power plant lecture notes - chapter-2 steam power plant cycles

كلية الھندسة –الجامعة المستنصرية يـــةانيكـــــالميكالھندســــــــة م ــــقس

ةــــــــــــــــــــــات طاقــــــــــــمحط

CHAPTER(2)Steam Power Plant Cycles

عبد االميرد. مشعل أ.م.

05‐Oct‐14

Chapter2

SteamPowerPlantCycles

Simple vapor cycle and its components: Boiler, Turbine, Condenser, Pump, Carnot Cycle for Steam, Disadvantages of Carnot Cycle application, Rankine Cycle and its components: Steam Generator, Turbine, Condenser, Feed Pump, Cycle net work, Work Ratio, Steam Rate, Heat Rate, Efficiencies in Steam Power Plant: Thermal efficiency, Mechanical efficiency, Isentropic efficiency, Example (1), Mean Temperature of Heat Addition, Effect of Superheat, Effect of inlet pressure, Reheat, Example (2), Regeneration, The Stirling Cycle, The ideal regenerative cycle, Type of regenerative feed water heaters, Open type regenerative feed water heaters, Example (3), Closed type regenerative feed water heaters with drain cascaded backward, Closed type regenerative feed water heaters with drain pumped forward, Example (4), Cogeneration: Back pressure Turbine, Pass-Out Turbine, Example (5), Tutorial Sheet 2.

Power Plant Engineering TUTORIAL SHEET ‐ 2 كلية الھندسة –الجامعة المستنصرية

Steam Power Plant Cycles اقةــــــــمحطات ط –قسم الميكانيك

40

1‐ Draw a simple sketch then show its processes on the (T‐s) and (h‐s) diagrams for each

ideal cycle listed in the table below. Cycle Type Steam Condition Closed FWH Direct

Contact FWH

Turbine inlet Reheat Outlet Condenser Drain Cascaded Backward

Drain Pumped Forward

A Rankine 4 bar, Dry ‐ 0.035 bar ‐ ‐ ‐

B Rankine 60 bar, 410 Co

‐ 0.07 bar ‐ ‐ ‐

C Reheat 100 bar, 410 Co

60 bar, 410 Co 0.07 bar ‐ ‐ ‐

D Regenerative 60 bar, 410 Co

‐ 0.07 bar ‐ ‐ 20 bar

10 bar

E Regenerative 60 bar, 410 Co

‐ 0.07 bar 20 bar ‐ 10 bar

F Regenerative 60 bar, 410 Co

‐ 0.07 bar ‐ 20 bar 10 bar

G Regenerative 60 bar, 410 Co

‐ 0.07 bar 20 bar 10 bar ‐

H Regenerative 60 bar, 410 Co

‐ 0.07 bar ‐ ‐ 20 bar

10 bar

2 bar

I Regenerative 60 bar, 410 Co

‐ 0.07 bar 20 bar ‐ 2 bar

10 bar

J Regenerative 60 bar, 410 Co

‐ 0.07 bar ‐ 20 bar 2 bar

10 bar

K Regenerative 60 bar, 410 Co

‐ 0.07 bar 20 bar 10 bar 2 bar

L Reheat‐Regenerative

100 bar, 410 Co

25 bar, 410 Co 0.07 bar ‐ ‐ 12 bar

2 bar

0.5 bar

M Reheat‐Regenerative

100 bar, 410 Co

25 bar, 410 Co 0.07 bar 12 bar ‐ 0.5 bar

2 bar

N Reheat‐Regenerative

100 bar, 410 Co

25 bar, 410 Co 0.07 bar ‐ 12 bar 0.5 bar

2 bar

O Reheat‐Regenerative

100 bar, 410 Co

25 bar, 410 Co 0.07 bar 12 bar 2 bar 0.5 bar



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2‐ Draw all the details of the (T‐s) diagram of the ideal steam power plant layout shown in

the figure below.

3‐ For the following steam cycles that are listed in the table below, find (a) in (kj/kg) (b)

in (kj/kg) (c) in (kj/kg) (d) (e) S.S.C in (kg/kW.hr) and (f) moisture fraction at the

end of the turbine process. Show the results in tabular form with your comments.

Cycle Type Boiler Outlet Condenser Pressure

A Ideal Rankine, Neglect WP 10 bar, Saturated 1 bar

B Assume 75% 10 bar, Saturated 1 bar

C Ideal Rankine 10 bar, Saturated 0.1 bar

D Ideal Rankine 10 bar, 300 Co 0.1 bar

E Ideal Rankine 160 bar, 600 Co 0.1 bar

F Reheat to 600 Co at maximum I.P to limit end moisture to 15% 160 bar, 600 Co 0.1 bar

G Reheat to 600 Co at maximum I.P to limit end moisture to 15%

but with 75%

160 bar, 600 Co 0.1 bar

H Single open feed water heater at 110 Co 10 bar, Saturated 0.1 bar

I Two open feed water heaters at 90 Co and 135 Co 10 bar, Saturated 0.1 bar

J Two closed feed water heaters with drain cascaded backward at 90 Co and 135 Co

10 bar, Saturated 0.1 bar



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4‐ In an ideal steam cycle, steam at (20 bar, 360 Co) is expanded in a turbine to (0.08 bar).

