Computer aided operability analysis via interactive graphics

A comprehensive computer-aided design methodology utilizing the highly interactive capabilities between a graphics computer and the user is described. The program, CHESOPS, enables a flexible simulation of any arbitrary chemical process by synthesizing the process design about several steady state values and extending the analysis to the effects of design changes on process operability. In this way the process may be visualized within a dynamic environment from which interactive control system design and dynamic simulation takes place. The highly flexible nature of the program enables efficient and comprehensive investigation of alternative designs, control structures, and optimal operating conditions.     

Databases for computer-aided process plant design

The needs of a database system for computer-aided process plant design are matched with anticipated developments in software and hardware. An adaptive, distributed database using a universal data model functioning on a loop network of mini- or midi-computers is proposed.     

Interactive solution to multiple criteria problems in chemical process design: An approach by pairwise comparison

A process design problem is considered as a multiobjective problem that is characterized by conflicting objectives such as economics, operability, and so on. A method developed for solving multiobjective problems in man-machine interactive mode has been extensively applied to the basic process design of chemical process systems. AS an illustrative example, an optimal design of a simple, yet practical, chemical process system has been taken up to show the practical usefulness of the present method.     

Modelling of the pressure swing air seperation process

A theoretical analysis is given of the separation of oxygen and nitrogen in air by a single column pressure swing gas separation process. The problem treated includes changes in mass flow due to adsorption. The findings are compared with data obtained using molecular sieve adsorbent.     

Rectification of process measurement data in the presence of gross errors

A systematic strategy is developed for the location of the source and the rectification of gross, biased measurement errors in a chemical process. The proposed strategy proceeds in three levels: (a) A structural analysis of the balance equations identifies subsets of balances with measurements which are suspected to possess gross errors. (b) A sequential analysis of the balance equations with suspect measurements further reduces the size of the problem. Statistical criteria are used in this step. (c) Finally, a sequential analysis of the suspect measurements appearing in the reduced set of balances leads to the identification of the source of the gross errors.The proposed strategy: (i) reduces the size of the data reconciliation problem significantly, even for large-scale chemical processes, (ii) is computationally simple and (iii) it conforms with the general process of variable monitoring in a chemical plant.Numerical examples are presented to clarify the elements of the procedure involved and demonstrate their value and effectiveness in dealing with realistic situations.     

Optimization of the sulfuric acid process with a flowsheet simulator

The sulfuric acid process is one of the oldest and most common in the chemical industry. Due to stricter pollution regulations, this process has recently received broader application to the production of sulfuric acid from SO₂ in the waste gases from metallurgical roasting. Little work has been reported on the economic optimization of the sulfuric acid process, particularly for metallurgical operations.This paper presents a method for simulation and optimization of the sulfuric acid process using the PROPS simulation model and the adaptive random search algorithm. Optimal results are presented for plants to handle various SO₂ gas strengths and to meet different pollution regulations. The effectiveness of the optimization is measured by comparing the cost of the simulation and optimization study with the improvement in annual earnings for older, near optimal, plants and modern facilities.     

On the relevance of mass transfer limitations in the Fischer-Tropsch slurry process

Satterfield and Huff[1] reported recently on significant mass transfer resistances in the FT slurry process. However, their conclusions are at least partly based on a study with an unsuitable catalyst. In the present communication FT studies with 8 different catalysts and bubble columns, respectively, were analyzed using new and reliable results on hydrodynamic properties. In all cases, mass transfer resistances were found to be small compared to reaction resistances. As long as much more active catalysts are not developed significant mass transfer limitations cannot be expected in the bubble column if operated under appropriate conditions. The absence of mass transfer limitations is mainly a result of the high gas holdups attainable with molten paraffin as liquid phase.     

A model-based scheme for the on-line optimization of a liquid extraction process

The on-line optimization of a liquid extraction process using a model-based scheme is described. Four steady-state process models are first investigated for their ability to predict the process performance; these models are subsequently used in the optimization study. The optimization scheme incorporates a simple model-updating technique and is based on an efficient method for constrained optimization which has been developed as part of this study. Rapid convergence to the true process optimum occurs, provided the predictions of the direction of change of the objective function are locally correct. In a few cases, however, poor model predictions result in failure to converge, or give convergence to a point other than the true optimum.     

