Question

a) A steam power plant operates on an ideal reheat-regenerative Rankine cycle. Steam enters the high-pressure turbine (HPT) at a pressure of 10 MPa and temperature of 550°C. The steam expands through the HPT stage to a pressure of 0.6 MPa. Some of the steam at the end of the expansion process in HPT is extracted for a regeneration process in a closed-type feedwater heater. The steam leaves the heater as a saturated liquid and then is throttled to the condenser pressure of 10 kPa. The remaining steam at the end of HPT is reheated at constant pressure of 0.6 MPa to a temperature of 500°C before entering the low-pressure turbine (LPT). The steam finally expands through the LPT to the condenser pressure of 10 kPa. The water leaves the condenser as a saturated liquid. The feedwater in the heater is preheated to saturation temperature of the reheat pressure. The plant produces a net power output of 115 MW. i. Show the cycle on a temperature-entropy (T-s) diagram. ii. Determine the mass fraction of the extracted steam. Calculate the mass flow rate of the steam, kg/s. iv. Compute the thermal efficiency,%. ili.

Answer 1

15580 Tompa 5 4 500°c 个 T 0.6 MPa 3 8 lo lepa 7 S -> The above shown is the entire cycle of the system, where Pia Compa, P220-6MPa, P3 2 10kPa - 10 MPa (ii) Now Now let us determine the enthalpies at every points in in the cycle. hiz 3459 kJ/icg, Siz 6.562 kJ/icgle at 550c and Similarily, at 0.6MPa, hgh2 = 27576] /icg and hf 2670:6K 1/icg V3 1:101 x 103 m3 leg. Since 4-3 is an is entropic process for ideal Cycle, h3+ V3 (Pi-P2) hz ht 2

2 67016 + 1.101x163 (10X10- 0.6x10 [/veg 1 - 101 X10?(104-06x103) 680.94 kJ ie W34 10:34 109 /icg. ho 2 2 2 hg ² ho 2 Now at 500°c, 0-6 MPa 3 483 kJ J/kg. at 10k pa 2585 II lig. hfa hi 191.83 le Il vege V7 1.01x10-3 m3/149 Now 7-8 is an risentropic process. Wis Ny (Pe- P3) voi x103 (0.6x103 - 10) 0.595 kJ/kg : hg hy + wis 191.83 + 0595 192-425 kJ / reg. 2 2 2 2 2 y reheat 5o Enthalpies at every point is found. Let be the mass fraction of Now considering energy balance at 3- Ein fout ie y ha +(1-y) hs h3 by Substituting, 2 2

y x 2751 (-y)! 192: 425 2 670 6 0.3 2. Y le Mass fraction is 0-3 Til from the above lycle, Wout 2 Chi-hz) + (1-4) (hr-ho) 3459-2757) + (1-0-3)(34 3483 2585) * 1330-6. II/icg 2 Win 2 2 ((-4) (h8-67) + Cha-hs) - (-03) (192.425 - 191.425 + (680-94 - 610-6) 10:156 10 J /leg: m (Wout-win) where m Mass flow rate in lg ls 115 x103 kJ m (1330-6-10-756) 87-13 lcg is Now Whet m 2 Mass flow rate is 87.13 1cgls

iv 2 for thermal Efficiency, qin Chi-ha) +(8-4) (ha-ha) + (1-4) Ch3-hs) > (3459- 680.94) + 0.1(3483 -2757) +0-1 (670-6-192.425) 3621.6825 KJ /icg gout 2 (1-9)(h.6-by) tych2-h3) 0.7 (2585-191183) + 0-3 ( 2757 670-6 2301'! IcJ kg . thermal Efficiency, q qout qin 23011 362126825 0: 364 36-40% V