Coal Flow Optimization with B&W PGG s EvenFlow System

Transcription

1 Technical Paper BR-1865 Coal Flow Optimization with B&W PGG s EvenFlow System Authors: B. Hosseininejad T.A. Fuller E.D. Fuller Babcock & Wilcox Power Generation Group. Inc. Barberton, Ohio, U.S.A. A. Murkerson J. Krajna Lakeland Electric, McIntosh Station Lakeland, Florida, U.S.A. H. Bilirgen Lehigh University, Energy Research Center Bethlehem, Pennsylvania, U.S.A. Presented to: Power-Gen International Date: December 13-15, 2011 Location: Las Vegas, Nevada, U.S.A.

2 Coal Flow Optimization with B&W PGG s EvenFlow System B. Hosseininejad T.A. Fuller E.D. Fuller Babcock & Wilcox Power Generation Group, Inc. Barberton, Ohio, U.S.A. A. Murkerson J. Krajna Lakeland Electric, McIntosh Station Lakeland, Florida, U.S.A. H. Bilirgen Lehigh University, Energy Research Center Bethlehem, Pennsylvania, U.S.A. Presented at: Power-Gen International Las Vegas, Nevada, U.S.A. December 13-15, 2011 BR-1865 Abstract Coal flow imbalance is an issue of concern for many pulverized coal-fired boilers in the power generation industry. Achieving balanced coal flow to burners can have a positive impact on carbon monoxide (CO) and nitrogen oxides (NOx) emissions, loss on ignition (LOI) and slagging. For this reason, balancing coal flow is a primary objective of combustion optimization. In collaboration with the Energy Research Center at Lehigh University, Babcock & Wilcox Power Generation Group, Inc. (B&W PGG) has developed a device to control the distribution of coal flow to burners. Key to its development, the device has been proven to accurately control the coal distribution with negligible impact on the primary air flow distribution. B&W PGG has incorporated this advancement into a commercial system known as the EvenFlow coal flow controller. The first utility-scale demonstration of the EvenFlow coal flow controller was recently completed at Lakeland Electric s McIntosh Station. Testing of the system included traditional sampling methods, as well as real-time feedback from other systems. This paper presents an overview of this demonstration project, including installation, testing and results. Introduction Background For pulverized coal-fired boilers, poor coal distribution to the burners can have a significant, negative effect on combustion and emissions. High coal flow to burners can create carbon-rich zones of reducing atmosphere which leads to increased slagging, increased carbon monoxide (CO) emissions, and increased LOI. Burners with too little coal flow can create oxygen-rich zones that may increase nitrogen oxides (NOx) emissions. Further, the parameters that affect coal quality (hardness, moisture, energy content, etc.) may create varying conditions during boiler operation that necessitate online changes to coal flow distribution. Therefore, identifying an online, real-time system to adjust the distribution of coal has been a long sought after goal of many in the fossil power industry. Traditional online coal flow distribution systems involve adjustable restrictions in the burner lines such as variable orifices. However, testing has shown that these systems affect the primary air flow in a pipe significantly more than the coal flow. This could have undesirable and potentially dangerous consequences for combustion. A system that can effectively manipulate the coal flow without greatly affecting the primary air flow would be advantageous. With these issues in mind, B&W PGG collaborated with the Energy Research Center at Lehigh University (ERC) to develop the EvenFlow coal flow controller for pressurized, vertical-spindle pulverizers. The EvenFlow system was developed and tested using computational modeling and laboratory-scale testing at ERC laboratories. At the successful completion of laboratory testing, the system was installed in a B&W Roll Wheel 75G pulverizer at Lakeland Electric s McIntosh Generating Station for utility-scale testing. Development Development of the EvenFlow system began at the ERC s facilities in Bethlehem, Pennsylvania. Initial designs for a flow control element (FCE) were developed and Babcock & Wilcox Power Generation Group 1

