Re: DIG-L: Thermophillic

["Jim Groman" <jgroman@varec.com>]

U.S. systems typically do not use water utubes for that reason, and also for the reason that these can become easily clogged with bacterial growth or the liquid can evaporate, allowing air into the system.  We manufacture a weight loaded pressure and vacuum relief valve and typically mount it on top of a flame arrester to prevent any possibility of flame getting into the lagoon.  Also, if the vacuum is controlled by a draft range pressure switch, we keep the system operating within the range of the pressure vacuum device such that air does not enter the system.

Best Regards,
   ----- Original Message ----- 
   From: Simm 
   To: Jim Groman 
   Cc: digestion@crest.org 
   Sent: Friday, February 18, 2000 12:06 AM
   Subject: Re: DIG-L: Thermophillic


   To keep such a cover under vacuum wouldn't do the job. Practically all lagoons in Germany have such a cover today. They are kept under a pressure 20 mm water column just like the rest of the system. Their egdes are usually submerged. 

   Few were ever torn off by storms. 

   What might cause problems is air intruding the system thru the U-shape water-filled safety valve, as a result of lack of gas when pumping out sludge. According to a telephone conversation I once had with an insurance company, explosive atmospheres cause about 5 incidents yearly at Germany but I have not heard of one that was clearly related to a biogas plant. (Foul gas occurs in every sludge tank.)

   Anthony Simm

   At 03:19 PM 02/17/2000 -0800, you wrote: 
   >>>>

     Just an anecdote, since I am more interested in the consequences (biogas) of digestion than the process tself.\ I believe there are many "un-intentionally" hermophillic digesters in the form of covered anaerobic lagoons. Lagoon systems re used quite extensively in the meat processing industry and many times he project involves converting aerobic lagoons to anaerobic. This sually involves using a "rubber" cover which is invariably black. herefore it absorbs a lot of heat from the sun and the lagoon quickly heats to the thermophillic phase. Since many of these lagoons were previously in service, they tended to hav a substantial fat and grease layer on top. Imagine the surprise of the first designers of these systems when the tarted pumping out 10 times as much gas as they expected! One side note as long as I brought up the ubject...if you have a covered lagoon system, make sure you draw out the biogas with a lower to keep the cover under a slight vacuum. This will prevent the cover from ballooning and getting ripped in the wind. For what its worth, I think lagoons can be an effective low cost system. Jim Groman Inside Sales Manager Vapor Product Manager Varec Vapor Control Inc. 714-229-3230 hone 714-952-2701 Fax