Genetic algorithm development for multi-objective optimization of batch free-radical polymerization reactors

An improved genetic algorithm approach, based on a new ranking strategy, has been proposed to conduct multi-objective optimization of chemical engineering problems. New operators have been introduced to enhance the algorithm performance and reduce the computational effort. A Pareto-set filter operator has been implemented to avoid missing Pareto optimal points during the evolutionary process. A niche operator has been adopted to prevent genetic drift, and an elitism operator, to insure the propagation of the best result of each objective function. A fitness function based on each rank population size and rank level has been used to determine the reproduction ratio. Constraints are handled through a fuzzy penalty function method. The algorithm has been applied to a batch free-radical styrene polymerization process in order to maximize the monomer conversion rate and minimize the concentration of initiator residue in the product. The algorithm proved to be robust, handling satisfactorily multi-modal and multidimensional problems.     

Nitrogen compounds characterization in atmospheric gas oil and light cycle oil from a blend of Mexican crudes

The distribution of basic and non-basic nitrogen compounds along the distillation curves of the middle distillates atmospheric gas oil (AGO) and light cycle oil (LCO), used as feedstocks for diesel fuel production, is presented in this paper. For this purpose, the total and basic nitrogen content of true boiling point distillation fractions of AGO and LCO were obtained, followed by nitrogen compounds identification by a GC-MS technique. The ratio of quinoline, indole and carbazole derivatives was determined as 1/0.75/2.5 in AGO. In LCO, a 1/2.3/12.2 ratio of aniline, indole and carbazole derivatives was found. A complete physical and chemical characterization of both AGO and LCO is also presented.     

掺炼催化重柴油对加氢反应特性及催化产品分布的影响

分析催化裂化柴油(LCO)加工路线及转化技术,提出催化裂化轻、重柴油分别抽出,轻柴油加氢精制后作为产品柴油;催化重柴油(HLCO)经加氢开环后,再经催化裂化反应,将部分柴油转化为汽油和液化气.通过中试实验确定了蜡油加氢原料蜡油掺炼不同比例HLCO,对蜡油加氢反应特性及产品性质的影响.工业生产运行结果表明,蜡油加氢原料掺...     

催化裂化柴油综合利用技术及其发展

催化裂化柴油(LCO)具有芳烃含量高、十六烷值低的特点,已成为炼厂的主要低价值油品。如何高效利用LCO中富含的芳烃,国内外相继推出了LCO的综合利用技术。本文主要从技术特点、反应机理、工艺流程、催化剂和应用数据等方面简要介绍了4类LCO综合利用技术,包括LCO加氢改质技术、LCO加氢裂化技术、LCO加氢-FCC组合技术、LCO加氢-芳烃抽提组合技术。分析表明LCO综合利用技术不仅可生产清洁柴油,还可生产高辛烷值汽油或BTX轻组分,炼厂可根据自身的实际情况与市场需求,选择合适的技术路线,在追求产品质量升级的同时,实现经济效益最大化,同时适应了现代炼油企业油、化结合的发展趋势。     

面向产品分布协调的两段提升管催化裂解多目标优化

根据两段提升管重油催化裂解过程工艺特点和经济运行要求，基于过程机理模型，考虑多种约束条件，构造了同时最大化丙烯、汽油产量以及最小化干气产量的多目标操作优化问题，并采用标准化法向约束方法求解获得了完整、均匀分布的Pareto最优解。仿真结果表明，多目标优化结果可以定量地描述出丙烯、汽油和干气收率间的最优折中，以及操作变量、约束条件对产品分布的影响，可以为过程优化操作提供指导。     

分子尺度的复杂反应体系动力学模拟（Ⅱ）DCC-Ⅰ反应动力学模型的建立

以Monte Carlo模拟和结构导向集总相结合的方法对复杂反应体系DCC-Ⅰ系统的反应动力学进行了模拟,建立了包括75条反应规则的DCC-Ⅰ的反应网络.模拟结果表明各种产物的产率随反应深度的变化趋势是合理的,主要产物丙烯和汽油在最佳反应深度时的产率和产品性质能够很好地和标定数据拟合,建立的模型能够很好地反映出催化裂解的反应特性.     

