U.S. patent application number 12/708895 was filed with the patent office on 2011-08-25 for method and system for sootblower flow analyzer.
This patent application is currently assigned to NRG Energy, Inc.. Invention is credited to Michael Clark Hymel.
Application Number | 20110203535 12/708895 |
Document ID | / |
Family ID | 44475406 |
Filed Date | 2011-08-25 |
United States Patent
Application |
20110203535 |
Kind Code |
A1 |
Hymel; Michael Clark |
August 25, 2011 |
Method and System for Sootblower Flow Analyzer
Abstract
The present invention relates to a method and a system for
optimizing steam or other cleaning medium used during soot removal
in a boiler in which energy is generated by fuel combustion, with
accompanying production of soot, and heat energy is transferred
from the product gases to a heated medium via heat exchanger tubes
on which the soot collects, by; monitoring the mass flow rate of
the cleaning medium, determining which set of sootblowers are in
operation, calculating appropriate high flow alarm set point and
low flow set point for each particular sootblower, notifying an
operator whether the sootblowers are operating within the setpoints
so that appropriate action can be taken to the set of sootblowers.
In addition, the invention performs leak detection by monitoring
for a system bottled up situation and notifies the operator when a
steam leak is detected.
Inventors: |
Hymel; Michael Clark;
(Batchelor Pointe Coupee, LA) |
Assignee: |
NRG Energy, Inc.
Princeton
NJ
|
Family ID: |
44475406 |
Appl. No.: |
12/708895 |
Filed: |
February 19, 2010 |
Current U.S.
Class: |
122/379 ;
122/390 |
Current CPC
Class: |
F28G 15/00 20130101;
F28G 1/166 20130101; F22B 37/56 20130101; F28G 15/003 20130101 |
Class at
Publication: |
122/379 ;
122/390 |
International
Class: |
F22B 37/56 20060101
F22B037/56; F28G 1/16 20060101 F28G001/16; F28G 15/00 20060101
F28G015/00 |
Claims
1. A method for increasing the efficiency of boiler operation by
improving the sootblower operation, comprising: determining which
sootblowers are in service; operating each sootblower to collect
flow data and adjust sootblower to within specification; monitoring
the cleaning medium flow through said sootblowers by utilizing a
mass flow measurement device and adjusting the said sootblowers to
within specifications; producing an indication of the sootblowers
in operation and the mass flow rate of the cleaning medium used in
the set of sootblowers; monitoring of the cleaning medium pressure
measuring device and controlling to within a particular pressure
change; entering collected data and calculating high and low flow
setpoints for a particular soot blower or set of sootblowers based
on a set of sootblowers operating and the cleaning requirements;
providing a means to notify a boiler operator of said mass flow
rate and whether said mass flow rate extends outside the range
defined by said high flow set point and said low flow set point
with notification of a high alarm and low alarm; monitoring said
mass flow rate of said cleaning medium during the cleaning of a
boiler; and adjusting said sootblowers to operate below said high
flow set point and above said low flow set point.
2. The method of claim 1, including; providing leak testing by
stopping all sootblowers; blocking in the physical drains in the
closed position; applying a slight pressure in the boiler; and
providing a means to notify a boiler operator when a leak of
cleaning medium is detected.
3. The method of claim 1, wherein the means to notify a boiler
operator of said mass flow rate and whether said mass flow rate
extends outside the range defined by said high flow set point and
said low flow set point includes a visual indication as well as an
audible alarm in a control room.
4. The method as defined in claim 2, wherein the means to notify a
boiler operator includes a visual indication as well as an audible
alarm if a leak is detected within the sootblower operation.
5. The method as defined in claim 3, wherein a distributive control
system is used in calculating said high flow set point and said low
flow set points and providing a means to notify a boiler operator
of said mass flow rate and whether said mass flow rate extends
outside the range defined by said low flow set point and said high
flow set point.
