Posted by Krzysztof Lis on April 1, 2008
In this article we’ll answer the question: which gaseous biofuel is better: biogas or wood gas? Both of those fuels may be used as energy source for your engine or boiler. They differ in composition and heating value, but they’re both combustible and that’s important. If you need to know anything more about those two fuels, check the articles I posted (biogas and wood gas). For now it has to be enough.
Wood gas can be made from wood. Or straw. Or rice husks. The feedstock needs to be dry. The less ash the better. The less volatile fractions (tar), the better.
Biogas can be made from almost any biomass. It is produced in landfills, marshes, swamps and such. So if you have wet grass, leaves or some other biomass residues, you can make biogas, but not wood gas.
If you want to make wood gas, you start the gasifier. The gas is produced when it is necessary, so sometimes it is called producer gas. The wood gas production is not very difficult to start or stop on demand. You just need some electricity to power the fan used for startup.
Making biogas is not easy and cannot be regulated. Biogas is produced by some bacteria. You can’t tell them “start making biogas now” or something like that. When you input some biomass to the digester, some gas will come out later. When exactly? You can’t determine it precisely.
If you really need to store energy in biogas or wood gas, biogas is your choice. It has greater heating value per unit volume, so you can store more energy in a tank of given volume.
Powering your car
Biogas can’t be used directly in your car because of two main reasons. First is the inability to control the biogas production. Second is the inability to carry the digester around on your car. It is far too big and heavy, it is a stationary device… So you make some biogass and compress it and put it into your car’s gas tank. I guess it’d be suitable to use CNG gas tank. For every liter of the tank’s volume you’ll be able to store energy of 1/8 liter of gasoline!
If you want to use wood gas, you make it while driving your car. As I mentioned above, storing this fuel under pressure is not energy efficient. You’ll waste a lot of energy to compress the gas to required level and you’ll have to carry really large tank with you! So you carry the gasifier. And fuel for it.
If you have large amounts of different biomass to be disposed, make biogas out of it! If you get some tank to store biogas for some time, you can use it for making electricity, heating or cooking in your home. Without the tank it’d be difficult, since you wouldn’t be able to get as much biogas as you would need. You can also use this fuel for your car, but it’s not very wise…
If you need this fuel to drive your car, use wood gas. It’s much easier to produce than biogas.
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