A heat-integrated prefractionator arrangement is studied for a ternary separation of a propane-butane-pentane mixture. These types of integrated prefractionator arrangements have large energy savings compared with the best of the direct or indirect sequence with no heat integration. However, a heat-integrated distillation system can be more difficult to control than a non-integrated arrangement, so good control systems are essential. In this work, the focus is on selecting control variables that will ensure that the promised energy savings are achieved. The method of self-optimizing control (Skogestad, 2000) has been used to provide a systematic procedure for the selection of controlled variables, based on steady state economics. The results show that the integrated prefractionator arrangement can have large energy savings compared with non-integrated arrangements and that controlling the ratio of the distillate flow to the feed flow has good self-optimizing properties.

A heat-integrated prefractionator arrangement is studied for a ternary separation of a propane-butane-pentane mixture. These types of integrated prefractionator arrangements have large energy savings compared with the best of the direct or indirect sequence with no heat integration. However, a heat-integrated distillation system can be more difficult to control than a non-integrated arrangement, so good control systems are essential. In this work, the focus is on selecting control variables that will ensure that the promised energy savings are achieved. The method of self-optimizing control (Skogestad, 2000) has been used to provide a systematic procedure for the selection of controlled variables, based on steady state economics. The results show that the integrated prefractionator arrangement can have large energy savings compared with non-integrated arrangements and that controlling the ratio of the distillate flow to the feed flow has good self-optimizing properties.

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in Wiley InterScience (www.interscience.wiley.com). The minimum energy requirements of six different heat-integrated multieffect and three nonintegrated distillation arrangements for separating a ternary mixture have been considered. The focus is on a heat-integrated complex distillation configuration, called a multieffect prefractionator arrangement. The comparison of the different arrangements is based on the minimum vapor flow rates at infinite number of stages, which are easily visualized and compared in a V min diagram. This tool can be used as a basis for screening and the best arrangement(s) can be studied further using more rigorous simulation methods.

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