Converting DAE models to ODE models: application to reactive Rayleigh distillation

This paper illustrates the application of an index reduction method to some differential algebraic equations (DAE) modelling the reactive Rayleigh distillation. After two deflation steps, this DAE is converted to an equivalent first-order explicit ordinary differential equation (ODE). This ODE involves a reduced number of dependent variables, and some evaluations of implicit functions defined, either from the original algebraic constraints, or from the hidden ones. Consistent initial conditions are no longer to be computed; at the opposite of some other index reduction methods, which generate a drift-off effect, the algebraic constraints remain satisfied at any time; and, finally, the computational effort to solve the ODE may be less than the one associated to the original DAE

The energy Extended Resource Task Network, a general formalism for the modeling of production systems:Application to waste heat valorization

While real-time control of process plays an important role, it is now increasingly necessary to forecast and plan production systems in order to be energy efficient and to ensure a balance between energy demand and production. In this context, a short-term planning approach of energy supply chain is presented in this paper. Because of the presence of enthalpy balance in the optimization model, the core of this system is based on the formulation and the resolution of a Mixed-Integer Non Linear Programming (MINLP) model. To facilitate the instantiation of this optimization model and its adaptation to different kinds of value chain, a specific graphical formalism named Energy Extended Resource Task Network (EERTN) is exploited. This generic framework makes it possible to model in an unambiguous way the material and energy flows passing through any type of production system. In addition, it takes into account the influence of temperature on the physicochemical phenomena involved in the process. To illustrate the potentiality of this modeling framework, it is applied to a case study aimed at carrying out the operational planning and performance evaluation of a waste heat recovery chain. This system consists, on the one hand of an industrial unit whose heat requirements are provided by a steam utility plant, and on the other hand, of a district heating network (DHN). In this study, the problem consists to optimally plan the energy use of the district heating network by recovering the flus gas (the waste heat) from the industrial site’s power plant. The planning system leads to a significant reduction in the primary fuel consumption of the overall system and an efficient exploitation of the waste heat generated by the industrial site

Definition of a Robustness Indicator for Assessment of Heat Exchanger Network Performances

Due to process variabilities and operational modifications, operation parameters of the HEN may alter its output temperatures. Flexibility of HEN refers to the ability of a system to operate for a finite number of points. The first level of flexibility concerns the robustness (ability of the system to absorb disturbances without changing utility flowrates). Assuming that some parameters p vary with a normal distribution characterized by its mean value pmean and standard deviation psd, a linear system is solved where the left-hand term involves matrices representing the HEN (fluctuations of the HEN characteristics, except topology) and right-hand side involves fluctuations of input temperatures of the HEN. Due to this linear formulation, the normally distributed inputs also propagate along a normal distribution output temperatures. A robustness criterion is then defined evaluating the probability of a selected critical value output distribution to fall within a predefined interval. This robustness criterion can only be significant when a thorough data analysis is carried out to identify the relevant perturbations and their frequency of occurrence

The extended resource task network: a framework for the combined scheduling of batch processes and CHP plants

The issue of energy has emerged as one of the greatest challenges facing mankind. In an industrial perspective, the development of site utility systems (generally combined heat and power (CHP) systems) for the generation and management of utilities provides a great potential source for energy savings. However, in most industrial sites, a master–slave relationship usually governs this kind of system and limits the potential operating capacity of CHP. To improve the decision-making process, Agha et al. (2010. Integrated production and utility system approach for optimising industrial unit operation. Energy, 35, 611–627) have proposed an integrated approach that carries out simultaneous and consistent scheduling of batch production plants and site utility systems. The modelling of the problem relies on a mixed integer linear programming (MILP) formulation. Nevertheless, although it is a powerful mathematical tool, it still remains difficult to use for non-expert engineers. In this framework, a graphical formalism based on existing representations (STN, RTN) has been developed: the extended resource task network (ERTN). Combined with an efficient and generic MILP formulation, it permits various kinds of industrial problems, including production and consumption of utility flows to be modelled homogenously. This paper focuses on the semantic elements of the ERTN formalism and illustrates their use through representative example

PiXAR : Pinch and eXergy for the Analysis and Retrofit design of industrial processes

This paper intends to present a novel approach, called PiXAR, combining Pinch technology and Exergy Analysis for the analysis and retrofit design of existing industrial processes. This methodology divided into three steps : modeling and simulation within a process simulation software, analysis of the process with a combined utilisation of pinch and exergy analysis, and finally the retrofit design of the process based upon a case-based reasoning system. The PiXAR methodology, which is intended to be pragmatic, is illustrated through two case-studie

