Lecture 2 - The Ranking Cycle.pptx power

powerplant 2 lecture

1. Rankine Power Cycles

2. Today’s Lecture The Rankine Power Cycle The Ideal Rankine Cycle Performance Parameters Modification in Rankine Cycle Superheat Rankine Cycle Reheat Rankine Cycle Solved Problems Example 2.1 – Ideal Rankine Cycle (El Wakeel) Example 8.3 – Reheat Cycle (Moran and Shapiro) 2

3. I am Dr Muhammad Alam Zaib Khan You can find me at @ [email protected] Hello! 3

4. Rankine Power Cycles Power Generation – Vapor Power Systems 1 4

5. The Rankine cycle is the dominant technology for global electricity generation. It is the foundation for approximately 65-70% of the world's electricity. This translates to an estimated 45,000 to 50,000 Rankine-cycle power plants of significant size worldwide. 5

6. Fossil-Fueled Rankine Power Plant 6 Fuel Handling and Combustion System (The "Heat Source") Steam Generation System (The "Boiler") Power Generation System (The "Engine") Feedwater and Preheating System (The "Recycling Loop") Our main concern in these lectures will be subsystem B (in the schematic) , where the conversion of heat into work occurs. Fossil-Fueled Vapor Power Plant Top-View of Coal Fired Vapor Power Plant in West Burton A, in Lincolnshire

7. Ideal Rankine Cycle 7 Process 1 – 2: Isentropic expansion of the working fluid through a turbine from saturated vapor at state 1 to the condenser pressure. The quality decreases from unity. Process 2 – 3: Heat transfer from the working fluid as it flows at constant pressure through the condenser with saturated liquid at state 3. Process 3 – 4: Isentropic compression in the pump to state 4 in the compressed liquid region. Process 4 – 1: Heat transfer to the working fluid as it flows at constant pressure through the boiler to complete the cycle. P – v  coordinates]   [ T – s coordinates] [ h – s coordinates] Carnot cycle ? Schematic & T – s Diagram of an Ideal Rankine Cycle

8. Performance Parameters 8 Thermal efficiency: Using the enthalpies, heat and work quantities and expressions, the thermal efficiency of the power cycle is;   Alternatively, the thermal efficiency can also be expressed in terms of net Heat Inputs;   Back Work Ratio , or bwr , defined as the ratio of the pump work input to the work developed by the turbine, it is written as;   The effect of irreversibilities ? The Rankine cycle is less efficient than the Carnot cycle for given maximum and minimum temperatures

9. Enhancements of, and Effect of Design Parameters 9 The heat addition is continued past the point of vapor saturation, into the Superheat with P 4 (= P a = P 1 = P 1’ ). This does several things. First, it increases the mean temperature at which heat is added, T m2 , thus increasing the efficiency of the cycle. Second is that the quality of the two-phase mixture during the expansion is higher with superheating, so that there is less moisture content in the mixture as it flows through the turbine. Hence, decreasing the mechanical deterioration of the blades. P – v  coordinates]   [ T – s coordinates] [ h – s coordinates] Carnot cycle ? Schematic & T – s Diagram of an Ideal Superheat Rankine Cycle

10. Enhancement in Performance Parameters 10 Thermal efficiency: The thermal efficiency of the ideal Rankine cycle with superheating is ;   Alternatively, the thermal efficiency of Superheat Rankine Cycle can also be expressed in terms of net Heat Inputs;   The effect of Degree of Superheat ? Compared to the basic cycle, superheating has increased the turbine work, increased the mean temperature at which heat is received, T m2 , and increased the cycle efficiency T – s Diagram – Comparison of an Ideal Rankine Cycle & Carnot Cycle

11. Enhancements of, and Effect of Design Parameters 11 To alleviate the problem of having moisture in the turbine, one can heat again after an initial expansion in a turbine. This process is known as reheat. The main practical advantage of reheat (and of superheating) is the decrease in moisture content in the turbine because most of the heat addition in the cycle occurs in the vaporization part of the heat addition process. Thermal efficiency: The thermal efficiency of the ideal Rankine cycle with superheating is ;   Schematic & T – s Diagram of an Ideal Reheat Rankine Cycle

12. The Effect of Pressures 12 Effect of exit pressure on Rankine cycle efficiency Effect of maximum boiler pressure on Rankine cycle efficiency The Effect of Pressure Minimum Pressure for Condenser Maximum Pressure for Boiler The average temperature in both cases is increased over the original cycle, so that the efficiency increases

13. Solved Problems Power Generation – Vapor Power Systems 2 13

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15. 15 Schematic & T – s Diagram of an Ideal Reheat Rankine Cycle

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17. Any questions ? You can find me at [email protected] Thanks! 17