Water Chemistry

Question 1

What are cations, What are Anions

Answer 1

Cations are positively charged ions and Anions are negatively charged ions

Question 2

What is pH

Answer 2

pH is defined as the logarithm of the reciprocal of the hydrogen ion activity. Or a measure of a substances acidity or alkalinity

Question 3

What is sodium phosphate used for.

Answer 3

Sodium phosphate is a sludge conditioner that allows impurities to floc together and settle out of a solution

Question 4

Name 3 conditions in a boiler that could cause foaming

Answer 4

High pH, high dissolved solids and colloidal substances in the boiler water could lead to foaming

Question 5

Why do we treat feed water

Answer 5

To eliminate or reduce contaminates that cause scale, corrosion, and caustic embrittlement on boiler heating surfaces and unacceptable conditions in boiler water such as priming, foaming, and carryover

Question 6

What are the two (2) sources of water?

Answer 6

Surface water is water that comes from lakes, ponds and rivers and Ground water from wells

Question 7

What are the impurities in water

Answer 7

Suspended solids are organic materials such as mud silt and clay that you can see, they are removed by filtration.
Dissolved solids are mineral salts that can’t be removed by filtration. Examples include Calcium, Magnesium, and Sodium
Dissoved gases are entrained gases that exist in the water that are removed by dearation/degasification such as O2, CO2, and H2S

Question 8

What pH level is maintained in boilers

Answer 8

We try to maintain the boiler pH between 9.5 to 10.5

Question 9

What is foaming? What causes foaming in a boiler

Answer 9

Foaming is a layer of foam on the surface of the boiler water due to high alkalinity, high dissolved / suspended solids or the presence of oil or other colloidal solids

Question 10

What is priming? What is carryover

Answer 10

Priming is the carryover of large slugs of water with the steam from the boiler. Carryover is the carryover of fine droplets of water and/or suspended/dissolved solids with the steam from the boiler

Question 11

Where in a boiler will scale form

Answer 11

Scale will form in a boiler below the waterline

Question 12

How are boilers laid up?

Answer 12

Boiler(s) are laid up using either the wet method (available on short notice) or the dry method (for longer periods).

Question 13

How often should boilers be blown down

Answer 13

The bottom blowdown valves should be operated at least once per day but it is better to base the frequency on water testing. The use of surface/continuous blowdown will limit the use of bottom blowdown valves

Question 14

What is galvanic corrosin

Answer 14

Galvanic corrosion ( happens in condensers) is an electrochemical process that occurs when two dissimilar metals are in contact in an electrolyte solution (water). the weaker metal gets attacked (higher corrosion rate). Cathode protection uses a small electrical current on the softer metal to reduce galvanic corrosion or use a sacrificial metal to let it get attacked rather than the tubes in a condenser per se

Question 15

Name some common chemicals used in boiler feedwater treatment

Answer 15

• For O2 scavengers, Sodium sulfite, Na2SO3 and Hydrazine, N2H4
• For pH control, Sodium Hydroxide, NaOH and Ammonia, NH3
• For sludge conditioning Phosphates, NaPO4,
  Polyphosphonates, and Chelants
• For return line corrosion, Amines

Question 16

Why do we treat feedwater

Answer 16

1 prevent sludge from depositing on boiler surfaces
2 prevent scale from forming on boiler surfaces
3 prevent corrosion of boiler metal
4 prevent carryover with the steam leaving the boiler

Question 17

What is a common test for corrosion

Answer 17

pH

Question 18

What is meant by phosphate hideout

Answer 18

Loss of phosphate residual on load upswing. Residual recovery on downswing due to resolubilizing. Temporary upset in the ability to neutralize caustic.

On high loads phosphate “hides out” on boiler surfaces and indicates no phosphate present during testing. You add more phosphate to the boiler and when you decrease load phosphate will resolubilize in the water. Now you have too much phosphate

Question 19

What is caustic embrittlement

Answer 19

• Requires stressed condition such as cracked plate, riveted joint, porous condition, defects such as steam leaks
• Free caustic in system (NaOH) becomes concentrated and leads to crystalline cracking of the plate/ shell

Question 20

What is the corrosion caused by Oxygen

Answer 20

Pitting

• main corrosion caused by Oxygen, happens around the NOWL.
• Active pitting has active pits indicated by a shiny surface
• inactive pitting has a layer of magnetite (orange brownish color)

Question 21

Explain the corrosion caused by CO2

Answer 21

This is the main corrosion that happens in condensate return lines. CO2 in the lines can lead to the formation of carbonic acid which attacks the thickness of the pipe, especially at the threads

Question 22

What are chelants

Answer 22

Chelants - EDTA, NTA, HEDTA
No precipitation
Work differently than phosphates by keeping impurities soluble in the water and allow impurities to be removed more easily by surface blowdown

Question 23

How are polymers used in boiler water treatment

Answer 23

Polymers - Polyacrylite, Polymethacrylite, HTP-2/ULTRASPERSE

Keeps impurities in solution, allows for removal with surface blow down

Question 24

Describe what is meant by a co ordinated phosphate program

Answer 24

• Primarily a solubilizing program with precipitation as upset control.
• Uses mono, di, and trisodium phosphate.
• Adjusts pH and provides phosphates to the boiler
• Requires some bottom blowdown

Question 25

Describe what is meant by a phosphate program

Answer 25

Use just phosphate

• precipitating program (high bottom blowdown rates required)
• The phosphates cause impurities in the boiler to form a soft sludge. Impurities fall to the bottom of the boiler and is periodically removed by the botttom blowdown

Question 26

How do we lay up a boiler wet

Answer 26

• Clean fire side and steam and water side of the boiler
• Close up steam and water side
• Fill the boiler with warm treated water until water comes out the vent
• close the vent
• maintain a pressure in the boiler slightly higher than atmospheric

Question 27

How do we lay up a boiler dry

Answer 27

• Clean fire side and steam and water side of the boiler
• Dry out boiler completely
• Close all valves on the boiler to prevent moisture from entering drums
• Lay trays of moisture absorbing chemicals in boiler drums
• Close steam and water side
• Check moisture absorbing chemicals periodically and replace when required

Question 28

What is meant by cycles of concentration

Answer 28

It is the concentration of dissolved solids in water divided by the dissolved solids in the make up water to the boiler. This indicates the number of times the water in the boiler has cycled up. ASME CODE Section 7 provides guidance for cycles of concentration

Question 29

What is scale

Answer 29

Scale is an inorganic mineral matter precipitated from the boiler directly onto boiler surfaces. It is usually crystalline , dense, and laminated. It interferes with heat transfer

Question 30

What is sludge

Answer 30

A sedimentary deposit formed by suspended matter or by precipitation due to chemical treatment (phosphates)

Question 31

What are chlorides

Answer 31

Chloride ions( chlorides) are mineral salts that can cause scale to form on boiler surfaces and are used to monitor cycles of concentration and control blowdown rates. The chlorides test is most conveniently done on the P alkalinity test done on boiler water. This is because the chlorides test will not work on high pH boiler water. P alkalinity neutralizes the pH in that test