Note: Descriptions are shown in the official language in which they were submitted.
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INTRODUCTION
One of the biggest challenges in boiler water trea~men~
lies in the development of simple, easily monitored, and easily
controlled programsO Ideally would be one product which can
prevent scale, provide heat transfer surface pro~ection, and
protect condensate sys~emsO ~owever, the state-of-the-art
practices have not been able to meet this challenge. Chelan~
programs, for example, are capable of eliminating hardness
deposi~s. they are also known, however, ~o cause corrosion under
cer~ain conclitions. While the chelants are capable o~
soluhilizing hardness metal ions, their s~rong afinity toward
i;on ions may ac.ually be the corrosion mechanism. Excessive
residual chelants may not only prevenc the forma~ion of magne~ite
bu~ also strip the boiler of it5 protective magne~itP films~
The purpose o~ this inven~ion is to~
(1) develop programs which provide exceptional scale
preYention without the corrosion potential;
(2) develop prog.ams which provide similar scale
prevention capabilities as chelants without the
corrosion potential associated wi~h chelant applica~ion.
The~e purposes are accomplished utili2ing certain water-soluble
anionic vinyl polymers in a particular dosage range either albne
or in conjunction with certain low molecular wei~ht water-soluble
polymeric dispersn~s inclu~ing sulphona~e-containing, hardness-
dispersing polymers.
THE INVENTION
The invention provides a me~hod of trea~ing hardness
present in boiler wasers and scale formed on heat transfer
surfaces in contac~ with such waters to preven~ and remove scale
caused by ~uch hardness which comprises treating such waters with
a water-soluble anionic vinyl polymer containing at leasl 30%
and, preferably, 70% - 100% by weigh~ of carboxylate
functionality with said polymer having a molecular weightl
within the range of 500 - 50,000 and with the amoun~ of such
polymer being sufficient to provide between 1 - 30 ppm per ppm OL
hardness present in the boiler waters. By the term, ~hardness, n
we mean ~o include soluble and insoluble compounds of calcium,
magnesium, iron, copper, aluminum, and the like.
In addition to the above characteristics, the water-
soluble anionic vinyl polymer must also interact wi~h hardness
ions to se~uester them. The sequestration must be of such
magni~ude as t:o yield a chelation value of at least 200 as
measured by specific ion electrodes.
In a preferred embodiment of the lnvention, the
molecular weight range of ~he carboxyla~e polymers is within the
range of 1~000 - 30~000O
In another preferred embodiment, there is utilized in
combination with the anionic water-soluble vinyl polymers another
water-soluble polymer having dispersant properties such as a
sulphonate-containing polymer which is capable of acting as a
dispersant for any excess hardness not acted upon by the
sequestrant anionic water-soluble vinyl polymer.
The Water-Soluble Seqùestrant Anionic Vinyl Polymers
These polymers, as indicated, have molecular weights
ranging between 500 ~ 50,000, with a preferred molecular weight
range being within the range of 1,000 - 30,000.
The polymer may be homopolymers or copolymers of vinyl
Molecular weight is the average molecular weight.
-- 2 --
carboxylate-containing monomers. ~Carbox~late-containlng
monomers~ means tha~ the carboxylic acid groups are either in the
form of the free acid or of a wa~er-soluble sal~ thereo such as
alkali metal, ammonia or amine. In the case of acrylic acid
polymers, it would include the amide.
Thus, the homopolymers of acrylic acid, me~hacrylic
acid, maleic acid, fumaric acid, itaconic acid~ and the like may
be used. Polyacrylamide, when added to ~he boiler water,
undergoes hydrolysis tO convert portions or all of the amide
groups to carboxylate groups, and as such, is also included.
In addition to using these homopolymers, water-soluble
copolymeric forms may also be employed. When the copolymers are
used, the amount of carboxylate should be ae least 30% by monomer
weight ratio of ~he copolymers.
A preferred 5roup of carboxylate polymers are those
derived by the hydrolysis of the corresponding polyacrylamides.
These materials, after ei~her caustic or acid hydrolysis, will
contain between about 10 - 30% by weight of amide groups. A most
preferred group of carboxylate polymers are those obtained by
polymerizlng acrylic acid with acrylamide at a 3:1 monomer weight
ratio.
As indicated, the amount of polymers used to treat the
hardness contained in the boiler waters should be between 1 - 30
ppm per ppm o hardness.
It has been found that the preferred water-soluble
anionic vinyl polymers must exhibit a chelation value in excess
of ~00, and pref2rably in excess of 300. When applied to ~he
invention, chelcltion value means the average chelation value from
both calcium and magnesium determina~ions.
