Method of removing iron oxide deposits from heat transfer surfaces

Iron oxide deposits which are found on heat transfer surfaces can be removed by first contacting these deposits with an aqueous solution of a hydrolyzable tanning extract such as sumach, valonea, or chestnut tannin which conditions the deposits and forms a complex thereof. The thus-formed complex is subsequently removed by treatment with dilute solutions of citric acid.

INTRODUCTION 
Most industrial heat exchangers are composed of bundles of ferrous metal 
tubes. In some instances, non-ferrous metals such as admiralty metal are 
used. These heat exchange systems are water-cooled, with the heat absorbed 
by the water being removed atmospherically by cooling towers. These 
industrial cooling systems rapidly form iron oxide deposits which reduce 
their heat transfer efficiency. It is common to mechanically clean these 
systems when the iron oxide deposits become excessive. Mechanical 
cleaning, while effective in many cases, is time-consuming and expensive. 
The heat exchangers thus described should be distinguished from the heat 
transfer surfaces of boilers. The distinction is that the scale in boilers 
is most often composed of calcium or magnesium salts and is relatively low 
in iron oxide. Industrial heat exchangers of the type described normally 
contain deposits which are predominantly composed of the oxides of iron. 
Therefore, the specification and claims, when referring to heat transfer 
surfaces and heat exchangers, means industrial heat exchangers and not 
boilers.

THE INVENTION 
A method for removing iron oxide deposits from heat transfer surfaces which 
comprises the sequential steps: 
(a) contacting such surfaces with an aqueous solution which contains at 
least 25 parts per million of a hydrolyzable tanning extract and has a pH 
of not more than 8.5 for a period of time sufficient to modify a 
substantial portion of the iron oxide deposits; and then, 
(b) removing the modified deposits formed in step (a) with an aqueous 
solution having a pH not greater than 4 which contains at least 1000 parts 
per million of citric acid. 
The Hydrolyzable Tanning Extract 
This group of tanning extracts represents a distinct species of tannins 
over the so-called condensed tanning extracts. The hydrolyzable tanning 
extracts most advantageously employed in the practice of the invention are 
sumach, valonea, or chestnut tannin, with the latter being preferred. For 
a more detailed discussion of tannins, see the Encyclopedia of Chemical 
Technology, Second Edition, Volume 12, Interscience, 1972, page 321 et. 
subs. 
The hydrolyzable tanning extracts are most preferably employed at ranges 
between 50-1000 ppm with solution concentrations of 100-300 ppm appearing 
to be optimal. The pH of these solutions should not exceed 8.5 and is 
preferably within the range of 3.0-7.5. While the hydrolyzable tanning 
extracts are effective when used alone, it is oftentimes beneficial that 
they be used in conjunction with a water-dispersible surfactant, 
preferably a nonionic surfactant. Surfactants of this type are described 
in McCutcheon's Detergents & Emulsifiers, 1974 North American Edition, 
Published by McCutcheon's Division, Allured Publishing Corporation. A 
preferred surfactant is nonyl phenol reacted with 9 moles of ethylene 
oxide. The amount of time necessary for the hydrolyzable tanning extract 
to act upon and complex with the iron oxide deposits varies depending upon 
a number of conditions. A general rule is that the minimum time required 
is at least 12 hours with time periods ranging from between 12 hours to as 
long as several days sometimes being required to adequately complex with 
the iron oxide deposits. Such variables as the temperature of the system 
during the treatment with the hydrolyzable tannin extract, the nature and 
quantity of the deposit, the pH of the system, and the like will govern 
the time of the treatment which cannot be expressed with exactitude. The 
optimum conditioning parameters for chestnut tannin were found to be a 
100-500 ppm solution circulated for 2-3 days with the pH being about 3-7. 
Citric Acid 
The citric acid treatment which follows after the hydrolyzable tanning 
extract treatment should employ citric acid solution which contains at 
least 1000 ppm with the pH not being in excess of 4. In most instances, 
the pH of the citric acid solution should be about 3.0-3.4. A pH of 
2.8-3.8 should be maintained to obtain maximum advantage of citric acid. A 
preferred dosage range of the citric acid is within 2000-4000 ppm. 
The time required for the citric acid to remove the hydrolyzable tannin 
extract iron deposits will vary between a few hours up to as long as a day 
or more depending upon the environment of the system, e.g. pH, tannin 
extract employed, quantity of suspended or tannated iron oxide in the 
system, temperature and the like. In most cases, a time of about 18 hours 
using optimum citric concentration and pHs will give good cleanup. 
Rather than continuing the citric acid treatment for a fixed period of 
time, it is possible to monitor the soluble iron levels during the citric 
acid treatment. The treatment can be discontinued when the iron levels are 
above about 500-600 ppm. 
Temperature 
The treatment with the hydrolyzable tannin extract and the citric acid may 
be conducted over a wide temperature range but below the boiling point of 
the treating solutions used to practice the invention. While ambient 
temperatures may be used, it is preferred that the temperatures in excess 
of 100.degree. F. be used with a preferred temperature range being 
100.degree.-150.degree. F. 
