Improved Boiler System Operation with Real-Time Chemical Control

Debbie Bloom, Nalco Company

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

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

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

Until Recently, Control of Boiler Chemistry was Test and Adjust

• Gather sample

• Test

• Adjust chemical feed

• “Repeat as necessary”

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

SiteBoiler Type

Pressure psig/barg

Cycles of Concentration

First 1% (hrs)

Half-life or 50%

(hrs)Last 1%

(hrs)

Campus A Firetube 125 / 9 10 0.1 4 25

Campus A Watertube 125 / 9 10 0.1 6 41

Chemical Co. B HSRG 1000 / 69 29 0.1 10 67

Chemical Co. B Power 1000 / 69 29 0.3 18 120

Paper Mill C Recovery 1250 / 86 45 0.2 16 109

Paper Mill C Recovery 1250 / 86 45 0.4 26 174

Holding Time

Scale Control

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

Corrosion Control

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)

-600

-400

-200

0

200

400

0.1 1 10 100 1000

OR

P (

mV

) 40

0F, 2

04C

Dissolved Oxygen (ppb)

Oxidizing

Reducing

Mo

re R

edu

cin

g

-600

-400

-200

0

200

400

0.1 1 10 100 1000

OR

P (

mV

) 40

0F, 2

04C

Dissolved Oxygen (ppb)

Oxidizing

Reducing

Mo

re R

edu

cin

g

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

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

-100

-600

-700 -600

-500

-400

-300

-200

-100

0

-200

-300

-400

-500AT O

RP

(m

v) R

T O

RP

(mv)

Time (hrs)

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

Opportunities for Energy Savings

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

16

Midwestern University

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

Manual Control Leads to Human Error

19time

Monitoring Phase – AT ORP Response Prior to Control

AT ORP Maintains Desired Feedwater Reductant Levels to Minimize Corrosion

20

% S

ulfi

te P

um

p O

utp

ut

Time(2 weeks)

AT O

RP (m

V)

Before / After Improvement in Scale Inhibitor Feed

21

Feed

wat

er P

rodu

ct (p

pm)

Scale Inhibitor vs. Steam Flow

22

Fe

edw

ater

Pro

duct

(ppm

)

Prod

uct P

ump

Out

%

Energy and Water Savings ($/yr)

23

Before Installation

After Installation Difference

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

Gulf Coast Refinery

24

Before MOC Review of System . . .

25

Only 45% of feedwater hardness readings were in control

Blowdown was Done Manually

26

Boiler cycles ranged from 2 to 22

After - Feedwater Quality Improved

27

Hardness was in target zone 89% of time

All-Polymer Dosage Controlled by Fluorometer

28

Can be automatically increased based on input from hardness analyzer

Prod

uct D

osag

e (p

pm)

Improved Cycles Control will Save an Estimated $406k in

Water and Energy

29

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