-- 3
Chelatlon Value
Chelation value is defined as the milligram~ of calcium
or magnesium expressed in terms of calclum carbonate complexed by
one gram of active sequestrant. In this work, it is measured by
specific ion electrode techniques. A known increment of
sequestrant is added to a system containing a known amount of
free (uncomplexed) calcium or magnesium. The decrease in
calcium/magnesium activity (concentration) is ~hen a direct
measure of complexed speciesO Thls amounl is then converted
(ra~ioed) to yield the chelation value.
The ef~ective mole ratio can also be computed using this
information. By dividing the chelation value into 100,000 an
equivalent wei~ht for the ~equestrant is determined. If the
molecular wei~yht is known, then the mole ratio is found by
dividing che molecular weight by the equivalent weight. ~or ED~A
and NTA, ~he value should approximate unity. For polymers, this
number varies with the molecular welght and is generally greater
than unity.
The Polymeric Dispersants
In a preferred mode of the in~ention, the carboxylate
polymers described above are used in conjunction with a water-
soluble polym~r which is capable of dispersing hardness.
The polymeric dispersants used in this preferred mode of
the invention are anionic water-soluble vinyl polymers. To be
operative t they must be capable of dispersing suspended mat~er
that normally occurs in boiler waters. They may be further
characterized a,s containing eirher carboxylate functionality or
sulphonate functionaltiy. Additionally, they may be
chara~terized ~as having a molecular weight of at least 500 to
about 50,000,
- 4 --
Z~7
~ , .
The water-soluble dispersing polymers useful in this
invention may be chosen from the carboxylate con~ainlng
water-soluble vinyl polymers such as, vinyl sulphonate-acrylic
acid copolymers, vinyl sulfonate methacrylic acid copolymers,
sulfonated styrene-maleic anhydride copolymers, and acrylamide/
acrylate copolymers.
The preferred water soluble dispersing polymer is a
vinyl sulphonate copolymer synthesized from vinyl sulphonate and
acrylic acid. This dispersant molecule generally contains from 5
- 25 mole percent of the vinyl sulphonate or its alkali metal
tpreferably Na) salts and from 95 - 75 mole percent of acrylic
acid and it~ water-soluble alkall metal or ammonium salts.
Preferably, the acrylic acid-vinyl sulphonate copolymers con~ain
10 - 20 mole percent of the vinyl sulphonate and from 90 80
mole percent of acrylic acid. The molecular weights of ~hese
preferred dispersant ~olymers range from as low as 500 to as high
as 50,000. Molecular weight ranges of from 750 - 50,000 are
preferred with a molecular weight range of approximately 900 -
15,000 being especlally preferred. Ideally, the molecular weigh~
will range from 1,000 - 6,000. It is surprising to find that
these dispersant molecules may or may not be chelant or
seques~rant molecules if treatment levels are drastically
increased.
Another class of polymeric dispersants are the low
molecular weigh~ polyacrylic acids and their water-soluble
salts. These materials have a molecular weight range of l,OOU -
5,000. The ratios in which these materials are used with the
carboxylate polymers are the same as described a-bove for the
acrylic acid vinyl sulphonate copolymers.
Yet, another class of polymeric dispersants are the low
1,
!3~7
molecular weight sulphonated copolymers of styrene and malelc
anhydride. These materlals are preferably present as the sodium
salt of sulphonated copolymers of styrene and maleic anhydride
and are typically known and commercially sold as versa TL~-32
products. Other sulphonated copolymers of styrene and maleic
anhydride are also found useful in this application when combined
wlth the above-described carboxylate polymers having sequestran~
properties.
To summarize with respect to ~he mos~ preferred
operational method, it may be stated ~hat ~he preferred method of
treating hardness present in boiler waters which are in contact
with heat transfer surfaces to prevent and remove scale caused by
such hardness comprises treating such waters with:
~a) a water-soluble anionic vinyl polymer containing at
least 30% by weight of a carboxylate functionality, said
polymer having a molecular weigh~ within the ran~e of
500 - 50,000, and
(b) a second anionic watPr-soluble vinyl polymer
dispersant.
To summariæe with respect to the most preferred
polymeric dispersan~s, it may be stated that the boiler wa~ers
are preferably simultaneously treated wi~h both the sequestrant
(chelant) water-soluble anionic vinyl polymer mentioned above and
a second anionis water~soluble vin~l polymer dispersan~ chosen
from the group consisting of carboxylate-containing,
water-soluble ~:inyl polymers, vinyl sulphonate-acrylic acid
copolymers, vinyl sulphonate-methacrylic acid copolymers,
sulphonated styrene-maleic anhydride copolymers, and
acrylamide-acry:Lic acid copolymers.
