(Demo) Road and Bridges May 2010 : Page 46
reclaimed asphalt pavement (RAP) in an asphalt mix does not directly reduce fuel combustion and CO2 e 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 ac- count 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. NAPA’s Greenhouse Gas Calculator is a first step in providing an automated analysis of carbon footprint. Further refinements are possible as more info becomes available. Equal footing EPA provides a greenhouse-gas com- bustion 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 rela- tion 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 calcula- tor can be used to estimate actual plant CO2 e emissions, even factoring in equip- ment fuel usage and the plant’s electrical consumption. The calculator also can be used to estimate potential changes in CO2 e 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 46 May 2010 • ROADS&BRIDGES e per ton of mix, or an annual total of 5,155 metric tons of CO2 e. 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 CO2 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 CO2 e threshold criteria, and the plant’s operators are not required to report their greenhouse-gas emissions. The top right corner of the calcula- tor shows an interactive matrix where the user can manipulate the operating parameters in order to get estimates of CO2 e emissions based on changing e emissions of more than 30%. NAPA’s Greenhouse Gas Calculator is a first step in providing an auto- mated analysis of carbon footprint. Further refinements are possible as more information becomes available. For example, although the inclusion of conditions. In this example, the typical aggregate moisture has been held to 3% and the mix temperature has been re- duced to 250°F, consistent with running warm mix. The result of these operating conditions is a reduction in potential CO2 Beyond the numbers To summarize, typical asphalt-mix plant facilities will probably not be required to report their greenhouse-gas emissions under current federal guide- lines, 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 green- house-gas emissions (carbon footprint); for instance, emissions can be reduced by implementing warm mix and reduc- ing 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 Green- house 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 feder- al level or the state level. Understanding your facility’s greenhouse-gas emissions, i.e., your carbon footprint, is becoming increasingly important. R&B Marks is the director of environmental services for NAPA, Lanham, Md.
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