General methodology for exergy balance in ProSimPlus® process simulator

This paper presents a general methodology for exergy balance in chemical and thermal processes integrated in ProSimPlus® as a well-adopted process simulator for energy efficiency analysis. In this work, as well as using the general expressions for heat and work streams, all of exergy balance is presented within only one software in order to fully automate exergy analysis. In addition, after exergy balance, the essential elements such as source of irreversibility for exergy analysis are presented to help the user for modifications on either process or utility system. The applicability of the proposed methodology in ProSimPlus® is shown through a simple scheme of Natural Gas Liquids (NGL) recovery process and its steam utility system. The methodology does not only provide the user with necessary exergetic criteria to pinpoint the source of exergy losses, it also helps the user to find the way to reduce the exergy losses. These features of the proposed exergy calculator make it preferable for its implementation in ProSimPlus® to define the most realistic and profitable retrofit projects on the existing chemical and thermal plants

A systematic approach: combining process optimisation exergy analysis and energy recovery for a better efficiency of industrial processes

Exergy analysis has been shown to be a powerful tool for assessing and improving the energy efficiency of thermal and chemical processes. However, the lack of systematic procedures in examining and interpreting the results of the exergy balance or the exergy efficiency makes this kind of analysis more or less limited to the academic world. This paper intends to promote an efficient energy usage through pinch, exergy analyses and energetic optimisation and by providing the engineer with specific improvement means by using a case-based reasoning (CBR) system. To make exergy analysis more understandable, it was decided to develop two methodological tools: a supporting graphical representation of the exergy analysis and a CBR system to help the user in developing alternatives. Both tools are grouped together into a general methodology for the analysis and retrofit design of industrial sites. This new approach is illustrated through an ammonia processing plant case stud

Flexibility Assessment of Heat Exchanger Networks: From a Thorough Data Extraction to Robustness Evaluation

Due to process variabilities and operational modifications, operating parameters of Heat Exchanger Network (HEN) may alter its output temperatures. Nevertheless, the impact of these disturbances depends largely on the topology of the HEN. As a consequence, it can be relevant to evaluate the flexibility of a HEN after its synthesis. Flexibility of a HEN refers to the ability of a system to operate at a finite number of set points. In this framework, the implementation of this property is broken down into several aspects. In this contribution, the first level of flexibility concerning the robustness (ability of the system to absorb disturbances without changing utility flowrates) is addressed and compared to other contribution, this criterion is not formulated as a generic one but as a criterion that strongly depends on the studied process. As a consequence, to evaluate its value, the first step is to perform an enhanced data collection by identifying the most frequent disturbances and by pointing out the critical streams i.e. the streams whose output temperature absolutely needs to be kept into a strict interval; then, given this information, a robustness criterion can be formulated for a given HEN. In this paper, a methodology relying on several models is developed to address this issue: a Mass Equilibrium Summation enthalpy non-linear model (MESH) dedicated to the enhanced data collection, a Mixed Integer Linear Programming (MILP) model used for the HEN synthesis and finally a linear model developed for the modeling of the HEN response to disturbances. This methodology is first illustrated through a basic academic example and finally applied to an industrial case study

Heat Integration optimization in a Multiproduct Biorefinery

The biorefining is a fast-growing topic and laboratory data about biorefineries accumulate sharply, but this type of process is still mainly unknown at the industrial scale. In this context, it is necessary to propose a method that permits to evaluate the industrial interest in order to design and to build the biorefinery. Moreover, the optimization of water and energy consumption represents two of the most important operating costs in a biorefinery. Thus, to limit utilities consumption, energy integration has to be incorporated for all process design alternatives. The proposed MILP program minimizes utilities consumption in coupling cold streams and hot streams through heat exchangers

Design and optimization of Heat Integrated Distillation Column “HIDiC”

Distillation is the most applied separation technology. However, its major drawback is the low thermodynamic efficiency (typically around 10%). In response to environmental issues that concern energy consumption of distillation columns, HIDiC (heat integrated distillation column) is expected to have a large impact on energy saving. The aim of this study is to optimize the HIDiC sensitive parameters so as to minimize the Total Annual Cost (TAC). For this, a HIDiC simulation model is developed by using commercial software ProSimPlus. GA (Genetic Algorithm) is used to find the optimal HIDiC configuration where multivariable are optimized without initialization. Binary (Benzene/Toluene) separation case is examined. As a result, 7.4% and 13.9% TAC reductions are realized in comparison with the reported solutions in previous works