01. Deionized Water
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Transcript of 01. Deionized Water
Chemical Plant Utilities Lab BKC 3761
MODULE 1
DEIONIZED (DI) WATER SYSTEM
MODULE CONTENT
1.0 Introduction
1.1 Water Deionization Process Explained
1.2 Deionization Systems
1.2.1 What is Deionization?
1.2.2 Continuous or batch?
1.2.3 Counter current regeneration
1.2.4 Power Purge regeneration
1.2.5 Sophisticated PLC Automation
1.2.6 Ion Exchange Reaction
1.2.7 Ion Exchange Chemistry,
Chelated Resins
1.2.8 Chelated Resins
2.0 System Design
2.1 Feed Water Analysis
2.2 Product Water Specifications
3.0 Process Description
3.1 Raw Water Tank
3.2 Raw Water Pumps
3.3 Cartridge Filters
3.3.1 Initial Start Up
3.3.2 Operation And Maintenance
3.4 Carbon Filters
3.4.1 Initial Start Up
3.4.2 Operation And Maintenance
3.5 Portable Mixed Bed Ion Exchangers
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Chemical Plant Utilities Lab BKC 3761
3.5.1 Initial Start-Up
3.5.2 Operation And Maintenance
3.6 Final Filters
3.6.1 Initial Start Up
3.6.2 Operation And Maintenance
4.0 Equipment Specification
5.0 Drawings
6.0 Conclusion
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Chemical Plant Utilities Lab BKC 3761
1.0 INTRODUCTION
1.1 WATER DEIONIZATION PROCESS EXPLAINED
The process used for removal of all dissolved salts from water is referred to as
deionization. Deionization requires the flow of water through two ion exchange materials
in order to effect the removal of all salt content.
Deionization. The terms demineralization and deionization are used somewhat
interchangeably by the industry. While the term demineralization is generally better
understood, deionization is especially apt.
The passage of water through the first exchange material removes the calcium and
magnesium ions just as in the normal softening process. Unlike home equipment,
deionization units also remove all other positive metallic ions process and replace them
with hydrogen ions instead of sodium ions.
As the metallic ions in the water affix themselves to the exchange material, the latter
releases its hydrogen ions on a chemically equivalent basis. A sodium ion (Na+)
displaces one hydrogen ion (H+) from the exchanger; a calcium ion (Ca++) displaces two
hydrogen ions; a ferric ion (Fe+++) displaces three hydrogen ions, etc. (Recall that home
softeners also release two sodium ions for every calcium or magnesium ion they attract.)
This exchange of the hydrogen ions for metallic ions on an equivalent basis is chemical
necessity that permits the exchange material to maintain a balance of electrical charges.
Now because of the relatively high concentration of hydrogen ions, the solution is very
acid.
At this point the deionization process is just half complete. While the positive metallic
ions have been removed, the water now contains positive hydrogen ions, and the anions
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Chemical Plant Utilities Lab BKC 3761
originally in the raw water.
The partially treated water now flows through a second unit, this time an anion exchange
material normally consist of replaceable hydroxyl anions and fixed irreplaceable cations.
Now the negative ions in solution (the anions) are absorbed into the anion exchange
material. Released in their place are hydroxyl anions.
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WATER CONTAINING VARIOUS MINERAL CONTAMINANTS ENTERING
HERE
All that emerges from such a two unit system is ion-free water. It still contains the
positive hydrogen ions released in the initial exchange plus the negative hydroxyl ions
released in the second exchange.
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What has become of these two ions? Through the magic of chemistry they have
combined (positive to negative) to produce water molecules which are in no way
different from the water in which they were produced.
The result of this two-stage ion exchange process is water that is mineral-free.
Equipment for use in the deionization process may be of several types. Available are both
multiple bed and single bed units. Multiple bed units have pairs of tanks, one the cation
exchanger, the other for the anion exchangers, mixed in a single tank.
Deionized water has a wide range of uses in industry. Chemical production,
pharmaceuticals, electroplating, television tube production and leather goods processing
are among the many diversified applications for deionized water.
