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Big Sandy Plant. Update Loesche Dynamic Classifier 2012. Executive Summary. 20% increase in fuel thru put was noticed on this pulverizer Total overall project cost: ~ $1 million (labor and material) Project time line - 8 weeks (one shift); 6000 man hours **
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Big Sandy Plant Update Loesche Dynamic Classifier 2012
Executive Summary • 20% increase in fuel thru put was noticed on this pulverizer • Total overall project cost: ~ $1 million (labor and material) • Project time line - 8 weeks (one shift); 6000 man hours ** • Initial testing shows installation on all 6 pulverizers would produce a spare pulverizer (based on this one) • System wide revenue potential ~ $9.5M based on lost MWH’s from GADS data • Other potential benefits include NOx reduction with improved fineness, increased mill performance and increased boiler efficiency thru improved combustion • Project under review by AEP Program Management Office as an Engage 2 Gain idea ** All craft hours – removal and install
Background • Big Sandy Plant’s Unit 2 is an 800 MW Foster Wheeler Boiler with six MB23 hybrid MPS 89 Pulverizers. • Full load requires all six Pulverizers. • One Pulverizer O/S is approximately 100 MW curtailment.
History • MPS mills in 2010 accounted for 286,080 MWH’s of curtailments on the 800 and 1300 series units. • The 800mw series without spare mills lost 263,850 MWH’s while the 1300mw series with spare mills only lost 22,230 MWH’s • Inspections and rebuilds accounted for 150,000 MWH’s of curtailments in 2010 on the 800mw series. • Pulverizer Inspections (only) were the 4th Largest driver of Plant EFOR in 800mw units in the last 7 years. • Given these statistics AEP is looking for ways to reduce these curtailments.
Project • Loesche approached AEP and it was agreed to install one of their Dynamic Classifiers at Big Sandy Plant on the #21 Pulverizer. • Loesche claimed 15% - 20% increase in thru put at the current fineness or improved fineness at same thru put. • If successful and installed on all mills, this would allow minimal unit load curtailment when one mill is out of service.
Removal of existing classifier • During the fall outage of 2012 the installation / removal began on Pulverizer 21. All the coal piping, shutoff gates and walkways on top of the mill had to be removed to clear the top area and the classifier reject chute was cut loose from the inside. The existing seal air piping for the roll wheels was removed to later be reinstalled going thru the new classifier housing. • Once these items were removed, the top flange of the classifier housing was all that needed to be unbolted to remove the housing and classifier assembly as a whole. Once removed the reject chute was lifted up thru the top opening of the mill. • No other internal parts had to be removed and the large maintenance doors stayed closed on the mill. For safety reasons, the spring tension was released for fear of not knowing what forces could be on a 40 year old housing after removing the top section.
Removal Continued • The removal of the existing classifier and housing had some challenges. The existing trolley beams could not make the lift due to the angle of the pull. Lifting beams had to be fabricated to keep a straight pull on the structure. • The tight clearances were the biggest challenge to overcome. We had to find dimensionally small chain hoist and shackles that were load rated. Once found, there was only 4 inches clearance between the upper and the lower housing. • The yoke seal air piping on the pulverizer next to this one had to be removed to allow for room to lower the old classifier and housing to the ground. There was only a few inches on each side between the two pulverizers when setting on the floor.
Installation • The new classifier was made in two sections. This helped with the installation since the overall height of the new classifier was taller. The lower housing section included the classifier lower cone which hung below the flange line. This required this section to be raised high to clear the housing on the pulverizer. Loesche accounted for these issues in the design and engineering and installed lifting lugs such that the new lifting beams worked on the two new sections.
Installation • The classifier fit perfectly. No modifications were needed. • The ancillary equipment however did need slight modifications. The walkways, platforms and seal air pipe had to be modified in the field to make them fit. Loesche performed a laser survey of the area prior to the project and used it in the design all of the equipment. However, there were still some modifications necessary. Loesche provided quick assistance on correcting these and any other problems or issues that would arise. • Some of the new coal pipe spool pieces were already completely fabricated while some required to be field fit and the flange welded on.
