Essentials for a sound boiler water treatment program

Essentials for a Sound Boiler Water Treatment Program Presented by Steve Connor & Debbie Bloom April 23, 2014

Presenter

Presentation Notes

Note: This presentation includes a full script under separate cover…

Mechanical Aspects

What needs to be removed from

the water?

Most Economical Long-Term Approach

Tolerances are Based on

Pressure & Temperature

Chemical Aspects

The Necessity of Water Treatment

Today’s Topics

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Essentials for a Sound

Boiler Water Treatment Program

Boiler Water Treatment

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Water is an excellent heat transfer medium, but it must be properly treated

in both steam and hot water systems or serious problems will ensue, robbing

energy and reducing the life of the asset.

Boiler Water Treatment

Steam Systems Hot Water Systems

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Necessity of Boiler Water Treatment

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• Scaling • Porous Deposition • Corrosion • Efficiency Loss • Life of the Asset • Steam Quality

• % moisture • Steam Purity

• Silica • Sodium ion

What Needs To Be Removed

Dissolved Minerals • Hard Scale Formers

• Calcium • Magnesium

• TDS • Calcium • Magnesium • Sulfate • Sodium • Silica • Chloride • Alkalinity

• Dissolved Gas • Free Oxygen • Free Carbon Dioxide

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Waterside Scale

Waterside Corrosion

Tolerances are Based on Pressure & Temperature

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Feed Water Boiler Water Oxygen Silica Iron & copper Total Alkalinity Total Hardness Free OH Alkalinity pH Specific Conductance Non-Volatile TOC (Total Organic Carbon)

Oily Matter ASME Guidelines:

Broken down by feed water and boiler water, and then by firetube and watertube boilers.

Water Constituent Tolerance: 0-300 operating psig

Mechanical Chemical

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Chemical Treatment Only • Phosphate Treatment • Polymers • Hybrid

Phosphonate/Polymer • Sulfite Treatment • Precise Control &

Monitoring • Extensive Blowdown • Wastes Water, Chemicals

& BTU’s

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Mechanical Chemical

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Mechanical Removal

Removes • Calcium • Magnesium

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Water Softener

(Resin Tanks)

Brine Tank

Cation Resin Bead Composition

Chemically engineered polystyrene beads (resin) with an affinity for positive ions.

Will exchange weaker positive ions for stronger positive

ions • Sodium (Na+) for Calcium (Ca++) and Magnesium (Mg++)

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Presenter

Presentation Notes

The cation exchange material used most often is polystyrene resin, which takes the form of spheres or beads; they are insoluble in water and have a negative electrical charge. The standard resin bead is less than 1/32 of an inch in diameter, and is the site where the exchange of ions actually occurs. Cation resin beads attract positively charged ions and hold them until the beads encounter some other cations for which they have a greater affinity.�

Hard Water Soft Water

Cation Exchange Process

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Service Cycle • Na+ ions are exchanged for

Ca++ and Mg++ ions

Ca++ & Mg++ Na+

Presenter

Presentation Notes

In the beginning of the water softening cycle, the resin beads are covered with soft sodium (Na+) ions by washing them in a rich sodium chloride brine solution. These beads are contained in a pressurized vessel called a resin tank. The untreated hard water enters the resin tank and passes through the bed of resin.�The negatively charged resin beads have a greater attraction for the two positive charges in each ion of calcium (Ca++) and magnesium (Mg++) than they do for the single positive charge of the sodium (Na+) ion. Therefore, sodium ions on the resin beads will be displaced by the calcium and magnesium ions. In effect, the resin beads exchange the sodium ions for the "hard water" ions, allowing "soft" water to flow from the resin tank.


Exhausted Condition • Cation beads can be used in the

service cycle until they are saturated with Ca++ and Mg++

• Requires regeneration

Ca++ or Mg++

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Presenter

Presentation Notes

A softener will continue to give soft water only as long as there are sufficient sodium ions remaining on the resin beads. After a vast number of calcium and magnesium ions from the water have become attached to the resin beads, the exchanger will become exhausted.


Regeneration or Brining • Sodium Chloride (NaCl) solution

(brine) is passed through the resin to drive off the Ca++ and Mg++ ions to be rinsed away with the Cl- ions

Resin bead will be replenished with Na+

Ca++ or Mg++

Na+

Cl-

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Presenter

Presentation Notes

In the regeneration process, the resin beads are washed with a strong solution of salt water, known as brine solution. Although the resin beads prefer calcium and magnesium ions, the overwhelming concentration of sodium ions overcomes this affinity. The sodium ions in the brine solution force the calcium and magnesium ions off the beads to be discharged as waste. The resin bed is then rinsed to remove the excess brine solution from the tank, and the resin beads are ready to produce soft water again. The frequency of this regeneration process is determined by the capacity of the softener, the hardness of the water, and the water usage. The chloride ions carry a negative charge just like the resin beads and are therefore repelled. They wash out of the system with the rest of the solution and are discharged as waste as well.

