Objective 08: Dealkalization System

Question 1

Besides Hardness Removal, what other kind of water purification is required by most boiler operations?

Answer 1

Alkalinity Reduction

Question 2

Can Zeolite Softening reduce alkalinity?

Answer 2

No

Question 3

What are the primary causes of alkalinity in boilers?

Answer 3

Carbonate and Bicarbonate anions

Question 4

What are the typical components of a Dealkalization System?

Answer 4

1. Pressure tank partially filled with weak acid cation exchange resin
2. Concentrated acid measuring tank
3. System for the dilution of the acid to provide the hydrogen ions for regenerating the resin
4. Degassifier to remove the carbon dioxide generated by the ion exchange process
5. Alkaline neutralizer system, containing an alkali (e.g. NaOH) to neutralize the acidic effluent from the hydrogen zeolite unit

Question 5

Describe the Dealkalization process

Answer 5

Water containing alkaline anions and hardness cations passes through the resin and the resin exchanges its hydrogen ions for the alkaline and hardness ions in the water.

Question 6

Describe the Regeneration process of Dealkalization Systems

Answer 6

1. Unit backwashed
2. Concentrated acid from a measuring tank is diluted to the proper concentration and passed down the resin bed
3. The hydrogen ions from the regenerate reoccupy the zeolite
4. Slow and fast rinses flush the spent acid and ions from the resin

Question 7

What happens in the Degassifier of Dealkalization Systems?

Answer 7

Carbonic acid is reduced to carbon dioxide by cascading the water over a packed bed of plastic saddles causing it to break up into tiny droplets. Air, supplied by the blower, flows upward and carries the released carbon dioxide to atmosphere. An alkaline neutralizer, NaOH, is added to the degassifier effluent to neutralize acidity.

Question 8

What product of Dealkalization Systems must be removed some alternate means lest extremely hard scale be produced?

Answer 8

Sodium Silicate