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Climate change and the growing problems of waste management combine to make biogas an advantageous and even necessary source of energy. In the first place, the burning of biogas — unlike fossil fuel sources embedded deep within the earth — does not contribute additional carbon dioxide (CO2) into the atmosphere since its origins, or substrate, possess carbon already drawn from the atmosphere. Moreover, biogas is derived from substrate that is, for the most part, buried in landfills or otherwise discarded: food scraps and by-products; animal manure and droppings; sludge and sewage; and rotting vegetation. How, though, do these undesirable substances become energy?
Whether employing fossil fuels or greener organic matter — as with biogas — energy producers seek to extract gases for combustion. In power plants, this combustion spurs mechanical energy that, once magnetized, is converted to electricity. In boilers, this ignition releases heat for homes and offices. In vehicles, it creates the energy whereby the engine will convey its thrust. Indeed, gasification was the driving force behind the Industrial Revolution and the subsequent momentum toward modernity. Yet connecting the dots between a geological or biological substance and incendiary gases involves a series of specific chemical reactions.
In the cases of petroleum or coal, for instance, the feedstock material is heated to over 1,200 degrees Fahrenheit while oxygen and steam are closely calibrated so combustion does not occur. The gas released from this transaction is called synthesis gas — syngas, for short. This gas contains both CO2 and carbon monoxide (CO) as well as nitrogen (N2) and hydrogen (H2). It can be ignited at a higher temperature than un-gasified coal or oil. This means that it burns more efficiently. The high thermodynamic value of syngas obtained from fossil sources is one reason why these materials are hard to give up.
Biogas, Biomass and Energy Production
Strictly speaking, the organic materials that originate biogas can be considered biomass. However, properly understood, biomass is itself burned for energy whereas the substrate that gives rise to biogas undergoes a lengthy order of reactions known as anaerobic digestion. Here oxygen is nowhere to be found and this absence allows for particular bacteria to work on the organic materials. This work, over the course of many days, leads to the release of CO2, methane (CH4) and a host of other compounds of lower content. The methane is purified of its co-compounds and is then suitable for myriad applications.
As indicated, biomass is gasified by means of — at least in part — oxygen. By contrast, biogas can only result from a process that is devoid of oxygen. Furthermore, biomass is generally grown for the purpose of alternative fuel and power; biogas comes largely from organic substance that would otherwise be discarded. In short, biomass is the subject of gasification while biogas is the result — IF anaerobic digestion can be thought of as the biogas gasifier.
Gases arising from biogas combustion include harmful effluvia and particulates like tars, alkali metals, chlorine and nitrogen compounds. Raw biogas, for its part, is often tainted by hydrogen sulfide, siloxanes and other corrosive chemicals. Depending on the ultimate destination of the biogas or gasified biomass, cleaning must be performed according to one or more regimens: water cleansing, anime absorption, activated carbon adsorption, char-bed filters and bio-oil scrubbers.
Gasified biomass and biogas might sound like the same thing but, in fact, they are quite different. Gas from biomass can be achieved quickly through the agency of steam and oxygen. Biogas is produced slowly as bacteria breaks down decaying organic matter. Both serve as renewable energy sources but biomass is raised as such; the feedstock for biogas consists largely of waste products.