Note: Descriptions are shown in the official language in which they were submitted.
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INTELLIGENT SOOTBLOWER
BACKGROUND
The entrainment of fly ash particles from the lower furnace of an industrial
boiler to the convection sections of the boiler is an inevitable process. The
accumulation of these particles in the fireside heat exchanger surfaces
reduces the
boiler thermal efficiency, creates a potentially corrosive environment at the
boiler tube
surfaces and, if the accumulation is not properly controlled, may also lead to
costly
unscheduled boiler shutdowns due to plugging of the gas passages.
Knowledge of the flue gas temperatures across the boiler heat transfer
surfaces is therefore an important piece of information that can be used to
evaluate
fireside deposit characteristics, to improve boiler cleaning operation through
intelligent deposit removal processes, and to optimize boiler operation and
combustion processes. Conventional temperature sensors positioned in fixed
locations on boiler walls or other internal boiler structures do not monitor
flue gas
temperatures across the boiler heat transfer surfaces. There is, therefore, a
continuing need for effective ways of monitoring the internal temperature of
flue
gasses across heat transfer surfaces inside of industrial boilers.
Sootblowers are by far the most widely used equipment to remove the fireside
deposit accumulations in industrial boilers, such as oil-fired, coal-fired,
trash-fired,
waste incinerator, as well as boilers used in paper manufacturing, oil
refining, steel,
and aluminum smelting and other industrial enterprises. A sootblower consists
of a
lance tube with one or more nozzles. During the deposit removal process, the
sootblower lance rotates and extends through a small opening in the boiler
wall, while
blowing high pressure cleaning fluid (e.g., steam, air or water) directed into
the tube
banks. After the lance is fully extended, it rotates in the opposite direction
as it
retracts to its original inactive state.
The sootblower carriage consists of one or two electric motor(s), a gearbox
and a packing housing. The electric motor is the main drive that moves the
lance
tube forward and backward during the cleaning cycle. The motor converts
electrical
energy into rotation motion, which is then used by the gearbox to rotate and
move the
lance tube along the gear rack. As the steam enters a sootblower, it is
directed to
four components in the following order: poppet valve, feed tube, lance tube,
and
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nozzles. The lance tube is the main component that travels within the boiler
while
supplying the sootblower nozzles with high pressure steam directed by jets
toward
the boiler tubes. The lance travel includes insertion into and retraction from
the
boiler. During the cleaning process, the lance extends into the boiler and
forms a
structure similar to a cantilevered beam. Hence, the lance has to be designed
to
have sufficient strength to support its own weight in a high temperature
environment.
To avoid overheating the lance tube during internal boiler operation, the
blowing fluid, which also acts as a cooling medium, needs to be supplied
continuously
to the lance. The minimum amount of the cleaning media required to prevent the
lance from overheating is known as the minimum cooling flow. The minimum
cooling
flow of a lance tube depends on the material, the length of the lance tube,
the steam
and flue gas temperatures. Knowledge of the lance tube temperatures as the
lance is
being exposed to hot flue gas inside the boiler is very important to prevent
lance tube
overheating and to devise emergency sootblower retraction control strategy. A
continuing need therefore exists for effective ways for monitoring the
temperature of
the lance tube as the lance is exposed to hot flue gas inside the boiler.
SUMMARY OF THE INVENTION
The present invention meets the needs described above in an intelligent
sootblower method and system for cleaning a heat transfer surface in a boiler.
The
intelligent sootblower includes an elongated lance tube configured to travel
within the
boiler while directing a cleaning fluid through one or more nozzles toward the
heat
transfer surface to remove fireside deposits from the heat transfer surface. A
temperature sensor carried by the lance tube within the boiler obtains
temperature
measurements of flue gas within the boiler while the lance tube is located
within the
boiler. A boiler cleaning controller activates the sootblower to measure a
temperature
adjacent to the heat transfer surface, identifies a region of the heat
transfer surface
as a region that requires cleaning based at least in part on the measured
temperature, and activated the sootblower to clean the region in response to
the
identification of the region that requires cleaning.
A data transfer device, such as a slip ring, may be used to transmit data from
the temperature sensor to a non-rotating device. The non-rotating device may
include the boiler cleaning controller or a data acquisition unit in
communication with
the boiler cleaning controller.
