Section 2.

6
CONDENSATE POLISHING

Huge volumes of treated water are evaporated to produce steam for heating, process use, and
power generation in commercial, institutional, industrial, and utility plants. When condensed, at
temperatures ranging from 150-300°F (66-149°C), the product water is a valuable resource, and
its recycle is considered essential to the economics of steam and power production. The value of
this condensate includes the cost of water, sewer, initial treatment, and its intrinsic heat value.

Contamination can occur in both the vapor phase (steam) and liquid phase (condensate).
This can take one or more forms that are dependent on a number of factors:
• Boiler operating pressure and steam temperature
• Boiler water chemistry
• Amount and type of mechanical liquid carryover from the boiler, e.g., boiler salts
• Volatilization and carryover of dissolved substances in the steam, e.g., silica
• Dissolved solids leakage from condensers and heat exchangers, typically raw or treated water
• Process system in-leakage, both inorganic and organic
• Dissolved and suspended solids and metals from corrosion of metal components
• Condensate recovery system chemistry
• Entrained, dissolved, and evolved corrosive gases, e.g., CO2, O2, NH3, H2S, and SO2
• Lubricants, sealants, and hydraulic fluids from mechanical equipment, such as pumps and
compressors
• Products of reactions between treatment chemistry and dissolved gases, e.g., amine or
ammonia bicarbonates
• Decomposition products from organics intentionally or unintentionally added to the system,
e.g., acetic acid, formic acid, glycolic acid, and CO2

INTRODUCTION
In many low-pressure steam plants, condensate developing filtration systems for the removal of
can be reused with little concern for the trace corrosion products such as iron and copper
impurity content. The use of higher pressure and oxides (typically referred to as crud) and hydro-
temperature boilers makes these impurities more carbons. It soon became apparent that the trace
troublesome. Under these conditions, they can levels of soluble salts from various sources of
cause deposition and corrosion, leading to contamination also had to be removed. This led
overheating and failure of the tube metal. to utilization of ion exchange units following the
filters. Because of the low concentrations of
In order to prevent damage to system compo- impurities involved, the term condensate polish-
nents such as boilers and turbines, manufacturers ing was applied.
established standards for the purity of high-
pressure boiler feedwater and steam that re- Early installations confirmed that ion exchange
quired treatment of the condensate streams. condensate polishers could operate at higher
Early forms of treatment concentrated on flow rates than those normally used for makeup

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CONDENSATE POLISHING

preparation without significantly sacrificing • Increases the overall efficiency of the system,
quality or capacity. It was also demonstrated primarily because internal surfaces and turbine
that resin beds, compacted by higher flow rates, blades remain cleaner because deposition is
could successfully filter out some of the particu- reduced
late metal oxides without sacrificing the ability
to remove ionic contaminants. As a result of • Helps conserve energy by reducing boiler
these findings, capital investment and space blowdown and makeup requirements
requirements for condensate polishing without • Extends turbine operating runs. As a rule,
filtration were substantially reduced. The turbines operate at 90-100% load for 5 years
process became widely used, particularly in (30-year total life). Reducing condensate
utility power generation facilities where mixed contaminants allows the turbine to operate at
bed polishers were installed. higher efficiency for a longer time, giving
substantial fuel savings.
In industrial plants, the use of mixed bed
• Recovering the heat content of condensate
demineralizers as condensate polishers was
reduces boiler fuel costs
largely limited to petrochemical, chemical, and
fertilizer plants. In such plants, relatively high • Elimination of contaminating solids, corrosion
quality condensates were commonly recovered products, and silica reduces tube deposits, acid
from process operations, and boiler makeup as a cleanings, and potential failures. Increased
percentage of feedwater was lower than in steam purity reduces the need for turbine
many industries. In the pulp and paper industry, caustic washing, thereby reducing
which operated at lower boiler pressures, higher maintenance on both the turbine and washing
percent makeup, and with higher condensate system.
contaminant concentrations, the installations
• Increases the boiler load factor. Having a purer
used strong acid cation resins in the sodium
condensate because the total dissolved solids
cycle for hardness and particulate removal.
(TDS), iron, and copper are removed reduces
However, increases in operating pressures for
the deposit-forming potential of the boiler
black liquor recovery boilers have resulted in
feedwater. Thus, more heat can be applied,
the application of mixed bed polishers in that
allowing the boiler to carry a higher average
industry as well.
load.
In some high-pressure plants, the pre-filtration • Increases boiler availability because of fewer
systems may use powdered resin precoat and be outages and faster start-ups and restarts.
in service during normal operations while the • Allows time to plan and organize for a
mixed beds are in service during start-up, with shutdown after experiencing a condenser tube
high crud loads, or during periods of high leak, when using high TDS water for
volume condenser leaks. Filter systems are also condenser cooling.
installed downstream of condensate polishers to
remove resin fines and broken beads released • Allows the use of condensate that would
from the polisher resin beds. Filter systems may otherwise need to be sewered.
be the only external treatment applied in low-
pressure applications.

The following benefits are derived from the use CONDENSATE FILTRATION
of properly selected, designed, and operated SYSTEMS
condensate polishing systems: Filtration systems are used alone or in conjunc-
tion with ion exchange systems. Filters usually

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CONDENSATE POLISHING

require a lower capital investment, are typically leaks that can foul the mixed bed condensate
cheaper to operate and maintain, and generate polishers downstream.
little or no waste as compared to ion exchange
systems. However, they are limited to applica- Special grades of low-ash, activated carbon are
tions where the main condensate contaminant is needed to minimize contamination of the
particulate in nature (typically iron and copper), effluent. Contamination would add to the ionic
and hardness or other contaminants are either loading of downstream treatment systems such
absent from the condensate or not objectionable as mixed bed polishers. There are many types of
at the levels present. activated carbon, which may be petroleum based
or made from materials such as coconut shells.
The following are examples of the type of The ash content of such carbons varies consider-
filtration systems that are commonly used to ably. Industrial and commercial demand for
treat and recover condensate. activated carbon sometimes causes extreme
shortages of low-ash carbon.

BAG FILTERS Even low-ash carbon leaches undesirable

These consist of a pressure container with one or impurities into the effluent. Leaching declines
more woven bags. The bags are of a material slowly with time for some carbon materials,
resistant to the condensate chemistry and while others continue to leach high concentra-
temperature and are supported on an internal tions of contaminants for considerable time.
structure to expose as much surface area as Some supposedly low-ash carbons leached a
possible. Condensate entering the unit must pass combined calcium and magnesium of approxi-
through the bag to reach the outlet. Particulates mately 20 ppm, silica of 1 ppm, sodium of
are removed by straining until such time as 2.5 ppm, and chlorides of approximately
pressure differential indicates that bag replace- 20 ppm. Condensate contamination from
ment is required. carbon filters results in premature exhaustion
of the ion exchange polishers downstream,
Frequency of replacement is dependent on leading to early regeneration.
influent quality. This type of filter is usually
effective for coarser particles only, and effluent As a result of leaching problems, the use of this
iron may be 0.1 ppm or higher. It is typically not equipment is often restricted to times when
suitable for high-pressure, high heat transfer rate condensate contamination from hydrocarbons or
boilers. This design cannot be used with precoat other organics is detected or anticipated. Detec-
materials or polymers to enhance performance. tion is dependent on successful operation of an
analyzer that will detect the hydrocarbon or
Maintenance costs are high because of the labor organic. In-line monitors linked to automatic
requirement for bag changing and the cost of dump systems can provide reliable protection if
replacement bags. the system is designed properly, valves are
exercised monthly, and sensors are calibrated as
recommended by their suppliers.
CARBON FILTERS
Large pressure filters containing deep beds of Carbon filters are quite successful at adsorbing
activated carbon have been installed in some hydrocarbons. However, their volume capacity
high-pressure steam plants in the petrochemical is limited, and once consumed, they must be
and chemical industries. These provide protec- restored by external rejuvenation. This cannot be
tion against hydrocarbon and process chemical performed in-situ with steam as the temperature
can neither be elevated sufficiently nor main-

