Energy crisis closer than you think?

15 02 2013

I’ve been considering making a methane digester for years now, but procrastination rules.  Much of what I need has been hoarded, and now this article in the Drum has appeared, it might be time for me to get my act together….

Within the next three years, three massive gas export terminals in Queensland will begin operating. This will allow them to export vast amounts of gas by ship to Asia. The price they can get for the gas in Asia is around $15 per Gigajoule, around four times the amount we pay in Australia (see table 22, p75).

These companies will not sell gas to Australian factories, power stations or households for a quarter of the price they can get overseas. Once the export terminals start operating, if Australians want gas, they are competing with the Asian market and will have to pay Asian prices minus the cost of exporting it. This means the price in Australia is likely to at least double, or even triple (see Chart A, p7).

And that’s if you can get it.

Last October the Queensland Department of Energy and Water Supply predicted domestic gas prices increasing to over $10/GJ by 2015 and gas scarcity for domestic contracts. 

AND – UPDATE 12 March 2013:

Inpex tells Territory it has no more gas for sale
By Jane Bardon

Japanese company Inpex has confirmed all of the gas from its Ichthys fields off the coast of north-western Australia has already been forward-sold and none is available for domestic needs in the Northern Territory.

So there you have it.  Not only are we going to have petrol shortages soon, but gas too.  We don’t use a lot of gas.  Three 9kg bottles of LPG a year, for a total cost of just over $60.  If that cost tripled, it might put a dent in the beer budget, but it wouldn’t break us.  So why bother with a biogas digester?

Methane digesters yield two useful products from animal manure: methane gas (CH4) and a liquid fertilizer. The fertiliser can be applied directly to the garden and the gas can be used as a source of energy. The technology is simple and easy to reproduce. The unit requires about 4L of slurry per day in order to maintain a charge, and yields about one hour of burn time per day. Below are instructions for making a floating drum system.
two 200L drums (one with a tight fitting lid)
one 160L plastic rubbish bin
1200mm of PVC pipe 150mm diameter
2 pieces of plastic tubing 2400 long and 25mm diameter
1 valve to moderate flow of methane
Silicone sealant
Cut a hole in the lid of one of the 200L drums, near the outer edge. The holebiogas1
should be the same diameter as the PVC pipe. Now cut away a 600mm section of half the PVC pipe as shown in the illustration at right (PVC can be cut with a saw). Slide the pipe into the hole and all the way down until it rests on the bottom of the drum. Seal the fitting between the pipe and the lid with silicone.

Now cut a smaller hole (sized to fit the tubing) near the opposite edge of the lid and attach one of the pieces of 25mm diameter tubing with silicone. Run the tubing into the bottom of the rubbish bin, and slide it into the drum so that it runs the depth of it. Be certain to seal all fittings with silicone.

biogas2Cut a second hole in the bottom of the 160L bin, sized to fit the valve from the tubing. Attach the valve to the hole. Fill the second 200L drum (without a lid) with water. Invert the rubbish bin, open the valve, slide the drum into the 200L drum with water, and then close the valve. Now your digester is set up and ready to be filled with a manure slurry.

Manure from any type of farm animal can be used. Cow and pig manure tend to be preferred for a Biogas digester but I will use what I’ve got, chook, duck, and goat manure. Harvest the manure into a bucket and add water. Mix the water and manure until it forms a slurry of a thin enough consistency to be poured into the digester (about 50% water, 50% manure). It is best to start your digester with an initial charge of 200L (or whatever the capacity of your drum is). Subsequently you can add manure as needed.  You will need to add about 2% of your digester’s volume daily.biogas3
Fill the digester by pouring the slurry into the PVC pipe. I think a funnel of sorts would be a good idea… BE SURE that the level of slurry is always maintained at a level higher than the cut-away part of the pipe. If the level drops below this point, gas will escape out the top of the pipe. Before adding new slurry, an equal volume of slurry must be removed from the 4 inch charging tube. This can be done using a bailer—for example, you can use a 2L milk bottle with its bottom removed, attached to a stick. The removed slurry can be used immediately and at full strength as a garden fertiliser.

Once the digester is charged there will be a waiting period before the manure begins to cook and release CH4 and CO2. The digester does not need to be in direct sun but it should be in a place that heats up to at least 25°C during the day. Depending on ambient temperatures, you may need to wait seven to ten days for gas production to begin. As the temperature rises the manure will start fermenting and releasing gas. The gas flows through the plastic tube and is released into the inverted rubbish bin. It bubbles out into the water where the CO2 is dispersed and methane gas bubbles to the top. As the drum fills with methane, it will start to rise up in the water. Once the drum has risen, you can begin using your methane as a fuel. At this point you can connect your methane blow-off tube to a cookstove and start running it with naturally generated methane gas.


Most stoves are fitted with LPG jets.  Mine is, but I was given jets for the purpose of using natural gas when I bought it.  Make sure you change the jets!

By placing a brick on top of the inverted rubbish bin that holds the methane, you can create enough pressure to do the job……..




5 responses

16 02 2013

That is just brilliant. Wow. I’ve always fretted over how to pressurise the gas.

Has anyone built this? The weight of the inverted bin, creating the pressure, will also push the slurry up the 150 mm pipe a bit. That’s probably why it’s got a bit of a rise in the diagram.

By the way, you want to use “silicone” the sealant, not “silicon” the mineral 🙂

31 08 2013

By using a sewer pvc pipe (can take pressure) with a threaded end and a screw on cap, the fermenting drum can take enough pressure to compensate for the weight of a brick (even a concrete block). just dont forget to remove the weight before unscrewing the lid to ad slurry. A one way flap valve is also a good addition to the hose conecting both drums. Natural gas jets work work on low pressure, but still need some to function properly. Also for outdoor use only (in a well ventilated area) as methane digester produce some carbon monoxide.

16 02 2013

Thanks for pointing out the typo…….. Search through youtube and you will find loads of devices like these……

16 12 2014

Thanks for the concise info. I am interested to know how long the scrubbing water can be used and or needs to be changed? Given “The process produces a biogas, consisting of methane, carbon dioxide and traces of other ‘contaminant’ gases” And if the water does need renewing where does one dispose of the waste water containing the contaminants?

16 12 2014

Good question. The short answer is, I don’t know. However, what I do know is that methane does not dissolve in water, and CO2 does, turning the water acidic (as is happening to the oceans) in the form of Carbonic Acid H2CO3….. Acids can be neutralised with alkaline solutions, like baking soda (Ca(HCO3)2
though there may be too much Carbonic ions in that reaction…. maybe someone else who knows more chemistry than me can tell you?

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s