Question

In a marine steam power cycle employing regeneration, the feed water heater for waste heat recovery is placed after the

• A. boiler
• B. turbine
• C. condenser
• D. pump

Hint:

Trace the water circuit in a Rankine cycle: Condenser \(⇒\) Pump \(⇒\) Feedwater Heater(s) \(⇒\) Boiler. The pump's job is to pressurize the cold liquid; the heater's job is to warm up the pressurized liquid before it enters the boiler.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Regeneration in a steam power cycle is the process of preheating the feedwater (the liquid water going to the boiler) using steam extracted from the turbine. This improves cycle efficiency. The question asks where the feedwater heater is placed in the cycle's circuit.
Step 2: Detailed Analysis of the Regenerative Rankine Cycle:
Let's trace the path of the feedwater from the condenser back to the boiler.
1. Steam expands in the turbine and is then exhausted to the condenser, where it is condensed into saturated liquid.
2. The liquid water (condensate) then enters a pump (condensate extraction pump), where its pressure is raised to the boiler pressure.
3. After the pump, the high-pressure liquid feedwater is cold. The goal of regeneration is to heat this water before it enters the boiler.
4. Therefore, the feedwater heater is placed in the feedwater line after the main pump and before the boiler.
5. In the heater, the high-pressure feedwater is heated by steam bled from an intermediate stage of the turbine.
6. The now preheated feedwater then flows to the boiler.
Based on this sequence, the feedwater heater is placed after the pump.
Step 3: Why This is Correct:
The logical place to heat the feedwater is after it has been pressurized by the pump, as it is then on its way to the boiler. Placing it before the pump would be impractical and could cause cavitation in the pump if the water is heated too close to its saturation temperature. Placing it after the boiler is nonsensical. Placing it after the turbine would mean it's in the exhaust steam line, not the feedwater line. Therefore, the only correct location is after the pump.