Methodology for design and analysis of reactive distillation involving multielement systems

A new methodology for design and analysis of reactive distillation has been developed. In this work, the element-based approach, coupled with a driving force diagram, has been extended and applied to the design of a reactive distillation column involving multielement (multicomponent) systems. The transformation of ordinary systems to element-based ones and the aggregation of non-key elements allow the important design parameters, such as the number of stages, feed stage and minimum reflux ratio, to be determined by using simple diagrams similar to those regularly employed for non-reactive systems consisting of two components. Based on this methodology, an optimal design configuration is identified using the equivalent binary-element-driving force diagram. Two case studies of methyl acetate (MeOAc) synthesis and methyl-tert-butyl ether (MTBE) synthesis have been considered to demonstrate the successful applications of the methodology. Moreover, energy requirements for various column configurations corresponding to different feed locations are determined to verify whether the optimal design can be identified by following the proposed methodology.     

A method of alarm system analysis for process plants

The design and improvement of alarm systems in process plants has been given considerable attention recently. A methodology is presented in this paper which can be used as an aid in the design of new alarm systems or in the improvement of existing alarm systems. The methodology is incorporated in computer software into which expert knowledge of a given process plant can be entered and used to select alarm systems.

Scope—Alarm systems play a very important role in process plants. They aid the operator in his primary tasks of detecting and interrupting progression of a failure, and diagnosing and providing corrective actions for fault conditions. There are, however, operator difficulties in handling alarms. A particular alarm system design can significantly affect the operator's success likelihood in receiving and processing alarms.

Several factors are important in the design or improvement of a given system. Human likelihood of success using a given alarm system under a given fault condition is one obvious factor. Economical aspects of selecting alarm systems, given probable types and frequencies of fault conditions, should also be considered in the design or improvement of alarm systems. A systematic approach is necessary to consider the effects of all these factors in evaluating a set of proposed alarm systems and in selecting the most appropriate alarm system. The purpose of this paper is to provide a method for determining the worth of a given alarm system by considering all factors which influence that worth.

In complex process plants, applications of the methodology presented in this paper can be very difficult without the aid of a computer. Therefore, a computer program is also described to carry out the methodology. Information regarding the process plant is entered into the program using the goal-tree concept. The goal tree contains the expert knowledge of the process which in turn is used in the design or modification of alarm systems.

Conclusions and Significance—A methodology has been presented to perform systematic evaluation of alarm systems. The methodology is based on the goal-tree concept through which process plants can be modeled.

Goal trees excellent tools for cause-consequence determination. The methodology makes use of decision trees which are constructed in parallel to goal trees to show all operator action(s) required to achieve each goal, and to show the consequences of operator's failure to achieve each goal. The decision trees can also model the progression of an initiating fault condition. The operator's likelihood of success of achieving each goal for a given alarm system design or alarm system modification can be estimated and used in the decision tree to estimate anticipated consequences of a given alarm design or modification. Anticipated consequence is defined as the probability of not achieving a goal times the consequence of not achieving that goal. Finally, alarm system designs or modifications with a low anticipated consequence and low implementation cost can be identified for further evaluation as potential alarm systems for the process.

The methodology has been modeled in a system of computer codes called UMPIRE-I. Process knowledge is entered into the computer through a goal tree coupled with human success likelihoods. The rest of the analysis is performed by UMPIRE-I. The code is user-friendly and can be used with minimal training. An example is provided in the paper to further clarify the methodology.

This method has been applied to several limited-scale engineering processes with rather significant success.     

Engineering neural stem cell fates with hydrogel design for central nervous system regeneration

Injuries and disease to the central nervous system (CNS) are accompanied by severe consequences, as the adult CNS has very limited capacity to replace the lost neural cells. Different sources of neural stem cells for CNS tissue regeneration exist, including embryonic stem cells (ESCs), fetal stem cells, adult stem cells, and induced pluripotent stem cells (iPSCs), and so on. However, before stem cell therapy can be a viable option for treatments, many issues still need to be resolved, including low viability, lack of control of stem cell fate, and low cell engraftment after transplantation. Though controlling these parameters is extremely challenging, engineering structures that create permissive niches for the transplanted cells, such as the use of biocompatible hydrogels, is a promising approach. This review will focus on highlighting existing hydrogel systems currently being investigated for CNS tissue regeneration, as well as discuss design criteria for hydrogels and methods for manipulating stem cells within hydrogels systems. Finally, the use of these hydrogel systems as carriers for stem cell transplantation in CNS injury and disease models will be discussed.     

