Exam Question
(a) Describe the effects of freshwater feed on auxiliary boilers (6)
(b) Describe the measures taken to reduce these effects (4)
(c) Describe FIVE principle boiler water tests starting the reason for EACH (6)
Class 4 (4th Engineer)
MEKG
📅 Aug 2022
Reference Answer
### (a) Effects of Freshwater Feed on Auxiliary Boilers (6 Marks)
Untreated or improperly treated freshwater feed can have several detrimental effects on the operational integrity and efficiency of an auxiliary boiler. These effects are primarily categorized as scale formation, corrosion, and carryover.
1. **Scale Formation**:
* **Mechanism**: Freshwater, especially from shore supplies or evaporated sources, contains dissolved mineral salts, primarily calcium (Ca) and magnesium (Mg) bicarbonates and sulphates. These are known as hardness salts. When heated within the boiler, bicarbonates decompose to form insoluble carbonates (e.g., Calcium Carbonate, CaCO3) which precipitate directly onto the hottest surfaces, such as furnace walls and smoke tubes.
Untreated or improperly treated freshwater feed can have several detrimental effects on the operational integrity and efficiency of an auxiliary boiler. These effects are primarily categorized as scale formation, corrosion, and carryover.
1. **Scale Formation**:
* **Mechanism**: Freshwater, especially from shore supplies or evaporated sources, contains dissolved mineral salts, primarily calcium (Ca) and magnesium (Mg) bicarbonates and sulphates. These are known as hardness salts. When heated within the boiler, bicarbonates decompose to form insoluble carbonates (e.g., Calcium Carbonate, CaCO3) which precipitate directly onto the hottest surfaces, such as furnace walls and smoke tubes.
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