1

Feed Water Chemistry & Control

Nalco Indonesia ~

Power Industry Seminar

Pullman, Central Park ~ Jakarta

13-14 June 2012

Agenda

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Key Issues

Guidelines for Condensate, Feed Water, and Steam Chemistry Control

Practical considerations in application and control

New Technology

Steam Cycle

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Key Issue #1 : Steam Turbine Requirements

4

Steam purity specs can be stringent!

Industry experts differ on specific allowed limits.

Different manufacturers have different limits

Limits may depend on design, service, age of unit

Limits vary with the boiler treatment selected.

Cation conductivity is principle measure in most plants (< 0.15, < 0.2, < 0.3, < 0.8 mS/cm as cation conductivity)

Na and SiO2 are more specific measures of contamination.

Cl- and SO4 measurement important, but not commonly found on-line

Critical Steam Cycle Chemistry Parameters

5

Boiler and feedwater chemistry driven by steam purity requirements

Turbine/Feedwater

Cation conductivity (indirect measure)

Sodium (NaOH)

Silica

Chloride (HCl)

Sulfate (H2SO4)

Organic acids

Sources of Chemicals in Steam

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Volatile Carry Over

Higher pressure = greater volatility

Cu an issue at > 2400 psi (160 bar)

Mechanical Carry Over

Occurs in all boilers all the time

Drops contain all boiler water solids

Contamination via Attemperation

Shortcut of feedwater to turbine

SiO2

NaOH

HCl

H2SO4

Cu(OH)2

NaCl Na3PO4

Volatile Mechanical

Key Issue #2 : Cation (Acid) Conductivity

Conductivity after strong acid ion exchange

Neutral salts become strong acids

Magnifies conductivity 3-5 times

Targets Cl- and SO42-

“De-gassed” cation conductivity

uses a small boiler or N2 sparging

to strip off CO2 from carbonic acid

Also removes amine and

ammonia, but not organic acids

Na, Ca, Mg : Cl salts to HCl

Na, Ca, Mg : SO4 salts to H2SO4

Na, Ca, Mg : HCO3 salts to H2CO3

CO2 to H2CO3

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Key Issue #3 : High Purity Make Up

Purity

Generally must be as good as feedwater.

EPRI specifications are a good target for modern plants.

Deaeration

Few plants deaerate make up or condensate storage tanks, or hot well during standby.

Technically feasible – from 7 ppm to 100 ppb O2

Vacuum deaeration, steam sparging, nitrogen sparging, membrane deaeration

Parameter EPRI Std VGB Std

Specific Cond, mS/cm < 0.1

Cation Cond, mS/cm < 0.2

Na, Cl, SO4, ppb < 3

Silica, ppb < 10 < 20

TOC, ppb < 300

Key Issue #4 : Condensate and Feed Water Quality

Condensate

Cogen plants must guard against contamination from steam host

Feedwater

Feedwater used for attemperation must meet steam purity specs.

- The LP section of most HRSGs is upstream of attemperation, and is treated as feedwater. (AVT)

Feedwater purity and consistency drive treatment selection.

- Minimizing corrosion and corrosion product transport is critical.

- FW heaters corrode on both shell and tube side!

EPRI Guidelines are excellent targets, but:

May be difficult for older plants to meet without capital investment in system upgrades.

All plants should develop unit specific guidelines, taking design, pressure, service, and water quality into account.

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Key Issue #5 : Control of Dissolved Oxygen

EPRI research and field study led to reduction in O2 target

From < 20 ppb at CPD to < 10 ppb at CPD

For all treatment programs

Required for corrosion control

Overfeed of passivator is not a good option

Too strong of a reducing environment contributes to FAC

Excess hydrazine and carbohydrazide produce ammonia

Excess organic passivators can add to TOC, organic acids

EPRI recommends / Nalco concurs:

