Improved Boiler System Operation with Real-Time Chemical Control

1. Improved Boiler System Operation with Real-Time Chemical Control Debbie Bloom, Nalco Company

2. A Need for Measureable Environmental Return on Investment … • Increasingly competitive marketplace • Extend equipment life • Reduce fuel and water costs • Optimize operational labor costs • Increased environmental awareness • Corporate/government initiatives to • Reduce greenhouse gas emissions • Fuel and water consumption

3. Primary Water-Related Challenges For an Operating Boiler • Mineral Scale • Dissolved minerals exceed solubility • Typically magnesium, calcium, iron, silica based • Impedes heat transfer • Commonly treat with phosphate, polymers, chelants and by improving feedwater quality • Corrosion • Causes metal loss, perforation of equipment surfaces • Causes iron deposits in boiler • Commonly treat with oxygen scavengers and pH control agents

4. Traditionally, scale and oxygen control chemicals have been measured and controlled in the boiler water • Analytical detection not low enough for feedwater • Sample already existed • Variability of the feedwater system

5. Until Recently, Control of Boiler Chemistry was Test and Adjust • Gather sample • Test • Adjust chemical feed • “Repeat as necessary”

6. Why Feedwater instead of Boiler Water? • A boiler typically has a very long holding time • BD sample has little direct correlation to the feedwater at any time • Every boiler will have unique lag time • Based on design, feedwater quality and operating conditions • Lag time is always VERY LARGE relative to dosage control

7. Scale Control

8. Automated Scale Control Utilizes a Stable Inert Trasar • Provides a stable inert monitor of system performance Patented LED fluorometer • Inert tracer chemistry survives in boiler system (FW & BW) • Good for boiler systems up to 1000 psig/69 barg • Works for both on-line and grab sample monitoring • Provides indication of carry-over if seen in the condensate • Provides positive feedback that chemical treatment is fed

9. Corrosion Control

10. Corrosion/ORP Basics Corrosion is an electrochemical process Corrosion involves both oxidation and reduction (REDOX) reactions ORP = Measures the net voltage (mV) produced by all REDOX reactions taking place ORP is a good indicator of feedwater corrosion

11. Reducing Conditions Minimize Corrosion(More Negative ORP)

12. Many Factors Affect the ORP Fingerprint of Each System • Chemical • Dissolved oxygen • Oxygen scavenger/passivator chemistry and dosage limitations • Scavenger mixing, residence time • Condensate treatment recycle • pH • Process contamination leaks • Corrosion products Mechanical • System design metallurgy • Deaerator tray alignment • Feedwater heater • Economizer leaks • Pump leaks Operational • Deaerator venting, steam supply • Steam load changes • Start up and shut down • Condensate vs. make up ratio • Process leaks • Temperature • Feedwater demand • Economics

13. Comparison of RT ORP to AT ORP • Room temperature ORP probes: • Can become polarized (inaccurate) over time • Are less sensitive • Require cooling of the water sample • Changes water chemistry • Lag time reduces responsiveness

14. Comparison of AT ORP to Conventional Measurement and Control Techniques • AT ORP: • Addresses multiple MOC corrosion mechanisms simultaneously • Works with any metallurgy • Works with any scavenger/passivator chemistry • AT ORP is much more sensitive • AT ORP has a fast response

15. Opportunities for Energy Savings

16. Opportunities for Energy Savings • Dosage adjusted in real-time, minimizing potential for scale • Overdosing of solids-contributing chemicals eliminated – feed just enough • Sulfite • Caustic • Accurate cycles determination and optimization

17. Midwestern University

18. Background • 3 water tube boilers with economizers, 175-psig • Natural gas fired • Softened make-up water • Steam supplies absorption chillers, heat, and reheat for campus, hospital, and laboratory buildings • Polymer fed relative to feedwater flow/steam load • Sulfite fed to maintain desired boiler water residual • Boiler blowdown controlled manually based on conductivity

19. Manual Control Leads to Human Error Monitoring Phase – AT ORP Response Prior to Control time

20. % Sulfite Pump Output AT ORP Maintains Desired Feedwater Reductant Levels to Minimize Corrosion AT ORP (mV) Time (2 weeks)

21. Before / After Improvement in Scale Inhibitor Feed Feedwater Product (ppm)

22. Scale Inhibitor vs. Steam Flow Feedwater Product (ppm) Product Pump Out %

23. Energy and Water Savings ($/yr)

24. Gulf Coast Refinery

25. Before MOC Review of System . . . Only 45% of feedwater hardness readings were in control

26. Blowdown was Done Manually Boiler cycles ranged from 2 to 22

27. After - Feedwater Quality Improved Hardness was in target zone 89% of time

28. All-Polymer Dosage Controlled by Fluorometer Can be automatically increased based on input from hardness analyzer Product Dosage (ppm)

29. Improved Cycles Control will Save an Estimated $406k in Water and Energy

30. Summary • Economic challenges require a fresh look at ways to reduce operating costs, protect asset life, and improve productivity • Numerous benefits to feedwater automation including: • Improved asset preservation, increase boiler system reliability • Optimized scale and corrosion control, including optimized feed of internal treatment and oxygen scavenger • Process visibility – data management • Real time, on-line communication