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.
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.
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.
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:
When there are no sootblowers in service, the system is blocked in with physical drain valves 26 in closed position.
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
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.
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