_ . _ _ _ _ _ _ . _ _ _ _ _ _ _
~Registered Trademark of National Starch and Chemical
Corporation
It is particularly lnteres~ing to no~e tha~ most of the
chelant or sequestrant anionio vinyl polymers show an ability ~o
disperse solids in boiler water systems if treatment levels are
below those required to chelate hardness ions. As a result of
this observa~ion, the chelan~ or sequestran~ polymer may be usec3
in quantities above those quanti~ies necessary to chelate all of
the hardness initially found ln the boiler system. When th L5
occurs, it has been observed that any hardness ions or scale
existing in the boiler system may be removed f~om ~he system and
the additional chelant polymer may act as a dispersant, as well
as a se~uestrant for hardness contamination.
Thus, the expression and related terms relating to the
addition of a second anionic wa~er-soluble vinyl polymer
dispersant in combination wi~h ~he seguestrant polymer is mean~
to include the phenomenon described above, i.e~, use of excess
sequestrant polymer to provide both sequestra~ion and dispersancy.
Ratio of Sequestrant to Dispersant Polymers
The ratio of carboxylate polymer to acrylic acid-vinyl
sulphonate copolymer, when they are used, is within the range of
30 1 to 1:30 with 20:1 to 30:1 being a preferred range, with 20:1
being most preferred.
In general, the ratio of sequestrant carboxylate polymer
to dispersant polymer is also wltbin the range of 30-1 to 1:30.
A preferred sequestrant polymer ~o dlspersant polymer ratio is
be~ween 30:1 and 10:1 with a most preferred ra~io of seques~rant
polymer to dispersant polymer being 20:1. In all cases, chls
ratio is on a weight:weight basis.
To illustrate the many advantages of the invention, the
following is presented by way of example.
Experimental
For purposes of understanding the following tests, a
series of various polymers and known boiler water treatment
chemicals were evalu~ted. These evaluations were performed in
two series of ~esting programs. The first testing program
involved the measureme~t o the chelation values of various
polymers so as to determine by initial screening ~he potential of
each polymer to function adequately as a boiler transport
material.
The experimental design used to test the chelation value
of a series of polymers was as follows:
Solutions of calcium or magneslum ions were titrated
with solutions of various polymeric and other sequestering
agents. The residual unsequestered metal ion concentration (or,
more correctly, activity) was measured by mea~ of a Specific ~on
Electrode (henc~forth S~IoE~ ) ~ This data was ultimately
converted to graphical represen ations o~ seques~rant per-
formance. Sequestran~ perormance for Ca ion was measured by a
calcium specific electrode, manufa~tured by Orion Research, Model
93-20. 5e~uestrant performance for Mg ion was measured by a
Divalent cation electrode, Model 93 - 32, again manufactured by
Orion ~esearch. The electrode response is measured, as ~he
sequestrant solution is added incrementally to the hardness
solution. The desired solution p~ is automatically maintained by
feeding potassium hydroxide solution from a Mettler DV10 which is
controlled by a Mettler DK10/11 system.
A short: period oE time is allowed after each se~uestran~
addition before taking a readlng so that the electrode can come
to equilibrium wi~h the solu~ion. Noise levels are typically
0.2 mV using mechanical stlrring (higher using a magne~ic
stirrer).
-- 8 --
Prior to each titracion, the S.I.E. was calibrated with
standard solutions containing 1~000, 100, 10~ and 1 ppm calcium
or magnesium.
The S.I.E. responds to activity rather than con-
centration. ~or calcium measurements, a high, constant, ionic
strength is main~ained by addition of 6 g/l potassium chloride tO
all solutions (l.e., s~andards, sequestrant, and calcium
sample). This maintains a constan~ activity coefficient for the
calcium ion. The divalent sensing electrode used for magnesium
measurements is subject ~o interference from both sodium and
potassium ions at fairly low concentrations so no ionic strength
buffer can be used in this case.
Typical operating conditions were 2 or 3 g/l active
polymeric sequestrant ti~rated agains~ (in all cases) 100 ml of
100 ppm metal ion. Under these conditions, most titrations were
essentially complete af~er the additlon of 40 - 50 ml of
sequestrant. Sequestrant solutions were usually added in 2 to 3
ml increments. Seq~estrant was added slowly so as to avoid the
formation of bubbles whirh could be trapped at the base of the
electrodes and result in incorrect readings~
All measurements were made at room temperature
(measurements above about 40C will result in rapid electrode
deterioration).
The data from ~hese experiments was graphically
dlsplayed or perferably converted to a usable form by a computer
program which was written specifically for these experimen~s.