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CONDENSATE POLISHING

tained suitably long to accomplish restoration. Condensate entering the units must pass through
The only option available is off-site charring or the cartridges to reach the outlet. Particulates are
incineration at a commercial facility. Unfortu- removed principally by straining until such time
nately, the material returned will most likely as pressure differential or particle breakthrough
have a higher ash content and higher leachables indicates that replacement is required. Practical
than the original material. experience indicates metal particulates smaller
than 5 µm in size are not removed by cartridge
filtration without greatly decreasing cartridge
CARTRIDGE FILTERS service life.
Cartridge filters consist of pressure containers
filled with disposable cylindrical cartridges, Frequency of replacement is dependent on
which are 0.75-10 inches (19-254 mm) diameter influent quality. This design cannot be used with
and of appropriate lengths. The cartridges are precoat materials or polymers to enhance
commonly made of special materials that are performance.
resistant to the condensate chemistry and
temperature and are supported on a wire core. Maintenance costs can be high because of the
A variety of materials are used including cotton labor requirements for cartridge changing and
yarn, synthetic yarns, pleated paper, specialty the cost of replacement cartridges.
products, and stainless steel. When stainless
steel is used, the filters are employed with
various types of applied precoat materials, and ELECTROMAGNETIC FILTERS
the elements are not disposable. Natural or Electromagnetic filters, such as the one illus-
synthetic yarns are wound in selected patterns in trated in Figure 2.6.1, are used primarily for iron
one or more layers to provide specific removal removal from condensate. These units consist of
capability. The number of cartridges required nonmagnetic pressure vessels filled with a
and their filtration capacity varies with influent matrix of magnetically susceptible metal mesh
viscosity, suspended solids content, system or type 430 stainless steel balls. The vessels are
pressure, and particle size retention. surrounded on their exteriors by a coil that
creates a magnetic field greater than 5 kilogauss.
Cartridges are rated by pore size and are avail- Magnetically susceptible iron and copper
able in a variety of grades ranging from 0.5- particles are captured on the matrix media when
400 µm nominal. They can also be provided the electromagnet is energized and condensate is
with absolute particle size ratings. Absolute passed through the unit. Greater than 95% of the
ratings signify 100% removal of the specified magnetite present in condensate can be removed.
size particles. If cartridges with very small,
absolute ratings are installed in a condensate Weakly magnetic species such as hematite and
stream with high concentrations of relatively copper can also be removed; however, conden-
large particulates, the cartridges will plug sate with high percentages of hematite (Fe2O3) is
rapidly and must be replaced frequently. Selec- usually treated with a strong reducing agent to
tion of cartridge rating can be difficult, espe- ensure conversion to the magnetite (Fe3O4) form
cially where particulate size varies considerably. and improve removal rates. The pH of the
It is sometimes necessary to install a number of condensate stream will affect the filter perfor-
filters in series with pore size ratings becoming mance. Ideally, a pH between 9.3 and 9.5 should
gradually smaller. be maintained to optimize removal. Temperature
and flow rate also influence the efficiency of an
electromagnetic filter. In practice, condensate
containing a high percentage of magnetite sees

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CONDENSATE POLISHING

good removal at flow rates up to 1.1 ft/s (0.34 POROUS BLOCK FILTERS
m/s) with a sphere matrix filter and 450 gpm/ft2 Filter elements for these units can be made of
(1100 m3/h/m2) of media with a mesh-type carbon, graphite, stainless steel, or Teflon in a
matrix filter. Depending on conditions in a wide variety of porosities and forms. They are
particular application, over 90% of the total iron corrosion and temperature resistant and function
and over 50% of the copper may be removed. very well for many applications. However, the
pores plug rapidly from condensate with high
When the pressure drop across the unit has particulate loading and cannot be cleaned by
reached a predetermined limit, the unit is simply simple methods such as backwashing. If used
isolated from the system, de-energized, and with a suitable precoat material on the filter
backwashed. element, such filters can be effective in conden-
sate service.
Electromagnetic filters may be used either alone
or as prefilters ahead of ion exchange demineral-
izers, depending on polished condensate purity PRECOAT FILTERS
requirements. Electromagnetic filters have been There are two basic types of precoat filters:
found particularly useful in utility power plants
and in paper mills, where large amounts of iron 1. Tubular element
are present during start-up and shutdown of 2. Plate-and-frame or disk type
paper machines. However, many industrial
plants lack the power necessary to operate Whatever the type, design of the elements is
such devices. critical for successful operation. They must be
corrosion resistant and sufficiently rugged to
prevent damage or distortion from a high
pressure differential. The open area must be
sized to retain the precoat material effectively,
but still allow adequate condensate flow at
satisfactory pressure differential.

Precoat materials may include silica-free cellu-

lose fiber, powdered carbon, diatomaceous earth,
or combinations of these materials. Diatoma-
ceous earth is not suitable for all applications, as
it will leach silica into the filtrate under some
service conditions. Similarly, carbon may leach
dissolved impurities such as hardness and
carbon fines into the effluent. Some cellulose
materials can operate at temperatures up to
248°F (120°C) in non-alkaline conditions but
become less effective and difficult to remove
under higher pH conditions.

Figure 2.6.1 – High gradient magnetic

condensate filter

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CONDENSATE POLISHING

Design operating flow rates are usually 2-5 gpm/ Tubular Element
ft2 (5-12 m3/h/m2) of filter surface area, but this These units are usually vertical pressure vessels
varies slightly with precoat media type as well filled with tubular elements suspended from an
as contaminant concentration. Such filters can upper plenum plate. (See Figures 2.6.2 and
handle high loads of insoluble iron, yielding 2.6.3.) The elements may be of porous materials,
filtrates generally with less than 25 ppb. They carbon, fine mesh screen, or spiral wound wire
can remove up to 20-30 ppm of oil present in the (such as stainless steel well screen).
condensate from reciprocating engines and other
sources. Oil removal generally requires a Condensate enters the unit at the bottom, passes
continuous body feed of the media, in addition through the precoat material on the outside of
to the precoat application, at a ratio approxi- the tubes, and up the tube into the collecting
mately equal to 1.5-2.0 parts media to 1 part chamber at the top. The elements are precoated
oil in order to absorb and hold the oil in the prior to the service cycle, continuously fed with
filter cake. Filtrate oil levels of 1 ppm or less a precoat body feed, and when they become
are achievable provided the filter is operated dirty, are cleaned by compressed air and back-
properly. wash water.

The media precoat is typically applied at

8-10 lb/100 ft2 (0.4-0.5 kg/m2) of filtering area
with a coat thickness of 1/16-1/8 inch
(1.6-3.2 mm). It is first applied as a slurry to a
recirculating flow through the elements. Recir-
culation is usually more than 15% of the design
service flow and is continued until clear filtrate
is seen. The time required to precoat is generally
4-5 times that required to displace one vessel
volume. Condensate is the desired slurry water,
but if the condensate is hotter than 212°F
(100°C), flashing will occur, and another
source of suitable water should be found.

The expected service runs can vary from 4 days

to 4 weeks dependent on condensate quality.
If service flow through the unit stops for any
reason, the precoat cake may fall off the ele-
ments, and the unit must be backwashed and
precoated again.

See the Ion Exchange section following for the

use of precoat media containing ion exchange
resins.

Figure 2.6.2 – Clarite vertical precoat

condensate filter

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CONDENSATE POLISHING

Figure 2.6.3 – Precoat filtration and demineralization

Plate-and-Frame
This design usually consists of a horizontal
cylindrical pressure vessel with a hinged,
removable head at one end. The vessel contains
a number of vertical circular disks placed at
suitable intervals along a central effluent outlet
shaft. The disks are constructed of an internal
coarse screen covered on both sides with a finer
polypropylene cloth or a wire cloth septum.
(See Figure 2.6.4.)

