Continuous ozone injection into water circulating between a cooling tower and heat exchanger with heavy scale deposits inhibits formation of further deposits, promotes flaking of existing deposits, inhibits chemical corrosion and controls algae and bacteria

French, K. R.

Howe, R. D.

Humphrey, M. F.

English

NASA Technical Reports Server

United States Patent 
Humphrey et aI. 
[54] OZONATION OF COOLING TOWER 
WATERS 
[76] Inventors: Robert A. Frosch, Administrator of 
the National Aeronautics and Space 
Administration, with respect to an 
invention of Marshall F. Humphrey, 
Duarte; Kenneth R French, La 
Canada; Ronald D. Howe, Sierra 
Madre, all of Calif. 
[21] Appl. No.: 946,992 
[22] Filed: Sep. 29,1978 
[51] Int. Cl.2 ................................................ CO2B 5/02 
422/9 
210/59, 61; 422/9 
[52] U.S. c1. .................................... 210/57; 210/63 2 
[58] Field of Search ................... 210/57, 58, 63 2, 50, 
[111 4,172,786 
[45] Oct. 30, 1979 
r561 References Cited 
U.S. PATENT DOCUMENTS 
1,103,211 7/1914 &ips ....................................... 422/9 
4,098,691 7/1978 Filby .................................. 210/63 Z 
FOREIGN PATENT DOCUMENTS 
2500947 7/1976 Fed. Rep. of Germany ........ 210/63 Z 
Primmy Examiner-Thomas G. Wyse 
Attorney, Agent, or Firm-Monte F. Mott; John R. 
Manning; Wilfred Grifka 
[571 ABSTRACT 
Continuous ozone injection into water circulating be- 
tween a cooling tower and heat exchanger with heavy 
scale deposits inhibits formation of further deposits, 
promotes flaking of existing deposits, inhibits chemical 
corrosion and controls algae and bacteria. 
6 Claims, 1 Drawing Figure 
https://ntrs.nasa.gov/search.jsp?R=19800006321 2020-03-21T01:59:49+00:00Z
U.S. Patent Qct. 30, 1979 
Ai R 
* 4,172,786 1 
OZONATION OF COOLING TOWER WATERS 
ORIGIN O F  THE INVENTION 
The invention described herein was made in the per- 
formance of work under a NASA contract and is sub- 
ject to the provisions of Section 305 of the National 
Aeronautics and Space Act of 1958, Public Law 83-568 
(72 Stat. 435; 42 USC 2457). 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to scale, corrosion and 
algae control in cooling towers and, more particularly, 
to a system and method of continuously treating cooling 
tower waters. 
2. Description of the Prior Art 
Water is the closest thing to a universal solvent 
known. In its pure condition (without dissolved materi- 
als) it is very corrosive. Most normally used industrial 
metals will gradually corrode or dissolve in distilled 
water. Some of the dissolved materials, like carbon 
dioxide, make water even more aggressive, both to 
metals and to non-metals. This solvent, water, which is 
a universal (and cheap) heat transfer medium, has a 
specific heat of 1 BtuflbPF. Water with its tremendous 
capacity to absorb and store heat, can absorb 33 times 
more heat than lead and 10 times more than iron. 
All water utilized as the heat transfer medium in 
cooling towers has traditionally required some form of 
treatment. In the past chromium salts, generally in an 
acid condition, have been extensively used. Cooling 
tower water treatment implies that the waters are pas- 
sivated in such a way that the following major problems 
do not develop or are greatly reduced: 
(1) Scale build-up to the point of equipment or func- 
(2) Corrosion of metals or degradation of wood to the 
(3) Biological contamination to the point of function 
Airborne particles carry with them microorganisms 
which, after coming in contact with the cooling water, 
are distributed throughout the cooling water system to 
form algae, slime, and bacterial growths. Algae growth 
can accumulate to the point at which it interferes with 
the water flow in the cooling system. Slime in condens- 
ers restricts the water flow and acts as an insulator 
reducing the cooling capacity. This results in higher 
head pressures and increased load on circulating pump 
motors with corresponding increases in power con- 
sumption. Accumulations of organic matter can cause 
localized corrosive attack, resulting in premature equip- 
ment failure. Fungus action can cause wood destruction 
in towers. 
These growths have been controlled with ozone. The 
tion failure. 
point of function failure. 
failure. 
L 
involving the corrosion of metals submerged in water, is 
electrochemical in nature. In cooling water systems, 
electrolytes are always present-namely ions dissolved 
in the water. Electrodes (anode and cathode) are also 
5 present. These electrodes may be two different metals, 
such as copper condenser tubes and steel condenser 
heads of the shell, or different areas of the same metal. 
In dissimilar metal corrosion, the less noble metal (an- 
ode) through corrosion will proceed to the more noble 
lo metal (cathode) (called galvanic corrosion). Corrosion 
of the same metal surface occurs if a difference in poten- 
tial exists between two areas of the metal. One will act 
as the anode and the other as the cathode. Disintegra- 
tion of metal will occur only at the anode. However, 
l5 anode and cathode areas may shift periodically, result- 
ing in uniform corrosion instead of pitting. 
Past use of the chromium treatment did little to pre- 
