way to zero. The stoichiometer cell will measure the amount of oxygen deficiency during
these reducing conditions. The trends in your DCS can be set up for a lower range limit of
-1 or -2% oxygen to depict the level of oxygen deficiency.
You can see if your control recovery actions are having the desired effect. These types of
events do not occur frequently, but knowing the parameters of the situation prevents
over-correcting while coming out of the reducing condition. The stoichiometer feature
requires purchasing the acid resistant stoichiometer cell and the stoichiometer feature
inside the Rosemount Xi.
NOTICE
Make sure the DCS is configured for the same range as the Rosemount Xi. For instance:
-1% O
2
to 10% O
2
.
3.5.3
Programmable reference
The zirconium oxide sensing technology has historically measured process oxygen by
using ambient or instrument air as a reference (20.95% oxygen). The sensor develops most
of its signal at the low oxygen levels typically found in combustion flue gases (2 to 4%
oxygen) and is most accurate at these levels. When measuring near 20.95% O
2
, the sensor
develops only a few millivolts of signal, and accuracy degrades.
The programmable reference feature permits you to use a bottled reference gas of low
oxygen value (0.4% oxygen recommended). When measuring at or near 21% oxygen, a
strong negative oxygen signal results with much improved accuracy. A bottle of reference
gas typically lasts about a month at the low flows required. Typical applications would be:
•
Flue gas recirculation
- controlling the mixing of flue gases into the burner windbox
ahead of the burner to reduce NO
x
emissions.
•
Moisture monitoring
- measuring the amount of moisture coming off of industrial
dryers by noting that the dilution effect water vapor has on the normal 20.95% ambient
drying air (non-combusion drying processes only).
•
Enriched oxygen concentration
- pure oxygen is sometimes mixed in with the
combustion air to increase heat at the flame. This is used in steel and other metals
reduction processes and in some catalyst regenerators.
Configure
Reference Manual
October 2022
00809-0100-4889
32
Rosemount Xi