Installation and Operation Experiences with the Clyde Bergemann SmartCannon System at Alabama Power s Plant Miller

Transcription

1 Installation and Operation Experiences with the Clyde Bergemann SmartCannon System at Alabama Power s Plant Miller Presented at Electric Power Conference 2003 Charles Boohaker Brian Mead John Sorge Southern Company

2 Installation and Operation Experiences with the Clyde Bergemann SmartCannon System at Alabama Power s Plant Miller Introduction After the transition to Powder River Basin coal during the mid-1990 s, Alabama Power Company s Plant Miller began experiencing problems associated with the water lance sootblowing system due to the higher sootblowing requirements of the sub-bituminous coal. The water lances were set to run cyclically without input on actual cleanliness, visual or otherwise, of the waterwalls, leading to the possibility that the water lances could spray water directly on a clean tube section, intensifying thermal quench cracking and reducing the useful life of the tubes. Additionally, the increased sootblowing requirements caused a shortage of the condensate water supply. These problems directed plant engineers to seek an alternate cleaning method for the furnace waterwalls. In response Alabama Power contracted with Clyde-Bergemann Inc. (CBI) in 2001 to install and commission the SmartCannon waterwall cleaning system on Miller s Unit 1. The SmartCannon system uses heat flux sensors to determine the need and location for sootblowing frequency. To obtain a better understanding of the technology and potential benefits, Southern Company and EPRI sponsored the demonstration. This paper describes the experiences and findings to date regarding the installation and operation of the water cannon system Technology Description There are four Clyde Bergemann Model 100 water cannons installed in Miller Unit 1. Clyde Bergemann has installed water cannons at a number of other sites (~60 as of first quarter 2002). The major elements of a WaterCannon system are: Water cannons (four installed at Miller 1) Clyde Bergemann developed controls Furnace waterwall heat flux sensors (24 are installed at Miller 1) Variable speed pump supplying water to the cannons The heat flux sensors installed are type K thermocouples that measure the temperature of the surface and subsurface of the tube. These sensors are placed throughout the boiler to allow for the most coverage by the cannons. The placement of these sensors and the CBI water cannons can be seen in Figure 3.

3 Figure 1 Water Cannon CB 100 Figure 2 Variable Speed Pump Water Cannon Heat Flux Sensor Outside Right Side Wall Outside Rear Wall Outside Left Side Wall Outside Front Wall Figure 3 Boiler Layout Test Program Description The primary goal of the test program is to document the benefits of the water cannon system. Aspects to be evaluated include the following:

4 Condensate Requirements Measure reduced condensate requirements of waterlances Measure water plant condensate daily requirements Faster wall cleaning cycles Cracking of Waterwall Tubes Visible inspection of waterwall tubes in area of previous damage Tube sample in area of previous damage Use of tube failure models if any reliable ones exist Furnace Heat Absorption and Efficiency Economizer exit gas temperature Furnace exit gas temperature Spraywater flow measurements Main steam flow Superheater steam temperature Reheat steam temperature Cold reheat steam temperature Impact on Generation Capacity Emissions reductions Measure NOx emissions Testing consists of both short- and long-term components. The long-term testing has been passive, with the unit running as normal. Short-term testing consists of tests conducted by both SCS and Clyde Bergemann. Test Program Progression Testing has been ongoing throughout the project. Two independent onsite tests have been accomplished to date by SCS, as well as performance testing by CBI. The first SCS test, occurring on November 11, 2002, was performed with the unit at approximately 75% of full load and the water cannon system out of automatic mode to allow for greater slagging of the furnace. This was done to ensure valid data could be collected. The second date, January 15, 2003, was performed under full load (~710 MW) and the water cannons were running in full automatic mode. This testing was to collect data under normal operating conditions of the cannons. An Agilent 34970A high-speed data logger was used to collect the data at a higher rate than the CBI fast data collection method (~15 ms vs. ~200 ms). The faster data was taken using the spare thermocouples on the CBI heat flux sensors. The CBI performance testing was conducted February 18-21, The entire testing period was performed under full load. Elements of the testing included testing of the temperature and gaseous composition at the nose of the furnace, data logging through the DCS/PI and the CBI system, and furnace wall emissivity.