Heavy metal content of bottom ashes from a fuel oil power plant and oil refinery in Cuba

Fly and bottom ashes from fuel oil power plants and oil refineries may contain hazardous trace elements, such as heavy metals, which have a negative impact on the environment with time due to potential leaching through acid rains and into groundwaters. This study provides levels of As, Cr, Cu, Hg, Mn, Ni, Pb, Ti, V and Zn of bottom ashes from a thermal power plant and an oil refinery placed in Cienfuegos Bay, Cuba. Trace elements were measured using X-ray fluorescence (XRF) with a SPECTOR X-LAB PRO 2000 system. High contents of Cr, Ni, Pb, Ti, V and Zn were found in the ashes, with values significantly higher than those reported in literature. According to Cuban regulations these ashes are classified as hazardous waste. For this reason we discuss some management alternatives.This study represents the first report of heavy metals in bottom ashes from power plants and oil refineries in Cuba.     

Multi-objective optimization of an industrial fluidized-bed catalytic cracking unit (FCCU) using genetic algorithm (GA) with the jumping genes operator

The multi-objective optimization of industrial operations using genetic algorithm and its variants, often requires inordinately large amounts of computational (CPU) time. Any adaptation to speed up the solution procedure is, thus, desirable. An adaptation is developed in this study that is inspired from natural genetics. It is based on the concept of jumping genes (JG; transposons). The binary-coded elitist non-dominated sorting genetic algorithm (NSGA-II) is adapted, and the new code, NSGA-II-JG, is used to obtain solutions for the multi-objective optimization of an industrial fluidized-bed catalytic cracking unit (FCCU). This unit is associated with a complex model that is highly compute-intense. The CPU time required for this problem is found to reduce fivefold when NSGA-II-JG is used, as compared to when NSGA-II is used. Solutions of similar two-objective optimization problems for the FCCU are compared. NSGA-II-JG also gives improved convergence characteristics and spread of the optimal Pareto points for two simpler multi-objective optimization problems studied here. Indeed, in one problem, where several optimal Pareto fronts exist, the new code gives the correct, global optimal Pareto set, while the original code (binary-coded NSGA-II) converges to local Paretos. The JG operator is associated with some kind of macro–macro-mutation and introduces higher exploratory capabilities, counteracting the effect of elitism in NSGA-II. We, thus, have a better algorithm incorporating the advantages of elitism. This adaptation can prove to be of considerable value for solving other compute-intense problems in chemical engineering.     

Modeling and optimization of an industrial hydrocracking unit to improve the yield of diesel or kerosene

Hydrocracking is used in the petroleum industry to convert low-quality feedstocks into highly-valued transportation fuels. This process is the best source of low-sulfur and low-aromatics diesel fuel as well as high-smoke point jet fuel. Many approaches have been proposed for solving optimization of hydrocracking units in the last decades, but they usually neglect the reaction in hydrotreater where hydrocarbon cracking often occurs, thus leading to suboptimal solutions in industrial problems. Unlike existing literature, this paper considers the hydrocarbon cracking reactions in hydrotreater and hydrocracker simultaneously. The models are based on energy balance, mass balance and a discrete lumped model approaches for kinetic modeling. Before optimization, the properties of feedstock are predicted with ASPEN PLUS by using laboratory data from the refinery, and then the model parameters are estimated with genetic algorithm (GA) based on industrial data and validated by comparing the simulating results with industrial data. To improve the yield of the lighter products, the operation conditions are optimized by GA and Sequential Quadratic Programming (SQP). The yields of the diesel or kerosene increase with the proposed approach.     