It then enters a condenser where it is condensed to saturated liquid water. Then the

pump feeds back the water into the boiler. Find per kg of steam (a) (b) (c)

if 80% , find the percentage reduction in and . Ans. (a) 969.61 (kj/kg)

(b) 32.5% (c) 20.1 % (d) 20.1 %

5‐ Neglect the feed pump term, compare the Rankine cycle efficiency of a high pressure

steam plant operating at (80 bar) with that of a low pressure plant at (40 bar). In both

cases, the maximum temperature is (400 Co) and the condenser pressure is (0.07 bar).

Explain your result briefly. Also find the ratio of the heat rejected from the condensing

plants. Assume that the turbines are to produce the same power. Ans. 0.391, 0.357, 0.83

(H.P/L.P)

6‐ An ideal reheat cycle works between pressures of (120 and 0.035 bar). The steam is

superheated to (570 Co) and after expansion to the dry saturated state is reheated to

(500 Co). Calculate the thermal efficiency of the cycle taking account of the feed pump

work. Ans. 0.453

7‐ A steam turbine is supplied with steam at (40 bar, 450 Co) and exhausted at (0.035 bar).

Neglecting the feed pump term, find the ideal Rankine cycle efficiency of the plant, and

compare it with the ideal efficiency which would be obtained if regenerative feed water

heating were employed. Assume the use of open heaters and (a) One bleeding point (3

bar), (b) Three bleeding points at (15, 3, and 0.5 bar). Ans. 0.391, (a) 0.173 kg, 0.415, (b)

0.114, 0.083, 0.08 kg, 0.429

8‐ Saturated steam at (30 bar) enters a high pressure turbine and expands isentropically to

a pressure at which its dryness fraction is (0.841%). At this pressure, the moisture is

extracted and returned to the boiler via feed pump. The remainder, assumed to be dry

steam, is expanded isentropically to (0.04 bar) in a low pressure turbine, and the

condensate is returned to the boiler via a second feed pump. Calculate the cycle

efficiency when the isentropic efficiency of each turbine and feed pump is (0.8). What is

then the dryness fraction at the exit of each turbine? Ans. 0.357, 0.291, 0.88, and 0.871.



43

9‐ A steam turbine gets its supply of steam at (70 bar), (450 Co). After expanding to (25 bar) in high pressure stages, it is reheated to (420 Co) at the constant pressure. Next, it is expanded in intermediate pressure stages to the extraction point for a direct‐contact feed water heater to an appropriate minimum pressure such that part of the steam bled at this pressure heats the feed water to a temperature of (180 Co). The remaining steam expands from this pressure to a condenser pressure of (0.07 bar) in the low pressure stage. The isentropic efficiency of the high pressure stage is (78.5%), while that of the intermediate and low pressure stages is (83%) each. Draw a simple sketch of the cycle and show its processes on the (T‐s) and (h‐s) diagrams, then determine the following. (a) The minimum pressure at which bleeding is necessary. (b) The quantity of the steam bled per kg of flow at the turbine inlet. (c) The thermal efficiency of the cycle. (Neglect pumps work). Ans. (a) 10 bar, (b) 0.206 kg/kg steam flow at the turbine inlet, (c) 35.92%.

10‐ In an ideal reheat cycle, steam initially at (150 bar, 550 Co) expands in a turbine to a condenser pressure of (0.1 bar), and the moisture in the condenser inlet is (5%). Determine (a) The reheat pressure, (b) The cycle efficiency, and (c) The steam rate. Ans. (a) 13.5 bar, (b) 43.65%, (c) 205 kg/kW.hr.

11‐ The net power output of an ideal reheat‐regenerative cycle is (80 MW). Steam enters the

HP turbine at (80 bar) and (500 Co), and expands till it becomes saturated vapor. Some

of the steam then goes to an open feed water heater and the balance is reheated to (400

Co), after which it expands in the LP turbine to (0.07 bar). Determine (a) The reheat

pressure, (b) The steam mass flow rate to the HP turbine, and (c) The thermal efficiency.

Ans. (a) 6.5 bar, (b) 58.4 kg/s, and (c) 43.7%.

12‐ The net power output of an ideal reheat‐regenerative cycle is (100 MW). Steam enters the HP turbine at (90 bar) and (550 Co). After expansion to (7 bar), some of the steam goes to an open feed water heater and the balance is reheated to (400 Co), after which it expands in the LP turbine to (0.07 bar). Determine (a) The steam mass flow rate to the HP turbine in (ton/hr), (b) The total pump work, and (c) The thermal efficiency. Ans. (a) 256. 186 (ton/hr), (b) 9.767 (kj/kg), and (c) 44.36%.

power plant lecture notes - chapter-2 steam power plant cycles

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