Help with Organic Rankine Cycle Project

[Dolph1983]

Help with Organic Rankine Cycle Project please!

Moderator's note: this thread is from May 2011

Hi there everyone, I'm posting here in the hope that someone will be willing to help an engineering layman do some calculations, I'm a plumber not an engineer. Thanks to anyone who decides to help me out.

The project:

build an electric generation device using organic rankine cycle and scroll expander as turbine. Fueled by biomass/waste products.

So far i have built a boiler which will raise 80 degrees C in my heat transfer fluid (water) and a pump to deliver the fluid to my heat exchangers.

Rankine circuit will use Butane as working fluid.

Turbine will require a flow of 6 CFM butane vapour at 6bar. This has been tested using an air compressor to simulate butane flow.

Questions:

How do i work out the correct size for my evaporator plate heat exchangers? and my condenser plate heat exchangers?.

Many thanks,

Dolph

 

[Dolph1983]

I will try and give a bit more information just incase anyone is interested in assisting me.

Below is a link to a thesis which i found helpful, however the working fluid and input temperatures are different to what i hope to experiment with, so there is a limit to this document relevance to my project.

http://organicrankine.com/orc_documents/scroll_non_auto/TFE_SQ010607.pdf

Please check out my YouTube channel for information on my project:

http://www.youtube.com/user/DoLpH1983?feature=mhum

I will be very thankful for any help and assistance provided!

Thanks

 

[Curl]

The "size" of the heat exchangers depends on what heat rate you are planning on having (determined from the temperature change of the fluid and the flow rate). After that, you'll need to know the conduction and thickness of the metal you are using for the heat exchangers, the total surface area, and some knowledge of the convection issues (temperature of air, air circulation, etc). With this information you can determine the areas you need for the proper heat removal.

 

[Dolph1983]

Thanks for the reply Curl,

The only known data and figures i have at the moment are the inlet temperature of the heat transfer fluid (80-85) at the evaporator heat exchangers and a flow rate of 10-15 litre per min through the heat exchangers can be ahieved.

The heat exchangers I'm looking at are 50 plate stainless steel with power rating of ca 90Kw.

I need to know how much Butane i can vapourise using these temperatures/flow rates for the above heat exchangers. Will they supply enough flow rate to the turbine.

For the prototype turbine to rotate i will need at least 6CFM of butane at 6bar inlet pressure.

?

P.S I'm now thinking about doing some formal engineering training as i can't really progress without it. Trial and error cost's too much, money and safety.

 

[Curl]

You need to find some tables or data fits for the thermodynamic properties of Butane. Unfortunately I couldn't find any. There are some other ways of doing this, however it is too tough for me to explain here. The only properties I found are here:
http://en.wikipedia.org/wiki/Butane_(data_page)#Thermodynamic_properties
What you need to look for is the enthlapy of the fluid at the temperatures and pressures you have in your cycle.

You also need to know the pressure of the fluid that comes out of your turbine. It totally depends on the device you are using, the only theoretical calculation I can make is for a perfect turbine which yours isn't.

 

[Dolph1983]

Curl, thanks very much,

This is what i have found, hope it is of use.

http://www.chemicalogic.com/mollier/Butane.jpg

http://www.nt.ntnu.no/users/haugwarb/Phase_diagrams_and_thermodynamic_tables/PhaseDiagrams/n-Butane.PDF

The turbine outlet pressure will be 2 to 3 bar lower than the inlet, based on a study of a similar system, i think.

Thanks

 

[Curl]

You got the right idea with those charts, but those are for saturated fluids. No guarantee that your fluid will be saturated at any major point in the cycle (although you can design it to be, and you should). Where are you located?

 

[Dolph1983]

Curl, I'm located in the north west of UK.

I want to keep the liquid Butane as close to saturation as possible between the pump and vapouriser. Without complicating the system too much.

On leaving the scroll expander turbine the Butane will condense as it passes through a group of condenser heat exchangers, the liquid Butane will then collect in a small cyclinder. From the collector the liquid Butane is pumped through the vapouriser heat exchangers to become high pressure vapour/gas flowing either through the turbine or by-pass.

After leaving the collector the liquid butane could flow through a recuperator so that it is as close to boiling point as possible when it hits the vapouriser.

Any design input wold be a great help Curl,

Thanks

 

[Dolph1983]

Hi,

just thought i would post an update on my project. It would be great to hear from people who would like to get involved with my project.

http://www.youtube.com/user/DoLpH1983?feature=mhum#p/u/0/2-Dj3m7v3a0

Thanks

 

[watermotorman]

seems that video is set to "private" setting. How are we to view it then?