Prosyn—an MINLP process synthesizer

This paper reports the development of the program PROSYN, an automated implementation of the modelling/decomposition (M/D) strategy by Kocis and Grossmann (Computers chem. Engng 13, 797–819, 1989) for the MINLP optimization of process flowsheets. A systematic procedure is first presented for the decomposition of general superstructures of process flowsheets that avoids the optimization of units with zero flow. A model for simultaneous optimization and heat integration is also proposed that can account for area and energy considerations. Finally, a computer implementation is described that is suitable for the complex logic involved in the M/D strategy for the synthesis and heat integration of process flowsheets. Examples are presented to illustrate each of these points, as well as the performance of PROSYN.     

Retrofit of absorption heat pumps into manufacturing processes: Implementation guidelines

Integration of absorption heat pumps (AHP) in industrial processes has not yet been fully exploited due to the lack of clear implementation guidelines for this technology. In this work, a systematic methodology for the integration of AHPs in a process has been developed and is presented. Guidelines are formulated for the proper selection of heat sources and sinks that will maximise the benefit derived from heat pumping while respecting process constraints and operating requirements of the AHP. The principles of AHP operation and its efficient process integration are thus described. The methodology relies on data extracted from a Pinch Analysis of the plant. The advantages and outputs of the methodology are illustrated using an AHP implementation in a Kraft pulping process. Two realistic implementation options are presented along with their detailed design and preliminary economic evaluation.     

Complex integration of processes

Pinch analysis is nowadays a practical tool for designing heat exchanger networks in chemical and process industries. Rules for integrating process units have also been worked out in the last decade or two. Process units can be described as different types of energy unit operations, donors and acceptors. Yet, heat integration alone is not sufficient for process integration. The largest savings are achieved when simultaneously optimizing enthalpy and mass flows — energy and material recycling is required to save the natural resources and protect the nature. Mathematical programming is increasingly used to optimize the problems both in continuous and batch operations. Task integration is spreading out: multifunctional units lower the capital investment, thus, the total annual cost Recent development of the complex integration with examples and reasonable forecast of the future development is presented in the paper.     

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.     

基于模拟分析技术和随机搜索算法的化工过程能量集成方法研究

夹点和模拟分析技术已在化工能量集成中广泛应用.今以夹点技术为基础,对化工过程系统用能进行诊断,根据"过程用能一致性"原则提出能量集成改造方案,通过改变塔压实现塔顶冷凝器与塔底再沸器的热集成多效蒸馏.夹点技术实现的优化目标仅是热回收最大或公用工程能耗最小,不能实现包括设备整体费用最小的过程全局最优化.研究基于模拟技术,通过灵敏度分析,得到精馏塔各操作参数的样本映射数据,通过多项式拟合得到参数关联方程,并在遗传算法及模式搜索中设计过程费用函数,提出了将模拟分析技术与随机搜索算法相结合的,以过程费用函数最小化为优化目标的能量集成方法.工业实例的成功设计应用证明了其有效性和可行性.     

The FluxMax approach for simultaneous process synthesis and heat integration: Production of hydrogen cyanide

Resource and energy efficiency are essential in process synthesis of chemical plants as they combine economic with ecological benefits. The two main targets of the process synthesis problem—mass and energy flux optimization—are typically split into two steps: single unit optimization and subsequent energy integration preventing the identification of the globally optimal solution. This article presents a single-step procedure for resource-efficient process synthesis through simultaneous heat and mass flux optimization called FluxMax approach (FMA), which is demonstrated for the production of hydrogen cyanide (HCN). The impact of simultaneous heat integration on the optimal process structure is demonstrated and two resource-optimal processes for HCN production are identified consisting of a combination of different reactor and recycling strategies reducing total variable cost by 68%. For convex objective functions, the globally most resource-efficient process is identified highlighting the potential of the FMA for site planning and retrofitting of existing plants.     

