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Improved Boiler System Operation with Real-Time Chemical Control

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Presentation on theme: "Improved Boiler System Operation with Real-Time Chemical Control"— 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

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

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