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
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
Patented LED fluorometer

9. Corrosion Control

10. Corrosion/ORP Basics Corrosion is an electrochemical process
4/1/2017
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)
(This graph shows the response of adding Sodium sulfite to consume 140 ppb DO at 400ºF (RT pH = 9.2))
We have ORP values on the Y axis - these values are typically expressed as mV
generally we’ll be in the negative value region to control corrosion
And more negative is less corrosive
So – positive ORP values = bad
Negative ORP values = good
More negative ORP values = even better

12. Many Factors Affect the ORP Fingerprint of Each System
4/1/2017
Many Factors Affect the ORP Fingerprint of Each System
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
Chemical
Dissolved oxygen
Oxygen scavenger/passivator chemistry and dosage limitations
Scavenger mixing, residence time
Condensate treatment recycle pH
Process contamination leaks
Corrosion products

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
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
time
Monitoring Phase – AT ORP Response Prior to Control

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

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)
Before Installation
After Installation
Difference
Blowdown Energy Cost
38,147
22,577
15,570
Blowdown Sewer Cost
11,114
6,578
4,536
Make-up Water Cost
10,002
3,198
6,804
Subtotal (Costs)
58,263
32,353
26,911
Net Savings or (Costs), $/yr
26,910

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