Limit air inleakage – have active detection and repair program

Deaerate make up

Nitrogen cap hotwell for standby

Corrosion ~ Iron ~ Deposition ~ Corrosion 11

For high purity boiler systems, iron is the focus of performance

CORROSION leads to IRON

IRON leads to DEPOSITION

DEPOSITION leads to CORROSION (again) & OVERHEAT

Corrosion ~ Iron ~ Deposition ~ Corrosion

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NaOH

NaOH

Fe3O4 porous deposit

Water In

Steam Out

NaOH

NaOH

Magnetite

Chemically Influenced BTFs

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13

2001 survey results

1997 survey results

Organizations having chemically influenced BTFs

81% 61%

•Hydrogen damage 57% 37%

•Acid phosphate corrosion 25% 17%

•Corrosion fatigue 45% 43%

•Pitting 40% 7%

•Stress corrosion cracking 28% 18%

•Caustic Gouging 11% 11%

Source: 2002 EPRI Study, “ Priorities for Corrosion R&D”

Boiler Tube- Hydrogen Damage

14

14

Key Issue #6 : Metal Passivation

Passivation:

Iron oxides to magnetite (reducing environment)

- Passivation Reactions: Hydrazine

N2H4 + 6Fe2O3 4Fe3O4 + N2 + 2H2O

N2H4 + 4CuO 2Cu2O + N2 + 2H2O

- Passivation Reactions: Carbohydrazide

12 Fe2O3 + (N2H3)2CO --- 8Fe3O4 = 3H2O + 2N2 + CO2

8CuO + (N2H3)2CO --- 4Cu2O + 3H2O + 2N2 + CO2

Or magnetite / hematite mix (neutral or oxidizing environment)

Copper oxides to cuprous form (Cu2O)

- Less protective cupric oxide surfaces have 30 times the Cu release!

- Cuprous oxide will oxidize to cupric within 10 hours in O2 environment!

Iron Oxide Passive Layer ~ Reducing Environment

Source: EPRI, Cycle chemistry Guidelines for Fossil Plants, Phosphate Continuum and Caustic Treatment, 2004.

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Iron Oxide Passive Layer ~ Neutral-Oxidizing Environment

Source: EPRI, Cycle chemistry Guidelines for Fossil Plants, Phosphate Continuum and Caustic Treatment, 2004.

Key Issue #7 : Flow Accelerated Corrosion

Over half of utilities report FAC

Two failure mechanisms – single-phase and two-phase

Occurs in

- Condensate and Feedwater

- Piping around BFP

- Piping to Economizer Inlet Header

- Economizer Inlet Header Tubes

- Deaerators

- Heater Shells and Drains

- Steam Turbine Exhaust

- LP Evaporators

Second-most common failure mechanism

What is FAC ?

Dissolving of protective magnetite layer (Fe3O4)

Influenced by several factors:

Velocity

Flow geometry

Two phase flow

Temperature

pH

Oxygen concentration

Overfeed of Passivators

Metallurgy

that contribute to magnetite solubility

Factors Affecting FAC - Temperature

Extremely temperature dependent:

Occurs in HRSG IP & HP Economizer tubes & headers, and in LP evaporators & drums.

Occurs in cold re-heat return lines, FW heater drip lines.

Tendency for

FAC

Saturation

Pressure

Deg C Deg F psia

Moderate Range 80 176 7

150 302 70

Severe Range 150 302 70

180 356 146

Moderate Range 180 356 146

230 446 409

Temperature

Factors Affecting FAC – pH

Factors Affecting FAC

~ Oxidizing & Reducing Environment

Source: EPRI, Cycle chemistry Guidelines for Fossil Plants, Phosphate Continuum and Caustic Treatment, 2004.

FAC Solution

Material upgrade to 1 or 2% chrome

Maintain pH in proper range with ammonia or amines

- Higher end of range is better!

- Pay attention to amine distribution ratio in multi-pressure HRSGs

Avoid a highly reducing environment!

- Do not allow excess feed of reducing agents!

- Cycling units: do not feed high levels of reducing agent to compensate for

high O2 at start up.

- Monitor feedwater ORP, consider control of passivator to ORP

Monitor with soluble iron tests before and after suspect areas

- Need proper sample points!