A typical cleaning procedure for an iron fouled heat exchanger would be as 
follows: 
1. Discontinue the corrosion inhibition program, if used. 
2. Add 200-300 ppm tannin and 5-10 ppm of Comp. N.sup.1 to the system and 
circulate. Maintain the pH at 6-7 and a temperature of 
110.degree.-130.degree. F. As the tannin concentration is reduced to less 
than 50 ppm by consumption, add more tannin to increase the dosage to 
200-300 ppm. 
FNT .sup.1 See Glossary, page 8(a). 
3. Discontinue tannation after 2-3 days depending upon the severity of the 
fouling. 
4. Dump the system or blow-down heavily. 
5. Refill with clean water and add citric acid at 2,000-4,000 ppm, pH 
2.7-3.2, and a temperature of 110.degree.-130.degree. F. 
6. Monitor soluble iron levels and when soluble iron reaches 500 ppm, 
blow-down heavily and add more citric acid. 
7. Repeat step 6 for three or four times. (Blow-down may contain fragments 
of iron tubercles at this stage.) 
8. Blow-down system and return to the normal corrosion inhibition program, 
if used. If possible, the system should be monitored for leaks throughout 
the program and discontinue treatment if leaks develop. 
Unusually thick iron oxide deposits or deposits containing large amounts of 
silica are extremely difficult to remove using the above chemical 
treatment. In such cases, the mass of deposit should be removed by 
mechanical means prior to chemical treatment. 
Iron-Tannin Complex Solubility Studies 
Iron complexes of gallotannic acid, Quebracho tannin, wattle tannin, and 
chestnut tannin were prepared in the following manner. Ten grams of 
FeCl.sub.3 dissolved in a minimum of water was added to five grams of the 
appropriate tannin or tannic acid dissolved in water. The dark purple to 
black precipitate that formed was filtered, washed, and dried. In the case 
of chestnut tannin, its iron complex was extremely finely divided and 
probably colloidal. A water suspension of this complex had to be 
evaporated to dryness for the solubility tests. 
To determine the solubility of each of the iron complexes in citric acid 
(and hence its ease of removal from a tannated iron substrate), the 
following scheme was used. A 100 mg. sample of each iron complex was 
placed in a separate 100 ml portion of citric acid ranging in 
concentration from 500 to 5,000 mg/l. After two hours of intermittent 
stirring, the suspensions were filtered and dried. The amount of 
dissolution was determined by weight differences before and after citric 
acid treatment. Data from these experiments, conducted at 72.degree. and 
120.degree. F. are shown in FIG. I. 
Clearly, the solubility of the iron-Quebracho complex is far too low to be 
considered for practical usage. Indeed, Quebracho might lead to fouling in 
iron laden systems that would not be recovered in the subsequent citric 
acid step. Based solely on solubility considerations, the chestnut tannin 
is preferred since its chance of dissolution approaches 100 percent in 
heated systems. The iron-gallotannic acid complex is adequately soluble in 
citric acid; however, the high cost of the acid could preclude its usage. 
Heat Transfer Unit Tests (HTU) 
Heat transfer unit experiments were run to determine the effects of tannins 
and citric acid on mild steel heat transfer tubes. In most cases, the heat 
flux was 10,000 BTU/ft.sup.2 /hr. and the flow rate was 2.8-3.6 ft/second. 
Bulk water temperature was 125.degree. F. Three types of water were used 
ranging in hardness from 100 to 1200 ppm Ca, but no significant 
differences were evident. 
Twelve of the most significant runs are outlined in Table I. All were 
conducted in three cycle Chicago tap water. After each test listed, the 
significance of the findings of that test is given. Many of the findings 
of the solubility testing were verified during this phase of the work. The 
appropriate tannin type, concentration, time of tannation, and the 
relative unimportance of pH during deposit conditioning were determined. 
Optimum conditioning parameters were found to be chestnut tannin, 100-500 
ppm, 2-3 days, and pH 3-7. 
Citric acid must be applied at a minimum dosage of 1000 ppm and a pH of 
3.0-3.4. Lower concentrations and higher pH values are not effective in 
deposit removal. However, higher concentrations and lower pHs improve the 
rate of deposit removal at the expense of increased corrosion rates. 
Surfactants and dispersants have some utility in the process, primarily 
for systems with oil or silt present. 
Pilot Cooling Tower Runs (PCT) 
Eleven pilot cooling towers were used to verify all the conditions found 
for optimum iron oxide cleanup during previous testing. Significant 
differences between PCT and HTU tests are lower temperatures for the PCTs 
(100.degree. F. vs. 125.degree. F.) and slightly lower flow rates (0.1-2.5 
ft/sec. vs. 2.8-3.6 ft/sec). The PCTs also incorporate the possibility of 
using mixed metallurgies with the inherent possibility of fouling from 
corrosion of other tubes in the system. 
Two of the pilot cooling towers, A and B, used 7-tube shell side heat 
exchangers. These towers as well as Towers D and E used heat exchanger 
tubes equipped with thermocouples to follow fouling and defouling during 
all phases of the procedure. 