2
= The boiler cleaning controller may activate the lance tube to travel
adjacent to
the heat transfer surface during a first pass to cause the temperature sensor
to create
a temperature profile for the heat transfer surface. It then activate the
lance tube to
travel adjacent to the heat transfer surface during a second pass to cause the
sootblower to clean the region identified as requiring cleaning. The boiler
cleaning
controller typically causes the sootblower to emit a minimum cleaning flow
sufficient
to prevent the lance tube from overheating during the first pass. The system
may
also include a lance tube temperature sensor carried by the lance tube. In
this case,
then the boiler cleaning controller causes the sootblower to increment the
minimum
cleaning flow during the first pass in response to a temperature of the lance
tube
measured by the lance tube temperature sensor.
The boiler cleaning controller typically identifies the region requiring
cleaning
by comparing the temperature profile for the heat transfer surface to a clean
surface
threshold temperature based on a temperature profile for the heat transfer
surface in
a clean condition. The boiler cleaning controller may also identifies the
region
requiring cleaning by comparing the temperature profile for the heat transfer
surface
to a dirty surface threshold temperature based on a temperature profile for
the heat
transfer surface in a dirty condition.
In addition, the boiler cleaning controller may identify the region requiring
cleaning by determining that the region is hotter than a clean surface
threshold
temperature based on a temperature profile for the heat transfer surface in a
clean
condition. If the temperature sensor is located downstream in a flue gas path
from
the heat transfer surface; the boiler cleaning controller may identify the
region
requiring cleaning by determining that the region is cooler than a clean
surface
threshold temperature based on a temperature profile for the heat transfer
surface in
a clean condition.
The sootblower may also be a first sootblower adjacent to a first side of the
heat transfer surface and the system may include a second sootblower adjacent
to a
second side of the heat transfer surface. In this case, the boiler cleaning
controller
may identify the region requiring cleaning by determining a differential
temperature
between temperatures measured by the first and second sootblowers.
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An aspect of the invention provides for a method for cleaning a heat transfer
surface in a boiler, including the steps of providing a temperature sensing
sootblower
comprising an elongated lance tube configured to travel within the boiler
while directing a
cleaning fluid through one or more nozzles toward the heat transfer surface to
remove
fireside deposits from the heat transfer surface; providing a temperature
sensor carried by
the lance tube within the boiler configured to obtain temperature measurements
of flue
gas within the boiler while the lance tube is located within the boiler;
activating the
sootblower to measure a temperature adjacent to the heat transfer surface
during a first
pass to cause the temperature sensor to create a temperature profile for the
heat transfer
surface; activating the sootblower to emit a minimum cleaning flow sufficient
to prevent
the lance tube from overheating during the first pass; incrementing the
minimum cleaning
flow during the first pass in response to a temperature of the lance tube
measured by a
lance tube temperature sensor carried by the lance tube; identifying a region
of the heat
transfer surface as a region that requires cleaning based at least in part on
the measured
temperature; and activating the lance tube of the sootblower to clean the
region adjacent
to the heat transfer surface during a second pass in response to the
identification of the
region that requires cleaning.
In view of the foregoing, it will be appreciated that the present invention
avoids
the drawbacks of prior boiler temperature measuring systems and provides an
improved temperature sensing sootblower. The specific techniques and
structures for
creating the temperature sensing sootblowers, and thereby accomplishing the
advantages described above, will become apparent from the following detailed
description of the embodiments and the appended drawings and claims.
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BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a schematic illustration of a temperature sensing sootblower.
FIG. 2 is a conceptual illustration of the temperature sensing sootblower
measuring the temperature of flue gas across a heat transfer surface in a
boiler.
FIG. 3 is a side view of a temperature sensing sootblower showing the location
of the slip ring data transfer device.
FIG. 4 is a perspective view of a temperature sensing sootblower lance.
FIG. 5 is an enlarged view of Detail A of FIG. 7 showing the end of the
temperature sensing sootblower lance.
FIG. 6 is an end view of the temperature sensing sootblower lance.
FIG. 7 is an enlarged view of Detail B of FIG. 6 showing the thermocouple
temperature sensor, protective welding wire, and overlay weld.
