Some other liquid in boilers

[New User]

Why only water is used in water in boilers at steam power plant? can we use other liquid?

water has high boiling point and latent heat of vaporization so it requires more energy to make steam from it, what if we use some other liquid having lower latent heat of vaporization and use its vapours for same purpose as steam , can we save energy which is wasting in conversion of water to steam?

[Janus]

It is the latent heat in the steam that we extract for the power generated, it isn't wasted.

[Wilmot McCutchen]

There is the organic Rankine cycle.

 

Only 30% of the energy in the fuel goes into rotating the turbines to make electricity, and 70% is wasted into the atmosphere. Along with enormous amounts of fresh water. Thermal power plants are the biggest consumers of fresh water, worst of all users. The obsolete wet cooling technology needs a serious look.

[John Cuthber]

Slightly frighteningly, they do use other liquids.

http://en.wikipedia.org/wiki/Naphtha_launch#Naphtha_engine

[Enthalpy]

CO₂ is proposed especially for cycles with a limited temperature difference, like the Oceanic temperature gradient. It has a high boiling pressure at moderate temperature, a high heat capacity, a huge density that shrinks all tubes and turbines and reduces the blade speed.

 

In general use, water is hard to replace, because of its huge heat capacity, small viscosity, etc.

 

The latent heat isn't completely wasted. At least in water-cooled nuclear reactors, vapour is saturated because the heat source isn't very hot, and a part condenses in the turbines, releasing heat. Surprisingly, the turbine blades resist many months under these conditions.

 

I too read and heard "overheat steam to avoid condensation hence improve efficiency" but things aren't that simple... Without condensation, a water-cooled nuclear power plant just couldn't achieve 30% efficiency.

[alpha2cen]

This is a diagram of the maximum efficiency of a heat engine.

Turbine efficiency can be calculated by using this equation.

Efficiency =( H_h - H_{turbine, out})/(H_h - H_{iso-entropy, out})

H; enthalpy

Edited November 21, 2012 by alpha2cen

[New User]

Thank you all. One more clarification please, Is it latent heat or the kinetic energy of the steam/vapours which runs the turbine? And i am asking about the one in which steam directly falls on the turbine blades.

Edited November 23, 2012 by New User

[alpha2cen]

At the turbine, steam expansion step occurs. So, expansion energy turns the turbine blade. Directly impacting the turbine blade method is Pelton waterwheel method. This method is not used for the steam turbine.