HEAT EXCHANGERS

Power Plant Basics

CLOSED

OPEN

by Bechtel Power Corporation

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 HEAT EXCHANGERS

POWER PLANT BASICS

BECHTEL POWER CORPORATION

This document is provided for the express use of training power plant
personnel. Any other use of this document requires the prior concurrence of
Bechtel Power Corporation.
 HEAT EXCHANGERS

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TABLE OF CONTENTS
11 Page

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I. INTRODUCTION 1

II. HEAT TRANSFER 2

I! A. Radiation 2
B. Conduction 2
IJ c. Convection 3

11 III. HEAT FLOW 4

IV. FLUID FLOW AND FLOW PATHS 5

t?

A. Fluid Flow 5
t)
B. Flow Paths 6

t1 v. SHELL-AND-TUBE EXCHANGERS 9

Jl A. Shells 9
B. Tube Bundles 13

~ c.
D.
Channels
Rear-End Enclosures
17
18

~ VI. FEEDWATER HEATERS 21

I VII. VENTING 25

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 . . . • ·-- •. ·- , - ·- . - , . - - -· * •• ·- •.•. ~ -· • •· .

TABLE OF CONTENTS (CONTINUED)

27
VIII. DRAINS

i IX. DIRECT CONTACT HEATERS 28

Principles of Deaeration 28
A.
B. Types of Deaerators 29

I x. CONDENSERS 31

I A. What is a Condenser? 31
31
B• . The Condenser's Job

I c.
D.
Parts of a Condenser
Condenser Major Features
31
32
35
I E.
F.
Conde~ser Waterboxes
Condenser Operation 37

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 I. INTRODUCTION

In power plants, it is the rotating equipment such as turbines, generators,

pumps, and fans that catches our attention as it transforms energy from one
form to another. Much less conspicuous, but just as important, is the quiet
transfer of energy that goes on in heat exchangers. The array of equipment
included in this term is so vast that this lesson is limited to direct
contact and shell-and-tube types. Surface condensers, a shell-and-tube type
heat exchanger, are also discussed.

1
 II. HEAT TRANSFER

Heat exchangers, as the name implies, transfer heat from one substance to
another. All three methods of heat transfer-radiation, conduction, and
convection-usually come into play to varying degrees in all heat
exchangers. Let's take a look at these three methods.

A. RADIATION

The process of heat transfer by radiation is similar to the passage of light

through space. Radiant heat, like light, travels in straight lines and at
the same speed as light (186,000 miles per second). Both are energy or wave
motions, but at different frequencies and wave lengths.

We are all familiar with the radiant heat from the sun, a fire, or a hot
stove. This form of energy transfer takes place without the aid of any
substance in between, working even in a vacuum. Radiant heat plays a
relatively minor part in power plant heat exchangers, since an extremely
high temperature is required to adequately transfer an appreciable amount of
heat.

B. CONDUCTION

Conduction is the process of transferring heat through a material from

molecule to molecule. The amount of energy moved, or the heat transferred,
depends on (a) the temperature difference between the two faces of the
substance, (b) the area of the heat path, and (c) the nature of the
substance.

In most heat exchangers, metal walls separate one fluid from another at a
different temperature. Heat or energy will flow through the walls by
molecular motion from the higher temperature fluid to the lower temperature
fluid.

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 C. CONVECTION

Convection heat transfer takes place by movement of the heated material

itself. Most liquids and gases readily transfer heat by means of
convection. When a liquid or gas is heated, it expands and becomes lighter
(less dense). The cooler and heavier portion will tend to push the heated
portion upward and displace it. In turn, the heavier portion is heated and
also pushed upward. The result is a continuous flow of the cooler fluid to
the heated area and the heated fluid to a cooler area, where it gives up its
heat to some material placed in the convection current.

If we move the liquid or gas by means of a pump, fan, or other device,

instead of depending only on natural currents resulting from the heating and
cooling action, we have "forced convection. 11 By forcing the fluid to flow
over the he~t source at higher velocities, we can raise the rate of heat
transfer, within limits. Faster forced flow of the fluid makes it possible
to carry heat at a greater rate to where it is wanted.