The PCT experiments are outlined in Table II with a summary of each run 
given at the end of the test. For Towers A, B, D, and E, FIGS. 2-5 show 
graphically the results of each phase of the program. 
Many of the parameters and conditions discovered in HTU work were confirmed 
and new facts were uncovered. For instance, chestnut tannin is preferable 
to wattle tannin; concentrations of 50-200 ppm are adequate, thick, aged 
deposits are difficult to penetrate and remove; oil and silt should 
present no unsolvable problems; low pH conditions are absolutely necessary 
for citric acid to adequately remove tannated deposits; repeated "shocks" 
up to 3,000 ppm of citric acid are preferable to constant feeding, 
long-term treatments; high concentrations of ferric ion cause increased 
corrosion and should be removed as soon as possible; and it is possible to 
passivate a cleaned system with Comp. F.sup.1 and an appropriate corrosion 
inhibitor. 
FNT .sup.1 See Glossary, page 8(a) 
The Heat Transfer Unit tests (HTU) as well as the Pilot Cooling Tower tests 
(PCT) are described in detail in the article, "Small-Scale Short-Term 
Methods of Evaluating Cooling Water Treatments. . . Are They Worthwhile?" 
by D. T. Reed and R. Nass, Nalco Chemical Company, presented at the 36th 
Annual Meeting of the International Water Conference, Pittsburgh, PA, Nov. 
4-6, 1975, which is incorporated herein by reference. Various lettered 
materials used in Tables I & II are set forth in the Glossary. 
GLOSSARY 
B--Benzotriazole 
D--A glassy polyphosphate 
E--A low molecular weight sodium polyacrylate 
F--A film forming passivator for metal systems containing sodium 
pyrophosphate, sodium acid pyrophosphate, nonyl phenol R.sub.x 8 moles 
ethylene oxide (surfactant), and benzotriazole. 
G--Corrosion inhibitor containing chromate and zinc in a 7 to 1 ratio. 
H--A scale dispersant containing hydroxyethylidene diphosphonic acid and 
sodium polyacrylate. 
I--A biocide whose active agents include methylene bis thiocyanate and 
2,4,5-trichlorophenol. 
J--A corrosion inhibitor containing sodium lignosulfonate, zinc chloride, 
and polyolester (see U.S. Pat. No. 3,502,587). 
L--Deposit from a commercial cooling tower basin, Chicago area. Contains 
28% Si, 21% Ca, 17% Fe, 7% Al, 4% Mg, 4% S, 2% Zn, 13% carbonate, and 5% 
CHCl.sub.3 extractables. 
M--Modified polyethoxylated straight chain alcohol (nonionic). 
N--Octyl phenoxy polyethoxyethanol (surfactant). 
0--A corrosion inhibitor containing a glassy polyphosphate and polyolester 
(see U.S. Pat. No. 3,502,587) 
P--A surfactant-dispersant combination containing: 
(a) octyl phenoxy polyethoxyethanol; 
(b) polyethoxylate; 
(c) a low molecular weight sodium polyacrylate. 
TABLE I 
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SUMMARY OF HEAT TRANSFER UNIT STUDIES 
Test 
No. 
Treatment, Concentration, pH, Duration 
Results 
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1. 
(a) Tannic acid, 1000 ppm, pH 6-8, 5 days 
Darkened deposit after 2 hours. 
(b) Citric acid, 2000 ppm, pH 3.2-3.6, 3 days 
Immediate flaking of deposit. 
(c) Comp. F.sup.1 130 ppm, pH 6, 1 day 
Maintained clean surface. 
Significance: 
Tannic acid modifies iron corrosion deposits equally well at 
higher pH values as 
it does at lower values. The overall treatment will 
successfully modify and re- 
move deposits and passivate the cleaned surface. Costly tannic 
acid should be re- 
placed by less expensive alternative. 
2. 
(a) Tannic acid, 500 ppm, pH 3-4, 6 days 
Darkening of oxides after 1-2 hours. 
(b) Citric acid, 1000 ppm, pH 3.2-3.4, 2 days 
Immediate flaking of deposit followed by 
darkening 
of cleaned metal. 
Significance: 
Lower levels of tannic and citric acid clean corroded surfaces 
in approximately 
the same time as higher levels. 
3. 
(a) Tannic acid, 500 ppm, pH 3-4, 6 days 
Identical results as in test 2. 
Comp. L, 1000 ppm 
Comp. E, 20 ppm 
(b) Citric acid, 1000 ppm, pH 3.2-3.4, 2 days 
Same as in test 2. 
Comp. E, 20 ppm 
Significance: 
The process is successful in the presence of silt. A 
dispersant, Comp. E, may help 
keep removed solids from resettling heat transfer surfaces. 
4. 
(a) Chestnut tannin, 500 ppm, pH 6-7, 2 days 
Deposit turned purple after a few hours. 
(b) Citric acid, 2000 ppm, pH 3.0-3.4, 1 day 
Purple color disappeared within minutes. 
Flaking 
started within 30 minutes. The tube was 85% 
clean in 1 hour. 
Significance: 
Chestnut tannin may be substituted for tannic acid with no loss 
in reactivity. 
5. 