Efforts to produce mineral-free water through multiple distillations have proved to be
extremely complex and require elaborate and costly equipment.
1.2 DEIONIZATION SYSTEMS
1.2.1 What is Deionization?
The deionization process removes all ions from a solution. Cation exchangers remove all
cations (positively charged ions such as Sodium, Calcium, and Magnesium) and anion
exchanger remove all anions (negatively charged ions such as sulphate, bicarbonate, and
chloride). The cation exchanger is operated in front of the anion exchanger and converts
the salts to acids.
CaSO4 + 2R-H CaR2 + H2SO4
NaCl + R-H R-Na + HCl
The anion exchanger removes the acid from solution:
H2SO4 + 2R-OH R2SO4 + H2O
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Chemical Plant Utilities Lab BKC 3761
HCl + R-OH RCl + H2O
The result is water ions. Some Sodium will leak from the Cation exchange and this whar
determines the purity of the water leaving the system. One ppm Sodium is equal to 5
micromhos conductance (or 0.2 megohms resistance).
1.2.2 Continuous or batch?
Deionization systems can be either continuous or batch mode operations. In a continuous
system, there are duplicate sets of columns when one set has expired, the system switches
to the other set and regenerates the first. In a batch system, there is only one column pair
and the system is off-line for several hours when regenerating. Batch mode systems are
less expensive but require larger tanks for storage if you plan to continue supplying
deionized water while regenerating. A batch system is sized larger to make up for the
time lost during regeneration.
1.2.3 Counter current regeneration -
Counter current regeneration maximizes regenerant contact efficiency and results in high
water quality. Older style, less sophisticated systems use co-current regeneration where
the regenerant flow is in the same direction as the normal water flow. This results in
overall low water quality because the bottom part of the bed is only partially regenerated.
Countercurrent systems pass the regenerant in the direction opposite the normal water
flow, fully regenerating the bottom of the beds which minimizes leakage resulting in very
high water quality.
1.2.4 Power Purge regeneration
Regeneration is a 3 step process for Deionizing systems:
1. Rinse, to remove sediment, undersize resin particles, and reclassify the bed;
2. Regenerate with acid or caustic (depending on resin type);
3. Rinse again to remove excess regerant.
Traditional systems run all three cycles sequentially, using the second to push out the first
and the third to push out the second. If you think about it, you will see that you will get
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Chemical Plant Utilities Lab BKC 3761
dilution of the regenerant and no clear break between the regenerant and this rinse water.
Our Power Purge ion exchange regeneration system isolates the regenerant by removing
all (over 98%) of the water from the column before adding the regenerant to the system.
After regeneration, we purge the remaining regenerant from the system before adding any
rinse water. This reduces the overall rinse water requirements dramatically. Final rinsing
is a rinse-leach-purge step rinse operation that efficiently uses the minimal amount of
water. Each time the column fills with rinse water, the system waits until the water and
resin reach an equilibrium condition (concentration inside the bead = concentration in the
water) then we purge the water and refill. This allows us extensive control over the
process and, in some cases, even allows us to mix anion and cation bed rinse water to
achieve mutual neutralization.
1.2.5 Sophisticated PLC Automation
Remco Engineering sells fullly automated systems using microprocessor based
programmable logic controllers to control the regeneration process. We find that manual
deionization system are very uneconomical to operate when viewed from both your costs
to operate and the costs to support continous personnel training and retaining. We put our
expertise in a box inside the control panel so you don't have to call us every time you
regenerate to figure out which valves to open and close. Because we sell automated
systems that are computer ready, we can integrate pump and level controls alarms,
conductivity and other process sensors, and remote interfaces. We offer the most
sophisticated deionization systems available.
Sizing a system based on water use. Two requirements determine the size of a system :
1. Maximum demand (gpm peak),
2. Average demand (gpm average per day).
The first governs the amount of storage you will need, the second sizes the flow rate.