In heat exchangers, convection is an important aid to conduction. The

convection effect makes a fluid heated at a surface mix with nearby cooler
fluid and, in turn, heat it. In addition, movement of the heated fluid from
the heating surface allows a steady flow of cooler fluid to take its place
and also become heated.

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 III. HEAT FLOW

In all cases of heat exchange, the three forms of heat transfer are involved
to varying degrees. A typical example is heat flow from steam through a
tube wall into a fluid. Heat is carried to the tube surface and transferred
by a combination of convection, conduction, and radiation. (The radiation
effect is so small it can be ignored.) Heat then flows through the wall by
conduction to the inner surface, where it is transferred to the fluid by a
combination of conduction and convection.

Three factors control heat flow by pure conduction: (a) the temperature
difference between the surfaces, (b) the area of the heat path, and (c) the
nature of the substance.

The effect of the nature of the

substance can be graphically
shown. With the same
temperature drop between two
surfaces separated by the same
distance, a small area of metal
transmits as much heat as a much
greater area of vapor or gas.

Heat transfer is affected by the nature of the material and is measured by

the material's heat transfer coefficient. The heat transfer coefficient is
the rate at which a substance conducts heat. If three different materials
have the same cross-sectional area and the same temperature difference
between their surfaces, the respective rates of heat transfer depend
directly on their respective abilities to conduct heat, or their
coefficients of heat transfer.

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 IV. FLUID FLOW AND FLOW PATHS

A. FLUID FLOW

When a gas or liquid flows through a

tube in a laminar flow, the
{ @ ~ p LA,.N,\R FLOW )

velocity is fastest in the center of the stream and decreases uniformly to

zero at the tube wall.

TURBULENT FLOW
With turbulent flow, the velocity
varies less across the tube section.
Since turbulent flow usually steps up the coefficient of heat transfer, it
is the basis of the design point in heat exchangers. Turbulent flow means
more pressure drop, therefore more pumping power.

Fluids change temperature constantly as they flow through a heat exchanger.

How the temperatures of the two fluids in an exchanger vary depends on the
relative directions of flow and the respective natures of the fluids.

When two liquids or gases with constant specific heats are exchanging heat,
the area between their temperature curves is a measure of the total heat
being transferred. If the fluid inlet temperatures are kept constant,
increasing the heat transfer area does not cause an equivalent increase in
heat transferred. For given conditions, counter-flow arrangements transfer
more heat than parallel-flow arrangements and usually prove to be the most
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economical to use. This is because in heat exchangers with parallel flow,
temperatures can only approach each other, regardless of how much heat
transfer area is used.

Adding area to counter-flow heaters pays off' more than adding area to
parallel-flow heaters. If enough surface is provided, the leaving cold-fluid
temperature can be raised above the leaving hot-fluid temperature. This
cannot be done in parallel-flow heaters, where temperatures can only
approach each other, regardless of how much surface is used.

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 B. FLOW PATHS

Splitting fluid streams into several paths increases the heat transfer
surface between them for an exchanger of a given volume. The familiar
shell-and-tube exchanger does this by passing one fluid inside the tubes and
the other about the exteriors of the tubes, within the shell. Paths of
fluids through shell-and-tube exchangers can be varied in many ways,
depending on the job to be done.

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1. Single-pass tube and
single-pass shell
---
II

2. Two-pass tube and

single-pass shell ----

II)
3. Two-pass tube and

II two-pass shell
------
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 4. Four-pass tube and
two-pass shell. This
arrangement can be
duplicated by putting
------ ------
two heaters like (2)
in series for both tube
fluid and shell fluid
flows.

Shell fluid tends to take the shortest path from shell inlet to outlet.
This does not make use of the total surface available, so steps are taken to
make the shell fluid flow over the tube exteriors in all parts of the
exchanger. This is done by using an arrangement of baffles to control the
flow path.

