Sunday, March 08, 2009

Making Electricity from a Methane Digester

How is electricity produced using biogas, is a common question being asked by our visitors. In fact over 150 per week are seeking the answer to that question.

To answer the question I have written a new page at the Anaerobic Digestion web site, and I have tried to keep the article accessible as possible to all readers.

For my blog and email readers I have summarised the article as follows:

It is possible to generate electricity from the natural gas or biogas from an Anaerobic Digestion Plant (Biogas Digester) using a number of systems. The two types used are by an internal combustion gas engine, and a gas turbine.

A gas engine is similar to a automobile car engine, and a gas turbine is similar to a jet engine.

The first stage is to produce mechanical energy from the chemical energy released in the expansion produced by the heat rise of the burning gas. The mechanical energy in a rotating drive shaft is then coupled into an electrical generator.

The mechanical energy is utilized to drive the AC (alternating current) in magnetic windings in the generator giving us electricity. A turbine acts similarly.

It may seem a little strange to us at first, to use gas in an engine, but the principle is actually very old and goes back to the first days of engine development. Early automobile engines used methane and coal gas.

However, the person deciding to start a digester project must always consider the cost of connection into the local power grid when planning to build a biogas digester to produce electricity.

Another plus can be that carbon dioxide emission credit is available. Credits may be given reflecting the difference in greenhouse effect index between releasing landfill methane gas to the atmosphere and releasing the methane gas to the atmosphere after burning it to form carbon dioxide. In some cicumstances this can be registered on emission credit markets.

Biogas digesters are already producing electrical power in many countries, and the number is growing.

A Combined Heat and Power (CHP) system is always worth considering for all AD Plants.

Without the "cooling" provided by CHP, this heat goes into the atmosphere without serving any purpose.

CHP is a good way to gain better efficiency of power use, and usually it should bring in further income to fund the biogas digester operation.

For the full article visit the Anaerobic Digestion web site and the Making Electricity from a Methane Digester page.

1 comment:

sara said...

It is great that more and more people are realizing the importance of utilizing waste as a resource instead of neglecting the high energy value it makes available. The comprehension of how this product called "biogas" can be turned into usable electricity is a somewhat difficult one to grasp, especially when it comes to the mechanical and engineering aspects. Thanks for the good overview. A company called BIOFerm ( is creating these systems to produce biogas from any kind of high solids waste stream...which just happens to be a lot of the waste that is created all over the world (food waste, yard waste, agricultural waste, etc.). Check it out to see how their process works.