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Chemical Plant Utilities Lab BKC 3761
For example:
1. If you need 200 gallons to fill a tank 3 times per day and 2 gpm continously for
rinsing, then over an 8 hour day, you would need a total of 1560 gallons (8 x 120 gal/hr +
600) or about 3.25 gallons per minute. A 5 gpm system would be large enough with a 300
gallon storage tank for fills. If the tank fills were all at once, you wolud need enough
storage to cover all of them.
2. Ten(10) gpm required continously with tank fills of 85 gallons each every hour. The
total requirement would be about 11.5 gpm. We would recommend a 12-15 gpm system
with about 200 gallons of storage as a minimum.
Column Sizing a 5 gpm system. (calculations) The actual pysical size of system you will
need will vary depending on the quality of the water you eish to deionize. Deionization
systems use a resin that has a certain capacity given as kilograins of calcium carbonate
per cubic foot. A grain is 17.1 ppm. The actual operating capacity is less than 100% and
is based on the amount of regenerant (acid or caustic) added during regeneration. Doing a
complete regeneration wastes a lot of regenerant so systems are regerated to an
economical range of 60-70 percent of theoretical capacity.
There are a lot of alculation to determine actual capacity of a specific resin with a specific
water chemistry so we have a quick formula to do a rough 80% estimate of capacity.
Cation columns
1. Take your water TDS (total dissolved solid) analysis.
Look at Calcium, Magnesium and Sodium concentration in ppm.
2. Add up the total ppm and divide by 17.1 (i.e., 250 ppm/17.1 = 14.6
grains/gal).
3. Assuming a conservative 16 kilograin/cu. ft. capacity with an economical
regeneration, now divide 16,000 by 14.6 (16000/14.6 = 1095).
4. You will get over a thousand gallons of decationized water per cubic foot
of resin.
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Anion columns
1. Next add up the anions, they should be equal to the cations plus silica
(SiO2) and dissolved CO2.
2. Add up the anions plus silica and carbon dioxide in ppm. Lets say total
carbonate and silica is 20 ppm.
3. Take the total anion ppm and divide by 17.1 (270(250+20)ppm/17.1 =
15.8 gr/gal..).
4. Divide 14 kilogram/cu.ft by you answer (14,000/15.8=886 gallons per
cubic foot).
5. A 5 gpm system would require about 2.5 cu.ft. of cation resin and about 3
cubic feet of anion resin, resulting in about 2500 gallons of DI water
between regenerations.
If you need more than 2500 gallons between regenerations such as 5 gpm for hours then
regenerate at night, you would have to double the resin capacity of the system to 5000
gallons.
Factors effecting the capacity of the system are the relative amount of Sodium, Chloride,
and weak acids in the water. These can change the capacity by 20 to 30% as can the
regenerant laoding used.
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Chemical Plant Utilities Lab BKC 3761
1.2.6 Ion Exchange Reaction
Ion exchange is a reversible chemical reaction where in anion (an atom or molecule that
has lost or gained an electron and thus acquired an electrical charge) from solution is
exchanged for a similarly charged ion attached to an immobile solid particle. These solid
ion exchange particles are either naturally occurring inorganic zeolities or synthetically
produced organic resins. The synthetic organic resins are the predominant type used
today because their characteristics can be tailored to specific applications.
An organic ion exchange resin is composed of high-molecular-weight polyelectrolytes
that can exchange their mobile ions for ions of similar charge from the surrounding
medium. Each resin has a distinct number of mobile ion sites that set the maximum
quantity of exchanges per unit of resin.
Most plating process water is used to cleanse the surface of the parts after each process
bath. To maintain quality standards, the level of dissolved solids in the rinse water must
be regulated. Fresh water added to the rinse tank accomplishes this purpose, and the
overflow water is treated to removed pollutants and then discharged. As the metal salts,
acids, and bases used in metal finishing are primarily inorganic compounds, they are
ionized in water and could be removed by contact with ion exchange resins. In a water
deionization process, the resins exchange hydrogen ions (H+) for the positively charged
ions (such as nickel, copper, and sodium), and hydroxyl ions (OH-) for the negatively
charged sulphates, chromates and chlorides. Because the quantity of H+ and OH ions is
balanced, the results of the ion exchange treatment is relatively pure, neutral water.