1. Shell fluid will flow by the

shortest route from inlet
to outlet.
----- - - -----------

2. Sectional baffling_ leads shell

fluid to contact tube surface
along tube length.

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 3. Disk-and-doughnut baffling
is another method of control-
ling shell fluid flow.

4. Baffles with annular orifices

produce turbulence in the
shell fluid flow.

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 V. SHELL-AND-TUBE EXCHANGERS

Shell-and-tube heat exchangers are suitable for many jobs, such as feedwater
heating, lubricating oil cooling, compressed air cooling, heat reclaiming
from blowdown, transformer oil cooling, and water heating. These exchangers
are also used as gland condensers, vent condensers, hydrogen coolers,
transformer oil coolers, inter and after condensers on steam jet air pumps,
blowdown heat exchangers, deaerators, evaporators, and refrigeration
evaporators and chillers.

All are similar in construction. Materials selected depend on operating

conditions. In most exchangers, fluids in both shell and tubes flow
continuously during operation. When both fluids are liquids or both are
gases, there is usually no change of state, simply a change in temperature
in the fluids. In many of the heating types of exchangers, steam is the
energy supply. In giving up its heat, the steam usually condenses and is
returned to.the system.

Some idea of the diversity of types and services can be gained by studying
the main assemblies and component parts of these exchangers.

A. SHELLS

Shells house the tubes and direct the flow of one of the fluids. A
single-pass shell has the simplest construction, with inlet and outlet on
opposite ends. Connections may enter at any angle.

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A two-pass shell has a welded or packed baffle, and the inlet and outlet are
on opposite sides of the shell. This type of shell may be used for vapor,
gas, or liquid.

A divided-flow shell has a longitudinal baffle for vapor flow distribution

along the length in both directions. The condensate outlet is on the bottom.

:If.; - -
I
/
/- - - - - -.~- -,1
//
-;; -;; -=-=-:;;,:;f
i

A divided-flow shell without a baffle depends on two outlets, one

at each shell end, to distribute the flow through the full length. The
inlet is at the top.

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 A double divided-flow shell has two vapor inlets, two condensate outlets,
and two longitudinal vapor baffles. This type is used for very long
exchangers.

I;_:
f

A desuperheating feedwater heater has a baffle or shroud at the inlet to

confine the incoming superheated steam around the tubes with the hottest
water. This adds a few degrees to the water temperature that could not be
obtained from heating at the saturated steam temperature corresponding to
the pressur·e.

/
/

--- - - -- -
,L..- - - - - - -

A drain-cooling feedwater heater has a baffle or shroud before the

condensate outlet to confine condensate around the tubes carrying the
entering feedwater, before the condensate flashes to a low~r-pressure heater
to release its heat at a lower temperature. This adds a few degrees to the
feedwater temperature that. could not be realized for the same heat under
less pressure.

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 Some high pressure heaters may have both desuperheating and drain cooling
sections. These heaters may be installed in either the horizontal or
vertical position.

By helping to give uniform distribution of vapor to the tube bundle, steam

belts may reduce impingement erosion of the tubes caused by the entering
steam.
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II When shell fluid is clean and will not scale tube exteriors, welded tube
sheets may be used. This type of shell is usually employed on smaller heat

ll exchangers.

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 When· temperatures are expected to vary widely, shell expansion joints must
be provided on units with welded tube sheets.

Where more flexibility must be provided, an expansion bellows may be fitted

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on the shell.
expansion joints.
These bellows are more subject to corrosive action than

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B. TUBE BUNDLES

The layout of tube bundles must allow for expansion and for cleaning. Tube
pitch may be square or triangular, depending on the space needed for
cleaning the tube exteriors. Triangular tube pitches are recommended for
feedwater heaters.

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To avoid exterior tube erosion at steam inle-ts, tubes should be covered by
impingement baffles opposite the inlets. These turn the steam aside so that
it enters the tube bundle around the bundle's periphery. For effective
heater performance, baffles must fit snugly around tubes and to the shell
interior. Any openings allow steam or condensate to short circuit around
passes and thus fail to do an effective job. On the other hand, joints must
allow differential movement between shell and tubes caused by temperature
changes. Also it must be possible to separate tube bundle and shell for
inspection and repairs.