Removes • Bicarbonate & Carbonate

Alkalinity • Sulfate • Nitrate

Dealkalizer

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Mechanical Process

Presenter

Presentation Notes

Slides # 12Dealkalizers Dealkalizers are used in applications where the water is known to have high alkalinity. The dealkalizer reduces bicarbonate alkalinity, which minimizes Carbon Dioxide production (the major cause of condensate line corrosion), decreases chemical consumption, and lowers blowdown rates which will reduce fuel consumption.

Alkaline Water Dealkalized Water

Anion Exchange Process

Service Cycle • Chloride (Cl-) ions are exchanged

for Carbonates of Alkalinity (-)

Alkalinity Cl -

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Presenter

Presentation Notes

In the beginning of the water softening cycle, the resin beads are covered with soft sodium (Na+) ions by washing them in a rich sodium chloride brine solution. These beads are contained in a pressurized vessel called a resin tank. The untreated hard water enters the resin tank and passes through the bed of resin.�The negatively charged resin beads have a greater attraction for the two positive charges in each ion of calcium (Ca++) and magnesium (Mg++) than they do for the single positive charge of the sodium (Na+) ion. Therefore, sodium ions on the resin beads will be displaced by the calcium and magnesium ions. In effect, the resin beads exchange the sodium ions for the "hard water" ions, allowing "soft" water to flow from the resin tank.

What Needs To Be Removed

Dissolved Minerals • Hard Scale Formers

• Calcium • Magnesium

• TDS • Calcium • Magnesium • Sulfate • Sodium • Silica • Chloride • Alkalinity

• Dissolved Gas • Oxygen

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Waterside Scale

Waterside Corrosion

Oxygen Corrosion

50 F

86 F

122 F

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RULE OF THUMB

• Almost 2 times more corrosive at 122oF than at 86oF

• Dissolved Oxygen is ~ 10 times more corrosive than CO2

Reference Chart Courtesy of: http://www.engineeringtoolbox.com/oxygen-steel-pipe

Presenter

Presentation Notes

And speaking of air, it is probably a good time to remind you of the corrosiveness of oxygen when it is present in a steam system. It is highly corrosive and damaging to boilers, piping and other equipment it comes in contact with in a hot environment. For instance, looking at this chart, you see how oxygen corrosion excelerates as the temperature rises from 50 degrees to 122 degrees; certainly a much lower temperature than what you would experience in a steam boiler and its connected piping….As a matter of fact, oxygen is 2.5 times more corrosive at 195 DF than at 140 DF and 10 times more corrosive than CO2…

http://www.engineeringtoolbox.com/oxygen-steel-pipe

Mechanical Removal

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Deaeration Removes • Oxygen • Free Carbon Dioxide

Heat Agitate Liberate

Mechanical Removal

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Column Spray Tray

Packed Column Deaerator

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Water In Venting Out

Column Packing Rings

Steam In

Boiler Feed Tank

Presenter

Presentation Notes

Heats, agitates, liberates gasses. Counter flow of steam and water. Significant head room, but an excellent DA. Can also handle more high pressure returns than a Spray type.

Spray Deaerator

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Presenter

Presentation Notes

Two stages of deaeration. First stage is the initial contact of steam and water in the spray nozzle dome or housing. This gets about 60% of the job done. The second stage (remaining 40%) is in the bottom cone area where the water and steam is compactly co-mingled, bouncing off of baffles and then sprayed out of the nozzle, giving it the final agitation.

Tray Deaerator

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Steam

Water

Vent

Trays

Presenter

Presentation Notes

Sstl cabinet holds the trays. Water comes in from the Sstl top and cascades over the trays, top to bottom. Steam enters on the top side and fills the vessel, transferring heat (conduction/convection) across the Sstl cabinet to the water. The vent line passes through the Sstl dome (water inlet) and with a mix of steam (1/10th of 1 %) and gasses gives up much of its heat to the incoming water.

Mechanical Removal

Automatic blowdown system senses anything that adds conductivity • Calcium • Magnesium • Sodium • Silica • Sulfate • Chloride • Iron

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Conductivity Sensor

TDS Control with Blowdown Heat Recovery

Water inlet To drain To drain

Separator Heat exchanger ?