Condensate flows into the pressure vessel,

passes through the precoated disks, and into
the central effluent pipe.

A high differential pressure indicates when Figure 2.6.4 – Horizontal precoat condensate
the disks are dirty. They are then sprayed filter
with water, while rotating, to wash off the
accumulated media cake and particulates.
The accumulated media and removed crud
are flushed out of the bottom.

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OIL REMOVAL FILTERS The major differences between utility, and

Removal of oil from condensate can be a major process plant condensates are temperature, the
operating problem with a high capital cost. The amount and kind of contamination, and quality
precoat filters previously mentioned can be quite of effluent required. Temperatures of utility
effective but costly to operate. There are propri- condensate usually range from 70-120°F
etary filter designs also available, but they have (21-49°C) and higher; process condensate
mostly been applied for the removal of gross temperatures commonly range from 180-230°F
amounts of hydrocarbon from waters other (82-110°C) and higher.
than condensate used as boiler feedwater. For
example, they use walnut and pecan shells as When it became possible to use ion exchange
media and mechanical agitation for oil removal. resins at high flow rates (25-50 gpm/ft2;
61-122 m3/h/m2) for condensate polishing
At one time, pressure filters containing beds of without filters, several options became available.
anthracite were commonly used for oil removal. One uses sodium cycle cation exchange. Another
These incorporated a precoat and a body feed of uses conventional deep mixed beds of cation
soda ash and aluminum sulfate floc to adsorb the and anion exchange resins. Still another uses
oil. Use of this system has been discontinued thin layers of regenerated mixtures of powdered
because of the possible formation of tenacious cation and anion exchange resins applied to
aluminum based scales in boilers. septum filters.

STRONG ACID CATION CONDENSATE

CONDENSATE POLISHING BY ION POLISHERS
EXCHANGE
The resin used in ion exchange systems to treat Sodium Cycle – In-situ Regeneration
or polish condensate may be categorized as: Strong acid cation sodium cycle polishers,
commonly referred to as high-rate sodium cycle
• Strong acid cation resin
polishers, are widely used in industrial boiler
• Mixed (cation and anion) resin systems operating up to a range of 900-
1500 psig (6.2-10.3 MPag). This type of system,
• Powdered mixed (cation and anion) resin
which is regenerated in place, is illustrated in
Figure 2.6.5. Iron and copper particulates are
The systems or process may be further described
removed by filtration that takes place primarily
by:
in the top of the bed. Other cations such as
• Regenerated ionic form in which the resin is calcium, magnesium, and dissolved iron and
operated, i.e., strong acid cation resin in the copper are also removed by ion exchange. Any
sodium form, amine form, or ammonia form amines or ammonia present in the condensate
and mixed bed demineralizers in the are exchanged as well. All ionic substances
hydrogen/hydroxide form or ammoniated form removed by the ion exchange mechanism are
• Method of regeneration, i.e., in-situ or replaced in the condensate by equivalent
externally with resin transfer amounts of sodium ion.

• Regenerable resin or non-regenerable

(disposable) resin

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 Section 2.6
CONDENSATE POLISHING

Figure 2.6.5 – High-rate sodium cycle condensate polishing system (in-situ regeneration)

Because of the increase in sodium concentration, including condition and design of the internal
the effluent from this system is unsuitable for distribution and collection systems. These
use in steam attemperation. In addition, the factors are outlined in detail below.
increased sodium must be considered for its
effect on the boiler drum chemistry during Service Flow Rate – Success of this system is
routine operation (especially coordinated largely dependent on the use of a high flow rate
phosphate and Phosphate Continuum type as measured in gpm/ft2 (m3/h/m2) of unit cross
programs) and as a result of inadvertent sodium sectional area. The flow rate on individual units
increases following regeneration and rinsing. should be higher than 22 gpm/ft2 (54 m3/h/m2) to
maintain bed compaction and filtering capability
Because cation resins are stable at temperatures and less than 35 gpm/ft2 (86 m3/h/m2) to prevent
up to 300°F (149°C), they can be used for excessive pressure drop, bed channeling, and
sodium cycle polishing of process (industrial) resin breakage.
condensates. Operation at the elevated tempera-
ture saves both fuel and water. To make condensate polishing by ion exchange
economically feasible, cost had to be minimized.
This process is capable of producing effluent This was accomplished by increasing flow rate
concentrations of 10 ppb iron, 5 ppb copper, and through the polishers, making it possible to
less than 500 ppb total hardness. Some equip- reduce unit size. Only traces of impurities are
ment manufacturers stipulate expected conden- involved, so higher flow rates can be used
sate quality based on percent removal of iron without significantly sacrificing quality or
and copper, stating 60-85% removal of iron and capacity. In addition, the higher rates improve
75-90% removal of copper. Actual performance suspended solids removal through increased
is very dependent on a number of factors that surface-active phenomena (electrolytic attrac-
greatly influence the final condensate quality, tion) between the resin beads and the insoluble,

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and sometimes colloidal, impurities present in following mid-cycle backwash will cause
the condensate. Unless there is condenser increased hardness leakage into the feedwater.
leakage, runs are usually terminated when the
pressure drop across the bed reaches 20-25 psi Subsurface washers are separate distributors,
(138-172 kPa). usually cruciform in shape, installed approxi-
mately 12 inches (305 mm) below the top of the
Flow rate should be controlled by an adjustable resin bed and equipped with orifices pointing to
rate recirculation system that measures the the side. These distribute condensate laterally to
system outlet flow and recirculates condensate loosen the top portion of the resin bed, break up
so that the flow rate can be kept relatively any agglomerated particulates, and wash them
constant and above the specified minimum. out of the unit without disturbing or mixing the
Measurement and control on the polisher inlet is rest of the bed.
inaccurate because of the additional flows
caused by backwashing of the units. Because the resin depth to be washed is shallow
and there is probably over 300% freeboard
Rapid changes in the unit flow rate, whether available for this depth, the subsurface backwash
caused by removal of a unit from service for rate should be equal to the full backwash rate for
regeneration or return to service after regenera- the unit. The operation should continue until the
tion, will definitely cause increased suspended effluent is clear.
solids in the effluent of any other unit in service.
These increases in particulate oxide can be over This operation releases bed compaction by
2 ppm, depending on the resin bed condition at stopping downward flow, loosening small
the time. particulates trapped lower in the resin bed or
formed from the washing operation. The unit
Subsurface Backwash – One of the most must receive a rinse to sewer following every
important functions performed by a condensate subsurface backwash at the same rate used for
polisher is to filter out the particulate matter the fast rinse during regeneration. The mid-cycle
picked up by the condensate. Because the rinse should continue until the effluent is clear
condensate contains only small amounts of of particulates. This step minimizes increased
soluble contaminants, polisher runs tend to be suspended solids from the unit just receiving a
very long. Consequently, the filtration mecha- subsurface backwash, but increased crud levels
nism results in accumulation of crud, or particu- should be anticipated in the effluent from other
late iron and other suspended solids, on the on-line units.
surface and upper 4-6 inches (102-152 mm) of
the resin bed. Failure to remove this crud results Regeneration – The primary regenerant for the
in a large pressure differential across the bed, resin is sodium chloride at a dosage of 15 lb/ft3
bed channeling at the high flows used, and high (240 kg/m3) of resin, which is injected as a 10%,
effluent iron. To prevent these conditions, the by weight, solution. The concentration is slightly
units are equipped with subsurface washers, and higher than that used for sodium softening. This
each unit should be subsurface washed daily. serves to swell the resin and helps remove the
However, it is important that mid-cycle full shell of insolubles coating the beads. On occa-
backwash not be utilized. sion, an acid treatment is applied to remove any
accumulated iron and copper. Sodium cycle
Full backwash between regenerations tumbles cation regeneration is normally carried out in-
the resin, allowing the heavier exhausted beads place because it is easier to do and requires less
to fall to the bottom of the bed. Return to service capital expense for equipment.

