Biogas Refrigeration

jasonw
By jasonw on Thu, Feb 14, 2013 - 5:16pm

Seeking knowledge and experience with biogas generators / digesters.  Anybody doing research or experimenting with biogas? 

My local Alternative Energies group is working on a number of projects this year to explore energy resiliency for our community (wood gas generators, solar setups, etc) and one project is to design and build a solar ice maker as a demonstration for off-grid food chilling / preservation.  As an alternative to the solar ice maker / ice box setup - I am hoping to explore a setup using a propane refrigerator running off a biogas digestor for a off-grid renewal chilling system.  There seems to be lots of small trailer size refrigerators that run of propane. 

Can biogas be a replacement?  Any thoughts or insights? 

2 Comments

kd6iwd@gmail.com's picture
Status: Bronze Member (Offline)
Joined: Nov 17 2011
Posts: 25
homebrew solar refrigeration

The Crosley icyball was a refrigeration unit made in the 20's that used two balls for a ammonia absorbtion refrigeration system. The user would charge the system by putting one ball over a fire which would evaporate ammonia from a water solution. Pure ammonia would condense in the other ball with water cooling to help condensation. After removing from the fire, the ammonia filled ball would get down to -11 degrees f because the ammonia was evaporating to recombine with the water. These units have been home made and plans are available. It would be better to update the working fluid to something less toxic than ammonia. I seem to remember that a water- silica gell system could generate the same sort of cooling but is likely to be less efficient that the ammonia system because solids would transmit heat slowly so the heating cycle to regenerate the water would be much slower. It may be possible to make this system solar powered with a concentrating solar collector. There are many possible working fluids and some research should allow a very inexpensive model to be produced.

 

Best Regards

 

Jim

kd6iwd@gmail.com's picture
Status: Bronze Member (Offline)
Joined: Nov 17 2011
Posts: 25
refrigeration

I looked up cooling systems with silica gel absorbers and water as the working fluid. There are many examples indicating that this possible solution is a workable and very inexpensive method capable of converting solar or fuel energy to cooling purposes.

the simplest system would consist of a tube filled with silica gel. This tube would be connected to a similar but shorter tube containing the space for condensation of water.  The water saturated silica gel and the condenser tube would then be connected to a vacuume pump and all of the air would be pumped out. A valve between the silica gel absorbant and the condenser tube would allow storage of coolant till time of need or for cloudy days. perhaps a rubber tube could be used to connect the two tubes. The system is charged by heating the silica gel tube to 100 degrees centigrade while simultaneously cooling the condensation tube with cool water. This causes the water in the silica gel to boil out and recondense in the second tube. The system is now charged. With the valve in the closed condition this system will store the water for later evaporation and cooling. When cooling is needed the valve is opened and the water evaporates and is absorbed by the silica gel tube which is now cooled by a bucket of water. This system should easily freeze water. The water in the evaporation tube will sublime and keep the temperature low even after freezing.

The system could be charged by a cylindrical trough solar collector which focuses sunlight on the pipe and has the potential to attain temperatures in excess of 150 centigrade. Trough collectors only need forming in one direction and so are easy to form from plywood or other simple materials.The system could also be charged by heating from burning fuels or from waste energy from other industrial processes. Many references to this type of cooling technique are available.

 

Best Regards

 

Jim

 

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