The 6th edition of the
Interdisciplinarity in Engineering International Conference
“Petru Maior” University of Tîrgu Mureş, Romania, 2012
METHODS OF REDUCING THE CORROSIVE POTENTIAL
OF DEMINERALIZED WATER
Nicolae CHIRILĂ
Industrial Engineering and Management Department, Petru Maior University
Nicolae Iorga Street, No. 1, Targu Mures, Romania
[email protected]
ABSTRACT
The objectives of this project are to study the method of obtaining demineralized water by
using an ion exchange column type Purolite A200MBO, Purolite C100MBH. Considering
the fact that we intend to use this type of water for the production of the steam used in the
energetic industry, it is very important that the corrosive potential of water to be highly
reduced. We have made chemical determinations for the water that enters in the ion
exchange column and for the final water, which is the demineralized water.
The results that we obtained emphasize that the corrosive capacity of the water is
intensely diminished following this process.
Keywords: water quality, chemical analyses, analyzing methods, demineralized water, corrosive potential
1. Introduction
The operation of the energetic boilers depends to a
great extent on the quality of the water used for
producing the steam.
The ion exchange processes are part of the double
exchange reactions category that take place in solid
liquid heterogeneous systems.
This process of water treatment is based on the
property of some metals to replace the ions from
water with their ions. There are two types of ion
exchange resin: one which exchanges the cations and
another one which exchanges the anions.
Ion exchange occurs when the hard water is
passed through a column (or bed) containing an ion
exchange material1.
This material can be either a natural porous
sodium aluminosilicate polymer called zeolite or a
synthetic resinous material. These polymeric
materials ionize to produse two type of ions; fixed
ions that remain attached to the polymer surface and
free mobile counterions. The counterions are onest
hat exchange places with the undesirable ions when a
hard water is passed through the resin.
In the following chemical equations the action
mechanism of ion exchange is illustrated: the
cationits retain the cations from water releasing the
1
R.H. PETRUCCI, W.S. HARWOOD, „General Chemistry.
Principles and Modern Applications”, pp786, MacMillan Publising
Company, New York,1993.
hydrogen ions (cationites in form H+) and the anionits
retain the anions releasing OH- ions (anionits in form
OH-).
Ion exhange reactions on which the water
deionization processes are based are:
Ca (HCO3)2 + 2HSO3[cat] = Ca [(SO3)cat]2 +
2H2O
CaSO4 + HSO3[cat] = Ca[(SO3)cat]2 + H2SO4
NaCl + HSO3[cat] = NaSO3[cat] + HCl
The cationites regeneration in form H+ is made by
treating the cationites with a sulfuric acid solution
according to the following reaction:
2NaSO3[cat] + H2SO4 = 2HSO3[cat] + Na2SO4
We can observe that the acids that results from
the fixing process of the cationites are eliminated
from the system by an anionic exchange reaction:
2[an]OH + H2SO4 = [an]2SO4 + 2H2O
The regeneration of the anionites is realised by
washing the column with a basic solution of
Regenerarea anioniţilor se realizează prin spălare
cu o soluţie bazică de sodium hydroxide or sodium
carbonate:
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[an]SO4 + 2NaOH = Na2SO4 + 2[an]OH
In everyday life, the ion exchanges are used at a
large scale for water softening (the elimination of the
ions of divalent metals). In this case, cationites in
form sodium (Na+) are used, and their regeneration
can be made using sodium chloride.
The mostly used method of water treatment is in
column. In this way, the water previously released
from suspensions and dissolved organic impurities is
passed over a fixed bed of granules. In this
conditions, the ion exchange resin gradually exhausts
from the upstream area to downstream area. In the
moment of the exhaustion, we pass to the
regeneration of the column exchange by introducing a
regenerated solution in the column and washing it
from abundence with water.
The extended applying of this process is limited
because of two factors: one is the high costs of the
regeneration and the other one is the resin
degradation. Another important disadvantage of the
ion exchange is the forming of regenerating products
which constitute aqueous residues whose final
evacuation causes significant difficulties. The
situation changes when the retained salts on the ion
exchange columns and eliberated at regeneration find
an industrial utility.
2. Principles and methods of work
For obtaining this type of water we used plant
IC46D with these technical features:
Technical Data
Technical Data
IC46D/
500
NaOH (scales) Kg.
2.2
• Diluition water lt.
50
Or
• NaOH in solution 30% lt
5
• Diluition water lt
45
Water necessary for rinsing:
100
• first rinsing lt
• second rising lt
200
Feed voltage V.
220
Complessive watts absorbed (points)
Watt
300
We used ion exchange Purolite A200MBOH and
Purolite C100MBH type, one is for anions exchanger
other is for cations exchanger.
Tabel 1
IC46D/
500
Feed water pressure atm.