FIG. 8 is a further enlargement of the groove in the temperature sensing
sootblower carrying the thermocouple temperature sensor, protective welding
wire,
and overlay weld.
FIG. 9 is a cut away view of the end of the temperature sensing lance tube
showing the boiler gas monitoring location and the end of the unmodified lance
tube.
FIG. 10 is a conceptual cross sectional side view of a sootblower lance
carrying a temperature sensor for measuring the temperature of the cleaning
fluid
inside the lance.
FIG. 11 is a conceptual illustration of a sootblower lance measuring a
temperature profile inside a boiler.
FIG. 12 is a graph illustrating a sootblower cleaning approach comparing a
measured temperature profile to an optimal temperature threshold.
FIG. 13 is a conceptual illustration of a sootblower with a gas temperature
sensor detecting an area of lower than optimal temperature indicating a dirty
heat
exchanger area that needs cleaning.
FIG. 14 is a conceptual illustration of a sootblower with a gas temperature
sensor detecting an area of higher than optimal temperature indicating a dirty
heat
exchanger area that needs cleaning.
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FIG. 15 is a graph illustrating a sootblower cleaning approach comparing a
temperature profile measured upstream from a heat exchanger surface with a
temperature profile measured downstream from a heat exchanger surface.
FIG. 16 is a logic flow diagram illustrating a routine for activating a boiler
cleaning operation in response to flue gas temperatures measured with the
temperature sensing sootblower.
FIG. 17 is a logic flow diagram illustrating a routine for retracting the
lance to
protect the lance from overheating.
FIG. 18 is a logic flow diagram illustrating a routine for using a sootblower
lance with a gas temperature sensor to identify heat exchange surfaces to
clean.
FIG. 19 is a logic flow diagram illustrating a routine for cleaning dirty heat
exchanger surfaces.
FIG. 20 is a logic flow diagram illustrating a routine for verifying whether a
heat
exchanger surfaces is clean.
DETAILED DESCRIPTION OF THE PREFERED EMBODIMENTS
This invention can be embodied in a temperature sensing sootblower that may
be configured as a modification to an existing sootblower or a specially
constructed
sootblower that, in addition to its normal soot blowing functions, has the
capability to
measure the flue gas, lance tube, and/or cleaning fluid temperatures. One or
more
thermocouples or other temperature measuring devices are carried by the
sootblower
lance tube that travels within the boiler. This allows for the temperature of
the flue
gas, lance tube, and/or cleaning fluid to be measured as the sootblower lance
tube is
inserted into and retracted from the boiler. Multiple temperature measuring
devices
may be located on the sootblower lance to measure the temperature across heat
transfer surfaces and at different locations along the lance tube. A data
transfer
device transmits the temperature measurements from the rotating thermocouple
to a
non-rotating data acquisition unit for use in boiler cleaning and other
operations.
A data transfer device, such as a slip ring, is used to transfer the signal
from
the thermocouple to a data acquisition unit located on the non-rotating part
of the
sootblower. The invention may also be used in sootblowers that are partially
inserted
in the boiler (sometimes called half-track sootblowers). It may also be used
in
sootblowers that are continually inserted into the boiler gas path. The
temperature
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sensor may be a thermocouple, a Resistance Temperature Detector (RID), or
other
suitable type of sensing device that is attached to the lance tube of the
sootblower.
FIG. 1 is a schematic illustration of the temperature sensing sootblower 10
including the lance tube 12 extending from a flange 16 that supports one end
of the
lance tube to the nozzles 14, which oppose each other to balance the force
imposed
on the lance by the fluid jets emitted from the nozzles. The lance tube is
inserted
through a hole in the boiler wall into interior of the boiler, where it is
extended and
retracted to clean heat transfer surfaces inside the boiler. The nozzles can
be
installed anywhere in the lance tube where one or more cleaning fluids, such
as
steam, air or water, are supplied to the nozzles to clean the fireside
deposits from
internal boiler heat transfer surfaces. The lance tube rotates as it travels
in the
insertion direction (from flange toward the tip of the lance), blowing a
spiral of
cleaning fluid as is travels across an adjacent heat transfer surface. The
lance tube
rotates in the opposite direction (from the tip of the lance toward flange) as
it travels
in the retraction direction.