The computer program obtains the best straight line fit through
the origin using a reit.erative, leas~-squares approach, allowlng
calculation of chelation value for each polymeric species.
~ g _
~9~
For calcium measurements, a pH of 10 was used in most
cases. Initial studies gave results indicating chelation grea~er
than theoretical. At a p~ of 9, the results were in good
agreement with theory. The discrepancy at pH 10 may be due ~o a
competing reaction (e.g., magnesium hydroxide formation). All
magnesium measurements were made at a pH of 9 after this~
An attempt was made to correct magnesium results for the
ef~ec~s of any sodium pr@sent. However, when corrections
ob~ained from sodium chloride solutions were applied to an
NTA.Na3.H2O titration, the ~correctedH results were very
unreasonable (~uch greater than ~heoretical chela~ion). Nc
further attempts to correct for sodium were made.
Chelation values were determined from ~he initlal slope
of the titxation curve which plots percent metal ion sequesterQd
versus grams of active polymer added. This calcula~ion glves
practical chelation values in that no considera~lon has b~en
given to which complexes are formed, the effects of competing
equilibria, or various stability constants.
In the case of the polymers studied, a comparison of
chelation values may be more valid than they might be in the case
of strong complexing agents, such as EDTA or NTA, where a simple
comparison of chelation values ls not necessarily a good guide to
chelation performance.
No evidence of "threshold effects~ was observed for any
of the poly~ers ~ested. As later results will show, to be
ef~ective as a transport agent in boilers, the chelation value
for the polymeric se~uestrant must be above 200 and must give
clear solutions for both calcium and magnesium ion test
solutions. The preferred average chelation value is above 300.
Most of the polymers tested appeared co sequester magnesium ion
better
-- 10 --
than chey were able to seques~er calcium ion. However, to be
successful, a polymer musc have, as stated above, a ohela~ion
value above 200, preferably above 300, and be able to sequester
both calcium ions and magnesium ions to give clear solurions.
The data in Table I compares different sequestrants and
the chelation values obtained using the above described cest. As
can be seen from ~his Table, the sequestran~s tested include no~
only well-known complexing agents such as EDTA and ~TA but also
polymeric sequestrantst as well as other sequestrants. As will
be shown later, only those sequestrants which have chelation
values above ~00 can be shown ~o function as effective transport
agents in a boiler sys~em.
Other se~uestrants on the li5t are not satisfac~ory as
transport agents because of known thermal degradation in a boiler
system. 5uch agents are the phospha~e containing compounds
listed in Table I.
Table II identifies each of ~he polymeric species tesced.
Table III lists results for the polymeric sequestrants
of this invention, as well as other more common sequestrants
versus magnesium lon. Again, as can be seen, those polymeric
sequestrant agents which have chelation values above 200 and are
thermally stable give excellent results in boiler transport. Of
particular note in Table III is the result for citric acidO
Although, a very large chelation value is obtained, this material
does not effectively transport magnesium or calcium hardness wher.
tested in the boiler. It is expected that these results are due
to the fa~t that citric aid thermally decomposes when exposed to
boiler operating conditions. This very well may be the benefit
for the low molecular weight polymeric carhoxylate polymers of
this invention, that is, that thermal stability is obtained while
-- 11 --
maln~aining sequestrant activity for hardness ions at proper
dosages.
Of particLIlar note in Table III is the fact tha~ Polymer
C, though giving a chelation value in excess of 200/ yields a
somewhat cloudy solulion wi~h magnesium at pH 9 and would not be
expected to perform as well as the other carboxylate con~aining
polymeric sequestrants of this inven~ion. This problem mighr be
solved by increasing the concentration of this polymer or by
combining this polymer with o~her materials giving improved
results. The polymeric materials that did not perform well wi~h
calcium were not tes~ed for magnesium since both ions must be
complexed before ade~uate boiler transport systems can be
achieved.
- 12 -
TABLE I
Sequestrants vs. Ca , pll = 10
Mole
Product % Active M.W. C.V.~Ratio
EDTA 100 292 3~7 1.01
NTA 100 191 5~1 1.03
Citric Acid 100 192 392 0.75
1,2,~ - tricarboxy-2 50 256 610 1.56
phosphono-butane
amino-tri (methylene- ro 299 559 1 67
phosphonic) aci.d
diethylene triamine-
penta (methylene 50 573 701 ~.01
phosphonic) acid
hexa-potassium sa.lt of
hexamethylenediamine 23 492 282 1.39
tetra (methylene
phosphonic) acid
**l-hydroxy ethylidine l, 60 206 961 1.98
I-di phosphonic acid
**Sodium tri-pol.y 100 368 553 1.
phosphate
Polymer A 25.5 1000-5000 479 13.9
(ave 2300)
Polymer B 50 2500-7500 37~ 19.1
(ave 5100)
Polymer C 100 1000-2000 29~ ~.7
(ave 1600)
Polymer D 25 2500-7500 386 18.9
(ave ~900)
Polymer E 65 1000-3000 300 6.3
(ave 2:L00)
Polymer ~ 50 Not available 300
Polyrner G 22.75 " " 291
Polymer l-l 31.6 " " 252
Polymor I - - 1~5
['olymer J - - 105
Polynler K - - 19
* Chelation values calculated on the basis of 100% active material for all
cases.