6. The method as defined in claim 3, further including the step of
a boiler operator manually making adjustments to said set of
sootblowers based on the mass flow rate extending outside the range
defined by the high flow set point and low flow set point.
7. The method as defined in claim 3, wherein the pressure change is
controlled to a small percentage of the system operating
pressure.
8. A system for increasing the efficiency of boiler operation by
improving the sootblower operation, comprising: a set of
sootblowers installed on a boiler to be utilized in cleaning a
boiler; a mass flow measuring device; a pressure measurement device
and a pressure regulating valve maintaining a certain system
pressure; a flow transmitter; a temperature measurement device and
a temperature transmitter; physical drain valves located near the
bottom of said boiler; a cleaning medium line providing cleaning
medium to said set of sootblowers and a manual isolation valve
upstream of said pressure measurement device and a pressure
regulating valve; said mass flow measuring device installed on said
cleaning medium line near the top of said boiler and upstream of
the boiler and downstream of the pressure measurement device; said
temperature measuring device installed upstream of said mass flow
measuring device and downstream of said pressure measurement device
such that the cleaning medium can be monitored; a means for
receiving the temperature and pressure readings of the cleaning
medium from said flow transmitter, said pressure differential and
said temperature transmitter and entered into a flow model to be
manipulated with software to calculate the mass flow rate; said
flow model to determine if a blower from a flow group is on and if
one or two blowers are on within that group of blowers and to
calculate a high flow set point and low flow set point and to
generate a high and low alarm based on the readings relative to the
set points from the pressure measurement device and mass flow
measuring device; and a display for communicating to a boiler
operator the mass flow rate, the high flow set point, the low flow
set point and a notification when said mass flow rate extends
beyond the range defined by the low flow set point and the high
flow set point.
9. A system according to claim 7, including: a capability to block
in the boiler by closing the physical drain valves and to apply a
slight pressure to test the boiler for leaks in the sootblower
system; and a leak detection alarm for when said sootblowers are
not in service and system is tested and identifies a leak.
10. A system according to claim 7, including: a mass flow measuring
device with a pressure based flow meter measuring a differential
pressure;
11. A system according to claim 8, wherein the cleaning medium used
is steam and the certain system pressure is maintained at 600 psig
+/-5 psig.
12. A computer program product, residing on a computer readable
medium, for use in improving the effectiveness of a sootblower
operation by monitoring the mass flow rate, the computer product
comprising instructions for causing a computer to: receive data
corresponding to the pressure, change in pressure and temperature
of the cleaning medium used in the sootblowers and the active
status of each sootblower; identify if a blower flowgroup is on and
if one or two sootblowers are on within that group of blowers;
calculate the mass flow rate of the cleaning medium based on the
change in pressure, temperature and pressure readings; calculate a
high flow set point and a low flow set point for the cleaning
medium flow; generate a high and low flow alarm when the mass flow
extends outside the range defined by the low flow set point and the
high flow setpoint; and generate outputs for the system displays to
be communicated so that an action can be taken regarding said set
of sootblowers.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to increasing the
efficiency of boiler operation and specifically to improving
sootblower operations by optimizing cleaning medium usage during
boiler cleaning. This invention will also detect system leaks or
clean medium flows above or below system specifications, this will
reduce the potential for boiler tube erosion.
DESCRIPTION OF THE RELATED ART
[0002] The combustion of coal and other fossil fuels during the
production of steam or electricity produces combustion deposits,
i.e., ash or soot, that builds up on the surfaces in the boiler.
When soot accumulates on the heat transfer tubes, the heat transfer
efficiency of the tubes decreases and thus the boiler efficiency is
reduced. These deposits are removed periodically by directing a
cleaning medium, e.g., air, steam, water or mixtures thereof,
against the surfaces upon which the deposits have accumulated at a
high pressure or high thermal gradient with cleaning devices known
generally in the art as sootblowers. Sootblowers may direct the
cleaning medium to a number of desired points in the boiler,
including the heat transfer tubes.
