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Biofuels (Energy)

Biofuels refer to a specific form of Biomass_Energy most commonly used for transportation and generally in a liquid form. In practice, biofuels can be in liquid, solid or gaseous form and they may be used to fuel diesel, gasoline, propane or other internal combustion engines in a vehicles and stationary equipment. The major benefit of biofuels in comparison to other novel, sustainable or alternative energy sources is that biofuels tend to be usable with minimal or zero modification in existing vehicles, engines and fuel distribution systems. Thus, while electricity or hydrogen requires a wholesale shift from gasoline and diesel engines to engines built to use these fuels, biodiesel or ethanol allows the use of existing vehicles with only minor retrofits such as seals or other internal wear parts. In the case of both biodiesel and ethanol, partial blends can be used without risk of compromising engine components. These are now commonly used in many public transit fleets and are now approved for use by some vehicle manufacturers, including Chrysler, Ford and General Motors1). A whole range of other manufacturers have also approved biodiesel blends and up to 85% ethanol (E85) in at least some of their vehicles 2).

Biofuel Types

Some of the most commonly used forms of biofuels are as follows:

  • Liquid ethanol from corn, sugar beets or cane sugar
  • Liquid methanol from fermentation of wood waste or agricultural residues
  • Liquid biodiesel from canola (rapeseed), soybeans, jatropha, palm or other oilseeds
  • Liquid biodiesel produced from animal fats used in cooking or industrial processes
  • Liquid oils from vegetable (soy, canola, olive, palm, jatropha, etc.) or animal sources such as rendered fats from slaughter facilities
  • Gaseous methane from anaerobic digestion of animal and human wastes or landfill materials
  • Solid biofuel or biomass such as wood, grass and wood wastes

Ethanol

Ethyl alcohol or ethanol is also known as grain alcohol. Chemically it is the same as the alcohol found in alcoholic beverages. However, rather than the 40% or 80-proof concentration found in most vodka or whiskey ethanol for biofuel use is as close to 100% pure alcohol as possible. As with alcohol for human consumption, ethanol is produced by fermenting a starch or sugar and then using a series of stills in order to extract the water. After reaching around 95% ethanol / 5% water, chemical desiccants such as molecular sieves are often used to extract the remaining water in order to yield anhydrous ethanol (anhydrous = “without water”) suitable for engine fuel. In most countries ethanol is denatured with a bitterant or a toxin or both in order to discourage consumption or “bootlegging” of racing fuels and transport biofuels.

In Brazil, ethanol is made from sugarcane and incorporated into all gasoline in blends such as E25 (25% ethanol, 75% gasoline) by law. In the United States, agricultural subsidies for corn-based ethanol have dramatically increased production since around 2005. There is some debate about the environmental efficacy of ethanol grown with modern industrial agricultural techniques such as in the United States 3), as it may in fact consumer more energy than it produces, making it a net energy loss. With standard production techniques which are used in Brazil however, there is little question that Brazilian ethanol yields a net energy gain of several times over, making it an environmentally and economically sustainable practice.

Biodiesel

Biodiesel is a fuel functionally similar to petroleum diesel fuel, but made from fats or oils. It is produced through a chemical process called transesterification, most commonly using lye (sodium hydroxide) and ethanol or methanol. The process breaks down the mono-, di, and triglyceride molecules (the fats or oils) and creates glycerine and fatty acid methyl esters or ethyl esters depending on whether methanol or ethanol is used in the reaction process. Transesterification is a similar reaction to the process of saponification used for making soap, with the reagents for the process mixed together in different proportions. Once the vegetable oils or animal fats have been processed into biodiesel, they can be used in any biodiesel / diesel blend from B1 (1% biodiesel / 100% diesel) up to B100 (100% biodiesel.

Methanol

Methanol is broadly similar to ethanol, but it is produced from wood or agricultural wastes rather than grains. It is poisonous to humans. If consumed, it can lead to blindness and death.

Straight Vegetable Oil (SVO)

Straight vegetable oil refers to pure, unrefined vegetable oil or to virgin oil – that is, oil which has not been used for cooking. The other form of straight vegetable oil for biofuel purposes is known as Waste Vegetable Oil or WVO. Straight vegetable oil is generally less problematic to use as a fuel, since it has a lower or non-existent water content and no risk of containing food particles or cleaning solvents. There is an accepted straight vegetable oil fuel standard in Europe known as the Weihenstephan pure plant oil (PPO) standard 4) to plant oils must conform in order to be sold as transport fuel.

