What is Rankine cycle ? | Four stages of rankine cycle

 What is the Rankine cycle?

Ranking cycle is a very important operating cycle of the power plant it is also called as Rankine vapor cycle that converts heat energy into mechanical energy. The thermodynamics cycle using vapor as a working substance is called a vapor power cycle. The power plants using steam as a working substance are called steam power plants.

Rankine cycle is an ideal reversible cycle for steam power plant 

What are the four processes of Rankine cycle?

Rankine cycle

Prosses (1-2) = Pumping of feed water to the boiler from pressure, pb to pressure p1.The compression process is reversible.

Process (2-3) =conversion of feed water into the steam at the constant pressure equals the boiler pressure p1. The heat supply during this process is qi.

Process (3-4) =Reversible expansion of steam in turbine from boiler pressure, p1 to backpressure Pb, turbine work is WT

Process (4-1) =The steam is condensed at constant pressure pb in the condenser. The steam rejects its latent heat of vaporization to the cooling water equal to qr

Rankine cycle

Rankine cycle

Analysis of  Rankine cycle:-

Assume 1 kg of stream flow in the cycle 

1) Process (2-3) in boiler:-

               Heat supplied, qi  = (h3 - h2)                    ....................(since work done is zero)

2) Process (3-4) in turbine:-

               Turbine work, wt  = (h3 - h4)                    ....................(since heat transfer is zero)

3) Process (4-1) in condenser:-

       Heat rejected to cooling water, qr = (h4 - h1)    ....................(since work done is zero)

4) Process (1-2) in feed pump :-

         pump work,       wp  =  (h2 - h1)                        ....................(since heat transfer is zero)

         pump work,        wp = ∫ -v dp

wp  = -v  ∫ 

Magnitude of wp   =  v (p1 - pb)

Specific volume of water,    v =0.001m³/kg . if pressure are measured in bar, then 

                                 wp = 0.001 (p1 - pb) x 10^5 Nm/kg or j/kg

                                 wp =  [0.001 (p1 - pb) x 10^5]／1000 kj/kg

                                 wp = [(p1-pb ／ 10] kj/kg = (h2 - h1)

shaft works, ws 

                                ws=wt-wp         or ws=(h3 - h4) - (h2 - h1)

The efficiency of Rankine cycle, η R

η R = shaft work ws ／  Heat supplied qi

       

       = (h3 - h4) - (h2 - h1)  ／ (h3 - h2)

Steam rate or specific steam consumption:-

 Steam rate , S.R  = 3600 ／ ws =3600／(h3 - h4)  -  (h2 - h1) kg/Kh