Optimal design of a multi-product biorefinery system

In this paper we propose a biorefinery optimization model that can be used to find the optimal processing route for the production of ethanol, butanol, succinic acid and blends of these chemicals with fossil fuel based gasoline. The approach unites transshipment models with a superstructure, resulting in a Mixed Integer Non-Linear Program (MINLP). We consider a specific problem based on a network of 72 processing steps (including different pretreatment steps, hydrolysis, fermentation, different separations and fuel blending steps) that can be used to process two different types of feedstock. Numerical results are presented for four different optimization objectives (maximize yield, minimize costs, minimize waste and minimum fixed cost), while evaluating different cases (single product and multi-product).     

Optimal economic operation of liquid petroleum products pipeline systems

The majority of overland transport needs for crude petroleum and refined petroleum products are met using pipelines. Numerous studies have developed optimization methods for design of these systems in order to minimize construction costs while meeting capacity requirements. Here, we formulate problems to optimize the operations of existing single liquid commodity pipeline systems subject to physical flow and pump engineering constraints. The objectives are to maximize the economic value created for users of the system and to minimize operating costs. We present a general computational method for this class of continuous, non-convex nonlinear programs, and examine the use of pump operating settings and flow allocations as decision variables. The approach is applied to compute optimal operating regimes and perform engineering economic sensitivity analyses for a case study of a crude oil pipeline developed using publicly available data.     

Separation of aromatic components from light cycle oil by solvent extraction

To improve the versatility of light cycle oil (LCO), separation of aromatic compounds from LCO by solvent extraction was investigated. LCO was analyzed to identify 35 components: 19 aromatics and 16 alkanes. The batch liquid–liquid equilibrium extraction of LCO was performed using furfural, sulfolane, and methanol as extraction solvents. In each solvent, the aromatics present in LCO were selectively extracted relative to the alkanes. The separation selectivities of aromatics relative to alkanes were larger in sulfolane than in the other solvents. Among the aromatic components, di- and tricyclic compounds were selectively extracted relative to the monocyclic ones.     

Preparation of bio-fuels by catalytic cracking reaction of vegetable oil sludge

Biofuel production from vegetable oil is potentially a good alternative to conventional fossil derived fuels. Moreover, liquid biofuel offers many environmental benefits since it is free from nitrogen and sulfur compounds. Biofuel can be obtained from biomass (e.g. pyrolysis, gasification) and agricultural sources such as vegetable oil, vegetable oil sludge, rubber seed oil, and soybean oil. One of the most promising sources of biofuel is vegetable oil sludge. This waste is a major byproduct of vegetable oil factories. It consists of triglycerides (61%), free fatty acid (37%) and impurities (2%). The hydrocarbon chains of triglycerides and free fatty acid are mainly made up of C₁₆ (30%) and C₁₈ (36%) hydrocarbons. The others consist of C₁₂-C₁₇ hydrocarbon chains. Transesterification can help in converting vegetable oil sludge into biofuel. The disadvantage of this method is that a large amount of methanol is required. The alternative method for this conversion is catalytic cracking. The objective of this research is to evaluate and compare the pyrolysis process with cracking catalytic reaction of vegetable oil sludge by Micro-activity test MAT 5000 of Zeton-Canada.A ZSM-5/MCM-41 multiporous composite (MC-ZSM-5/MCM-41), was successfully synthesized using silica source extracted from rice husk. The material has the MCM-41 mesoporous structure, and its wall is constructed by ZSM-5 nanozeolite crystals. The porous system of the material includes pores of the following sizes: 5 Å (ZSM-5 zeolite), 40 Å (MCM-41 mesoporous material), and another porous system whose diameter is in the range of 100-500 Å (mesoporous system) formed by the burning of organic compounds that remain in the material during the calcination process. This pore system contributes to an increase in the catalytic performance of synthesized material.The results of vegetable oil sludge cracking reaction show that the product consists of fractions such as dry gas, liquefied petroleum gas (LPG), gasoline, light cycle oil (LCO), and (heavy cycle oil) HCO, which are similar to those of petroleum cracking process.MC-ZSM-5/MCM-41 catalyst is efficient in the catalytic cracking reaction of vegetable oil sludge as it has higher conversion and selectivity for LPG and gasoline products in comparison to the pyrolysis process. Product distribution (% of oil feed) of cracking reaction over MC-ZSM-5/MCM-41 is coke (3.4), total dry gas (7.0), LPG (31.1), gasoline (42.4), LCO (8.9), HCO (7.2); and that of pyrolysis are coke (19.0), total dry gas (9.3), LPG (16.9), gasoline (28.8), LCO (13.7), and HCO (12.3).These results have indicated a new way to use agricultural waste such as rice husk for the production of promising catalysts and the processing of vegetable oil sludge to obtain biofuel.     

