.The author references the repeated use of unsuitable materials and proposes a solution by the development of more detailed and positive specifications for plant and equipment. A problem faced by many manufacturers is the fact that as a result of broad, open specifications they are forced to use inferior materials in order to remain competitive. The author discusses the use of both corrosion resistant linings and operating experience. In summary, the paper correlates the operating conditions with selection of materials.     

Mathematical modelling of ambient air-breathing fuel cells for portable devices

Competitive costs, instant recharge, and high energy density make fuel cells ideal for supplanting batteries in portable electronic devices. In this study, we derive a semi-analytical model to elucidate the transport of ions, heat and mass in air-breathing fuel cells. The model includes an empirical correlation for membrane conductivity that improves accuracy when modelling membrane dry-out. A detailed comparison with experimental data demonstrates that the model accurately predicts fuel cell performance through detailed accounting of catalyst layer specifications, including variable width, and electrochemical parameters. A comprehensive parametric study resolves the trends associated with a variety of design specifications and operating conditions. Membrane dry-out is identified as the primary limitation on current density, and is shown to be strongly dependent on heat transfer. The study also identifies some unique effects of coupling between ambient air temperature and humidity on the performance of air-breathing fuel cells.     

环丁砜萃取精馏过程模拟分析及工艺参数优化

以环丁砜-烃类相平衡数据和NRTL-RK热力学方法为基础，对环丁砜萃取精馏过程进行了全流程模拟和工艺操作参数优化。综合考虑各个操作变量及其关联，提出了基于局部耦合参数迭代优化的整体协同优化的策略。通过文献数据回归和Aspen Plus物性估算系统相结合，补充修正了缺失的模型参数，并以此模拟分析了各关键操作参数对环丁砜萃取精馏过程能耗和分离效果的影响。结果表明：当萃取精馏塔操作压力为0.17 MPa，溶剂回收塔操作压力为0.05 MPa时，贫溶剂最佳温度为100℃，原料饱和气相进料的最佳进料位置为第50块塔板；溶剂回收塔最佳回流比为0.33；最佳进料位置为第6块塔板，汽提水量为2853 kg·h^-1。优化后，装置最小热公用工程由1.158 GJ·t^-1下降至0.802 GJ·t^-1，节能效果显著。     

A computer simulation of continuous ion exchange membrane electrodialysis for desalination of saline water

A computer simulation program including the principle of ① mass transport, ② current density distribution, ③ energy consumption and ④ limiting current density is developed for predicting desalinating performance of a continuous (one-pass flow) electrodialysis process. In this simulation the following parameters are inputted; ① membrane characteristics such as overall transport number, overall solute permeability, overall electro-osmotic permeability, overall hydraulic permeability, direct current electric resistance etc. ② electrodialyzer specifications such as flow-pass thickness, flow-pass width and flow-pass length of a desalting cell etc. and ③ electrodialytic conditions such as current density, electrolyte concentration in a feeding solution, linear velocity in desalting cells, standard deviation of normal distribution of solution velocity ratio etc.In a practical-scale electrodialyzer, electrolyte concentration in a desalting cell is decreased along a flow-pass and it gives rise to electrolyte concentration distribution. It causes electric resistance distribution and current density distribution. Solution velocities in desalting cells vary between the cells, and give rise to solution velocity distribution. In this simulation, these distributions are taken into account assuming that the frequency distribution of solution velocity ratio is equated by the normal distribution. Further, the influences of electrodialyzer specifications and elctrodialysis conditions described above on the performances of an electrodialyzer (desalting ratio, current efficiency, electrolyte concentration at the outlets of desalting cells, cell voltage, energy consumption, electrolyte concentration distribution, current density distribution, and limiting current density) are predicted. The simulation model is developed on the basis of the experiments and its reasonability is supported by the performance of electrodialyzers operating in salt-manufacturing plants.     

优化工艺条件,提升催化裂化催化剂筛分质量

通过提高成胶过程胶体固含量,优化喷嘴、旋转体材质和垫片规格的方式,达到改善催化剂产品内、外在质量,稳定生产过程条件控制和产品质量的目的。结果表明,成胶过程固含量的提高以及喷嘴、旋转体的材质和垫片规格的改进,不仅能够改善催化裂化催化剂的筛分集中度和颗粒圆球度,而且能够确保催化剂产品筛分质量和装置操作条件的稳定,同时使生产成本得到降低,从而充分满足各炼化用户对催化剂产品筛分质量持续严格的要求以及适应竞争愈加激烈的催化剂市场。     

Modeling and Optimization of a Tunnel Crape Dryer

A mathematical model of a tunnel dryer for the dehydration of grapes is presented and applied to the determination of optimal operating conditions of the dryer. The dryer is of semi-batch structure, operating with trucks and trays. The cycle period is determined by meeting appropriate quality specifications for the final product. The nominal conditions were evaluated bv suitably minimizing. the total fuel demand, expressed as fuel consumption to production capacity, under some constraints regarding the production rate of the dryer and the maximum permissible air temperature. An nominal air humidity value was evaluated suggesting a minimum cycle period value for the production capacity and fuel demand. The nominal conditions required operation of the dryer on the maximum permissible air temperature. The optimum operation was evaluated by maximizing the total profit resulting from the operation of the dryer. The optimization variables were temperature and humidity of the drying air stream. A charteristic case study of industrial grape was included to illustrate the effectiveness of the proposed approach.     

