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

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Presentation on theme: "Improved Boiler System Operation with Real-Time Chemical Control Debbie Bloom, Nalco Company."— Presentation transcript:

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 2

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 3

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 4

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 6

7 Scale Control

8 Automated Scale Control Utilizes a Stable Inert Trasar 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 8 Patented LED fluorometer Provides a stable inert monitor of system performance

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 11 Reducing Conditions Minimize Corrosion (More Negative ORP)

12 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 13

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 14

15 Opportunities for Energy Savings

16 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 16

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 18

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

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

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

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

23 Energy and Water Savings ($/yr) 23 Before Installation After Installation Difference Blowdown Energy Cost38,14722,57715,570 Blowdown Sewer Cost11,1146,5784,536 Make-up Water Cost10,0023,1986,804 Subtotal (Costs)58,26332,35326,911 Net Savings or (Costs), $/yr26,910

24 Gulf Coast Refinery 24

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

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

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

28 All-Polymer Dosage Controlled by Fluorometer 28 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 29

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 30


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