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| | | Forum Newbie
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Last Login: 6/27/2008 4:07:27 PM
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| | I have noticed a phenomenon happening in our anaerobic digester. We are in Texas and it appears that my 200,000 gallon digester self heats at night with a rise in temperature of about .5 to 1 degree F. Anyone know what might cause this? |
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Junior Member
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| | Heat transfer can occur by conduction (e.g. transfer of heat from one end of a metal bar to the other), convection (transfer of heat by mixing or tubulence), or radiation (absorption of energy from infrared wavelengths and release as thermal energy). My guess is radiation of thermal energy at night absorbed by the concrete tank during the day could cause the phenomon you have observed. In my own experience, I have noticed in my home that the maximum temperature indoors will not be reached until well after sundown. Maybe it is the same phenomenon. Any mechanical engineers out there?
ttfn |
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| | | Supreme Being
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| | Are you mixing at night differently or more intensely than during the day? Are you measuring with an online monitor? If you are its performance and calibration may change slightly with the cooler ambient temperature on the sensor , electronics and cabling? Regards TerryF |
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| | | Forum Newbie
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| | The agitators are a top and bottom side mixer. I set them and never chang them. They have been running at 95 % for the top and 90% for the bottom for the past 3 months. I could believe the comment about the ambient temperature but it is happening on two seperate meters. Both on line. One, the temperature sensor is in a well in the side of the tank and the second is the gas flow meter which is past my scrubber. I say these two meters because the self heating affects both. When the temperature drops during the day, gas production picks up and when it begins to warm in the tank in the middle of the night the gas production falls. This is happening every night with no changes on my end. I am lost as to what might be causing the self heating tank. I also do not believe it is heat transfer from the ground as we have a min. of concrete surface of less than 1' exposed to the sunlight and a transfer of heat from the agitators should remain constant since they are never adjusted. |
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| | What about feeding? Are you feeding more during the day vs. night? Does the temp of the feed sludge vary? |
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| | | Forum Newbie
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| | Nothing is manually or automatically changed at night. Something in the microbes are causing the heating at night and I am not sure what it is. |
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| | | Junior Member
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| I liked the "thermal mass" idea but since you've got only 1' above ground, I don't think you're storing much of the sun's energy in the walls (concrete cover, perhaps???).
Is your feeding consistent throughout the day or do you feed once or twice a day? A daily morning (or midday) feeding schedule could explain a few of these phenomenon. You mention your gas production picks up in the morning when it is cooler. A new batch of cold, fresh sludge could explain both observations. The bugs likely spike in activity, producing heat throughout the day...and perhaps into the night. Since now that cooler sludge is heated by the mixers and the slightly exothermic digestion, your temp sensor picks up the added heat. But, by the time the tank is heated the bugs have gotten to the easily-digested sludge and the gas production drops off. The bugs and mixers maintain the heat through the night until the new batch of cold sludge comes in the next day. Sound possible?
I'm making some assumptions and probably oversimplifying this guess...comments? Criticism? |
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