Book - School of Science and Technology

218 Pumps and other auxiliary equipmentThe outer shell is often constructed in cast iron but may be of welded mild steel. Tubesmay be formed in steel or copper, the latter being the more usual material, and areindividually expanded into the tube plate which is commonly of brass, the formation inend view being staggered as shown in Figure 8.15(a). The steam chest, usually of cast iron,mounts the tube plate to the shell and provides facilities for steam and condensate pipeconnections as Figure 8.15(b). Since the tubes and tube plate are a heavy assembly, theyare sometimes provided with a trolley type runway within the shell to facilitate removalfor inspection: the pipe connections should be arranged to make this convenient.Calorifier-condensate cooler unitsReference has been made previously (p. 162) to the recovery of flash steam. In circumstanceswhere non-storage calorifiers are supplied with other than low pressure steam,discharge of the resulting condensate may give rise to problems and, in any event, apotential for energy saving will exist. Equipment suited to flash steam recovery is availablein the form of two heat exchanger shells close-coupled, as illustrated in Figure 8.16.The upper unit is a normal steam-to-water calorifier equipped with a trapped outlet whichdischarges a mixture of flash steam and condensate to a tubular heater battery in thelower unit. The hot water circuit is directed through the two heat exchangers in series andin counterflow.Plate heat exchangersConstructed as a `sandwich' from a number of corrugated plates which provide passagesthrough which separated primary steam (or water) and secondary water circuits flow,the appropriate number of plates to produce the required rate of heat transfer aremounted to a frame pulled together by long compression bolts; flanges on one endSteam inletHot water flowSteam trapCondenseoutletHotwaterreturnFigure 8.16 Steam-to-water calorifier and condensate cooler assembly