Key Issue #8 : Use of Organic Amines & Passivators

EPRI & VGB recommend Ammonia and Hydrazine

Stuttgart Conference on Organics – June 2005 Co-Sponsored by EPRI and PowerPlant Chemistry

Organic Amines

- Used safely for many years

- No factual evidence of contribution to turbine corrosion

- Some breakdown to organic acids, contributing to cation conductivity

- Ammonia counter ion neutralizes the acids

- Many feel okay to continue use

Organic Passivators

- Some breakdown to organic acids, contributing to cation conductivity

- No alkaline counter ion

- Most believe should not use

Carbohydrazide

- Produces CO2 on breakdown. Excess carbohydrazide will produce ammonia.

- CO2 not believed to cause any significant corrosion in steam cycle

- Estimate that 20 ppb Carbohydrazide contributes 10 ppb CO2, and creates 0.08 mS/cm cation conductivity from the CO2.

- Most believe carbohydrazide is okay to use

Organic Amine & Passivator – CO2 Myth

CO2 is not solid so it won’t be deposited in the LP blade and creating localized acidic condition

It is required ~ 200 ppb of CO2 to drop the pH of pure water from 6.5 to < 6.0

At low pressure, V/L of CO2 is quite the same with Ammonia and higher than neutralizing amines. It is mean all of CO2 will be neutralizing by proper dosing of ammonia/amines.

There are some literatures from independent parties that clearly explained that CO2 won’t depress pH of initial condensation in the level that we commonly found boiler operation (<2 mS/cm) and when the alkalizing agent is exist (Robert Svoboda and Alstom)

Nalco 1250 (ELIMIN-OX)

• Active Content : CARBOHYDRAZIDE (CHZ)

• ALL VOLATILE & NON-SOLIDS Contribution in Steam Cycle

• It is used as a METAL PASSIVATOR

• Much SAFER than HYDRAZINE

• NOT A SUSPECT CARCINOGEN

• Slight increase in cation conductivity from CO2 20 ppb CHz contributes 10 ppb CO2, which contributes 0.08 mS/cm cation conductivity (But 0 degassed cation conductivity)

NH2-NH-C-NH-NH2

O II

CARBOHYDRAZIDE

MECHANISM REACTION of ELIMIN-OX

At LOW Temp.

(T 1350C)

1 ppm Elimin-Ox

29 ppb (,or

0.029 ppm) CO2

& NO IMPACT to

STEAM & CON-

DENSATE

corrosivity

Practically, it is very simple to check @ BFW sample, as residual of

10 – 30 ppb (as N2H4) ~ local (site) BFW sampling w/t T > 1800C

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Passivation Better than Blank

at All Temperatures

Temperature (oF)

Incr

easi

ng

Pass

ivati

on

*

*

* *

Blank Carbohydrazide Methlyethylketoxime

150 200 250 300 350 400

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Passivation Better than Blank

at High Temperatures

* Blank Hydrazine Erythorbic Acid

Temperature (oF)

Incr

easi

ng

Pass

ivati

on

150 200 250 300 350 400

*

*

*

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Passivation Equal to Blank

* Blank Sulfite DEHA Hydroquinone

* *

*

Temperature (oF)

Incr

easi

ng

Pass

ivati

on

150 200 250 300 350 400

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Feedwater Iron Reduction in 1500 psig boiler

with ELIMIN-OX

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Feedwater Copper Reduction in 1500 psig boiler

with ELIMIN-OX

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Reaction and/or Breakdown Products

Chemical/Formula % C (wt.)

Reaction and/or Breakdown Products

Hydrazine

N2H4

0 Nitrogen, water, ammonia

Carbohydrazide

(N2H3)2CO

13.3 Hydrazine, nitrogen, water, ammonia, carbon dioxide

Hydroquinone

C6H4(OH)2

65.5 Benzoquinone, light alcohols, ketones, low molecular weight species, carbon dioxide

Diethylhydroxylamine

(CH3CH2)2 NOH

53.9 Acetaldehyde, acetic acid, dialkylamines, ammonia, nitrate, nitrite

Methylethylketoxime (CH3)(CH3CH2)C=NOH

55.2 Methylethylketone, hydroxylamine, nitrogen, nitrous oxide, ammonia, carbon dioxide

Erythorbic Acid

C6H8O6

40.9 Dihydroascorbic acid, salts of lactic and glycolic acid, carbon dioxide

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Comparison of Acute Toxicology of

