Water Hardness and Impurities Treatment

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Questions and Answers

What is the cause of temporary hardness in water?

Bicarbonates of calcium and magnesium precipitating at temperatures below the boiling point (correct)
Presence of silica ions
Formation of hard, dense scale on boiler surfaces
Sulfates of calcium and magnesium precipitating when the water boils

How is colloidal silica reduced in water treatment?

By reverse osmosis
Through distillation units
Through agglomeration techniques used in a clarifier (correct)
By ion exchange

What effect do sludge and scale have on boiler efficiency?

Increase heat transfer from the flue gas
Decrease heat transfer from the flue gas (correct)
Help in maintaining optimal heat transfer
Have no impact on heat transfer

What causes foaming in the boiler?

Presence of dissolved gases such as nitrogen and ammonia (C) Signup and view all the answers

Which dissolved gas is of primary concern due to its ability to produce boiler corrosion?

Oxygen (D) Signup and view all the answers

How can dissolved oxygen be effectively removed from boiler water?

Raising the water temperature close to the saturation temperature using deaerators (C) Signup and view all the answers

What is the main purpose of treating water in an energy plant?

To eliminate damage to boilers and other components (B) Signup and view all the answers

Why is it important to prevent scale formation on the boiler tubes?

To avoid overheating and possible tube rupture (C) Signup and view all the answers

What is the potential consequence of sludge forming in boiler or steam drums and tubes?

Insulation of metal surfaces and inefficient heat transfer (A) Signup and view all the answers

What can cause corrosion or pitting in a boiler system?

High dissolved or suspended solids (D) Signup and view all the answers

What may result from carryover of boiler drum water and dissolved or suspended solids?

Overheating of tube surfaces or even tube failure (A) Signup and view all the answers

Which of the following is a common reason for boiler water treatment?

To prevent corrosion or pitting caused by high dissolved gases (A) Signup and view all the answers

What type of impurities are suspended solids?

Substances that have not been dissolved, but are held or suspended in the water (A) Signup and view all the answers

What can suspended solids in a boiler water stream lead to?

Reduced heat exchange at the tube walls and metal failure (B) Signup and view all the answers

What is the most common method of reducing the levels of suspended solids?

Gravity settling (clarifiers) and pressure filtration (A) Signup and view all the answers

What are dissolved solids usually composed of?

Ionic compounds dissolved in water (B) Signup and view all the answers

What is the main problem caused by hardness in the boiler water?

Boiler tube scaling and reduced heat transfer efficiency (D) Signup and view all the answers

How are the concentrations of different ions often determined?

By conducting hardness tests and using a conductivity probe (B) Signup and view all the answers

What does a high pH boiler water cause?

Dissolution of the magnetite coating (A) Signup and view all the answers

What is the 'safe range' of pH for boiler steels according to Figure 1?

8.5 - 12.7 (C) Signup and view all the answers

What can high pH levels in boiler water result in, when combined with high boiler metal stress?

Caustic embrittlement (A) Signup and view all the answers

What is commonly added to raise the pH of boiler water?

Sodium hydroxide (NaOH) (B) Signup and view all the answers

What does a pH lower than 8.5 cause in the boiler system?

Increased boiler system corrosion (D) Signup and view all the answers

What may result from high pH levels in the presence of high boiler metal stress?

Caustic embrittlement (C) Signup and view all the answers

What does a 'continuous blowdown rate' help achieve in a boiler?

Reduce the pH of the boiler water (D) Signup and view all the answers

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Study Notes

Water Treatment in Energy Plants

Temporary hardness in water is caused by the presence of bicarbonate ions.

Boiler Efficiency and Scale

Sludge and scale formation on boiler tubes can reduce boiler efficiency.
Scale formation on boiler tubes can be prevented by treating water in an energy plant.

Boiler Corrosion and Foaming

Dissolved oxygen in boiler water can cause corrosion, and its effective removal is crucial.
Deaeration is a method to effectively remove dissolved oxygen from boiler water.
Foaming in the boiler is caused by high levels of dissolved solids.
Dissolved oxygen is of primary concern due to its ability to produce boiler corrosion.

Sludge Formation and Consequences

Sludge formation in boiler or steam drums and tubes can lead to boiler failure.
Sludge formation is caused by the presence of suspended solids in boiler water.

Suspended Solids and Impurities

Suspended solids are a type of impurity that can cause corrosion or pitting in a boiler system.
Carryover of boiler drum water and dissolved or suspended solids can lead to corrosion or pitting.
Suspended solids in boiler water can lead to sludge formation and boiler failure.

Reducing Suspended Solids

The most common method of reducing suspended solids is through sedimentation and filtration.

Dissolved Solids and Hardness

Dissolved solids are usually composed of minerals such as calcium and magnesium.
Hardness in boiler water is caused by the presence of calcium and magnesium ions.
The main problem caused by hardness in boiler water is scale formation.

pH Levels and Boiler Water

pH levels in boiler water are often determined by analyzing the concentrations of different ions.
A high pH in boiler water can cause caustic corrosion and damage to boiler tubes.
The 'safe range' of pH for boiler steels is between 8.5 and 10.5.
High pH levels in boiler water, combined with high boiler metal stress, can result in caustic corrosion.
A pH lower than 8.5 can cause acidic corrosion in the boiler system.
High pH levels in the presence of high boiler metal stress can result in caustic corrosion.

Raising pH Levels

Sodium hydroxide is commonly added to raise the pH of boiler water.

Continuous Blowdown Rate

A continuous blowdown rate helps achieve a consistent concentration of dissolved solids in the boiler water.

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