Targeting energy integration

Balakrishna, S. and Biegler, L.T., 1992b. Targeting strategies for the synthesis and energy integration of non-isothermal reactor networks. Industrial and Engineering Chemistry Research, 31(9), 2152. 

There is clearly scope for energy integration between these four streams. Two require heating and two cooling and the stream temperatures are such that heat can be transferred from the hot to the cold streams. The task is to find the best arrangement of heat exchangers to achieve the target temperatures. 

Balakrishna, S. and L. T. Biegler. Targeting Strategies for the Synthesis and Energy Integration of Nonisothermal Reactor Networks. Ind Eng Chem Res 31 2152-2164 (1992). 

While synthesis strategies are well developed for energy integration and separation systems, relatively little work has been done in synthesizing reactor networks. This is due to the complex and nonlinear behavior of the reacting system, coupled with the combinatorial aspects inherent in all synthesis problems. This paper provides a brief summary of work to date in this area, focusing on targeting approaches for reactor network synthesis. 

The optimization model in the sequential case had 342 equations and 362 variables for the reactor flowsheet optimization (96 CPU seconds on the VAX 6320) and 200 equations and 161 variables for the energy integration (170 CPU seconds). The simultaneous optimization model (542 equations, 523 variables) was solved in 1455 CPU seconds and was initialized with the solution to the sequential model. Table I presents a comparison between the results for sequential and simultaneous modes to synthesis. A target production rate of 40,000 Ib/h is assumed for the desired product B. 

Here, we devise a reaction separation network featuring energy integration for the following system using the proposed targeting scheme. 

Similarly to energy integration, techniques have been developed for targeting and optimisation of operations based on the exchange of mass. Simple graphical representations are not available yet, but appropriate computer methods could facilitate the application of this concept in the design practice in the future. 

The synthesis of a Heat Exchanger Network consists of three main activities a. Targeting. Set a reference basis for energy integration, namely ... 

The rules for forming the required matrix elements from the veirious energy integrals are inverted that is formulated so that we answer the question I have a particular (MO) integral to hand, where does it appear in the target matrix being formed ... 

Within each of the three general approaches toward process synthesis, key decisions are made about the flowsheet design that have a bearing on the operability characteristics of the plant. For example, in a hierarchical procedure (Ref. 6) we will make decisions about whether the plant is batch or continuous, what types of reactors are used, how material is recycled, what methods and sequences of separation are employed, how much energy integration is involved, etc. In a thermodynamic pinch analysis, we typically start with some flowsheet information, but we must then decide what streams or units to include in the analysis, what level of utilities are involved, what thermodynamic targets are used, etc. In an optimization approach, we must decide the scope of the superstructure to use, what physical data to include, what constraints to apply, what disturbances or uncertainties to consider, what objective function to employ, etc (Ref. 7). 

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