AERCO SWDW68 U-Tube Double-Wall Heaters w/ECS - Manual (Page 21)

Rev B Mar 2013 3-1
CHAPTER 3 FUNCTIONAL DESCRIPTION
3.1 INTRODUCTION
The AERCO DW-series steam-to-water heat exchangers incorporate double–wall heat tubes, in which
steam circulating in a bundle of immersed double-wall primary tubes heats the service water in the heat
exchanger’s shell. The following Mechanical Description (3.2) briefly discusses how double-wall heat
tubes work and describes each of the principal steam-to-water heat exchanger components. The
Mechanical Description is followed by a discussion of the Electronic Control System (3.3), which regulates
the heat exchanger water temperature and activates alarms and shutdown processes in the event safety
limits are exceeded.
3.2 MECHANICAL DESCRIPTION
3.2.1 Overview
Referring to Figure 3-1, cold service water entering the heat exchanger through the Cold Water Input is
dispersed evenly throughout the heat exchanger shell. As the cold water flows upward, it is heated by
steam circulating through the immersed tube bundle. The heated service water exits through the Hot
Water Output connection in the upper head assembly.
AERCO
STEAM INPUT
CONDENSATE
OUTPUT
SHELL
COLD WATER
INPUT
HOT WATER OUTPUT
CONTROL BOX
RECIRCULATION
PIPING
RECIRULCATION
PUMP
UPPER HEAD ASSEMBLY
CXT-E CONTROL
VALVE
CXT-E ACTUATOR
LOWER HEAD
ASSEMBLY UPPER
TUBESHEET
LOWER
TUBESHEET
Figure 3-1. AERCO Steam-to-Water Double-Wall Heat Exchanger
The heating steam enters through the CXT-E Control Valve at the bottom of the heat exchanger
assembly and flows through the inner tubes of the double-wall tube bundle. The flowing steam transfers
its heat to the service water contained within the shell, condenses and exits through the Condensate
Output connection.
The flow rate of the heated water varies according to the demand for hot water. The flow rate of the
steam is regulated by the Temperature Controller in the Control Box so as to maintain the temperature of