Ion exchange reactions are stoichiometric and reversible, and in that way they are similar
to other solution phase reactions. For example:
NiSO4 + Ca(OH)2 = Ni(OH)2 + CaSO4
In this reaction, the nickel ions of the nickel sulphate (NiSO4)mare exchanged for the
calcium ions of the calcium hydroxide [Ca(OH)2] molecule. Similarly, a resin with
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Chemical Plant Utilities Lab BKC 3761
hydrogen ions available for exchange will exchange those ions for nickel ions from
solution. The reaction canbe written as follows:
2(R-SO3H) + NiSO4 = (R-SO3)2Ni + H2SO4(2)
R indicates the organic portion of the resin and SO3 is the immobile portion of the ion
active group. Two resin sites are needed for nickel ions with a plus 2 valence (Ni+2).
Trivalent ferric ions would require three resin sites.
As shown, the ion exchange reaction is reversible. The degree the reaction proceeds to
the right will depend on the resins preference or selectivity, for nickel ions compared
with its preference for hydrogen ions. The selectivity of a resin for a given ion is
measured by the selectivity coefficient. K. which in its simplest form for the reaction
R-A++B+=R—B++A+ (3)
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Chemical Plant Utilities Lab BKC 3761
Is expressed as: K = (concentration of B+ in resin/concentration of A+ in resin) X
(concentration of A+ in solution/concentration of B+ in solution).
The selectivity coefficient express the relative distribution of the ions when a resin in the
A+ form is placed in a solution containing B+ ions. Table 1 gives the selectivity of strong
acid and strong base ion exchange resins for various ionic compounds. It should be
pointed out that the selectivity coefficient is not constant but varies with changes in
solution conditions. It does provide a means of determining what to expect when various
ions are involved. As indicated in Table 1, strong acid have a preference for nickel over
hydrogen. Despite, this preference, the resin can be converted back to the hydrogen form
by contact with a concentrated solution of sulfuric acid (H2SO4):
(R—SO4)2Ni + H2SO4 -> 2(R-SO3H) + NiSO4
This step is known as regeneration. In general terms, the higher the preference a resin
exhibits for a particular ion, the greater the exchange efficiency in terms of resin capacity
for removal of that ion from solution. Greater preference for a particular ion, however,
will result in increased consumption of chemicals for regeneration.
Resins current available exhibit a range of selectivity’s and thus have broad application.
As an example, for a strong acid resin, the relative preference for divalent calcium ions
(Ca+2) over divalent copper ions (Cu+2) is approximately 1.5 to 1. for a heavy-metal-
selective resin, the preference is reserved and favors copper by a ratio of 2.300 to 1.
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Table 1.
Selectivity of ion Exchange Resins.
In Order of Decreasing Preference
Strong acid cation Strong base anion
exchanger exchanger
Barium Iodide
Lead Nitrate
Calcium Bisulfite
Nickel Chloride
Cadmium Cyanide
Copper Bicarbonate
Zinc Hydroxide
Magnesium Fluoride
Potassium Sulphate
Ammonium Sodium
Hydrogen
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Chemical Plant Utilities Lab BKC 3761
Ion Exchange System
1.2.7 Ion Exchange Chemistry, Chelated Resins
Ion exchange is a simple process where an organic molecule has been substituted with
acid or base exchange sites. As a solution with exchangeable ions passes through the
resin, the ions are captured and exchanged for the ions on the resin. For example, some
weak acid ion exchange resins can use the carboxylic acid radical, in the sodium form, R-
COO-Na as the exchange site. As solutions of metal ions such as Magnesium (Mg),
Calcium (Ca), or Copper (Cu) pass through the resin, they are exchanged for the Na
(Sodium) at that site. The molecule would now appear like this R-COO-Ca, for a Calcium
exchange.
R-COO-Na + Ca+2 = R-COO-Ca + 2 Na+
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Chemical Plant Utilities Lab BKC 3761
These resins are used in water softeners where the alkaline earth metals such as Calcium
and Magnesium are exchanged for Sodium. In a water softener Sodium Chloride (salt,
NaCl), is used to “regenerated” the resin. The salt solution is passed through the resin in
very high concentrations and the sodium displaces the metals attached to the active sites.
