chapter 9 Steam Power Cycle

9-1 The Rankine Cycle Vapor Carnot cycle T s There are some problems: (1)Compressor (2)turbine

Rankine cycle

Trained as a civil engineer, William Rankine ( )was appointed to the chairman of civil engineering and mechanics at Glasgow in He worked on heat, and attempted to derive Sadi Carnot's law from his own hypothesis. He was elected a Fellow of the Royal Society in Among his most important works are Manual of Applied Mechanics (1858), Manual of the Steam Engine and Other Prime Movers (1859). Sadi Carnot

The efficiency of Rankine cycle q absorb = h 2 - h 1 q exhaust =h 3 – h 4

Usually, The properties: p 1, t 1 and p 2 are available for a power plant,then: h 1 : From p 1, t 1, get h 1, s 1 h2:h2: From p 2, get s 2 ’, s 3 ” h 2 ’, h 2 ” So, x can be known h3:h3: From p 2, get h 2 ’, s 2 ’. h 3 = h 3 ’ s 3 = s 3 ’ h4:h4: From p 1, s 1 = s 4 get h 4

9-2 The Influence of Steam Property Exhaust Pressure To decrease the exhaust pressure can increase the efficiency of Rankine cycle. But the dryness fraction will increase too. This can lead some damage to steam turbine

Inlet temperature To decrease the inlet temperature can increase the efficiency of Rankine cycle. But this increase depends on boiler material

Inlet pressure To increase the inlet pressure can increase the efficiency of Rankine cycle greatly. But this increase also depends on boiler material

boiler condenser Feed water pump Steam turbine Equipments of Reheat Cycle Reheater 9-3 Reheat Cycle

9-3-2 Efficiency T-s diagramEfficiency

The properties: p 1, t 1, p m, t n (equals t 1 usually), p 2 are available for a reheat power plant,then: h 1 : From p 1, t 1, get h 1, s 1 hm:hm: From p 2, s 2 =s 1, get h m hn:hn: From p m, t n, get h n h2:h2: From p 2, get s 2 ’, s 3 ” h 2 ’, h 2 ” So, x can be known

h3:h3: From p 2, get h 2 ’, s 2 ’. h 3 = h 3 ’ s 3 = s 3 ’ h4:h4: From p 1, s 1 = s 4 get h 4

9-4 Regenerative Cycle Ideal Regenerative Cycle

9-4-2 Regenerative Cycle boiler condenser Feed water pump Steam turbine Feed water heater Steam drainage pump a

T s The feed water is heated by steam bleeding out from steam turbine. The average temperature of heat absorption process increases then.

boiler condenser Feed water pump Steam turbine Feed water heater drainage pump a 6 b

T s The more stages of bleeding steam, the higher efficiency the cycle has

9-4-2 The efficiency of regenerative Cycle As to a two stages regenerative cycle,the properties: p 1, t 1, p a, p b, p 2 are available. If neglect the pump work, the T-s diagram should be as following. T s a b 6

The enthalpy of each point h1:h1: From p 1, t 1, get h 1, s 1 ha:ha: From p a, s 1, get h a hb:hb: From p b, s 1, get h b T s a b 6 h2:h2: From p 2, get s 2 ’, s 3 ” h 2 ’, h 2 ” So, x can be known

T s a b 6 h3:h3: From p 2, get h 2 ’, h 3 = h 2 ’ h5:h5: From p b, get h b ’, h 5 = h b ’ h6:h6: From p a, get h a ’, h 6 = h a ’

As to the 1 st stage heater haha h5h5 h6h6 According to the first law of thermodynamics

As to the 2 nd stage heater According to the first law of thermodynamics hbhb h4h4 h5h5

9-5 Other Steam Power Cycle Super-critical Cycle

9-5-2 The Combined Gas-Vapor Power Cycle

9-5-2 Binary-vapor Cycle

The End of This Chapter Thank you