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U.S. Carbon Cycle Science  Program
Updated 1 December, 2003

Research and Current Activities
Reducing Emissions of Other Greenhouse Gases

 

Document #
DOE/PI-0001
Dated
November 2003

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Contents

Global Warming Potentials
(100 Year Time Horizon)
GAS
GWP
Carbon dioxide (CO2)
1
Methane (CH4)
23
Nitrous oxide (N2O)
296
Hydrofluorocarbons
HFC-23
12,000
HFC-125
3,400
HFC-134a
1,300
HFC-143a
4,300
HFC-152a
120
HFC-227ea
3,500
HFC-43-10mee
1,500
Fully Fluorinated Species
SF6
22,200
CF4
5,700
C2F6
11,900
C4F10
8,600
C6F14
9,000

The concept of global warming potential (GWP) was developed to compare the ability of each GHG to trap heat in the atmosphere relative to another gas. In this case, CO2 is the reference case. Methane, for example, has a GWP of 23 over a 100-year period. This means that on a kilogram for kilogram basis, methane is 23 times more potent than CO2 over a 100-year period.

(IPCC Third Assessment Report)

Other greenhouse gases cover a broad array of gases other than CO2, principally methane (CH4), nitrous oxide (N2O), sulfur hexaflouride (SF6), and other chemicals that are effective global warmers. These other GHGs are more potent as energy absorbers than CO2 (per unit weight) and have cumulatively contributed between one-fifth and one-third of the total estimated global warming potential since pre-industrial times. Therefore, reducing non-CO2 GHG emissions is an important component of any GHG mitigation strategy.

The U.S. is a world leader in reducing emissions of non-CO2 GHGs. These emissions come from many sources and sectors, including energy production (coal mining and oil and gas systems), agriculture, transportation, waste disposal, heating and cooling applications, aluminum and magnesium production, semiconductor manufacturing, and electricity transmission. By working closely with specific emitting sources, voluntary programs have demonstrated the value of technology in reducing non-CO2 GHG emissions and have identified emerging technologies with the promise of larger future emission reductions. Two areas demonstrate these types of activities and progress: methane recovery from coal mines and SF6 substitution in magnesium production.

 
Pie-chart showing greenhouse gas emissions from the U.S. (by gas) CO2 from burning fossil fuels is the dominant GHG source category in the U.S., typically comprising close to 80 percent of all GHG emissions. However, other GHGs must not be overlooked. DOE, EPA, and USDA are working closely with industry and agriculture to achieve voluntary reductions through new management practices and technology.

Methane Recovery from Coal Mines

BHP Billiton Ltd
Thermal Oxidation of Ventilation Air Methane Using Megtec's Flow Reversal Reactor at CONSOL Energy, BHP Billiton Ltd
EPA and DOE are working cooperatively with CONSOL Energy to demonstrate thermal oxidation of ventilation air methane using Megtec's Flow Reversal Reactor. Ventilation air methane equipment, such as the Megtec Vocsidizer, uses up to 100 percent of the methane released from a mine ventilation shaft. It generates heat that can be used for power production.

Methane is liberated during underground and surface coal mining as part of normal mining operations. Most emissions result from natural degasification or ventilation systems employed at underground mines to ensure that methane levels remain within safe concentrations. EPA and DOE are working with the coal industry through the President's Climate VISION Initiative to reduce emissions by recovering methane gas liberated during mining. Innovative technologies are being developed to capture and produce coalbed methane (CBM) and coal mine methane (CMM). In particular, technologies to oxidize the low-concentration methane contained in mine ventilation air have the potential to substantially reduce emissions. Furthermore, the development of advanced drilling technologies such as in-mine and surface directional drilling systems may enable fewer wells to produce more gas, thus increasing efficiency and reducing emissions.

SF6 from Magnesium Production

For more than 25 years, magnesium metal producers and casting companies have used SF6 mixed with dry air and/or CO2 as a protective cover gas to prevent the oxidation and burning of molten metal. EPA and the U.S. magnesium industry, with the support of the International Magnesium Association (IMA), are working in a voluntary partnership to eliminate SF6 emissions. Promising new cover gas alternatives are now commercially available and are undergoing further evaluation in production-scale trials. The partnership's early success has led to growing industry optimism that it can eliminate all SF6 emissions by 2010, as part of the President's Climate VISION Initiative.

Photos by 3M TM Performance Materials Division

Process using SF6 as a cover gasSF6, a potent GHG, is used as a cover gas in the magnesium industry to prevent the burning of molten metal. Alternative cover gas technologies are now being developed that meet or exceed current performance requirements and offer significant environmental benefits. The top photograph uses a cover gas while the second photo is without a cover gas.

Process that does not use SF6 as a cover gas

 

 


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