[0003] Coal-fired power plants use a set of sootblowers to rid
their boiler's internals of ash or soot. The typical system is
operated either once per set period of time or based on operator
experience to determine an as needed basis. At some plants,
sootblowing is done once per day or once per shift. Another common
operation of sootblower systems is "intelligent sootblowing" these
intelligent systems detect when an area of the boiler requires
cleaning and controls the sootblowers according.
[0004] Different types of soot blower designs are known including
those that are fixed, rotating and/or retractable. It is also known
to modify nozzles on sootblower lances to improve sootblowing
efficiency as well as adjusting direction of the cleaning medium
spray.
[0005] Sootblowers may be activated periodically to direct jets of
steam, air and/or water onto the surfaces where deposits form to
remove deposits. Large boilers have many sootblowers for cleaning
the boiler. It is known to equip sootblowers with control devices
to operate blowers individually or in groups on command by a boiler
operator and/or according to a predetermined pattern. Sootblowing
is often run according to a schedule either manually by an operator
or automatically. Sootblowing can also be run by intelligent
sootblower systems automatically based on measured boiler fouling.
U.S. Pat. No. 6,736,089 (Lefebvre) discloses using boiler
performance goals to determine cleanliness targets and/or operating
settings.
[0006] A common strategy for removing deposits from the convection
sections of a boiler is to increase the sootblowing pressure and
frequency. But in many cases, doing so makes the cleaning system
part of the problem rather than the solution, by increasing the
risk of tube erosion caused by the sootblowing operation. It is
important that the surfaces in the boiler not be cleaned
unnecessarily or excessively. Injection of a cleaning medium into
the boiler can prematurely damage heat transfer surfaces in the
boiler, especially if they are over cleaned. Boiler surface and
water wall damage resulting from sootblowing is particularly costly
because repair requires boiler shutdown, cessation of power
production and immediate attention that cannot wait for scheduled
plant outages. Conversely, undercleaning can have the effect of not
removing enough of the soot buildup and thus decreasing the
efficiency of the boiler operation as measured by net heat
rate.
[0007] U.S. Pat. No. 6,736,089 (Lefebvre et. al.) discloses use of
sensors within the boiler to determine cleanliness levels and to
monitor the effectiveness of soot blowing operations as well as
determination of the sootblowing sequence. Problems with the use of
sensors for determining soot buildup include 1) the difficulty in
installing and maintaining the sensors within the boiler, 2) the
costs of installing the sensors and 3) the requirement to shut the
boiler down for installation or repair. Sensors can be effective at
identifying for an operator which sections of a boiler require
additional cleaning based on the soot buildup.
[0008] The objective of maximizing boiler cleanliness is typically
balanced against the costs of cleaning in order to improve boiler
efficiency. Boilers typically have multiple heat zones and
different areas of the boiler may accumulate deposits at different
rates and require different levels of cleanliness. The different
heat zones will require different amounts of cleaning to attain a
particular level of cleanliness. Systems such as U.S. Pat. No.
4,996,951 (Archer) are known to assist in determining when to
operate a set of soot blowers by evaluating the increased cost of
transferring heat energy versus the cost of soot removal operation
from a thickness indication of the soot deposit layer.
[0009] A Digital Soot Blower Control Systems is disclosed in U.S.
Pat. No. 4,085,438 (Butler). Butler discloses a digital sootblower
control system wherein selected sootblowers are monitored through
software techniques. Specific blowing patterns are developed by an
operator and initiated automatically. Butler discloses providing
visual indicia of whether a sootblower is operating to determine if
the sootblower is operating according to a predetermined schedule.
Butler fails to provide a monitoring system or method for
controlling the mass flow rate of the cleaning medium and ensure
operation within high and low setpoints for optimization of
cleaning medium usage and sootblowing operation effectiveness.