Synthesis of mechanical driver and power generation configurations,Part 2: LNG applications

Optimization framework for the synthesis of power systems has been presented in Part 1 of this article, which systematically identifies the most cost‐efficient number, type, and model of mechanical drivers, together with optimal arrangement for compressor stage, helper motors or generators, and power plants. The developed methodology is applied to an LNG case study in which optimal and near‐optimal systems at various economic scenarios are identified. Also, a systematic methodology for the integrated design of refrigeration and power systems has been addressed to improve the overall design of low temperature processes. Additional key degrees of freedom such as stage pressure ratios and plant capacity are optimized, alongside other design variables, which provide greater flexibility in the matching of power supply and demands. This strategy is applied to an LNG case study and shows the convenience of this approach as the interactions between the refrigeration and power systems are systematically exploited. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Heterogeneous catalytic reactor design with optimum temperature profile II: application of non-uniform catalyst

A new methodology has been developed to design non-isothermal, non-adiabatic heterogeneous catalytic fixed bed and tubular reactors with optimal temperature profiles inside a reactor. Catalyst characteristics such as pellet diameter, shape and activity distributions inside a pellet are considered simultaneously for reactor design. Various types of non-uniform activity distributions inside a pellet are modelled and optimised for the maximisation of an objective such as yield or selectivity. Dirac-δ, layered and general non-uniform distribution profiles such as egg-shell, egg-yolk and middle peak distributions are applied for the reactor design. The research demonstrates that different catalyst distribution profiles can approach the optimum performance. Whilst it is known that the Dirac-δ profile (and its step-function equivalent) always gives the best performance for clean catalyst, other profiles can approach this performance and might offer advantages in catalyst manufacture and under degraded conditions. A profile-based synthesis approach is applied to generate various shapes of activity profiles for multiple sections along the reactor during the optimisation of non-uniform catalyst pellets. A case study with the ethylene oxidation process illustrates that the catalyst characteristics, such as activity distribution profiles inside a pellet, sizes and shapes can be manipulated to control the temperature through the reactor very effectively, leading to significant improvements in selectivity or yield. The non-uniform catalyst pellet is further applied to various reactor configurations such as inert mixing and side stream distributions. This work is the first to consider all of these effects simultaneously.     

IMC controller design for multivariable systems

A systematic internal model control (IMC) controller design methodology has been developed for various types of multivariable processes. When we try to apply IMC to various systems several implementation problems are encountered. In this paper, we resolve these problems and suggest a systematic IMC controller design methodology. IMC shows very good performance and is easy to tune for open-loop stable systems. For unstable systems we apply IMC after stabilizing the systems using the pole placement technique. A combination of quadratic programming and IMC can handle constraints on manipulated and controlled variables.     

Studies on simultaneous energy and water minimisation—Part I: Systems with no water re-use

This paper addresses the simultaneous management of energy and water. A new systematic methodology has been developed for targeting and design that simultaneously minimises the requirements of energy and water. Using this new approach, the design of a water system for maximum energy recovery can be achieved, taking into account the mixing opportunities offered by water networks, while maintaining the water quality to processes in terms of contamination. Direct and indirect energy recovery are analysed and a strategy developed to decrease the number of heat transfer units based on the generation of separate systems and non-isothermal stream mixing. Initially, the analysis is restricted to no water re-use.     

Conceptual design of single-feed hybrid reactive distillation columns

It is well known that reactive distillation offers benefits by integrating distillation and reaction within a single unit. While there are procedures available for the synthesis of non-reactive distillation processes and of reaction-separation systems, the design of reactive distillation columns is still a challenge. This work presents a new synthesis and design methodology for hybrid reactive distillation columns, featuring both reactive and non-reactive sections; reactive equilibrium is assumed. The approach is based on graphical techniques; therefore it is restricted to systems with two degrees of freedom according to Gibbs phase rule. The design method allows rapid and relatively simple screening of different reactive distillation column configurations. The results are useful for initialising more rigorous calculations. The methodology is illustrated for MTBE and ethyl formate production.     