** Produced cloudy solutions.
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;,,;
TABLE II
Polymer Iclentifi.cati.on
Polymer Chemical Designation Mole Wt.
Polymer A Polyacrylic Acid 1000-5000
(ave 2300)
Polymer B Polyacrylic Acid 2500-7500
(ave 5100)
* Polymer C Styrene-maleic anhydride 1:1 1000-2000
copolymer (ave 1600)
* Polymer D Vinyl ~ulfona-te-acrylic acid 2500-7500
1:3 copolymer (ave 4~00)
Polymer E Polyacrylic acid 1000~3000
(ave 2100)
Polymer F Polymaleic anhydride (est.) 700-3500
* Polymer G Acrylic acid-acrylamide 4:1 not avail.
copolymer - below SOJ 000
* Polymer H Acrylic acid-acrylamide 3:1 not avall.
copolymer - below 50,000
Polymer I llydrolyzed polyacrylonitrile not avail,
- below 50,000
Polymer J Sodium salt of sulfonated co- not avail.
polymer of styrene and malei.c - below 50,000
anhydride
Polymer K Acrylic acid-acrylamide 1:3 (est,)5000-15,000
copolymer
*Ratios are monomer weight ratios
- 14 _
TABI,E III
Sequestrants v~. Mg~ pll = 9
Product ~ Active M.W.C.V.~ Mcle Ratio
L~DTA Acid 100 292 345 1.01
N~'A Acid 100 191 461 0.88
Citric Acld 100 1~2 762 1.46
Polymer A 25.5 -- 910 --
Polymer D 50 2500-7500 691 35.
~ave 5100i
Polymer C~ lV0 1000-2000 231 4.5
J ~ lave 1600)
~' PQlymer D 25 2500-7500 603 Z9.5
] (ave 4900
Polymer ~ 65 1000-3000 527 9.S
(ave 2100
Polymer F 50 -- 607 --
~olymer G 22.75 -- 291
PoJymer H 31.6 -- 493 --
* All Fesults expressed ln terms of 100~ active materials.
C.V. and Mole Ratio e~presse~ as CaC03
roduced cloudy sol~ltiolls
~ t7
Some of the more promising carboxylate-containing
polymers having chelation values above 200 were tried in
experimental boiler water systems. The experimental boller is
described in the paper, ~The Investi~ation of Scaling and
Corrosion Mechanisms ~sing Process Simulation,~ by J. A. Kelly,
P. ~. Colombo, and G. W. Flasch, paper No. IWC-80-10, given at the
41s~ Annual Meeting, InternatioQal Water Conference, Pittsburgh,
Pennsylvania, October 20-22, 1980.
Table IV indicates the formulations and sequestran~
polymers chosen to be tested in the experimental boiler pro~ram.
Included in these tests were a phosphorous-con~aining seques~ran~ r
as well as a wa~er-soluble polymer which does not con~ain
measurable amoun~s of carboxylate functionality.
In the following discussion, reference is made to the
attached drawi:ngs in which:
Figures l, 2 and 3 show dosage profiles for co~positions
I~ IV and V respectively,
Figure 4 shows hardness recoveries using composition
I ,
Figure 5 shows hydrogen readings during a composition I
~est, and
Figure 6 shows iron content readings during a com-
position I test.
- 16 -
TABL~ IV
Te~t Ingredients Eor Experimental
~oiler Work
Composition Ingredients
I 20/1 active ratio Compo~ition II/IV
II Polymer 11
III Polymer A
IV P~lymer D
V Polyacryla~ide (M.W. - 40003
VI Polymer ~
VII Diethylenetrtaminepenta tmethylene
! phosphonlc acid~
t' VIII Ethylene dichloriae - Ammo~la copolymer
(M.W. - 25000 - 60000)
EDTA Ethylene~ia~înetetraacetic acid
G~7
The Experimen~al Scale Boiler
Most of the experiments were conducled at 1,000 pslg,
110,000 Btu/ft -hr heat flux, and 10 concentration cycles. The
Composltion I polymer was tested more extensively at 250, 600, and
1,500 psigO This laboratory boi:ler is of ~he rype described in
U.S. 3,296,027.