When the concentration of sodium is low, the sites prefer the alkaline metals again and
the resin can be used to “softener” water again.
1.2.8 Chelated Resins
The same principals apply in industrial ion exchangers except that usually a strong acid
or base is used to regenerate the resins (except in industrial water softeners). To remove a
metal from your waste stream at low pH using ion exchange, the most cost effective
method is to use a weak acid chelating resin. An iminodiacetic acid resin is useful to
remove a metal when a chelate such as ammonia or EDTE is present. The pH is adjusted
to the correct range remove the metal, but kept under 6 to prevent the formation and
precipitation of hydroxides and oxides of metals.
This resin has a hierarchy of preferences, i.e., it prefers Copper more than Zinc. This
requires their use mainly in compatible metal systems. If only one metal is being passed
through the column, there is no competition for sites and the progress of the system is
easier to monitor. Reclaiming the metal is also easier as multiple metal systems are
difficult to plate.
The ion exchange resin used in most metal recovery systems is what is called a “weak
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Chemical Plant Utilities Lab BKC 3761
acid” resin. This system allows low chemical usage, usually about 1.25 times the
theoretical amount to regenerate the column. This resin is used in the sodium form. This
allows us to regenerate with an acid and recover the metals in a useful form. The resin is
then conditioned so that the pH does not drop to low when we start up the column.
The basic chemistry of this system is as follows:
1. The solution is adjusted to a pH which is optimum for the resin but low enough to
prevent hydroxides from forming and high enough to ensure the capture of the metals.
2. The solution is passed through s media filter to remove any solids and then through
the lead/lag columns where the a metal is exchanged for sodium ions. The capacity of the
columns is about 1.8 pounds of metal per cubic foot of resin depending on the competing
ion passing through with the metal.
3. When a column is saturated with a metal, “breakthrough” occurs. This results in a
greatly increased passage or metal ions to the lag column. This is when you will
regenerate the first column.
4. The regeneration chemistry is in 5 steps, they are:
a. Water backwash to remove any broken beads. This recycles to the main holding tank.
b. Acid backwash to remove the metal. A recirculating acid tank ensures full metal
removal.
c. Water backwash to remove residual metal and acid from the column. A timing cycle
ensures the backwash goes to the acid tank until the steam is acid free.
d. An caustic soda backwash which removes the acid (recycles to the holding tank for
pH adjust before passing throuth the column), and replaces the H+ with Na+ ions. This
prevents the pH from dropping when the column goes on line.
e. A final water backwash to restratify the resin and remove the remaining caustic from
the system.
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Chemical Plant Utilities Lab BKC 3761
The main things to remember when setting up a system is to not let organic solvents, oil,
or grease in the system as these will foul the column.
Feed line segregation is very important for successful utilization of ion exchange. Call for
a segregation scheme for your facility.
2.0 SYSTEM DESIGN
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Chemical Plant Utilities Lab BKC 3761
2.1 FEED WATER ANALYSIS
The following water analysis is expressed as the ion mg/l unless otherwise
indicated, represents the anticipated water to be treated by the water
purification system specified by this manual.
Parameter Value
pH 6-8
Turbidity < 1.0 NTU
Conductivity 135 micro-mhos
Suspended Solids Trace
Temperature 24 ~ 32 deg C
2.2 PRODUCT WATER SPECIFICATIONS
Resistivity (at 25 Deg C) > 10 Megaohm.cm
Design Capacity 20 USgpm
3.0 PROCESS DESCRIPTION
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Chemical Plant Utilities Lab BKC 3761
Essentially, this 20gpm (4.5m3/h) water treatment plant comprises of:-
1) 1 no. of Raw Water Tank
2) 2 nos. of Water Feed Pump (100% standby)
3) 2 nos. of 5 micron Cartridge Filter
4) 2 nos. of Carbon Cartridge Filter
5) 2 nos. of Portable Mixed Bed Ion Exchanger, and
6) 2 nos. of Final Filters
3.1 RAW WATER TANK
The Raw Water Tank is supplied in 5.0m3 capacity. It is important as a storage
tank to ensure continuous water supply of 4.5m3/h for approximately one (1) hour
in the case of water supply failure. A manual float switch is installed to ensure
automatic fill up of water to maintain high level at all time.