Continuous countercurrent deterpenation of lemon essential oil by means of supercritical carbon dioxide: Experimental data and process modelling

A thermodynamic model based on the Peng-Robinson equation of state was developed in order to perform high-pressure phase equilibria calculations for the system carbon dioxide-lemon essential oil. The multicomponent natural oil was simulated by a mixture of three key components, one for each relevant class of compounds (monoterpenes, monoterpene oxygenated derivatives and sesquiterpenes). Firstly the proposed model was validated on semi-batch experimental data and then it was used to simulate the behaviour of a continuously operated countercurrent column. Experiments on deterpenation process on a packed column, operating as a stripping section, were carried out in the temperature range 50-70 °C and pressure range 8.7-11.2 MPa. The comparison between experimental results and process simulation demonstrated that the proposed model is capable of reliable predictions on the behaviour of the countercurrent continuous deterpenation process. Furthermore, an average height equivalent to a theoretical plate of about 40 cm was estimated, for the stated packing and operating conditions. A case study for the production of 10-fold high quality oil, with strict specifications for the recovery of oxygenated compounds (99%), was investigated by simulations of a continuous countercurrent process with an external reflux. The linkage between the number of theoretical stages, the reflux ratio and the solvent to feed ratio was investigated throughout the above-mentioned pressure and temperature ranges. Operating conditions at higher pressure and temperature proved to be more favourable. As an example, operating a 20 theoretical stage column at 70 °C and 11.2 MPa, it is possible to attain process specifications with a solvent to feed ratio of about 63.     

Modeling and Optimization of a Tunnel Crape Dryer

ABSTRACT

A mathematical model of a tunnel dryer for the dehydration of grapes is presented and applied to the determination of optimal operating conditions of the dryer. The dryer is of semi-batch structure, operating with trucks and trays. The cycle period is determined by meeting appropriate quality specifications for the final product. The nominal conditions were evaluated bv suitably minimizing. the total fuel demand, expressed as fuel consumption to production capacity, under some constraints regarding the production rate of the dryer and the maximum permissible air temperature. An nominal air humidity value was evaluated suggesting a minimum cycle period value for the production capacity and fuel demand. The nominal conditions required operation of the dryer on the maximum permissible air temperature. The optimum operation was evaluated by maximizing the total profit resulting from the operation of the dryer. The optimization variables were temperature and humidity of the drying air stream. A charteristic case study of industrial grape was included to illustrate the effectiveness of the proposed approach.     

Energy conservation in an optimized electrochemical process

In industrial electrochemical process, cost resulting from energy consumption and investment are balanced by operating at an optimum current density. Energy conservation measures such as technical process improvement or changes in energy prices often result in new optimum operating conditions. This has to be considered in assessing the effect of suh measures. The inter-relationship between process operating conditions, product cost, and energy consumptions have been studied by means of model calculations     

Microwave improvement of catalyst performance in soot oxidation without additives

The application of microwaves allows to overcome technical hitches related to the regeneration of soot-filters allowing to perform it independently on the engine operating conditions. The performance of a SiC foam filter during microwave regeneration was investigated with and without a catalyst coating. The regeneration efficiency and the energy required for regeneration were evaluated for catalytic and uncatalytic SiC foams by varying the operating conditions of soot trapping.

Results showed that for both catalytic foams, Fe/V/K and Cu/V/K, the capability to be heated independently of the amount of soot allows to maintain temperature sufficiently high to perform a complete foam filter regeneration. Moreover, the microwave absorbing properties of the catalytic phases allow to perform regeneration with a lower energy consumption with respect to the uncatalytic case. The presence of a catalyst also allows to overcome the dependence of microwave-assisted regeneration process on the operating conditions of soot loading.     

Vapour–liquid slip in a parallel-plate electrochemical fluorination reactor

A mathematical model was used to study the effect of slip between the gas and liquid phases on the performance of an electrochemical fluorination reactor. The model incorporates two-phase flow with differential material, energy and pressure balances. The effect of slip on the temperature, pressure, gas fraction and current distribution in the reactor is presented under relatively severe operating conditions. In addition, the effect of slip on the cell voltage, current efficiency and energy usage is shown at different flow rates over a wide current range. It was found that slip of the gas past the liquid is insignificant under normal operating conditions, but it is significant at high cell currents and low flow rates. Under these more severe operating conditions, slip significantly reduces the cell voltage, and hence the energy usage, since less gas resides in the reactor.     

