A decomposition approach for the scheduling of a steel plant production

In this paper we present a decomposition strategy for solving large scheduling problems using mathematical programming methods. Instead of formulating one huge and unsolvable MILP problem, we propose a decomposition scheme that generates smaller programs that can often be solved to global optimality. The original problem is split into subproblems in a natural way using the special features of steel making and avoiding the need for expressing the highly complex rules as explicit constraints. We present a small illustrative example problem, and several real-world problems to demonstrate the capabilities of the proposed strategy, and the fact that the solutions typically lie within 1–3% of the global optimum.     

Dynamic hybrid simulation of batch processes driven by a scheduling module

Simulation is now a CAPE tool widely used by practicing engineers for process design and control. In particular, it allows various offline analyses to improve system performance such as productivity, energy efficiency, waste reduction, etc. In this framework, we have developed the dynamic hybrid simulation environment PrODHyS whose particularity is to provide general and reusable object-oriented components dedicated to the modeling of devices and operations found in chemical processes. Unlike continuous processes, the dynamic simulation of batch processes requires the execution of control recipes to achieve a set of production orders. For these reasons, PrODHyS is coupled to a scheduling module (ProSched) based on a MILP mathematical model in order to initialize various operational parameters and to ensure a proper completion of the simulation. This paper focuses on the procedure used to generate the simulation model corresponding to the realization of a scenario described through a particular scheduling.     

Modeling and simulation of energy distribution systems in a petrochemical plant

A systematic method for analysis and design of plant-wide energy distribution systems is proposed to minimize the net cost of providing energy to the plant. The method is based on the steady-state modeling and simulation of steam generation process and steam distribution network. Modeling of steam generation process and steam distribution network were performed based on actual plant operation data. Heuristic operational knowledges are incorporated in the modeling of steam distribution network. Newton’s iteration method and a simple linear programming algorithm were employed in the simulation. The letdown amount from superheated high-pressure steam (SS) header and the amount of SS produced at the boiler showed good agreement with those of actual operational data.     

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.     

Optimization of hybrid systems

An overview of dynamic optimization problems with hybrid systems embedded is presented. The control parameterization approach is examined in detail, where the possibility of mode switching within the hybrid system causes nonsmoothness in the Master problem, thus invalidating gradient based solvers. To handle this, a decomposition approach is proposed that divides the general problem into smooth subproblems. The subproblem of determining the optimal mode sequence given fixed transition times is considered for continuous time linear time varying hybrid systems. A mixed-integer reformulation of the problem is proposed that retains the linear structure of the embedded hybrid system. A deterministic branch-and-cut framework incorporating outer approximation cuts and a dynamic bounds tightening heuristic is then employed to solve the nonconvex mixed-integer problem to guaranteed global optimality with a finite number of iterations. It is shown that the dynamic bounds tightening heuristic can have a dramatic effect on accelerating convergence of the algorithm. Future directions for research are also discussed, including the application of recent developments in semi-infinite programming for the formal safety verification of processes under uncertainty.     

Optimal synthesis of compression refrigeration system using a novel MINLP approach

The optimal design of a compression refrigeration system (CRS) with multiple temperature levels is very important to chemical process industries and also represents considerable challenges in process systems engineering. In this paper, a general methodology for the optimal synthesis of the CRS, which simultaneously integrates CRS and Heat Exchanger Networks (HEN) to minimize the total compressor shaft work consumption based on an MINLP model, has been proposed. The major contribution of this method is in addressing the optimal design of refrigeration cycle with variable refrigeration temperature levels. The method can be used to make major decisions in the CRS design, such as the number of levels, temperature levels, and heat transfer duties. The performance of the developed methodology has been illustrated with a case study of an ethylene CRS in an industrial ethylene plant, and the optimal solution has been examined by rigorous simulations in Aspen Plus to verify its feasibility and consistency.     

热法磷酸装置热能利用优化及低温位余热回收系统流程模拟

以75 kt/a热法磷酸装置为例,分析和计算装置产生的热量,提出在目前余热回收副产饱和蒸汽的基础上将蒸汽过热提高能量品位用于发电,并利用磷酸吸收反应及稀释的低温位热能副产低压饱和蒸汽的工艺方案.采用CHEMCAD软件对此方案进行流程模拟,认为从理论上是有可能实现的.     

Room Temperature,Electrochemical Generation of Ozone with 50% Current Efficiency in 0.5M Sulfuric Acid at Cell Voltages < 3V

The electrochemical generation of ozone by Ni/Sb-SnO₂ anodes immersed in 0.5M H₂SO₄ was assessed in both flow and recycle systems using the same electrochemical cell. The anodes were found to exhibit current efficiencies of up to 50%?for ozone generation under flow conditions at room temperature, with an optimum mole ratio in the precursor solutions of ca. 500:8:3 Sn:Sb:Ni and optimum cell voltage of 2.7V. A comparison of the data obtained under flow and recycle conditions suggests that the presence of ozone in the anolyte inhibits its formation. The minimum electrical energy cost achieved, of 18 kWh kg^?1 compares favorably with estimated costs for Cold Corona Discharge generally reported in the literature, especially when the very significant advantages of electrochemical ozone generation are taken into account.     

