Plant synthesis problem

The methodology deals with two types of problems, namely, the wastewater minimisation problem within a given plant structure and the plant synthesis problem. Each of these is dealt with in the form of two mathematical formulations. The first mathematical formulation deals with the scheduling of an existing operation as to produce near zero effluent. The second mathematical formulation deals with the... 

As can be seen from Fig, 3.7, the pinch decomposes the synthesis problem into two regions a rich end and a lean end. The rich end comprises all streams or parts of streams richer than the pinch composition. Similarly, the lean end includes all the streams or parts of streams leaner than the pinch composition. Above the pinch, exchange between the rich and the lean process streams takes place. External MSAs are not required. Using an external MSA above the pinch will incur a penalty of eliminating an equivalent amount of process lean streams from service. On the other hand, below the pinch, both the process and the external lean streams should be used. Furthermore, Fig. 3.7 indicates that if any mass is transferred across the pinch, the composite lean stream will move upward and, consequently, external MSAs in excess of the minimum requirement will be used. Therefore, to minimize the cost of external MSAs, mass should not be transferred across the pinch. It is worth pointing out that these observations are valid only for the class of MEN problems covered in this chapter. When the assumptions employed in this chapter are relaxed, more general conclusions can be made. For instance, it will be shown later that the pinch analysis can still be undertaken even when there are no process MSAs in the plant. The pinch characteristics will be generalized in Chapters Five and Six. 

These tests demonstrated that the Lurgi Rectisol process provides an extremely pure synthesis gas which can be charged directly to the metha-nation plant without problems of sulfur poisoning of the nickel catalyst. However, in order to cope with a sudden sulfur breakthrough from Rectisol as a result of maloperation, a commercial methanation plant should be operated with a ZnO emergency catchpot on line. 

The zero effluent synthesis formulation not only determines the optimal number and size of the storage and processing units, but also determines the schedule that will allow the resulting plant to operate in a near zero effluent operation. This is beneficial since scheduling considerations are taken into account during the plant synthesis phase. The exact problem considered in this formulation is given in the following section. 

Having described the overall process system, its three main interactive components (i.e., the chemical plant, the heat recovery system and the utility system), as well as the three subsystems of the chemical plant (i.e., the reactor system, the separation system, and the recycle system) we can now define the process synthesis problem. 

Control System Synthesis. The synthesis problem for control systems is to select the controllers needed to meet specified control goals for a fixed plant configuration. The designer selects his goals by stating which variables he wishes controlled. The synthesis algorithm selects which variables to measure, which to manipulate and what type of controllers to use. 

The next example will revisit the plantwide problem of HDA plant, this time viewed as a process synthesis problem where flowsheet design and controllability are examined at the same levels of the hierarchical methodology. 

Krarup, J., and Pruzan, P. M. (1983), The Simple Plant Location Problem Survey and Synthesis, European Journal of Operational Research, Vol. 12, pp. 36-81. 

The regulation of the biosynthetic pathway for cysteine appears to present the plant with a variety of problems, (a) The formation of cysteine represents the confluence of two separate pathways which produce OAS and the sulfide precursor. Are the rates of these pathways coordinated Is cysteine formation ordinarily limited by the availability of sulfide, OAS, neither, or both (b) In plants, synthesis of sulfide occurs via a pathway which branches after APS to lead to sulfide or to PAPS, the precursor of sulfate esters and, probably, of sulfonolipids. If sulfide formation is regulated, how is provision... 

The mathematical formulation of the process synthesis problem for continuous plants can be stated as follows [7,10]... 

After wrestling with the ammonia synthesis problem for about a decade, Ertl and coworkers were able to meet Emmett s challenge They showed that a combination of the kinetic parameters associated with the individual reaction steps shown in Fig. 5.22 furnishes a steady-state yield of ammonia from the elements which, for a range of conditions, accurately reproduces the real-life yields measured at industrial plants. This agreement has demonstrated that, in the case of the ammonia synthesis, the surface science approach to catalysis is capable of providing no less than a quantitative description of an industrial process. 

A significant feature of the operation of the two plants is that only a small deviation in feed gas composition is tolerable when using a stoichiometric gas. Greater deviations in the H2/CO ratio and in the residual C02 content of the feed gas will cause serious problems regarding SNG specifications. Thus, methanation of a stoichiometric synthesis gas is reasonable only when there are no stringent requirements for SNG specification. 

Dr. Moeller A methanation plant does not have a problem of selectivity. Whether you operate at low or high temperature, when using a nickel catalyst you will form only methane and no higher hydrocarbon. But with the Fischer-Tropsch synthesis, you have a wide range of possible products which can be formed. If you want to have a certain product, you must keep your temperature at a certain constant value. 

Fig. 3. Example operations planning problem. (Reprinted from Comp. Chem. Eng., 12, Lakshmanan, R. and Stephanopoulos, G., Synthesis of operating procedures for complete chemical plants, Parts I, II, p. 985, 1003, Copyright 1988, with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington 0X5 1GB, UK.)...

The synthesis of operating procedures for continuous chemical plants can be represented as a mixed-integer nonlinear programming problem, and it has been addressed as such by other researchers. In this chapter we have attempted to present a unifying theoretical framework, which ad-... 

Real-time synthesis of operating procedures. Most of the ideas and methodologies, presented in this chapter, are applicable to the a priori, off-line, synthesis of operating procedures. There is a need though to address similar problems during the operation of a chemical plant. Typical examples are the synthesis of operational response (i.e., operating procedure) to process upsets, real-time recovery from a fallback position, and supervisory control for constrained optimum operation. 

A system has been constructed which allows combined studies of reaction kinetics and catalyst surface properties. Key elements of the system are a computer-controlled pilot plant with a plug flow reactor coupled In series to a minireactor which Is connected, via a high vacuum sample transfer system, to a surface analysis Instrument equipped with XFS, AES, SAM, and SIMS. When Interesting kinetic data are observed, the reaction Is stopped and the test sample Is transferred from the mlnlreactor to the surface analysis chamber. Unique features and problem areas of this new approach will be discussed. The power of the system will be Illustrated with a study of surface chemical changes of a Cu0/Zn0/Al203 catalyst during activation and methanol synthesis. Metallic Cu was Identified by XFS as the only Cu surface site during methanol synthesis. 

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