EHSQ OF DM PLANT
De-mineralization plant is employed for removal of minerals
or dissolved salts from the water. Salts on dissolving dissociate
into electrically charged particles called ions: for example common
salt will be split into sodium ion (a positively charged ion
or cation) and chloride (a negatively charged ion or an anion). If
such a solution is brought into contact with a suitable ion exchange
material (called resin), some ions from the solution are taken up by the
resin and an equivalent number are transferred from the resin to the
solution. Ion exchange is thus a reversible interchange of ions
between a liquid and a solid.
A simple Demineralization Plant consists of two beds of chemically treated resin beads operating in series. The first column- cation exchanger- converts the dissolved solids in the raw water to the equivalent acids; these acids are removed as the water passes through the second column- anion exchanger. The final product from this process consists essentially of pure water. When exhausted, the cation exchange resin is regenerated with acid and the anion exchange resin with alkali.
In essence the DM plant comprises of resin vessels with charge of strong cation and anion resin; control-panel encompassing a conductivity measurement and alarms, etc; acid and caustic injection facility from bulk, semi-bulk or carboy containers.
A simple Demineralization Plant consists of two beds of chemically treated resin beads operating in series. The first column- cation exchanger- converts the dissolved solids in the raw water to the equivalent acids; these acids are removed as the water passes through the second column- anion exchanger. The final product from this process consists essentially of pure water. When exhausted, the cation exchange resin is regenerated with acid and the anion exchange resin with alkali.
In essence the DM plant comprises of resin vessels with charge of strong cation and anion resin; control-panel encompassing a conductivity measurement and alarms, etc; acid and caustic injection facility from bulk, semi-bulk or carboy containers.
The high-purity water from a demineralization plant is typically
used as feed water for high pressure boilers in many industries; as
wash water in computer chip manufacture and other micro-electronics
manufacturing processes, as pharmaceutical process water, and any process
where high-purity water is a requirement. DM water is used as
process water in the manufacture of chemicals and fertilizers, food
products such as soft drinks, automobiles for rinsing of parts,
textiles, etc.
Two-bed INDION DM plants are made in all sizes, from small portable units for laboratories to large multi-stream installations for Thermal power stations, refineries, petrochemical and steel plants.
Two-bed INDION DM plants are made in all sizes, from small portable units for laboratories to large multi-stream installations for Thermal power stations, refineries, petrochemical and steel plants.
The type of resins
employed and selected depends on numerous factors: Treated water quality
required- If silica removal is not required, anion exchange resin
used in two- bed DM plants is usually INDION 850 weak base
anion resin. If silica level of 1.0 ppm can be tolerated, then INDION N-IP
strong base Type -2 resin is offered. When water free from silica is required,
the anion exchanger is charged with INDION FF-IP strong base Type -1 anion
resin.
- Input water quality
Presence of organic foulants- In cases where water has high level of organic foulants such as humic and fulvic acids occurring in natural surface waters, Macroporous resins such as INDION 810- Type 1strong base resin are better suited for the application than INDION FF-IP - Flow through plant required
- Considerations of minimization of operating costs in terms of regenerant chemical consumption: In order to reduce regenerant chemical consumption in large plants, INDION 850 resin (which is very efficient for removal of strong acids such as HCl and H2SO4 with minimal requirement of alkali for regeneration) is used in combination with INDION FF-IP strong base resin which is best suited for removal of weak acids such as carbon dioxide and silica from water
The regeneration is usually carried out in three steps.
Firstly, the ion exchange column is backwashed with an upflow of water.
The pressure vessel has about 50% free space above the resin bed (known as
free board). This free space allows removal of any entrained solids, and
re-classification of the resin bed by backwashing. Backwashing
also relieves bed compaction. Secondly, a predetermined amount of acid or
alkali is injected into the column in a downward direction (same direction
as the service flow or co-current) to displace sodium/calcium/magnesium in the
cation exchanger and chlorides/sulphates/alkalinity in the anion exchanger
taken up during the service cycle. Lastly, the column is rinsed to remove
excess regenerant. The entire operation takes about 3 hours for a two-bed DM
plant.
With counter-flow regeneration, the regenerant acid or
caustic passes in the direction opposite to the flow of water during
the service cycle. With counter-flow regeneration, the fresh
regenerant enters at the bottom of the resin bed and passes in
an upward direction (opposite to the downflow direction during service
cycle- or counter-current). Hence, bottom layer of the resin bed is
always in highly regenerated condition. This means lower leakage or
slip of ions during the service cycle producing better quality of
treated water than the co-current method.
The mixed bed is a single column of INDION 225 cation
exchanger and INDION FF-IP anion exchanger mixed together. Water passing
through the column comes into contact with these materials and is subjected to
almost infinite number of demineralizing stages. Thus demineralized water of extreme
purity is produced.
As with two-bed demineralizers, mixed bed units are regenerated with acid and alkali: but the ion exchange resins must be separated before this can be done. Bed separation is accomplished by backwashing: this carries the lighter INDION FF-IP resin to the top of the bed and the heavier INDION 225 sinks to the bottom. Two completely separated layers are thus formed, into which the acid and alkali solutions and rinse water are introduced through specially designed distributors. After regeneration, the two resins are mixed with compressed air.