A straight tube bundle offers the advantage of easy mechanical cleaning of

tube interiors, but must be removed from the shell for exterior cleaning •

..........
·.' ·.:.....
..
·.:-:•

A U-tube bundle simplifies the expansion problem and reduces the number of
tube sheet joints. However, the tubes are difficult to clean mechanically.

A bowed tube bundle can be solidly bolted to the shell at each end. The bow
in the tubes takes care of differential expansion.

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To eliminate gasketed joints in a high pressure circuit, coil-type heaters
may be used. They are also used in small water heaters.

Single-pass tube bundles may be fitted with an expansion joint internal to

the shell to eliminate employing a floating head seal.

Bayonet tube bundles are used for some types of tank heaters. Steam enters
the center tube and returns through the annular space to the intermediate
fluid chamber.

Rolled tube joints are the most common method of fastening tubes in tube
sheets. Cold rolling flows the tube metal into annular grooves cut in the
tube sheet holes.

15
When considerable expansion must be handled, welded tube joints usually
remain tighter than rolled joints. Sometimes, rolled joints are also welded.

Double tube sheets give positive protection against accidental leakage of

either fluid into the other. If tubes leak in either tube sheet, the
leakage shows as a drip between the two sheets.

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 C. CHANNELS

Channel or heater head layout follows one of several basic. forms.

Bonnet heads direct the flow of fluid through the tube bundle. The low cost
of bonnet heads is offset by the need to disconnect piping for inspection of
the tube sheets.

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Channels and covers do the same duty as bonnets, but allow for easy
inspection of tube sheets by simply removing the cover. Two-piece
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construction is more expensive, because it requires an extra gasket seal.

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Integral tube sheet channels eliminate gasketed joints between head and tube
sheet. They are used for high pressure and high temperature fluids.
Partition plates may be welded in as needed.

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D. REAR-END ENCLOSURES

The type of rear-end enclosure used depends on the service needs.

A flat plate ·cover may be used on a channel formed by the shell end and a
welded tube sheet. The cover is bolted to the shell flange and must be
sealed with a suitable gasket.

A dished plate cover may be used on non-removable tube bundles. The cover
is sealed with a gasket or a suitable packing material and bolted to the
tube sheet flange.

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Another type of rear-end enclosure is a floating head~ A floating head may
incorporate a shell-cover design that reduces the clearance between the tube
bundles and shell wall. In this case, the tube bundle cover must first be
removed before the bundle can be pulled through the shell.

A floating head designed to readily allow tube bundle pull-through has a

separate shell cover. The tube sheet and cover move independently ·of the
shell. A large annular space exists between the tube bundle and shell.

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 An outside-packed floating head may incorporate a dished plate cover that is
bolted to the shell flange. The two outside packing rings are separated by
a lantern ring with weep holes. Evidence of leakage from either side shows
by drips coming from the holes in the lantern ring.

An outside...,packed floating head may incorporate a flat cover plate on a

channel with an integral tube sheet. The packed integral gland and gland
ring seal the shell and allow the floating head to move independently of the
shell as fluid temperature varies.
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 VI. FEEDWATER HEATERS

Feedwater heating is the process of heating the boiler water supply before
it enters the economizer. Feedwater heaters normally use steam bled from
the turbine as their energy source. Their prime purpose is 'to raise the
thermal efficiency of the steam and water cycle by use of the regenerative
heating principle. For feedwater heaters to effect an improvement in unit
efficiency, it is necessary that the feedwater be heated by steam extracted
from the turbine after it has passed through some of the turbine stages and
has done work. Steam withdrawn from the turbine at points between the first
stage of bleeding and the condenser will have already converted some of its
heat into work. Most of the remaining heat can be absorbed by the feedwater
as it is pumped to the boiler. The point of steam withdrawal is called
"bleed point." This cycle is called the regenerative feedwater heating
cycle, and although not all the potential work is realized from the heat of
the steam withdrawn, the heat remaining is returned to the cycle.

