Vapour and Combined Power Cycle

Rankine Cycle 

Rankine cycle is an ideal cycle for Vapour Power Cycles and is normally used for Electricity Generation.

The Rankine cycle consist of following steps:

• 1 ↝ 2 : Isentropic Compression in Pump.
• 2 ↝ 3 : Constant Pressure Heat Addition in Boiler.
• 3 ↝ 4 : IsentropicExpansion in Turbine.
• 4 ↝ 1 : Constant Pressure Heat Rejection in Condenser.

Energy Balance:

Since, all the devices which Rankine Cycle posses are steady flow devices, so the energy balance for Rankine cycle is:

》For Pump ( q = 0 ):

》For Boiler ( w = 0 ):

》For Turbine ( q = 0 ):

》For condenser ( w = 0 ):

The thermal efficiency of Rankine Cycle is:

How can we Increase the Efficiency of A Rankine Cycle:

The efficiency of a Rankine cycle can be increased:

1. Increasing the avg. temperate at which heat is added 
2. Decreasing the avg. Temperature  at which heat is rejected.

The above two objectives can be achieved by following three methods:

1. By Superheating the steam in the Boiler:

By superheating the fluid, the area W2 is added, so increase its efficiency.

2. By Increasing Boiler Pressure:

By increasing the boiler pressure, the area W2 is added, so increase its efficiency.

3. By Decreasing the Condenser Pressure:

By Decreasing the condenser pressure, the area W2 is added, so increase its efficiency.

Boilers 

 A fuel-burning apparatus or container used for heating water is called Boiler.

Types of Boilers:

There are many types of boilers but commonly used boilers in Industries are:

1. Fire-Tube Boilers:

In fire-tube boiler, flue gases or combustion gases are inside the tubes and water will be in the shell. They are big in size, require much time for heat transfer, require greater maintanences and are suitable for low pressure industrial applications.

2. Water-Tube Boilers:

In water-tube boiler, water is inside the tubes and hot gases will be in the shell. They are small in size, require not much time for heat transfer, require less maintanences and are suitable for high pressure industrial applications.

Dalton's Law of Partial Pressure:

It states that:

Total pressure of a cylinder is equal to the sum of pressure of individual gases.

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