Biogas

Posted by Krzysztof Lis on May 13, 2008

Biogas is gaseous alternative fuel. It is produced when biodegradable matter (biomass) is broken down biologically in the absence of oxygen, in a process called anaerobic digestion. Because of that, biogas is considered a biofuel.

Biogas can be compared with natural gas. The main component of both is methane. Think of biogas as of a natural gas, diluted with nitrogen and carbon dioxide. For now let’s assume that biogas is 66% methane (natural gas is over 95% methane), 28% nitrogen and 6% carbon dioxide.

How to use biogas?

Well, you can use biogas in almost every place that you can use natural gas. For burners, boilers, central heating, even for car engines! Some adjustments will be required, because biogas has smaller heating value than natural gas. To get the same amount of energy you have to burn more biogas, so you need to adjust fuel/air mixture in your burner. In most cases this is obtained by simply changing the burner.

This will be explained in more details later.

How to make biogas?

This is relatively simple. Biogas is produced naturally, in places where anaerobic digestion takes place. Examples of such places are landfills (in such a case we call it landfill gas), swamps and marshes. It can be made of almost any biodigestible matter — municipal waste, cut grass, garden refuse, manure, energy crops and any other biomass.

To make biogas you simply put the waste in an airtight container. It needs to be tight, because the biomass must be separated from oxygen in order the anaerobic digestion to happen. Then the bacteria start to eat the biomass, producing the biogas. They work the best in temperature ranges of 30-38°C (86-100°F) and 49-57°C (120-135°F). So in colder climate you have to heat the biogas processor (digester).

If you want to make biogas on small or medium scale (like one or three households), take a look at those two great books on DIY biogas plants.

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