3 evaluated using computational modeling techniques. The most promising design underwent physical flow testing in the Pneumatic Conveying Laboratory, shown in Figure 1. Laboratory testing identified the final design criteria for the FCE and demonstrated that a system of FCEs installed in a mill could successfully change coal flow distribution while having a negligible effect on primary air flow. Further development of the EvenFlow system occurred at B&W PGG s headquarters in Barberton, Ohio, to build the FCEs into a complete system for utility-scale pulverizers. Additionally, the laboratory tests were used in combination with computational modeling to identify the neutral position the position at which the FCEs had negligible effect on pulverizer operation. The next phase of the system s development would be testing on a utility boiler. Test site Unit 3 at Lakeland Electric s McIntosh Generating Station is a 350 MW Radiant Boiler designed by B&W PGG. The boiler, shown in Figure 2, was designed to produce 2,510,000 lb/hr of steam at 2640 psig and 1005 F. The boiler has a total of 32 burners located on the front and rear wall. There are four rows of four burners on each wall. The burners are fed by four B&W Roll Wheel 75G pulverizers. Each pulverizer has eight outlet pipes and feeds two consecutive elevations of burners. The EvenFlow system was installed on Mill 31, which feeds the lower two elevations of burners on the rear boiler wall. The EvenFlow system The EvenFlow coal flow controller consists of a number of FCEs that are used to manipulate coal flow to one or more pulverized coal outlet pipes. FCEs can be moved individually or in groups to achieve a balanced coal flow distribution to the burners. The FCEs are installed in the outlet distribution turret of the mill. Each FCE is independently positioned; they can be equipped with electric actuators or adjusted manually. Fig. 2 McIntosh Unit 3. Several designs exist for the EvenFlow system. The exact design used on a given installation depends on the pulverizer s size and the number of coal outlet pipes. For McIntosh Unit 3, B&W PGG supplied a cartridge design. The cartridge design provides a single major component for ease of installation. The cartridge consists of a new coal inlet pipe surrounded by a sealed compartment that houses and protects the device s mechanical components. The cartridge and FCEs are manufactured using a hardened material suitable to withstand the harsh environment inside the pulverizer. The EvenFlow cartridge used at McIntosh is shown in Figure 3. The flow control elements mount to the outside of the cartridge, located in the turret of the pulverizer. The FCEs are positioned using electric actuators with built-in positioners that are located at the top of the cartridge. The actuators are linked to the FCEs through hardware in the cartridge s sealed compartment. Installation The EvenFlow coal flow controller was installed in Mill 31 during a maintenance outage on Unit 3 in February Fig. 1 ERC coal flow test facility. Mechanical Since the EvenFlow cartridge includes a new coal inlet pipe, the existing internal portion of the coal inlet pipe to the pulverizer was removed. The exterior portion of the coal 2 Babcock & Wilcox Power Generation Group

4 Fig. 3 EvenFlow cartridge for Lakeland McIntosh. inlet pipe was disconnected and moved aside for installation. In addition, one of the coal outlet pipes was disconnected and moved aside to provide clearance for the new cartridge. The EvenFlow cartridge was lowered into the place of the former coal inlet pipe, as shown in Figure 4. The cartridge was hoisted above the pulverizer and lowered into place. A flange, located at the top of the cartridge, directly beneath the actuators, was welded to the pulverizer top plate. Once the cartridge was fully lowered and secured, the FCEs were installed on the cartridge from inside the pulverizer. Mounting rods, shown in Figure 5, were installed for the FCEs. The cartridge contained an integral system for lubrication and also required the connection of instrument air lines to maintain the sealed compartment. Electrical/controls The EvenFlow system included a dedicated programmable logic control (PLC) system, which allowed for fully automated adjustment of the FCEs. The PLC system, including a touch screen interface, was completely contained within a single control cabinet. A second cabinet was installed to house power connections and fuses for the actuators. The Fig. 5 FCE mounting rods. two enclosures were mounted on a platform near Mill 31, as shown in Figure 6. Each FCE was independently controlled and positioned using an electric actuator and positioner module. Electrical lines for 110 VAC power and a 4-20 ma position signal were connected from the electrical and control cabinets to the actuators on the top of the pulverizer. The control system was designed to accept manual position inputs from a local touch screen display or remote position inputs (e.g., from an optimization system) for closed-loop control. Testing The EvenFlow system was tested throughout 2010 and 2011 with the intent of evaluating the effect on boiler and pulverizer performance. Specifically, the effects of the system on coal and air flow needed to be analyzed. Procedure To gauge the effects of the EvenFlow system, an accurate and consistent means of coal and air flow measurement was needed. For these purposes, B&W PGG elected to conduct dirty air and coal recovery tests. Lakeland Electric s performance group also conducted several clean air tests. All Fig. 4 EvenFlow cartridge installation. Fig. 6 Electrical/controls cabinets. Babcock & Wilcox Power Generation Group 3