Installation • Due to limiting seal air available from our existing pulverizer seal air system, Loesche provided two seal air fans to provide seal air for the bearing cavity on the classifier; a duty and backup fan. These were sized to provide enough air for any additional classifiers and occupy approximately 6 ft x 10 ft section of floor. • We also had no expansion room in our existing DCS system and limited available power in the local motor control center. Loesche designed and provided a PLC control system, a variable speed drive unit for the classifier motor, a transformer, a motor control section and a HMI for the new classifier. All of these items required approximately 6 ft x 15 ft section of floor. • The new MCC section had to be powered from the 600 VAC switchgear in the 4kv room. Overall there was a considerable amount of cable pulls that had to be made.
Installation / Removal • Overall, the installation and removal went well. There were minor issues that were always quickly resolved. • The total contractor labor was approximately 6000 man hours for both the removal and installation. This is for all crafts; electrical, mechanical, insulators (lead abatement) and the scaffold contractor. • The controls were a bit more difficult. The company that had built and tested the PLC programming logic inadvertently had left simulated points in the programming and did not get all the point names changed to the correct program before shipping. This took several hours to decipher before things worked as they should.
Installation / Removal continued • Reasons for high man hours: 1) First time evolution. 2) This pulverizer has limited access from one side. All coal pipes, platforms and anything lifted had to be coordinated and made from one side. (Any other pulverizer 22 – 26 has access from both sides making coordinating lifting easier.) • Loesche had a service man on site to help oversee the installation, startup and testing during the project. They provided guidance, answered questions and found solutions to any issue. They wanted to prove success as much as we wanted it.
Future Installs • For future installs on the remaining 5 pulverizers, the electrical system would have to be copied 5 times over with the exception of the PLC. The MCC’s could be reduced in foot print but would need to be fed from more than one 600 VAC buss to obtain reliability. This would require several square feet of real-estate. (This may not be required for everyone) • While the seal air fans provided by Loesche are larger than required for the one classifier, consideration should be given to power feeds to provide reliability in the event a 600 volt buss had to be removed from service. • Overall project cost would be reduced. Most engineering and design should be completed. Advanced planning and coordination would reduce labor time since this has now been performed.
Testing • No other internal work or maintenance was performed on this pulverizer to obtain a true test of what the classifier could produce on it’s own. • Once the unit returned to service, testing was performed following the procedure from Loesche. • Testing was conducted before and after the change out to determine what if any improvement was made with the new classifier. • AEPSC, Loesche, REO and plant personnel assisted in the test work using the EUCoalsizer laser probe to perform the fineness testing.
Test continued • The following are the test results:
Testing Conclusion • While the goal was to increase thru put without effecting fineness, it can be seen in the test results this was achieved along with the potential for increased fineness. • This mill was previously limited to approximately 87,000 – 90,000 lb/hr coal thru put due to excessive dribble and primary air limited. There were multiple fires from coal build up both internal in the mill and in the pyrites in the past. • With the Loesche Classifier, we were able to obtain significantly more PA Differential and pass 115,000 lb/hr coal flow with out any dribble while maintaining fineness at pre change out levels.
Conclusion • When the unit returned to service this mill had an original 600 hp motor. While testing at 115,000 lb/hr coal flow, mill amps continued to increase over time. Fearing an overload trip, the mill was reduced to 110,000 lb/hr without mill amperage increasing. This is over a 20% increase in thru put on this mill. • Mill amperage was a limiting factor in the higher RPM trials while determining the improvement in fineness and this is why the faster speeds could not be maintained and allow more thru put. • During our most recent outage, this pulverizer motor has been increased to 700 hp and new testing will be conducted to determine maximum output on the mill and also an optimum speed for the classifier to obtain the best fineness with maximum output.
Conclusion • While the Loesche Classifier did what they promised, other manufactures also make dynamic classifiers. • Other technologies that predict saving time with reduced maintenance, provide increased thru put and improve mill performance need to be looked at and tested. • We (AEP) need to continue to focus on improving pulverizer performance both in output and reduced outages. Remember 286,080 MWH’s is a lot of curtailments and lost revenue.