2
Max flow rate of H2O production lt/h
500
Purity of demineralized water produced
> ohms
5 MΩ
Corresponding saline residue < mg/l
0,2
H2O cyclic production rate referred to
total salinity of treated water expressed
in CaCO3:
• 20°F/si (200 mg/l) lt
3.000
• 30° F/si (300 mg/l) lt
1.900
• 40°F/si (400 mg/l) lt
1.300
• Reactives for regenerating substances:
• Hcl 30 % (20°bè) lt
4.5
• Diluition water lt
11.5
Fig. 1 - Operating diagram
1. Electric three position commutator “regeneration o - production”
2. Electric wsitch for manual mixing of resins
3. Programmer, electronic timer with reading of
purity of water produced
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4. Little protection box containing terminal board for
electric connections
5. Valve for manual inlet of feed water
6. Water pressure reducer with manometer
7. Liter counter
8. Filter
9. Three ways ball valve
10. Flow rate control valve
11. Valve to send produced water to the storage tank
12. Flowmeter
13. Demineralized water storage tank
14. Demineralized discharge
15. Alkaline solution tank
16. Acid solution tank
17.Demineralized water tank/use cut-off valve
18. Demineralized water storage tank discharge valve
19. Raw water inlet filter
20. Raw water inlet
To produce demineralized water, proceed as
follows:
• three ways ball-valve (Fig. 1 no. 9) open to
discharge the first water produced (in case of
any cycle beginning after regeneration
operations)
• little handwheel for manual valve control: at
position “1” (Fig. 1 no. 21)
• three-position commutator at “production” (Fig.
1 no. 1)
The plant will produce water which will go to
discharge.
Vertical scale of right leds of programmer will
indicate
purity
values
expressed
in
megaohms/microsiemens.
When purity value is sactisfactory, send water
produced to utilization (tank 13), closing ball valve
(Fig. 1 no. 9).
On request demineralizer can be provided with a
supplementary automatism o signal the end of
productive cycle by means of an alarm and eventually
to stop automatically production.
In this case the electric board will have, instead of
a switch already discribed for “manual mixing”,a
commutator with three position “manual production0-manual mixing”.
At the beginning of each productive cycle (after
operations of regeneration) put said commutator at
“Manual production” to produce water even if not
sufficiently pure, cancelling alarm signal.
The same will be put at rest position, as soon as
values of water purity will be superior to the min.
prefixed with the little knob no. 4 (Fig. 2).
The apparatus will produce water which can be
send to utilization.
At the end of the cycle, supplementary
automatism will go in prealarm and with a delay of
about 60” will operate an alarm signal.
It will be possible then to stop production
positioning the switch located back the board at
“Alarm and stop of production”.
3. Discussions and results
Table 2
water
deminer
alized
water
pH
7.2
6.91
Ionic conductivity
248.5
1.732
0
0
25
<0.05
40
4.2
µS/ cm2
Nitrite
[mg/l]
Nitrate
[mg/l]
water hardness
[ºgermane]
pH was determined by using the Hanna
Instruments pH meter, HI113; the ionic conductivity
was determinated by using the Fisher Scientific
conductometer, Accumet Basic AB30; Hardness
measurements were made by volumetric dosing using
HCl 0.1n for the temporary hardness and EDTA 2Na
0.1n for the determinations of the permanent hardness
(this way, the calcium hydrogen carbonate, the
magnesium hydrogen carbonate quantities and the
calcium carbonate, magnesium carbonate quantities),
written in Table 1; the quantities of ion nitrite, nitrate
or ammonium were determined using the
spectrophotometric
method
with
PF
11
spectrophotometer, the Visocolor method.
By analizying the results from table 2, we
observed that the purity of the water obtained using
this process is very high. Consequently, we
recommend the usage of this kind of water in order to
obtain the energetic steam.
4. Conclusions
- High purity water is obtained;
- pH and conductivity presents herself well articulated
values;
- In this conditions, the aggressive character of the
water is much reduced;
- The oxidation-reduction reactions speed is much
reduced;
- The necessary costs for obtaining this type of water
are compensated by the long-term use of the
industrial installations.
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- Anorganic substances can produce an increasing of
the hardness. In this case, the water with a high
degree of hardness produce deposits and reduce the
thermic transfer capacity.
- In the case of power plants, but even in other
industries, which demand quality conditions of water
it is necessary to use demineralized water.
References
[1] Petrucci, R.H. and Harwood, W.S. (1993),
General Chemistry. Principles and Modern
Applications, pp. 786, MacMillan Publishing
Company, New York.
[2] Harland, C.E. (1994), Ion exchange: Theory and
Practice, The Royal Society of Chemistry,
Cambridge, 1994.
[3] Zagorodni, A.A. (2006), Ion Exchange
Materials: Properties and Applications,
Elsevier, ISBN: 0-08-044552-7.
[4] Litter, M.I., Morgada, M.E. and Bundschuh, J.
(2010), Possible treatments for arsenic removal
in Latin American waters for human
consumption, Environmental Pollution, Volume
158, Issue 5, pp. 1105-1118.
[5] Van Dam, D., Heil, G.W., Heijne and B.,
Bobbink, R. (1991), Throughfall below
grassland canopies: A comparison of
conventional and ion exchange methods,
Environmental Pollution, Volume 73, Issue 2,
pp. 85-99.
[6] Shrimali, M. and Singh, K.P. (2001), New
methods of nitrate removal from water,
Environmental Pollution, Volume 112, Issue 3,
pp. 351-359.
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