Design of Coolers for Use in an Existing Cooling Water Network

摘要

It is usual practice to design coolers without considering how they will behave whenrnthey are installed in a cooling water network and the effect that they will have upon thernperformance of the coolers already operating in the system. The dangers of this practicernhave recently been highlighted by Tavares et al. (2010). These workers presented arnstudy in which a new exchanger was installed in an existing network. The unit had beenrnover-designed. However, it still did not provide adequate performance. The hot streamrnoutlet temperature was 5 ℃ above the required value. This study is a clearrndemonstration of the need to specify the design objectives for coolers in a systemsrncontext. Unlike the recent work of Picon Nunez et al. (2009), Giorgia et al. (2009) andrnCastro et al. (2000) the work of Tavares et al. (2010) did not include a consideration ofrncooling tower performance. This is unfortunate for the installation of a new exchangerrngenerally results in increase in the temperature at which the cooling water is returned tornthe tower. This increase, in turn, results in an increase in the temperature of the coolingrnwater returning from the tower and being fed to the coolers constituting the network.rnAnother shortcoming, in this otherwise important work, is that a very detailed model ofrnheat exchanger performance is used. This model is restricted to shell-and-tube heatrnexchangers. This restricts the practical application of the work for it cannot be appliedrnwhere other exchanger types (such as plate-and-frame units, spiral units andrnCompablocTM units) are often employed and where tube inserts can often be used tornrectify the adverse effects of installing a new exchanger into an existing system. In thisrnwork we show how thermo-hydraulic simulation can be applied to cooling waterrnsystems incorporating a wide range of different exchanger types. We then demonstraternhow coolers for installation into existing cooling water networks can be approachedrnusing systems analysis. However, we start by demonstrating the need for such anrnapproach by considering how coolers are currently designed.