(a) Quebracho tannin, 500 ppm, pH 5-6, 2 days 
Deposit darkened, but somewhat slower than 
with chestnut tannin. 
(b) Citric acid, 2000 ppm, pH 3.0-3.4, 3 days 
Only partial removal of modified deposits. 
Significance: 
Difficulties in removing the treated deposits may be 
encountered if Quebracho tannin 
is substituted for chestnut tannin. 
6. 
(a) Wattle tannin, 500 ppm, pH 3-4, 2 days 
Darkening of deposit at a rate similar to 
chestnut. 
(b) Citric acid, 2000 ppm, pH 3.0-3.4, 3 days 
Over 50% of deposit flasked off leaving a thin 
brown coating. 
Significance: 
The effectiveness of wattle tannin is intermediate to chestnut 
and Quebracho. 
7. 
(a) Chestnut tannin, 1000 ppm, pH 5.0-5.6, 2 days 
Same as in test 4. 
(b) Chestnut tannin, 10,000 ppm, pH 4.5-5.0, 3 days 
No change 
Significance: 
Simple tannin dosage increases will not cause softened deposit 
to flake off under these 
flow conditions. 
8. 
(a) Chestnut tannin, 50 ppm, pH 6.5, 7 days 
Deposit began to darken after 
1 day. 
(b) Citric acid, 2000 ppm, pH 3.0-3.4, 
Immediate flaking of deposit 
4 days. followed by dark brown deposit on 
surface. 
Significance: 
If the case warrants, high dosages of chestnut tannin for 
short 
periods may be replaced by low dosages for long times. The 
final 
results are identical. 
9. 
(a) Chestnut tannin, 250 ppm, pH 6.0-6.5, 
Same darkening as before, but 
7 days deposits on glass portions clean up 
Comp. E, 10 ppm in this step. 
Comp. N, 5 ppm 
(b) Citric acid, 2000 ppm, pH 3.0-3.4, 
2 days Immediate deposit spalling. 
Significance: 
Addition of a dispersant, Comp. E, aids in cleaning up 
loosely held deposits even in the tannin step. It is 
not possible to see any benefit in the removal of 
tenaciously held oxides. 
10. 
(a) Chestnut tannin, 100 ppm, pH 6.5, 7 days 
The deposits gradually darken over the 7 day 
Comp. G, 40 ppm period. 
(b) Citric acid, 2000 ppm, pH 3.0-3.4, 4 days 
The deposits finally flake off, but much more 
slowly then in other tests. 
Significance: 
The overlay of a chromate/zinc corrosion inhibition program 
will slow, but not 
prevent adequate deposit removal. Obviously, much of the tannin 
is oxidized by 
the chromate. 
(a) Chestnut tannin, 250 ppm, pH 6.0-6.5, 18 days 
Thorough darkening of the deposits, but no 
evidence 
of spalling. 
Significance: 
Use of a one-step tannin procedure softens and tannates iron 
deposits, but this 
alone will not cause flaking of the deposit. 
(a) Chestnut tannin, 250 ppm, pH 6.0-6.5, 4 days 
Same as before. 
(b) Citric acid, 2000 ppm, pH adjusted to 6.0, 
10 days No deposit removal. 
Significance: 
Use of citrates at higher pH's for long times are not effective 
for removing 
modified deposits. 
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TABLE II 
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PILOT COOLING TOWER RUN A 
__________________________________________________________________________ 
Test and Tower No: 
1, A (Shell Side Exchanger) 
Purpose of Test: (a) To determine the effects of wattle 
tannin on corroded and non-corroded sur- 
faces, (b) To examine the effects of water 
velocity and heat flux on deposit removal. 
Water Type: Three cycle Chicago tap; 0.1 ft/sec. 
Tannin, Concentration, pH, 
Wattle, 200 ppm; pH 6-7; 
Reaction Time: 5-7 days. 
Other Additives: 25 ppm Comp.B; 100 ppm Comp.N daily. 
Specimens: Admiralty tubes, 5000 and 15,000 BTU/ft.sup.2 /hr; 
stainless steel tubes, 5000 and 15,000 
BTU/ft.sup.2 /hr.; mild steel tubes, 5000, 10,000 
and 20,000 BTU/ft.sup.2 /hr. 
Transition Between Tannin 
Stop tannin feed, slug in removal agent, 
and Deposit Removal Agent: 
and maintain dosage. 
Removal Agent, Concentration, pH: 
Citric Acid, 2000 ppm, pH 3.4-3.8. 
Other Additives: 25 ppm Comp.B; 100 ppm Comp.N daily. 
Transition Between Deposit 
Stop citric acid feed, high level with 
Removal Agent and corrosion inhibitor. 
Corrosion Inhibition Program: 
Passivation Technique 
Comp.J 150 ppm for 4 days, pH 7.6-8.0. 
and Agents: 
Transition Between Passivation 
Lower Comp.J level to 50 ppm. 
and Maintenance Program: 
Summary of PCT Run: The addition of wattle tannin caused tannation of 
the 
mild steel tubes within a few hours. The stainless steel and admiralty 
tubes 
also began significant buildup as the reaction proceeded due to 
transported 
iron tannate or degradation products. As the citric acid was added, 
immediate 
clean-up of the high heat flux mild steel tubes ensued; however, the 
stain- 
less steel and admiralty tubes continued to foul. The higher heat flux 
mild 
steel tubes failed to clean as well as the low heat flux tubes. Overall, 
the 
low velocity of the water was not as detrimental as expected. See FIG. 