Depending on the space available, heaters may be mounted either horizontally

or vertically and either head up or down. A two-pass tube design needs a
long shell of small diameter, while a four-pass tube design uses a shorter
shell of larger diameter. Figures VI-1 through VI-4 illustrate typical

I extraction heater types.

The straight condensing horizontal heater (Figure VI-1) takes in bleed steam
at the top right and leads it around baffles for good contact along the full
tube length. Condensate falls to the bottom and drains off at the lower
left.

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 SHELL STEAM
INLET TUBE
SHELL RELIEF
CONNECTION
VALVE SHELL PRESSURE OUTLET

\ GAGE
I
"' SEALING
PLATE

/
SHELL DRAIN
TUBE
CONNECTION
INLET

FIGURE Vl-1 STRAIGHT CONDENSING

The desuperheating heater (Figure VI-2) leads superheated steam through an

enclosed entry section to raise the outlet water temperature to the maximum
possible level.

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SHELL PRESSURE SHELL STEAM TUBE
DRIP GAGE INLET CONNECTION
INLET SHELL RELIEF \ DESUPERHEATING / /OUTLET
\ VALVE \ ZONE BAFFLES
IMPACT '--'_ _'\._,
BAFFLE

SEALING
PLATE

J CONDENSATE
OUTLET TUBE
CONNECTION
INLET
J FIGURE Vl-2 DESUPERHEATING

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The drain cooling heater (Figure VI-3) has the bottom tubes shielded from
the main condensing sections. Condensate collects at the shell bottom,
completely covering the lower tubes. Subcooling zones can be concentrated
around the entering section of the f eedwater tubes or can extend along the
length of the shell.

SHELL STREAM TUBE

INLET CONNECTION
OUTLET

IMPACT SEALING
BAFFLE PLATE

CONDENSATE INLET
TO SUBCOOLING ZONE
TUBE
SUBCOOLING CONNECTION
ZONE BAFFLES INLET

FIGURE Vl-3 DRAIN COOLING

Three-step heaters (Figure VI-4) desuperheat, condense, and cool drain

condensate to achieve maximum possible thermal gain in the feedwater-heating
cycle when bleed steam is superheated.

SHELL PRESSURE
DRIP GAGE TUBE
INLET CONNECTION
OUTLET

IMPACT
BAFFLE

DRAIN SUBCOOLING
ZONE BAFFLES
TUBE
CONNECTION
INLET

FIGURE Vl-4 DESUPERHEATING AND DRAIN COOLING

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rl!
n Successful performance of feedwater heaters depends on proper venting and

r correct draining.
operation.
These apparently minor considerations make or break the

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 VII. VENTING

As steam condenses in either a horizontal or

vertical (Figure VII-1) heater, the
condensate falls to the shell bottom and
forms an effective seal against steam
blow-through. However, this seal also
prevents noncondensable gases from leaving
.the heater • Any accumulation of
noncondensables can "air-blanket" a heater,
reducing its effectiveness or even putting
it out of action completely. This becomes
BLEED
especially critical in heaters operating STEAM
below atmos~heric pressure. In fact, closed
heaters operating at subatmospheric VENT
pressures can and will lose their heat i
transfer capability within a few minutes if
precautions are not taken.
The cause is twofold: 1) loss of
l temperature differential,
in the average heat-transfer
and 2) reduction
coefficient.
ORAi~

FIGURE Vll-1 VERTICAL HEATER

J · Both come from a buildup of noncondensable
gases within the heater.

l A closed feedwater heater is primarily a condenser, even though a

desuperheater and/or a condensate subcooler are made an integral part of
l it. Incoming steam vapor, plus some entrained noncondensable gases, enters
the condensing space, and most of the liquid condenses out. Condensate
1 leaves from a bottom connection, wnich, as previously mentioned, is always
under an effective liquid seal. Unless special exits are provided, the

1 noncondensables can move no further and tend to build up in concentration.