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If the salt is dissolved in cold water, the concen- However, because the resin may be degraded by
trated brine is oxygen saturated. When diluted conditions such as oxidation, thermal shock, and
and injected into the unit, this oxygen can metallic fouling, macroporous grades of resin,
oxidize dissolved iron in the pores of the resin or more resistant to these factors, are preferred.
on the surface of the beads and increase fouling
that is not readily removed. In addition, the Unit and System Design and Construction
oxygen attacks the resin and causes loss of – The vessels and piping are normally carbon
capacity, decrease in crosslinking, an increase in steel, which is common to most of the conden-
water retention, and eventually leads to the need sate system. Application of various types of
for resin replacement. To minimize these effects, linings to the vessel interior surfaces for corro-
sodium sulfite is added to the brine at a dosage sion protection has generally been found to be
of 0.25 lb Na2SO3/ft3 (4 kg/m3) of resin during unsatisfactory unless reapplied frequently. The
every regeneration. linings tend to crack because of thermal shock
and because of the expansion and contraction of
When units are run with condensate tempera- the steel vessels under normal service and
tures above 140°F (60°C), a combination of regeneration conditions.
oxidative damage and thermal shock is noted
from regenerating with cold water. The greatest In pulp and paper mill applications, the potential
damage from oxidation seems to occur in the for external corrosion to vessels and piping often
transition range of 120-140°F (49-60°C). results in the use of stainless steel vessels and
Therefore, if cool water is used in regeneration, piping. Selection of the proper alloy is important
a low flow rate cool down step at 1-2 gpm/ft2 because of the frequent contact with chloride
(2.4-4.9 m3/h/m2) is recommended just prior to solutions. Periodic use of a reducing agent also
regeneration of the exhausted resin. Likewise, affects the protective oxide layer on stainless
a low flow rate warm up step is needed just steels.
before final rinse and return to service of the
unit. Vessel internal distributors and collectors should
be constructed entirely of stainless steel alloys
To reduce iron fouling of the resin and to allow because corrosion assisted breakage of carbon
the regenerant to penetrate the beads fully, a steel components is a common occurrence.
stronger reducing agent such as sodium hydro- Plastic materials cannot be used because of
sulfite replaces the sulfite every fourth regenera- temperature limitations.
tion. This is added as a dilute solution to the
brine at a dosage of 1 lb/ft3 (16 kg/m3) of resin. When the temperature of the condensate being
treated exceeds 212°F (100°C), the water in the
Even though the ion exchange capacity is vessel, as well as within the resin beads them-
seldom fully exhausted, the units should be selves, will flash whenever the operating pres-
regenerated at predetermined intervals ranging sure is relieved such as during subsurface wash
from one week to a month. The interval should or regeneration. The flashing that occurs will
be set as needed based on the amount of sodium damage vessel internals and cause resin break-
contribution that is acceptable. age. Pressure can be maintained by installation
of a backpressure valve on the regeneration
Strong acid cation resins are basically stable at outlet piping.
temperatures up to 300°F (149°C), and standard
resins are frequently used in this process.

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Sodium Cycle – External Regeneration taken to prevent resin damage from thermal
The service and operating parameters outlined shock and oxidation.
for in-situ regeneration still apply to this system.
The only changes are those that apply to trans- Resin transfer piping should be welded with no
ferring the resin for regeneration to a system screwed joints and with no flow restrictions.
external to the service vessel. All bends should be long radius elbows as a
minimum, with no tees, and all resin transfer
External regeneration of resin is accomplished valves should be full bore ball valves. Lines
by removal of all resin from the service vessel, should be designed for a slurry velocity of
transfer to a separate and external regeneration approximately 2-4 ft/s (0.6-1.2 m/s).
system, and subsequent return of regenerated
resin to the service vessel. This is simply done The resin storage vessel may be a pressure
by pressurizing a slurry of resin and water and vessel if desired or an atmospheric tank of
transferring it through piping that incorporates plastic or fiberglass construction. In some
special features. Experience has shown there is systems, the brine-measuring tank serves as a
no significant damage to the resin, rather clean- storage tank. The regeneration pressure vessel
ing of the resin surface is enhanced by the can be made of carbon steel or suitable alloy
turbulence and agitation. construction with a lower design pressure.

External regeneration is most efficient if two Changes to Service Vessels – The service
additional tanks are installed: vessels are not exposed to the regenerant solu-
tions so they may be constructed with steel or
1. One for the backwash, regeneration, and low grade alloy steel (e.g., type 304 stainless
chemical cleaning of the resin steel) if desired. Because the full charge of resin
2. Another for storage of the regenerated resin is not backwashed in-situ, the backwash free-
until needed board can be reduced and the vessel made with
shorter sides. No regenerant distributor is
Frequently, an extra charge of regenerated resin required.
is maintained in the storage tank, which should
be large enough to hold one complete charge. Because optimum performance is contingent on
With a spare charge in the system, a service removing all resin for regeneration, the bottom
vessel can be emptied and the spare charge collector (underdrain) must not offer any restric-
installed in one hour or less, allowing return of tion to resin movement. Special design under-
the unit to service in minimum time. The drains are used.
exhausted, dirty resin in the regeneration vessel
can then be chemically cleaned if necessary and Amine or Ammonia Cycle
regenerated when convenient to the operators. When operated in the sodium cycle, strong acid
cation condensate polishers contribute sodium
Resin transfer is best accomplished by injecting ions equivalent to all the hardness and dissolved
transfer water above the resin bed and a smaller metals in the condensate, as well as any ammo-
flow from the bottom through the underdrain nia (NH3) or amines present from the condensate
while opening a resin outlet valve. Transfer treatment program. In addition, sodium is also
water preferably should be condensate, if its discharged to the condensate when the polisher
temperature is below 212°F (100°C). However, is regenerated or when upset conditions occur.
the loss of condensate might be undesirable so a
clean substitute can be used if extra steps are

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Amines have been used to regenerate condensate Hydrogen Cycle – Ammonia Removal
polishers, essentially converting the resin to Application of this variety of condensate polish-
amine form, to prevent the removal of valuable ing unit is not common, and installations have
amine treatment and to eliminate the sodium been made primarily in ammonia fertilizer plants
contribution to the feedwater. The amines used for recovery of ammonia laden condensate
to accomplish this task can be either pure amine, streams. The simplest explanation of the process
such as morpholine, or an amine salt. is to consider it equivalent to on-line ammonia-
tion of hydrogen form cation resin. It is a
Strong acid cation resins have the following variation of the processes described in the
order of selectivity for ions: preceding section.