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.     

优化整合醋酸精馏系统降低装置能源消耗

通过认真分析聚乙烯醇车间醋酸乙烯和聚乙烯醇两套独立醋酸精馏系统的特点,优化醋酸精馏系统的运行方式,实现流程再造,将两套生产装置的醋酸精馏系统优化整合,并合理利用醋酸乙烯装置精馏塔采出精醋酸的热能,从而有效降低装置能耗。     

Enhanced energy storage density and high efficiency of lead-free Ca1-xSrxTi1-yZryO3 linear dielectric ceramics

Ca_1-xSr_xTi_1-yZr_yO₃ (0.40 ≤ x ≤ 0.60, 0.1 ≤ y ≤ 0.4) ceramic samples were fabricated by conventional solid state method. The microstructure of ceramic samples were studied by XRD and SEM, and the influence of Zr⁴⁺ doping on the electric properties and energy storage performances were systematically studied. The results showed that the introduction of Zr⁴⁺ results in an inhibition of interfacial polarization and enhancement of grain boundary barrier effect. Ca_0.5Sr_0.5Ti_1-yZr_yO₃ ceramic samples exhibit excellent energy storage properties, with breakdown strength being on the order of 390 kV/cm versus 280 kV/cm for the counterpart Ca_0.5Sr_0.5TiO₃ ceramic samples, together with energy efficiency above 95%. Meanwhile, a maximum breakdown strength of 390 kV/cm, a high energy storage density of 2.05 J/cm³ and an ultrahigh energy efficiency of 85% at high temperature of 125 ℃ were obtained in the sample with y = 0.1 as well, indicating it as a good candidate for linear energy storage fileds.     

The Inhibition of Ozone Generation at Ni/Sb-SnO2 Electrodes in High Concentrations of Dissolved O3

The work reported in this paper investigated the observation that high concentrations of ozone in the electrolyte inhibits the electrochemical ozone evolution process at Ni/Sb-SnO₂ anodes in aqueous sulfuric acid. We show that inhibition does indeed take place and that this inhibition does not affect the current density and hence appears to reflect an increase in the ratio of O₂ to O₃ evolved. A possible mechanism for the inhibition is proposed. It was found that Celgard 2400 membrane was an acceptable alternative to Nafion in the divided electrolysis cell employed.     

乙烯综合能耗计算

阐述了新旧两种乙烯能耗计算方法，并用具体的数据进行了比较，以其结果说明新的方法的合理性。     

渣液转换器操作系统的技术改造

针对渣液转换器中零件的扭曲和变形,经过改造将电动操作系统改造为气动操作系统,并增加了行程限位器和信号反馈系统,取得了良好的经济效益和社会效益。     

热能在乙烯厂生产中的合理利用

蒸汽动力系统是石化企业的重要组成部分,为整个生产过程提供蒸汽、电力等公用工程。由于生产中产品品种变化及季节不同,必然引起公用工程用量的变化,相应的蒸汽动力系统能否适应所发生的变化,是否具有可调性,将决定企业的产品成本、经济效益和能源利用程度。热能合理利用成为工厂深入挖潜、节能增效的一项重要工作。     

Modeling and optimization of polygeneration energy systems

The forecasted shortage of fossil fuels and the ever-increasing effect of greenhouse gas (GHG) emissions on global warming and environmental stability are two international problems with major technical, economic and political implications in the 21st century. Therefore, it is urgent to restructure present energy production and utilization systems in order to ensure that fossil fuels are used with high efficiency and low to zero emissions. Polygeneration energy systems combine power generation and chemical fuel synthesis in a single plant (producing both electricity and fuels) and thus provide a promising alternative pathway towards achieving sustainable and flexible economic development. Mixed-Integer programming (MIP) is useful in constructing long-term decision models that are suitable for investment planning and design of polygeneration infrastructure systems. This paper presents a model for the investment planning of a polygeneration energy system and a case study addressing a system for production of methanol and electricity in China during the period from 2010 to 2035. It contains five different feedstocks and twelve polygeneration technologies.     

鲁宁管线各加热站输油温度的优化计算

鲁宁输油管线主要承担着胜利油田和黄岛进口原油的外输任务,文中以节能降耗为目的,以热力费用、动力费用之和最小为衡量指标,建立了鲁宁输油管道优化运行的数学模型。在建立的模型中,既有连续变量,又有离散变量,用MDCP法求解所建立的数学模型,可以比较好的解决这一问题。该优化方法具有速度快,计算准确的特点,在鲁宁管线中取得了良好的效果。     

乙烯装置急冷系统能量回收工艺特点分析

乙烯装置急冷系统接收来自炉区的高温裂解气，为降低乙烯装置能耗，必须尽可能回收裂解气中的热量。文中针对KBR乙烯流程，介绍了乙烯装置急冷系统能量逐步回收的过程及其工艺特点。     

乙烯装置降低能耗的技术措施及实施效果评估

从实际出发介绍了吉化乙烯装置开车几年来特别是近一两年来，在降低装置能耗方面所采取的措施。