Therefore, vents should be located at each end of the steam space (Figure
VII-2). In addition to removing gases, the vents help to distribute the
] steam uniformly throughout the shell, thereby making better use of the
available heat transfer surface.

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 BLEED
IMPACT
STEAM~
BAFFLE
AIR SHROUD
OPENING
AIR
SHROUD

VENT "-.. CONDENSATE VENT

OUTLET

FIGURE Vll-2 VENT PLACEMENT

Baffles in the shell at the entrances to the vent holes make the gas-laden
steam flow first over the coldest tube pass, in order to condense out as
much steam as possible. Each heater can be vented to a heater of
successively lower pressure, with the lowest-pressure heater vented to the
air cooling section of the main condenser. At times, vents are led to a
common header that goes to the main condenser; in other systems each heater
vents individually to the condenser. Still others have vents to the air
pump, or combinations of the foregoing.

Any vent piping system needs suitable regulating valves to permit optimum
gas withdrawal. Only by experiment can this rate be established. By
definition, it is the smallest opening that has no appreciable effect on the
terminal temperature difference. Excessive venting wastes high grade
uncondensed steam.

For a day-to-day check on operating effectiveness, heater data should be

followed closely. If there is any sudden decrease in heat transfer in the
feedwater heater, its cause is almost certainly in the venting system,
especially if the temperature of the condensate drains shows a corresponding
drop.

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 VIII. DRAINS
n
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Positive removal of collected condensate is
a vital part of any condensing process. It FEEDWATER FEEDWATER
can be done intermittently or continuously, IN OUT
n
11 but whatever the method, an effective seal
must be maintained at all times to prevent
blow-through of uncondensed vapor with an
accompanying loss of latent heat.

Condensate or drain must be held within

narrow limits. If the condensate rises too LEVEL
high in either vertical or horizontal CONTROLLER
NORMAL
heaters, ac-tive condensing surface is put LIQUID
LEVEL
out -of service. If the condensate drops
too low in a vertical heater with a FIGURE Vlll-1 VERTICAL CONDENSATE
subcooling zone (Figure VIII-1), live steam
t discharges through the drain and subcooling drops off. If this happens in a
similar horizontal heater (Figure VIII-2), subcooling again drops off.
Close regulation is more critical in a horizontal heater, because. a greater
percentage of the effective tube condensing surface is covered by a small
rise in condensate level than in a vertical heater.

FEEDWATER NORMAL
OUT LIQUID
LEVEL LEVEL
CONTROLLER

.
--t"''"'11a-.'

FEEDWATER
IN

REGULATING/
VALVE

FIGURE Vlll-2 HORIZONTAL CONDENSATE

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 IX. DIRECT CONTACT HEATERS

While most feedwater heaters are of the closed type, some open types are in
use. These mixing, or direct contact, heaters break up the feedwater into
small particles to present the greatest surface for vapor absorption. This
process is known as deaeration.

A. PRINCIPLES OF DEAERATION

There is a physical law stating that the solubility of any gas in a liquid
is directly proportional to the partial pressure of the gas above the liquid
surface. Another law states that the solubility of a gas in a liquid
decreases with an increase in temperature of the liquid. Also, experience
has shown that more rapid and more complete removal of noncondensable gases
from a liquid occurs when the liquid is vigorously boiled or scrubbed by
condensable carrier gas bubbles.

To make efficient use of these facts, the deaerating heater must be designed
to heat the feedwater to as high a temperature as possible, namely, the
temperature corresponding to the steam pressure. It must then vigorously

'I boil and scrub the heated water with fresh steam, which can carry any traces
of unwanted oxygen or carbon dioxide to the liquid's surface.

low as possible, particularly at the

The partial
pressure of the waste oxygen and carbon dioxide in the steam atmosphere must
be maintained as point where the

I deaerated water separates from the steam. Finally, noncondensable gases

must be continually withdrawn from the heater at the rate at which they are
being liberated. To avoid waste o( steam, an efficient vent condenser is
r required to concentrate the noncondensable gas mixture as it leaves the
heater.

