Question 65

The Correct Answer is A ### 1. Why Option A ("Main condensate pump") is correct The **Main condensate pump (MCP)** takes condensate from the hotwell (the lowest pressure point in the cycle) and pumps it through various low-pressure components (like LP heaters, gland steam condenser) up to the deaerating feed tank (DFT). * **Constant Speed:** MCPs in conventional power plants are typically fixed-speed centrifugal pumps driven by constant-speed AC motors. * **Delivery Location:** It delivers the water directly to the DFT (or deaerator). * **Constant Pressure:** The DFT is a low-pressure vessel whose internal pressure is maintained by boiler steam stabilization. Since the required elevation lift and the pressure inside the DFT remain essentially constant regardless of plant load changes, the head (pressure) required from the MCP remains nearly constant throughout its operation. ### 2. Why the other options are incorrect **B) Main feed booster pump** The main feed booster pump takes suction from the DFT and delivers water to the suction of the Main Feed Pump (MFP). While it often operates at a constant speed, its function is to provide the necessary Net Positive Suction Head (NPSH) to the MFP, not to deliver water to the deaerator (DFT). **C) Main circulating pump** The main circulating pump (or cooling water pump) is used to circulate cooling water (e.g., seawater or river water) through the main condenser to condense exhaust steam. It does not handle condensate or feed water, and it does not deliver water to the DFT. **D) Main feed pump** The main feed pump takes suction from the DFT (or booster pump) and delivers water *into the boiler*. This pump must overcome the very high boiler drum pressure. Therefore, its discharge pressure must be highly variable and adjustable (often controlled by variable speed drives or steam turbine speed changes) to regulate feed flow based on boiler load and water level. It does not operate at a constant pressure.