Shared and practical approach to conserve utilities in eco-industrial parks

Conserving utilities in an eco-industrial park (EIP) by exploiting the synergistic heating/cooling needs of its inhabitants can have significant economic and environmental benefits. However, a successful implementation of an EIP-wide heat integration involves much more than the simple minimization of utility usage. Like any collaborative endeavour involving independent and diverse profit-making enterprises, an EIP-wide heat integration faces several real and practical challenges such as exchanger locations, stream transports over long distances, etc. In this work, we propose a mixed-integer nonlinear programming model (MINLP) for configuring an EIP-wide multi-enterprise heat exchanger network (HEN). We propose a practical and rational strategy that (1) considers all the major capital and operating costs, and utility savings, (2) selects an optimum HEN location with the highest net present value, (3) uses a third-party logistics provider for managing and operating the HEN, and (4) ensures an identical rate of return on investment for all participating enterprises.     

Design of flexible heat exchanger network for multi-period operation

Heat exchanger networks (HENs) increase heat recovery from industrial processes by matching hot and cold streams to exchange heat and reducing utility consumption. The design of HENs is a very complex task which generally involves mixed-integer non-linear programming (MINLP).This work evaluates and critically compares existing HEN design methods. It then presents a systematic methodology in the design of HENs under multiple periods of operation. The model presented in this work is a superstructure-based MINLP model which minimises the total annualised cost containing heat exchanger area cost and utility costs. The model is based on the superstructure by Yee and Grossmann [1990. Simultaneous optimisation models for heat integration—II, heat exchanger network synthesis. Computer & Chemical Engineering 14(10), 1165-1184], which was later formulated for multiple periods by Aaltola [2002. Simultaneous synthesis of flexible heat exchanger network. Applied Thermal Engineering 22, 907-918]. It includes a multi-period simultaneous MINLP model to design the HEN structure, and an NLP model to improve the solution and allow for non-isothermal mixing. Modifications to Aaltola's model include the use of maximum area per period in the area cost calculation of the MINLP objective function, and the removal of slack variables and weighed parameters from the existing NLP improvement model.The new model has been applied to one industrial case study, demonstrating that the new combined MINLP-NLP model can obtain better solutions by not relying on the average area assumption in the MINLP stage.     

Operational strategy and planning for raw natural gas refining complexes: Process modeling and global optimization

Optimal operational strategy and planning of a raw natural gas refining complex (RNGRC) is very challenging since it involves highly nonlinear processes, complex thermodynamics, blending, and utility systems. In this article, we first propose a superstructure integrating a utility system for the RNGRC, involving multiple gas feedstocks, and different product specifications. Then, we develop a large‐scale nonconvex mixed‐integer nonlinear programming (MINLP) optimization model. The model incorporates rigorous process models for input and output relations based on fundamentals of thermodynamics and unit operations and accurate models for utility systems. To reduce the noncovex items in the proposed MINLP model, equivalent reformulation techniques are introduced. Finally, the reformulated nonconvex MINLP model is solved to global optimality using state of the art deterministic global optimization approaches. The computational results demonstrate that a significant profit increase is achieved using the proposed approach compared to that from the real operation. © 2016 American Institute of Chemical Engineers AIChE J, 63: 652–668, 2017     

多流股换热器网络综合方法在原油预热系统中的应用

以原油常减压蒸馏装置原油预热网络为研究对象,进行了多流股换热器网络的实例综合. 基于超结构物理模型建立了改进的多流股换热器网络综合数学模型,提出将该网络综合问题由混合整数非线性规划问题转化为简单的非线性规划问题的求解策略,并利用改进的遗传/模拟退火新算法进行了原油预热网络的综合. 与Hextran软件的综合结果以及现场换热网络的对比表明,本模型和求解策略可以应用于工业规模的多流股换热器网络综合,有可能取得较好的经济效益.     

Interval based MINLP superstructure synthesis of combined heat and mass exchanger networks

An interval based superstructure approach for combining the synthesis of heat and mass exchanger networks is presented in this paper. The technique involves combining the interval based MINLP superstructure (IBMS) for the synthesis of heat exchanger networks (HENs) with that of mass exchanger networks (MENs). The two networks are made to interact through the lean stream in the mass exchange network. The new approach involves the use of the lean substream concept to explore potential mass exchange temperatures. An example which involves a one-lean stream mass exchange problem alongside regeneration and hot and cold utilities is presented.     

