(46b) Revamping Crude Units: Pre-Heating Trains and Pumparound Load Adjustnment

Crude fractionation units are energy intensive. Therefore any measures taken to heat integrate these units saves operating expenses.

These units make use of so-called pump-around circuits (liquid extracted from the column, cooled down and sent to a few trays above), as means of distributing the reflux of the condenser. These circuits were originally installed aiming at "balancing the traffic of liquid". It was later found, after the energy crisis, that they are also effcient in reducing energyu consumption because they could be effectively used to pre-heat the crude fed to the column.

In a recent string of papers (Bagajewicz et al, IECR) a new methodology to design crude fractionation columns has been presented. The methodology makes use of process simulation to determine fractionation needs in conjunction with heat demand supply diagrams. This allowed the appropriate determination of pump around circuits loads to minimize energy consumption. This is a targeting method that uses the well-know ?plus-minus? principle of pinch technology. The technique provided good targets for subsequent heat exchanger network designs.

In a 2006 AICHe conference paper we presented a method where we replaced the demand-supply diagrams by HEN,MILP-based, synthesis methods (Barbaro and Bagajewicz, Computers and Chemical Engineering, 2005), under conditions in which we simulatneously vary the pumparound rates thus capturing the level of pumparound loads that lead to most appropriate balance between capital and energy costs.

In this presentation we will focus on retrofit under similar conditions. Retrofit is based on adding exchangers as well as altering the effective area of existing ones.