Published for the 2013 EPRI Feedwater Heater Technology Seminar
Author: Thomas J Muldoon, PE and President of American Exchanger Services, Inc. (AM-EX).
In Electric Power Research Institute (EPRI) conferences during the 70’s and 80’s, discussions on high reliability feedwater heaters included consideration of the use of long partial pass drainscoolers (L-DC) in horizontal feedwater heaters. The result of these reports was a recommendation by EPRI to use L-DC’s for greater reliability than the S-DC. These reports point out that the external DC’s are the most reliable and efficient but are considerably more expensive. Since then, contrary to the EPRI recommendations, there have been very few long drainscoolers or even external drainscoolers put in service in the United States. Short full pass drainscoolers (S-DC) are the standard. While S-DC have provided good service, there have been many heaters replaced or expensive repairs made due to problems with the design and operation of these zones. Many utilities have experienced high drainscooler approaches, shroud weld failures, water hammer in outlet piping and tube failures as a result of the operation of the S-DC. The L-DC design is more robust and less sensitive to low pressure and off-load operation. Eliminating the drainscooler end plate (DCEP) through the use of a L-DC, eliminates many of the problems associated with the S-DC. Submerging the shroud also reduces the high cost of shroud weld issues. The principal advantage of the S-DC is a slightly lower cost and simpler thermal design than the L-DC.