Globally optimal power cycle synthesis via the Infinite-DimEnsionAl State-space (IDEAS) approach featuring minimum area with fixed utility

This paper demonstrates the use of the Infinite DimEnsionAl State space (IDEAS) approach in synthesizing optimal power cycles featuring minimum heat exchange area. IDEAS is used to synthesize power cycle networks which include splitters, mixers, pumps, turbines, and heat exchangers and feature a single or multiple working fluid(s). The overall synthesis goal is to minimize heat exchange area requirements, while delivering a fixed percentage of the maximum net power obtainable from a given set of hot and cold utilities. The global optimality of the obtained power cycle network configuration is guaranteed, since IDEAS gives rise to convex (linear) programs. The power of the proposed approach is demonstrated on a case study involving the generation of electricity by a bottoming cycle with a pure ammonia working fluid. Real thermodynamic data for pure ammonia and rigorous equipment models are employed in carrying out the proposed optimization.     

Synthesis of ternary distillation process structures featuring minimum utility cost using the IDEAS approach

A synthesis method for ternary distillation process structures is proposed on the basis of the infinite‐dimensional state‐space (IDEAS) approach. The proposed synthesis procedure consists of two steps. At the first step, the utility cost is minimized. The result of the first step contains many tiny flows among the modules because the number of flows is not included in the objective function. Then, at the second step, an evolutionary procedure for process simplification is executed. In this step, the weighted sum of flow rates is minimized recursively while updating the weights at each iteration. The practical process structure is finally determined from the result of the second simplification step. The developed synthesis procedure was applied to the separation problem of a ternary mixture consisting of benzene, toluene, and o‐xylene. It demonstrated that the proposed procedure provides a process whose liquid composition profile is quite similar to that of a Petlyuk column. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1285–1294, 2018     

数学规划与图形方法相结合设计热集成用水网络

将数学规划法与图形方法相结合探究单杂质用水网络与换热网络的集成问题。首先构建混合整数非线性规划模型（MINLP）,在最小公用工程消耗下优化流股参数未知情况下的分离系统组合曲线面积,得到了最为节能、换热面积最小的用水网络结构。在此基础上,提出了新的分离系统组合曲线演化步骤和规则,可以得到换热单元数目较小的换热网络结构。算例表明,与现有的基于分离系统的热集成用水网络设计方法相比,在最小化公用工程用量的同时可以进一步降低换热器数目与总换热面积。     

IDEAS based synthesis of minimum volume reactor networks featuring residence time density/distribution models

This work addresses for the first time, the synthesis of globally minimum volume reactor networks, featuring segregated flow reactors (SFR) and/or maximum mixedness reactors (MMR), with the same normalized residence time density (NRTd) function. Global optimality is ascertained by demonstrating that the input–output information maps of SFR and MMR with general RTd/RTD models satisfy all properties required for the application of the infinite dimensional state-space (IDEAS) approach to the RTd/RTD reactor network synthesis problem. The resulting IDEAS formulation is shown to possess a number of novel properties, which can be used to facilitate its solution. The power of the proposed methodology is demonstrated on three case studies featuring segregated laminar flow reactors (SLFR) in which the Trambouze reaction scheme is carried out. In one of the case studies, the identified reactor network is shown to have volume that is as low as half the volume of a single reactor.     

线性唯象传热定律下热驱动分离过程最优性能

考虑传热和传质过程分别服从线性不可逆热力学中的线性唯象传热定律和线性传质定律,研究了热驱动分离过程的最小耗热晕和最大生产率.得到了线性唯象传热定律下给定功率输出时的内可逆热机最大效率的解析解,导出了热驱动分离过程的最小耗热量和最大生产率的解析解,并将两种不同传热规律下的优化结果进行了比较,结果表明传热规律影响热驱动分离...     

Global optimization of reactive distillation networks using IDEAS

In this work, we present a methodology for the global optimization of reactive distillation (RD) networks, through the Infinite DimEnsionAl State-space (IDEAS) approach. Within the IDEAS framework, network synthesis is formulated as an infinite dimensional linear optimization problem. The IDEAS conceptual framework is realized through solution of a series of finite dimensional linear programs whose optimum values converge to the infinite program’s infimum. The proposed optimal design methodology is demonstrated on a case study involving reactive distillation-based synthesis of methyl tert-butyl ether (MTBE) from isobutene and methanol.     

Incorporation of Mass and Energy Integration in the Optimal Bioethanol Separation Process

A techno‐economic analysis for the separation process in bioethanol production is presented. Optimized azeotropic separation processes in conjunction with process integration (mass and energy) are considered to simultaneously enhance the results from economic and environmental points of view. Process integration improves significantly the separation process because it helps to reduce the overall energy required in the reboilers based on energy integration and additionally to diminish the amount of required solvent based on mass integration. The SYNHEAT optimization model was applied for energy integration whereas a direct recycle strategy was implemented for the mass integration process. The best separation processes obtained correspond to an integrated conventional separation sequence with energy integration to ethanol‐water mixture III and integrated optional separation sequences with energy integration to ethanol‐water mixture III, with significant savings in utility costs and possible recycling of nearly all solvent.     

