Making the Transition to PRB Case Study: CSU Martin Drake

1. Making the Transition to PRBCase Study: CSU Martin Drake John Melon, Control Room Operator Colorado Springs Utilities

3. Unit #5 • Riley Balanced Draft Boiler (1960) Capable of Full Load Steam Flow Firing Pulverized Coal or Natural Gas • Three Riley 556E Pulverizers • Fed from Three Riley Drum Feeders • Supplying Six 4A Horizontal Flare Burners each w/14” Coal Head • Design: • S/H Outlet Steam 950F • Steam Flow MCR 425 Klbs/hr @ • 1450 psi Drum / 1300 psi S/H

4. Unit #6 • Babcock & Wilcox Forced Draft, Two-Drum Stirling Type Boiler Capable of Full Load Steam Flow Firing Pulverized Coal or Natural Gas • Three B&W EL-70 Mills Supplying 9 DRB-XCL Burners • Design: • S/H Outlet Steam 955F • Steam Flow MCR 685 Klbs/hr @ 1325 psi • Coal Flow ~ 99,000 lbs/hr total • Primary Air Flow 51-56 Klb/hr per Pulverizer Group • Mill Inlet Temp 595 F • Mill Outlet Temp 135 F

5. Unit #7 • Babcock & Wilcox Forced Draft, Radiant Steam Generator - S/H and R/H - Capable of Full Load Steam Flow Firing Pulverized Coal or Natural Gas • Four B&W EL-76 Mills Supplying 12 DRB-XCL Burners • Design: • S/H Outlet Steam 1005F • Steam Flow MCR 960 Klbs/hr @ 1600 psi • Coal Flow ~152,000 lbs/hr total • Primary Air Flow 66 Klb/hr per Pulverizer Group • Mill Inlet Temp 595 F • Mill Outlet Temp 140 F

6. Reasons to Transition • Reduced Emissions • SO2 • NOx • Reduce LandfilledFlyash • Low Cost, Abundant Fuel Supply • Win/Win Environmentally & Economically

7. Testing & Inspection • Full Load Capableat the Expense of Combustion Efficiency • Challenged by: • High Mill Motor Amps • High Mill dp’s • High CO Levels • As Load Levels Increased, Fineness Decreased Causing CO Levels to Increase

8. Testing & Inspection • Significant Clean Air Testing • Individual Coal Pipes • Deviation between pipes was very small as tested on all but two pulverizers (6A & 7B) • Multiple Classifiers • Stationary and Adjustable • Modified at Various Times Throughout • All to be Replaced

9. Pulverizer Modifications • Purpose • To provide greater fineness control in preparation for low NOx operation when burning Black Thunder Eastern PRB coal while maintaining original MCR steam flow. • Do It Right. Do It Safely.

10. Pulverizer Modifications • Increased Motor Size from 200hp to 300hp • Standard Size • Increased Margin • High Spin Classifiers • High Temperature Configuration • High Moisture Content Required IncreasedHot Air Inlet Temps • Increased Temp Differential Made Grinding Rings More Susceptible to Cracking

11. Post-Modification Results • Increased • Reduced * Results with >99% Through 50 Mesh, >70% Through 200 Mesh

12. Post-Modification Results • Combustion with PRB is generally easy due to high volatility. However, heat absorption into our furnace as designed was difficult. • Greater RH Temps • Attemperation Sprays @ 100% • Due to Either: • More Reflective & Persistent Ash Layer on Waterwalls • Shorter Residence Time in Furnace because of the Greater Overall Gas Weight.

16. Addressing Downstream Issues

21. Addressing Downstream Issues • Resized Attemp Nozzle on RH System • Greater Capacity • Immediate Control was the Goal • Ideally, we will get to where extra capacity is not necessary • Extended Nose Arch from 10’ to 13’ • More Residence Time in Furnace • Better Distribution of Flue Gas as it Enters into the Backpass

22. Addressing Downstream Issues • Over Fire Air • Increase Residence Time • Ensure we are absorbing as much heat as possible into the lower furnace • Target Nox .221 lbs/mmbtu • Sidewall Ports • Lack of Furnace Depth • Sootblowing

26. Dealing with the Ash • Low Ash Coal • Mass of Coal Burned Goes Up • Overall Ash Volume Doesn’t Necessarily Increase • Question is: Does One Change Outweigh the Other? • Martin Drake does not sell the ash, but PRB ash can affect a plant’s sales revenue stream because it may not meet the buyer’s specifications. • Changing that waste stream from a revenue stream to an expense can have considerable impact.

27. Dealing with the Ash • PRB Ash can be very white ash & it can (depending on the alkali constituents) have a greater tendency to: • Slag • Cause furnace plugging, and/or • Reduce absorption through waterwalls • Tendency to Bridge • Unit #5 Last Pass Hoppers • Sonic Horns • Ash Handling Lines

28. Safety & Handling • Reclaim Dust Collector (2012) • Increased pipe size & flow • System runs 24/7: • When not loading is continuously venting any residual CO levels. • New isolation valves are full open when loading to bunkers and partial open when static (8" to 4"). • CO monitoring system (2013) • In both the Reclaim and the Unit Train Unloading System • Increased from 3 detection points to 24. • System and PLC's broken down in to 3 zones. • (Tripperdeck (12), Reclaim system (6), UTUF (6) • Modular System leaves room for more detection points.

29. Safety & Handling • Fire Detection & Prevention • Fire wire at five points on all but one conveyor • Three on the carry side and two on the return side. • Covers all idlers, bearings, motors • Pulverizer Steam InertingSystem • Coal Bunker CO Monitoring

30. Currently • Unit #7 Burner Tuning • Coal and Gas Air/Fuel Curves • CO Optimized • NOx Optimized • Full Load Gas Burns • Unit #6 Combustion Air • Tuning-out a Swing • Unit #5 PRB & Biomass Blending

31. Looking Forward • Venturi Style Measuring Devices • Historically Inaccurate in Highly Turbulent Environments • Due to Configuration of Ductwork it is Economically Unfeasible to not have Turbulent Atmosphere Between PA Fan & Pulverizer • Significant Variances Between Installed Air Measuring Devices at Lower Loads/Flows • Suggests Future Upgrades • Averaging Air Flow Pitot Tubes or Measurement Array System • Subsequent Mill Re-tuning for Optimal Operation

33. Making the Transition to PRB John Melon Control Room Operator (719) 668-8585 jmelon@csu.org