Question 5 QMED03 - Oiler

The Correct Answer is D **Explanation for Option D (Main condensate pump):** The Main Condensate Pump (MCP) is designed to operate continuously at a **constant speed** (often driven by a constant-speed motor) to pull condensate (water) out of the main condenser hotwell. It discharges this condensate, usually through various stages of low-pressure (LP) heaters and polishers, directly to the **deaerating feed tank (DFT)** or deaerator. Since the hotwell level is maintained constant and the pump operates continuously at a fixed speed, it handles a relatively steady flow rate (determined by the steam flow/load). The MCP's discharge pressure must be sufficient to overcome the friction losses and the static head necessary to reach the DFT, which is usually elevated. Therefore, the pump operates at a constant speed and delivers water to the DFT at a **nearly constant pressure** corresponding to the required head for that flow path, fulfilling both conditions of the question. **Why the other options are incorrect:** * **A) Main feed pump:** The main feed pump (MFP) takes suction from the DFT and discharges water to the main boiler/steam generator. This pump's speed (and thus its discharge pressure) must constantly vary to match the boiler's demand, which changes significantly with the plant load. It operates at variable speed and variable pressure, not constant speed and constant pressure. * **B) Main circulating pump (or Circulating Water Pump):** This pump takes suction from the sea, river, or cooling tower basin and supplies cooling water to the main condenser. While it usually operates at a constant speed, it pumps cooling water, not feed water, and it does not deliver water to the deaerating feed tank. * **C) Main feed booster pump:** This pump is typically installed upstream of the main feed pump to ensure sufficient Net Positive Suction Head (NPSH) for the MFP. While it often operates at a constant speed and pumps feed water, its primary purpose is boosting the pressure at the suction of the MFP, not delivering the water to the DFT. The condensate pump (D) is the primary mover that delivers water *to* the DFT.