vent biological problems from developing in cooling 
2o towers; however, as an inhibitor, it was very effective 
(and cheap) in protecting metals from corrosion. The 
acid condition of the treatment was also conducive to a 
reduced tendency for biological growth or scale devel- 
opment. Recent restrictions by the Environmental Pro- 
25 tection Agency (EPA), on the use of chromium materi- 
als has made the search for alternative treatment materi- 
als necessary. 
While the combined acid chromate treatment has 
long been the dominant technique for treating cooling 
30 tower waters, the non-chromate alkaline treatments are 
gaining popularity (by necessity). In some ways the 
modern alkaline type treatment resembles that which 
previously was known as the threshold treatment. This 
was a use condition where polyphosphates and selected 
35 organic materials were used in relatively low concen- 
trations (threshold limit) to produce a partial sequestra- 
tion of the calcium carbonates. Scale forming materials 
were prevented from giving hard scales, but they did 
allow a soft mud to accumulate in the reservoirs of the 
40 system. The new formulations that are being offered for 
this purpose are more sophisticated and higher in costs. 
They require much more supervision, monitoring, and 
control. 
4s SUMMARY OF THE INVENTION 
It has now been discovered that the maintenance of 
high levels of ozone in the cooling water in absence of 
any other chemical treating agents or electrochemical 
or electromechanical apparatus prevents further scale 
so formation, removes existing scale, passivates the metal 
surfaces to inhibit further corrosion and at the same 
time is an active biocidal agent which fully disinfects 
the water to prevent algae growth. The ozone is in- 
ss jected into the cooling water and maintained above a 
minimum level of 2 mg/l up to about 20 mg/l. The 
ozone is usually provided by subjecting oxygen or air to ozone is dissolved in the cooling water where it attacks 
the bacteria and microorganisms and destroys them by a COrOna discharge- Ozonated air appears to provide 
oxidation. However, the ozone level is very low of the enhanced flaking of scale probably due to disinfecting 
order of 0.2 mg/l of Ozone and the Ozone has always 60 of the biological slimes and/or adhesives that cause 
been used in conjunction with other chemical agents or adherence of the scale materials. Thus, there is no need 
electrochemical or electromechanical controls. to add chemical corrosion inhibitors nor biocides or 
Corrosion is a destructive attack on metals which other algae control agents. 
may be chemical or electrochemical in nature. Direct These and many other attendant advantages of the 
chemical corrosion is limited to unusual conditions in- 65 invention will become readily apparent as the invention 
volving highly corrosive environments or high temper- becomes better understood by reference to the follow- 
ature or both. Examples are metals in contact with acids ing detailed description when considered in conjunction 
or alkalies. However, a large part of the phenomena with the accompanying drawings. 
4.172,786 
BRIEF DESCRIPTION OF THE DRAWING 
The FIGURE is a block schematic view of a cooling 
water treatment system according to this invention. 
DESCRIPTION OF THE PREFERRED 
EMBODIMENTS 
The system of the invention generally includes an 
ozone generating and injection section 10, a cooling 
tower 12 and heat exchanger 14. The cooling tower 12 
operates by the latent heat of evaporation of air and can 
be an atmospheric type or the mechanical draft type in 
which a fan 16 is utilized to blow air through water 
falling downwardly through grids and slats 18 into a 
basin 20. The cooled water in basin 20 is ozonated by 
recirculating a portion of the water through a circuit 
containing an outlet conduit 22 connected to the inlet 
side of ozone injection pump 24 and a recycle conduit 
26 through a sludge frlter 21 connected to the outlet side 
of the pump and terminating in a nozzle end 28 dis- 
charging into the basin 20 or by direct injection into the 
low pressure side of the recirculation pump 40. 
Ozone is generated from a gas such as air or oxygen 
which is preferably dried in a column 30 containing a 
dessicant such as silica gel or by refrigeration to the dew 
point of the air since humidity in the air reduces ozone 
production. The dried air is delivered to an ozone gen- 
erator 32. The ozone generator can be a commercial 
state of the art corona-discharge-type ozone generator. 
The output 34 from the generator is introduced at the 
suction side 36 of the circulating pump 24 or 40. The 
turbulence within the pump thoroughly mixes the 
ozone and dissolves it in the water. Oxidation of organic 
impurities begins immediately. By the time the ozonated 
water reaches the basin sump 20, most of the microor- 
ganism kill has been accomplished. The remainder of 
the dissolved ozone remains in the basin water and 
travels through the cooling circuit where it passivates 
metal surfaces, attacks slime or other bacterial deposits 
and prevents and removes scale. 
The cooling circuit includes a separate circulating 
pump 40 having its inlet side 42 connected to the basin 
