B. BFW Chemistry & Control

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Feed Water Chemistry & Control

Nalco Indonesia ~ Power Industry Seminar Pullman, Central Park ~ Jakarta 13-14 June 2012

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Agenda 

Key Issues



Guidelines for Condensate, Feed Water, and Steam Chemistry Control

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Practical considerations in application and control

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New Technology

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Steam Cycle

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Key Issue #1 : Steam Turbine Requirements 

Steam purity specs can be stringent!

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Industry experts differ on specific allowed limits.  Different manufacturers have different limits  Limits may depend on design, service, age of unit

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Limits vary with the boiler treatment selected.

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

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Na and SiO2 are more specific measures of contamination.  Cl- and SO4 measurement important, but not commonly found online

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Critical Steam Cycle Chemistry Parameters 

Boiler and feedwater chemistry driven by steam purity requirements

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Turbine/Feedwater  Cation conductivity (indirect measure)  Sodium (NaOH)  Silica  Chloride (HCl)  Sulfate (H2SO4)  Organic acids

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Sources of Chemicals in Steam 

Volatile Carry Over  Higher pressure = greater volatility  Cu an issue at > 2400 psi (160 bar)

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Mechanical Carry Over  Occurs in all boilers all the time  Drops contain all boiler water solids

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Contamination via Attemperation  Shortcut of feedwater to turbine

Cu(OH)2 H2SO4

SiO2

NaOH

Na3PO4

NaCl

HCl

Volatile

Mechanical

Key Issue #2 : Cation (Acid) Conductivity 

Conductivity after strong acid ion exchange

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Neutral salts become strong acids

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Magnifies conductivity 3-5 times Cl-

and SO4

2-

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Targets

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“De-gassed” cation conductivity uses a small boiler or N2 sparging to strip off CO2 from carbonic acid

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Na, Ca, Mg : Cl salts to HCl

Na, Ca, Mg : SO4 salts to H2SO4

Na, Ca, Mg : HCO3 salts to H2CO3

Also removes amine and ammonia, but not organic acids

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. Parameter Specific Cond, mS/cm

EPRI Std < 0.1

Cation Cond, mS/cm

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VGB Std < 0.2

Na, Cl, SO4, ppb

5000 mg/kg

370 mg/kg

Acute dermal LD50 - rabbits

>2000 mg/kg

420 mg/kg

Primary eye irritation - rabbits (24 hr) Primary dermal irritation - rabbits

Non-irritating (0.33/110)

Irritating (26.5/110)

Mild irritant (0.23/8.0)

Severe irritant (7.0/8.0) May be corrosive. (Most suppliers ship as a corrosive liquid) 34

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References of Nalco 1250/Elimin-Ox

Steam & Condensate Equipment Steam Turbine – Advantages of Amines 

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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 neutralizeI organic acids in this particular area

Species

Relative V/L

Destination

Carbonic Acid

High

Final condensation

Acetic & Formic Acid

Low

Early stage of condensation

Ammonia

High

Final condensation

Low or high

Early & final stage of condensation

Amines

(initial condensation)

Nalco 5711 

Minimum contribution of cation conductivity. Deliver