To measure the temperature of the flue gas and the lance tube inside the
boiler, the temperature sensing sootblower 10 carries temperature sensors, in
this
illustration a multi strand thermocouple 20 that extends longitudinally along
the lance
tube. The thermocouple is connected to a data transfer device, in this
illustration a
slip ring 22 that transfers the temperature measurements from the thermocouple
to a
data acquisition unit 24 while the thermocouple rotates with the lance tube.
The data
acquisition unit 24, in turn, transmits the temperature measurements to a
boiler
cleaning controller 25 or other processor that may use the measurements for a
variety
of purposes, such as displaying the temperature profile across heat transfer
surfaces
inside the boiler, activating sootblowers and other boiler cleaning equipment,
adjusting boiler operation, retracting the lance tube to prevent overheating,
and so
forth. As the data acquisition unit 24 includes a processor, it may create
temperature
and perform some of these functions.
The thermocouple 20 is typically a stranded wire containing a number of two-
wire thermocouples allowing for multiple temperature sensing locations 26
along the
lance tube. For example, the thermocouple may include six wires providing
three
Type K thermocouples. This provides knowledge of the lance tube temperature so
that the lance tube can be retracted to prevent overheating. The temperature
along
the lance tube may be monitored at multiple locations, as desired.
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The thermocouple may also include a boiler gas monitoring location 30
positioned beyond the tip of the lance in the lance insertion direction. To
obtain the
temperature of the boiler flue gas rather than the lance tube, a lance tube
extension
28 supports the thermocouple beyond the tip of the lance in the lance
insertion
direction. The thermocouple also extends a bit beyond the lance tube extension
28
so that the temperature monitoring location 30 is supported in the flue gas
without
physically touching the lance tube extension. For example, the lance tube
extension
28 may extend four to six inches beyond the tip of the lance and the
thermocouple 20
may extend another half inch to the boiler gas monitoring location 30. The
lance tube
extension 28 may also include one or more vents 34 to for cooling purposes.
The
lance tube extension is typically made from the same type of material as the
lance
tube and welded onto the tip of the lance.
FIG. 2 is a conceptual illustration of the temperature sensing sootblower 10
measuring the temperature of flue gas across a heat transfer surface 32 in a
boiler.
The boiler gas temperature monitoring location 30 of the thermocouple 20
measures
the temperature of the flue gas as the sootblower lance 12 travels adjacent to
and
across the heat transfer surface 32. The data acquisition unit 24 (Fig. 1) the
boiler
cleaning controller 25 (Fig. 1) or another processor creates a profile of the
internal
temperature of the boiler across the heat transfer surface. The temperature
profile
generally indicates whether the heat transfer surface is carrying fireside
deposits
reducing the heat transfer capability of the heat transfer surface, allowing
for
intelligent boiler operation including intelligent sootblower operation.
The
temperature monitoring location(s) 26 also measure the temperature of the
lance tube
allowing the lance tube to be retracted to prevent overheating.
In general, the measured temperature above the clean surface reference
temperature (optimal) or below the clean surface reference temperature
(optimal) may
indicate a dirty area on the heat exchanger needing cleaning. In particular, a
measured temperature above the clean surface reference temperature indicates a
dirty area on the heat exchanger needing cleaning. On the other hand, a
measured
temperature below the clean surface reference temperature may indicate a clean
heat
exchanger surface when the lance is upstream from the heat exchanger surface,
or it
may indicate a dirty area on the heat exchanger needing cleaning when the
lance is
downstream from the heat exchanger surface. The boiler cleaning algorithm
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described with reference to FIGS. 16-20 implements boiler cleaning in view of
this
situation.
FIGS. 3-7 show an illustrative embodiment of the temperature sensing
sootblower substantially to scale. FIG. 3 is a side view of the temperature
sensing
sootblower 10 indicating the location of the slip ring data transfer device 22
and the
flange 16. The slip ring is typically mounted to a non-rotating plate
positioned about
six inches ahead of the flange 16 to prevent damage to the slip ring in the
event of a
steam leak from the flange. The slip ring includes a ball bearing or similar
race with
an inner sleeve that rotates with the lance tube and a non-rotating outer
sleeve fixed
to the plate. wires connected to the inner sleeve are connected to the
thermocouple
while wires connected to the outer sleeve are connected to the data
acquisition unit.