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 B. TYPES OF DEAERATORS

Three types of deaerators are cormnonly used:

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a. Spray deaerator. The spray deaerator sprays feedwater into a
steam-filled space, where it is heated and scrubbed to
release gas. As fresh steam enters the unit, the feedwater
undergoes a second agitation to liberate most of the remaining
impurities.

b. Tray deaerator. The tray deaerator directs feedwater into a

series of cascading trays. Water falls from tray to tray by
overflowing or by passing through small holes. Steam, which
engulfs the trays, heats and deaerates the water as it falls.

c. Combination heater. The combination heater brings the spray

and tray principles together (Figure IX-1). Feedwater first
sprays into a steam-filled space, then rains down on a series
of trays through which it passes for further agitation and

I scrubbing.

I In the combination heater, live steam entering the deaerator

meets the hottest water first, stripping it of dissolved gas.
Carrying this gas along, the ~team moves across and up through
I the cascading water, gathering additional impurities as it
flows. As it moves upward in the deaerator the steam is
J gradually condensed. Noncondensable gases are drawn off at a
high point in the unit, where little steam remains.

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PERFORATED

I DEAERATING
TRAYS

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HORIZONTAL SHELL ON

I HORIZONTAL STORAGE TANK

I OUTLET TO SERVICE

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I FIGURE IX-1 COMBINATION HEATER

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 X. CONDENSERS

A. WHAT IS A CONDENSER?

A condenser is a vacuum-tight shell-and-tube heat exchanger in which the

cooling water flows through the tubes while the turbine exhaust passes over
the outside of the tubes.

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Surface condensers are a very important turbine auxiliary. Turbines could
operate without condensers by exhausting steam into the atmosphere, but that
process would be very uneconomical. Makeup water demand would be great, heat
energy in the steam would be wasted, and turbine size would be restricted.
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B. THE CONDENSER'S JOB
I Surface condensers do two big jobs. First, and usually most important, they

I reduce back pressure on the

extracted from the steam.
turbine so
Second,
that maximum heat energy can be
surface condensers recover low-oxygen

I content, full-temperature condensate.

C. PARTS OF A CONDENSER
I
Figure X-1 is a basic diagram of a condenser. It shows the following parts
I and assemblies:

I 0

0
low pressure exhaust trunk
condenser tubes

I 0

0
tube sheet
inlet water box
outlet water box
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0

0 manhole
0 hotwell
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I LOW-PRESSURE EXHAUST T R U N K ~

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I TUBESHEET-i+------i1•1 ________c_o_N_D_E_NS_E_R_T_u_e_e________~

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I OUTLET INLET

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I HOTWELL

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I FIGURE X-1 DIAGRAM OF A BASIC CONDENSER

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D. CONDENSER MAJOR FEATURES
I
1. TUBE LAYOUT

I All tube surfaces take an active part in carryingi, away the latent heat of

I condensing steam. Modern condensers use an open arrangement for the tubes
. hit first by high-velocity exhaust steam. As steam penetrates deeper into

I the tube bank and condensation reduces

becomes closer.
the steam's volume, tube spacing
The tightest tube arrangement is usually found in the air
cooler section.
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I 32

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2 • HEATING-DEAERATING

A portion of steam coming directly from the turbine exhaust bypasses the
condensing tubes and is used to scrub the condensate on its way to the
hotwell. This deaerates and heats the condensate for introduction into the
feedwater system. The hotwell stores the condensate.

3. CONDENSER SUPPORT

There are four basic schemes for providing condenser support:

a. The condenser may be anchored firmly to the foundation, with

expansion taken up by the turbine exhaust pipe.

b. The exhaust pipe may be rigidly attached to the condenser,

with expansion taken up by spring supports.

c. The condenser may be attached rigidly to the exhaust pipe and

suspended therefrom.

d. The condenser may be mounted on the foundation and supporting

turbine.

4. DIFFERENTIAL EXPANSION

Differential expansion between the shell and tubes may be taken care of by
shell expansion joints (Figure X-2) • The tube ends may be fixed and the
tubes bowed, with fixed or sliding support plates. Or, one end of the tubes
may be fixed and the other end packed with fiber and metallic rings to allow
the tube to slide.