5 tests were conducted using the appropriate ASTM probes and procedures based on those specified in the ASME Power Test Code. All of the tests were conducted using test ports located between five and ten feet beneath the burner elbow in a vertical run, as shown in Figure 7. During tests, the mill feeder speed was set in manual and held at approximately 30.5 tons/hr. Baseline tests During the initial round of testing, several baseline tests were conducted to enable repeatable and consistent results with the manual coal recovery tests. For the baseline tests, all FCEs were placed into the neutral position. Figure 8 displays the coal distribution for each of the baseline tests. Coal distribution was calculated using the following formulas: where bal avg is the average coal mass flow rate, n is the number of coal pipes (8), R i is the coal mass flow rate for a given pipe, and dev i is the percentage deviation from average for a given pipe. As shown in Figure 8, the baseline test results found most samples for each coal pipe to be within a 10% margin. Baseline testing also proved that the system, while in the neutral position, did not have a measureable effect on mill parameters including mill pressure drop, mill motor amps, or fineness. Also noted was that Pipe 7 had relatively high coal flow and Pipe 3 had relatively low coal flow. Initial results The effect of the EvenFlow system on coal flow distribution was verified by moving all FCEs together across their entire operating range in eight coordinated steps. At each Fig. 8 Baseline distribution for initial tests. step, a coal recovery test was conducted. The results of the tests, shown in Figure 9, illustrate that the EvenFlow coal flow controller has significant effects on the distribution of coal to each pipe. Further, it was demonstrated that each pipe could be affected in both the positive and negative directions. At least a 50% variation in coal flow was measured in each pipe across the FCE output range. In addition, it was noted that many of the coal pipes had several high and low points (peaks and valleys) as the FCE positions were changed. To measure the effect of the EvenFlow controller on air flow distribution, a test was conducted in which only two FCEs were moved by a significant amount. The remaining FCEs were held at a constant position. This test was representative of what would be considered a typical adjustment to the system. Dirty air and coal recovery tests were conducted before and after the change in position. The results of the test are illustrated in Figure 10. For all eight coal pipes, coal flow was found to vary by over 10%, which can be considered a significant change in distribution. Changes in air flow of approximately 16% and 9% were observed on Pipe 6 and Pipe 5, respectively. Less than a 5% change in air flow was observed on the remaining six coal pipes. These results proved that, for typical adjustments (i.e., position changes made for most situations), Fig. 7 Test port locations. Fig. 9 Distribution changes through FCE adjustment range. 4 Babcock & Wilcox Power Generation Group

