Ram Lavie

Dynamics of plants with recycle

Abstract The effect of recycle on plant dynamics is examined. The overall plant response will have a longer characteristic time and higher steady-state gain tha

Retrofit design of new units into an existing plant: Case study: Adding new units to an aromatics plant

Abstract The design of a process plant generally follows recursive steps of synthesis, analysis, and evolution. Retrofit design makes changes or additions to the plant in order to achieve expanded and/or more economial operation. A retrofit design algorithm which was developed in this study, uses a process synthesis approach with heuristic rules based on engineering experience, detailed process calculations and detailed economical evaluations leading to an optimal design. This approach was tested extensively and successfully on the flowsheet of an existing aromatics plant. The intervention of experienced engineering judgement leads to improved and more profitable retrofit design or to the optimal choice between alternate downstrem process additions. Cascading distillation towers and reactors, maximal utilization of processing unit capacities, and the reuse of supersede equipment improves the economics of the design. A grassroot design of the whole plant will in most cases be more economical than constructing an initial small plant and then expanding it gradually. Economical failure can result from poor guesses of future prices of feedstocks and products. It was show for the plant studied in this paper by redesign under historical conditions that the added value of the chemicals in the good years made up for the poorer performance in bad years.

Stepwise periodic distillation—I: Total reflux operation

Abstract The theoretical predictions of doubled overall efficiency for plate distillation columns operated in the controlled cycling mode have not been confirmed by pilot scale experiments. In an attempt to circumvent the hydrodynamic problems causing this failure, we have found a new periodic operating mode where the liquid flow is manipulated directly, and not indirectly through pulsations of the vapour flow rate (as in controlled cycling). In this paper we present the theory of stepwise periodic distillation, under assumptions allowing a comparison with known results for controlled cycling. We show that the two processes have the same asymptotic efficiencies for large values of the number of trays while periodic stepwise distillation is slightly more efficient than controlled cycling for a finite number of trays

An automated catalytic system for the sequential optimal discrimination between rival models

Abstract An on-line, computer controlled, automatic experimental setup for the determination of reaction kinetics in gas phase heterogeneous catalytic reactions is presented and demonstrated through the sample study of a simple reaction. The system is automatic to the extent of being capable to carry out, with little or no human intervention, an optimal sequence of experimental runs and single out from a set of plausible rate equations the one that fits best the experimental results. Application of the system to the study of Pt-catalyzed ethylene oxidation around 350°K and atmospheric pressure, showed the classic Langmuir-Hinshelw

Synthesis of flexible and reliable short-term batch production plans

This paper considers the definition and evaluation of flexibility and reliability indices for short-term batch plant operation schedules. A deterministic flexibility metric (F), a stochastic flexibility metric (SF) and a stochastic reliability metric (SR) are defined in a form that is compatible with uniform discretization time MILP models. The stochastic metrics can be combined to form a single SRF index, quantifying the probability of successfully dealing with the expected uncertainty in both the operating parameters and in the availability of processing equipment. In what concerns reliability analysis, the approach exploits the task network representation of batch operation plans. Thus, the estimation of the reliability of an operation plan can be transformed into the evaluation of the reliability of an associated network, which can then be established by one of several known techniques.

Stepwise periodic distillation—II: Separation of a binary mixture

Abstract Stepwise periodic operation of a distillation column in which a binary feed is separated in top and bottoms product is described. A simple but realistic model, both for stepwise periodic and controlled cycling operation and a simulation algorithm are proposed. The results of an extensive parametric study of stepwise periodic operation are presented along those for ideal controlled cycling (no axial mixing). Although in some cases inferior to controlled cycling, it is shown that, for reasonable tray efficiencies and difficult separations, stepwise periodic operation can compare favorably or be superior to ideal controlled cycling.

Limit cycles in fixed beds operated in alternating modes

Abstract Fixed beds, exchanging mass or energy with a flowing fluid according to a linear phenomenological law, are considered. When the plant is alternated periodically between two sets of operating conditions, the state of the fixed bed converges to a limit cycle. The nature of this cycle is explored for co-current and counter-current operation.

Continuous cyclic zone adsorption

Abstract A theoretical study of a continuous version of the cyclic zone adsorption separation process, providing us with a new understanding of the parameters that determine the existence of a separation effect and its extent is presented. A mathematical model is proposed and then solved analytically. Conditions under which a separation effect can be achieved are established, leading to the definition of dimensionless parameters that control the process. Finally, optimal operating conditions are derived and discussed.

Teaching advanced process control to undergraduates

Abstract This paper describes the advanced process control course sequence offered to undergraduates at the Technions Department of Chemical Engineering. Presented here are the educational objectives of the sequence, as well as the format of the three courses involved. The paper will focus on the methods used, and in particular in the computer aided design and analysis tools utilized. As it turns out, the elective courses tend to attract the more capable and motivated of our students. The unreserved enthusiasm expressed by the students indicates that we seem to be on the right track.

Introducing shallow knowledge in batch operations models

Abstract This paper explores two alternative methods to introduce experience and operating preferences during the automatic generation of MILP batch operation models: 1) The imposition of “hard” constraints, which reduce the size of the solution space by dropping task allocations; 2) The addition of “soft” constraints, that tend to preserve desired features of the resulting plan and avoid undesired ones.