Distillation sequencing thermal coupling

Figure 11.16 The thermally coupled indirect sequence for crude oil distillation.

The majority of atmospheric crude oil distillation columns follow the configuration shown in Figure 11.17, which is basically the partially thermally coupled indirect sequence. 

Consider now ways in which the best arrangement of a distillation sequence can be determined more systematically. Given the possibilities for changing the sequence of simple columns or the introduction of prefractionators, side-strippers, side-rectifiers and fully thermally coupled arrangements, the problem is complex with many structural options. The problem can be addressed using the optimization of a superstructure. As discussed in Chapter 1, this approach starts by setting up a grand flowsheet in which all structural features for an optimal solution are embedded. 

Thermally coupled sequences, for distillation, 22 300-301 Thermally stimulated conductivity (TSC), 19 586... 

Control Performance of Thermally Coupled Distillation Sequences with Unidirectional Flows... 

S. Hernandez, S. Pereira-Pech, and V. Rico-Ramirez. Energy efficiency of an indirect thermally coupled distillation sequence. Can. J. Chem,. Eng., 81 (5) 1087-1091, 2003. 

J.G. Segovia-Hernandez, S. Hernandez, and A. Jimenez. Control behaviour of thermally coupled distillation sequences. Trans. IchemE, 80(Part A) 783-789, 2002. 

Another class of separation problem attacked has been that of designing the most effective thermally coupled distillation column arrangement to separate a multicomponent mixture. Sargent and Gaxninibandara (1975) present a general column superstructure which they optimize. Imbedded in the superstructure are all the alternative thermally coupled and ordinary column sequences to be considered. The optimization eliminates those portions of the superstructure which are not economic leaving, hopefully, the optimal substructure. 

Due to the tremendous costs associated to distillative separations, many alternate schemes to the simple column shown above have been proposed over the past several years both to improve on some of its inherent costs. Traditionally, when purifying a multicomponent mixture, an entire series of distillation columns are used in series, and the way in which these columns are sequenced may make a tremendous difference in the eventual process costs. However, due to the large energy requirements of even the most optimal sequence, more complex column arrangements have been proposed and subsequently utilized. These arrangements include thermally coupled columns such as side rectifiers and strippers, the fully thermally coupled columns (often referred to as the Petlyuk and Kaibel columns). 

Caballero, J.A. and Grossmann, I.E. (2014) Optimal synthesis of thermally coupled distillation sequences using a novel MILP approach. Computers Chemical Engineering, 61,118-135. 

Long, N.V.D. and Lee, M. (2013c) Debottlenecking the retrofitted thermally coupled distillation sequence. Industrial Engineering Chemistry Research, 52,12635-12645. 

Segovia-Hernandez, J.G., Hernandez-Vargas, E.A. and Marquez-Munoz, J.A. (2007) Control properties of thermally coupled distillation sequences for different operating conditions. Computers Chemical Engineering, 31, 867-874. 

Dynamic Study of Thermally Coupled Distillation Sequences Using Proportional - Integral Controllers... 

A comparative study of the energy requirements and control properties of three thermally coupled distillation schemes and two conventional distillation sequences for the separation of ternary mixtures is presented. The responses to set point changes under closed loop operation with proportional-integral (PI) controllers were obtained. Three composition control loops were used, and for each separation scheme, the parameters of the PI controllers were optimized using the integral of the absolute error criterion. The effects of feed composition and of the ease of separability index were considered. The results indicate that there exist cases in which integrated systems may exhibit better control properties than sequences based on conventional distillation columns. 

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