活塞式航空发动机燃用生物航煤与RP-3燃料的适用性对比

以大豆油为原料，经催化裂解、精馏、芳构化和加氢过程制备生物航煤，并分析了其组成及理化性能；进一步采用活塞式航空发动机进行发动机台架试验，对比分析了生物航煤与RP-3燃料的燃用适用性。研究结果表明：生物航煤的基本组成为直链烷烃74.54%、环烷烃13.04%、芳香烃10.31%、醚类1.07%和非α-链烯烃1.04%；生物航煤的热值较高(44.4 MJ/kg)，冰点低(-48 ℃)，但黏度较高(2.11 mm²/s)。与RP-3燃料相比，生物航煤具有更低的启动温度；温升速度(相差4 ℃之内)、油耗(相差小于0.02 g/s)与RP-3燃料接近，当发动机转速超过4 200 r/min时，过量空气系数波动较大(0.8~1.2)，燃烧状态恶化。台架试验后发动机拆解检查发现，燃用生物航煤后出现结焦积炭现象，这是由于该批次生物航煤黏度较大(>2 mm²/s)，对雾化效率、燃烧充分程度等发动机工作性能产生影响。     

Catalytic degradation of waste high-density polyethylene into fuel products using BaCO3 as a catalyst

Waste high-density polyethylene (HDPE) was degraded thermally and catalytically using BaCO₃ as a catalyst under different conditions of temperature, cat/pol ratio and time. The oil collected at optimum conditions (450 °C, 0.1 cat/pol ratio and 2 h reaction time) was fractionated at different temperatures and fuel property of the fractions and parent oil was evaluated by their physicochemical parameters for fuel tests. The results were compared with the standard values for gasoline, kerosene and diesel oil. Boiling point distribution (BPD) curves were plotted from the gas chromatographic study of the samples and compared with that of the standard gasoline, kerosene and diesel. The oil samples were analyzed using GC/MS in order to find out their composition. The physical parameters and the composition of the parent oil and its fractions support the resemblance of the samples with the standard fuel oils. The light fractions best match with gasoline, the middle fractions match with kerosene and the heavier fractions match with diesel oil in almost all of the characteristic properties.     

High quality diesel by hydrotreating of atmospheric gas oil/light cycle oil blends

An improved process for high-quality diesel fuel production by hydrotreating atmospheric gas oil (SRGO) and light cycle oil (LCO) blends is presented in this paper. For this purpose, a set of blends of 5, 10 and 15% by volume of LCO with final boiling points of 300, 325 and 350 °C with a full range gas oil (FBP 350 °C) was hydrotreated in a pilot plant at 340-380 °C, 5.4 MPa, 2.5 h⁻¹ LHSV using a commercial Co-Mo catalyst. A relationship between the concentration of refractory sulfur compounds (those boiling above 316 °C) and aromatics content in the feedstock with the hydrotreating temperature required for meeting a 0.05% sulfur specification was found.The experimental data obtained during the desulfurization was quantitatively represented by a 1.50 to 1.56 order rate equation, with activation energies between 18.9 and 34.1 kcal/mol, depending on the feedstock.     

Olefins and BTX-production by thermal cracking of hydrotreated vacuum gas oil and related fractions

Aramco vacuum gas oil was catalytically hydrotreated to conversions of 20, 40 and 60%, and subsequently fractionated into naphtha, kerosene, gas oil, and hydrotreated vacuum gas oil. These fractions were thermally cracked to test their potential as feedstock for olefins and BTX production. The olefin yields from the hydrotreated vacuum gas oil obtained from hydrotreating with 40 and 60% conversion favorably compare with those of straight-run naphthas. Cracking in conventional naphtha/atmospheric gas oil units becomes possible. The naphtha, kerosene and gas oil fractions are preferably added to standard refinery streams.     

