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Questions and Answers
In an ideal regenerative Rankine cycle, the temperature of the feedwater is decreased to increase the average temperature during heat addition.
In an ideal regenerative Rankine cycle, the temperature of the feedwater is decreased to increase the average temperature during heat addition.
False
A closed feedwater heater is a type of feedwater heater where the steam mixes with the compressed water from the pump.
A closed feedwater heater is a type of feedwater heater where the steam mixes with the compressed water from the pump.
False
The water leaves the open feedwater heater as a saturated vapor at the heater pressure.
The water leaves the open feedwater heater as a saturated vapor at the heater pressure.
False
In an ideal regenerative Rankine cycle, steam from the boiler expands in the turbine to the boiler pressure.
In an ideal regenerative Rankine cycle, steam from the boiler expands in the turbine to the boiler pressure.
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The main objective of the regenerative Rankine cycle is to decrease the fluid average temperature during heat addition.
The main objective of the regenerative Rankine cycle is to decrease the fluid average temperature during heat addition.
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The mass flow rate at the boiler is the same as the mass flow rate at the turbine.
The mass flow rate at the boiler is the same as the mass flow rate at the turbine.
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The saturated water at the feedwater heater is at the boiler pressure.
The saturated water at the feedwater heater is at the boiler pressure.
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The steam extracted from the turbine is sent to the condenser.
The steam extracted from the turbine is sent to the condenser.
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The cycle repeats again after the water is heated in the boiler.
The cycle repeats again after the water is heated in the boiler.
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The pump that sends the saturated water to the feedwater heater is the same as the pump that sends the water to the boiler pressure.
The pump that sends the saturated water to the feedwater heater is the same as the pump that sends the water to the boiler pressure.
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Study Notes
Regenerative Rankine Cycle
- Steam power plants generate most of the electric power in the world, and efforts are constantly made to improve the efficiency of the cycle.
- The ideal regenerative Rankine cycle increases the fluid average temperature during the heat addition process.
Limitations of Simple Rankine Cycle
- In a simple Rankine cycle, heat is added to the cycle during process 4-4'-1, but the temperature of the water is low during this stage.
- This reduces the average temperature during heat addition (process 4-4'-1).
Regeneration Process
- Regeneration increases the temperature of the feedwater (water leaving the pump and entering the boiler) by extracting steam from the turbine to heat the feedwater.
- The heat exchanger where heat is transferred from steam to feedwater is called a regenerator, or a feedwater heater.
Types of Feedwater Heaters
- There are two main types of feedwater heaters: open and closed feedwater heaters.
- Open feedwater heaters mix steam with compressed water from the pump, while closed feedwater heaters do not mix the steam with the compressed water.
Open Feedwater Heater
- An open feedwater heater is a mixing chamber where the steam extracted from the turbine mixes with the water exiting the pump.
- In an ideal condition, the water leaves the heater as a saturated liquid at the heater pressure.
Ideal Regenerative Rankine Cycle
- Steam from the boiler expands in the turbine to an intermediate pressure, and some of the steam is extracted and sent to the feedwater heater.
- The remaining steam in the turbine continues to expand to the condenser pressure.
- Saturated water from the condenser is pumped to the feedwater pressure and sent to the feedwater heater.
- At the feedwater heater, the compressed water is mixed with the steam extracted from the turbine and exits the feedwater heater as saturated water at the heater pressure.
- The saturated water is pumped to the boiler pressure by a second pump, then heated to a higher temperature in the boiler, and the cycle repeats again.
- The mass flow rate at each component is different, with y kg of steam extracted to the feedwater heater and (1-y) kg continuing to expand to the condenser pressure.
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Description
Learn about the improvements and limitations of the Rankine cycle in steam power plants, focusing on efficiency and temperature during the heat addition process.