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PILOT COOLING TOWER RUN B 
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Test and Tower No.: 
2, B (Shell Side Exchanger). 
Purpose of Test: Test is to be similar to Tower A test. 
However, the effects of Comp.P will be 
observed. A comparison of the tanninization 
effectiveness of wattle and chestnut tannin 
can be made. 
Water Type: Three cycle Chicago tap; 0.1 ft/sec. 
Tannin, Concentration, pH, 
Chestnut, 200 ppm; pH 6-7; 
Reaction Time: 5-7 days. 
Other Additives: Comp.P, 170 ppm; 25 ppm Comp.B; 100 ppm 
Comp.I daily. 
Specimens: Seven tubes as in Tower A, same heat fluxes. 
Transition Between Tannin 
Stop tannin feed, slug in deposit removal 
and Deposit Removal Agent: 
agent and maintain dosage. 
Removal Agent, Concentration, pH: 
Citric acid, 2000 ppm, pH 3.6-3.9. 
Other Additives: Comp.P, 170 ppm; 25 ppm Comp.B; 100 ppm 
Comp.I daily. 
Transition Between Deposit 
Stop citric acid feed, high level with 
Removal Agent and corrosion inhibitor. 
Corrosion Inhibition Program: 
Passivation Technique 
Comp.J, 200 ppm for 4 days, pH 7.6-8.0. 
and Agents: 
Transition Between Passivation 
Lower Comp.J dosage to 50 ppm. 
and Maintenance Program. 
Summary of PCT Run: This run was considerably more successful than the 
wattle 
run. Some buildup of deposit on all tubes was noted as the tannin feed 
began. 
However, as the citric acid was added fouling decreased on all tubes, 
including 
the alloy tubes. In one day, the resistance of all tubes was below that 
of 
the corroded level. Minor fouling remained on the mild steel tubes. This 
test indicates that chestnut tannin is preferred to wattle. The 
dispersant 
may have aided in clean-up, but since the tannin was different in this 
tower, 
dispersant effectiveness cannot be estimated. No Comp.J data were 
collected. 
See FIG. 3. 
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PILOT COOLING TOWER RUN C 
__________________________________________________________________________ 
Test and Tower No.: 
3, D (Tube Side Experiment) 
Purpose of Test: Test will compare effects of tube side 
water conditions as opposed to shell side 
conditions. Again, the effects of fouling 
of non-corroded surfaces will be studied. 
The effects of heat flux on fouling rate 
and degree will be examined. 
Water Type: Three cycle Chicago tap; 5 ft/sec. 
Tannin, Concentration, pH 
Chestnut, 200 ppm; pH 6-7; 
Reaction time: 5-7 days. 
Other Additives: 200 ppm Comp.P; 25 ppm Comp.B; 100 ppm 
Comp.I daily. 
Specimens: Mild steel tubes, 5000 and 15,000 BTU/ft.sup.2 /hr.; 
stainless steel tube 10,000 BTU/ft.sup.2 /hr.; 
admiralty tube, 5000 BTU/ft.sup.2 /hr. All 
pre-corroded in LOTS rig. 
Transition Between Tannin 
Same as Towers A and B. 
and Deposit Removal Agent: 
Removal Agent, Concentration, pH: 
Citric acid, 2000 ppm; adjusted to pH 
3.4-3.8 with aqueous ammonia. 
Other Additives: Same as in tannin step. 
Transition Between Deposit 
Stop citric acid feed, then high level 
Removal Agent and with corrosion inhibitor 
Corrosion Inhibition Program: 
Passivation Technique 
Comp.J, 150 ppm for 4 days, pH 7.6-8.0. 
and Agents: 
Transition Between Passivation 
Lower Comp.J level to 50 ppm 
and Maintenance Program: 
Summary of PCT Run: This PCT run was quite similar to the Tower B run, 
except 
the flow velocity was 50 times greater and the total volume of the basin 
and 
hence the total amount of chemical fed was one-fourth that of Towers A 
and 
B. Build-up of deposit continued as the chestnut tannin was fed. Citric 
acid caused deposit removal within hours and left all tubes essentially 
clean. 
See FIG. 4. 
__________________________________________________________________________ 
PILOT COOLING TOWER RUN D 
__________________________________________________________________________ 
Test and Tower No.: 
4, E (Tube Side Experiment) 
Purpose of Test: Similar to that of Tower D. To compare 
deposit transport by wattle tannin with 
that of chestnut tannin. To compare relative 
cleanliness of cleaned wattle specimens 
with those subjected to chestnut tannin. 
Water Type: Three cycle Chicago tap; 5 ft/sec. 
Tannin, Concentration, pH, 
Wattle, 200 ppm; pH 6-7; 
Reaction Time: 5-7 days. 
Other Additives: 25 ppm Comp.B; 100 ppm Comp.I daily. 