Design of mixed energy‐integrated batch process networks by Pseudo‐direct approach

In this article, a novel framework for the design of mixed (combined direct and indirect) integration for batch process systems is presented. The framework is based on the concept of pseudo‐direct energy integration (PDEI) which reformulates indirect integration as direct integration using pseudo‐process streams. Two algorithms are presented to achieve energy integration for batch processes operating cyclically (in a campaign mode). The first algorithm targets maximization of energy recovery and overcomes the limitations of some of the existing contributions for design of mixed integrated systems. The second algorithm provides a network reduction methodology to generate a cadre of integrated designs while exploring the trade‐off between capital (number of heat exchangers and storage units) and operating costs (utility consumption). The proposed framework is illustrated using a benchmark example of two hot and two cold streams. © 2017 American Institute of Chemical Engineers AIChE J, 63: 55–67, 2018     

Limitations in using Euler's formula in the design of heat exchanger networks with Pinch Technology

Pinch Technology developed by Linnhoff and other workers has been widely adopted and considered to be one of the most successful techniques in process energy integration. The number of heat exchanger units is one of the most important aspects in the problem and Euler's formula has been applied in correlating the number of units and loops in the network. However, planarity of a graph is required for the application of Euler's formula, a fact that has been ignored in previous literature. It is demonstrated in this paper that Euler's formula cannot always be applied in Pinch Technology, by presenting examples of non-planar graphs resulting from thermodynamically feasible heat exchanger networks.     

Minimization of the nonrenewable energy consumption in bioethanol production processes using a solar‐assisted steam generation system

The multiobjective optimization of a corn‐based bioethanol plant coupled with a solar‐assisted steam generation system with heat storage is described. Our approach relies on the combined use of process simulation, rigorous optimization tools, and economic and energetic plant analysis. The design task is posed as a bicriteria nonlinear programming problem that considers the simultaneous optimization of the plant profitability and the energy consumption. The capabilities of the proposed methodology are illustrated through a 120,000,000 kg/year corn‐based bioethanol plant considering weather data of Tarragona (Spain). © 2013 American Institute of Chemical Engineers AIChE J 60: 500–506, 2014     

化工过程系统用能诊断和调优的“夹点分析”法

把热力学与系统工程的方法相结合，进一步将“夹点分析”应用于化工过程系统的用能诊断及调优。首先，从能量的角度将以能量驱动的过程单元如，反应器、精馏塔、压缩机等与换热器网络中的冷、热流股统一起来；然后，利用格子图，总组合曲线（ＧＣＣ）、扩充的总组合曲线（ＥＧＣＣ）、分离的总组合曲线（ＳＧＣＣ）等诊断工具，对化工过程系统进行用能诊断，给出相应的调优措施，并将该方法应用于实际的化工过程。     

大型复杂过程系统用能的诊断与调优

针对大型复杂过程系统用能的诊断与调优，发展了夹点分析（夹点技术）方法。提出采用虚拟温度法，确定各流股匹配换热的传热温差；将过程的夹点分析区分为操作型夹点计算与设计型夹点计算两个层次：操作型夹点计算用于过程用能的诊断；设计型夹点计算指导过程用能的调优。基于以上改进，开发了大型复杂过程系统用能诊断与调优策略，并应用于国内某厂乙烯装置的节能改造，可使该装置吨乙烯能耗降低４．１８７ＧＪ。应用表明本文提出的方法是指导大型复杂过程系统用能诊断与调优的有利工具。     

Energy-environment closed-loop through Oxygen Pinch

Oxygen Pinch emphasizes oxygen management and integration by splitting and recycling of oxygen/substrate requiring processes to achieve minimum “fresh” oxygen supply and maximum biodegradation per unit mass and hence to reduce energy consumption, to shorten operating times and to improve plant capacity. The presented approach considers not only the concentration differences that represent the mass transfer driving force between streams of varying substrate concentration but also the influence substrate utilization kinetics have on this driving force. Through the use of classical Pinch Principles, the maximum amount of substrate required to maintain a healthy sludge is identified assuming oxygen concentration is not limiting. The challenge posed by the presented case study towards improvement of an existing plant is not to reduce the oxygen supply (the oxygen is always maintained in excess), but to improve the substrate utilization for the same amount of supplied oxygen thereby increasing the capacity of the plant and lowering the energy consumption per unit volume of wastewater. It is reported that the principles introduced by the Thermal Pinch concept can work successfully for environment protection purposes and finally can again be returned to their original address leading to energy saving.     