Fe +3 > Al +3 > Ca +2 > Mg +2 > K + > NH 3+ > Na + > H + If the ammonia is present as a salt, hydrogen
form strong acid cation resin is applicable. If the
Amines fall into the same range as NH3+. Like ammonia is present in the free base form, weak
the acid ion H+, an amine solution cannot replace acid cation resin may also be used.
those ions of greater selectively unless fed at
very high concentrations (%) during regenera- In the known applications of this process, the
tion. However, amines show a marked decrease polished condensate is recovered by injection
in the percent ionization as the amine concentra- into the makeup water upstream of the deminer-
tion increases, and it is only the ionized portion alization system.
of the amine that is effective in the regeneration
process. Therefore, the resin must first be placed There is the potential for release of extremely
in the hydrogen form using acid before it is small volumes of free gases in this process, and
regenerated into the amine form. The low pH an automatic venting system is used to prevent
present within the bed when the resin is in the accumulation of a gas dome. A gas dome, being
hydrogen form assures that all amine will be compressible, can interfere with regeneration
ionized and usable in the regeneration process. flow rates or even cause internal damage.
Alternatively, a prepared, proprietary amine salt
can be used in a single step regeneration without Hydrogen Cycle
prior conversion to the H+ form. This type of unit is installed as a primary
treatment system ahead of mixed bed polishers,
When condensate polishers are operated in this particularly where parts per trillion (ppt) effluent
form, the adverse effects of sodium on boiler purity is required such as in some nuclear and
water chemistry are eliminated. The soluble supercritical steam plants. Standard guaranteed
iron, copper, and hardness in the condensate performance is less than 100 ppt sodium and
will be exchanged for the amine on the resin chloride and less than 200 ppt sulfate under
exchange sites. In addition, the effluent quality normal operating conditions. This increases to
is acceptable for attemperation water injection. less than 200 ppt sodium and chloride and less
than 500 ppt sulfate with moderate condenser
Outside of the change in regenerant chemical, leaks. On-line ion chromatography is the only
the equipment and operation is the same as for means of monitoring performance at these low
the sodium form condensate polishers. concentrations.

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Primary cation units convert all salts in the concentration is a concern, particularly in some
condensate to their respective acids, thereby nuclear plant designs, because of mechanical
providing a favorable exchange environment in deformation or denting of exchanger tubes.
the following mixed resin bed. In addition, iron
is removed, which prevents subsequent fouling The kinetic rate of sulfate exchange is much
of the downstream anion resins and provides slower than that of chloride or other anions in
faster kinetic exchange rates in the mixed beds. the mixed bed anion resin component, so the use
The primary cations can also be backwashed at of a predominantly anion resin bed is beneficial.
higher rates for the removal of accumulated Sulfate contamination of condensate can arise
crud. from cation resin breakdown product sloughage
or from the sulfuric acid cation resin regenerant.
When primary cation units are used, the follow-
ing mixed beds may have a cation to anion resin After regeneration is completed, the primary
ratio of 1:3 in order to specifically address cation bed is placed in standby for 24 hours and
sulfate removal from the condensate. Sulfate then receives a pre-service rinse to minimize

PERFORMANCE STANDARDS
Following are guidelines for monitoring polisher performance:

Sodium Cycle Cation Polishers

Contaminant Effluent
Iron 60-85% removal
Copper 75-90% removal
Hardness less than 500 ppb

Mixed Bed Polishers (Utility Plant)

Contaminant Effluent
Total dissolved solids 7-25 ppb
Iron 5-10 ppb
Copper less than 2 ppb
Silica less than 5 ppb
Cation conductivity less than 0.1 µS/cm
Chloride unit specific, specification can range from 0.1-10 ppb
Sulfate 0.2 ppb (see Hydrogen Cycle Section)
Sodium unit specific, specification can range from 0.1-5 ppb

Powered Resins
Contaminant Effluent
Total dissolved solids 25 ppb
Total suspended solids 10 ppb
Total iron less than 5 ppb
Total copper less than 2 ppb
Dissolved silica 5 ppb
Cation conductivity 0.1 µS/cm

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sulfate throw to service. The cation resins are Typical units contain both strong acid cation
replaced regularly after treating a preset volume resin, operated in the hydrogen form, and strong
before sulfate sloughing intensifies. base anion resin, operated in the hydroxide form.
Anion resins in the hydroxide form are less
stable than cation resins in the hydrogen form.
MIXED BED DEMINERALIZERS The Type I anion resins typically installed in
This section contains details of different con- condensate polishing mixed beds should not be
figurations of mixed bed ion exchange deminer- used at temperatures above 140°F (60°C).
alizer plants used to polish condensate in
industrial and utility power plants. These The cation regeneration dosage is generally in
configurations may include: the order of 10-12 lb/ft3 (160-192 kg/m3) when
using 100% sulfuric acid (H2SO4). Hydrochloric
• Operation in hydrogen/hydroxide cycle acid (HCl) is infrequently used for condensate
• Operation in ammonia or amine/hydroxide polishers because of materials compatibility;
cycle plastic internals are not suitable for condensate
temperatures, and suitable alloys are prohibi-
• In-situ regeneration
tively expensive for HCl use. The caustic
• External regeneration dosage for the anion resin is also in the 10 lb/ft3
(160 kg/m3) range but is frequently adjusted to
Mixed bed demineralizers remove all cations, achieve neutral pH effluent when the waste
anions, silica, and carbon dioxide. When oper- regenerants are mixed. The higher dosages are
ated in the hydrogen/hydroxide cycle, they also used to ensure maximum regeneration of ion
remove any amine or ammonia present in the exchange sites. Chemical cost is not as critical
condensate. The treated effluent is essentially due to the infrequency of regeneration.
neutral at approximately 6.5-7.0 pH. Since this
pH is not acceptable for feedwater purposes, any Dilute regenerant concentrations and flow rates
amine or ammonia removed must be replaced to are similar to those applied to makeup treatment
elevate the effluent pH to the desired range. demineralizers. However, unless there is signifi-
cant hardness contamination of the condensate,
Mixed beds are widely used in industry to stepwise injection of sulfuric acid is not neces-
produce high-purity water. They are used in a sary to prevent calcium sulfate precipitation.
primary position when the raw water to be
treated is low in dissolved solids and the ex- In service, the two resins are intimately blended
pected water purity is acceptable. They are in a homogeneous mixture. The high-purity
widely used to refine, or polish, the effluent effluent achieved by these units is due to this
from primary demineralizers and membrane intimate mixture, which forms an “infinite”
deionization. They are also applied as high flow chain of two bed demineralizers in series –
rate condensate polishers in industrial plants and hydrogen form cation beads each immediately
fossil fueled and nuclear power generation. adjacent to hydroxide form anion beads. As a
hydrogen ion is displaced from the cation bead,
It is necessary to understand the chemical and it immediately reacts with a hydroxide ion from
operating principles of mixed beds in order to the anion bead, instantly forming water. This is
understand how they are best applied to conden- unlike a separate cation bed in which the solu-
sate polishing, whether for industrial or utility tion contains eluted ions, such as sodium, that
plant operations. have influence on the equilibrium and cause

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increased leakage into the effluent. The neutral In higher-pressure fossil fueled and nuclear
condition existing in the solution surrounding utility plants, special system designs have been
the beads in mixed beds causes no such effect, developed to separate the resins completely for
and very high-purity effluent is possible. external regeneration.

