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Track and Control Thermal Fatigue Impact
with ASI's Thermal Impact ModulE™ (TIME)
Water has been demonstrated to
be an effective and even necessary cleaning media for boilers
burning lignite and sub-bituminous coal. The use of water
for cleaning of boiler heat transfer surfaces has also resulted
in thermal fatigue damage, sometimes necessitating furnace
wall tube replacement, when water cleaning has been mis-applied
or used in excess.
For proper application of water
cleaning devices, there are two key control elements. First,
the heat transfer surfaces being cleaned should be dirty,
and second, the water cleaning device operating parameters
should produce an acceptable level of thermal fatigue to
the furnace wall tubing.
Two modules have been developed,
which integrate directly with our sootblower controls and
Boiler Cleaning Management Systems (BCMS) to address the
cleanliness status and the thermal fatigue impact. The modules
are the Furnace Cleanliness Module™ (FCM) and the Thermal
Impact ModulE™ (TIME). The features and benefits of
the TIME module are described in this update.
TIME Module
Functional Description
The TIME module, as defined in
adaptive sootblowing-cleaning patent , provides real time
monitoring and assessment of each water cleaning cycle at
each cleaning location. TIME also monitors areas where cleaning
should not occur to prevent inadvertent water washing and
associated tube damage.
Based on the EPRI report CS-4914
and subsequent field studies, the expected or reasonable
magnitude of thermal fatigue impact and thereby the expected
tube life is defined during setup of the TIME software
During operation, the TIME module
captures the tube metal temperature transient, using installed
heat flux sensors (same sensors used by the FCM to determine
cleanliness), resulting from each water cleaning cycle and
assesses the thermal fatigue impact. Locations experiencing
higher than desired impact are immediately identified so
that adjustments to the cleaning system can be made before
any significant furnace wall tube damage is experienced.
Furthermore, to detect inadvertent
cleaning of areas that are not to be cleaned on a routine
basis, membrane mounted thermocouples are installed. TIME
monitors these locations and provides immediate alarms if
water wetting and thermal cycles are detected.
TIME Module
Outputs and User Information
The specific information stored and
outputs available from the TIME module are:
- Metal Temperature Change - One
of the four thermocouples in the existing heat flux sensors
is used to determine the metal temperature transient during
the water cleaning cycle. The metal temperature change is
stored for each cleaning cycle.
- Metal Temperature Transient
The temperature transient for each cleaning event is recorded
and stored with a time resolution of 200 milliseconds. The
temperature transient for any zone can be recalled for review
and analyses.
- Assessment of Thermal Cycle Impact
Following each cleaning cycle, the severity of the thermal
cycle is assessed. Each cycle is categorized as low, moderate,
or high impact. Cycles with high thermal impact will result
in an alarm on the operator interface. The assessment of
each cleaning cycle is stored.
- Number of Thermal Cycles For
each furnace zone the number of thermal cycles is stored.
- Cumulative Thermal Fatigue Impact
The metal temperature changes, the assessment of the cleaning
cycle impact, and the number of cleaning cycles are used
with a structural model to determine and compile the cumulative
thermal fatigue impact. For each cleaning zone, the cumulative
thermal fatigue impact is expressed as through wall crack
growth and/or estimated useful tube life remaining. The
cumulative thermal fatigue impact is stored for each zone.
click to enlarge
Operator Interface and Tools
TIME integrates directly with existing
ASI sootblower controls and Boiler Cleaning Management Systems.
No additional monitors or computers are required.
When a thermal fatigue transient
is detected, the TIME module indicates whether the cycle
resulted in a low, moderate, or high impact event. The figure
above is available to obtain information of the most recent
cycle, any previous cycle, and the thermal cumulative impact.
To determine if the target for tubing years of service and
through wall crack is being met on daily basis, the summary
graph button provides the figure below.
click to enlarge
Network Ready
TIME information is available to
operational, maintenance, and engineering personnel across
companies' networks and can be directly logged to historian
systems, such as PI.
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