This allows the slip ring to transmit the temperature measurements from the
rotating
thermocouple to the non-rotating data transfer unit. Another type of data
transfer
device may be used, however, such as a wireless data link between the
thermocouple
and the data acquisition unit or any other suitable type of data transfer
device.
FIG. 4 is a perspective view of the tip of the lance portion of the
temperature
sensing sootblower lance 12 with the groove 40. FIG. 5 is an enlarged view of
Detail
A of FIG. 4 showing the end of the temperature sensing sootblower lance
including
the lance tube extension 28. FIG 6 is an end view of the temperature sensing
sootblower lance 12 and FIG. 8 is an enlarged view of a Detail B of FIG. 7
showing
the groove 40. FIG. 8 is a further enlargement of the groove 40 carrying the
thermocouple 20, the protective welding wire 42, and the overlay weld 44. The
groove, which extends from the slip ring to the end of the lance tube
extension, may
be machined or cut into the lance tube with saw. The thermocouple 20 is
positioned
at the bottom of the groove 40 with the protective welding wire 42 positioned
above
the thermocouple. An overlay weld 44 is welded over the grove to seal the
thermocouple in the groove. The protective welding wire prevents the
thermocouple
from being damaged during the welding process. The groove 44 is cut
approximately
the same size as the protective welding wire to provide a snug interference
fit
between the groove and the welding wire. The thermocouple may be the same size
or a smaller than the welding wire.
FIG. 9 is an enlarged cut-away view of the end of the temperature sensing
sootblower lance tube 12 showing the boiler gas temperature monitoring
location 30
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at the end of the thermocouple extending beyond the end of the lance tube
extension
28. FIG. 9 also shows the rounded end 60 of the unmodified lance tube.
FIG. 10 is a conceptual cross sectional side view of a wall 11 of the
sootblower
lance 12 carrying a multi-strand thermocouple 20 within a grove 40, as
described
previously. In this example, the sootblower include a hole 41 extending from
the
grove through the wall 11. This allows a thermocouple to extend through the
lance
wall into the interior of the lance tube where it measures the temperature of
the
cleaning fluid inside the lance. It
will be appreciated that any number of
thermocouples can be deployed to measure the temperature of the lance tube,
the
gas outside the lance tube, and/or the cleaning fluid inside the lance tube at
any
desired locations along the lance tube. Thermocouples may also be used to
measure
the temperature of the lance tube on the inner surface, the outer surface, or
at any
desired depth within the lance tube wall.
FIG. 11 is a conceptual illustration of a temperature sensing sootblower lance
12 measuring a temperature profile 100 as it moves across a heat exchanger
surface
32. The sootblower lance 12 maintains a minimum cooling flow of fluid through
the
lance at it travels past the heat exchanger surface 32. The objective is to
measure
the temperature profile 100 for comparison to a clean surface reference
profile
(optimal) for the surface to identify dirty areas on the surface that need
cleaning. The
measured temperature profile 100 may also be compared to a reference profile
for
the heat exchanger surface in a typical dirty condition to further help
identify dirty
areas on the surface that need cleaning. The identified dirty areas are
typically
cleaned in a subsequent pass so that the emission of a high flow of cleaning
fluid
does not interfere with the temperature measurement.
FIG. 12 is a graph illustrating a measured temperature profile 100 that is
lower
than the optimal temperature profile 102 in regions A and C and higher than
the
optimal temperature profile in region B. Dirty areas of the heat exchanger are
identified by the comparison of the graph 100 and 102 taking into account
whether
the temperature measuring sootblower lance is upstream or downstream in the
boiler
gas path from the heat exchanger surface. A heat exchanger region with higher
than
optimal measured temperature, such as the region B in FIG. 12, is a fouled
heat
exchanger area that needs cleaning. In particular, if the lance is upstream
from the
heat exchanger surface, the fireside deposit 104 on the heat exchanger 32
blocks the
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flow of flue gas causing increased heating of the heating the lance upstream
from the
region of the deposit.
