While biofuels have technically been used since the advent of fire, they are gaining popularity in recent years and have caught the eye of environmentalists and businesses alike. Biofuels are derived from renewable sources – usually previously living plants – and can come in the form of solid, liquid or gas. In some cases, algae, animal manure or litter, land-fill trash or wastewater treatment products, among other feed stocks are used for producing biofuels. Examples of conventional biofuels include bioethanol, biodiesel, renewable diesel, bio-methane, fuel pellets, and syngas.
Bioethanol is the most prevalent biofuel and is added to most gasoline sold in the U.S. at a percentage of at least 10%. According to the Renewable Fuels Association, in 2013 210 manufacturing plants produced 13.3 billion gallons of bioethanol for the year.
Almost any plant-based material can be used as ethanol feedstock. All plants contain sugars, and these sugars can be fermented to make ethanol in a process called “biochemical conversion.” Plant material also can be converted to ethanol using heat and chemicals in a process called “thermo chemical conversion.” The bioethanol is then added to gasoline and sold to the general public for use in their automobiles.
Biodiesel Biodiesel is a diesel replacement fuel that is manufactured from animal fats, cooking and vegetable oils and/or recycled cooking greases. This is commonly referred to as FOG, for fats, oils and grease. The biodiesel must meet strict ASTM D6751 standards to be sold on the market as biodiesel.
Because plants produce oils from sunlight and air, and can do so year after year on cropland, these oils are considered to be renewable. Animal fats are produced when the animal consumes plant oils and other fats. They too are renewable. Used cooking oils are mostly made from vegetable oils, but may also contain animal fats. Used cooking oils are both recyclable and renewable.
The biodiesel manufacturing process converts oils and fats into chemicals called long chain mono alkyl esters, or biodiesel. These chemicals are sometimes also referred to as Fatty Acid Methyl Esters or FAME, for short.
Renewable Diesel is another product that is derived from further processing of the biodiesel. This process, known as cracking, is very similar to that which is used for producing petroleum diesel. In fact, the chemical composition of renewable diesel is extremely close to its petroleum cousin.
Biomethane is a gaseous fuel that is often derived from landfills, waste water treatment facilities and animal farms. The rotting garbage in a landfill, the products of a waste water treatment facility and the waste produced from animals all create methane gas. We know this by the distinct smell that these facilities emit. The methane from these processes is captured and cleaned for use in engines. Most of the engines are connected to an electric generator for producing electricity that can be sold. Or, some will further clean the fuel for use in farm equipment or a truck fleet.
Fuel pellets are becoming increasingly popular with homeowners located in the colder regions of the country. Homeowners use fuel pellets in wood stoves that are usually made specifically for using these pellets. They are known as pellet stoves, and are used for heating the home. Many of these stoves have automatic fuel feed systems that convey the fuel into the stove for burning, much the same way a pump for oil or a valve for gas furnaces is used in conventional heating equipment.
Fuel pellets are mostly made from ground wood chips or saw dust that may be left over from a furniture manufacture or other wood product producer. They also come from small tree branches or trimmings, that are then converted into the pellet form.
Syngas, or synthetic gas, has been around for at least a century. Originally, on a large scale, coal was used as the feedstock for syngas production. The syngas was piped throughout a city and used for lighting, cooking and heating. Today, in the renewable energy world, syngas is used with waste plastic as a feedstock. The plastic is processed and gasified, where it is then transformed back into its original petroleum component. Mostly diesel fuel is produced with this process and the fuel quality matches very closely to petroleum diesel products.
The future of biofuel
In the future, I expect to see anaerobic digesters being much more commonplace in the U.S. at live-stock farms such as poultry, dairy, and swine farms. This type of equipment reduces odor and also enables clean manure handling for treatment so manure does not seep into ground water. Biogas can be used in the production of combined heat and power for producing electricity and heat for use in greenhouses and the like. The spent solids from the process can be used for animal bedding or solid fertilizer, and the spent liquid makes a great fertilizer as well.
With the prices of crude oil dropping in recent months and expected to stay low for the near future, I expect less emphasis placed on biodiesel and bioethanol production based on loss of margins as they compete with crude oil. However, I see an upstart in alternate uses of bioethanol technology to produce higher value “green” chemicals instead of fuels, such as acetone and butanol for example.
Biogas can even be treated to a point that it can be classified as “pipeline grade.” That means this fuel has the same properties as natural gas and can actually be injected right into the natural gas pipeline grid.
The equipment and technology related to biofuels continue to evolve. As does the potential uses for different biofuels. The U.S. and many other countries are turning to more and more renewables to support their energy mix and meet growing energy demands, and biofuel is likely to play an important role in this. We continue to see interesting developments emerge, such as using fungi and even gastrointestinal bacteria to produce biofuel. What other uses of biofuels have you heard of?
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