煤燃烧中影响NOx生成因素的分析

概述了煤燃烧中空气分级燃烧技术,分析了NOx生成的影响因素。影响NOx形成的主要锅炉操作参数为:初级燃烧区化学计量比为0.7～0.9,停留时间较长时,NOx的生成量较少;温度的影响与环境的氧化/还原气氛有关;增加过量空气,NOx生成量增加。影响NOx生成的最主要的煤性质是氮含量和挥发分,氮含量的影响与燃烧所采用的控制技术有关,随挥发分含量增加,NOx的生成量减少。     

基于能量目标的芳烃萃取精馏溶剂评价模型

以NRTL活度系数模型为基础，利用Aspen Plus对不同单组分萃取剂回收芳烃的萃取精馏装置进行了全流程模拟和工艺操作参数优化。综合考虑各操作变量及其关联，提出了基于局部耦合参数迭代优化的整体协同优化策略，在保证分离要求的条件下，以能耗为目标，对萃取精馏塔（EDC）、溶剂回收塔（ERC）的进料位置、ERC回流比等关键操作参数进行优化，建立过程能耗的物性关联模型。通过分析不同溶剂对芳烃萃取精馏过程能耗和分离效果的影响，提出了基于能耗目标的芳烃萃取精馏溶剂评价模型，结果表明影响芳烃萃取精馏过程能耗的关键物性为溶剂的分子量及常压沸点，所建立的过程能耗关联模型具有较高的关联性，其R ²均大于0.9，可有效指导萃取精馏溶剂选择，为计算机辅助分子设计提供简化的目标函数。     

Analysis of Operating Variables in the Catalytic Purification of Butene-1 in a Trickle Bed

A mathematical model for analyzing and simulating selective hydrogenation of butyne-1 and 1,3-bu-tadiene in industrial trickle bed reactors operated to obtain high purity butene-1 is presented in this work.Fromthe analysis of typical operating conditions,only the relevant phenomena are finally retained in the model formu-lation.The model is then employed to analyze the effect of operating variables and catalyst selectivity in processperformance.In particular,the search for the minimum hydrogen flow rate necessary to fulfil butene-1 purityspecifications is undertaken.     

Superheated Steam Drying: An Overview of Pilot and Industrial Dryers with a Focus on Energy Efficiency

According to the principle of sustainability, modern industry should preserve nonrenewable energy sources and develop more efficient processes, especially in terms of energy consumption. The depletion of fossil energy reserves, the environmental impact of greenhouse gases, and the possible threats of environmental taxes are the main reasons to develop new processes in general, and new drying processes in particular, for the existing industries. Using superheated steam as a drying medium instead of hot air can improve the energy efficiency by reusing the energy from exhausted steam and prevent gas emission into the atmosphere by condensation. The present review is focused on both lab-scale pilots—including impingement jet, fluid bed, kiln, fixed bed, and flash drying—described in the literature and existing industrial facilities, with a specific analysis focused on energy efficiency. The usefulness of superheated steam drying pilots for experimental research and for the design of industrial dryers is analyzed. The impact on quality specifications of the dried product for different operating conditions is also presented. Documentation on industrial superheated steam dryers is very rare. Nevertheless, this work presents and analyses the key data available for superheated steam drying of beet, alfalfa, industrial pulp, and paint sludge. Energy recovery and process integration, with a focus on specific technological challenges for industrial dryer implementation, are also presented. This document will result in a discussion of some new ideas for possible R&D in superheated steam drying.     

基于持续节能的多周期换热网络优化设计

在石油化工工业中,换热网络的操作条件时常发生改变,尤其是结垢热阻随运行时间不断增大。针对操作条件的改变,有研究者提出多周期换热网络最优综合的设计与改造方法。但是,这些方法不涉及结垢热阻对设计结果的影响。然而,换热器结垢不可避免,传热系数随之改变,将导致操作工况偏离最优值,难以实现持续节能优化。以多周期换热网络优化为基础,提出一种基于持续节能的多周期换热网络综合设计方法,以换热网络累积总费用为目标函数,考虑换热器结垢对多周期换热网络优化结果的影响,进而实现多周期换热网络的最优综合。首先,结合示例分析换热器结垢对多周期换热网络优化结果的影响,得出考虑到结垢热阻的影响多周期换热网络在各个周期内的优化结果将改变;然后,基于持续节能优化,以换热网络累积总费用为目标函数,提出一种多周期换热网络优化方法;最后,结合示例验证了该设计方法的有效性。     

Steady state multiobjective optimization of continuous copolymerization reactors

The multiobjective nature of optimization problems related to homopolymerizaton and copolymerization processes implies a vector objective formulation for a correct approach. Two copolymerization systems, methyl methacrylate-vinyl acetate (MMA-VA) and styrene-acrylonitrile (ST-AN) are simulated, and some aspects of the steady state optimality of continuous operation are analyzed. The determination of non-inferior sets through the concept of Pareto optimality permits a clear decision on trade-offs related to operating conditions and product specifications.