Green Meadow Farms, Inc.

"Where the Latchstring is always out"

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Shop & Crop Milking Center Young Stock Methane Digester Manure Treatment

 

The Methane Digester is the newest project here at Green Meadow Farms.  We take the methane and run it through a V16 Caterpillar Motor capable of producing 800 Kwh. 

The manure will now be diverted into the digester before it goes into the treatment plant.  By doing this we should be able to cut down on the cost of the ferric chloride that we use in the treatment process.

When the manure makes it to the digester the sand is already out of it.  It makes it's way into the left pit in the picture on the left.  When the manure comes out of the digester it winds up in the pit on the right in the picture on the left.  The picture on the right are the two pumps that we use to move the manure to and from the pits.

The picture on the right is the heat exchangers.  The heat exchangers do exactly what their name implies.  It consists of two sets of pipes that run next to each other.  One set carries hot manure (out of the digester)  the other carries cool manure (on its way to the digester).  The pipes run so close together that the hot manure cools and the cool manure warms.  We do this so that we get as much heat transferred to the cool manure as possible.   It has to be 102 degrees when it gets into the digester.

  The larger exchanger works as a pre-heater, using hot manure that has come out of the digester to warm the cool manure that is on its way into the digester. This is a very easy way to gain heat with out the use of outside energy.  We usually gain around 8 to 10 degrees using the pre-heater.  After the manure we are trying to heat goes through the large pre-heater it travels into the smaller heat exchanger that is on the left.  Here the manure exchanges heat with hot water that is heated with the boiler.  When it comes out of the small exchanger it is then pumped into the digester.

Pictured at left is the boiler that we use to heat the water going in the heat exchanger.  We are using cow gas (that's what Don our main man in charge of the digester  affectionately calls methane) instead of propane to run the boiler. 

 

In the picture at right you can see how clean cow gas burns.  This is the fire that is burning inside the boiler.

 

 


Now that the manure is in the digester (which is the three tanks that you see at the top of the page) it can start to make its cow gas.  Inside the tank wall and floor are heating tubes that make sure that the manure stays the correct temperature.  Each of the tanks is a digester by itself.  They can be run independently or together.  For now we are running all of the tanks the same.  Each tank has a diameter of 85 feet and is 24 feet high, with part of the tank being under the ground.  They hold around 900,000 gallons of manure each.  As we add new or fresh manure to the tank (near the bottom) the older manure which has been in the tank for some time is forced out of the top of the tank.  The older manure then makes its way back to the pre-heater to heat up the fresh manure.  When it is done exchanging heat it goes back out into the pit we talked about earlier (the pit on the right in the top left picture).  From there the manure goes through our treatment system.  To learn more about that system go to our
manure treatment page.

Back in the tank the manure is agitated periodically, this makes sure that the manure solids don't settle out.  This also helps re-circulate the warmer manure that is near the wall and floor farther into the tank helping maintain consistent temperature.

As the manure gives off methane it is collected in the domes on the top of the tank.  From there it can be sent to three different places, the generator, the boiler, or the flare.  The ideal place for it to end up is the generator where it can be used to make electricity.  When the generator is running we are able to use the heat produced from the production of electricity to heat the water to send to the heat exchanger.  The flare should only be used if the generator is down for some reason.
 

The flares (pictured at left) are an environmentally friendly way of destroying methane and releasing carbon back into the air.  We do this by forcing the cow gas out the flare where it is lit by an electric fencer.  You can not see the flame when the flare is running during the day, but you can see the flame at night.  I will have to remember the camera next time I am over there at night.
 

The whole digester process is run by computer (pictured at right).  We can set agitation time, which tank gets how much manure and at what time, and what temperature we want.  The computer also keeps track of information that is sent to it by the gas analyzer (pictured below).  The gas analyzer tells you what other gases are being collected other than methane.

 

 
After the gas makes it through the analyzer it is on its way to one of the three final destinations above.  Hopefully the generator option is the most used, because that means that we are creating green energy which is the whole goal of this project.

 

6400 Hollister Rd
Elsie, MI 48831

 phone: (989) 862-4291
fax: (989) 862-4292
email:
darcydorr@aol.com