A heat exchanger region with a lower-than-optimal measured temperature
represents an uncertain situation. If the lance is downstream from the heat
exchanger surface, the regions A and C where the measured temperature profile
100
is below the optimal temperature profile 102 indicate the presence of a dirty
heat
exchanger surface. This situation is illustrated in FIG. 13, where the
fireside deposit
104 on the heat exchanger 32 effectively blocks the flue gasses from heating
the
lance 12 in the region of the deposit. On the other hand, if the lance is
upstream from
the heat exchanger surface, the regions A and C where the measured temperature
profile 100 is below the optimal temperature profile 102 indicate the presence
of a
clean heat exchanger surface.
As a result, a measured temperature above the target temperature indicates a
heat exchanger region that needs to be cleaned, whereas a measured temperature
below the target temperature is ambiguous in that it may indicate a clean heat
exchanger region if the lance is upstream from the heat exchanger surface or
it may
indicate a dirty heat exchanger surface if the lance is downstream from heat
exchanger surface. To resolve any ambiguity, FIG. 14 illustrates the use of
two
temperature sensing sootblowers 12A and 128, with sootblower 12A located
downstream from the heat exchanger 32 and sootblower 128 located upstream from
the heat exchanger. Fireside deposits can be accurately located with a
combination
of sootblowers taking temperature profiles in this configuration, which also
allows
both sides of the heat exchanger surface to be cleaned. FIG. 15 is a graph
illustrating a sootblower cleaning approach comparing a temperature profile
106
measured upstream from a heat exchanger surface with a temperature profile
measured 100 downstream from a heat exchanger surface. The differential
temperature 108 can then be compared to a differential temperature threshold
to
identify dirty heat exchanger areas requiring cleaning. A measured
differential
temperature more than a threshold amount above the expected differential
temperature for the heat exchanger surface for the given heat input condition
indicates a dirty heat exchanger surface that needs cleaning.
FIG. 16 is a logic flow diagram illustrating a routine 1600 for activating a
boiler
cleaning operation in response to flue gas temperatures measured with the
temperature sensing sootblower. In step 1610, a reference temperature for a
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heat transfer surface is obtained, typically by measuring the temperature of
the heat
transfer surface when it is known to be in a clean state or through computer
simulation. Step 1610 is followed by step 1612, in which a reference
temperature for
a heat transfer surface carrying accumulated slag (fireside deposit) is
obtained, again
by measuring the temperature of the heat transfer surface when it is known to
be in
an impacted state or through computer simulation. Step 1612 is followed by
step
1614, in which the boiler cleaning controller is programmed with a cleaning
threshold
temperature based on the clean and dirty reference temperatures. For example,
the
cleaning threshold temperature may be set to be half way between the clean and
impacted reference temperatures. Step 1614 is followed by step 1616, in which
the
boiler cleaning controller activates the temperature sensing sootblower to
measure
the boiler temperature while maintaining a minimum cleaning fluid flow
necessary to
avoid overheating of the lance. Routine 1700 shown in FIG. 17 is a methodology
for
controlling the minimum flow rate to prevent overheating of the lance while
the
temperature profile is measured. Step 1616 is followed by step 1618, in which
the
boiler cleaning controller determines whether the measured temperature is
above the
cleaning threshold temperature. If the measured temperature is above the
cleaning
threshold temperature, the "YES" branch is followed to step 1620, in which the
sootblower is activated to clean the detected impacted surface. If the
measured
temperature is not above the cleaning threshold temperature, the "NO" branch
is
followed to step 1622, in which the sootblower cleaning controller waits for
another
scheduled test. Step 1620 is also followed by step 1622, which loops to step
1616, in
which the boiler temperature is measured with the temperature sensing
sootblower.