Normally mixed bed unit treats water from the two-bed DM plant that is already of high purity and their ionic load is low. They can consequently be operated at high flow rates, and are of relatively smaller size.
As with two-bed demineralizers, mixed bed units are regenerated with acid and alkali: but the ion exchange resins must be separated before this can be done. Bed separation is accomplished by backwashing: this carries the lighter INDION FF-IP resin to the top of the bed and the heavier INDION 225 sinks to the bottom. Two completely separated layers are thus formed, into which the acid and alkali solutions and rinse water are introduced through specially designed distributors. After regeneration, the two resins are mixed with compressed air.
Normally mixed bed unit treats water from the two-bed DM plant that is already of high purity and their ionic load is low. They can consequently be operated at high flow rates, and are of relatively smaller size.
Electrical conductivity is used to express the purity
of demineralized water. Depending on the
application pH and/or reactive silica in DM water may also
be specified as parameters to measure the purity of DM water.
The quality of the water depends on the type of scheme used:
The quality of the water depends on the type of scheme used:
Cation-Anion-Polishing Mixed Bed
For standard plants our guarantees are as follows:
1) Conductivity 0.1 micromhos /cm-1.0 micromhos/cm. at 25°C (We guarantee conductivity of 0.1 micromhos/cm in very large projects only)
2) Sodium 0.01 mg/l - pH: 7 +/- 0.2
3) Reactive silica 0.02 mg/l -0.05 ppm
For standard plants our guarantees are as follows:
1) Conductivity 0.1 micromhos /cm-1.0 micromhos/cm. at 25°C (We guarantee conductivity of 0.1 micromhos/cm in very large projects only)
2) Sodium 0.01 mg/l - pH: 7 +/- 0.2
3) Reactive silica 0.02 mg/l -0.05 ppm
Cation-Anion (Counter-Current Regeneration)
For standard plants our guarantees are as follows:
1) Conductivity 0.5 to 1.0 µS/cm at 25°C- 30 micromhos/cm (We guarantee conductivity less than 10 micromhos/cm in large projects only)
2) Sodium 0.05 to 0.1 mg/l - pH: 7.5 - 9.0
3) Reactive silica 0.025 mg/l - less than 0.5 ppm (with FF-IP we can guarantee less than say 0.3 ppm)
For standard plants our guarantees are as follows:
1) Conductivity 0.5 to 1.0 µS/cm at 25°C- 30 micromhos/cm (We guarantee conductivity less than 10 micromhos/cm in large projects only)
2) Sodium 0.05 to 0.1 mg/l - pH: 7.5 - 9.0
3) Reactive silica 0.025 mg/l - less than 0.5 ppm (with FF-IP we can guarantee less than say 0.3 ppm)
Cation-Anion (Co-Current Regeneration)
With typical co-current regeneration, the outlet quality will depend on the regenerant applied, resin employed and raw water quality
1) Conductivity 5 to 30 µS/cm at 25°C- conductivity can be upto 2 to 5 % of conductivity of raw water
2) Sodium 0.5 to 3 mg/l
3) Silica 0.1 to 0.3 mg/l - less than 1.0 ppm
With typical co-current regeneration, the outlet quality will depend on the regenerant applied, resin employed and raw water quality
1) Conductivity 5 to 30 µS/cm at 25°C- conductivity can be upto 2 to 5 % of conductivity of raw water
2) Sodium 0.5 to 3 mg/l
3) Silica 0.1 to 0.3 mg/l - less than 1.0 ppm
For the sizing of a demineralization plant, a good in-depth water
analysis is normally required which gives the breakdown of total anions and
total cations and any potential organic foulants. The final water quality
specification, as well as flow rate and water used per day is required.
The alkalinity or bicarbonates and carbonates present in raw
water appear as carbonic acid or dissolved carbon dioxide at the outlet of
cation exchanger. Weak base anion resin such as INDION 850 does not remove weak
acids such as carbon dioxide or silica. The demineralized water is therefore
passed through a degassing tower for removal of carbon dioxide or CO2.
The tower, made of rubber-lined steel is filled with packing rings through
which the demineralized water percolates. Low pressure air introduced at the
bottom of the tower scrubs out CO2, and the degassed water collects
in a sump beneath the tower.
All INDION DM plants are provided with conductivity indicators
that have two basic elements: a conductivity cell with electrodes of special
design between which demineralized water flows and a sensitive milliammeter for
measuring the current passing between the electrodes. This current is
proportional to conductivity of the water.
Defects
|
Causes
|
Remedies
|
a.
Increase in ionic load
b.
Flow recorder defective
c.
Insufficient chemicals used
d.
Resin dirty
e.
Plant being used intermittently
f.
Channelling in bed
g. Resin fouled
h. Resin deteriorated
i.
Resin quantity insufficient in unit
|
Check
by analysis
Check
Check
Give
prolonged backwash
Avoid
this
Check
and ensure uniform distribution /collection
If
cation, give HCl wash; if anion, resin give alkaline brine treatment
Check
and replace charge
Check
and top up
|
|
a.