换热器网络同步最优综合方法──改进的MINLP转运模型法

针对现有的换热器网络最优综合方法的局限性，采用分级超结构转运模型和物流吸、放热潜力的概念，提出了非等温混合线性约束的换热器网络同步最优综合混合整数非线性规划（MINLP）的改进模型．该模型不仅可以对公用工程费用、换热面积、换热设备台数及物流的匹配选择进行多目标同步优化，而且在线性约束的条件下消除了等温混合的不合理假设，只需求解一次MINLP问题就可得到包括分流情况在内的最优网络结构．算例表明，该模型优于以往的几种同步优化模型．     

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。     

MINLP synthesis of optimal cooling networks

A mixed-integer nonlinear programming (MINLP) algorithm for the synthesis of cooling networks is presented. As opposed to previous models in which the minimization of utility consumption has been formulated, the algorithm considers simultaneously the capital cost for the coolers and the utility costs. The strategy is based on a superstructure that allows bypass and splitting of utility streams. Also, the superstructure considers a combination of arrangements in series and in parallel that allows for an efficient use of cooling streams. The typical arrangement of cooling networks in parallel usually conducts to higher total costs. Also, it is shown that the use of minimum amounts of cold utilities does not necessarily conduct to the minimum total cost. Three case studies are used to show the application of the proposed method.     

过程系统能量集成同步最优综合法

将换热网络超结构混合整数非线性规划多目标同步最优综合方法进一步扩展到与过程系统的联合优化,提出了改进的过程热集成同步综合方法,并以反应分离过程与换热网络能量集成为例,建立了同步优化超结构模型,采用混合整数非线性规划的遗传算法求解,可同时得到热集成系统最优的流程结构和操作条件。     

Optimal processing pathway for the production of biodiesel from microalgal biomass: A superstructure based approach

In this study, we propose a mixed integer nonlinear programming (MINLP) model for superstructure based optimization of biodiesel production from microalgal biomass. The proposed superstructure includes a number of major processing steps for the production of biodiesel from microalgal biomass, such as the harvesting of microalgal biomass, pretreatments including drying and cell disruption of harvested biomass, lipid extraction, transesterification, and post-transesterfication purification. The proposed model is used to find the optimal processing pathway among the large number of potential pathways that exist for the production of biodiesel from microalgae. The proposed methodology is tested by implementing on a specific case with different choices of objective functions. The MINLP model is implemented and solved in GAMS using a database built in Excel. The results from the optimization are analyzed and their significances are discussed.     

过程全局夹点分析与超结构MINLP相结合的能量集成最优综合法

提出了过程全局夹点分析与超结构混合整数非线性规划 (MINLP)相结合的能量集成最优综合法 .各单过程内部换热优化匹配后 ,进行各过程剩余冷、热负荷与公用工程系统的全局夹点分析 ,确定全局热集成目标 ,在此基础上建立包含过程剩余热负荷产生各等级蒸汽、剩余冷负荷使用各等级蒸汽加热的各种可能匹配方案的公用工程换热网络超结构及其MINLP模型 ,采用混合连续进化算法求解得到过程与公用工程换热网络最优改造方案 .大型乙烯装置能量集成应用算例表明 ,可充分发挥全局夹点分析法确定改造目标的简洁实用性和超结构MINLP寻求最佳方案的优点     

改进的无分流换热器网络最优综合法

提出了不分流换热网络改进的同步最优综合混合整数非线性规则模型，通过引入处理带０－１整型变量的规则，提出了采用非线性规划求解换网络综合ＭＩＮＬＰ问题的方法，只需求解ＮＬＰ问题就可得到连续变量和０－１变量同步优化的网络结果。算例表明，该模型和方法是有效的。     

Optimal design of reverse-osmosis networks for wastewater treatment

An optimization study of reverse-osmosis networks (RON) for wastewater treatment has been carried out by describing the system as a nonconvex mixed-integer nonlinear problem (MINLP). A mixed-integer linear problem (MILP) is derived from the original nonlinear problem by the convex relaxation of the nonconvex terms in the MINLP to provide bounds for the global optimum. The MILP model is solved iteratively to supply different initial guesses for the nonconvex MINLP model. It is found that such a procedure is effective in finding local optimum solutions in reasonable time and overcoming possible convergence difficulties associated with MINLP local search methods. Examples of water desalination and wastewater treatment from the pulp and paper industry are considered as case studies to illustrate the proposed solution strategy.     

某焦化厂供水网络多目标建模及优化

对某焦化厂的供水网络进行了详细的分析,在用水供需平衡满足生产要求的前提下,以新鲜水供给量最小以及新鲜水供给成本与循环水及除盐水的浪费成本之和最小作为两个优化目标,建立了多目标混合整数非线性规划(MINLP)的数学模型.利用文献提出的Pareto规则下的多目标改进文化差分进化算法对模型进行了求解.所得的计算结果与现场实时操作数据相比,模型及算法实现的优化操作减少了新鲜水消耗量,降低了新鲜水供给成本与循环水及除盐水的浪费成本,达到了很好的优化效果.     