6 20% low, and Pipes 3 and 6 to be approximately 15% low. The remaining four pipes were within a ±10% distribution. Using the EvenFlow system and the balancing strategy, B&W PGG was able to create a uniform coal flow distribution, nearly entirely within a ±10% deadband. The results of this test are shown in Figure 11. Fig. 10 Change in distribution from typical adjustment test. the EvenFlow controller can significantly affect coal flow distribution with very little impact on air flow distribution. By comparison, testing of orifices installed in burner coal lines showed that a 19% change in coal flow resulted in an 82% change in primary air flow. To further test air flow distribution effects, a gross adjustment test was conducted. In the test, a significant position change was applied to all of the FCEs. Typically, an adjustment of all of the FCEs by a large magnitude would not be necessary. However, this type of movement would establish the maximum effect that the EvenFlow controller would have on primary air. Dirty air and coal recovery tests were conducted prior to and after the adjustment to calculate changes in air flow and coal flow. Even with this extreme movement in the EvenFlow device, the average change in air flow was less than 10% with five of the pipes changing by less than 5%. As expected the coal flow changed considerably more with the average change being greater than 20% and six of eight pipes changing by more than 15%. Both of the air flow tests confirmed that the EvenFlow coal controller had minimal effect on air flow while significantly redistributing the coal flow from the mill. This is a considerable improvement over other devices such as variable orifices. Mill operational data was evaluated through both the typical adjustment test and the gross adjustment test and compared to the same parameters before the installation of the EvenFlow system. No measureable changes were observed in mill pressure drop, mill motor amps or fineness. Balancing Coal Flow Distribution Based on the initial testing, a strategy was developed to use the EvenFlow coal flow controller to balance the coal distribution. The strategy involved taking several iterative steps first by making adjustments to multiple FCEs, then by making fine adjustments to only one FCE until the coal flow distribution was nearly uniform and within a ±10% deadband. A baseline coal recovery test found Pipe 1 to be approximately 55% high in coal flow, Pipe 5 approximately Long-Term Hardware Evaluation In March 2011, over a year after the EvenFlow coal flow controller was installed, a maintenance outage occurred for McIntosh Generating Station Unit 3. During the outage, B&W PGG inspected the EvenFlow cartridge and FCEs. When the system was installed, the FCEs were painted with four layers of paint prior to installation so that the amount of erosion could be evaluated. During the inspection, B&W PGG observed that the top layer of paint was still intact on most of the FCEs and that there were no significant signs of degradation or damage to any of the other EvenFlow system s parts. Therefore, the hardware and materials used were proven to be acceptable and sufficient for the harsh environment within the pulverizer. Conclusion Laboratory testing and computational modeling were used to develop a novel coal flow control device that overcomes the performance problems with burner line-installed devices like variable orifices. The EvenFlow system, installed internal to a pulverizer, was designed to control coal flow to individual coal outlet pipes with negligible effects on primary air flow. The first utility-scale demonstration of the EvenFlow coal flow controller proved that the system can manipulate coal flow distribution from the pulverizer with a minor effect on primary air flow. In addition, the system was used to successfully balance coal flow distribution from the mill in a case where the imbalance was as high as 55%. Hence, the EvenFlow system could be utilized to balance coal distribution to burners and improve boiler combustion, emissions and slagging. Fig. 11 Balancing coal distribution with EvenFlow. Babcock & Wilcox Power Generation Group 5

7 Future Work The EvenFlow coal flow controller was successfully proven as a tool for changing coal distribution to the burners without negatively affecting air flow. It worked well when manually positioned using a PLC-based control system. Future work will focus on integrating the EvenFlow controller with a closed-loop, automatic optimization system. EvenFlow and B&W Roll Wheel are trademarks of Babcock & Wilcox Power Generation Group, Inc. Copyright 2011 by Babcock & Wilcox Power Generation Group, Inc. a Babcock & Wilcox company All rights reserved. No part of this work may be published, translated or reproduced in any form or by any means, or incorporated into any information retrieval system, without the written permission of the copyright holder. Permission requests should be addressed to: Marketing Communications, Babcock & Wilcox Power Generation Group, Inc., P.O. Box 351, Barberton, Ohio, U.S.A Or, contact us from our website at Disclaimer Although the information presented in this work is believed to be reliable, this work is published with the understanding that Babcock & Wilcox Power Generation Group, Inc. (B&W PGG) and the authors are supplying general information and are not attempting to render or provide engineering or professional services. Neither B&W PGG nor any of its employees make any warranty, guarantee, or representation, whether expressed or implied, with respect to the accuracy, completeness or usefulness of any information, product, process or apparatus discussed in this work; and neither B&W PGG nor any of its employees shall be liable for any losses or damages with respect to or resulting from the use of, or the inability to use, any information, product, process or apparatus discussed in this work.