LNG轻烃分离与乙烯冷分冷量联合

乙烯深冷分离过程需要冷剂为分离过程提供不同等级的冷量,可以把乙烯深冷分离过程作为一个冷阱;LNG气化过程中,需要加热,可以作为冷源.考虑到冷阱冷源的相互匹配,提出通过将LNG经过轻烃分离,为乙烯深冷分离提供冷量,降低了制冷公用工程消耗,同时LNG气化装置降低了加热公用工程消耗,且LNG分离出的轻烃直接供给乙烯装置作为裂解原料使用,优化乙烯装置裂解原料.以300万吨/年的LNG装置和64万吨/年的乙烯装置为例进行模拟计算得到,LNG轻烃分离装置可为乙烯冷分提供冷量41464 kW,降低乙烯冷分三元冷剂消耗75%,为乙烯装置提供优质裂解原料约65万吨/年.     

ADSORPTIVE DISTILLATION: OPTIMUM SOLIDS PROFILES

The new process called Adsorptive Distillation is extended by allowing solids loading per stage to vary. The optimization problem is to uncover the unique solids profile which produces the minimum total solids needed for a prescribed separation. Two types of optimum designs are studied: (i) uniform loadings within sections but unequal sectional loadings, and (ii) unequal solids loadings in every stage of the cascade. In both cases, unique optimum profiles and feed stage locations are uncovered. The optimization problems posed above lead to 15% and 22% reductions, respectively, in total solids relative to the idealized case of uniform loadings throughout the cascade. Furthermore, the profiles uncovered for the second problem show solids loading to be always maximum at the feed stage diminishing to minimum loadings at the ends of the cascade. This smooth variation in stage capacity (diamond profile) leads to a condition of zero reflux.     

MODIFICATIONS IN THE DESIGN OF GAS INDUCING IMPELLER

The new process called Adsorptive Distillation is extended by allowing solids loading per stage to vary. The optimization problem is to uncover the unique solids profile which produces the minimum total solids needed for a prescribed separation. Two types of optimum designs are studied: (i) uniform loadings within sections but unequal sectional loadings, and (ii) unequal solids loadings in every stage of the cascade. In both cases, unique optimum profiles and feed stage locations are uncovered. The optimization problems posed above lead to 15% and 22% reductions, respectively, in total solids relative to the idealized case of uniform loadings throughout the cascade. Furthermore, the profiles uncovered for the second problem show solids loading to be always maximum at the feed stage diminishing to minimum loadings at the ends of the cascade. This smooth variation in stage capacity (diamond profile) leads to a condition of zero reflux.     

Non-ideal reactor network synthesis through IDEAS: Attainable region construction

The attainable region (AR) for non-ideal reactor networks is constructed for the first time using the Infinite DimEnsionAl State-space (IDEAS) framework. The axial dispersion model is used to represent a non-ideal reactor, and it is shown that the IDEAS framework and associated Shrink-wrap algorithm are applicable to this model. A case study demonstrates that the AR for a reactor network featuring non-ideal dispersion models is larger than the AR for a reactor network featuring only ideal CSTR/PFR models.     

Integrated design of diesel hydrotreating processes

This work presents an integrated approach for the design of diesel hydrotreating processes employing a simulated annealing optimisation algorithm. The modelling of reactor, separation and heat recovery system for diesel hydrotreating processes is discussed, and a novel optimisation framework is developed for the design of complex refinery processes. A comparison with conventional approach to process design, i.e. sequential evolution of design, is given to illustrate the ability of proposed approach to obtain overall hydrotreating process designs with minimum total annualised costs. The proposed integrated approach takes into account the trade-offs between capital and operating costs, as well as interactions between the hydrotreater, distillation column, and the associated heat exchanger network.     

基于换热网络集成的二甲苯分离精馏塔参数优化

精馏是化工过程中重要的耗能设备,其产品温度的改变将影响换热网络的集成.针对二甲苯分离吸附的实际生产过程,利用复合曲线系统分析精馏塔DA604塔压增大至170kPa及230kPa后塔顶和塔底产品流股温度改变对换热网络的集成和公用工程消耗量的影响,可实现精馏塔操作与换热网络的同步集成,相较与之前只考虑流股温位对换热网络的影响更加全面.结果表明,该精馏塔的塔压由110kPa增至170kPa时,系统的冷却公用工程用量增大1765.0kW,加热公用工程量减少1948.5kW,无需消耗加热公用工程;压力由110kPa增加至230kPa时,系统冷却公用工程用量增大4964.1kW,加热公用工程用量节省共计8172.4kW,此时加热公用工程用量减小为0且可在高温段向外界供给6223.9kW热量.该分析结果与夹点法的计算结果相同,由该结果可得普适性结论,当精馏塔塔顶塔底出口物流均为源时,增大塔压,系统加热公用工程减小,冷却公用工程增加,整体上有利于系统的节能.     