FIG. 17 is a logic flow diagram illustrating a routine 1700 for protecting the
temperature sensing sootblower to avoid potential overheating, which may be
applied
while the lance is obtaining a temperature profile while emitting a minimum
cooling
flow (see FIG 16, step 1616). In step 1710, the boiler cleaning controller
is
programmed with a threshold temperature for protecting the lance tube to avoid
overheating of the lance tube, which is typically based on the material
specifications
for the lance tube and experience. For example, the threshold temperature may
be
set to 1,200 F. Step 1710 is followed by step 1712, in which temperature
sensing
sootblower is located within the boiler, typically for cleaning or temperature
sensing
operations while maintaining a minimum cleaning fluid flow necessary to avoid
overheating of the lance. Step 1712 is followed by step 1714, in which the
boiler
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cleaning controller determines whether the measured temperature of the lance
tube is
above the threshold temperature indicating potential overheating of the lance
tube. If
the measured temperature is above the threshold temperature, the "YES" branch
is
followed to step 1716, in which boiler cleaning controller determines whether
the
cleaning fluid flow through the sootblower is set to its maximum level. If the
measured temperature is not set to its maximum level, the "NO" branch is
followed to
step 1718, in which the boiler cleaning controller increases the cleaning
fluid flow
through the sootblower by an incremental amount, such as 10% of the maximum
cleaning fluid flow through the sootblower. If the measured temperature is set
to its
maximum level, the "YES" branch is followed to step 1720, in which the boiler
cleaning controller retracts the sootblower lance to prevent overheating.
Returning to
step 1714, if the measured temperature is not above the threshold temperature,
the
"NO" branch is followed to step 1722, in which the boiler cleaning controller
waits for
the next scheduled test. Step 1718 is also followed by step 1720, which loops
back
to step 1712, in which the temperature of the lance is measured.
FIG. 18 is a logic flow diagram illustrating a routine 1800 for using a
sootblower lance with a gas temperature sensor to identify heat exchange
surfaces to
clean. In step 1810, the sootblower control system obtain the target of the
gas
temperature profile for a given heat input condition. This typically involves
cleaning
any dirty heat exchangers as much as possible or cleaning just enough to
achieve
desired heat transfer efficiency. This is because it may not be cost effective
to
always attempt to clean dirty heat exchangers as much as possible, but in some
cases cleaning just enough to obtain desired heat transfer efficiency may be
the most
effective cleaning approach. It should be noted that the target gas
temperature
profile depends on the given heat input condition and must be carefully
selected to be
appropriate for the heat input condition existing in the boiler at the time of
cleaning.
That is, the desired target gas temperature profile will vary depending on the
heat
input condition existing at the time of cleaning. To accommodate different
heat input
conditions, the sootblower control system may store a number of target gas
temperature profiles for a particular heat exchanger surface for different
heat input
conditions. The sootblower control system may also generate target gas
temperature
profiles on the fly by interpolating between stored profiles or by using
boiler
simulation software.
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Step 1810 is followed by step 1812, in which the sootblower lance is inserted
and retracted to obtain a temperature profile for the heat exchanger surface
to be
cleaned. The measuring step is implemented with a minimum flow rate through
the
lance to minimize the effect of the emitted fluid on the temperature
measurement
while still preventing the lance from overheating. Routine 1700 shown in FIG.
17 is a
methodology for controlling the minimum flow rate to prevent overheating of
the lance
while the temperature profile is measured. Step 1812 is followed by step 1814,
in
which the sootblower control system identifies and records areas where the
measured gas temperature profile is below the target temperature profile.
These
areas correspond to the regions A and C in FIG 12. Step 1814 is followed by
step
1816, in which the sootblower control system identifies and records areas
where the
measured gas temperature profile is above the target temperature profile.
These
areas correspond to the region B FIG 12.
In general, the region B requires cleaning whereas the regions A and C require
cleaning when the sootblower lance is downstream from the heat exchanger
surface
to be cleaned but not when the sootblower lance is upstream from the heat
exchanger
surface to be cleaned. This is explained in greater detail with reference to
FIG. 19,
which is a logic flow diagram illustrating a routine 1900 for cleaning dirty
heat
exchanger surfaces. Step 1816 from FIG. 18 is followed by step 1910, in which
the
sootblower control system determine whether the measured temperature profile
at a
particular location is above the target temperature profile. If the
measured
temperature profile at a particular location is above the target temperature
profile, the
"YES" branch is followed from step 1910 to step 1912, in which that area is
flagged
as an area that needs to be cleaned. Step 1912 is followed by step 1914, in
which
the sootblower control system implements cleaning for the flagged region of
the heat
exchanger surface. Step 1914 is followed by step 1916, in which the sootblower
control system determines whether the heat input to the heat exchanger has
changed. If the heat input to the heat exchanger has changed, the "YES" branch
is
followed from step 1916 to step 1810 on FIG. 18 to begin a retest for the new
heat
input level. If the heat input to the heat exchanger has not changed, the "NO"
branch
is followed from step 1916 to step 1924, in which the system waits for the
next
scheduled test and then returns to step 1812 on FIG. 18 to begin the next
scheduled
test.