3.2 RAW WATER PUMPS
Two (2) units of Raw Water Pumps (one duty, one standby) are installed to
deliver 4.5m3/h of raw water to the treatment system. The pumps are
protected with a low water level cut off switch to prevent run dry condition.
3.3 CARTRIDGE FILTERS
Two (2) units of cartridge filter (5 micron rating) are installed in parallel to
remove particulate matter greater than size of 5 micron.
Influent enters the housing under pressure and must pass through the filter
elements in order to exit the housing. In the same time, majorities of particles
larger than the filter’s size rating (5 µm) are blocked and retained at the filter
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Chemical Plant Utilities Lab BKC 3761
elements.
3.3.1 Initial Start Up
Flow into the filtration module is controlled by inlet and outlet isolation valves.
During start-up, the inlet valve is opened to allow water in. The outlet valve
shall also be opened to allow water and air flow out, either to drain or to the
down manufacturing detergents before they can be put into service.
3.3.2 Operation And Maintenance
When the filter elements become clogged with impurities, pressure will drop
across the cartridge filter system. To avoid insufficient pressure at the
downstream, the filter elements shall be replaced. A 15psi clean differential
pressure drop is the usual specification indicating the needs to change new filter
elements.
3.4 CARBON FILTERS
Two (2) units of carbon cartridge filter are installed in parallel to remove free
chlorine and some organic matter in the feed water. Elimination of free chorine is
very importance because it can attack and damage resins.
Although the filter also accomplishes some filtering or turbidity, it is incidental to
the prime purpose of the filter. Greater amount of turbidity in the inlet water can
decrease the effectiveness of the carbon, shortening its useful life.
3.4.1 Initial Start Up
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Chemical Plant Utilities Lab BKC 3761
Flow into the filtration module is controlled by inlet and outlet isolation valves.
During start-up, the inlet valve is opened to allow water in. The outlet valve shall
also be opened to allow water and air to flow out, either to drain or to the down
stream equipment. New filter elements must be rinsed to remove loose particles,
carbon fines and manufacturing detergents before they can be put into service.
3.4.2 Operation And Maintanance
Carbon media does not have an unlimited life. Eventually the carbon will no
longer have the capacity to adsorb organic and chlorine to a useful degree. When
this occurs, carbon filter elements must be replaced. High levels of chlorine and
organic can reduce the media life while low levels can increase the life. The best
way to determine the condition of the carbon bed is to periodically check the filter
effluent for excessive signs of chlorine and organic.
Based on the city water quality, we estimated a life span of 5 to 6 months for the
carbon filters.
3.5 PORTABLE MIXED BED ION EXCHANGERS
Ion Exchange Theory
Ion Exchange may be defined as the reversible interchange of ions between a
solid and a liquid phase in which there is no permanent change in the structure of
the solid. The solid is the ion exchange material. “Reversible” and “No Permanent
Change” are key points in this definition and in ion exchange. Ion exchange has
important applications in water conditioning such as softening and deionization.
With few exceptions, the great utility of ion exchange rests with the ability to use
and re-use the ion exchange material. For example, in water softening:
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Chemical Plant Utilities Lab BKC 3761
2R Na+ + Ca2+ R2Ca2+ + 2Na+
The exchange R in the sodium ion form is able to exchange for calcium and thus
remove calcium from hard water and replace it with and equivalent quantity of
sodium. Subsequently, the calcium-loaded resin may be treated with sodium
chloride solution, bringing it back to the sodium form, ready for another cycle of
operation. This conversion step is commonly called regeneration. The reaction is
reversed, the ion exchange is not permanently changed. Millions of gallons of
water may be treated per cubic foot of resin during an operating period of many
years.