~ eedwater was ~ypically deionized water contalning 1 ppm
Ca, 0.5 ppm Mg, and 0.5 ppm SiO2. Sulfite resldual was
maintained at 25 ~ 5 ppm at 6~0 psig and 10 ~ 5 ppm at 1,000
psig. Boi].er water 'O' alkalinit~ was maintained at 160 - 180
ppm. The pH of the polymers was adjusted to 9.
The ~xperimental Scale Boller Results
A. Dosage Profiles
Dosage Profiles of a number of polymers were obtained
under three conditions. It is apparent in Pig. 1 tha~:
1. the recommended dosage of Comp. I combination
polymer for hardness control is about 5.3 ppm active
polymers/ppm total hardness at 1,000 pslg, and
2. a~ dosages below the recommended, the combination
polymer preferentially transports Ca rather than Mg
ionsO
Figs. 1, 2, and 3 indlcate that Comp. I as well as Comp.
III and Comp~ IV have rhreshold inhibition capability at low
dosages for the Ca ions, and chelate hardness ions at hlgh
treatmenr levels.
In general, all the tested acryla~e-, acrylamide-, and
vinyl sulphonate-based polymers give excellent hardness control
_ _ _ _ _ _ _ _ _ _. _ _
3Sequestration may be a more appropria~e terminology, however,
chelation appears to be the mechanism.
at high dosa~es, as long as they contain sufficient carboxylate
functionality. Among those, Comp. II and IV are the most
effective. Results are listed below.
Condition 1:
Boiler Pressure = 1,000 psi, Heat Flux ~ 110,000 Btu/ft2-hr,
Ca - 1~ Mg = 0.5, SiO2 - 0.5 ppm ln the feedwater.
Treatment Treatment Ratio4 % Ca Recovery ~ Mg Recovery
Comp. I 0.53 16 trace
1.05 41 6
2.1 75 47
3,15 40 33
6.3 129 141
Comp. III 4,8 66 44
6.72 84 73
8.54 106 104
Condition 2:
Boiler Pressure = 1,000 psi, Hea~ flux = 250,000 Btu/ft2-hr
Feedwater contained 1 ppm Ca, 0.5 ppm Mg, and 0.5 ppm SiO22
Treatment Treatment Ratio % Ca Recovery % Mg Recovery
None 47 trace
Comp. I~ 6.72 118. 101
8.64 122 114
Comp. I 4.2 90 78
5,~5 96 89
6.3 107 107
7.~5 109 117
4Defined as ppm active polymer per ppm total hardness.
- 19 -
I
8~09 107 112
9.03 10~ 109
Comp. III 8.64 102 105
9~6 99 106
Co~p III 8.64 101 102
+ 1 ppm 9.6 102 108
Comp~ VII
Comp~ VI 8.64-9.6 127 118
Comp. V 8.64 82 120
Comp. IV 8O64 112 105
Condi~io~ 3:
Boiler Pressure - 600 psi, Heat Flux - 110,000 Btu/hr-ft2,
Ca = 1, Mg - 0.5, SiO2 - 0O5 ppm in the feedwater
Treatment Treatment Ratio % Ca Recovery % Mg Recovery
Comp. IV 0.15 104 trace
0.3 87 trace
0.6 41 trace
1.2 94
2.~ 87 41
4.8 120 13~
Comp. III 0.15 67 ~race
0.3 55 ~race
0.6 42 trace
1.2 73 4
2.4 53 29
4.8 93 90
Comp. VI 0.15 64 ~race
0.3 57 trace
0~6 42 trace
1.2 72 trace
2,4 67 32
4.~ 104 86
- 20 -
Comp. VIII 0.3 53 trace
4.8 54 trace
25.0 114 16
8. Comp. I Performance at lt500 psig
Hlgher re~ommended dosage is required for hardness
control at higher boiler p~essure. the increase in
treatment level is probaly due to the decomposition of
po lyme r I
As the da~a helow indlcate, ~he dosage requir~d for
a complete hardness recovery increased at 1,500 psig~
Corrosion rate, a.s measured by the iron conrent in the
blowdown, did not increa~e.
Ca = 1, Mg - 0.5t SiO~ = O.S ppm in the feedwater.
Pressure - 1,5~00 psig, heat Flux z 110,000 Btu/ft2-hr
Pol~mer Trea~ment Ratio % Ca Recovery ~ Mg ~ecovery
Comp. I 15.75 89 105
21.0 9g 108
26~25 99 107
C. Comp. I Per~ormance at 250 psig
The combination polymer had no problem controlling
hardness at low pressure (250 psi) boiler applications.