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Returning to step 1910, if the measured temperature profile at a particular
location is below the target temperature profile, the "NO" branch is followed
from step
1910 to step 1918, in which that area is flagged as an area that needs further
clarification. Step 1918 is followed by step 1920, which is a clean condition
routine
2000 shown on FIG. 20. Step 1920 is followed by step 1922, in which the
sootblower
control system determines whether the heat exchanger surface is considered
clean
by routine 2000. If the heat exchanger surface is considered clean, the "YES"
branch
is followed from step 1922 to step 1916, in which the sootblower control
system
determines whether the heat input has changed. If the heat exchanger surface
is not
considered clean, the "NO" branch is followed from step 1922 to step 1912, in
which
the heat exchanger surface is flagged for cleaning.
FIG. 20 is a logic flow diagram illustrating routine 2000 for verifying
whether a
heat exchanger surface is clean. In step 2010, the sootblower control system
determines whether an upstream temperature measurement is available. If an
upstream temperature measurement is available, the "YES" branch is followed
from
step 2010 to step 2012, in which the sootblower control system obtains the
maximum
differential temperature (upstream temperature versus downstream temperature)
for
the heat exchanger surface in a clean condition (e.g., a threshold amount
above the
expected differential temperature for the heat exchanger surface in a clean
condition,
or a threshold amount above the expected differential temperature for a
sufficiently
clean the heat exchanger surface). Step 2012 is followed by step 2014, in
which the
sootblower control system calculates the measured differential temperature
(upstream temperature versus downstream temperature) for the heat exchanger
surface. Step 2014 is followed by step 2014, in which the sootblower control
system
determines the difference between the target and measured differential
temperatures.
If the measured differential temperature is below the target differential
temperatures,
the "NO" branch is followed from step 2016 to step 2018, in which the heat
exchanger
areas is flagged as clean. Step 2018 is followed by step 1922 on FIG. 19 with
the
heat exchanger region flagged as clean. If the measured differential
temperature is
above the target differential temperatures, the "YES" branch is followed from
step
2016 to step 2020, in which the heat exchanger areas is flagged as heavily
fouled
and in need of cleaning. Step 2020 is followed by step 1912 on FIG. 19 with
the heat
exchanger region flagged as dirty.
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Returning to step 2010, if an upstream temperature measurement is not
available, the "NO" branch is followed from step 2010 to step 2022, in which
the
sootblower control system obtains a dead zone set point. Step 2022 is followed
by
step 2024, in which the sootblower control system determines whether the
measured
temperature is below the dead zone set point temperature. The dead zone set
point
represents a threshold level below the expected temperature downstream from
the
heat exchanger surface to be cleaned. A measured temperature below the dead
zone set point indicated a fireside deposit on the heat exchanger surface
upstream
from the temperature sensor as shown in FIG. 13. If the measured temperature
is
below the dead zone set point temperature, the "YES" branch is followed form
step
2024 to step 2020, in which the heat exchanger areas is flagged as heavily
fouled
and in need of cleaning. Step 2020 is followed by step 1912 on FIG. 19 with
the heat
exchanger region flagged as dirty. If the measured temperature is above the
dead
zone set point temperature, the "NO" branch is followed form step 2024 to step
2018,
in which the heat exchanger areas is flagged as heavily fouled and in need of
cleaning. Step 2018 is followed by step 1922 on FIG. 19 with the heat
exchanger
region flagged as clean.
In view of the foregoing, it will be appreciated that present invention
provides
significant improvements in sootblowers and boiler temperature monitoring
systems
and that numerous changes may be made therein without departing from the
spirit
and scope of the invention as defined by the following claims.