Availability and reliability considerations in the design and optimisation of flexible utility systems

Industrial utility plants are usually comprised of many interconnected units that must constitute a flexible and reliable system capable of meeting process energy requirements under different circumstances (e.g. varying prices, demands, or equipment shutdowns). Also, in order to avoid large economic penalties, the design and operation of a utility plant should consider that the equipment is not fully reliable and that each item needs to receive preventive and corrective maintenance. Conventionally, these issues are handled by installing additional units according to rules of thumb or heuristics, which usually imply excessive capital costs and might even result in designs that cannot satisfy the specified demands for certain situations. In contrast, during the present work a systematic methodology has been developed to address the design and operation of flexible utility plants incorporating reliability and availability considerations. The suggested method is based on a novel modelling and optimisation framework that can address grassroots design, retrofit, or (pure) operation problems in which design and operational parameters are optimised simultaneously throughout several scenarios. Thereafter, it is possible to define maintenance and failure situations in different operating periods to ensure that the plant will be able to cope with them, while meeting process requirements at minimum cost. Hence, for design cases, the most cost-effective elements of redundancy can be determined without pre-specifying any structural options in the final configuration (e.g. equipment sizes, types, and number of units). Furthermore, the proposed (multiperiod) MILP formulation is robust enough to tackle problems of the size and complexity commonly found in industry, and has the potential of yielding significant economic savings.     

The optimum plate aspect ratio for the best performance in a flat-plate thermal diffusion column of the frazier scheme

The effects of plate aspect ratio on the degree of separation, production rate and plate surface area in a flat-plate thermal diffusion column of the Frazier scheme, have been investigated. Theoretical considerations show that when the thermal diffusion columns of the Frazier scheme are constructed with the best plate aspect ratio, maximum separation, maximum production rate or minimum plate surface area can be obtained. The optimum plate aspect ratio for maximum separation is obtained with given production rate and plate surface area, while that for maximum production rate is determined with the degree of separation and plate surface area fixed, and that for minimum plate surface area is estimated with known degree of separation and production rate. It is interesting that the optimum plate aspect ratio for maximum separation is exactly the same as that for minimum plate surface area. The maximum separation and maximum production rate are achieved without changing any total expenditure, while the design with minimum plate surface area results in minimizing the total expense.     

The importance of proper economic criteria and process modeling for single- and multi-objective optimizations

This paper provides an overview of the influences that different economic objectives have on the efficiencies of those optimal process designs obtained by using single- and multi-objective optimizations. Optimizations of monetary criteria, like the profit, lead to operationally and environmentally more efficient but economically less attractive designs than optimization of non-monetary economic objectives, like the internal rate of return. The net present value produces compromise designs with intermediate efficiencies and environmental impacts. These differences are significant only if the processes’ mathematical models are sufficiently accurate for establishing appropriate trade-offs between investment and cash flow. The Pareto curves obtained by different economic objectives vary regarding the maximum environmental impacts and in the intervals of the environmental indicators. The composed criteria that combine the economic and environmental indicators into one single objective produce smaller differences between optimum designs that are closer to those designs with minimum possible environmental impacts.     

基于最佳ΔTmin的催化裂化装置低温余热回收网络设计

为使石化企业大量的低温余热得到充分利用,以某12万t/a加工重油的催化裂化中试装置单元存在的低温余热作为研究对象,采用问题表格法讨论了该系统最小传热温差ΔTmin对最小公用工程加热负荷QH,min的影响,得到最佳的ΔTmin为15℃,在此ΔTmin下,该过程最小公用工程加热负荷QH,min为409 364.10 kW,所需的最小公用工程冷却负荷QC,min为163 763.95kW。介绍了夹点技术,换热网络设计采用夹点之上的设计和夹点之下2步分别优化,并得到最终的综合换热网络。     

Simultaneous synthesis of distillation trains and heat exchanger networks

A new mathematical formulation for the optimal synthesis of heat-integrated distillation systems that accounts for constrained heat matches between columns and the rest of the process is presented. The definition of temperature intervals commonly used by heat exchanger network synthesis procedures is embedded in the proposed formulation that can be regarded as a generalization of the network flow model of Cerdá and Westerberg (1983, Chem. Engng Sci.38, 1723) under conditions of variable stream temperatures. The minimization of the total flow-sheet utility cost has been chosen as the design target.The problem has been represented through a mixed-integer linear program. By performing the search with a standard branch-and-bound technique the global optimality of the solution found is guaranteed. Three case studies involving the separation of a ternary mixture by distillation have been solved. The consideration of the rest of the process produces in two of them new distillation train designs costing less overall.     

Simultaneous process optimization and heat integration based on rigorous process simulations

This paper introduces a simultaneous process optimization and heat integration approach, which can be used directly with the rigorous models in process simulators. In this approach, the overall process is optimized utilizing external derivative-free optimizers, which interact directly with the process simulation. The heat integration subproblem is formulated as an LP model and solved simultaneously during optimization of the flowsheet to update the minimum utility and heat exchanger area targets. A piecewise linear approximation for the composite curve is applied to obtain more accurate heat integration results. This paper describes the application of this simultaneous approach for three cases: a recycle process, a separation process and a power plant with carbon capture. Case study results indicate that this simultaneous approach is relatively easy to implement and achieves higher profit and lower operating cost and, in the case of the power plant example, higher net efficiency than the sequential approach.