[0010] During the sootblowing operation it is challenging to
understand what is occurring inside of a boiler and specifically
what is occurring relative to a specific sootblower and section of
the boiler and whether damage is occurring to the heat exchanger
tubes. Sootblowers can get stuck inside a boiler flowing steam
which can lead to heat transfer tube leaks or higher than normal
tube erosion. The sootblowing process results are often provided
only after a boiler is back in operation and either evidence of
overcleaning or undercleaning becomes obvious. Sootblowers can also
become damaged allowing for excessive cleaning medium flow. A
boiler may be required to be taken out of service due to heat
transfer tube damage from the sootblowing. Early identification of
leaks inside a boiler can help to manage the boiler operation and
help to plan for boiler shutdown and repair. Early leak detection
of mass flow rates of the cleaning medium outside of the high or
low set points can also provide for rapid response and prevent
damage to the boiler.
[0011] During the sootblowing process, variations of the cleaning
medium flow rates outside of a certain range can cause problems and
reduce the effectiveness of the operation. A cleaning medium
directed at a heat transfer tube at too high of a flow rate can
quickly cause damage to a section of heat transfer tube requiring
the boiler to be shut down for repair. A cleaning medium directed
at a heat transfer tube at too low of a flow rate can lose its
effectiveness in removing soot from the tubes. In either case, the
cleaning medium is not being optimized and adjustments need to be
made to the sootblowing process.
[0012] Current technologies regarding sootblowing have focused on
tools to determine where to direct sootblowing (i.e. sensors for
estimating soot buildup), how to improve sootblowing with tools
such as revised spray nozzles, retractable blowers and developing
routines to determine how long to operate a sootblower within a
particular section of the boiler. The existing technologies have
not focused on the mass flow rates of the cleaning medium and in
regards to optimizing the use of cleaning medium and thus improving
boiler efficiency.
SUMMARY OF THE INVENTION
[0013] The invention includes a method and a system for monitoring
the cleaning medium use during the boiler cleaning process. The
logic of the invention could also be included in a computer
program. The most common cleaning medium for sootblowing of coal
fired boiler is steam due to its effectiveness and availability.
Large boilers often have numerous sootblowers and these may be
operated in sets. The initial step includes determining which
sootblowers are in service. Then we operate each sootblower to
collect flow data and adjust sootblower to within specification.
The cleaning medium flow is then monitored through a sootblower by
utilizing a mass flow measurement device and then adjusting the
sootblower to within specifications. An indication of the mass flow
rate of the cleaning medium used in the set of sootblowers is then
produced. The appropriate high and low flow alarm setpoints for a
particular soot blower or set of soot blowers is calculated. These
alarm set points are then used to inform the control room operator
visually and audibly that the steam flow through the soot blower
system is at the correct level for the soot blowers that are in
service at that moment in time. The mass flow rate is monitored
during the cleaning of a boiler and adjustments made to the
sootblowers to operate below said high flow set point and above
said low flow set point and respective high alarm and low alarm
notifications are provided to the boiler operator. In one
embodiment of the invention, the notification will include an
audible and/or visual alert in the control room. The process may
also check for steam leaks by monitoring for a system bottled up
situation were everything is pressurized but closed off. If steam
flow is detected, then a boiler operator will be alerted. This may
be through a visual and/or audible indication in the control
room.
[0014] The invention focuses on the flow of the cleaning medium and
thus improves the efficiency of the sootblowing process and the
boiler availability rating due to reduced tube leaks. The invention
improves the net plant heat rate numbers. Rapid identification of
specific sootblower flow rates outside of specific set points can
prevent significant damage to the boiler.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a power plant boiler drawing with a cutaway
showing the heat exchanger tubes and the location of the
sootblowers, the mass flow measurement device and the temperature
measuring device.
[0016] FIG. 2 is a drawing of a sootblower lance spraying cleaning
medium on the heat exchanger tubes to remove soot.
[0017] FIG. 3 is a schematic of the logic used to determine the
mass flow and identify if there is a leak in the system.