Demineralization is the process of removing dissolved ionic impurities from
water. These positively charged cations and negatively charged anions allow
conductance of electricity and are called electrolytes. Electrical conductivity is
thus a measure of water purity, with low conductivity corresponding to high.
Weakly ionized contaminants such as silica contribute only slightly to the
conductivity of water.
Ion exchange demineralization is basically a two-step process involving
treatment with both cation and anion exchange resins. This treatment can be a
series operation or in a common bed depending on process conditions and
requirements.
In most demineralization systems, the water is first passed through the cation
exchanger. Here Ca2+, Mg2+, and Na+ are exchanged for H+.
R-H+ + Na+ R-Na+ + H+
2R-H+ + Mg2+ R2 Mg + 2H+
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Chemical Plant Utilities Lab BKC 3761
2R-H+ + Ca2+ R2 Ca + 2H+
The degree of removal of these ions depends on the cation resin selectivity.
Cation resins exhibit a much greater selectivity for divalent calcium and
magnesium ions than for monovalent sodium ions (also potassium if present).
Thus any leakage (non-removal) from the cation exchanger tends to be sodium
rather than calcium or magnesium.
The demineralization process is completed by anion resin treatment, with the feed
being the acids of the anions in the raw water feed. These anions are exchanged
for hydroxide.
The hydroxide neutralizes the acid as the water proceeds through the column. The
choice of the anion exchange resin(s) is most critical to the water quality
achievable and economics of the system. When high quality water is required, a
strong base anion exchange resin is used.
R+OH- + Cl- R+Cl- + OH-
2R+OH + SO42- R2SO4 + 2OH-
R+OH- + HCO3- R HCO3 + OH-
Since the OH- released is neutralized by the acids, a favorable acid-base
equilibrium exists and there is no acid leakage. Even the silica and the carbon
dioxide are reduced to very low levels. Regeneration is accomplished by a strong
base solution such as caustic.
Theory of Operation – Mixed Bed Concept
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In the mixed bed unit, strong acid cation and strong base anion resins are thoroughly
mixed to form a homogeneous bed. A series of many cation/anion beds are formed in this
one unit allowing for the removal of the small quantities of impurities not removed in the
cation or anion units. When the unit is exhausted, it is regenerated with hydrochloric acid
and sodium hydroxide.
Chemical reactions in the mixed bed unit are the same as in the individual cation and
anion exchange units.
Indications of Resin exhaustion are:-
Increase in sodium leakage
Increase in silica leakage
Decrease in resistivity
Increase in pressure drop across bed
(maximum permissible pressure drop = 35 psi)
There are two common types of resin used in a portable mixed bed unit:-
25
C
A
C
A C
A
C
A
INLET
OUTLET
SCHEMATIC MIXED BED EXCHANGER
Chemical Plant Utilities Lab BKC 3761
1. Regenerable type resin
2. Non-regenerable type resin
As the name implies, regenerable resin can be regenerate and re-use after exhaustion,
while non-regenerable resin have to be upon exhaustion because separation of cation and
anion resin is impossible in this type of resin. Generally quality of product water from
non-regenerable resin is much higher and stable compared to regenerable type.
3.5.1 Initial Start-Up
The Portable Mixed Bed Unit is normally come in regenerated form and is ready
to be put in service:-
1.) Connect the service Inlet, Service Outlet and the rinse/drain valve to the
columns.
2.) Perform Air mixing if necessary.
3.) Open Service Inlet and rinse/drain valve.
4.) Rinse the resin with post-filtered water until achieved the desired quality.
Note: Product water quality may differ depending on the feed water quality.
5.) Close the rinse/drain valve and open Service Outlet valve to allow the unit to
service.
3.5.2 Operation And Maintanance
Over time, the resin will become exhausted with ionic impurities. When the resin
is exhausted, the ionic impurities will start to leach into product water, typically
sodium (Na+) will be the first ion to leach out from cation resin and silica (SiO2)
is the first from anion resin. Water resistivity will started to drop when the time
comes and the resin is required to be regenerated.
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Chemical Plant Utilities Lab BKC 3761
In system using regenerable resin in their portable mixed bed, it is a common
practice to send the exhausted columns to regeneration plant to perform external
regeneration.
