Preemptive dynamic operation of cryogenic air separation units

As markets become more competitive and dynamic, manufacturing plants are undergoing transitions toward flexible, agile, and low costs operations. Appropriate coordination within the supply chain is an important factor in manufacturing systems' performance. In this study, the impact of preemptive control action in advance of an upcoming demand change on the economic performance of a cryogenic air separation unit is investigated. The effects of various factors are explored through optimization formulations utilizing a high‐fidelity collocation based dynamic process model. This includes the amount of lead time, choice of manipulated inputs, direction of demand change, and liquid product market conditions. Plant performance is evaluated and analyzed through a comprehensive multipart case study. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3845–3859, 2017     

降低空分装置电耗的措施

从工艺优化和生产管理两方面着手,提出降低空分装置电耗的措施,以达到节能降耗的目的.     

Demand response scheduling under uncertainty: Chance-constrained framework and application to an air separation unit

Recent increases in renewable power generation challenge the operation of the power grid: generation rates fluctuate in time and are not synchronized with power demand fluctuations. Demand response (DR) consists of adjusting user electricity demand to match available power supply. Chemical plants are appealing candidates for DR programs; they offer large, concentrated loads that can be modulated via production scheduling. Price-based DR is a common means of engaging industrial entities; its benefits increase significantly when a longer (typically, a few days) scheduling time horizon is considered. DR production scheduling comes with its own challenges, related to uncertainty in future (i.e., forecast) electricity prices and product demand. In this work, we provide a framework for DR production scheduling under uncertainty based on a chance-constrained formulation that also accounts for the dynamics of the production facility. The ideas are illustrated with an air separation unit case study.     

Modeling,simulation, and optimization of multiproduct cryogenic air separation unit startup

The startup of multiproduct cryogenic air separation plants takes several hours, during which time limited revenue is generated with high costs incurred due to the highly energy-intensive nature of these operations. This motivates the development of high-fidelity dynamic models to capture the complexity of the startup process to aid decision-making. This article focuses on the development of a startup model for a multiproduct air separation unit (ASU), and its use in dynamic simulation and optimization. To accomplish this, a first-principles based dynamic ASU model is extended by including various discontinuities using smooth approximations, adding dynamics to the primary heat exchanger, and extending the handling phase change within process streams. Dynamic simulations demonstrate plant response behavior during startup, including a failed startup resulting from an injudicious choice of input trajectory. In addition, improvement of startup operation is demonstrated through the incorporation of the model within a dynamic optimization framework.     

A non-Gaussian pattern matching based dynamic process monitoring approach and its application to cryogenic air separation process

Principal component analysis (PCA) based pattern matching methods have been applied to process monitoring and fault detection. However, the conventional pattern matching approaches do not specifically take into account the non-Gaussian dynamic features in chemical processes. Furthermore, those techniques are more focused on fault detection instead of fault diagnosis. In this study, a non-Gaussian pattern matching based fault detection and diagnosis method is developed and applied to monitor cryogenic air separation process. First, independent component analysis (ICA) models are built on the normal benchmark and monitored data sets along sliding windows. The IC subspaces from the benchmark and monitored data are then extracted to evaluate the non-Gaussian patterns and detect process faults through a mutual information based dissimilarity index. Further, a difference subspace between the two IC subspaces is computed to characterize the divergence of the dynamic and non-Gaussian patterns between the benchmark and monitored data. Subsequently, the mutual information between the IC difference subspace and each process variable direction is defined as a new non-Gaussian contribution index for fault identification and diagnosis. The presented approach is applied to a simulated cryogenic air separation plant and the monitoring results are compared against those of PCA based pattern matching techniques and ICA based monitoring method. The application study demonstrates that the developed non-Gaussian pattern matching approach can effectively monitor the complex air separation process with superior fault detection and diagnosis capability.     

化学链空分联合化学链制氢的煤制甲醇过程参数优化与分析

我国能源结构决定了以煤为主的甲醇生产路线。传统煤制甲醇过程主要存在过程能量效率低、CO₂捕集能耗高等问题。本文提出了一种化学链空分联合化学链制氢的煤制甲醇新过程,以降低能耗、二氧化碳排放及提高能源效率。化学链空分技术的集成可以替代传统煤制甲醇过程的空气分离单元,并在一定程度上降低能耗。化学链制氢技术的集成,一方面可以替代水煤气变换装置,并且可以极大程度降低二氧化碳捕集能耗;另一方面,化学链制氢技术还可生产用于调整合成气氢与碳比的氢。本文对新过程的核心单元进行了参数优化以及全流程的模拟,基于模拟对新过程的性能进行了分析,结果表明新过程与传统的煤制甲醇过程相比,空分和二氧化碳捕集能耗分别降低了41%和89%。同时,新过程的能量效率提高了18%,二氧化碳排放量降低了45%。     

Coupling membrane filtration and wet air oxidation for advanced wastewater treatment: Performance at the pilot scale and process intensification potential

Bio-refractory wastewater treatment is compulsory for a safe discharge into the environment. This paper aims to study the use of membrane processes to concentrate wastewater to be then treated by a hydrothermal process such as wet air oxidation for advanced and intensified wastewater treatment. The work focused on three different synthetic wastewaters of public or industrial interest: pharmaceutical wastewater, grey wastewater, and bilge wastewater. Membrane processes operated at the pilot scale enabled retentions as high as 100% of total organic carbon, more than 99% of turbidity, and 70% of hydrocarbon, respectively. High concentration factors were obtained. Membrane foulings were chemically reversible whatever the type of wastewater or the membrane process. Thanks to membrane filtrations, the volumes to be treated by wet air oxidation were drastically reduced, leading to high energy savings. Membrane retentates were then treated by wet air oxidation (300°C, 15 MPa) and resulted in more than an 83% mineralization rate, regardless of the effluent. The hybrid intensified process presented in this work strongly increased the possibility of discharging into the environment by mixing the process outputs or greatly reducing the discharge volume and ultimately the waste load.     