through conduit 44 and its output side 46 connected to 
the inlet side of the heat exchanger 53. The ozonated 
cooling water is distributed by means of header 48 into 
the tubes 50, collects in header 51 and flows through 
conduit 52 to the main header 54 of the spray tower 12 
where it is distributed to various nozzles 56 and sprayed 
upwardly to mix with the air from fan 16 before drop- 
ping to the slats and grids 18 below. Make-up water 58 
is added to the basin 20 as needed to compensate for 
losses in the system. 
Testing of the system was performed in a commercial 
size (678 gallon) forced air cooling tower used for space 
cooling and attached to a large heat exchanger. The 
water compositions are presented in the following table. 
TABLE I 
4 
TABLE I-continued 
Av Soft Av Hard 
Property PPm PPm 
Langelier Index + O S 1  +2.72 
The soft water is primarily well water as received and 
was concentrated to form hard water by operating the 
cooling tower without blowdown. 
As shown in the FIGURE, the cooling tower was 
fitted with a commercial corona-discharge-type ozone 
generator. Inlet air to the ozone generator was desic- 
cant dried producing one liter/hour of air containing 
3% ozone. 
Algae growth at the time of installation of the ozone 
system was extensive. Heavy scale deposits were on the 
cooling tower slats. Photographs were taken of the 
opened heat exchanger tube bundles. An analysis of the 
deposits indicated principally calcium carbonate with a 
2o small amount of iron oxide present. Steel and copper 
corrosion coupons were placed in the water recircula- 
tion line. Operation of the cooling tower with the ozo- 
nator producing a steady stream of ozone being injected 
into the cooling tower water lasted 1080 hours. The 
25 water temperature from the high temperature heat ex- 
changer varied according to the heating load but was 
generally from 70" F. to 85" F. During this period of 
operation (with no blow down), the total solids reached 
1700 mgfl and the water hardness reached 724 mgfl (as 
30 CaCO3). Water in the tower became crystal clear, the 
algae disappeared, and scale started flaking off the slats. 
Corrosion rates for the metal coupons were very low 
during the ozonation run. (Copper was 0.06 mildyear 
35 and steel was 1.86 mils/year.) Photographs taken of the 
heat exchanger tubes showed that the calcium scale 
previously on the tubes had decreased. It is not known 
by what mechanism the results can be attributed. It is 
possible that, since air was used for generation of the 
4o ozone, some nitrogen was also fixed producing a dilute 
nitric acid in the water and forming calcium nitrate with 
the scale. The actual concentration of nitrate increased 
in the tower water 51 times (from 3.2 mgfl to 164 mg/l). 
It is also possible that the dissolved ozone in the water 
45 reversed the calcium carbonate equilibrium toward the 
formation of the bicarbonate salt. Calcium bicarbonate 
is 10,ooO times more soluble in water than the carbon- 
ate. Also, by allowing the salinity to increase (no blow- 
down), the solubility of calcium carbonate is increased. 
50 For instance in sea water, calcium carbonate is 500 
times more soluble than in fresh water. 
The metal parts of the cooling system are protected 
by a continuous and adherent coating of metal oxide 
which forms almost instantaneously when exposed to 
It is to be realized that only preferred embodiments of 
the invention have been described and that numerous 
substitutions, modifications and alterations are permissi- 
ble without deDarting from the sDirit and scope of the 
10 
15 
55 ozonated water. 
~~~ ~~ 
60 invention as dckned in the following claims. Av Soft Av Hard What is claimed is: Property PPm ppm 
1. A method of inhibiting formation of scale, corro- 45 120 sion and algae growth on the surfaces in contact with Ca+ + Chloride 15 900 
Total Dissolved Solids (TDS) 280 1780 corrosive and scaling ion containing water circulating 
Total Hardness (as Ca++) 300 65 through a circuit including a heat exchanger and a cool- 
Iron ing tower in which air containing algae forming micro- 
organisms is blown through water downwardly falling Alkalinity (as CaCO3) PH 
Conductivity (micro mhos/cm) 
65 
- 0.02 
30/ 180 80/560 
8.2-8.9 7.0-7.9 
160 1800 into a basin comprising the steps of: 
4,172,786 
injecting ozone into the water in the basin at a level of 
at least 2 milligrams per liter in the abdnce of any 
other corrosion or scale inhibitor; and 
maintaining the ozone level in the water in the circuit 5 
at a level between 2 to 20 milligrams per liter. 
2. A method according to claim 1 in which tlk ozone 
is generated by subjecting an oxygen contaiping gas to 
a corona discharge. 10 
15 
20 
25 
30 
35 
40 
45 
6 
3. A method according to claim 2 in which the gas is 
air. 
4. A method according to claim 3 in which the air is 
dried before being ozonated. 
5. A method according to claim 3 in which the scale 
comprises calcium carbonate and further including the 
step of flaking the scale from the surfaces. 
6. A method according to claim 1 in which the scale 
comprises calcium carbonate. * * * * *  
50 
55 
60 
65 


Ozonation of cooling tower waters

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server