US20110203535A1

US20110203535A1 - Method and System for Sootblower Flow Analyzer

Info

Publication number: US20110203535A1
Application number: US12/708,895
Authority: US
Inventors: Michael Clark Hymel
Original assignee: NRG Energy Inc
Current assignee: NRG Energy Inc
Priority date: 2010-02-19
Filing date: 2010-02-19
Publication date: 2011-08-25

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.

Description

FIELD OF THE INVENTION

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

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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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

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.
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

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.

FIG. 2 is a drawing of a sootblower lance spraying cleaning medium on the heat exchanger tubes to remove soot.

FIG. 3 is a schematic of the logic used to determine the mass flow and identify if there is a leak in the system.

FIG. 4 is a schematic of the logic used for analyzing the steam flow.

FIG. 5 is a drawing of a control room display providing information to an operator in accordance with an embodiment of the present invention.

FIG. 6 is a flow diagram with various items identified.

DETAILED DESCRIPTION

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:
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.

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.