Solar heat underground biogas digester

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Thomas Setchel
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Solar heat underground biogas digester

I am thinking of converting my septic system to a biogas generator.    I am conserned that I will not be able to maintain a temperature adaquate to sustain  microbial growth so am thinking that I could create a solar thermal loop that would create a thermal siphon and supply the heat necessary.    I have not found on the internet where any one has done this.   I am looking for feedback.   

 

Thank You 

 

Tom Setchel

 

Nick Chase
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Hi Thomas,

Hi Thomas,
I was thinking about converting septic tanks to a biogas digester too some time ago. Then I found that the the two tanks I believed that they are septic tanks are absorbing wells...

The idea with the thermal loop and thermal siphon sounds interesting. question is: how big (cubic meters) is your system?

I'm adding TH and Mafu to the conversation.

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Thomas Setchel
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thermal loop sizing

Nick, I have really not gotten to the math of it all yet but am at a conceptual level at this point.   I am thinking that a closed loop system with some EVT collectors and a single check valve on the return line would create a flow of hot liquid and if the physics of it all works the he math matics of  energy requirements can easily be calculated.   Because I am very new to all of this and not a scientist but a back yard inventor I need to learn and understand just how much heat will be needed to maintain the temp I need.  How nuch heat will be generated by the microbial growth it self, how much geography and ground temperatures wiill come into play etc etc.    I am in Florida so will not have winder ground temp concerns.  the object of my work and research is to take they system to Haiti after proof of concept to feed digestor with human waste and agricultural waste for a fuel source for many things.    electric, cook fuel being the two main concerns.   Thanks for chiming in.   I am hoping to use just my standard PVC Plastic septic tank.   

Thomas Setchel
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size of septic tank (digestor)

So I have a 1000 gal septic tank which wquates to a 3.7 cm digestor.    I assume that the grount temp in my part of florida is around 75F.    so I do not have a huge distance to go but feel like I need to get to around the 100-110F range for efficent gigestion.    So the math on that I have not done yet but seems to be fairly simple.   Im thinking that once I calculate the BTU's I require, that sizing a copper coil to rest in or near the bottom of the tank in a closed loop configuration with a Solar heat imput device and a single check velv on the cold side will keep it warm.   I guess I could get into an over heat situation and need to turn off the hearter.   Not sure if automating that is necessary but could be fairly easy. 

 

Tom 

 

Nick Chase
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sounds great. over heating is

sounds great. over heating is a problem. I was talking to commercial biogas plant owners, they reported that overheating the methanogens by 2°C will result in a significant amount less biogas.

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