(303i) Increasing the Efficiency of Mass and Heat Exchange Networks

The most effective practical solution to heat exchanger network synthesis problems is a group of pinch methods. Pinch methods allow for the easy determination of the maximum integral heat exchange and minimum utility duties. A more difficult problem for pinch methods is the design of a practical scheme for heat exchangers. The designs obtained by this method consist of many small exchangers and intermediate heaters and coolers. The combinatorial methods are more flexible in specifying stream matches than pinch methods and may synthesize networks in which more heat is exchanged by a smaller number of heat exchangers as compared with networks synthesized by pinch methods. The advantages and disadvantages of the considered methods are shown. For complex chemical and technological systems, consisting of several sub-systems (separation, heat exchange, reactor sub-systems, etc.) heuristic methods with thermodynamic heuristics can be used for the solution of the sub-problem of the syntheses of heat exchanger networks. Using heuristic methods minimum temperature difference, Dtmin can be changed in the synthesis processes. The reconstruction of older refineries to take advantage of these efficiencies can be profitable if the changes are small and result significant cost savings. If the potential savings are large enough, but huge changes are required, it may be reasonable to build new facilities. However, partial reconstruction is possible, which can be carried out at the same time as scheduled maintenance. The synthesis of heat integrated separation system may be realized by means of a two-level Method. The described method for the synthesis of the heat-integrated systems of separation was organized for a gas-fractionation plant. The synthesized heat integrated separation system turned out to be 30% less expensive than the same without recuperation of heat. In the synthesized system of separation, auxiliary energy carriers were necessary for use in the column for the separation of butane and isobutane. Heat recovery may be increased using a heat pump. The possibility of using a heat pump for the butane and isobutane separation column is considered in this report.