You can make biogas energy with a DIY methane generator.
Producing methane from manure using your own small scale waste to energy biogas digester is feasible for many small farms.
What is Biogas Energy?
Biogas energy is fueled by burning methane produced by the decomposition of organic wastes.
Small scale biogas generator
Methane
is a gas – chemically CH4. It is colourless, odourless and, of course,
flammable. Methane is widely used as the main constituent of mains
natural gas.
Whenever organic materials are decomposed by
bacteria anaerobically (i.e. in the absence of oxygen) methane and
carbon dioxide are produced.
Small scale manure-to-energy methane generator plans are available
here.
Sources of Biogas Energy
Just
about any organic waste can be decomposed as a methane generator -
plant (soft material is better than woody material) and animal wastes,
and even human waste.
On a municipal level, rubbish tips act as
biogas digesters and are prodigious methane generators. Even in Perth,
Australia, companies are actively harvesting this methane to produce
climate friendly biogas electricity.
In fact, because un-burnt
methane released into the atmosphere is a powerful greenhouse gas, 10%
of our personal impact on the climate comes from the food refuse we put
in our garbage bins that ends up decomposing under landfill.
In a
small scale waste to energy situation it is possible to generate
methane from manure or even sewerage. And biogas energy is constantly
being manufactured in digestive systems like yours and your cow’s… yes,
farts are methane too!
Check out this video to see how to make a simple home digester:
Pros and Cons of Methane Generator Systems
Advantages
•
Makes good use of organic wastes. You can obtain fuel from sewage
sludge and animal slurries first, and prevent runoff and methane
emissions at the same time – and you still get fertiliser at the end of
the process.
• Is a clean, easily controlled source of renewable energy.
• Uses up methane, a powerful greenhouse gas.
• Reduces pathogen (disease agent) levels in the waste.
• Residue provides valuable organic fertilizer.
• Simple to build and operate.
• Low maintenance requirements.
• Can be efficiently used to run cooking, heating, gas lighting, absorption refrigerators and gas powered engines.
• No smell (unless there’s a leak, which you’d want to know about and fix immediately anyway!).
Disadvantages
•
Most practical to be generated and used at the source of the waste.
This is because the energy needed to compress the gas for transport, or
convert it into electricity is excessive, reducing the efficiency of
biogas energy production.
• For safety, basic precautions (see below) must be adhered to.
Small Scale Waste to Energy Methane Generator Systems
Biogas Energy
Each kilogram of biodegradable material yields around 0.4 m³ (400l) of gas.
So
in practice, in small scale waste to energy systems, if you have some
livestock, plus kitchen and human waste you can meet your cooking and
lighting needs easily:
• 2 gas rings for a couple of hours a day will use between 1-2 m³
• Gas lights need around 0.1 m3 (100l) per hour.
Driving any kind of engine (eg a generator or a pump) is, however, way beyond the domestic-scale. (Better to go for
algal biodiesel!)
What Size Methane Generator is Needed?
If
generating methane from manure, collect dung for several days to
determine average daily dung production. On this basis, the appropriate
size biogas digester plant can be calculated.
For example, where
55 kg of dung a day is available a 8 m3 plant is warranted; where it’s
only 6 kg of dung a day, a 1 m3 plant will suffice.
For a family of 8 with a few animals (say 8-10 cows), a 10m³ digester is a commonly used size in India, with 2 m³ gas storage.
Ideal Temperatures for Producing Methane from Manure
How
long you leave the material in a batch digester depends on temperature
(2 weeks at 50°C up to 2 months at 15°C). The average is around 1 month –
so gauge how much material you will add each day, and multiply it by 30
to calculate the size of the digester.
While anaerobic digestion
occurs between 32° F (0°C) and 150° F (65°C), the optimum temperature
range for methane generating microbial activity is 85°F (29°C) to 95° F
(35°C).
Little gas production occurs below 60°F (16°C). In colder
climates placing the digester in a greenhouse, and perhaps using some
of the methane to warm the system, are possible strategies.
Methane Generator Systems
• The
biogas digester
is the system component where the animal, human and other organic
wastes are introduced, usually as a slurry with water, to break down
anaerobically.
• A
storage container is used to hold the
gas produced, from which it is piped for burning as a fuel. Variable
volume storage (i.e. flexible bag or floating drum) is easier, cheaper
and more energy efficient than high pressure cylinders, regulators or
compressors.
• When the digester is emptied, the
spent effluent is dried for later reuse as a fertilizer.
Types of Biogas Digesters
The
two main digester types of digesters are the continuous and the batch.
Continuous digesters have a constant throughput of material, and batch
digesters extract the gas from a contained batch of material, which is
then emptied and a new batch added.
As firewood for cooking has
become scarce, millions of small scale continuous digesters are in use
in developing countries, especially India and China. Digesters tend to
be larger-scale in developed countries, taking animal slurries and human
sewage.
Methane Generator Design
The Indian
cylindrical pit design has become a popular choice around the world due
to its reliability and simplicity. It comprises two basic parts: a
slurry tank and a covered by a gas cap or drum to capture the gas
released from the slurry.
Domestic Scale Batch Biogas Digestor
Small experimental biogas digester at Redfield.
Waste material is put into the oil drum, neoprene cover rises when
full of gas, gas is tapped into container (upside-down plastic drum with
water seal) which rises as more gas enters.
When full, gas can be tapped off and used with the little gas ring.
Batch digesters based on a container (see photo, above) are feasible on the domestic scale.
Mini Methane Generator Project
Instructions to make a mini methane generator (suit education
project) are in the "Methane-Biogas Production Guide" which, along with
heaps of other free eBooks on sustainable living, can be accessed free
here.
Methane Safety
Like
electricity and other energy systems, safety is usually assured so long
as the risks are understood and sensible precautions are followed.
Fire or Explosion Risk
Methane is obviously flammable, and can even be explosive. With this in mind...
• The methane generator digester area must be well ventilated to prevent the accumulation of trapped gases.
•
In the vicinity of a digester no naked flames are permitted, electrical
equipment must be of suitable quality, normally "explosion proof", and
other sources of sparks are any iron or steel tools or other items,
power tools, normal electrical switches, mobile phones and static
electricity kept a safe distance away.
A flame trap should be
incorporated in the supply line, which must be of a minimum of 20 m
long. Instructions on building a flame trap can be found
here.
Asphyxiation Risk
Biogas displaces air, reducing the oxygen level so any digester area needs to be well ventilated.
Disease
While
the spent slurry has lost a lot of its pathogens, there’s a lot of
microbial activity at work in producing biogas energy!
So avoid
contact with the digester contents and wash up thoroughly after working
around the methane generator (especially before eating or drinking).
taken from
http://www.small-farm-permaculture-and-sustainable-living.com/methane_generator.html
So we can see that home
biogas is not something new around the house! Biogas is currently being used by
millions of people as a fuel for cooking and lighting in many countries. The
beauty of a home unit is that instead of some big company providing you with
gas, you are in charge of your own energy production.
So what is biogas? It is a combustible gas mixture
comprising around 60% methane and 40% carbon dioxide that is formed when organic
materials, such as animal (and human) dung or vegetable matter are broken down
by microbiological activity at warm temperatures (30 - 40°C or 50 - 60°C) in an
anaerobic environment.
