Question 8 1AE01 - First Assistant Engineer

The Correct Answer is D **Explanation for Option D (Correct Answer):** A cracked distillate pump vent line would allow non-condensable gases (primarily air) to be drawn into the vacuum system of the flash evaporator. Flash evaporators operate under deep vacuum (very low absolute pressure) to allow water to boil at low temperatures. The accumulation of non-condensable gases significantly raises the partial pressure within the evaporator stage. Since the total absolute pressure is the sum of the partial pressure of the water vapor and the partial pressure of the non-condensable gases (Dalton's Law of Partial Pressures), the addition of air leads directly to a **higher absolute pressure** inside the evaporator, hindering the flashing process and reducing efficiency. **Why the Other Options are Incorrect:** * **A) seawater feed temperature below 165°F:** A lower-than-design feed temperature means less heat is introduced into the system. This would result in less effective flashing and a **lower production rate**, but it would not inherently cause a high absolute pressure. In fact, if flashing is reduced, the pressure might slightly improve (become a deeper vacuum) if the steam ejector or vacuum pump is still running effectively. * **B) production of high salinity distillate:** High salinity distillate indicates carryover or priming (salt water droplets being carried into the distillate), usually due to excessive flashing violence or a clogged demister. This is a quality control issue and does not directly cause an increase in the absolute pressure of the vapor space. * **C) a leak in the first stage demister:** A demister (or mist eliminator) is designed to separate liquid water droplets from the steam vapor. A leak or hole would reduce its effectiveness, leading to the contamination described in Option B (high salinity distillate). Similar to B, this is a quality/separation problem, not a pressure problem that would introduce non-condensables or inhibit condensation enough to cause high absolute pressure.