Wednesday 13 November 2013

Problems related to demineralization plants

efects Causes Remedies
Decrease in capacity between two successive regenerations
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
Treated quality not upto the standard
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
Mixed bed quality not good
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
High residual CO2 from degasser
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
Unit rinse takes long time
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
Flow rate too less
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
Pressure drop across the bed increasing day by day
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
Flooding in degasser
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
Resin being lost
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
Ejector not working
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
Incorrect reading rota-meters
a. Chocked orifice lines/orifice
b. Dirty glass and float
Check and clean
check and clean
Improper reading from flow recorder integrator
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
Level electrodes system for measuring and dilution tank not functioning properly
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
Leakage from acid injection/unloading/transfer pumps
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
Corrosion in concentrated acid tanks and lines
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
Improper opening and closing of pneumatically operated valves
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
Improper operation of a certain regeneration cycle a. Defective relays in the control circuit Check and replace relays
Solid state programme not functioning properly
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


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