Q: What is the difference between diesel fuel and home heating oil?

A: Home heating oil and transportation diesel are chemically identical, but in the refinery they are processed in slightly different ways for their respective sectors. In addition to having specified regulations and taxes, transportation diesel has a low sulfur standard, meaning that it must contain 0.05 percent sulfur or less. Home heating oil is required by law to contain a maximum of 0.5 percent sulfur, but due to unintentional mixing of transportation diesel and home heating oil at the refinery, the sulfur content of home heating oil usually hovers around 0.2 percent. In order to distinguish home heating oil from transportation diesel, the refiner will typically dye heating oil a cranberry color, but otherwise these fuels are the same.

Q: Is there a natural gas crisis on the horizon?

A: No one knows for certain whether or not the United States is entering a natural gas crisis, although prices have risen at a faster rate than was previously predicted. Until recently, domestic natural gas supplies were plentiful and inexpensive enough that certain economic sectors, such as industry and electric power generation, began to use more natural gas than domestic reservoirs could sustain, and this trend has only continued. The rate of gas consumption is still rising in the electricity generation sector, although certain industries (such as the fertilizer industry) are beginning to curb their use of natural gas in response to higher prices.

In labeling the phenomenon of tighter natural gas supplies a "crisis," industry and government officials are responding to the possibility that consumption of natural gas may soon outpace supply. However, this is not an inevitable outcome: with some tailoring, conservation, and government-supported efficiency measures in the industrial, residential, and transportation sectors, a crisis may be averted. Some are suggesting more controversial options, like drilling for natural gas in the Alaska National Wildlife Refuge (ANWR), a protected area, or expanding offshore drilling leases and opening up more federal lands.

Q: What exactly is "clean coal?"

A: "Clean coal" refers to coal combusted using technologies that reduce or remove polluting components to render it less harmful for the environment and human health. Although "clean coal" does not mean the coal is entirely free of pollutants, it is substantially superior in cleanliness than traditional methods of coal use. Several technological methods currently exist to improve the emissions of coal; some are viable and in common use right now, and others (namely gasification) may not be employed on a large scale until costs are brought down. Some examples of some beneficial ways of making coal cleaner include:

Coal Benefication (pre-combustion cleaning): This process occurs "upstream," or before the coal is combusted, to remove pollutants: the coal is first crushed and screened to remove impurities, and then further cleaning techniques place the crushed coal in a liquid medium, where the solid impurities settle out. This process removes pyritic sulfur, which accounts for up to 30 percent of the sulfur content of coal.

Scrubbers (Fluegas Desulfurization Systems, or FGS): In this "end of pipe" cleaning procedure, after the coal is combusted the flue gas is sprayed with a slurry of water and an alkaline agent such as lime or limestone. The main impurity and one that accounts for the majority of acid deposition (acid rain) in the United States is sulfur dioxide (SO2), and this pollutant mixes with the slurry to form a pH-neutral compound such as calcium sulfate/sulfite, which is then eliminated in the form of a waste sludge.

Baghouses (electrostatic precipitators): Baghouse technology is another "end of pipe" method that operates after combustion to remove fly ash, the solid particulate ash emitted during coal combustion. As the fly ash passes through the baghouses, it is given an electric charge. The charge causes it to be attracted to a collector plate, and thus it is removed from the flue gas before it can enter the air. Coal plants often have a series of baghouse filters through which the gas passes before leaving the stack in order to remove as much of the particulate matter (PM) as possible.

Gasification (Integrated Gasification Combined Cycle, or IGCC): Gasification is a promising technology for future large-scale clean coal combustion. The technique for coal gasification is the same as that for biomass gasification: the coal is converted to form syngas, which is composed mainly of hydrogen (H2) and carbon monoxide (CO). In addition to biomass, petroleum coke, other petroleum residue, and industrial and municipal wastes can be used as feedstocks for gasification. The process takes place when the feedstock enters the gasifier and encounters oxygen (O2) and steam under high pressure and temperature conditions that allow the feedstock to be broken down into syngas and solid ash waste. The waste is removed, and the syngas undergoes heavy refining to eliminate particulates and other pollutants. Refining processes can also remove carbon dioxide (CO2) and recover hydrogen (H2).

Q: What is a Renewable Fuels Standard (RFS)? A Renewable Portfolio Standard (RPS)?

