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Organic Rankine Cycle for power and cooling?

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yoel280206

yoel280206

Mechanical
Feb 9, 2010
11
Dear all,
I am trying to design an Organic Rankine Cycle (ORC) for Power and Cooling.
The heat source is solar heat.
I use pure ammonia as working fluid.
Starting from ORC for power, it comprises turbine, condenser, pump and evaporator (boiler).
I use water as coolant in condenser.
Therefore the outlet temperature of ammonia from turbine is limitted by water temperature in condenser.
The inlet water temperature in condenser is 15 Celcius.
So the outlet temperature of turbine should be > 15 Celcius and in vapor phase.
For instance, the outlet temperature of ammonia from turbin is 28 Celcius with pressure is 11 bar.
So it will be in vapor phase.
Then the ammonia vapor is condensed by condenser to be liquid then pumped to evaporator as a cycle.
So, i am going to use this ORC also for cooling.
If i use turbine with discharge pressure of 2 bar, the outlet temperature of ammonia from turbine will be <15 Celcius, for example 5 Celcius.
So i can use it for cooling, then the ammonia temperature will be 12 Celcius.
At this point, the ammonia is in vapor phase.
However there is a problem.
How can i change this ammonia vapor with condition of 2 bar and 12 Celcius to be liquid phase?
So the pump can pump the liquid to evaporator as a cycle.
How about the condenser, it might be useless now?
Any other ways to use ORC with pure refrigerant as power and also for cooling?
Thanks so much..
 
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before designing anything, make sure you understand the basics:
turbine inlet:superheated vapour
turbine outlet:wet vapour or more safely slightly superheated
turbine:delivers energy (expander)
cooling:requires energy (compressor)
turbine cycle:evaporator (boiler) works with temperature/pressure above condenser temperature/pressure
(need for a pump)
compressor cycle:evaporator (cooler) works with temperature/pressure below condenser temperature/pressure
(need for expansion valve)
 
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Thanks @CH5OH
I understand what do you mean.
I also have idea to use compressor.
So the turbine cycle on the top and compressor cycle on the bottom.
The compressor compress the vapor and the vapor temperatur will increase and be higher than coolant of condenser.
However it means the compressor will consume the output power from turbine.
And above method is compressor refrigerator.
I ever hear about absorption refrigerator (without compressor).
In large industrial, it use ammonia and absorbent.
Does anybody know about this?
How to install it into the ORC system?
Thanks..
 
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absorbtion refrigerated cycle works on the principal that
when a fluid is mixed with another one, the temperature drops (like for example when water is mixed with salt)
so the cooling bit is the mixing, the regenerating bit (separate the two streams) is obtained by boiling.
commercially available cooling units using lithium bromide and water (if i remember correctly).probably same happens with ammonia and water.also intresting is when boiling ammonia out of the water,the more the water is getting rid of the ammonia, the higher the required temperature will be.
same effect for ORC cycle:it uses a liquid with a boiling range, rather than a boiling point(like water).
(with a boiling point, the amount of heat exchange depends on the delta T between the streams, with a boiling range, the delta T remains more or less constant, so the amount of heat exchange also.
google Kalina cycle
 
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recent advanacements in organic dual-fluid cycles are appleid to the LNG refirgeration idnsutry- and simialarly reversign that cycle with the same dual organic fluids is used to generate power in the geothermal industry. I think you should research those 2 fields fore recent papers and advancements to avoid "reinventing the wheel".

Also, some universities have available free software for simulating these cycles.

Also, ammonia NH3 is not organic per se- no carbon.
 
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@CH5OH and @davefitz
Thanks a lot for both of you.
So i can say that in case of absorption refrigeration, it should be dual fluids.
And it can not use only one working fluid.
I have read about these dual fluids such as Kalina cycle.
It uses absorber.
May i know what kind of pump which is used to pump the mixture to evaporator?
Is it liquid pump?
Because in a literature, an ammonia-water mixture with condition of 35 C and 2.7 bar at outlet absorber, i saw the water is liquid but the ammonia is vapour.
How can it be allowed to enter the pump?
It make me confused.

@davefitz
By the way, may i know the free software that you mean?
Thank you..
 
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Dear Postyoel280206,
In your original post you mention that the temperature from the turbine would be limited by the temperature of the cooling water in the condenser. This is not entirely true.

In the condenser the vapor condenses to liquid. This gives a decrease in specific volume, which leads to a pressure downstream of the turbine.

The temperature of the cooling water determines the achievable lowest pressure in your ammonia stream. Due to physical limitations and restrictions (e.g. tube layout, boundary layers, etc) will the low temperature of your ammonia cycle be somewhat higher.

If you use a compressor downstream of a turbine to create the lower pressure, you will be destroying energy, as the efficiency is low.

On the Kalina cycle several nice articles can be found on the internet.
 
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regarding the free software- see "F-chart software" , program = ees "engineeering equation solver", free version, and its modules that connect to REFPROP and other NIST property databases.. The EES is based on "Absorption chillers and heat pumps" by K.E Herold et al, 1995 CRC press.
 
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We are currently working on a system using ammonia/water. Heat is supplied from water jacket of a large engine.
Cooling is water. System uses heat exchangers 1 of each for;
condenser, evaporator, generator, absorber and 1 other.
purpose is to produce commercially viable refrigeration.
Working prototype systems to be installed in approx 3 months.
 
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