Maintaining Constant 28 C temperature in anaerobic digester 2

[guruji135]

Hi, I am working on a bi-phesic MB-HRAR (moving bed, high rate anaerobic reactor)for biogas generation with cattle dung as feed. I need to maintain constant temperature of 28 C in the reactor. It would require both heating/cooling system as from season to season, temperature varies between 7 C to 44 C. Presently the model is made up of acrylic, but if jacketed vessels of any other material is found suitable, I will change the set up. Kindly suggest solution. What is temperature circuit? Can it be helpful here?

 

[bimr]

Would expect that a tubular heat exchanger would be the conventional equipment for this application:

http://www.walker-process.com/prod_digestion_heatexchangers.htm

 

[cheute79]

I suspect that you also have need to maintain relative humidity, which will be harder in winter. Your target temperature is 28°, and your dew point is probably 23° to 25°. Air coming in at 7° will have a dew point less than that. If you have a design to spray excess water on packing and raise your humidity, that is best and ideal, but if you don't have the temperature control system, you don't know if the humidity system works, either.

If you have steam available, or can build a small 1 bar-a steam generator, that will be the best way to add both heat and steam, but you might be surprised how large it must be. Humidifying will also usually decrease the temperature, so only on the warmest days will you need to cool. Use a heat exchanger with chilled water on the cooling fluid side for those 3-4 months where cooling is needed. Depending the size of the reactor, a lab-scale chiller might work - and if you have built it of acrylic, it's probably quite small. Otherwise, a refrigeration or absorption chiller is also expensive!

 

[bimr]

This kind of application is generic in the waste industry.

I would not expect that you need to have a cooling system to control the temperature in the summer as the heat loss to the environment will suffice. You could also add more water in the summer which will be much less expensive that a cooling system.

Check the link below for an example of this application.

http://www.walker-process.com/pdf/08_PlantProfileGervaisFamilyFarm.pdf