5 Findings Characterization of Water Cleaning Events Over the course of this project, CBI has collected data from each cleaning cycle. This data, when plotted can show both the droop and the gain from each cleaning event (see figure 3). In Figure 4 and 5 are histograms characterizing the temperature droop and gain over several months where the water cannons have been in operation. In general, cleaning events with a droop greater than 100 F are considered undesirable. The count of the cleaning events where the temperature droop was greater than 100 F by day is shown in Figure 7. The plot shows that after the initial installation there were several days with frequent high droop (> 100 F) cleaning events. This was corrected after CBI was notified and made minor adjustments to the system. When looking at most cleaning events, two temperature drops can usually be seen. This is possibly due to the fact that the cannons will pass over a given area twice. When the cannon sweeps from one side to another, and then back again, the cleaned areas may overlap slightly. If a sensor is in this overlapped area, then the data will show two temperature drops. This is best illustrated by the short-term testing data from November 2002 (Figure 8 & 9). In general, these multiple impingements are undesirable. Sensor Gain Droop Temperature (DegF) Figure 4 Droop and Gain

6 Figure 5 Temperature Gain April 2002 January 2003 Figure 6 Temperature Droop April 2002 January 2003

7 Figure 7 Cleaning events with Droop > 100 F 900 Run 1 / Nov 22., Temperature (DegF) CB Daily File CB Fast Data Datalogger Time (Seconds) Figure 8 November 22, 2002 Test Data Water Cannon # 4

8 900 Run 1 / Nov. 22, Temperature (DegF) CB Fast Data Datalogger Time (Seconds) Figure 9 Datalogger data shifted in time and biased Impact of Water Cleaning on Boiler Tube Life In December 2002, SCS contracted with a consultant to create a simple model for waterwall tube thermal fatigue. The consultant created a model that would take temperature data from a cleaning event and determine an approximation for the amount of thermal fatigue caused by the event. The model gives an index rather than a measurable parameter. Therefore, one index must be compared to another index to determine if one event caused more or less thermal fatigue than another. Preliminary results have been inconclusive as to whether the cannons cause more or less thermal fatigue than the water lances. The data gathered from the November 22, 2002 testing was run through the model and from this data it cannot be determined that the cannons are better or worse than the water lances when comparing thermal fatigue on a per run basis. This is because of the fact that one run by the cannons shows a higher index than the lances and another run has a lower index than the lances. However, what can be determined is that the feedback controls is what lowers the thermal fatigue on the waterwalls. The reason for this is that with the feedback controls, there are fewer cleaning cycles over a given period of time than with the lances which are set up on a time based cleaning routine. SCS plans to run more data collected both by the CBI system and the Agilent data logger through this model.

9 Furnace Heat Absorption and Efficiency Base on testing conducted by CBI, there was no observable change in boiler efficiency with the installation of the water cannons. However, indications are that the heat transfer in the furnace is more uniform. There was also a slight reduction in furnace exit gas temperature (FEGT) with no change in load. Figure 10 shows a surface plot of the FEGT with the water lances and the cannons. Using Water Lances Using Water Cannons Alabama Power Company Miller Steam Plant Unit 1 HVT Test #1 February 18, 2002 Alabama Power Company Miller Steam Plant Unit 1 HVT Test #6 February 21, Figure 10 Surface Plot FEGT Make-Up Water Requirements The make up requirements for the condensate have changed since the installation of the water cannons. Unlike the water lances, the water that is sprayed by the cannons does not have to go through the water treatment process before being sprayed. The cannons have no problems using untreated water directly from, in this case, a river having only been strained to remove debris.

10 Water Lance Water Cannon Water Treatment Plant Strainer Condensate source (River, etc.) Figure 11 Water Treatment Process Emissions Reduction One of the postulated benefits was to reduce NOx emissions. During the CBI conducted performance testing in February 2002, NOx levels were reduced by approximately 10% at the nose of the furnace, however, no change was observed in stack emissions. The reduction is consistent with the lower furnace exit gas temperature observed at the nose. Equipment Reliability Since the installation of the water cannons, there have only been a few minor problems. Plant staff has a positive impression of the system and are installing water cannon systems on other units. Maintenance for the water cannons is much less than was required with the water lances. Summary

11 Overall, the experiences with the water cannon system have been positive. The water cannons have operated with relatively few interruptions for repairs or adjustments. The overall heat flux in the boiler is now more balanced. There are still a few open questions as to whether the cannons have reduced NOx emissions. There are still some cleaning events with droops over 100 F. This could probably be corrected with finer tuning of the heat flux sensors. However, the benefits of this system far outweigh the minor problems encountered. The feedback provided by the heat flux sensors has had a positive impact on the performance of the boiler, allowing cleaning events to only occur when an area is dirty. Also, with the reduced condensate make up, the water treatment facility for the plant should have a reduced load.