Specimens: Same as in Tower D. All pre-corroded 
in LOTS rig. 
Transition Between Tannin 
Stop tannin feed, slug in deposit removal 
and Deposit Removal Agent: 
agent, and maintain dosage. 
Removal Agent, Concentration, pH: 
Citric acid, 2000 ppm; pH adjusted to 
3.4-3.8 with aqueous ammonia. 
Other Additives: Same as in tannin step. 
Transition Between Deposit 
Stop citric acid feed, then high level 
Removal Agent and with corrosion inhibitor. 
Corrosion Inhibition Program: 
Passivation Technique 
Comp.D, 100 ppm, pH 6-7. 
and Agents: 
Transition Between Passivation 
Stop Comp.D feed and begin adding 130 
and Maintenance Program: 
ppm Comp.G gradually lowering dosage to 
45 ppm after 4 days. 
Summary of PCT Run: This run parallels the test in Tower D. Tannation by 
the wattle was effective. Addition of citric acid cleaned the mild steel 
tubes, but the admiralty tubes did not unfoul significantly. These data 
confirm 
those obtained from Tower A. Transported deposits, therefore, are quite 
difficult 
to remove when wattle tannin is used. See FIG. 5. 
__________________________________________________________________________ 
PILOT COOLING TOWER RUN E 
__________________________________________________________________________ 
Test and Tower No.: 
5, E (Tube Side Experiment) 
Purpose of Test: To determine the effects of the cleaning 
procedure on mild steel tubes corroded 
for 3 months with 30 ppm chromate and 
30 ppm Comp.H. To determine the effective- 
ness of air rumbling on tenacious deposits. 
Water Type: Three cycle Chicago tap; 2.5 ft/sec. 
Tannin, Concentration, pH, 
Chestnut, 200 ppm; pH 6-7; 
Reaction Time: 5 days. 
Other Additives: 170 ppm Comp.P; 100 ppm Comp.I daily. 
Specimens: Four extremely corroded M/S tubes, three 
of which had a heat flux of 10,000 BTU/ft.sup.2 /hr. 
and one unheated. 
Transition Between Tannin 
Stop tannin feed, slug in citric acid, 
and Deposit Removal Agent: 
maintain dosage. 
Removal Agent, Concentration, pH: 
Citric acid, 2000 ppm, uncontrolled pH 
(3.2-3.8). 
Other Additives: Same as in tannin step. 
Transition Between Deposit 
Stop citric acid feed, high level with 
Removal Agent and corrosion inhibitor 
Corrosion Inhibition Program: 
Passivation Technique 
Comp.O, 200 ppm, pH 6-7. 
and Agents: 
Transition Between Passivation 
Lower Comp.O dosage to 65 ppm. 
and Maintenance Program: 
Summary of PCT Run: Tannation appeared to proceed normally in this test, 
but because of the extremely thick deposit on all tubes it was difficult 
to 
determine when tannation had gone to near completion. Citric acid feed 
was 
started, but flaking of significant deposit was not evident. After 4 
days 
of citric acid feed with uncontrolled pH, one mild steel tube developed 
leak. The test was discontinued. This run points out the difficulties 
that 
might be encountered when treating any seriously corroded 
__________________________________________________________________________ 
system. 
PILOT COOLING TOWER RUN F 
__________________________________________________________________________ 
Test and Tower No.: 
6, F (Tube Side Experiment) 
Purpose of Test: To determine the detrimental effects of 
silt and process oils on the clean-up 
program. To compare Comp.M surfactant 
with high foamers. To examine the use 
of additional tannin as a passivating 
agent after deposit removal. 
Water Type: Three cycle Chicago tap; 2.5 ft/sec. 
Tannin, Concentration, pH, 
Wattle, 200 ppm; pH 6-7; 
Reaction Time: 3 days. 
Other Additives: 60 ppm Comp.H; 10 ppm Comp.M; 200 ppm process 
oil; 500 ppm Comp.L; 100 ppm Comp.I 
daily. 
Specimens: Three M/S tubes with 10,000 BTU/ft.sup.2 /hr. 
heat flux. Pre-corroded in the LOTS rig. 
Transition Between Tannin 
Stop tannin feed, slug in citrate, maintain 
and Deposit Removal Agent: 
dosage. 
Removal Agent, Concentration, pH: 
Citric acid, 3000 ppm, pH adjusted to 
3.2-3.4 with aqueous ammonia. 
Other Additives: Same as above except no oil or silt. 
Transition Between Deposit 
Slowly blowdown citric acid when cleaning 
Removal Agent and complete, add 200 ppm wattle tannin while 
Corrosion Inhibition Program: 
increasing pH to 5.5. 
Passivation Technique 
Wattle tannin at pH 5.5. 
and Agents: 
Transition Between Passivation 
None 
and Maintenance Program: 
Summary of PCT Run: The presence of limited oil and Comp.L did not deter 
the process. The wattle tannin reacted with the corrosion product at the 
same rate as did the chestnut tannin in other tests. Introduction of 
citric 
acid flaked most of the modified deposit leaving a clean surface. The 
Comp. 