[0018] FIG. 4 is a schematic of the logic used for analyzing the
steam flow.
[0019] FIG. 5 is a drawing of a control room display providing
information to an operator in accordance with an embodiment of the
present invention.
[0020] FIG. 6 is a flow diagram with various items identified.
DETAILED DESCRIPTION
[0021] For a fuller understanding of the nature and objects of the
present invention, reference should be made to the following
detailed description taken in connection with the accompanying
drawings, wherein:
[0022] FIG. 1 is drawing of a power plant boiler 10 with portions
broken away to show the heat exchanger tubes 14 within the power
plant boiler 10 which are to be cleaned by sootblowers 12. Attached
to the cleaning medium line 20 is a mass flow measurement device 16
and a temperature measuring device 18 installed upstream. The mass
flow measurement device 16 includes flow transmitter 23. The
temperature measuring device 18 includes a temperature transmitter
24. The steam pressure measuring device 27 of the cleaning medium
is measured upstream of the cleaning medium line 20. The physical
drain valves 26 are shown located at the system low point for
automatic removal of the cleaning medium, for example for steam
then water is removed. For leak testing, the physical drain valves
26 must be closed to pressurize the system. The cleaning medium
line 20 is located near the top of the power plant boiler 10. In
addition, the mass flow measuring device 16, temperature measuring
device 18, flow transmitter 23, temperature transmitter 24, and
pressure measuring device 27 are all located near the top of the
power plant boiler 10 on the cleaning medium line 20 just
downstream of the pressure measuring device 27. FIG. 6 also shows
the alignment of these items relative to each other and to the
system.
[0023] FIG. 2 shows a sootblower lance 15 with the cleaning medium
spray 13 cleaning the heat transfer tubes 14 to remove the soot
build up 19 inside the power plant boiler 10.
[0024] FIG. 3 is a schematic of the logic used to determine the
mass flow and identify if there is a leak in the system. The
Temperature Element TE consists of the mass flow measuring device
18 and the temperature transmitter 24. Temperature measuring device
18 measures the cleaning medium temperature. One embodiment of the
temperature measuring device 18 for use with steam as the cleaning
medium is a Type E Temperature transmitter or equivalent. The
temperature transmitter 24 and the flow transmitter 23 send the
data to an input device and so the data can be manipulated with the
software. A number of different types of flow measurement devices
may be used including a pressure based flow meter as shown in FIG.
3. The differential pressure is sensed with a differential pressure
transmitter 30. The pressure differential 30 is transmitted to an
input device and manipulated along with the temperature to
determine the mass flow rate 42. The mass flow measuring device 16
is shown in FIG. 3 and includes the temperature measuring device
18, the temperature transmitter 24, differential pressure 30, and
the mass flow rate 40. The mass flow calculation is a function of
change in pressure, temperature and pressure. Pressure can be input
as a constant or a measured value. The drain valve indicators 53
and 54 are shown.
[0025] When there are no sootblowers in service, the system is
blocked in with physical drain valves 26 in closed position. FIG. 5
will indicate a closed position for the drain valve indicators 53
and 54 during leak testing. When a leak is detected, a leak
detection alarm 66, which may be audible and/or visual, will notify
an operator as shown in FIG. 5.
[0026] FIG. 4 shows the logic for analyzing the cleaning medium
flow. First we must determine which sootblower or sootblower is in
service. Each sootblower must be operated during the initial system
setup. This is to collect flow data on each sootblower and to
adjust sootblowers that have flows out of specification. The
collected flow data is then entered into the modeling software so
that the model can calculate the appropriate high and low flow
setpoints for different combinations of blower operations. The
cleaning medium flow through the sootblower is monitored by the
mass flow measurement device and the sootblower is adjusted to the
sootblower specifications. It is quickly determined which
sootblowers 12 are in operation and displayed in FIG. 5 the active
status of sootblower 50 and 51. The steam pressure measuring device
27 is measured and the steam pressure change 44 evaluated. The
steam pressure change 44 is typically controlled to a small percent
of the system operating pressure. Particular embodiments of the
invention may use steam as the cleaning medium and operate the
steam pressure around 600 psig. Once all the mass flow rates 42
from all the sootblowers have been determined, they are entered in
the model and a low flow set point and high flow set point are
determined. If the mass flow rate 42 is lower than the low flow set
point 41 or higher than the high flow set point 40 then flow
indicator 65 will be activated with a visual or audible indication
in the control room.
