Clean fuels, those derived from non-fossil fuel sources, have many advantages. Those countries with a shortage of natural resources can control their own supply of energy, free of interference from embargoes or political machination. Clean fuels do not produce excess amounts of greenhouse gases (GHGs) that are associated with climate change and global warming. And they are sustainable; instead of relying on finite reservoirs, they can be produced from crops and organic matter endlessly.
Alas, producing large amounts of clean fuels has complications. They can distort food markets, absorb huge subsidies from the financial purse, and pose significant scaling up headaches on the long road between the lab and marketplace.
Ethanol is the most advanced clean fuel in the marketplace. The complex organic compound is produced at facilities that extract sugars from plants (corn in the US, sugarcane in Brazil), then ferment the sugar into alcohol using yeast. The alcohol, at 8% volume, is then repeatedly distilled until it reaches over 99% purity. While combustion of ethanol in vehicles does emit CO2, the life cycle of the plant based ingredients is considered carbon neutral in comparison to fossil fuels.
The market for ethanol is largely driven by government fiat. In the US, Congress enacted the renewable fuels standards (RFS) mandate in 2005 that guaranteed a market of 7.5 billion gal. of biofuel annually by 2012. In 2007, Congress bolstered the Renewable Fuel Standard (RFS) mandate by enacting the Energy Independence and Security Act (EISA), which required increased national production of renewable biofuels to 36 billion gal./y by 2022. By 2013, approximately 13 billion gal. of ethanol were being produced annually, slightly less than 10% of the US gasoline demand of 133 billion gal.
But ethanol has several significant shortcomings when compared to fossil fuels. Ethanol’s energy content is significantly lower; it takes approximately 1.5 ltrs of ethanol to drive as far as 1 ltr of gasoline. Ethanol is very corrosive, and high concentrations can dissolve seals and gaskets in pipelines, containers and engines. Price surges in staple commodities such as corn have been linked to its usage for fuel.
Biodiesel, the second largest clean fuel consumed in the US, is also mandated under EISA. The EPA set a target of 1.28 billion gal. for US markets in 2013 (or slightly over 100 million gal./month), in spite of objections from the refining industry and consumer groups that the fuel was expensive and unnecessary.
Although most biodiesel is made from soybean byproducts, anything from recycled oils from chip vats to coffee grounds can be used. The fuel is environmentally benign, biodegradable when spilled, and reduces the amount of exhaust particulates. The most common biodiesel production method is to react vegetable oil with methanol in the presence of lye. The process removes glycerine, and the resulting monoalkyl esters of long chain fatty acids perform similarly to petroleum diesel.
But biodiesel’s energy content is approximately 11% less than petroleum diesel, making it less fuel efficient by volume. Its high oxygen content also increases nitrogen oxide emissions. The fuel has been known to clog fuel filters, form gels in cold weather and absorb water (which reduces the heat of combustion and promotes corrosion and microbe growth). Finally, biodiesel is more costly than fossil fuel diesel.
Hydrogen has been the bridesmaid of clean fuels for decades. It reduces urban pollution, cuts down dramatically on GHGs, and enhances energy security for oil importing nations. It can easily be obtained from water through the electrolysis process; a strong electrical current is passed through water to generate bubbles of hydrogen at the cathode.
During the 2000s, hydrogen was touted by President Bush’s administration, and California Governor Arnold Schwarzenegger announced a hydrogen highway that would stretch the length of his state. As the 2010 Olympic Winter Games approached, the British Columbia government purchased 20 hydrogen powered buses to ferry folks from Vancouver to venues in the nearby alpine village of Whistler.
Most hydrogen is produced through the steam methane reformer (SMR) process. Natural gas is mixed with high temperature steam under pressure in the presence of a catalyst; hydrogen and carbon monoxide (CO) are produced. Approximately 50 billion ft3/d of hydrogen is already manufactured globally; the majority is used in refineries to upgrade less valuable fractions of crude into gasoline.
Unfortunately, hydrogen has many hurdles to overcome. Most hydrogen production also consumes fossil fuels directly (natural gas), or indirectly (coal fired plants). Although it costs approximately US$ 1 to produce 1 kg of hydrogen (415 ft3), delivering it to retail outlets raises the price into the US$ 14 - 15/kg range. The Department of Energy (DOE) estimates it would cost US$ 10 billion/y over the next 30 years to build a nationwide distribution system.
Algae biofuels, says the Obama administration, have great potential to cut foreign oil independence. Since 2009, the Department of Energy (DOE) and the Department of Agriculture have invested over US$ 100 million in various grants and loan guarantees to help researchers create commercial scale facilities.
It is easy to see algae biofuels’ attractions. They thrive in non-crop environments with little more than basic nutrients and sunshine. They grow far more rapidly than conventional crops, and generate a much higher fraction of their biomass as oil (up to 60%, versus 2 - 3% for soybeans).
Currently, algae biofuels are expensive. Industry estimates place the production costs anywhere between US$ 3.50 and US$ 15.00/ltr. One of the most significant costs consists in separating the biomass from solution. Typically, centrifuges are used to raise the concentration from around 1 mg/ltr to 200 mg/ltr; energy costs can run into thousands of dollars/t of dry product.
Clearly, energy independence, reduced GHGs and energy sustainability are goals that are worth pursuing. Equally as clearly, clean fuels represent one of the most hopeful means of achieving them. But the road is long, and the challenges both daunting and expensive. As the advent of hydraulic fracturing and horizontal drilling in fossil fuels showed however, ingenuity and new technologies can become game changers almost overnight.
Written by Gordon Cope, contributing editor, and adapted for the web by Claira Lloyd.
The full article can be found in the March issue of Hydrocarbon Engineering.
Read the article online at: https://www.hydrocarbonengineering.com/gas-processing/24022014/it_aint_easy_being_green193/