M appeared to work as well as the Comp.N with significantly less foam- 
ing. Use of additional tannin after the deposit removal and citric acid 
blowdown 
temporarily prevented re-corrosion, but a pH of 7.5-8.5 is necessary to 
make 
its inhibition effective for longer periods. 
__________________________________________________________________________ 
PILOT COOLING TOWER RUN G 
__________________________________________________________________________ 
Test and Tower No.: 
7, I (Tube Side Experiment) 
Purpose of Test: To compare results with those of Tower 
F since all conditions are the same except 
the tannin and surfactant used. Examine 
the use of a chromate/zinc program for 
passivation. 
Water Type: Three cycle Chicago tap; 2.5 ft/sec. 
Tannin, Concentration, pH, 
Chestnut, 200 ppm; pH 6-7; 
Reaction Time: 3 days. 
Other Additives: 60 ppm Comp.H; 10 ppm Comp.N; 200 
ppm process oil; 500 ppm Comp.L; 100 
ppm Comp.I daily. 
Specimens: Same as in Tower F. 
Transition Between Tannin 
Stop tannin feed, slug in citriate, maintain 
and Deposit Removal Agent: 
dosage. 
Removal Agent, Concentration, pH: 
Citric acid 3000 ppm, pH adjusted to 4.0 
with aqueous ammonia. If removal at this 
pH is not good, lower pH. 
Other Additives: Same as above except no oil or silt. 
Transition Between Deposit 
Blowdown citrates for one day and slug 
Removal Agent and in high level chromate/zinc program. 
Corrosion Inhibition Program: 
Passivation Technique 
Comp.G, 130 ppm, pH 6.5 
and Agents: 
Transition Between Passivation 
After 4 days at 130 ppm, lower Comp.G dosage 
and Maintenance Program: 
to 45 ppm. 
Summary of PCT Run: The results of this test were similar in some ways 
to 
those from Tower F. Again, the oil and silt did not slow the cleaning 
process. 
Tannation with chestnut tannin proceeded well; however, use of 3000 ppm 
citrate 
at a pH of 4.0 did a poor job of spalling the tannated deposit. Only 
after 
the pH was lowered to 3.5 did most of the deposit fall off. The use of 
Comp. 
N produced much more foam than did the Comp.M surfactant. High leveling 
with 
Comp.G provided poor proection to the mild steel. It will be 
advantageous 
when using citrates to proceed immediately to the lower pH values 
(3.2-3.4) to accomplish deposit removal. 
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PILOT COOLING TOWER RUN H 
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Test and Tower No.: 
8, J (Tube Side Experiment). 
Purpose of Test: To determine if higher dosages of tannin 
will improve the removal of corrosion 
product. To find the best conditions 
for using citric acid to remove tannated 
corrosion products. 
Water Type: Three cycle Chicago tap; 2.5 ft/sec. 
Tannin, Concentration, pH, 
Chestnut, 540 ppm; pH 5.0-7.3; 
Reaction Time: 5-7 days. 
Other Additives: 170 ppm Comp.P; 100 ppm Comp.I daily. 
Specimens: Four M/S tubes pre-corroded in LOTS rig 
for 11 days in Chicago tap water. 
Tranisition Between Tannin 
Stop tannin feed, slug in citrate, and 
and Deposit Removal Agent: 
maintain dosage. 
Removal Agent, Concentration, pH: 
Citric acid, adjust pH and dosage to obtain 
maximum deposit flaking. 
Other Additives: Same as in tannin step. 
Transition Between Deposit 
Blowdown citrates and introduce Comp.J 
Removal Agent and program. 
Corrosion Inhibition Program: 
Passivation Technique 
Use Comp.J at 210 ppm and pH 7.6-8.1. 
and Agents: 
Transition Between Passivation 
None 
and Maintenance Program: 
Summary of PCT Run: Higher concentrations of tannin and even longer 
tannation 
times did not prove advantageous over lower concentrations. Citric acid 
at 
2000 ppm and pH 4.5 caused little or no deposit removal. The increased 
time 
used for this experiment (13 days) caused more transported deposit and 
implies 
that too much tannin is detrimental. Flushing of all used citric acid 
and 
residual tannin made possible complete cleaning at 2000-4000 ppm citric 
acid 
at pH 2.6. Prior attempts at 4000 ppm citric acid at pH 3.2-3.7 were not 
effective, probably due to high soluble Fe in the system. The Comp.J 
program 
failed due to poor pH control and microbiological build-up after Comp.I 
was 
discontinued. High heat flux can cause increased citric acid clean-up, 
but 
also produces a residual brown film. 
__________________________________________________________________________ 
PILOT COOLING TOWER RUN I 
__________________________________________________________________________ 
Test and Tower No.: 
9, K (Tube Side Experiment) 
Purpose of Test: To determine the relationship between 
citrate concentration and pH for optimum 
deposit removal. To passivate cleaned 
systems with a chromate/zinc program. 
Water Type: Three cycle Chicago tap; 2.5 ft/sec. 
Tannin, Concentration, pH, 
Chestnut, 170 ppm; pH 5.6-6.0; 
Reaction Time: 3 days. 