Combustion characteristics of droplets composed of light cycle oil and diesel light oil in a hot-air chamber☆

Development of gas turbines fueled with light cycle oil (LCO) and oil mixture of LCO and diesel light oil (LO) requires an understanding of the droplet burning and vaporization characteristics of those oils. The present study is devoted to comparing the burning characteristics of isolated fuel droplets composed of an LCO and an LO. The tests were conducted in an atmospheric hot-air chamber preset at 1173 K, and the examined LCO had a lower cetane number but higher volatility and aromatics content compared to LO. It was demonstrated that the burning of the LCO droplet was sootier, while that of the LO droplet was more disruptive. At the tested temperature, coke formation was indistinct for both the oils, whereas slightly higher ignition delay time was shown for the LO droplet. The microexplosive burning more or less complicated the time-series droplet size d, an explicit burning rate constant, however, was still definable according to the d²-law to show the overall regression speed of the droplet surface area d² with burning time t. The rate constant exhibited little difference for smaller LCO and LO droplets but was greater for LO when the droplet was larger. The rate constant also gradually increased with increasing the initial droplet diameter d₀, which caused the relative size d/d₀ to be unified (normalized) into a single curve by a burning time t/d₀ⁿ (1.0<n<2.0). Analysis revealed that this unification resulted from the respective overlaps of the unsteady and quasi-steady burning phases for differently sized droplets. Further, it was clarified that the unification and analysis are generally valid to isolated liquid fuel droplet burning in hot ambiences.     

Optimization strategies and impact of low oil price on long term SAGD projects

Steam assisted gravity drainage (SAGD) has been known as a commercially proven high ultimate recovery process for bitumen and heavy crudes. It is an energy intensive process, which is economical when oil price is above certain value. When the oil price goes below the economic threshold of project, steam injection can be decreased or completely stopped for a certain period of time, and can resume thereafter when the condition alters. The objective of this study is to provide comprehensive information about the effect of steam injection interruptions on thermal project performance. An optimization strategy for the SAGD process, in cases where steam injection interruption occurs, is discussed using actual reservoir models of different geological formations. An economical model is used to evaluate operating strategy effect on the net present value (NPV) of the project. The parameters, like shut-in period, initial steam injection period, etc, are optimized for Athabasca type oil sand reservoirs. The results show several key mechanisms exist in the life cycle of the SAGD process that must be included to reflect the field scale behaviour; otherwise, the mechanistic simplicity of the models could lead to directional and semi-quantitative conclusions. Among the mechanisms, temperature effect on basic petrophysical properties of reservoir rocks was found to have an important role in the oil recovery, and considerably impacts the results of optimization. When the steam injection is interrupted, an optimum shut-in period can be determined to maximize the oil recovery. The optimum length of steam injection interruption depends on the initial steam injection period.     

Experimental investigation of liquid-fuel atomization using Hartmann acoustic generator

The Hartmann acoustic generator has been used in the present experiments to atomize high-speed diesel oil, aviation kerosene and light furnace oil. The effects of upstream air pressure (196–490 kPa), nozzle diameter, and frequency of sound field (5000–22000 Hz) on the mean droplet size of the spray have been investigated. The experiments showed that the degree of fuel atomization was much more sensitive to a variation in the upstream air pressure than to a variation in the acoustic frequency. Atomization was almost independent of fuel viscosity; thus burners incorporating these acoustic generators should prove particularly suitable for the atomization and combustion of heavy fuel oils. It was dependent mainly on surface tension and fuel density. A single correlation has been obtained for all three fuels, within the range of experimental conditions investigated, but attempts to develop a dimensionless expression incorporating surface tension and density were unsuccessful, partly because of the small range of these properties examined.