ELIMIN-OX and 35% Hydrazine

Study Performed ELIMIN-OX 35% Hydrazine

Acute oral LD50 -rats

>5000 mg/kg 370 mg/kg

Acute dermal LD50 - rabbits

>2000 mg/kg 420 mg/kg

Primary eye irritation - rabbits

(24 hr)

Non-irritating (0.33/110)

Irritating (26.5/110)

Primary dermal irritation - rabbits

Mild irritant (0.23/8.0)

Severe irritant (7.0/8.0) May be corrosive. (Most

suppliers ship as a corrosive liquid)

References of Nalco 1250/Elimin-Ox

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Steam & Condensate Equipment Steam Turbine – Advantages of Amines

If not neutralized, organic acids may drop the pH in initial condensation zone & cause corrosion in steam turbine

Low V/L Amine is a better choice than NH4OH to neutralize organic acids in this particular area

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Species Relative

V/L

Destination

Carbonic

Acid

High Final

condensation

Acetic &

Formic Acid

Low Early stage of

condensation

Ammonia High Final

condensation

Amines Low or

high

Early & final

stage of

condensation

(initial condensation)

Nalco 5711

Minimum contribution of cation conductivity. Deliver <0.2 mS/cm cation conductivity in system with no contamination (0.1-0.3 mS/cm lower than amine available in the market)

Containing low V/L amine that will increase the pH in early condensation zones in the LP turbine, feedwater heaters and extended steam distribution system

Low V/L amine will also improve pH in the LP section of multi pressure HRSG and minimize potential of FAC

Increase the pH with relatively same dosage with 19% NH3

Has higher boiling point. Safer to handle, easier to pump without off gassing, and produces fewer odor

Reference : PT. Freeport Indonesia

N5711 Dosage vs Ammonia

Amine Product Concentration vs. pH in pure water

-

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

8.6 8.7 8.8 8.9 9.0 9.1 9.2 9.3 9.4 9.5 9.6

Condensate / FW pH

Am

ine P

rod

uct,

mg

/L

19% NH3

1800

CA-300C

356

5711

Condensate, FW, and Steam Guidelines

Parameter Indus-

trial PC(L) PC(H)

Caustic

Treat AVT(O) AVT(R) OT

pH (all steel)

(Cu alloys)

9.0–9.6

8.8-9.2

9.2–9.6

9.0-9.3

9.2–9.6

9.0-9.3

9.2–9.6

9.0-9.3 9.2–9.6

9.2–9.6

9.0-9.3

D 9.0–9.6

O 8.0-8.5

Cat Cond, mS/cm < 0.3 < 0.2 < 0.3 < 0.2 < 0.2 < 0.2 < 0.15

Na, Cl, SO4 ppb < 5 < 2 < 3 < 2 < 2 < 2 < 2

Silica, ppb < 20 < 10 < 10 < 10 < 10 < 10 < 10

Fe, ppb @EI < 10 < 2 < 2 < 2 < 2 (1) < 2 < 2 (0.5)

Cu, ppb @EI < 10 < 2 < 2 < 2 < 2 < 2 < 2

Oxygen, ppb

@CPD < 20 < 10 < 10 < 10

Oxygen, ppb @EI

< 10 < 10 < 5 (< 2)

D 30-50

O 30 -

150

Reducing Agent yes no yes no

ORP, mV @DA In +/- 50

-300 to -

350

100 to

150

EPRI Guidelines

Condensate, FW, and Steam Guidelines

Parameter Indus-

trial PC(L) PC(H)

Caustic

Treat AVT(O) AVT(R) OT

pH (all steel)

(Cu alloys)

