Monitoring On Solid Alkaline Treated Systems - ABB AWT420 Operating Instruction

AW T4 2 0 | U N I V E R S A L 4 - W I R E , D U A L- I N P U T T R A N S M I T T E R | O I/A W T4 2 0 - E N R E V. B

Monitoring on solid alkaline treated systems

Generally, boiler waters treated with solid alkaline chemicals,
for example, sodium hydroxide, have relatively high
conductivities.
The dual input conductivity analyzer, in conjunction with a
cation resin column, can be used to indicate sample pH. If the
sample also contains salts (e.g. sodium chloride), the after-
cation conductivity reading reflects the acid conductivity
released by the salts, the reading is typically 3 times higher
than normal owing to the acid. Hence, to derive the
concentration and pH of the alkaline agent, 1/3 of the after-
cation conductivity increase must be subtracted from the
before-column reading. In addition, a factor must be applied
for the molar conductivity change of the alkaline agent.
The analyzer software applies the following equation:
1
log(BC – / AC)
3
1 +
F
Where:
BC = the before column reading
AC = the after column reading
F = molar conductivity change for the
alkaline agent (243 µS cm
for sodium hydroxide)
The maximum after-cation conductivity value is programmable
between 1.00 and 100.0 µS cm
After-cation values above this level generate an AFTER CAT.
HIGH error message and before-cation values above 100.0 µS
cm generate a BEFORE CAT. HIGH error message. The inferred
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pH range is 7 to 11 pH, values above 11 pH generate an Infr. pH
invalid error message. Refer to page 83 for a description of
error messages..
per mmol/l
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dependent on local conditions.
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The inferred pH feature can be used on solid alkali treated
systems only in the following circumstances:
1 On steam raising plant.
2 For boiler chemical treatment such as sodium hydroxide. In
this instance, A: Temp. Comp. must be set to NaOH and B:
Temp. Comp. must be set to ACID.
3 Where the after-cation conductivity value is less than
100.0 µS cm .
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NOTICE
Inferred pH measurement on AVT systems is inappropriate
to chemical treatments such as sodium phosphate, sodium
hydroxide and morpholine.
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