Design of integrated biorefineries

The paper outlines a systems approach with capabilities to address common complexities and practicalities in the design of real-life integrated biorefineries. The approach favors a decomposition of the problem into process synthesis, process integration and flowsheeting. The synthesis of paths introduces a graph representation sufficiently generic to model the general problem. Likewise, the development of product portfolios offers a generic cascade representation that combines thermodynamics with mathematical programming. The methodology renders high-throughput capacity and has been exploited to review large combinations of paths through exhaustive screening, subsequently leading to significant savings in capital and operating costs. The paper highlights results from the approach as it has configured the operation and the evolution of existing pilots and demos. The methodology is being extended to address strategic decisions and the better integration of the biorefinery concept. The paper explains limitations and opportunities of existing methods and tools, highlighting the scope for future developments and applications.     

Predicting mechanical properties of acrylonitrile-butadiene-styrene terpolymer in injection molded plaque and box

A methodology to predict mechanical properties in injection molded parts has been developed. Knowledge of part properties before actual molding and testing will be of immense help to part and mold designers in modification of design. This methodology involved the application of connectionist learning systems, injection molding computer simulation, and experimental evaluation of mechanical properties, to relate the thermomechanical history of injection molded parts to the resulting part properties of injection molded parts are dependent upon their thermomechanical history which in turn is greatly influenced by the processing conditions and part geometry. As the relationships between engineering properties and thermomechanical history are complex and highly nonlinear, the methodology developed was based on a backpropagation neural network algorithm that provided the means for a nonparametric mapping between the part properties and thermomechanical history. The proposed methodology has been successfully applied to two geometries, plaque and box. This methodology provides designers with the ability to predict mechanical properties in injection molded parts when significant thermomechanical history can be obtained from injection molding simulation.     

Computer-aided analysis and design of robust multivariable control systems for chemical processes

A conceptual framework to design robust process control systems is develope d and its realization through an interactive computer-aided design software is presented. The overall design methodology is based on a unified treatment of recent theoretical results in modern control and new computational techniques in symbolic logic manipulation, singular value decomposition and optimization. Several physical examples are given to demonstrate the application of the design approach and the utility of its computer software.     

模糊系统的模型化和优化

过程工业中的生产过程变量关系比较复杂，难于获得精确的模型，常使得过程系统的模拟和优化有较大误差。本文提出基于模糊逻辑表述和处理系统变量间的不精确近似关系，使模型方程间的冲突和不协调性趋于最小，模糊目标函数趋于最大。从而实现对模糊系统的模拟和优化。     

Simultaneous process synthesis and control design under uncertainty: A worst‐case performance approach

A new methodology that includes process synthesis and control structure decisions for the optimal process and control design of dynamic systems under uncertainty is presented. The method integrates dynamic flexibility and dynamic feasibility in a single optimization formulation, thus, reducing the costs to assess the optimal design. A robust stability test is also included in the proposed method to ensure that the optimal design is stable in the presence of magnitude‐bounded perturbations. Since disturbances are treated as stochastic time‐discrete unmeasured inputs, the optimal process synthesis and control design specified by this method remains feasible and stable in the presence of the most critical realizations in the disturbances. The proposed methodology has been applied to simultaneously design and control a system of CSTRs and a ternary distillation column. A study on the computational costs associated with this method is presented and compared to that required by a dynamic optimization‐based scheme. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2497–2514, 2013     

A new methodology for rapidly assessing interfacial bonding within fibre-reinforced thermoplastic composites

A new testing methodology is presented for determining the adhesion strength and failure at composite interfaces. An automated bonding evaluation system (ABES) has been adapted to process and test thermoplastic sandwich composites formed with various natural solid phase materials such as wood. Composites can be rapidly formed and then tested in situ over a range of temperatures to provide information on interfacial adhesion and shear strength between the thermoplastic and the substrate. This methodology is demonstrated for HDPE, PP, PLA and TPU composites comprising wood as solid phases. The interfacial properties depend on processing and testing temperatures, individual thermoplastic phase properties, and wood species. It is expected that this new test method will have applicability in thermoplastic composite design, manufacture and service life predictions for reinforced or filled thermoplastics.     

