Easy math

May 21, 2010

New rules from the U.S. Environmental Protection Agency require greenhouse-gas emissions to be monitored by specific sources, starting January of this year with reporting to begin March 2011.

New rules from the U.S. Environmental Protection Agency require greenhouse-gas emissions to be monitored by specific sources, starting January of this year with reporting to begin March 2011.

Does a typical asphalt-mix plant need to report their greenhouse-gas emissions? That question can only be answered by calculating the emissions of a plant. To aid asphalt pavement mix producers in this endeavor, the National Asphalt Pavement Association (NAPA) has launched an online tool called the Greenhouse Gas Calculator, which can be used to assess whether a mix plant needs to report greenhouse-gas emissions under the U.S. EPA Mandatory Greenhouse Reporting Rule or similar reporting rules by state agencies. The calculator can be found on NAPA’s website at www.hotmix.org/ghgc.

The EPA took its first step in regulating greenhouse-gas emissions from industrial sources on Oct. 30, 2009, in issuing their Mandatory Greenhouse Gas Reporting Rule (40 CFR Part 98). While the rule does not require permitting and control of greenhouse-gas emissions, reporting requirements under the rule will likely lay the foundation for future regulation to reduce greenhouse-gas emissions.

Greenhouse-gas emissions result from the combustion of fuels, which primarily release CO2, and in lesser amounts, nitrous oxide (NOx) and methane. In addition to these, there also are numerous process-related releases as well as specialty gases such as chlorofluorocarbons. EPA has assigned each individual greenhouse gas a potency factor based upon CO2; the universal measure is CO2 equivalent (CO2e). Generally, the more fuel combusted, or burned, the more CO2e is emitted. And asphalt plants burn fuel. The majority of fuel is combusted to dry the aggregate and heat the mix; to a lesser extent, fuel is used to heat the liquid asphalt binder and maintain the temperature of the mix. Therefore, CO2 is the primary greenhouse gas of interest in relation to mix plants.

Reporting in
Whether state environmental agencies will require small sources to report their greenhouse-gas emissions or to obtain air-operating permits is determined on a region-by-region basis, and on a state-by-state basis within a region. What is certain is that EPA will require some specified sources that emit greenhouse gases to report their emissions. EPA’s Greenhouse Gas Reporting Rule makes a distinction between listed sources and unlisted sources that must report. Asphalt-mix plants are not a listed source category, but they still must evaluate their emissions as part of EPA’s rule.

Even though asphalt plants are unlisted sources, if they meet both of the following criteria they are required to report their greenhouse-gas emissions to EPA:

  • Total fuel combustion capacity greater than 30 million Btu (MMBTU) per hour; and
  • Actual greenhouse-gas emissions greater than 25,000 metric tons per year.

Again, unlisted sources (including asphalt plants) are only required to report their emissions if they meet both of these criteria.

The burners on asphalt drum mixers typically exceed the 30 million Btu combustion rate. And so the question becomes, “Does an asphalt plant emit more than 25,000 metric tons of CO2e per year?” The short answer is that it is highly unlikely for a single mix plant. Unless a facility produces over 1 million tons of mix in a year, CO2e emissions will likely be below the federal threshold reporting criteria.

But a word of caution is in order. Various state agencies have recently implemented state greenhouse-gas reporting rules or are in the process of doing so. Many of the states are coordinating with regional greenhouse-gas initiatives. Some of these state-specific reporting criteria require sources to report emissions of as little as 5,000 tons CO2e annually, which is a level that could result from processing only about 200,000 tons of asphalt mix. Therefore, it is imperative that an asphalt-mix plant pay close attention to its state’s reporting requirements for annual CO2e emissions.

Equal footing
EPA provides a greenhouse-gas combustion calculation methodology for every fuel imaginable. These are default theoretical emission values, assuming complete combustion of the fuel. These emission values are slightly greater than those identified by EPA as part of their AP-42 Emissions Factors review for asphalt plants. EPA’s method is based closely on the Climate Registry’s (TCR) protocols for calculating greenhouse-gas emissions. The registry has become well recognized by both state environmental agencies and EPA as a credible source of coordination and guidance in relation to greenhouse-gas reporting. TCR’s methods also can be used to assess the carbon footprint of many activities. Visit the website at www.theclimateregistry?.org for more information.

NAPA’s Greenhouse Gas Calculator utilizes TCR’s methodology. The calculator can be used to estimate actual plant CO2e emissions, even factoring in equipment fuel usage and the plant’s electrical consumption. The calculator also can be used to estimate potential changes in CO2e emissions when plant conditions change, such as variations in aggregate moisture and final mix temperatures.

The calculator, which is found at www.hotmix.org/ghgc, is easy to use.

The calculator allows the user to select the type of fuel actually used and to input the amount of fuel consumed as well as annual mix production. In the example shown above, the calculator looks at a plant that consumed about 500,000 gal of No. 2 fuel oil to produce 250,000 tons of mix last year. At top left, it shows that the plant produced 45.5 lb of CO2e per ton of mix, or an annual total of 5,155 metric tons of CO2e. Adding in the plant’s use of vehicle fuel and electricity (see bottom left section), the overall annual facility emissions were 5,923 metric tons. Therefore, this plant’s emissions are below the 25,000 metric tons CO2e threshold criteria, and the plant’s operators are not required to report their greenhouse-gas emissions.

The top right corner of the calculator shows an interactive matrix where the user can manipulate the operating parameters in order to get estimates of CO2e emissions based on changing conditions. In this example, the typical aggregate moisture has been held to 3% and the mix temperature has been reduced to 250°F, consistent with running warm mix. The result of these operating conditions is a reduction in potential CO2e emissions of more than 30%.

NAPA’s Greenhouse Gas Calculator is a first step in providing an automated analysis of carbon footprint. Further refinements are possible as more information becomes available. For example, although the inclusion of reclaimed asphalt pavement (RAP) in an asphalt mix does not directly reduce fuel combustion and CO2e emissions, the use of RAP does offset greenhouse gases associated with the extraction of raw materials, including virgin aggregate and liquid asphalt binder. These offsets should ideally be included in a life-cycle carbon footprint model; however, there is currently no accepted model to account for these factors. It is anticipated that at some point in the future the information required for performing these life-cycle calculations will become available and will be incorporated into forthcoming models.

Beyond the numbers
To summarize, typical asphalt-mix plant facilities will probably not be required to report their greenhouse-gas emissions under current federal guidelines, but facilities producing more than 200,000 tons of mix annually may be required to report their greenhouse-gas emissions by some state environmental authorities.

For mix plant operators wishing to perform due diligence on greenhouse-gas emissions, NAPA’s Greenhouse Gas Calculator is intended to be a handy tool for calculating emissions. The calculator also can be used to assess how operational changes in an asphalt-mix plant might lower the plant’s greenhouse-gas emissions (carbon footprint); for instance, emissions can be reduced by implementing warm mix and reducing aggregate moisture. Another variable that can be assessed with the calculator is the use of different fuel types.

It is possible that EPA’s new Greenhouse Gas Reporting Rule will provide a basis for establishing an emissions cap-and-trade program that is currently being debated by Congress. Such a cap-and-trade scheme could eventually be expanded to cover smaller sources, such as asphalt-mix plants, at either the federal level or the state level. Understanding your facility’s greenhouse-gas emissions, i.e., your carbon footprint, is becoming increasingly important.

About The Author: Marks is the director of environmental services for NAPA, Lanham, Md.

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