Emerson Rosemount 6888A, Справочное руководство

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• Process upsets can be diagnosed by again profiling the duct stratification on-line by
sliding probe in and out and recording the O
2
levels at different insertion depths.
This provides a good diagnostic for balancing burners and tracking down upset
conditions caused by sticking burner sleeve dampers, roping in coal pipes, classifier
problems, etc.
• A probe can be slid to the most convenient location for a technician to access for the
purposes of conducing a calibration or diagnosing a probe problem.
The variable insertion mount consists of a slip-tube that is mounted to the furnace via a
flange or pipe thread. Slide the O
2
probe through this mounting and seal the probe outside
diameter to the slip-tube ID via valve packing material. A stop-collar is provided for safety
to ensure that a probe in a vertical installation does not creep through the packing
material due to gravity after installation. The stop collar has separate holes where screws
can be inserted to jack the probe out of the slip mount if debris builds up on the probe over
time. The packing material can be withdrawn with the probe in situations where the
buildup on the probe is heavy and cannot pass through the packing material.
Installation
An installation permitting variable insertion requires some special considerations:
• Removal envelope: There must be enough room for the probe to slide in and out.
• Utilities: Since the probe will be operating continually as its position is adjusted, the
electrical wires and pneumatic tubing must be able to travel with the probe.
• Duct pressure: Balanced draft and natural draft furnaces typically run at a slightly
negative pressure, so any small leaks in the packing material will draw air into the
furnace. When the probe is removed for service, a flow of fresh air into the furnace
also results. A positive pressure duct, however, releases hot flue gases when the
probe is removed.
• Be mindful that the slip-support holding the end of the probe inside the furnace will
likely be attached to the internal structure that may grow thermally more than the
furnace wall where the probe flange is mounted. A probe that is perfectly aligned
with the slip-support(s) during initial installation (with the furnace off) may be out of
alignment once the furnace heats up.
The variable insertion arrangement is set up for Rosemount 6888A probes with heavy-wall
abrasion-resistant probe bodies only. For probe lengths of 9 feet and longer, an outboard
slip support must be mounted inside the flue gas duct. The support structure may include
angle iron or tube bundles that will be at elevated temperatures during use. Plan for
thermal expansion when installing the outboard slip support.
WARNING!
GAS LEAKS
Some flue gas ducts operate under positive pressure. While the packing material will prevent
most flue gases from escaping into the ambient environment, some leakage can be expected.
Once the probe is fully extracted from the slip-tube, hot flue gases will freely exit the hole in
the slip tube until a replacement probe or core plug is inserted. Observe safety precautions
when removing or inserting a probe into a furnace operating at positive pressure.
Install
Reference Manual 25