A superstructure-based framework for simultaneous process synthesis,heat integration,and utility plant design

We propose a superstructure optimization framework for process synthesis with simultaneous heat integration and utility plant design. Processing units in the chemical plant can be modeled using rigorous unit models or surrogate models generated from experimental results or off-line calculations. The utility plant subsystem includes multiple steam types with variable temperature and pressure. For the heat integration subsystem, we consider variable heat loads of process streams as well as variable intervals for the utilities. To enhance the solution of the resulting mixed-integer nonlinear programming models, we develop (1) new methods for the calculation of steam properties, (2) algorithms for variable bound calculation, and (3) systematic methods for the generation of redundant constraints. The applicability of our framework is illustrated through a biofuel case study which includes a novel non-enzymatic hydrolysis technology and new separation technologies, both of which are modeled based on experimental results.     

Herstellung von Fahrbenzin aus Kohle oder Erdgas

Production of petrol from coal and natural gas . This article assumes an adequate knowledge of the Fischer-Tropsch process in its original form and as its modern variant, the Synthol process, and adopts the view that coal hydrogenation will only become implementable on an industrial scale in the early 1990. In detail, it considers the integration of the Mobil MTG process in the proven area of methanol production; operation of pilot plant has shown that this process is indeed suitable for industrial scale operation. The production of methanol from natural gas and coal is discussed, as is the subsequent conversion of methanol to petrol; emphasis is placed on the best possible integration of all process plant. Apart from the conventional steam reforming route for methanol production from natural gas, the alternative approach of combing a steam reforming plant with an autothermal cleavage step is also considered; the latter leads to a significant increase in efficiency and a reduction in investment costs. It is also shown for coal as raw material that simultaneous generation of petrol and SNG has considerable advantages of a thermal and financial nature. The principal process steps are described after the manner of keywords and the product costs are presented as functions of the various raw material costs.     

Integration of a Gas Fired Steam Power Plant with a Total Site Utility Using a New Cogeneration Targeting Procedure

A steam power plant can work as a dual purpose plant for simultaneous production of steam and elec-trical power. In this paper we seek the optimum integration of a steam power plant as a source and a site utility sys-tem as a sink of steam and power. Estimation for the cogeneration potential prior to the design of a central utility system for site utility systems is vital to the targets for site fuel demand as well as heat and power production. In this regard, a new cogeneration targeting procedure is proposed for integration of a steam power plant and a site utility consisting of a process plant. The new methodology seeks the optimal integration based on a new cogenera-tion targeting scheme. In addition, a modified site utility grand composite curve （SUGCC） diagram is proposed and compared to the original SUGCC. A gas fired steam power plant and a process site utility is considered in a case study. The applicability of the developed procedure is tested against other design methods （STAR？ and Thermoflex software） through a case study. The proposed method gives comparable results, and the targeting method is used for optimal integration of steam levels. Identifying optimal conditions of steam levels for integration is important in the design of utility systems, as the selection of steam levels in a steam power plant and site utility for integration greatly influences the potential for cogeneration and energy recovery. The integration of steam levels of the steam power plant and the site utility system in the case study demonstrates the usefulness of the method for reducing the overall energy consumption for the site.     