The two bed components must be separated to In both industrial and utility industries, a tech-
allow individual regeneration. They are sepa- nique of conversion of the cation resin to the
rated hydraulically by backwashing, and because ammonia or amine form has been applied to
the cation resin is denser than the anion resin, it displace sodium ions from the resin and to
settles below the anion resin. Because of a increase the final effluent purity to meet exact-
number of factors, hydraulic separation is not ing specifications for steam purity for steam and
complete, and there is a zone of intermixing at combustion turbine applications. This configura-
the interface of the two resins. tion maintains the amine and ammonia in the
condensate, and the effluent pH is typically
A special internal regenerant collecting system is above 7.
located at the theoretical interface. In fact, the
intermixed resin zone exists above and below In-situ Regeneration for Industrial
the mid-collector. This mixed resin is exposed to Applications
cross contamination by one regenerant chemical Mixed bed polishers are generally utilized
or the other. The cation resin is contaminated by in industrial applications when boiler
the sodium ions from caustic soda injected to operating pressures are greater than 1500 psig
regenerate the anion resin. Anion resin is in turn (10.3 MPag). All streams with a temperature
contaminated by either the sulfate or chloride less than 140°F (60°C) are usually treated.
ions from the acid regenerant of the cation resin.
As a consequence, the final treated water purity Normal service flow rates for industrial mixed
is affected by the presence of these contaminat- bed polishers run approximately 25 gpm/ft2
ing ions on the resin. (61 m3/h/m2). These units are commonly filled
with a cation:anion resin ratio of 1:1 (based on
A number of remedies for the intermixing have volume) to a total bed depth of 4 ft (1.2 m). It is
been tried, and the applicable remedy is dictated preferable that the minimum cation bed depth be
largely by the degree of purity required for each 3 ft (0.9 m) and that the ratio of 1:1 be based on
application of mixed bed condensate polishers. the Total Wet Capacity (meq/mL) of each resin.
In industrial applications, with boiler operating
pressures of 1500-1700 psig (10.3-11.7 MPag) The units are usually regenerated on a regular
or lower, in-situ regeneration without special frequency of once every 30 days and are not run
measures has sometimes been acceptable. In to exhaustion, even though the resins are harder
other cases, intermixing has been reduced by the to separate in the unexhausted form.
use of an inert resin layer that occupies the zone
where intermixing normally occurs during the These units are generally designed for maximum
regeneration. Units employing this method are service flow rates of 25 gpm/ft2 (61 m3/h/m2)
sometimes called Tri-bed or Trio-bed. Another because industrial condensates are generally
method used is application of specially manu- higher in dissolved impurities, and flow rates are
factured uniform particle size resins that more variable than in utility applications.
separate more completely because 99% of the However, as crud levels are normally lower than
cation beads are 650 µm diameter while 99% encountered in pulp and paper mill applications,
of the anion beads are 550 µm diameter, as well where condensate polishers are sodium cycle
as having different densities.

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softeners, the mixed beds usually are not In-situ Regeneration for Utility
equipped with recirculating flow control Applications
systems. The use of in-situ regenerated mixed bed
condensate polishers in high-pressure utility
In normal mix bed applications where the resins plants is not common. Applications of this
are in the hydrogen/hydroxide forms, the resin configuration are most likely to be found in
beds remove any condensate treatment amines plants with drum type boilers operating in the
added to protect the condensate system. These subcritical range (1800-2400 psig; 12.4-16.5
amines gradually convert the cation resin MPag), where it is possible to control and
exchange sites to the amine form. Any sodium remove concentrated boiler water dissolved
present is gradually displaced and moves solids by blowdown. When this configuration is
downward in the resin bed, displacing hydrogen used, operation in the ammonia cycle is prac-
ions. Eventually, the sodium reaches the bottom ticed to minimize sodium leakage. For additional
of the bed and is displaced into the effluent information, see the description included for
condensate at high concentration. This is known ammonia form operation.
as the sodium break or peak. While being of
relatively short duration (dependent on the External Regeneration for Utility
amount of sodium contamination during regen- Applications
eration), this discharge of sodium creates an The purity of condensate required for utility
upset in the boiler water chemistry and undesir- feedwater is typically much higher than for
able control conditions. industrial applications because of extremely
stringent steam purity requirements for steam
To eliminate this problem, the units are some- turbine operation. Treated condensate must
times converted to the amine form by using a usually meet specifications of:
condensate treatment chemical that is passed
through the complete resin bed following • 7-25 ppb total dissolved solids
regeneration and remixing. This process may • 5-10 ppb iron
extend the service run to 3-4 months before • ≤ 2 ppb copper
regeneration is required. • ≤ 5 ppb silica
• ≤ 10 ppb chloride
If high bed differential pressure is caused by the • ≤ 5 ppb sodium
accumulation of excessive crud load, the units • ≤ 0.1 µS/cm cation conductivity
are usually fully backwashed and regenerated.
Mid-cycle backwash causes bed fluidization and Once-through boilers, or steam generators,
resin separation, with exhausted cation beads operating in both the supercritical range
accumulating in the lower regions of the bed (≥ 3206 psig; 22.1 MPag) and subcritical range
near the underdrain system. High-purity (less than 3206 psig; 22.1 MPag) evaporate the
effluent can no longer be produced because water to dryness. Any dissolved solids present in
the exhausted resin beads establish the effluent the feedwater are deposited on the boiler tubes,
concentration. so full flow condensate polishing is required.
Full flow condensate polishing is also required
External regeneration facilities are rarely in nuclear plants.
installed for industrial mixed bed condensate
polishers, so any cleaning operations are usually Normal service flow rates for utility mixed
undertaken in-situ. Cleaning of resin in indus- bed polishers run approximately 50 gpm/ft2
trial plants is usually because of hydrocarbon or (122 m3/h/m2) or higher. The units are usually
black liquor contamination. filled with a deep bed charge of resin in a ratio

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CONDENSATE POLISHING

of 2:1 strong acid cation:strong base anion. Where condensate ammonia or amine concentra-
The resins used in this application may be tions are sufficient to exhaust the cation resin
conventional gel or macroporous types. capacity well before the anion resin capacity is
exhausted, or to reduce the frequency of costly
For high-pressure boiler systems, particularly regenerations, the hydrogen form cation resin is
those above 1500 psig (10.3 MPag), polishers operated until its capacity for ammonia or amine
are used because they contribute virtually no is gradually exhausted. As this occurs, any
sodium ions while removing the dissolved sodium ions in the cation resin are displaced,
solids, including silica, along with the particu- traveling down through the bed until break-
late iron and copper. The resin inventory in such through occurs. If the plant can operate success-
polishers enables them to remove contaminants fully through the sodium break without prob-
from leaking condensers for sufficient time to lems, the unit then continues until the amine or
allow operators to make corrections or to ammonia break occurs. When the bed is com-
remove a boiler from service before dangerous pletely in the amine or ammonium form (NH4+),
chemistry upsets occur. Deep bed demineralizers the effluent will contain the amine or ammonia
are especially appropriate for treating turbine and may show a trace sodium leakage (less than
condensates that are subject to contamination 1 ppb). The polisher then continues on-line until
by very high TDS cooling water. silica breaks through the anion resin and regen-
eration is necessary.
Deep mixed bed polishers may be operated with
the cation resins in hydrogen form from strong Special techniques and processes have been
acid regeneration and with the anion resin in developed and patented for regeneration of deep
hydroxyl form from caustic regeneration. (See mixed bed condensate polishers used in utility
Figure 2.6.6.) This gives low leakage and good service. These focus on minimizing in-service
polisher effluent purity. In many cases, where sodium leakage that results from incomplete
removal of ammonia or amines is undesirable, separation of cation resin from anion resin,
the cation resin may be converted to the ammo- leaving small quantities of cation resin to be
nia or amine form as a final step in regeneration. contaminated by the sodium hydroxide
regenerant.

Figure 2.6.6 – Deep mixed bed polishing arrangement showing external regeneration vessels

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 Section 2.6
CONDENSATE POLISHING

The deep resin bed provides a great reserve

capacity for the removal of soluble salts and is
of particular value where seawater and brackish
waters are used as cooling water in the con-
denser. The success of the high cross-sectional
flow rate deep mixed bed polisher depends upon
the ability of the mixed resin bed to contain
particulate matter driven into it, while perform-
ing an ion exchange function for removal of
dissolved solids entering the system through
condenser leakage or from other sources. The
packed bed of resin beads performs the filtering
function until the bed is loaded or disturbed by
an operating upset. It is then backwashed and
regenerated.