Mechanical Chemical

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Treatment for Steam Boiler Systems

Guidelines

• ASME • ABMA • OEM guidelines • Water treatment

companies

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Presenter

Presentation Notes

�

ASME Suggested Water Chemistry Limits Industrial Watertube, High Duty, Primary Fuel-Fired - Feedwater

Drum Operating Pressure psig (MPa) 0 - 300 (0 - 2.07)

Dissolved Oxygen ppm (mg/L) O2 – measured before chemical scavenger addition <0.007

Total iron ppm (mg/L) Fe ≤0.1

Total copper ppm (mg/L) Cu ≤0.05

Total hardness ppm (mg/L) as CaCO3 ≤0.5

pH @ 25oC 8.3-10.5

Chemicals for preboiler system protection NS

Nonvolatile TOC ppm (mg/L) C <1

Oily matter ppm (mg/L) <1

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Table 2

ASME Suggested Water Chemistry Limits Industrial Watertube, High Duty, Primary Fuel-Fired – Boiler Water

Drum Operating Pressure psig (MPa) 0 - 300 (0 - 2.07)

Silica ppm (mg/L) SiO2 ≤150

Total Alkalinity ppm (mg/L) as CaCO3 <1000

Free OH Alkalinity ppm (mg/L) as CaCO3 NS

Specific Conductance µmhos/cm (µS/cm) @ 25oC <7000

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Table 2

Scale and Deposits Boiler Corrosion

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Carryover

Improperly Controlled Water Chemistry

Presenter

Presentation Notes

Scale and Deposits Form in High Heat Flux Areas Where Steam is Generated

Effect of Scale & Deposits: • Calcium, magnesium, and iron inhibit

heat transfer • Raise tube metal temperature

• Blisters/overheat – mostly water tube boilers • Efficiency loss – firetube boilers

• Iron also causes under deposit corrosion

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We Can Minimize Scale and Deposition and Impact Boiler Cycles of Concentration by…

• Minimizing feedwater contaminants entering boiler • Using best treatment program for your system • Accurately controlling blowdown rate

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• Phosphate based • Very old, reliable chemistry • Dosed based on hardness

• Can be used with very high feedwater hardness • Requires higher blowdown rates • Amount of phosphate scale formed depends on

hardness present

Boiler Treatment for Scale / Deposition - Precipitating Programs

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Threshold Scale / Deposition Inhibitor

• Good fit for low-pressure boilers • Able to handle moderate to severe hardness upsets • Hybrid program that combines phosphonate (HEDP) and

polymer • Functions by distorting the crystal structure and

preventing scale formation

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• All-polymer or chelant programs • Dosed based on hardness • Conditions sludge and solubilizes

hardness • Clean boiler internals when fed at recommended

dosage • Reduces blowdown requirements

Boiler Treatment for Scale / Deposition -Solubilizing Programs

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Mild Steel Corrosion

• Mild steel used in boiler systems because of mechanical strength, high thermal conductivity and low cost

• Corrosion minimized over pH range of 8.5 to 12.5

Rel

ativ

e C

orro

sion

Att

ack

Approximate pH Value at 25oC/77oF

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Chemical Oxygen Scavenger

• Chemical removes trace oxygen left by deaerator/FW tank

• Sulfite is typically scavenger of choice in low-pressure systems

• Non-sulfite scavengers exist • Fed to deaerator/FW tank • Performance traditionally

determined by scavenger residuals

• Oxygen is not the only corrodent in the FW system 39

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Treatment for Hot Water Boiler Systems

Hot Water Systems

• Hot water boilers are used for many applications from 140oF to over 400oF

• Requirements to maintain all systems are similar

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Corrosion in Hot Water Systems

Water loss/make-up should not be more than 0.1 to 0.5% of system volume monthly (1.2 to 6% system volume yearly) • Special emphasis on finding and fixing leaks • As water make-up increases and water temperatures increase, oxygen

pitting becomes the most likely cause of corrosion-related failures

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Scale / Deposition in Hot Water Systems

• Softened make-up is recommended for all hot water boiler applications

• Primary species of concern: CaCO3, MgSiO3

• Scale potential is a function of: • Temperature: higher is worse • Holding Time: lower is worse since constant influx of make-up water

may increase the scaling load on the system • Water Chemistry: pH and dissolved ion levels • Dispersant in Program

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Chemical Programs

1. Nitrite/Azole program • Temperature <300oF and oxygen <1-2 ppm • Maintain Nitrite levels at 1000 ppm or higher • Azole ≥10 ppm

2. Combination Molybdate/Nitrite/Azole program • Temperature <300oF and oxygen <1-2 ppm • At least 1000 ppm Nitrite • Molybdate greater than 100 ppm • Azole ≥10 ppm

