Exam Question
Write short notes on the following:
(i) Low output of a fresh water generator (4)
(ii) Fuel oil purifier overflowing (4)
(iii) Alarming rise in engine room bilge level at sea (4)
(iv) Frequent shearing of pump-motor coupling pad (4)
Class 4 (4th Engineer)
MEP
📅 Jan 2023
Reference Answer
### (i) Low Output of a Fresh Water Generator
A low output from a Fresh Water Generator (FWG), typically a plate-type or shell-and-tube vacuum evaporator, signifies a deviation from its design operating parameters. The causes can be systematically diagnosed by examining the three critical systems: the heating medium, the seawater feed/brine system, and the vacuum system.
**1. Insufficient Heat Transfer:**
* **Scale Formation:** This is the most common cause. Hard calcium carbonate (CaCO₃) and magnesium hydroxide (Mg(OH)₂) scales form on the evaporator heating surfaces (plates/tubes). This layer acts as an insulator, drastically reducing the heat transfer from the jacket water to the seawater feed. The condenser surfaces can also foul, reducing condensation efficiency.
A low output from a Fresh Water Generator (FWG), typically a plate-type or shell-and-tube vacuum evaporator, signifies a deviation from its design operating parameters. The causes can be systematically diagnosed by examining the three critical systems: the heating medium, the seawater feed/brine system, and the vacuum system.
**1. Insufficient Heat Transfer:**
* **Scale Formation:** This is the most common cause. Hard calcium carbonate (CaCO₃) and magnesium hydroxide (Mg(OH)₂) scales form on the evaporator heating surfaces (plates/tubes). This layer acts as an insulator, drastically reducing the heat transfer from the jacket water to the seawater feed. The condenser surfaces can also foul, reducing condensation efficiency.
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