A: At present, state and federal legislators are attempting to craft energy policy that will take into account the beneficial effects of renewable fuel technologies. Whereas fossil fuels exist in finite supply, renewable fuels occur can be drawn upon indefinitely. To make the United States less dependent on fuel sources that will eventually be depleted, lawmakers in a 13 states have instituted Renewable Portfolio Standards (RPS) for electricity generation, and federal legislators are currently debating whether to do the same nationally. RPS legislation differs from state to state, but generally mandates that a certain percentage of electricity sold within a state be produced from renewable sources. Renewable sources may include windpower, solar power, geothermal power, biomass, landfill methane, and hydroelectric power. While RPS mandates focus on electricity consumed in the state, they do not mandate that the renewable electricity must be actually produced within the state. The state of Maine, for example, meets its RPS objectives in part by purchasing hydroelectric power from Canada.

The Renewable Fuels Standard (RFS) is a broader proposed federal mandate that focuses more on liquid fuels, which are used more for transportation than electricity generation. The emphasis of the RFS is to encourage the large-scale production of ethanol and its widespread use by blending it in with gasoline. (For more information on ethanol, please see the description of ethanol in the "Fuel Facts" section of our website.)

Q: What is so special about hydrogen (and why is the President talking about it)?

A: Hydrogen is currently attracting much attention in government and in the media for its potential as a fuel carrier. Hydrogen (H2) is a naturally occurring, plentiful element that can be converted into the lightest, simplest energy carrier available. Hydrogen is the simplest known element, but its energy content is the highest per unit of weight of any fuel (52,000 BTUs/pound). The problem is that hydrogen generally is bound with other elements creating molecules, such as in water (H2O), and to be useful it must be separated through fairly energy intensive processes.

After hydrogen has been separated, it is ideal for use in generating secondary energy (i.e., electricity). It can be combusted directly, added to natural gas or gasoline to reduce emissions, or stored for use in fuel cells - an emerging technology that has great potential for clean transportation and electric generation. The cleanliness of hydrogen fuel cells is why the President has highlighted hydrogen as an important research item for the future.

Hydrogen fuel cells are currently used aboard the U.S. Space Shuttle Program to run all the electrical systems, and crewmembers are able to drink the sterile water that is a byproduct of fuel cells. At present, NASA is the largest user of hydrogen power in the U.S.; other common venues for hydrogen use at present are chemical production, petroleum refining, metals treating, and electrical applications.

Q: What happens to the radioactive fuel from nuclear power plants after it is used?

A: Typically, nuclear power plants are refueled by replacing one-third of the uranium (U) fuel rods every 18 months. The spent fuel rods contain high levels of radioactive fission products and are very hot when removed, so they are placed in swimming pool-sized cooling tanks filled with boric acid immediately after removal. In the tanks, the most radioactive isotopes cool and decay, rendering the fuel rods less radioactive. Surrounding the tanks is a neutron-absorbing barrier composed of the same substance as the control rods used in nuclear reactors, and plant personnel monitor the tanks continuously for signs of emanating radiation. The tanks were originally only meant to provide temporary storage until the fuel decays sufficiently to the point where it can be stored permanently, but fuel rods can take thousands or millions of years to decay (uranium-235 or U235, the isotope used in some nuclear reactors, has a half-life of 700 million years), and there is no permanent storage as of yet. This method is not feasible in the long term because of the risks associated with overcrowded tanks. Another method of storage is called "dry storage" and involves placing the rods in on-site reinforced casks or concrete tombs after cooling it in tanks for about five years. An option for reducing nuclear waste is to reprocess the spent fuel, but reprocessing technology is more expensive than mining and refining new stores of uranium. There are several reprocessing units in Europe, and soon the technology may advance to the point where this recycling of nuclear fuel will be economically feasible.

Nuclear waste may be classified into several grades based on level of radioactivity. Low-level waste is comparatively less radioactive, with a half-life in the hundreds of years, and therefore it is buried relatively near the surface. The high-level waste mainly comprises highly radioactive spent fuel rods and is harder to store, but researchers working with the United States Department of Energy are currently exploring storage possibilities deep below Yucca Mountain in Nevada. Underground storage (officially known as "deep geological disposal") far from fault lines and human activity appears to be the solution of preference at this point, and the Yucca Mountain Deep Geological Repository is projected for completion by 2010.

Q: Can all automobiles run on ethanol?

A: All automobiles can run on certain blends of ethanol and gasoline. For example, reformulated gasoline (RFG), or gasoline mixed with 8 to 10 percent ethanol, can work using any car engines. Higher percentages of ethanol - even pure ethanol - can also fuel an automobile, but one with special modifications. Most cars produced after 1994 are able to use ethanol in higher concentrations, such as E85 (85 percent ethanol) or even pure ethanol. For more information, please see the "Ethanol" bio in our "Fuel Facts" section on the CECA website.