A 2:1 cation to anion resin mixture is commonly

used. At the high pH values encountered with
ammonia treated systems, however, a 1:1 resin
mixture is preferred. With a combination of high
pH and high temperature, the mixture should be
2:3 (40% cation and 60% anion). The higher
amount of anion resin will give better chloride
and silica removal. Prior investigations indicate
that the 2:3 mixture produces the best quality
water with the lowest conductivity at all flow
rates tested. (See Figure 2.6.7.)
Figure 2.6.7 – Lab data showing the relative
effect of flow rate and cation/anion ratio on
Side Stream Condensate Polishing effluent conductivity
In common with all types of ion exchange
condensate polishers, mixed bed polishers are
vulnerable to sudden flow surges caused by Regeneration
plant load trips and mechanical problems with Deep mixed bed condensate polishers are
valves and pumps. The change in cross-sectional typically regenerated in a separate, external
flow rate causes release of crud and resin system, particularly where special techniques for
fragments into the feedwater cycle. (See also the separation are used. Many of the same param-
section Problems with Organics below.) For this eters previously discussed for externally regen-
reason, mixed bed polishers may be inserted into erated strong acid cation polishers apply to the
a full flow recirculating loop, such as from the mixed bed polishers.
hotwell back into the condenser so that constant
flow rates can be maintained. This type of In deep mixed bed polishers, the exhausted resin
arrangement is called side stream polishing. mixture is hydraulically transferred from the
service unit to the resin separation tank. When

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CONDENSATE POLISHING

this operation is completed, a charge of transfer does not damage the beads as long as
previously cleaned and mixed resin from the the slurry velocity is correct and the transfer
storage tank is transferred to the service unit pipes and valves are properly designed.
for resumption of operation. The exhausted
mixture in the separation tank is backwashed to After initial resin separation in the separation
separate the resins and to remove some of the tank, a lot of small and loose particulate matter
accumulated crud. will be distributed throughout the anion resin.
The backwash rate in the separation tank is
After separation, the anion resin is transferred to governed by the anion resin density and particle
the anion regeneration tank. Both resins are then size and will not remove particulates that are
backwashed, regenerated, and rinsed separately heavier or larger than the cation resin. The anion
– the cation resin in the separation tank and the resin component is then sluiced to the anion
anion resin in the regeneration tank. Insufficient resin backwash and regeneration vessel. Any
backwashing will allow accumulation of particu- particulate matter moved to the anion regenera-
late matter, which will be recycled and poten- tion tank must be removed from the system each
tially increase pressure loss during operation. cycle, or it will be recycled to the operating unit.
After regeneration, the cation and anion resins This will cause an increase in pressure loss,
are transferred to a resin storage tank, where which can damage the resin, producing resin
they are mixed and held until needed. Resin fines that further aggravate the problem.

ADVANTAGES OF EXTERNAL REGENERATION

External regeneration offers a number of distinct advantages:
• Prevents accidental discharge of regenerant chemicals into the main condensate and feedwater
cycle because regenerant vessels are not directly connected to the feedwater system. Reduces
the potential for condensate contamination and severe damage to the boiler.
• Out of service time from regeneration of a unit is reduced from several hours to less than one
hour. Total system time availability is increased.
• The length of time that in-service units must operate under peak flow conditions at a higher
pressure differential is minimized. With one unit off-line during regeneration, the amount of
water available to the system may be restricted because of higher pressure differential across
the units remaining in service.
• Where high TDS water is used for condenser cooling, external regeneration ensures maximum
regenerated resin inventory is available when major, unexpected condenser tube leaks occur.
In addition, the total resin within a unit plus a spare resin charge, may be less than that required
by an in-situ regenerated unit designed to handle the maximum leakage rate of high TDS
cooling water.
• Regeneration of exhausted resin held in the external regeneration system can be scheduled at
the operators’ convenience rather than when exhaustion occurs.
• In cases where hydrochloric acid is used for regeneration, internal distribution systems using
special alloys resistant to chloride attack are confined to one vessel while less expensive
stainless steel can be used for underdrains in the service units.

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CONDENSATE POLISHING

Reducing Sodium Leakage from Mixed regenerated with acid, eliminating its sodium
Bed Polishers content. After regeneration with caustic in
Imperfect separation of cation and anion resins the anion regeneration tank, the anion resin
and the effects on demineralizer effluent purity receives a further regeneration with dilute
have been previously discussed. Similarly, the ammonia. This step ensures that any small
processes for converting the cation resin to the amount of cation resin that may have been
amine or ammonia form have been covered. transferred with the anion resin is fully
This section outlines some of the methods regenerated to the ammonium form and is
employed in utility plants to achieve maximum free of sodium. The two resins are com-
resin separation. pletely mixed, transferred to the service
vessel and returned to service. The balance
Ammonex Process – This process is used in of the cation resin then is converted to the
systems that operate at a pH above 9.3 with two ammonia form by the ammonia content of
units, each capable of providing 50% of the the condensate.
flow. A third unit of the same size is in stand-by. 2. Recycle ammoniation is accomplished by
Service vessels are designed for the full shut-off continuously circulating a dilute solution of
pressure of the condensate hotwell discharge ammonia (0.25-0.5%) through the previously
pumps. However, the regeneration vessels may regenerated hydrogen form cation resin and
only be designed for 75 psig (517 kPag). hydroxide form anion resin linked in series
for a period of 3-5 hours. The dosage is
Condensate polishers can be successfully approximately 5-6 lb of 100% NH3/ft3
operated in the ammonia/hydroxide cycle (80-96 kg/m3) of anion resin and 2.5-3 lb/ft3
provided the sodium content of the regenerated (40-48 kg/m3) of cation resin. The ammonia
cation resin is kept very low. The sodium solution from the anion bed is only slightly
content of the bulk of the cation resin is reduced contaminated by sodium from the trace
to a satisfactory level by regeneration with the cation resin present. This solution is passed
appropriate amount of sulfuric acid. The through the cation resin bed, which is already
Ammonex process then displaces sodium from in the ammonia form, to remove the sodium.
the cation resin present (and regenerated) with
the anion resin by means of a very dilute ammo- On stream and recycle ammoniation provide
nia flush (0.25-0.5% as ammonia). A large virtually the same results, but the operating costs
excess of ammonia is necessary at these low of the recycle procedure are lower.
concentrations to reduce the sodium to an
acceptable level. The remaining sodium does not
Calex Process – This process replaces sodium
produce excessive sodium leakage following
on any cation resin beads present in the anion
ammonia breakthrough, although it does reduce
resin removed for regeneration with calcium
the capacity of the bed for sodium resulting from
ions using a dilute solution of lime (calcium
condenser leakage. If the Ammonex process is
hydroxide). The solution contains approximately
not applied correctly, high sodium leakage will
1100 ppm of calcium as CaCO3. Cation resins
occur. The process can be performed two ways:
have a stronger preference for divalent calcium
1. On stream ammoniation is a technique ions than for monovalent sodium ions. As a
applied when it is advantageous to have the result, a little more than the stoichiometric
cation resin in the hydrogen form, such as on amount of calcium will displace essentially all
initial plant start-up or at times when there is sodium from the resin. After exhaustion to
a major condenser leak. The cation resin is ammonia, the polisher effluent should contain
less than 1 ppb of calcium.

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Using condensate, a 6% by weight lime slurry is Seprex Process – This process does not require
prepared in a slurry tank. After normal anion the use of a third regenerant, but relies instead
regeneration and rinse, a portion of this slurry is on a technique that results in complete separa-
diluted in-line 50:1 with condensate and passed tion of the cation and anion resins.
through a two-minute retention tank to allow
time for the lime to dissolve completely. This In other techniques, the take-off interface is
0.12% lime solution then passes through a located in the anion portion of the separated bed
cartridge filter to remove insolubles from the to minimize the transport of entrained cation
solution and is then applied to the anion resin resin to the anion regeneration tank. In the
(Figure 2.6.8). Seprex process, the take-off interface is located
in the cation portion of the bed. A small amount
The resin is rinsed by shutting down the lime of cation resin is deliberately removed with the
pump and allowing the dilution water flow to anion resin to the anion regeneration tank to
continue through the system. The rinse is ensure that no significant quantities of anion
stopped when the rinse effluent approaches a resin remain in the cation regeneration tank. The
specific conductance below 10 µS/cm. The cation resin is regenerated using sulfuric acid at
hardness of the lime solution entering and a concentration of 4-10% by weight.
leaving the anion regenerating tank provides a
quantitative measure of the sodium removed The anion resin is regenerated and separated
from the bed. from the cation resin in the anion regeneration
vessel by flotation with an 8-16% caustic
The sodium content of the polished condensate solution. The density of this solution causes the
is usually less than 2 ppb but could be higher anion resin to float and the cation resin to sink
during condenser leaks or the run immediately to the bottom of the regeneration vessel.
following a condenser leak.