Synthesis of industrial systems based on value analysis

In this contribution, we present a novel methodology for flexible design of industrial systems based on their detailed differential value analysis. Evolving from graph theory, this methodology devises a mechanism for systematic structural decomposition of large-scale industrial systems into basic processing elements (paths and trees), combination of elements into subsystems and evaluation of individual elements/subsystems to correlate with the overall system margin. This helps to reduce the size of the large combinatorial problems and comprehensively analyse the multiple objectives and the sets of optimal operating states, capital investments and marginal contributions at elemental/subsystems levels that are critical for flexible designs. The approach generates the whole set of optimal solutions compared to the one point solution of the deterministic approaches (MINLP) while allowing additional complexity of process level models in the site-wide integration due to the systematic structural decomposition of a system into its basic elements/subsystems. A recent industrial application on oil upgrading system design is used to illustrate the methodology.     

Studies on simultaneous energy and water minimisation—Part II: Systems with maximum re-use of water

A new systematic design methodology has been developed for the simultaneous management of energy and water systems that also feature maximum re-use of water. A two-dimensional grid diagram is proposed to exploit different options within water systems and also enable reduced complexity of the energy and water network. Isothermal and non-isothermal stream mixing between water streams are introduced to create separate systems between hot and cold water streams in the energy composite curves and provide a design basis for a better structure with fewer units for the heat exchanger network. In addition to allowing re-use of water, issues about heat losses inside unit operations have also been incorporated in the simultaneous management of water and energy.     

Conceptual design of single-feed kinetically controlled reactive distillation columns

Reactive distillation, simultaneous reaction and separation within a single unit, represents an exciting alternative to conventional processes, leading to significantly reduced in capital and operating costs. Process design for reactive distillation is facilitated by fast and effective methods for synthesis and conceptual design that take into account reactions that do not instantaneously reach equilibrium. This work presents a new methodology for synthesis and design of single-feed kinetically controlled reactive distillation columns. The design method allows rapid and relatively simple screening of different reactive distillation column configurations. Feasibility is assessed and operating conditions are determined using an extension of boundary-value methods. The approach is limited to systems with four or fewer chemical species. Both fully reactive and hybrid columns are considered. The methodology is illustrated for a metathesis reaction and for MTBE production.     

基于高斯模型的聚乙烯过程设计与控制集成优化

聚乙烯反应过程中物流-能流剧烈交叠、反应-传递相互耦合,使得过程具有强非线性以及多重稳态。传统的顺序设计方法不能保证系统有足够的控制自由度,当存在扰动和过程参数不确定性时,仅依靠设计控制器很难提高产品质量。提出一种聚乙烯工艺稳态设计与运行控制的集成优化方案,创造性地引入Kriging高斯模型同时预测模型动态和模型不确定性。另一个重要的贡献是在聚乙烯工艺设计阶段,设计性能指标,定量描述过程稳态设计对闭环动态的影响。所提出的方法已经通过对气相聚乙烯工艺设计和运行控制的集成优化进行了验证,并在参数不确定性和扰动存在情况下仿真证实了集成优化设计方案的高效性。     

Modelling the performance of membrane nanofiltration—recovery of a high-value product from a process waste stream

For traditional separation processes there are widely available process design methodologies for scale-up and optimization. However, there is an increasing need for such a rational approach to membrane separation processes, identifying at an early stage operating limits and process options. Such predictive models will reduce development risk and time, thus promoting the wider use of membrane technology in process industries such as pharmaceutical manufacture. Design methods exist that have been verified experimentally at the laboratory scale for simple aqueous solutions. There is now a need for the application of the existing theoretical and experimental methods to separations of real industrial interest.In this paper, we demonstrate this philosophy by describing the rationale for modelling the performance of membrane nanofiltration (NF) used in the recovery of sodium cefuroxime, an industrially important cephalosporin antibiotic having activity against most gram-positive cocci. Sodium cefuroxime is produced in a multi-stage biotransformation process with final purification achieved by low-temperature crystallization with excess quantities of sodium lactate. The efficiency of the crystallization process is not 100% and cefuroxime is lost in the waste stream from the crystallization units. Traditionally, this waste stream has been sent for industrial disposal as the concentrations of sodium cefuroxime are too low for normal separation processes to recover.A systematic study of three commercially available membranes indicated that the Desal-5-DK membrane was most suitable for the recovery process. Excellent agreement between the experimental findings and model predictions was observed for batch NF and a membrane charge isotherm was developed for use in process modelling. The full-scale recovery process was modelled theoretically and NF proved more than adequate for the separation required. An estimate of the industrial scale process operating constraints was made and the NF process was considered as a favourable modification to existing plants.