--- title: "Regeneration in steam plant with P-V and T-S" subject: "Power Plant Equipment" chapter: 7 key: "semester_7/power_plant_equipment:steam-regeneration-pv-ts" source: https://www.bctengineer.com/q/semester_7/power_plant_equipment/steam-regeneration-pv-ts site: BCT Engineering --- # Regeneration in steam plant with P-V and T-S Power Plant Equipment · Chapter 7: Thermal (Steam) Power Plant - Asked in: 2076 Chaitra, 6+2 marks - Video: [Rankine with Regeneration](https://www.youtube.com/watch?v=dG_jA5HOG1c) — Christi Patton Luks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/power_plant_equipment/steam-regeneration-pv-ts - Whole chapter: https://www.bctengineer.com/md/semester_7/power_plant_equipment/chapter-7 ## Question Explain how regeneration increases the output of the steam turbine power plant along with the neat sketch and show the cycle in P-V and T-S diagram. ## Short answer Regeneration heats feedwater with bled steam, raising the mean heat-addition temperature and reducing heat rejected to the condenser. Efficiency improves by 10–15%, and for the same exhaust flow, plant output increases. ## Answer **Regeneration** is the heating of boiler feed water by steam bled from the turbine, instead of by the boiler fuel alone. It recovers latent heat of the bled steam that would otherwise be lost in the condenser. #### Layout (one open feed water heater) ```text 1 +--------+------>+---------------+ +-----+ | Boiler | | Turbine |===| Gen | | + S/H | +---------------+ +-----+ +--------+ | m kg (2) | (1-m) kg (3) ^ 7 v v | +-----------+ +-----------+ +--------+ 6 | Open FWH | | Condenser | | Pump 2 |<---| (mixing) | +-----------+ +--------+ +-----------+ | 4 ^ 5 | +--------+ | | Pump 1 |<--------+ +--------+ ``` #### Working 1. Steam at boiler pressure enters the turbine (1). 2. At an intermediate pressure, $m$ kg per kg of steam is **bled** (2) and sent to the feed water heater. 3. The rest, $(1-m)$ kg, expands to condenser pressure (3) and is condensed (4). 4. Pump 1 raises condensate to heater pressure (5). In the heater the bled steam mixes with it and condenses, giving saturated water at heater pressure (6). 5. Pump 2 raises it to boiler pressure (7) and it enters the boiler much hotter than in a simple cycle. #### Why efficiency (and effective output) increases - Heat supplied in the boiler falls from about $(h_1 - h_5)$ to $(h_1 - h_7)$; the remaining heat is added at a higher temperature, so the **mean temperature of heat addition rises**. - The bled steam's latent heat goes to the feed water, not to the cooling water, so **heat rejected falls** to $(1-m)(h_3-h_4)$. - Although work per kg of boiler steam falls slightly, efficiency rises by about 10-15% with several heaters; fuel per kWh falls. - Smaller exhaust flow means smaller LP blades and condenser, and turbine size can be raised for the same exhaust area, so **plant output increases**. - Hot feed water reduces thermal stresses in the boiler; an open heater also deaerates the water. $$ m = \frac{h_6 - h_5}{h_2 - h_5}, \qquad \eta = \frac{(h_1-h_2) + (1-m)(h_2-h_3) - W_p}{h_1 - h_7} $$ where $W_p = (1-m)W_{p1} + W_{p2}$ is the total pump work. #### P-v diagram ```text p ^ | 7 ________________ 1 | | \ | | \ expansion |5,6_ _ _ _ _ _ _ _ _ _2 (m kg bled) | | \ | | \___ | 4|_________________________3 +--------------------------------> v 4-5, 6-7 pumps (water, very small v); 5 and 6 are both at heater pressure 7-1 boiler, 1-2-3 turbine, 3-4 condenser ``` #### T-s diagram ```text T ^ 1 | /| | f----------g | | / | | 7 | | 6 . . . . . . . 2 bleed (m kg) | / | | 5 | | 4-----------------3 (1-m) kg +-------------------------> s 4-5 pump 1, 5 and 2 mix in FWH -> 6, 6-7 pump 2, 7-f-g-1 boiler, 1-2-3 turbine, 3-4 condenser ``` ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In the one open heater cycle, how much steam goes to the condenser? A. m kg B. (1 - m) kg C. 1 kg D. (1 + m) kg Answer: B. m kg is bled to the heater, leaving (1-m) kg to expand to the condenser. (Key point: Bled steam fraction) 2. What happens in the open (mixing) feed water heater? A. Bled steam mixes with condensate, condenses and gives saturated water at heater pressure B. Steam is superheated C. Water is converted to steam D. Steam is expanded in a nozzle Answer: A. Mixing yields saturated water at heater pressure (state 6), which pump 2 sends to the boiler. (Key point: Open heater action) 3. Heat rejected in the condenser per kg of boiler steam in regeneration is: A. (h3 - h4) B. (1-m)(h3 - h4) C. m(h3 - h4) D. (h1 - h7) Answer: B. Only (1-m) kg reaches the condenser, so heat rejected falls to (1-m)(h3-h4). (Key point: Heat rejected) 4. Heat supplied in the boiler changes from (h1 - h5) to: A. (h1 - h2) B. (h1 - h7) C. (h1 - h6) + h5 D. (h2 - h7) Answer: B. Feed water enters the boiler at state 7, hotter than state 5, so less heat is needed. (Key point: Heat supplied) 5. How can regeneration increase effective plant output? A. Smaller exhaust flow allows larger turbines for the same exhaust area B. It removes the feed pump C. It increases condenser size D. It lowers boiler pressure Answer: A. Reduced steam flow to the LP end and condenser lets turbine size be raised for the same exhaust area. (Key point: Effect on plant output) ## Related in Power Plant Equipment - [Steam plant improvement methods and regeneration](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Asteam-methods-regeneration) — Power Plant Equipment, chapter 7, asked 2× - [Reheater in steam plant with layout](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Asteam-reheater-layout) — Power Plant Equipment, chapter 7 - [Gas turbine improvement methods and regeneration](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Agt-methods-regeneration) — Power Plant Equipment, chapter 6 - [Steam plant components and reheating](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Asteam-components-reheating) — Power Plant Equipment, chapter 7 - [How a regenerator improves gas turbine output](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Agt-regenerator-explain) — Power Plant Equipment, chapter 6 - [Gas turbine 6:1: power output and efficiency](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Agt-6-1-power-efficiency) — Power Plant Equipment, chapter 6, asked 2× ## Related in other subjects - [Pumped storage plant: power, turbine, setting, surge](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Apumped-storage-turbine-surge-numerical) — Hydropower Engineering, chapter 7 - [Simple Rankine plant 2 MPa / 20 kPa: efficiency, power](https://www.bctengineer.com/question.md?key=semester_2%2Ffundamental_of_thermodynamics_and_heat_transfer%3Arankine-2mpa-20kpa-50kgs) — Fundamental of Thermodynamics & Heat Transfer, chapter 6 - [Adiabatic steam turbine 50 MW: mass flow, isentropic efficiency](https://www.bctengineer.com/question.md?key=semester_2%2Ffundamental_of_thermodynamics_and_heat_transfer%3Asteam-turbine-5mpa-500c-50mw) — Fundamental of Thermodynamics & Heat Transfer, chapter 5 - [Adiabatic steam turbine 70% isentropic efficiency](https://www.bctengineer.com/question.md?key=semester_2%2Ffundamental_of_thermodynamics_and_heat_transfer%3Aadiabatic-steam-turbine-70-percent-moisture) — Fundamental of Thermodynamics & Heat Transfer, chapter 5