Figure 2.6.8 – Calcium hydroxide application system

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A controlled resin-free interface depth of 6-12 The high degree of separation is possible
inches (152-305 mm) between the anion and because of the density differential between
cation resins ensures complete isolation of cation and anion resin beads. Particle size does
cation resin and fines. The separated cation resin not affect the separation process.
is then sent back to the cation regeneration
vessel to be regenerated with the other spent The Seprex system is designed either to ammo-
cation resin (Figure 2.6.9). This holdover cation niate the resins in the regeneration holding tank
resin in sodium form does not add a significant or on-line as the ammonia content of the con-
load to the cation regeneration with sulfuric densate is removed by the hydrogen form cation
acid, because it is less than 5 ft3 (0.14 m3) in a resin over a period of time. Because ammonia-
typical condensate polishing system. tion before service is required only to convert

Figure 2.6.9 – Seprex separation

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hydrogen sites to ammonia, resin can be The unit can be run in either the hydrogen/
ammoniated at stoichiometric levels. hydroxide cycle or ammonia/hydroxide cycle
with in-situ or external regeneration. The inert
Other Ion Exchange Systems resin forms a layer between the two working
The need for higher purity demineralizer efflu- resins when all three are hydraulically separated
ent for use in utility power generation led to by backwash because of particle size and
the development of other methods and system density differences.
modifications for the application of ion ex-
change processes. Space does not allow dis- Tri-Pol – a non-mixed bed, ion exchange system
cussion of many of these or a listing of their comprised of three distinct and separate com-
advantages and disadvantages. However, it partments contained in a single vessel and
is wise to recognize the existence of some separated physically by screen type collector/
configurations and modifications. distributor systems. The chambers contain
strong acid cation (H+ form), strong base anion
Conesep – a modification of the resin separator (OH– form), and strong acid cation (H+ form) in
vessel to use a conical bottom tank with an inert series. On-line ammoniation is used to provide
resin layer to enhance separation by increasing maximum capacity for condenser leakage,
the actual depth of the inert resin as it moves but ammoniation following regeneration is
down in the cone during transfer. The cation also used.
resin has a decided specific conductance charac-
teristic while the inert resin has no specific Sulfite Rinse – an optional extra regeneration
conductance characteristic. Automatic termina- step used in mixed bed regeneration to displace
tion of cation resin transfer can be monitored chloride anions from the anion resin component
and controlled by a conductivity meter. when chloride leakage levels are critical.

Monion Process – a process originating in the Weak Acid Cation – can be used as a separate
United States to saturate both cation and anion primary treatment unit for removal of ammonia
resins in a mixed bed demineralizer with sodium to increase hydrogen/hydroxide mixed bed
hydroxide prior to separation to improve resin capacity for condenser leakage protection.
separation.

Top Cat – a process originating in Europe to PROBLEMS WITH ORGANICS

place a layer of hydrogen form cation resin as a A major steam purity concern in high-pressure
discrete layer on top of the fully regenerated steam turbine operation is the presence of
mixed resin bed. volatile organic substances in the steam that may
condense in the turbine and cause significant
Tri-Ammonex – a modification of the Ammonex corrosion problems. The Total Organic Carbon
process where inert resin is used temporarily in (TOC) limit imposed by steam purity require-
the resin separation stages, then removed and ments for turbine use defines the acceptable
stored in a separate vessel. It is used to correct concentration.
perceived purity problems associated with inert
resins. Organics may enter the condensate streams in
several ways:
Tri-Bed – a process using a colorless, inert resin
in conjunction with cation and anion resins in a • In-leakage of condenser cooling water
mixed bed demineralizer to enhance separation.

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• In-leakage of sealants and protective coatings POWDERED RESIN POLISHERS

used during maintenance
In a typical high-pressure utility boiler system,
• Organics present from volatilization of organic the most common location for this polisher is
compounds introduced into the boiler in the after the hotwell condensate discharge pumps
makeup water and before the low-pressure heater(s). Because
• Volatile decomposition products from of the limited ion exchange capacity, the system
compounds added to the boiler or feedwater is not suitable for applications where condensate
dissolved solids may exceed 1 ppm due to
• Ion exchange resin degradation products frequent condenser leaks of high dissolved
released as the resin ages naturally or is solids cooling water. In cases where the potential
degraded by a variety of conditions for a major condenser leak is very low, this
• Resin fines, broken resin beads, or whole resin system is sometimes installed downstream of
beads that enter the condensate stream, the low-pressure heaters.
perhaps as a result of equipment failure
These polishers use a mixture of ground cation
The condensate polishers may remove some of and anion resins, sometimes in conjunction with
the organics, but that depends on the nature, other special materials, applied as a thin precoat
concentration, and ionization state of the organic to permanent filter septum elements. Figure
material. 2.6.10 shows one such polisher. In addition to
the precoat application, continuous feed may be
Resin fines, particles, and beads can only be employed in some portions of the service cycle
prevented from entering the feedwater cycle by to improve unit performance and service run.
design and installation of external resin traps in
the service outlet of each condensate polisher. This process uses very finely powdered (90% at
less than 325 mesh particle size) resin mixtures
If the TOC content of the condensate exceeds of cation and anion resins as a disposable media.
acceptable limits, treatment methods other than In some nuclear applications, precoat cracking
ion exchange must be employed. In some plants, occurred and is now prevented by application of
trace amounts of soluble organic compounds a special fiber containing precoat that provides
have been successfully removed by use of a more uniform layer, eliminates the need for
precoat filters that use a homogeneous mixture de-clumping during precoating, and improves
of activated carbon and fibrous materials as a service run lengths.
disposable precoat.
This process eliminates the need for the storage,
Deep bed carbon filters have been applied in use, and disposal of regeneration chemicals.
industrial plants for hydrocarbon removal ahead Because of its small particle size, the powdered
of mixed bed polishers in high-pressure boiler mixture yields high suspended solids removal.
systems. Deep bed activated carbon filters have Boiling water nuclear reactors (BWR) often use
limited capacity for organic compounds and powdered resin technology because it minimizes
introduce leachable dissolved solids to the the radioactive waste disposal problem, by
effluent. See the earlier section on Carbon systematic disposal of the spent powdered resin
Filters. without generating large amounts of radioactive
liquid wastes from regeneration.

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This type of polisher is very efficient in remov-

ing particulate metal oxides from condensate.
The precoat layer is very thin compared to the
resin depths in conventional ion exchange
equipment, but good removal of dissolved
contaminants may be achieved for very short
periods of time. The applied volume of pow-
Powdex
dered resin is insufficient to provide protection
Precoat
against even relatively small in-leakage of high
TDS condenser cooling water. Powdered resin
systems will be found mainly in higher-pressure
Retaining
boiler plants (above 1500 psig; 10.3 MPag)
Cartridge
where sodium contamination from a polisher
cannot be tolerated and where the main polisher
function is to remove iron and copper crud.

Normal service flow rates for powdered resin

precoat type polishers are 4 gpm/ft2 (9.8 m3/h/
m2) of element surface area. Precoat thickness
is 0.125-0.25 inches (3-6 mm) and maximum
operating temperature is 220°F (104°C). Run
length is typically 20-40 days for a 25 psi
(172 kPa) pressure differential. After resin
exhaustion or after the pressure drop limit has
been reached, the powdered resin is backwashed
from the filter elements by a combination of air Figure 2.6.10 – POWDEX condensate polisher
and water and discarded.

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For your notes:

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For your notes:

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