集成炼油企业生产与能量系统的生产计划优化

炼油企业通常由物料生产系统与能量系统组成。传统的企业生产计划优化通常以生产系统物流优化为主, 能量系统基于物料生产优化结果进行产能优化以满足企业级能源供需平衡。此种优化方法不仅压缩了企业整体优化空间并且降低了燃料油与瓦斯等中间产品的利用率。基于装置能耗模型与能源供需以及中间产品的产耗质量平衡关系, 建立炼油企业生产系统与能源系统的集成优化模型, 通过求解MINLP模型进而实现企业生产物流与能流的集成优化。案例实践表明, 相较于传统分步优化方法, 集成优化方法不仅有效降低了全厂的生产成本, 并且实现了生产的节能减排。     

Synthesis of refrigeration system based on generalized disjunctive programming model

Refrigeration system holds an important role in process industries. The optimal synthesis cannot only reduce the energy consumption, but also save the production costs. In this study, a general methodology is developed for the optimal design of refrigeration cycle and heat exchanger network (HEN) simultaneously. Taking the heat integration between the external heat sources/sinks and the refrigeration cycle into consideration, a superstructure with sub-coolers is developed. Through defining logical variables that indicate the relative temperature positions of refrigerant streams after sub-coolers, the synthesis is formulated as a Generalized Disjunctive Programming (GDP) problem based on LP transshipment model, with the target of minimizing the total compressor shaft work in the refrigeration system. The GDP model is then reformulated as a Mixed Integer Nonlinear Programming (MINLP) problem with the aid of binary variables and Big-M Constraint Method. The efficacy of the process synthesis model is demonstrated by a case study of ethylene refrigeration system. The result shows that the optimization can significantly reduce the exergy loss as well as the total compression shaft work.     

Heat exchanger network design of large-scale industrial site with layout inspired constraints

This paper presents a systematic approach for the synthesis of the heat recovery network in total site using a Mixed Integer Linear Programming model. This model returns a near-to-optimal network configuration with minimum utility cost while allows to select geographically closest matches. The Heat Load Distribution is the subproblem of the network design and has been reported to be quite expensive to solve for large-scale problems. The computational complexity of HLD resides in the number of streams and the feasible networks. An additional challenge, raising particularly in industrial problems, has been the intermediate heat transfer network which aggravates the combinatorial complexity. The presented methodology deals with those difficulties by priority consideration based on the location of process units. It helps significantly reducing the computational time and also comes with a realistic network sketch with respect to the plant layout. Several examples are discussed along with a real industrial case study.     

Sustainable design and synthesis of algae‐based biorefinery for simultaneous hydrocarbon biofuel production and carbon sequestration

The superstructure optimization of algae‐based hydrocarbon biorefinery with sequestration of CO₂ from power plant flue gas is proposed. The major processing steps include carbon capture, algae growth, dewatering, lipid extraction and power generation, and algal biorefinery. We propose a multiobjective mixed‐integer nonlinear programming (MINLP) model that simultaneously maximizes the net present value (NPV) and minimizes the global warming potential (GWP) subject to technology selection constraints, mass balance constraints, energy balance constraints, technoeconomic analysis constraints, and environmental impact constraints. The model simultaneously determines the optimal decisions that include production capacity, size of each processing unit, mass flow rates at each stage of the process, utility consumption, economic, and environmental performances. We propose a two‐stage heuristic solution algorithm to solve the nonconvex MINLP model. Finally, the bicriteria optimization problem is solved with ε‐constraint method, and the resulting Pareto‐optimal curve reveals the trade‐off between the economic and environmental criteria. The results show that for maximum NPV, the optimal process design uses direct flue gas, a tubular photobioreactor for algae growth, a filtration dewatering unit, and a hydroprocessing pathway leading to 47.1 MM gallons of green diesel production per year at $6.33/gal corresponding to GWP of 108.7 kg CO₂‐eq per gallon. © 2013 American Institute of Chemical Engineers AIChE J, 59: 1599–1621, 2013     

Membrane system design for multicomponent gas mixtures via mixed-integer nonlinear programming

An optimal design strategy for membrane networks separating multicomponent gas mixtures based on an approximate permeator model and mixed-integer nonlinear programming (MINLP) is proposed. A permeator system superstructure is used to embed a very large number of possible network configurations and allows the permeator feed-side pressure to be fixed or a design variable. A MINLP design model is developed to minimize the total annual process cost by simultaneous optimization of the permeator configuration and operating conditions. Case studies for the separation of acid gases (CO₂ and H₂S) from crude natural gas mixtures with spiral-wound permeators are presented. Permeator configurations are derived for different number of separation stages for both continuous and discrete membrane areas. The method is sufficiently robust to handle product compositions that vary five orders of magnitude. The proposed approach provides an efficient methodology for preliminary screening of multi-stage membrane separation systems for multicomponent gas mixtures.