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TitleHow to Measure False Air
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Page 1

How to measure false air

PR-PYR P06-10 V1


Procedure Template developed by


False air is any unwanted air entering the system between two points (see figure below). The exact
amount of false air is difficult to measure. An indicator of false air amount can be the oxygen increase
between two points (usable for gas stream containing less than 21% of oxygen).


point 2 point 1

false air entering


Increase capacity of system (when the fan is pneumatically limited)
Decrease power consumption of the fan (less gas for transport)
Decrease risk for coal mill shop
Increase gas drying efficiency
O2 after pre-heater and in stack
Note that each 1% increase of oxygen means approximately 5% increase of gas volume (also nitrogen

is introduced from air)


Prepare an action plan for reducing false air together with production and maintenance departments
Do measurement on a regular basis and follow-up on progress.

Safety aspects

Measuring of false air is only possible during kiln line in operation.
Personal Protective Equipment is a requirement with special precaution in high temperature areas in the

lower pre-heater tower.

Never make any measurement alone and without contact to the central control room operators.


Constant kiln operation at nominal capacity.
Calibrated portable oxygen analyzer.
Ensure that the pump of the portable gas analyzer is strong enough to extract the gases from the

measurement location:
e.g: after raw mills: ~90 [mbar] / after pre-heater tower ~110 [mbar]

Additional equipment: Sampling probes, coarse dust filter, fine dust filter and silica gel package for

Page 2

How to measure false air

PR-PYR P06-10 V1


Procedure Template developed by

Sampling probes
< 800 [°C]: heat resistant steel pipe (simple)
> 800 [°C]: Water cooled or ceramic probe (simple, see picture in tools) to avoid oxidation of the
carbon in the steel (O2 0,0% / CO > max. Val)

Depending on the scope also installed oxygen analyzers can be used. ( take care about calibration)
Openings for measuring located with reference to false air critical parts (existing, accessible and open)

Time frame

Depending on measurement scope.
Never forget to add some spare time for blocked measurement locations.


Calculation formula:





PoFalseAir OO



Requirement: all values must be used on same basis, dry or wet. Recommendation is to do it on dry
basis. Be aware this is also valid for flow measurement.

Typical equipment set up:

Water cooled probe:

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