[0027] The sootblowers are set so that a group of blowers operate
at a mass flow rate 42 and additional groups of sootblowers may
operate at a different flow rates based on each blower's cleaning
requirements. i.e. location within the boiler, buildup of soot,
etc. The sootblowers are then adjusted to the specific flow rates
by adjusting the appropriate sootblowers 12. Each sootblower is run
and the steam through the sootblower is monitored. The sootblowers
are then adjusted to operate below the high flow setpoint 40 and
above the low flow set point 41 for each set of sootblowers. Once
all the flow rates are adjusted and known, the flow rates are
entered into the flow model so that it can calculate the correct
high flow set point 40 and low flow set point 41 for the cleaning
medium flow monitoring based on which sootblowers 12 are operating.
The system is then fully engaged.
[0028] Each block shown on FIG. 4 contains programming code. Blocks
labeled Groups 528, 628 and 678 and Groups 200, 370 and 478 signal
if a blower flowgroup is on and if one or two blowers are on within
that group of blowers. The block labeled IKFLOW_ALM receives
information from all sub systems. It then calculates the high flow
set point 40 and low flow set point 41. It also generates the high
and low alarms and generates outputs for the system displays. The
mass flow rate 42 as well as the pressure measuring device 27 are
inputs to this block.
[0029] The block labeled IKFLOW_ALM1 calculates the high and low
flow alarm limits and sends outputs to the IKFLOW_ALM block for
flow group 200, 370 or 478 on. It also sends high and low flow
setpoints for these flow groups to IKFLOW_ALM block.
[0030] FIG. 5 shows a Sootblower Flow Analyzer Display 90 with mass
flow rate 42 displayed as flow rate 62. The high flow set point 40
and low flow set point 41 are shown as display high flow 60 and
display low flow 61. When the flow rate 62 is higher than the high
flow set point 40 or the low flow set point 41 then flow alarm 65
will be activated. A date and time indicator 71 may also be shown.
The pressure measuring device 27 can be displayed in cleaning
medium line pressure 64 as well as the steam line pressure change
67. Sampling indicator 52 identifies when sampling is occurring.
The drain valve indicator status 53 and 54 identify whether a drain
is open or closed.
[0031] The data may be provided to the operator in many ways
including a digital display. The data may be numerical or the data
may be shown graphically as shown in the Graphical Display 70.
[0032] The logic referred to in FIG. 3 and FIG. 4 may be installed
within a computer program. Different types of control systems may
be used within a boiler operation to manage the operation including
the sootblowing operation. One example is the Foxboro Intelligent
Automation Distributive Control System. The control system would
receive the information from the temperature transmitter 24, flow
transmitter 23 and pressure measuring device 27, control the
various plant operations and provide notifications such as visual
indications on a control panel or audible alarm signals.
[0033] FIG. 6 is a flow diagram identifying various items. A manual
isolation valve is located upstream of the system. The pressure
measuring device 27 is shown along with a pressure regulating valve
upstream in the process. The process may be controlled at or around
600 psig if steam is used as the cleaning medium. Also, shown is
the temperature measuring device 18 and temperature transmitter 24
upstream of the flow transmitter 23 and pressure differential 30.
The steam or other fluid would then enter the boiler through the
cleaning medium line 20 and split into to two sections of the
boiler. The line size is increased just prior to the temperature
measuring device and then decreased after the flow transmitter as
shown, for example from a 3'' line to a 6'' line.
* * * * *