The Pros and Cons of Biofuels

There are many eco-benefits to replacing oil with biofuels like ethanol and biodiesel. For one, since such fuels are derived from agricultural crops, they are inherently renewable–and our own farmers typically produce them domestically, reducing our dependence on unstable foreign sources of oil. Additionally, ethanol and biodiesel emit less particulate pollution than traditional petroleum-based gasoline and diesel fuels. They also do not contribute to global warming, since they only emit back to the environment the carbon dioxide (CO2) that their source plants absorbed out of the atmosphere in the first place.

Biofuels are Easy to Use, but Not Always Easy to Find
And unlike other forms of renewable energy (like hydrogen, solar or wind), biofuels are easy for people and businesses to transition to without special apparatus or a change in vehicle or home heating infrastructure—you can just fill your existing car, truck or home oil tank with it. Those looking to replace gasoline with ethanol in their car, however, must have a “flex-fuel” model that can run on either fuel. Otherwise, most regular diesel engines can handle biodiesel as readily as regular diesel.

Despite the upsides, however, experts point out that biofuels are far from a cure for our addiction to petroleum. A wholesale societal shift from gasoline to biofuels, given the number of gas-only cars already on the road and the lack of ethanol or biodiesel pumps at existing filling stations, would take some time.

Are There Enough Farms and Crops to Support a Switch to Biofuels?
Another major hurdle for widespread adoption of biofuels is the challenge of growing enough crops to meet demand, something skeptics say might well require converting just about all of the world’s remaining forests and open spaces over to agricultural land.

“Replacing only five percent of the nation’s diesel consumption with biodiesel would require diverting approximately 60 percent of today’s soy crops to biodiesel production,” says Matthew Brown, an energy consultant and former energy program director at the National Conference of State Legislatures. “That’s bad news for tofu lovers.”

Does Producing Biofuels Use More Energy than They Can Generate?
Another dark cloud looming over biofuels is whether producing them actually requires more energy than they can generate. After factoring in the energy needed to grow crops and then convert them into biofuels, Cornell University researcher David Pimental concludes that the numbers just don’t add up. His 2005 study found that producing ethanol from corn required 29 percent more energy than the end product itself is capable of generating. He found similarly troubling numbers in making biodiesel from soybeans.

“There is just no energy benefit to using plant biomass for liquid fuel,” Pimentel says.

Conservation is a Key Strategy for Reducing Dependence on Fossil Fuels
There is no one quick-fix for weaning ourselves off of fossil fuels and the future will likely see a combination of sources–from wind and ocean currents to hydrogen, solar and, yes, some use of biofuels–powering our energy needs. The “elephant in the living room” that is often ignored when considering energy options, however, is the hard reality that we must reduce our consumption, not just replace it with something else. Indeed, conservation is probably the largest single “alternative fuel” available to us.

Source: About.com Environmental Issues

Main Commercial Biofuel Types

Biodiesel

Biodiesel is typically manufactured by a process called transesterification, which exchanges one ester alcohol group with another of vegetable oil or animal feedstock. Biodiesel is made of biomass such as vegetable oil from soybean, canola, etc. There are many applications of bio-diesel ranging from biodiesel powered trains to commercial boilers. The first step towards cleaner flying by the use of biodiesel was taken when a test flight from London to Heathrow was successful. Biodiesel is also used in the automotive industry to power vehicles, for instance Daimler Chrysler has intentions to use 20 percent biodiesel blends. The most interesting application of biodiesel is in trains, called “diesel trains,” which uses 80 percent biodiesel and only 20 percent petro diesel. Cellulosic ethanol produced from Lignocelluloses could be the future of fuel, as it produces 85 percent less carbon dioxide from production and reduces erosion.

Bio-Gases

Biogas is formed when biological materials ferment slowly over a period of 10 to 120 days depending on the ambient temperature. Fermentation of organic materials forms methane and carbon dioxide in the absence of oxygen when the pH level ranges from 6.5 to 7.5 at a constant temperature of 15C to 55C. Anaerobic fermentation of agricultural and organic waste, sludge digestion in tanks of sewage treatment plants, and organic residues in garbage piles can form a considerable amount of biogas. Also, harvesting this biogas enables us to reduce offensive smells and greenhouse gases.

Agricultural waste is collected in a primary pit and sterilized to remove harmful chemicals. The waste is then moved to a digester where the biogas produced is collected in a storage tank to provide a non-fluctuating flow of gas. This is then fed to a gas engine as the gas mixture produced in the digester consists of 50 to 70% methane. (CH4). This high concentration of methane makes biogas suitable for combustion in gas engines. The chemical energy is converted to mechanical energy in the gas engine. It is then converted to electrical energy using an alternator much like the type commonly found in automobiles that are used to recharge the vehicle’s electrical system.

Muncipal waste contains about 150 to 250kg of organic carbon per ton. This organic carbon is biodegradable and converted into landfill gas in anaerobic conditions. It has a relatively high calorific value of about 5 kWh/m3N and can be effectively used to generate power. If this gas is continuously extracted under controlled conditions, a tremendous amount of energy can be harvested. Almost 40 to 50% of methane is present in this type of landfill gas. To harvest this gas, perforated tubes are drilled into the landfill body and connected to a pipe system. A blower sucks the gas away from the landfill and it is then later compressed, dried, and fed to a gas engine. This energy is converted to electrical energy and fed into the local power grid.

Sewage gas is harvested in much the same way. Sewage sludge is first dried and then pumped into a digester. The gas emitted from the digester typically contains about 50 to 60% methane. The gaseous emissions are then compressed and fed to a gasometer. This acts a fuel tank to the actual electrical energy generator unit. Enough energy is generated to power the sewage treatment plant itself.

Bio-Alcohols

Bio-alcohols are typically made from the fermentation of sugars and starches. A benefit of bio-alcohols is that when combined with petrol or diesel they tend not to produce as much carbon emissions. This makes bio-alcohols a renewable source of energy that can be made many times over without depleting the earth’s resources. There are three types of bio-alcohols; Methanol, Ethanol, and Butanol. Methanol has been used since World War II as a fuel substitute. It has a higher octane rating which results in higher engine efficiency. According to Robert Evans, Ethanol is not suitable for use in aircrafts because it has a low energy density, however, Ethanol can be used in spark-ignition marine engines.  Around 350 million gallons of Butanol per year is currently being used throughout the world. Butanol is mainly used as a solvent, and hopefully will be used as a fuel in the future due to its physical properties.

Source: Excerpts from Wikidot

There is much controversy about whether biofuel is/should be the fuel of the future.  The human population is multiplying every second and more land will be required for food production.  If biofuel crops start competing with food crops (as they are already in many parts of the world) then conflict will arise.  Some farmers are getting better prices for food crops from biofuel manufacturers than they are from food markets- this situation is not sustainable in the long term.  However, if non-food crops such as Jatropha are cultivated on marginal lands (where food crops fail) then it becomes feasible.  Water efficient biofuel crops that  don’t require much energy input (e.g. fertilizer, mechanical harvesting, etc) should be selected and/or bio-engineered. Clear national guidelines should be produced so that biofuel crops are only planted on cleared/already degraded land if possible.  The clearing of rain forests, virgin bush and pristine environments should be strictly controlled or prevented.  Another factor to think about is water consumption of biofuel crops; water is a already a scarce resource and it will come under even more pressure as our population explodes. Water, not land may well be the limiting factor for future biofuel crop production.