9.0–9.6

8.8-9.2

9.2–9.6

9.0-9.3

9.2–9.6

9.0-9.3

9.2–9.6

9.0-9.3 9.2–9.6

9.2–9.6

9.0-9.3

D 9.0–9.6

O 8.0-8.5

Cat Cond, mS/cm

W/ organic amine < 0.3

< 0.6

< 0.2

< 0.4

< 0.3

< 0.6

< 0.2

< 0.4

< 0.2

< 0.4

< 0.2

< 0.4 < 0.15

Na, Cl, SO4 ppb < 5 < 2 < 3 < 2 < 2 < 2 < 2

Silica, ppb < 20 < 10 < 10 < 10 < 10 < 10 < 10

Fe, ppb @EI < 10 < 2 < 2 < 2 < 2 < 2 < 2

Cu, ppb @EI < 10 < 2 < 2 < 2 < 2 < 2 < 2

Oxygen, ppb

@CPD < 20 < 10 < 10 < 10

Oxygen, ppb @EI

< 10 < 10 < 5

D 30-50

O 30 -

150

Reducing Agent yes

Yes, if

cycling yes no

ORP, mV @DA In +/- 50

-250 to -

350

100 to

150

NALCO Guide for Implementation

The Nalco Latest Technology to

Monitor/Control Corrosion Tendency of Feedwater Systems

What is ORP ?

Corrosion = REDOX Reactions

REDOX Reactions Electron Flow

Electron Flow = ORP (Oxidation Reduction Potential)

ORP = bulk FW corrosivity ORP indicates the potential of

bulk water to corrode

ORP provide the best way to control BFW corrosion stress

MAGNETITE

Fe

MAGNETITE

BLACK OXIDE

O2 OH-

Precipitation of Red Oxide H2

Fe2O3

Reduction of Oxygen (CATHODE)

Precipitation of Black Oxide (CATHODE)

Oxidation and Hydrolysis

Hydrolysis of Dissolved Iron

lowers pH

Acid Pit Solution with Lower Oxygen

Content

Oxidation of Iron ANODE

o

o

o

o

FeOH++ + Fe(OH)+2

e-

o

Fe3O4

H++FeOH+

Fe+2

Evolution of Hydrogen (CATHODE)

o RED OXIDE

Corrosion and corrosion product transport varies

significantly in condensate and feedwater systems.

Corrosion varies with:

Metallurgy

Flow velocity (FAC)

Temperature

pH

Dissolved oxygen

Conductivity

Stability of oxide layer / passivation

Corrosion product transport varies with:

Load / flow velocity

Expansion / contraction

Vibration

Base Load

Cycling Two Shifting

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Monitor corrosion stress with

At Temperature ORP

(AT ORP)

Monitor corrosion product

transport with

Chemtrac Particle Monitor

Nalco, the logo, 3D TRASAR, and AT ORP are trademarks of Nalco Company.

Chemtrac is a trademark of Chemtrac Systems, Inc.

ORP1 and At Temperature ORP (AT ORP)

ORP correlates to the corrosion stress of the aqueous environment

More oxidizing - can be more corrosive

Potential difference between measuring and reference electrodes

More reducing – can be more passive

ORP is influenced by temperature, pH, O2, dissolved solids, etc.

RT ORP is measured on a cooled sample at room temperature.

AT ORP is measurement of ORP at the temperature and pressure of the condensate / feedwater system.

Greatly improves sensitivity and response. Allows AT ORP to be used for feedback control.

Development of AT ORP has been an industry goal.

Nalco is the first to develop a practical AT ORP system.

Developed by Dr. Peter Hicks of Nalco. Work began in 1992, commercial production from 2008.

Over 50 AT ORP units currently installed in Power plants globally.

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1. ORP and Oxidation / Reduction Potential are used in this presentation to

have the same meaning as Redox Potential.

+

0

-

EPRI Cycle Chemistry Guidelines for Fossil Plants:

Phosphate Continuum and Caustic Treatment, Jan 2004,

Appendix B.

“Thus ORP should be used to control the oxidizing power of the feedwater in all-ferrous systems or, and more importantly, the reducing power of the feedwater in mixed-metallurgy feedwater systems.”

“The future direction should be to develop the technology to measure ORP in-situ in feedwater, and to extend the mixed-potential model for use at the elevated temperatures, where components are actually in contact with high temperature water, such as in the boiler.”

