BeginnerTopic 34 of 105Thermodynamics & Fluids
Reheat and regeneration
Improve Rankine efficiency by raising mean heat addition temperature.
In depth
Reheat: re-heat steam after partial expansion, reducing moisture and increasing work. Regeneration: extract steam to preheat feedwater (open or closed heaters), raising mean temperature of heat addition. Together they raise efficiency by several percentage points.
Key points
- Feedwater heaters
- Optimal reheat pressure about 20–25% of boiler
- Carnot-like effect
ExampleModern plants have 6–8 feedwater heaters and one or two reheats.
What is Reheat and regeneration?
Improve Rankine efficiency by raising mean heat addition temperature.
Why is it important to understand reheat and regeneration?
Reheat and regeneration raise the average temperature at which heat is added in a steam cycle, which improves efficiency and reduces moisture at turbine exit.
What does reheat do?
It sends partly expanded steam back to the boiler for further heating, which raises the average heat addition temperature and reduces wetness in the low-pressure turbine.
What is regeneration?
Extracting steam from the turbine to heat the feedwater, which reduces the heat needed from the boiler and improves efficiency.
How is Reheat and regeneration used in practice?
Typical applications include adding a reheat stage to a large coal plant to reduce blade erosion, preheating feedwater with extraction steam to improve efficiency and designing a combined heat and power plant with extraction for district heating.
What should I learn before Reheat and regeneration?
Study "Rankine cycle" first (topic 33 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
What are the key points of Reheat and regeneration?
Feedwater heaters. Optimal reheat pressure about 20–25% of boiler. Carnot-like effect.
Can you give an example of Reheat and regeneration?
Modern plants have 6–8 feedwater heaters and one or two reheats.
What comes after Reheat and regeneration?
The next topic is "Combined cycle plants", which builds directly on this one.
How difficult is Reheat and regeneration?
It is classed as Beginner in Thermodynamics & Fluids (topic 34 of 105). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.