3.6 FINAL FILTERS
The Final Filters are used to prevent resin loss in unlikely event of an underdrain
failure. When resin from the Mixed Bed Deionizer passed through the filter, all
resin shall be trapped at the filter, this will cause increasing of pressure drop
across the filter. When this is detected, nozzles of the upstream Deionizers shall
be thoroughly checked.
The Final Filters have smaller pore size (1 micron), which can give a finer
filtration for the production water. Besides act as a resin trap, particulates larger
than the filter’s pore size in the process water shall be also trapped on the filter
while the clean water is pass through.
3.6.1 Initial Start Up
Flow into the filtration module is controlled by inlet and outlet isolation valves.
During start-up, the inlet valve is opened to allow water in. the outlet valve shall
also be opened to allow water flows out to the downstream equipment or directed
to drain. New filter elements must be rinsed to remove loose particles, carbon
fines and manufacturing detergents before they can be put into service.
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Chemical Plant Utilities Lab BKC 3761
3.6.2 Operation And Maintanance
Increase pressure drop across the filter is due o filter elements have been clogged
with impurities. To avoid insufficient pressure at the downstream, the filter
elements shall be replaced. A 10psi clean differential pressure drop is the usual
specification indicating the needs to change new filter elements.
4.0 EQUIPMENT SPECIFICATIONS
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Chemical Plant Utilities Lab BKC 3761
A. Raw Water Tank
* Quantity : 1 no.s
* Material : FRP
* Capacity : 5 m3
B. DI Water Transfer Pump
* Quantity : 2 no.s (1 no. standby)
* Maker : Grundfos
* Type : CHI 4-50 AWG BQQV
* Capacity : 4.5 M 3 @ 35 M
* Power supply : 415V/3P/50Hz
C. Pre-Filter
* Quantity : 2 no.s
* Brand : Cuno USA
* Material : PE
* Cartridge Length : 20 Inch
* Filter Rating : 5 Micron Nominal
* Capacity : 20 USgpm
D. Carbon Filter
* Quantity : 2 no.s
* Brand : Cuno USA
* Material : PE
* Cartridge Length : 20 Inch
* Capacity : 20 USgpm
E. Portable Mixed Bed (Regenable Resin)
* Quantity : 2 Sets
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Chemical Plant Utilities Lab BKC 3761
* Capacity : 10 USgpm/unit
F. Final Filter
* Quantity : 2 no.s
* Brand : Cuno USA
* Material : PE
* Cartridge Length : 20 Inch
* Filter Rating : 1 Micron Nominal
* Capacity : 20 USgpm
G. Resistivity Meter
* Quantity : 1 no.s
* Brand : Burkert German
* Type : 8225
* Power : 24 VDC
H. Control Panel : 1 set
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Chemical Plant Utilities Lab BKC 3761
5.0 DRAWINGS
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6.0 CONCLUSION
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Chemical Plant Utilities Lab BKC 3761
Water quality from deionizers varies with the type of resins used, feed water quality,
flow, efficiency of regeneration, remaining capacity, etc. Because of these variables, it is
critical in many DI water application to know the precise quality.
Resistivity /conductivity is the most convenient method for testing DI water quality.
Deionized pure water is a poor electrical conductor, having a resistivity of 18.2 million
ohm-cm (18.2 megaohm) and conductivity of 0.055 microsiemens. It is the amount of
ionized substances (or salts) dissolved in the water which determines water’s ability to
conduct electricity. Therefore, resistivity and its inverse, conductivity, are good general
purpose quality parameters.
7.0 EXPERIMENTAL WORK
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Chemical Plant Utilities Lab BKC 3761
WATER ANALYSIS
Purpose of Analysis
- to ensure the quality of water under the operation specificarion.
Parameter of Analysis
pH, Conductivity (25°C, 35°C, 45°C, 55°C), Tubidity, Chlorine, Teperature and
Total Dissolved Solid (TDS)
Sampling Points
- Water inlet (JBA Water)
- Water Outlet (DI Water)
- Distilled Water
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