Waste Vegetable Oil

Waste Vegetable Oil or WVO is reclaimed oil from fryers used in restaurants. This is the oil, or more frequently “grease” which is used to fry chips / fries, fish or chicken fingers, etc. It can be canola, peanut, sunflower or other plant oils. When used as a biofuel, it presents some fairly unique challenges not posed by some of the other fuel sources. The first is water – when cooking frozen items in hot oil, the oil picks up quite a bit of water which must then be extracted in some way. The second challenge is the fact that other fuel sources do not tend to have bacon, potato or bits of hamburger in them. The further challenge is the potential acidity of the oil after being used for cooking for an extended period of time. Depending on the type of plant oil used and the management practices of the individual restauranteur, the significance of this factor can vary.

There is no existing standard for WVO filtration or refining into fuel-grade oil for on-road use, although there is lively discussion and debate among grassroots organizations and backyard users. This author has personally processed tens of thousands of WVO for use as on-and-off-road fuel. My technique has consisted of:

  • Settling the oil out for anywhere from a week to several months at room temperature or higher. This allows the majority of water and food particles to sink to the bottom.
  • Decanting the cleaner oil from the top of the settled containers, through a coarse and then a fine screen or filter to remove the most obvious chunks of food and scraps. I would halt pouring well before reaching the water and sludge on the bottom of the container. I would then combine all the sludge together to re-settle for several more weeks or months.
  • Boiling the oil to at least 250F / ~121C and keeping it there until the oil ceases to bubble / snap. This step indicates that the majority of any free water has now been boiled away, as this is well above the boiling point of water
  • Filtering the oil (still hot )through a large engine filter intended for a highway tractor in order to further remove any impurities. I would generally “polish” the fuel with several additional stages of filtering

After completing this filtration protocol, the oil would smell like plain vegetable oil or occasionally popcorn butter – not like bacon and french fries and whatever else was cooked in it. While this was by no means a perfect or foolproof system, it achieved a high degree of uniformity and I was successful in running numerous vehicles on it for several years and many thousands of kilometers. However, if I accorded myself only $10 per hour the practice was not particularly economical, costing roughly the same as the then-market rates for fuel given the time-intensity of these practices.

Gaseous Methane From Anaerobic Digesters

Anaerobic digesters essentially compost wastes in controlled conditions to produce high concentrations of methane gas. Since natural gas is around 95% methane, this methane gas is a functional substitute for natural gas as a heating fuel or in suitable engines. Waste feedstocks for biodigesters of this sort include human or animal fecal matter, crop residues, food scraps and restaurant wastes, particularly the waste vegetable oil or WVO mentioned above.

The methane gas which is produced generally requires further treatment in terms of filtration, desiccation or removal of sulphur and other undesirable substances which can foul engines or heating apparatus. Once such post-processing is finished, the biogas can be compressed and stored or burned directly in natural gas boilers or natural gas-fired generators. Because of this, biodigester systems are becoming increasingly attractive to farmers and to large dairy farms in particular. The continuous, ready availability of cow manure creates a predictable input for the biodigester, and the anaerobic breakdown of the wastes actually reduces the incidence of pathogens. This has the dual effect of mitigating the pungent stench for which dairy farms are known allowing the use of such wastes as fertilizer without threatening human and nearby animal health.

Wood, Wood Wastes and Forestry Wastes

Wood can be used as a biofuel in one of several ways – by burning it directly in Solid_Fuel_Gasifiers, burning in a combined heat and power generator like a Bio-Lite_CampStove, Bio-Lite_HomeStove or other thermoelectric generator, or by running it through a gasifier and storing the resulting “producer gas” for later usage. This gas can be used in similar ways to the methane produced by a biodigester, with the exception that currently, all equipment requires substantial modification in order to burn producer gas directly. Wood is a rather difficult fuel to use as a transport fuel because of the logistical challenge of dragging a large weight of wood with you, and the challenge of continuously feeding solid fuel to a combustion chamber of some kind. For this reason, solid fuel has not been an especially popular transport fuel anywhere since the end of the Second World War.

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