Cheapest first heuristic

Solution. Using the information in Fig. 14.6, we develop the initial sequence in step one as shown in Fig. 14.10, where the numbers refer to separator numbers in Fig. 14.6 and an asterisk beside a number designates the lowest-cost separator for a given branching step. Thus, the cheapest-first sequence is 1-7-19-30 with a cost of 878,000/yr. This sequence, which is shown in Fig. 14.8, is identical to that developed from heuristics in Example 14.4. 

The effiuant streams from the first separator are examined and, if necessary, subjected to further separation. The sequence [s developed, gnided by the cost factor and the heuristic to choose the cheapest of all candidate separations next. The flowsheet is complete when all final effluent streams contain only one of the products of the predetermined set. 

Several heuristic rules directed to decrease energy and capital expenditures are used for selection The first rule is for the mixtures having the region of two liquid phases it is necessary to use the most interesting splits at heteroazeotropic and heteroextractive distillation described in the section 8.4.5. Such splits separate, in the cheapest way, the mixture into components. The second rule is to exclude sphts for which one of the products is binary azeotropic mixture, if other splits... 

There is some randomness incorporated into the heuristics because we need to generate different solutions to form the mating pool. The first customer to serve in each of the two VRPs is selected randomly using a random number generator. Then, the nearest customer is added to the route using the cheapest insertion... 

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