A3.4 Monitoring On Solid Alkaline Treated Systems - ABB AX410 User Manual

A3.4 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 three times higher than normal
owing to the acid. Hence to derive the concentration and pH of
the alkaline agent, one third 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:
log(BC –
Inferred pH = 11 +
Where: BC = the before column reading
AC = the after column reading
F = molar conductivity change for the
alkaline agent (243S cm
for sodium hydroxide
The maximum after-cation conductivity value is programmable
between 1.00 and 100.0S cm
conditions. After-cation values above this level generate an
error message and before-cation values
AFTER CAT. HIGH
–1
above 100.0S cm generate a
message. The inferred pH range is 7 to 11pH; values above
11pH generate an
Infr. pH invalid
Section 8 for description of error messages.
The inferred pH feature can be used on solid alkali treated
systems only in the following circumstances:
a) On steam raising plant.
b) For boiler chemical treatment such as sodium hydroxide.
In this instance,
A: Temp. Comp.
must be set to
B: Temp. Comp.
c) Where the after-cation conductivity value is less than
100.0S cm –1 .
Note. Inferred pH measurement on solid alkaline
treated systems is inappropriate to samples containing
sodium phosphate, ammonia or morpholine.
* Refer to Appendix to VGB Guideline VGB-R 450 L.
1
/ AC)
3
F
–1 per mmol/l
* )
–1
dependent on local
BEFORE CAT. HIGH
error message. Refer to
must be set to
NaOH
– see Section 5.3.
ACID
error
and
APPENDIX A
77