The Modern Importance of Biogas
Posted: Wednesday, July 14, 2004
by SimonF
http://www.madur.com
The use of biogas is increasing rapidly rapidly today for a number of reasons:
1. Fuel costs have been rising steadily for a number of years and the taxation burden increases as well, leading to a double load ofr the user to bear.
2. Attempts are now being made to improve the use of renewable energy sources.
3. The gas produced, mainly methane, is one of the major causes of the greenhouse effect.
4. The production is possible in small scale sites, obviating the need to supply energy to outlying areas.
5. Even a very basic construction using mostly used materials will produce gas if a few simple design rules are followed.
This is not meant to be a construction guide for biodigesters or any of the other equipment needed for this purpose, it is rather a discussion of the control systems in use for the landfill schemes that are in use in many countries already.
Nevertheless, a few points are worthy of mention. The links below will give some good information on this topic and hopefully clear up any queries that you might have.
The gas produced and the slurry being fermented are corrosive. This means that some of the fittings must be made of corrosion-proof material. Plastic can be used for many things, but where pressure and sunlight are involved, then stainless steel may be needed. Again, as the gas is corrosive due to the presence of hydrogen sulphide and other impurities, it may have to be collected in a stainless steel tank in some cases. The cost for such materials is high and may be prohibitive, but larger industrial systems will be forced to go in this direction to get a useful working life. Stainless steel is not cheap, but it has properties that make its use essential sometimes.
The gas produced may be used for a number of purposes, but one of the main uses in larger plants is driving engines for production of electricity. To this end it is essential to know the concentration of methane in the gas, allowing the mixture to be adjusted appropriately. The level of carbon dioxide and proportion of methane will give valuable information about the state of the fermentation process as well. Infrared sensors are the best means employed today for this purpose. The need for calibration is minimal or nonexistent and the small size, relatively low cost and minimal power consumption make them ideal for this type of application.
Infrared sensors may be of the more expensive two channel variety or the more popular single channel sensor. Whilst more prone to drift they are usually more than adequate for this task.
Measurements of carbon dioxide and methane in biogas have, nevertheless, shown a marked deviation from the behaviour of an ideal gas, with the sum of the calcualted partial pressures not equalling the total pressure. The result of these measurements must be taken into account in all cases where both sensors are employed.
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