Question 46 QMED03 - Oiler

The Correct Answer is D. **Why Option D ("condensing of the exhausting steam") is correct:** Vacuum in a main condenser is defined as a pressure significantly below atmospheric pressure. The primary function of the main condenser is to efficiently remove heat from the exhausted steam coming from the turbine(s) by causing it to change phase back into liquid water (condensate). This phase change (condensation) results in a dramatic reduction in volume—steam occupies thousands of times the volume of the resulting water. Because the volume of the substance inside the closed condenser shell decreases so drastically when the steam turns to water, it creates a large void, which manifests as a vacuum (low pressure). This process is the fundamental and continuous cause of the vacuum while the plant is operating. **Why the other options are incorrect:** * **A) suction drawn by the condensate pump:** The condensate pump removes the liquid (water) from the bottom of the hotwell (part of the condenser). While this removal is necessary for continuous operation, the pump is removing non-compressible fluid that has already condensed. It does not create the low-pressure condition (vacuum) in the large steam space above the hotwell; the condensation process creates the vacuum that allows the pump to be effective. * **B) aftercondenser loop seal:** The aftercondenser loop seal (or sealing loop) is typically associated with the air ejector system, allowing condensed steam from the air ejector condenser to drain into the main condenser hotwell while preventing non-condensable gases from traveling back up into the air ejector condenser. It is a necessary component for the air removal system but does not primarily cause the vacuum. * **C) main air ejector:** The main air ejector is crucial for maintaining the vacuum by removing non-condensable gases (like air that leaks in) that accumulate in the condenser. If these gases were allowed to build up, they would destroy the vacuum. However, the air ejector is an accessory device that **maintains** the vacuum by removing contaminants; it is the **condensation** of the steam that **creates** the initial and primary low-pressure condition.