炼油能量系统优化技术导则的开发研究与实践

炼油能量系统优化是从炼油过程的全局出发,整体优化和系统改进炼油过程的能量利用状况。文章在分析炼油能量系统优化关联因素基础上,提出了将能量系统优化分解为企业总体用能改进、工艺装置优化、装置间热集成、低温热综合利用和公用工程系统优化等五个相互关联任务过程的实施策略,并通过开发能量系统优化技术导则协助指导该项工作的进行。     

基于分解算法的功热交换网络多目标优化

功热网络设计问题指在流程设计中对变压和换热过程进行耦合优化设计的问题,以此来提高整体系统的能效并降低成本。前人工作中一般采用数学规划法对功热网络建模优化。然而,由于存在变压过程和换热器面积计算的非线性约束,以及换热匹配的二元变量,整体模型往往是一个高度非凸的混合整数非线性规划模型,难以求解。本文提出一种高效的功热网络优化方法。模型中分别用透平压缩机和换热器实现功热网络中轴功和热的交换。求解过程采用分解算法,主问题中用随机算法对关键变量优化,功和热两个子网络问题中用确定性算法求解。目标函数考虑了经济和环境影响。案例测试对比了不同优化目标得到的结果以及多目标Pareto曲线,验证了所提出方法的高效性。     

Techno-economic optimization of IGCC integrated with utility system for CO2 emissions reduction—Maximum power production in IGCC

Environmental legislation, with its increasing pressure on the energy sector to control greenhouse gases, is a driving force to reduce CO₂ emissions. In this paper, pre-combustion CO₂ capture through integration of a site utility system with an integrated gasification combined cycle (IGCC) is investigated as an option to provide a compressed CO₂-rich stream from a process site for sequestration. This work presents a two-step procedure for integration and optimization of a site utility system with an IGCC plant: (i) screening and optimization of IGCC plant performance parameters; (ii) integration and optimization of the utility system of the site with the IGCC plant. In the first step, an optimization approach applies the results of screening studies based on rigorous simulation of the IGCC. Having fixed the inlet fuel flow rate, the IGCC design parameters (including oxygen consumption, diluent flow rate and turbine exit pressure) are optimized for maximum power generation. Energy flows between the IGCC and CO₂ compression train are considered. In the second step, the economic and operating performance of the utility system integrated with the IGCC plant are modeled and optimized for minimum operating cost to find the most appropriate level of integration. In a case study illustrating the approach, 94% of the fuel is gasified; additional power generation offsets the operating costs of pre-combustion CO₂ capture.     

Experiences from using heat integration software to determine retrofit opportunities within a refinery process

Heat integration techniques can be used to optimize the energy requirement for both new and retrofit plant designs. Software tools for identifying retrofit options are becoming available. This paper reports our experiences from using heat exchanger network (HEN) optimization software for a retrofit case study of an oil refinery process. The HEN optimization software was used to automate the search for the most beneficial retrofit designs following the twostage process proposed by Asante and Zhu. The software provided three potential retrofit designs. Results from this analysis were used as the basis of a rigorous mass and energy balance simulation of the plant. The simulation corroborated the energy savings, but there were some important differences. The simulation required 20% more heat exchange area. Furthermore, the retrofit design involving one topology change was shown to be less economic than an alternative design. These differences are discussed and a revised methodology is proposed.     

Optimum heat storage design for solar‐driven absorption refrigerators integrated with heat exchanger networks

A methodology is presented for optimizing hybrid renewable energy‐fossil fuel systems with short‐term heat storage. The considered system is an absorption‐refrigeration (AR) cycle integrated with a heat exchanger network (HEN) requiring cooling below ambient temperature. The AR cycle can be driven by multiple energy sources including excess energy from hot process streams, renewable energy sources (solar and biofuels), and fossil fuels. A two‐step approach based on mixed integer nonlinear programming methods is used for the optimization. First, the problem of optimal energy integration in the hybrid energy system without heat storage is solved on a monthly basis by minimizing simultaneously the total annual cost and the overall greenhouse gas emissions. In the second step, the multi‐tank thermal energy storage (TES) design problem is solved. The design involves the identification of the optimal number of storage tanks, their sizes, configuration and operation policies. The TES optimization is carried out on an hourly basis while incorporating the design targets determined by the first step. © 2013 American Institute of Chemical Engineers AIChE J, 60: 909–930, 2014