The use of biogas is increasing rapidly rapidly today for a number of reasons:
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. Combined heat and power uses are increasingly common. This is probably the most effective use of the biogas produced, although there will be cases where the heat is more difficult to use profitably. In industrial schemes where there is a steady demand for steam or other heat resources, this will present no problem, but areas using the power for residential purposes will find the demand for heat is very much lower in summer than in winter for obvious reason, whilst the demand for electricity will be reduced, but not as greatly.
Infrared sensors may be of the more expensive two channel variety or the more popular single channel sensor. Whilst more prone to drift, single channel sensors are usually more than adequate for this task. Very small, househod schemes will get by without any form of sensor being used, but any scheme that relies on selling the gas will have to ensure and prove a constant quality of service.
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.
Measurements in biogas
Calculates the number of a type of animal needed to drive a desired size of engine.
Further links will be added in time!
LANDFILL GAS PAGE
BIOGAS WORKS - A very comprehensive description about biogas production and use, well worth visiting.
Information and Advisory Service on Appropriate Technology (ISAT)