The purpose of this work is to introduce the notion of synthesizing mass-exchange networks (MEN's). A systematic, two-stage, procedure is proposed for the synthesis of cost-effective MEN's. In the first stage, a thermodynamically-oriented procedure is used to identify the thermodynamic bottlenecks (pinch points) that limit the extent of mass exchange between the rich and the lean process streams. Preliminary networks, that feature maximum mass exchange, are generated at this stage. The objective of the second stage is to improve the design of these preliminary networks so as to develop a final configuration of the MEN that satisfies the assigned exchange duty at minimum venture cost. This approach is applied t o the synthesis of MEN's with singlecomponent targets as well as multicomponent, compatible targets. An illustrative example on the sweetening of coke-oven gas is presented to demonstrate the applicability of the proposed synthesis procedure.

Detailed balance is an overly strict condition to ensure a valid Monte Carlo simulation. We show that, under fairly general assumptions, a Monte Carlo simulation need satisfy only the weaker balance condition. Not only does our proof show that sequential updating schemes are correct, but also it establishes the correctness of a whole class of new methods that simply leave the Boltzmann distribution invariant.

No abstract

No abstract

No abstract

No abstract

No abstract

The concept of block relative gain (BRG) is introduced to define a measure of interaction for decentralized control structures. This new theoretical development generalizes the original Bristol's relative gain array (RGA) to block pairing of inputs and outputs that are not necessarily single-input single-output pairings. Various properties of BRG are rigorously derived and formulated in a mathematical framework suited to analysis and synthesis. Based on these important properties, a methodology is developed for the systematic generation and selective screening of alternative decentralized control structures. Subsequently, a controller design procedure for the most promising decentralized structures is given. A boiler furnace and a system of heat-integrated reactors are used to illustrate the significance and the utility of the proposed method for industrial processes. Vasilios SCOPEControl system synthesis consists of two subtasks: selection of measurements -nd manipulated variables, and deciding on the structure interconnecting the measured and manipulated variables along with the control law governing the interconnections.Within the last decade several attempts (Govind and Powers, 1982;Umeda and Kuriyama, 1978;Douglas, 1980;Morari et al., 1978; Morari and Stephanopoulos, 1980) have been made to develop mathematical formulations, algorithmic procedures, and systematic strategies to synthesize control structures for integrated complete chemical plants. For details, the reader is referred to the review article by Nishida, et al. (1981). In all these methods, process decomposition (partitioning the process into subsystems) and decentralized control (control of the individual subsystems) has been AIChE JournalJune 1986 accepted as the underlying principle. Such an approach not only guides the designer and facilitates the synthesis activity, but in real practice also leads to significant implementational advantages such as improved safety and fault tolerance, reduced communication cost, increased modularity and flexibility to update and expand the control system, and easier process monitoring and on-line controller tuning.To a large extent, the first subtask of control system synthesis-selection of measurements and manipulated variables-is fairly well understood and is addressed by the existing methods using a combination of heuristic and algorithmic procedures. However the second subtask-selection of the interconnection structure and the control law between the measurements and manipulated variables, which in turn determines the decentralized control system-is far from being resolved. In fact, today there exists no powerful technique to predict the dynamic performance of alternative decentralized control systems and to effectively screen for the best structures. In this paper we address Vol. 32, No. 6 99 1 these problems and develop the necessary mathematical framework to systematically guide the designer during the synthesis process. Two industrial examples are presented to demonstrate the power of the block re...