Hea~ flux was 110,000 ~tu/ft -hrO
Condi~ion 1:
Feedwater conta:ined Ca = 3, Mg - 1.5, Na2SO4 = 42.6,
NaCl = 10, SiO2 = 5, Fe = 1 ppm, and enough NaHCO3 to give an
M alkalinity 40 in the ~eedwater or 400 in boiler water,
S03 - 30 ppm in the blowdownc
Recovery
Treatment Ratio % Ca % M~ ~SiO2 %_Fe % Na~SO4
5,04 116 ~7 101 94 113
10.08 113 107 95 9S 111
20.16 115 122 92 96 109
~L .
Condi~ion 2:
Feedwater Contained 3 ppm Mg and all the other components listed
in 1.
Recovery
Treatment Ratio % ~a ~ MCL %si2 ~ Fe ~ Na~SO4
3.78 113 S7 83 3~ 107
7.56 11~ 79 88 91 116
15~12 113 136 99 85 116
D. Effect of ~ardness and Silica ~psets on Comp. I
Comp. I ~reatmen~ can recover from moderate
hardness, silica, and treatmen~ upsets.
Condition 1:
Pressure of the boiler = 1,000 psig, ~eat flux = 110,000
Btu/hr-f~2. Comp. I treatment ratio 7.88 polymer/ppm hardness
when lnitial hardness was 1 ppm Ca and O . 5 ppm Mg. Total polymer
held constant ~hroughout the test as hardness was varied.
Feedwater ~ecovery ~otal Hardness
Ca Mg SiO2 Fe by
~E~ ~E~ ~E~_ %Ca ~ 2 E~ titration
1.0 0.5 0.5 116 112 102 0O5 17.2 16.6
2~0 1.0 1.0 7~ 66 ~2 0.4 20.7 19.5
1.0 0.5 1.0 111 102 97 0.3 16.2 --
5.0 2.5 2.5 3g 32 ~5 0.3 27.2 26.5
1.0 0.5 0.5 116 128 134 0.1 18
Condition 2:
Ca/Mg/SiO2 Swing Effect
,000 p9i and 250,000 B~u/hr-ft2
Ca/Mg/SiO2, ppm Recovery
Polymer Treatmen~ Ratioin F.W. %Ca
Comp. II 8.64 1/0.5/0.5 12~ 114
6.721/0.5/0.5 118 101
.720~5/1/0~5 1~6 87
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6.72 0.5/1/2.0 1~7~2
Comp. IV 8.64 1.0/0O5/0.5 132107
8.46 0.5/1/0.5 10995
~.6~ 0.5/1/2.0 9~ 81
17.2~ 2/1/1 91 84
Condition 3 - For Comp. I^
Feedwater contained 1 ppm Ca, 0.5 ppm Mg, and 2.5 ppm SiO2,
l,OOQ psi and 110,000 Btu/hr-ft2O
Treatment
Ratio ~ Ca Recovery % Mg Recovery ~ SiO7 Recovery
7.88 100 97 103
15.75 106 14~ 102
E9 Scale Removal Usinq Comp. I
'.,cale removal using Comp. I appears feasible if
hardness and silica can be discharged by ~he blowdown.
Adequate Comp. I treatment can tran~port boiler deposits
in addition to ~he hardness in the feedwater. It
enhanced passivation of the boiler heat ~ransfer surface
and ~crmed a black, magne~ite film.
Condition 1:
Feedwater contained Ca - 1, Mg = 0.5, and SiO2 = 0.~ ppm
Pressure = 1,000 psigt Hea~ flux = 110,000 Btu/hr-ft2
Recovery ~or-al ~ardness
Fe By
Treatment Ratio ~ Ca g Mg ~ SiO~ titration
3.93 88 71 112 trace 12.7 12.8
7.88 140 183 104 trace 21.2 17.8
15.75 168 218 156 0.6 27.7 2~.6
23 -
Condition Z:Feedwater contalned no hardness and no sillca, a badly fouled
boiler.
Pressure = 1,000 psig, ~eat flux - 110,000 Btu/hr-ft2.
Treatment Ratio Recovery Total Hardness
(assume hard- Ca Mg SiO2 Fe PO4 ~y
ness = 1 ppm) ~ ppm ~ titration
23.63 10.2 16.4 ~.5 0.710.7 23.~ 23.4
47.25 18.1 15.9 6~8 0.812.2 35.9 24.1
70.88 2~,9 21.9 8.1 1.616.1 ~6.7 44.3
Condition 3:
Feedwater contained no hardness and no silica and the boiler was
relatively clean.