Sequential experimental design for model discrimination in the case of multiple responses

The sequential experimental design procedure for discriminating among single response rival models outlined in Chem. Engng Sci 1983 38, 225 is here extended to the case of multiresponse models. The method is illustrated with an example.     

An improved algorithm for diagnosis of system failures in the chemical process

The detailed techniques for improving the efficiency of a fault-diagnosis algorithm can be based on the signed directed graph. This graph represents the structure of the system, and the pattern on the graph represents a state of the system. The usefulness of the improved algorithm is demonstrated using a model of a chemical process comprising a reactor, a heat exchanger and a distillation tower.     

Applications of mixed-integer linear programming in process synthesis

It is shown that important problems arising in process synthesis can be tackled effectively using mixed-integer linear programming techniques. Two examples are considered: the synthesis of chemical complexes that maximize its present value for a given number of periods where prices and demands fluctuate; and the synthesis of stream generation systems that minimize the total annual cost. Numerical results are presented for both cases.     

Equilibrium theory of a pressure swing adsorption process

An equilibrium theory of the separation of two-component gaseous mixtures via the pressure swing adsorption process known as heatless adsorption is presented. Both components of the mixture are adsorbable. One is present at a trace level and is preferentially adsorbed.Principal predictions of the theory for the condition of complete removal of the trace component from the high pressure product stream when using the least possible amount of adsorbent are as follows. When the separation factor is large, high recovery of purified high pressure product is obtained and blowdown and purge losses are small. Recovery is increased and losses decreased by increasing the pressure ratio. Conversely, recovery of the purif high pressure product is small and blowdown and purge losses are large when the separation factor is small. In this case the use of high pressure ratio not improve performance.The trace level component in the combined blowdown and purge stream is derived increasingly from the blowdown as the pressure ratio is increased.     

Some characteristics of chemical crystallization in water purification process

Technological scheme for water purification using coprecipitation was analysed. Crystallization of BaCO₃ under the conditions of rapid mixing of reagent solution was investigated with special emphasis on: size distribution of crystals and aggregates by states in time, intensities of nucleation and growth of crystals, mean frequency of molecule binding to the surface during growth, etc. This analysis and results show that the above characteristics must be taken into account in optimization of the technological scheme.     

Observability and redundancy in process data estimation

By analogy to the development for dynamic systems, concepts of observability and redundancy may be developed with respect to a steady state system. These concepts differ from their counterparts for dynamic systems in that they can be used to characterize individual variables and local behavior as well as system and global behavior. Relations between local observability, global observability, calculability and redundancy are established and explored in this paper. It is shown that these concepts are useful in characterizing the performance of process data estimators with regard to bias and uniqueness of an estimate, convergence of estimation procedures and the feasibility and implications of problem decomposition.     

The pinch design method for heat exchanger networks

A novel method is presented for the design of heat exchanger networks. The method is the first to combine sufficient simplicity to be used by hand with near certainty to identify “best” designs, even for large problems. “Best” designs feature the highest degree of energy recovery possible with a given number of capital items. Moreover, they feature network patterns required for good controllability, plant layout, intrinsic safety, etc.     

Local thermodynamic models for high pressure process calculations

This paper discusses the local thermodynamic model concept in the context of high pressure chemical processes where equations of state are usually required for performing thermodynamic property evaluations. Functional forms for local K-value models are developed by simplifying the rigorous equations governing fluid phase equilibria. The local models have imbedded adjustable parameters that are evaluated by regression against either experimental data or thermodynamic properties calculated with more rigorous theoretically based models. During the course of the calculations the parameters in the local models are updated periodically, thereby ensuring that the local models continually provide accurate values for thermodynamic properties. Use of the concepts for process calculations is demonstrated in an example problem.     

Computer-aided reaction system synthesis based on structured process energy-exergy-flow diagram

A computerized thermodynamics-oriented procedure for reaction system synthesis is proposed. First, hierarchy structure of chemical reactions is discussed and the reaction system is categorized into three types; (1) combination with a heat source or sink, (2) combination with a reaction donor, and (3) decomposition of target reaction into subtargets. Then, the algorithm to find subtarget reactions and/or donor reactions is presented.