3. Molybdate/Azole program • Molybdate at 300 ppm or higher (500 ppm if temperature is >250oF) • Molybdate requires approximately 1 ppm oxygen to provide adequate

corrosion protection

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Sulfates & Chlorides

• Corrosion rates sensitive to increased chlorides and sulfates

• Both degrade nitrite and molybdate performance • Increase nitrite and molybdate dosage for chloride and

sulfate levels >50 ppm

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Sometimes Sulfite or Alternate Oxygen Scavengers are Used

• Sulfite is not compatible with nitrite • Minimize water loss/make-up • Deoxygenate make-up if rates are high

• Sulfite plus oxygen results in sulfate • Sulfate levels above 300 ppm increase yellow metal corrosion

• Some non-sulfite scavengers can add ammonia • Ammonia is known to increase yellow metal corrosion

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Monitoring and Control

Boiler

Steam

Boiler Feedwater

Boiler Blowdown

Heat

966,700 lb/Day @ 0 ppm TDS

1,000,000 lb/Day @ 100 ppm TDS = 100 lb/Day Solids

3.33% of Feedwater 33,300 lb/Day @ 3000 ppm = 100 lb/Day Solids

Based on Chemistry

Cycles 30 1003000

ion feedwaterion blowdown

==

30 Cycles = 3000 ppm TDS

BD 3.33% 30

100cycles100

==

Boiler Cycles and % Blowdown

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Presenter

Presentation Notes

-Simple Diagram of a Boiler In the boiler, water is converted to steam. Heat is applied to the water in the boiler, and steam is continuously produced. Boiler feedwater is fed to the boiler to make up for the steam that is lost. As the steam leaves the boiling water, dissolved solids originally in the boiler feedwater are left behind. The solids left behind become increasingly concentrated, and eventually reach a level where further concentration would cause scale or deposits to form on the boiler metal.

Determining Boiler Cycles

Conductivity • Good to use if feedwater conductivity is relatively high • Limited use if feedwater conductivity is low and contains ammonia or

amines Trace chemicals can aid cycles determination

• Inert fluorescent dye • Non-volatile • Non-precipitating • Non-reactive

Other Measurements • Silica • Chlorides • Sodium

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Presenter

Presentation Notes

For many waters, conductivity is an excellent tool, but it is a poor choice when boiler feedwater is demineralized makeup water. Concentrations of ammonia and amines, can be a large percentage of the ionic activity of the water. When this water enters the boiler drum, the amines and ammonia will flash from the water into the steam and the conductivity of the water goes down. For this reason, the ratio of boiler water to feedwater conductivity in demineralized water (or all condensate) will have little bearing on the boiler water cycles of concentration.

Blowdown Control Minimizes Chemistry Swings in the Boiler

With

Without

Time 50

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

Cycles of Concentration

% o

f F

eedw

ater

G

oing

to

the

Blo

wdo

wn

1 10 100 5 50

20 to 40 cycles saves 2.5% FW

5 to 10 cycles saves 10% FW

20 40

… And Can Save Water and Energy

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Presenter

Presentation Notes

Anne: By increasing up to 40 cycles from 20, only 2.5% of the feed water demand is reduced. Of course, the blowdown heat loss is cut roughly in half.

Blowdown Control is Only Half the Issue

• Perform chemical tests relative to treatment • Adjust chemical feed to

maintain dosage • Maintain boiler parameters to

prevent over-cycling • Testing can be automated

with feedwater control

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Midwestern University Case History

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

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Before / After Improvement in Scale Inhibitor Feed

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Feed

wat

er P

rodu

ct (

ppm

)

Scale Inhibitor vs. Steam Flow

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Fe

edw

ater

Pro

duct

(pp

m)

Pro

duct

Pum

p O

ut %

Automation Maintains Desired Feedwater Reductant Levels to Minimize Corrosion

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% S

ulfite P

um

p O

utp

ut

Time (2 weeks)

Cor

rosi

vity

(m

V)

Energy and Water Savings ($/yr)

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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) $59,263 $32,353 $26,910

Net Savings or Costs $/yr $26,910

Today’s Take-A-Ways

• Proper water treatment is a combination of mechanical and chemical remediation

• Has significant impact on efficiency and reliability attainment

• Chemical treatment varies based on watertube, firetube, pressure/temperature.

• Corrosion accelerates with temperature • Increasing cycles of concentration saves

fuel dollars • Heat from continuous blow down for TDS

control can be recouped • Hot water systems need to be chemically

treated too • Monitoring and control is ESSENTIAL

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Contact Us

Debbie Bloom Principal Consultant, Technical Expertise Center [email protected] 630-305-2445

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Tom Leunig Product Manager, Packaged

Water Systems [email protected] 414-577-3197

mailto:[email protected]

mailto:[email protected]

Education

Essentials for a sound boiler water treatment program