VARIABLE EFFECTING EFFICIENCY OF RANKINE,REHEAT,REGENERATIVE CYCLE
Rankine Vapor Cycle p v 1 6 5 4 3 2 p1 p2 S 4 6 1 2 3 T s 1 6 5 4 3 2
From the equation of the efficiency of rankine cycle, the factors affecting the efficiency of rankine cycle are:
1. － Pressure of Steam, Turbine Inlet 3 4 5 5’ 1’ 1 2 2’ －Unchange Two Cycles: ① 3-4-5-1-2-3 ② 3-4-5’-1’-2’-3
3 4 5 5’ 1’ 1 2 2’ Disadvantages: 1. decrease the turbine efficiency and erodes the turbine blades. Increase of requirements on pressure vessels and equipment investment. 2.
2. － Temperature of Steam, Turbine Inlet 3 4 5 1 1’ 2’ 2 6 －Unchange Two Cycles: ① 3-4-5-6-1-2-3 ② 3-4-5-6-1’-2’-3
Advantages: i ii Disadvantages: it decreases the moisture content 3 4 5 1 1’ 2’ 2 6 Advantages: i ii it decreases the moisture content of the steam at the turbine exit. Disadvantages: Superheating temperature is limited by metallurgical considerations.
3. － Condenser Pressure, Turbine Exit 4 5 1 3’ 2’ 2 6 4’ －Unchange Two Cycles: ① 1-2-3-4-5-6-1 ② 1-2’-3’-4’-5-6-1
i Disadvantages: ii i Condense pressure is limited 3 4 5 1 3’ 2’ 2 6 4’ i Disadvantages: i Condense pressure is limited by the sink temperature. ii It increases the moisture content which is highly undesirable. ii
Reheat Cycle Allows us to increase boiler pressure and temperature of the steam entering into the turbine without problems of low quality at turbine exit. The erosion and corrosion difficulties due to the presence of water particles in the steam can be avoided by reheating of steam, because the steam becomes dry after reheating. In reheating, whole steam is extracted from suitable point in the turbine and is reached with the help of the flue gases in the boiler furnace.
3 c 2 a 1 5 4 6 b
Regeneration Preheats steam entering boiler using a feedwater heater, improving efficiency Also deaerates the fluid and reduces large volume flow rates at turbine exit.
Boiler Turbine Regenerator Condenser Mixing Chamber Pump II Pump I 1 2 7 3 4 5 6 3(4) 2 7 1 6 5 1kg akg (1-a)kg T s
A more complicated cycle…
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