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Advanced Monitoring: At Temperature ORP

Oxidation / Reduction Potential (ORP) can now be measured and controlled in condensate and feedwater systems:

At system temperature and pressure.

On-line in real time.

To make corrosion events visible.

To allow the plant to correlate corrosion stress to plant operational and chemistry changes.

To respond with appropriate magnitude and sensitivity for feedback control.

To control chemical feed to maintain the system within an AT ORP control specification range.

- Reducing or oxidizing agent

- Feed on demand and eliminate over or under feed.

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Nalco Europe AT ORP

Control Equipment

Why is it important?

AT ORP can help the plant to maintain a more

consistent oxidation state on the metal surfaces.

Reduce condensate / feedwater system corrosion

Extend feedwater heater life

Reduce FAC in LP section of HRSGs

Reduce corrosion product deposition in boilers

Reduce boiler tube failures

Reduce boiler start up chemistry holds

Reduce frequency and duration of boiler chemical cleaning

Prevent turbine efficiency loss from deposition of corrosion products (Cu, Fe)

Lower heat rate, higher generation

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AT ORP Monitoring and Control Equipment

Control PLC,

Communications

AT ORP Electrode

Optional Sample

Conditioning

EPBRE (External Pressure

Balanced Reference

Electrode)

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AT ORP Electrodes: Pt measuring electrode, Ag/AgCl Reference Electrode

Sensor design limits

133 bar, 260 oC

Sample: 250-500 ml/min

Typical install is after condensate heating, but before feedwater pump.

Installation (prioritized)

Deaerator inlet or LP drum inlet

Condensate after chemical feed

LP drum or other point of interest

Existing sample may be routed through AT ORP and then to:

Sample panel instruments

Sample conditioning and Particle Monitor or drain

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Advanced Monitoring : Chemtrac® Particle Monitor

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• Corrosion product released in “crud bursts”.

– Occur every time there’s a thermal,

chemical, or hydraulic shock to the system.

– Usually invisible, as not monitored on line.

• On-line monitoring makes visible

• Particle monitor helps to:

– Correlate crud bursts to specific events.

– Correlate particle counts to ppb iron levels.

– Correlate particle counts to AT ORP.

– Correlate to metal passivation over time.

Introducing:

Nalco Corrosion Stress Monitor

Nalco Corrosion Stress Monitoring (NCSM)

with @T ORP Technology

What Types of System Stresses NCSM

can address ?

Mechanical Dearator Performance

Pump Leaks

Operational Load changes

Startup and shutdown

Condensate flow

Makeup flow

Process leaks

Temperature

Chemical Dissolved oxygen

(All) Oxygen scavenger/ passivator dosage

pH

Condensate treatment recycle

NCSM

What Types of Corrosion

NCSM can Minimize ?

Oxygen Pitting Corrosion

Flow Accelerated Corrosion (FAC)

NCMS is superior to conventional

measurements

Feature NCSM Scavenger

Residual DO Test DO Monitor

Corrosion

Monitor RT ORP

Response

Time V. Fast Slow Slow Med Slow Slow

Sensitivity V. High Med Med Med Poor Low

Accuracy High Med Med High Poor Low

Precision High Med Med High Poor Low

Dosage

Control High Poor Poor Poor Poor Poor Corrosion

Control High Poor Poor Med Poor Poor

NCSM Respond to Small Increase of

Dissolved Oxygen

NCSM Responds Air In Leakage in

Condensate Pump

NCSM Responds to Small Changes of

pH/Amine Feed Problem

Nalco Corrosion Stress Monitoring (NCSM)

3DTfB for Power

Nalco 3DT Corrosion Stress Monitoring (NCSM) Package

One @ T ORP controller per boiler, 2 probes each

One Particle Monitor per boiler, w/ 2 sensors

Nalco analytical support program

Nalco service / consulting support program

NCSM with

Nalco 3D TRASAR Platform Technology

Measure

Communicate

Detects

Response

Measure

Communicate

Detects

Response

NCSM with

Nalco 3D TRASAR Platform Technology

Control Your Boiler 24/7

from Anywhere ….

Thank You