Boiler Water Seminar

BASIC WATER CHEMISTRY
The amount of water on earth has always been the same, only the distribution areas have changed. Water treatment is an exact science; all chemical reactions are predictable and respondable as well. Water is known as the universal solvent.

• Scale: Calcium Carbonate
• Corrosion: Free oxygen and/or carbonic acid

• Calcium becomes less soluble as water temperature increases with-in the system.
• Calcium becomes less soluble as the alkalinity increases with-in the system.

Notation 1: precipitation occurs when a mineral becomes insoluble.
Notation 2: carbonate means, the mineral is in its raw state when precipitation occurs.
Special note: When we perform chemical tests, we are measuring and identifying only dissolved minerals not visible to the naked eye.

What is the cause of corrosion in a boiler?
Oxygen also becomes less soluble as the water temperature increases with-in the system.

1. As the oxygen becomes insoluble, it then is released as free agent; this bubble of air will then attach its self to the piping surface allowing a corrosion cell to develop at the site.

Steam used as a source of energy is most desired by industry due to its low productions cost, flexibility in use and it’s controllable targeting ability. Due to the much higher water temperatures demanded in steam production, the quality of the boiler make-up is of paramount concern.

• The water going to the boiler feed water tank must be rendered “soft”. If a softener control program is not in place at the plant site, then such a program must be installed.
• Chemicals added to the boiler feed water tank or directly to the feed water line going to the boiler should be controlled by the boiler feed water pump circuit.

parts per Million (milligrams per liter)

Grains: A very small unit of weight, originally equal to a “grain” of wheat. grains are used to describe the capacity of ion exchange resins used for water softening.

Resin: A common name for the strongly acidic polystyrene copolymer most commonly used for water softening.

“as CaCO3”: “as calcium carbonate equivalents” a convenient way of describing concentrations based on the number of ionic charges rather than the weight of the ions.

DVB (crosslinkage): “Divinylbenzene” The chemical used to strengthen resin beads. Increasing DVB increases physical strength and resistance to oxidation.

• It is highly recommended that every steam boiler be equipped with a continuous surface blow down.
• Bottom boiler blow downs should be brief open valve time periods and very few in number (no less than 1 bottom blow down per day)

• Test should be performed at least daily
• The testing should include the following;
• Soft water make up to boiler feed water tank : Total hardness, chlorides
• Boiler feed water: TDS,Total Hardness, “P” & “M” alkalinity, chlorides, sodium sulfite & pH
• Boiler water: TDS, “P” & “M” alkalinity, hydroxide alkalinity, chlorides, actual chemical residual levels in boiler: PO4, SO3,pH
• Condensate return: pH, iron

• CORROSION CONTROL = (Total alkalinity) refers to test indicator for alkali in water (Methyl orange) after testing for “P” alkalinity the test is continued on the same sample to determine total alkalinity.
• OXYGEN SCAVENGERS & PASSIVATORS
  Sulfite (neutralizes oxygen but requires a minimum water temperature of 428o for passivation to occur)

Hydrozine & N, N, diethylhydroxylamine (DEHA + HQ) are excellent oxygen neutralizers plus excellent passivators . DEHA/HQ combination also have the ability to protect the after boiler regions.

Special Note: Passivation of metal occurs when a highly protective deposit of an oxide film called magnetite is deposited on the metal surface, there-by protect that metal surface against corrosion attack.

Relationship of Water Temperature & Dissolved Oxygen

Temp. 135₀ 150₀ 180₀ 200₀ 210₀_
Oxygen 5.0ppm 4.2ppm 2.6ppm 1.0ppm   0.3ppm

Water softening equipment must be reliable and in place.

Chemicals are required as finishing treatments.
Phosphates – dequests – hydrate alkalinity – EDTA are the chemicals normally used for scale control.
Dispersants (sludge conditioners) are used to prevent boiler sludge or sludge scale in the boiler.

DEAE -CYCLOHEXALAMINE are the amines used by the industry.
Filming amines are also used by the industry

The alkalinity that enters the boiler via the soft city water make up is identified as “T”/ALK. Or “M”ALK when evaporated under boiler water temperatures will release a gas known as carbon dioxide (carbonic acid) the pH of this gas is in the range of pH 4.7. The steam that leaves the boiler is made up totally of only oxygen and hydrogen in the pH range of 7.0. The steam being pure H20 has no buffering protection so the pH of this unbuffered steam will now become the same as the gases pH which is a pH of 4.7. The pH of the neutralizing amines having a pH of 10.0 and the fact that these amines are highly volatile, will release and pass off with the steam there-by raising the steam pH from 4.7 to some desired range above 7.0 resulting in major reductions in steam condensate line corrosion. 80% of the boiler feed water “T”/A will be released as carbonic acid
Steam line treatments are always most effective and less costly if injected directly into the steam header.

Steam generator sq. ft. EDR steam div. by 140 = BHP

Hot water boiler sq. ft. EDR water div. by 223 = BHP

MBH ( BTU/HR.) div. by 33.5 = BHP

Sq. Ft. BHS div. by 10 (fire box) by 5 (package)

(BHS = Boiler Heating Surface) (EDR = Equiv. Direct Radiation)
(MBH = 1,000 BTU per Hour)

If Boiler Load is Known
8.5 gallons of oil per day = BHP

1004 CU/FT. of gas per day = 1 BHP

NOTE: LB. steam per hour divided by 8.3 = GAL/W/EV/HR.

Standard method used to determine the maximum allowable concentrations permitted to cycle in the boiler.