Water's Crucial Role in the Efficiency of Kalina Cycle Power Generation

[pranj5]

I hope may of us here have idea about Kalina Cycle. In this process, a mixture of water and ammonia is used and ammonia is the main working fluid to rotate the turbine (or other machinery) to produce power. In this process, water is first used to absorb ammonia at the Condenser and the this water-ammonia mixture is pressurised and this pressurised mixture is heated and inside a chamber, the pressurised mixture is released to a lower pressure level and the ammonia is separated from water. This hot ammonia then rotates a turbine (or other machinery) and produce power/electricity. After that, the comparatively colder ammonia goes to the Condenser and then remixed with the water again. The water is being cooled as much as possible before being injected into the Condenser again.
Now, question is, what's the role of water here and why ammonia isn't directly being compressed. The answer is simple. If, instead of being mixed with water, ammonia will be compressed directly; the power consumption will just simply skyrocket and it would be simply impossible for the cycle to produce net power. Ammonia, like other gases, will behave in the same manner when compressed alone. But, when mixed with water, it behaves like a liquid and takes far far less energy to compress.
That's my opinion. What do other think about this matter?

 

[Terrysv]

Hi pranj5,
Here is what I think is happening in the Katlina cycle. Water expands by about 1600 times when boiled at 100c and atmospheric pressure. Ammonia expands by about 850 times when boiled at −33.34 °C and atmospheric pressure.
This is like an organic Rankine cycle that is including an additional distillation process. The water simply reduces the quantity of ammonia required. As the temperature rises the ammonia boils first, increasing the pressure and increasing the point that the water will boil. If the ammonia content is too low then some water vapor will enter the cycle.
It seems like a good idea, a slightly modified household unit could provide electricity, hot water and moonshine.

 

[pranj5]

If what you have said is true, then just the ammonia would be enough. Kindly try to calculate the power necessary to compress ammonia in gaseous state and compare that with the power needed in Kalina cycle.

 

[Terrysv]

just the ammonia would be enough.

My opinion, is yes ammonia is enough, however water is cheaper. No calculations required.
Good Luck

 

[pranj5]

The ammonia here will be in closed loop and therefore whether it's more costly than water doesn't matter. What matter is the power consumption to compress ammonia alone in comparison to ammonia mixed in water. When mixed with water, ammonia will behave like a liquid and therefore much less power would be needed to compress it to higher pressure.

 

[Terrysv]

The Kalina cycle in the link below has more equipment than an ORC cycle they both use the same OP. All the additional equipment in the Kalina cycle is to separate the heat out of the stream coming from the turbine and move the heat past the cooling liquid. The system is better because the cooling section dose less cooling. I see no compressors.

http://www.globalgeothermal.com/Thermodynamic.aspx#

 

[pranj5]

The pressuriser here, that pressurises the ammonia-steam mixture does the job of compression here.