Pressure = 1,000 psig, Heat flux = 110,000 Btu/hr-ft2.
Treatment = 23.63 ppm Comp. I per ppm total hardness, assuming
total hardness = 1 ppm.
Recovery
No. of Days Ca ppm Mg ppm SiO~ ppm Fe ppm
0 3.6 5.0 11.5 5.8
1.8 1.7 2.g 1.3
6 1.7 1.4 1.5 1.4
7 2.1 1.4 1.1 0.9
8 ~.~ i.3 0.5 1.~
F. The Effect of Heat Flux on Comp. I Performance
Heat flux in the range of 110,000 to 250,000
Btu/hr~-ft had little influence on hardness recoveryO
At heal: fluxes greater than 300,000 Btu/hr-ft2 there
was a thin film of deposition on the heat transfer
su~face.
. - 24 -
Test Condition: 1,000 psi
Feedwater contained 1 ppm Ca, 0.5 ppm Mg, and aO5 ppm SiO2.
~eat Flux Treatment Recovery
Btu/hr-ft2 Ratio ~ Ca ~ % SiO~
100,000 9.03 112 140 117
3no f ooo 9.C3 1~1 171 122
G. Performance of Other Combination Polymers
Comp. III/Co~p. IV combination polymer, although
less effective than Comp. I, gave reasonable hardness
control a~ 1,000 spig~ This combination polymer could
be used in N~3 sensitive applications.
Conditions:
Ca = 1, Mg = 0.5, SiO2 ~ 0.5 ppm in the feedwater.
Pressuze - 1,000 psig, ~eat Flux = 110,000 Btu/ft2
Treatme!nt Ratio % Ca Recovery ~ Mg Recovery
7.8886 gl
10.5 g9 111
13.12102 108
Experimental Boiler Results
The combination polymer Comp. I was ini~ially added to
~he boiler at a dosage of 7.9 ppm ac~ive per ppm total hardness.
The dosage was maintained for eight daysO The average calclum
and magnesium recoveries were 118~ and 101%, respectively~
Initial hydrogen level was 11 ppb but dropped to 1.5 ppb the same
day. It leveled off to 0.4 ppb. ~ydrogen values of 1.0 - 1.2
ppb are e~uivalent to background levels. The high initial rise
of hydrogen frequently occurs in a boiler just brough~ on line.
In addition, sulfite residuals for the first few days were lower
than desired and contributed to hydrogen generation. Iron in the
blowdown star~ed off high at 2 - 3 ppm and declined ~o 1.1 ppm
after eight da~s. The condensate frequently had a pH greater
than 9, and contained small amounts of ammonla.
- 25 -
A~ ~his poin~ the polymer dosage was decreased to 3.9
and the test was continued at thls condition for six days. This
treatment level is less than 2/3 the recommendedO The average
oalcium and magnesium recoveries for this period were 96~ and
81~, respectively. It was an~icipated from the experimental
scale boiler resul~s that hardness recoveries would decline and
that magnesium would be more affected than calcium. Hydrogen
dropped to 0.3 ppb and iron decreased to 0.3 ppm. The
tempera~ure of the high heat flux area remained constant,
indicating no scaling.
At this point, the polymer dosage was Eur~her reduced tO
2.6 and held a~ this condi~ion for three days. Calcium and
magnesium recoveries declined to 89% and 78%, respec~ively, while'
hydrogen and iron levels were frac~ionally lower. During low
level treatment, the temperature in the horizontal test section
increased 30F which indicated that scale was being depositedO
The polymer dosaye was then restored to the original
level o 7.9 for fif~een days. Within ~he flrs~ day, the
tempera~ure of the horizontal test section dropped 30F. As
anticipated, calcium and magnesium recoveries increased
dramatically and averaged 122% and 111%, respectfullyu These
high recovery values suggest that the polymer treatmen~ program
is removing deposits previously laid down when under~treating.
Similarly, it is postulated that at the start of this test, the
118% calcium recovery was due to removal of boiler deposi~s that
remained in the system from the previous test. Hydrogen and iron
remained at relatively low levels.
Fi~s. 4, 5, and 6 depict percent hardness recovery, ~2
level, and iron level in the blowdown as a function of days of
tes~. Polymer treatment was then s~opped for 7 days. Only trace
~ 26 -
amounts of calcium and magnesium were recovered during this
periodr while hydrogen and iron remained virtually unchanged~
During the remaining period of the ~est, polymer dosage
at 7.9 was al~ernated with no tre,atment. In the presence of
polymer, recoveries of calcium and magnesium averaged 115~ and
106%, respectfully.
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