In this video, we will understand how the Kalina Cycle works.
Here, we will mainly investigate the various reasons behind its high thermal efficiency compared to the Rankine cycle.
So let's start.
The major difference between a conventional Rankine cycle and the Kalina Cycle is that...
...the Kalina Cycle uses a mixture of two fluids as the working fluid.
The most commonly used working fluid in a Kalina Cycle is a mixture of water and ammonia.
So what is the advantage of this? Why should we use a mixer as a working fluid?
Two good answers for this question; Lets see a temperature and pressure diagram of a conventional Rankine cycle and a Karina cycle.
Here it is.
The first one is diagram for a Rankine Cycle, and the second one is the diagram of the Kanina Cycle.
So here you can cotice a major difference between these two
In the Rankine Cycle during phase transformation temperature doesn't change, it remains the same.
You can see during heat addition process: Process 2 to 3, temperature does not increase during phase transformation.
Similarly in the condenser, the process 4 to 1 the temperature doesn't change due to phase change.
But this not the case with the Kalina Cycle. Here, even during phase change the temperature changes. You can see here.
During heat duration temperature rises, and during heat duration drops.Since we are using a mixture as a working fluid. This small deviation in thermal cycle makes all the difference in the Kalina Cycle.
This small deviation in thermal cycle makes all the difference in the Kalina Cycle.
This explains why the Kalina Cycle has much higher thermal efficiency compared to the Rankine Cycle.
Simply because of this reason:
You know the efficiency of a Carnot Engine can increase because of two reasons:
first when temperature decrease
or when temperature heat absorption side increases. So in order to use this formula,
we will take average heat addition temperature and average heat rejection temperature from both cycles.
For a Rankine Cycle average heat rejection and average heat addition temperature will be like this:
Average heat rejection temperature is the same because temperature is uniform during the process.
And roughly this will be our average heat rejection temperature
And these two average values for a Kalina cycle will be like this. We can see that it is much wider when compared to the Rankine cycle
It has higher average heat absorption temperature. And a lower average heat rejection temperature.
So basically you have high level thermal efficiency
Now let see how this cycle is implemented in actual case.
How does it work practically?
First we start with a very, very, simplified Kalina Cycle power plant.
It has got four major components like a Rankine Cycle: a steam turbine, a condenser, a compressor, and a boiler.
When the mixture expands through the turbine, power is generated over here.
But the main difficulty in a Kalina Cycle is over here: at the condenser!
Right after the turbine, the working fluid will have almost 70% of ammonia by weight.
Now according to the phase diagram, when concentration of ammonia is high, the condensing temperature Is very very low.
You can see it here.
When the concentration of ammonia is 70%, the condensation temperature is really low.
if you want to condense such a fluid you have to supply a
very low temperature coolant through the condenser. That is not practical anyway. So what we will do,
we will alter this concentration, we will try to decrease this condensation of ammonia with the help of a device called a separator
What this separator will do? It will separate the working fluid into a lean mixture and into rich mixture.
And this lean mixture, which is having almost 30% ammonia by weight...
... will mix with the exiting fluid of the steam turbine and will produce a mixture of almost 40% ammonia by concentration.
Now if we check it in phase diagram, such a mixture will have much higher condensing temperature, almost over here.
This can be condensed using a regular cooling water supply.
Now the condensation process is over but we have to regain the original concentration in other parts of the cycle.
For that purpose a rich mixture from separator will get mixed with incoming stream and the working fluid will regain its original concentration.
The 77% of concentration. If you check temperature-entropy diagram of the Kalina Cycle carefully, you can notice one thing over there.
Temperature at exit of steam turbine is much higher than temperature inlet of condenser.
Or temperature at point 4 is much higher than temperature point 2.We can see it over here.
But this is not the case in Rankine Cycle.
In Rankine Cycle these temperature levels were in another way. Temperature at point 4 was lower than temperature at point 2.
After this point 4 we are rejecting heat to the surrounding,
and after this point 2 we are absorbing heat from some external agency.
So why can't we supply some amount of heat from point 4 to point 2
Which will save some energy and basically increase the power plant efficiency. That's exactly what we do here>
We are introducing a heat exchanger called recuperator.
And the function of recuperator Is to transfer some amount of heat from point 4 to point 2
This is Obviously possible because temperature at point 4 Is higher than temperature at point 2.
And thanks to the recuperator, you need not supply the same amount of heat that was supplied before.
So the recuperator heat transfer increases thermal efficiency of the Kalina Cycle to a much higher level.
And all these things prove that the Kalina Cycle is power plant of the future
Thank you for Watching the Video have a nice day