Cation exhausted
b.
Anion exhausted
c.
Mixed bed exhausted
d.
MB resin not in uniform mixed state
e. Some valves like backwash leaking
f.
Na slip from cation high
g. SiO2 slip from anion high h. Unit idle
i.
Unit not sufficiently rinsed
j.
Excessive/low flow rate
k. Channelling l. Resin fouled
m. Resin deteriorated
|
Check
Check
Check
Repeat
air mix and rinse
Check
Check
raw water analysis; change in Na/TA and SiO2/TA ratio; use more chemicals
Check
raw water analysis; change in Na/TA and SiO2/TA ratio; use more chemicals
Check
Rinse
to satisfactory quality
Adjust
to between unit min/max flow rate
Check
and ensure uniform collection/distribution
Check
resin and give alkaline brine/ HCL treatment
Check
resin and replace
|
|
a.
Resin not separated during backwash properly
b. Air mix not proper
c.
Final rinse not proper
d.
Some valves may be leaking and contaminating the treated water
|
Give
extended backwash after exhausting the bed
Repeat
Repeat
Check
and examine
|
|
a.
It can be due to choked suction filter of degasser air blower
b.
Improper air flow to the degasser
c. Degasser blower not in operation
d.
Air seal not fitted/broken resulting in short circulating of air
|
Check
and clean filter
Check damper, speed of blower, discharge pressure
Check
and operate blower
Check
and replace fitting
|
|
a.
Flow rate too high
b.
Unit exhausted
c.
Backwash valve passing
d.
Anion resin organically fouled
e.
MB air mix not satisfactory
f.
Acid/alkali pockets formed in unit
|
Increase
flow rate
Regenerate
unit
Check
and rectify
Give
alkaline brine treatment
Carry
out air mix once again
Faulty
design check and rectify. Temporarily backwash (followed by air scour if MB)
and rinse again
|
|
a.
Choked valve and suction strainer of pump
b.
Cavitation in the pump
c.
Low inlet pressure
d.
Distribution or collecting system choked
e.
Resin trap at outlet choked
f.
Control valve shut due to low off-take
|
Check
Check
Check-pump
Check
Check
and clean
Increase
off-take
|
|
a.
Defective valves
b.
Packed resin bed and resin fines present
c.
Collecting system choked
d.
Pressure gauge defective
|
Check
Give
extended backwash with open manhole and scrap off fines from top surface of
the resin
Check,
repeat backwash
Check
and rectify/ replace
|
|
a.
Very high air flow rate
b. Packed tower chocked due to dirt or broken packing material |
Reduce
air flow rate by adjusting damper
Open
and check
|
|
a.
Excessive backwash pressure
b. Faulty collecting system
c.
Inlet strainer damaged
|
Check
inlet pressure and reduce if necessary
Examine
same for breakage
Check
and replace
|
|
a.
Low power water pressure
b.
Air lock in the unit
c.
Choked or defective valves
d.
Ejector nozzle may be choked
e.
Too much back pressure from the unit
f. Bulge in pipe lining |
Check
Backwash
& open air release
Examine
and rectify
Check
Check
for chokage of collecting system; passage of inlet/outlet valves
Check
and rectify
|
|
a.
Chocked orifice lines/orifice
b.
Dirty glass and float
|
Check
and clean
check
and clean
|
|
a.
Choked impulse lines/orifice
b.
DP transmitter requires recalibration
c.
Leakage in signal tube between transmitter and panel
d.
Low air pressure for DP transmitter or recorder
|
Check
and clean
Recalibrate
Check
Check
|
|
a.
Improper contact between electrodes and control
cabling
b.
Shorting of the two electrodes due to moisture or
any foreign material
c.
Improper working of the level controllers
|
Check
contact and rectify
Check and dry the contacts of moisture and dirt
Check
|
|
a.
Improper adjustment of the mechanical seal
b.
Low strength of sulphuric and presence of ferrous sulphate
|
Check
and adjust
Check
concentration and take appropriate action
|
|
a.
Low concentration of sulphuric acid
b.
Lining of HCl tank/pipe line damaged
|
Check
silica gel breather in acid storage tank and replace silica gel charge if
exhausted
Rectify
|
|
a.
Defective solenoid valves
b.
Leakage in airline from solenoid valve to the respective control valve.
c.
Improper contact of micro switch giving false indication to panel
d.
Fused mimic lamp giving false indication to the panel
|
Check
Check
Check
Check
|
|
a. Defective relays in the control
circuit
|
Check and replace relays
|
|
a.
The controller can be kept in "hold" due to the reasons explained
under operation
b.
Improper operation of the controls for the controller
c.
Defect in the inside of the controller
|
Remove
conditions which cause "hold" of controller
Press
test switch & check the complete cycle
Check
the instruments thoroughly from inside. Meanwhile, operation may be continued
by using bypass toggle switches
|
Posted 8th April 2012 by Dr. Amar Nath Giri-NAGARJUNA-GROUP-NFCL
No comments:
Post a Comment