INGOLD
Application Notes
Leading Process Analytics
pH Measurement in
Flue Gas Washing Plants
Background
The world produces millions of tons of disposable waste every year. Separation and recycling is possible only for a small portion of the materials contained in this waste. The disposal of one ton of waste
costs approximately $170 US dollars.
Absorber
Hydroclone
Process water
Vacuum filter
Slurry
spray
headers
Clean
flue gas
Gypsum
Recirculation
lines
Heat
exchanger
Flue gas
Oxidation
air
Absorber
tank
Gypsum
storage
Wastewater treatment
Figure 1:
General out line of a gas
washing process (gas scrubber).
Slurry
feed tank
Limestone slurry
pH Measurement in Flue Gas Washing Plants
2
METTLER TOLEDO
Tons of waste which produce flue gas must be incinerated
every year. This reduces the waste to 20 % of its original weight.
All flue gas from industrial incinerators must be cleaned. This
gas will be scrubbed with water at a defined pH value in
several steps.
Process
Four washing steps clean the waste gas:
pH 0:
adsorption of HF and HCl at 60 °C (140 °F)
pH 1:
adsorption of HCl and heavy metals
pH 4-6: adsorption (bypass system) of SO2 and Hg,
pH control and neutralization with NaOH.
pH 8:
outlet
pH measurement at high concentrations of HCl and HF
(0.1…0.5 g/l) gives rise to pH values around 0.5. HF
(hydrofluoric acid) is used in glass etching, so the membrane
of the electrode can easily corrode. Temperatures from
60 °C…100 °C (140…212°F) also place severe demands on
the measuring equipment.
Combination pH electrode InPro® 3252
Pre-pressurized liquid electrolyte eliminates
fill requirements to reduce maintenance.
Internal over-pressure ensures gradual
electrolyte outflow, efficiently cleaning the
diaphragm and preventing influx of process
medium into the reference electrolyte.
HF-resistant membrane to minimize
the effects of hydrofluoric acid.
Combination pH electrode InPro® 4250
Xerolyt® PLUS solid polymer electrolyte is
a low maintenance electrode (no re-fill of
electrolyte).
Integrated temperature sensor for optimal
measurement performance.
Increased lifetime in the presence of organic
solvents, acids and alkali.
No clogging problems increases measurement
performance due to the open aperture junction.
Ex-certificated.
Rugged IP68 rated quick connect
Vario Pin (VP) connector.
Mettler-Toledo Solution
Because of the harsh conditions of this process, the
InPro 3252 and the InTrac 777 e housing are recommended.
The InPro 3252 electrode is made with a special HF-resistant
glass and is filled with a liquid electrolyte at an overpressure
of 2.5 bar (30 psi) to ensure the outflow of electrolyte and
protect the reference system against contamination. The
InTrac 777 e housing in PVDF retracts the electrode
automatically when no pH measurement is needed,
increasing the lifetime of the electrode more than three times.
Application Note
Combination pH electrodes InPro® 4800/
InPro® 4801SG as an option
Low maintenance gel electrodes as an option.
Flat membrane version (InPro 4801 SG) with
integrated solution ground for abrasive media,
for improved process security.
Highly resistant towards chemical media like
acid, alkali, oxidizing media, sulfide, highly
contaminated media etc., due to unique design.
Designed for very high pressures
and temperatures.
Ex-certificated.
Rugged IP68 rated quick connect
VarioPin (VP) connector.
pH Measurement in Flue Gas Washing Plants
Retractable housing InTrac® 777 e
Rugged 316L SS and PVDF construction
for maximum chemical resistance.
Flushing chamber for automatic
cleaning and calibration reduces
overall sys-tem downtime.
Patented immersion tube design isolates
the sensor on retraction and guarantees
complete separation of the process from
the outside environment.
Safety interlocks prevent sensor
removal from housing while in
measuring position.
Manual or pneumatic operation.
«Hot Tap» retractable housing InTrac® 787
Fast and easy sensor maintenance
or replacement without process
interruption.
Double O-ring process seals.
Integrated blow-out protection.
Mechanical linkage ensures safe
operation.
Self-wiping retractable tube
reduces O-ring wear.
Mettler-Toledo AG
Process Analytics
Im Hackacker 15
CH-8902 Urdorf
Switzerland – 02/07
pH transmitter M300 pH/Redox
Ideal choice for basic
applications.
Easy operation, robust
construction.
Easy to install, panel-or
wall-mount version, with
removable terminal plugs.
Available as
1- or 2-channel version.
Transmitter pH 2100 e
Operational safety and reliability
due to continuous sensor and
transmitter diagnostics.
Easy installation and selfexplanatory operation through
pictographic user interface and
Sensoface®.
Loop autonomy and maintenance-free pH measurement
due to integrated PID controller.
Flexibility with 4 wire installation or alternatively
2-wire execution with HART® and/or Profibus® and/or
FF communication and EEx applications.
www.mt.com/pro
Visit for more information