A novel hybrid feedstock to liquids and electricity process: Process modeling and exergoeconomic life cycle optimization

This article proposes a novel hybrid low‐rank coal (LRC)/biomass/natural gas process for producing liquid fuels and electricity. The hybrid process highlights coexistence of indirect and direct liquefaction technologies, cogasification of char and biomass, and corefinery of LRC syncrude and Fischer–Tropsch syncrude. A process simulation based on detailed chemical kinetics is present to illustrate its feasibility. In addition, we propose an exergoeconomic life cycle optimization framework that seeks to maximize the primary exergy saving ratio, primary total overnight cost saving ratio, life cycle waste emissions avoidance ratio, and primary levelized cost saving ratio by comparing the proposed hybrid process to its reference stand‐alone subsystems. From the results, we can determine four optimal designs which yield competitive breakeven oil prices ranging from $1.87/GGE to $2.13/GGE. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3739–3753, 2014     

Curing behaviour of syndiotactic polystyrene–epoxy blends: 1. Kinetics of curing and phase separation process

The modification of the curing behaviour and the phase separation process for an epoxy resin blended with a crystalline thermoplastic was investigated in the case of the diglycidylether of bisphenol‐A (DGEBA)/4,4′‐methylene bis(3‐chloro‐2,6‐diethylaniline) (MCDEA) blended with syndiotactic polystyrene (sPS) and cured at 220 °C. Phase separation taking place during curing of the blend was investigated by differential scanning calorimetry (DSC) and optical microscopy in order to get a better understanding of the complex interactions between cure kinetics of epoxy matrix and crystallisation of sPS, both influenced by blend composition. Results suggested that phase separation and crystallisation of sPS occurred at almost similar times, with phase separation just being ahead of crystallisation. DSC and near‐infrared measurements were used for the determination of the cure kinetics. Slow delays on the cure reactions were observed during the first minutes for the sPS‐containing blends compared with the neat DGEBA/MCDEA system but, after some time, the reaction rate became faster for the blends than for the neat matrix. Phase separation occurring in the mixtures may explain this particular phenomenon. Copyright © 2004 Society of Chemical Industry     

Molecular characterization of statistical copolymers: 1. Potential and limitations of full adsorption–desorption procedure in separation of statistical copolymers

Dynamic integral desorption isotherms for a series of poly(methyl methacrylate) homopolymers and poly(methyl methacrylate)–polystyrene statistical copolymers were measured. Nonporous silica was the full adsorption–desorption (FAD) column packing and various adsorption‐promoting and desorption‐promoting liquids were used. The aim of this study was to evaluate the applicability of the FAD approach for separation of statistical copolymers. The effects of the adsorbing liquid and desorbing liquid nature were demonstrated on the positions and shapes of desorption isotherms. The desorption isotherms also strongly depended on both (co)polymer molar mass and copolymer chemical composition. This indicates large fractionation potential of the FAD procedure. Simultaneously, the interference of both above parameters prevents the direct use of FAD for fractionation of the copolymers. It is anticipated that the fractionation and/or reconcentration potential of the FAD procedure can be very effectively utilized in combination of FAD with size‐exclusion chromatography and/or with gradient elution liquid adsorption chromatography. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 857–864, 2000     

Heat exchanger network synthesis with detailed exchanger designs: Part 1. A discretized differential algebraic equation model for shell and tube heat exchanger design

A new method for the detailed design of shell and tube heat exchangers is presented through the formulation of coupled differential heat equations, along with algebraic equations for design variables. Heat exchanger design components (tube passes, baffles, and shells) are used to discretize the differential equations and are solved simultaneously with the algebraic design equations. The coupled differential algebraic equation (DAE) system is suitable for numerical optimization as it replaces the nonsmooth log mean temperature difference (LMTD) term. Discrete decisions regarding the number of shells, fluid allocation, tube sizes, and number of baffles are determined by solving an LMTD-based method iteratively. The resulting heat exchanger topology is then used to discretize the detailed DAE model, which is solved as a nonlinear programming model to obtain the detailed exchanger design by minimizing an economic objective function through varying the tube length. The DAE model also provides the stream temperature profiles inside the exchanger simultaneously with the detailed design. It is observed that the DAE model results are almost equal to the LMTD-based design model for one-shell heat exchangers with constant stream properties but shows significant differences when streams properties are allowed to vary with temperature or the number of shells are increased. The accuracy of the solutions and the required computational costs show that the model is well suited for solving heat exchanger network synthesis problems combined with detailed exchanger designs, which is demonstrated in Part 2 of the paper.