Other Additives: 170 ppm Comp.P; 100 ppm Comp.I daily. 
Specimens: Three M/S tubes pre-corroded in LOTS rig 
for 4 days and an admiralty tube. 
Transition Between Tannin 
Stop tannin feed, slug in citrates, maintain 
and Deposit Removal Agent: 
dosage levels. 
Removal Agent, Concentration, pH: 
Citric acid; as in Tower J, determine 
optimum dosage and pH. 
Other Additives: Same as in tannin step. 
Transition Between Deposit 
Bleed out citrates and slug in high level 
Removal Agent and corrosion inhibition program. 
Corrosion Inhibition Program: 
Passivation Technique 
Comp.G, 130 ppm; pH 6.4-6.8. 
and Agents: Maintain for several days. 
Transition Between Passivation 
Lower Comp.G to 48 ppm. 
and Maintenance Program: 
Summary of PCT Run: This run was similar to Tower J, except the chestnut 
tannin dosage was much lower for a shorter time. When 1900 ppm citric 
acid 
at pH 4.5 was used for deposit removal, flaking was minimal. However, at 
2700 ppm and pH 4.5 with rapid blowdown to decrease dissolved Fe and 
residual 
tannin clean-up of scale was nearly complete. Final scale removal was 
acccomplished 
by increasing the citric acid level to 4000 ppm at pH 3.4. Passivation 
with 
Comp.G looked good, but a heavy light-colored scale eventually formed on 
the 
M/S tubes in spite of good pH and microbiological control. 
__________________________________________________________________________ 
PILOT COOLING TOWER RUN J 
__________________________________________________________________________ 
Test and Tower No.: 
10, P (Tube Side Experiment) 
Purpose of Test: To determine ability of chestnut tannin 
to penetrate and modify very old deposits. 
To study the effects of citric acid on 
removing transported tannin complexes 
from admiralty tubes. To see if removal 
of large deposit chunks causes removal 
problems. 
Water Type: Three cycle Chicago tap; 2.5 ft/sec. 
Tannin, Concentration, pH, 
Chestnut, 185 ppm; pH 6.2-6.3; 
Reaction Time: 5 days. 
Other Additives: 30 ppm Comp.B; 215 ppm Comp.H; 100 ppm Comp. 
I daily. 
Specimens: Two extremely corroded M/S tubes (105 
days in 30 ppm chromate) and 1 admiralty 
tube. 
Transition Between Tannin 
Stop tannin feed, slug in citrates and 
and Deposit Removal Agent: 
maintain feed. 
Removal Agent, Concentration, pH: 
Citric acid, 2000 ppm: pH 4.5 
Other Additives: Same as in tannin step. 
Transition Between Deposit 
Blowdown cleaning solution and slug in 
Removal Agent and program. 
Corrosion Inhibition Program: 
Passivation Technique 
Add 200 ppm Comp.O at pH 7.6-7.9. 
and Agents: 
Transition Between Passivation 
None 
and Maintenance Program: 
Summary of PCT Run: This study was similar to Tower 5,E. Again, the 
extreme 
amount of corrosion product hampered complete tannation and deposit 
removal. 
No new information was obtained. 
__________________________________________________________________________ 
PILOT COOLING TOWER RUN K 
__________________________________________________________________________ 
Test and Tower No.: 
11, Q 
Purpose of Test: To determine long term effects of tannin 
at low dosage levels on iron deposits. 
To attempt deposit removal by shocking 
deposits repeatedly with citrates. To 
attempt a Nalprep treatment of a cleaned 
system. 
Water Type: Three cycle Chicago tap; 2.5 ft/sec. 
Tannin, Concentration, pH, 
Wattle, 50 ppm; pH 5.3-6.0; 
Reaction Time: 13-15 days. 
Other Additives: 120 ppm Comp.H; 25 ppm Comp.B; 100 ppm Comp. 
I daily. 
Specimens: Two pre-corroded M/S tubes and 1 admiralty 
tube. 
Transition Between Tannin 
Stop tannin feed, slug in citric acid, 
and Deposit Removal Agent: 
blowdown quickly and repeat. 
Removal Agent, Concentration, pH: 
Citric acid, 4000 ppm; pH 2.7-3.5. 
Other Additives: Same as in tannin step. 
Transition Between Deposit 
Blowdown heavily and quickly add Comp.F. 
Removal Agent and 
Corrosion Inhibition Program: 
Passivation Technique 
Comp.F, 1.25% overnight; pH 6.0. 
and Agents: 
Transition Between Passivation 
Blowdown heavily and add 215 ppm Comp.J, 
and Maintenance Program: 
pH 7.6. 
Summary of PCT Run: Tannation at a 50 ppm level produces essentially the 
same effect as that found at higher dosages for shorter times. Slugging 
the 
tannated deposit with citric acid at 4000 ppm at pH 2.5 for 4 times with 
complete 
draining and flushing between treatments was quite successful in 
removing 
the deposits. High heat flux aids, but was not essential for scale 
removal. 
A Comp.F passivation treatment was successful. Following passivation, 
a good start-up of the system with Comp.J was successful. 
__________________________________________________________________________