In addition to taking care of expansion, bowed tubes allow drainage when the
condenser is not operating. Bowing has also been used to prevent tube
vibration.

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I FIGURE X-2 SHELL EXPANSION JOINTS

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I 5. CONDENSER TUBES

Condenser tubes are usually expanded and flared at the inlet and expanded or
I packed at the outlet (Figure X-3). Serrations are sometimes used at inlets,
as are ferrules, with or without packing. Belling the inlets improves flow
I at tube entrances.

I
I
I
I FIGURE X-3 TUBE SEATING ARRANGEMENTS

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6. TURBINE EXHAUST EXPANSION JOINTS

I Figure X-4 shows some of the methods for allowing expansion between the

I turbine and the condenser neck:

a.
I b.
copper or stainless steel
copper or stainless steel
c. copper with stainless steel protectiop
I d.
e.
stainless steel
rubber

I f. slide joint with rubber hose and condensate seal.

I
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I d
e

I FIGURE X-4 TURBINE EXHAUST EXPANSION JOINTS

I
E. CONDENSER WATERBOXES

Together, the tube sheet and the condenser head make up the waterbox.

Waterboxes distribute cooling water to and from the condenser. Partitions

are used in the waterboxes according to the number of water passes in the
condenser.

I In a single-pass condenser, no partition is needed in the waterboxes,

because circulating water enters the front waterbox and discharges through
the back waterbox (Figure X-5).

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f
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I FIGURE X-5 SINGLE-PASS WATERBOX

'l In a two-pass condenser, the front waterbox is divided in half. The

circulating water enters one section of the front waterbox, passes through
t approximately one-half of the tubes to the back waterbox, reverses flow, and
passes through the remaining half of the tubes to the second section of the
front waterbox, where it is discharged (Figure X-6).

BAFFLE

....,_ WATERBOX

FIGURE X-6 TWO-PASS WATERBOX

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I A divided waterbox condenser has a partition in both the front and back
waterboxes. This permits half of the condenser to be operated at one time,
I permitting cleaning to be performed on the other half, when necessary, while
condenser and turbine remain in operation. Divided waterboxes are provided
I with duplicate inlet and outlet circulating water nozzles so that each half
of the tubes has an independent circuit of circulating water (Figure X-7).

I BAFFLE
BAFFLE

I
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I FIGURE X-7 DIVIDED WATERBOX

I F. CONDENSER OPERATION

I As shown in Figure X-8, steam from the low pressure

condenser through the low pressure exhaust trunk.
turbine enters
The steam circulates at
the

I high volume around, and makes contact with, the condenser tubes, which carry
cool water.

I Heat from the steam flows into the cooler water, and the water then carries
the heat away. The heat is thus rejected from the system.
I
The difference in temperature between the steam and the water acts as a
I driving force to set up a flow of heat from the area of higher temperature

I 37

I
- - - - - - - - - - 1

VAPOR 1111
TUBE SHEET
REHEAT
STEAM·

l
BAFFLE
AIR COOLER CONOEIIISER TUBES

l,.)
WATER
OUT
------
00

WATER ...__,,,._.,,. ,,,

1111 ""'
-- ----------
• I ' a • o ' O ' .,•

CONDENSER SHELL
WATER BOX WATER BOX

CONDENSATE OUT

FIGURE X-8 HORIZONTAL SHELL AND TUBE CONDENSER

I
I to the area of lower temperature. As the heat is conducted out of the

I steam, the energy of the steam is lowered.

the steam turns to water. Toe water falls
Condensation takes place,
into collecting trays
and
located

I below the condenser tubes.

sides.
The trays fill with water, which spills over the
Here, it comes into contact with some of the steam and is scrubbed
and reheated. Toe air and noncondensables that are released flow to the air
I cooler section of the condenser, where they are removed.
reheated condensate is collected in the hotwell to be pumped back into the
Finally, the

I system, thus completing the heat exchange process.

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I 39