Rankine cycle

1. • The Rankine cycle is an ideal cycle if water passes
through the four components without irreversibility's
and pressure drops. The ideal Rankine cycle
consists of the following four processes, as shown on
the T-s diagram on the left:
IDEAL Rankine Cycle

2. Actual Rankine Cycle
The actual vapor power cycle differs from the ideal Rankine cycle as
a result of irreversibility's in various components. The two
common source of irreversibility's are the
1) Friction
2) Undesired heat loss to the surroundings.

3. Adiabatic Expansion in
Turbine
Constant Pressure Heat
Rejection in Condenser
Pump Work
Sensible heat Addition in
Economizer
ENTROPY
T
E
M
P
E
R
A
T
U
R
E
Latent Heat Addition in
Evaporator (constt. Pressure) Super Heating
L + V
BASIC RANKINE CYCLE (SUB-CRITICAL)

4. EFFECTS OF LOWERING THE CONDENSER PRESSURE
• Lowering condenser pressure lowers the
temperature at which condensation
takes place thereby increasing the cycle
efficiency.
• LIMITATION AND SIDE EFFECTS :
 Lower limit is the saturation pressure
corresponding to the temperature of
cooling media.
 Creates possibility of ‘Air Leakage’
into the condenser
 Increases moisture content of the steam
at the final stages of turbine that
decreases the turbine efficiency and
causes erosion in turbine blades.

5. EFFECT OF SUPERHEAT
• Superheating the steam to higher
temperature without increasing the
boiler pressure increases thermal
efficiency.
• It also decreases the moisture content
of the steam at the turbine exit.
• LIMITATION:
Highest temperature of superheated
steam is limited by the metallurgical
constraint.

6. EFFECT OF INCREASING THE INLET
PRESSURE
• Increasing the inlet pressure
raises the mean temperature
at which heat is added in the
boiler thereby increasing the
efficiency.
• Side Effects:
 Increases moisture content at
the final stages of the turbine
that decreases the turbine
efficiency and erodes turbine
blades.

7. C
ENTROPY
T
E
M
P
E
R
A
T
U
R
E
RANKINE CYCLE (SUPERCRITICAL)

9. • Efficiency of fossil fired power plants can be increased by increasing
the pressure and temperature of the steam at the turbine inlet, if
possible, even beyond the critical point of water ie supercritical state.
• Increased efficiency of the Rankine-Steam Power Cycle results in
decreased amounts of fossil fuel consumed and emissions generated
besides lowering the per unit generation cost.
• An increase in power plant efficiency from 30% to 50% is estimated to
decrease CO2 emission by nearly 30%.
• To allow these increases, advanced materials are needed that are able to
withstand higher temperatures and pressures in terms of :
 Strength,
 Creep, and
 oxidation resistance.
INCREASING THE EFFICIENCY OF
RANKINE CYCLE