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Flexo Sustainable : Fall 2011
Gasoline Diesel 1.08 lb/hp-hr 1.15 lb/hp-hr 154 lb/MMBtu 164 lb/MMBtu FUEL OIL CO2, CH4, and N2O emissions are all produced during fuel oil combustion. Nearly all of the fuel carbon (99 percent) in fuel oil is converted to CO2 during the combustion process. This conversion is relatively independent of firing configura- tion. Although the formation of CO acts to reduce CO2 emis- sions, the amount of CO produced is insignificant compared to the amount of CO2 produced. The majority of the fuel carbon not converted to CO2 is due to incomplete combustion in the fuel stream. Formation of N2O during the combustion process is gov- erned by a complex series of reactions and its formation is dependent upon many factors. Formation of N2O is minimized when combustion temperatures are kept high (above 1475oF) and excess air is kept to a minimum (less than 1 percent). Additional sampling and research is needed to fully charac- terize N2O emissions and to understand the N2O formation mechanism. Emissions can vary widely from unit to unit, or even from the same unit at different operating conditions. Average emission factors based on reported test data have been developed for conventional oil combustion systems. CH4 emissions vary with the type of fuel and firing configu- ration, but are highest during periods of incomplete combus- tion or low-temperature combustion, such as the start-up or shut-down cycle for oil-fired boilers. Typically, conditions that favor formation of N2O also favor emissions of CH4. NATURAL GAS BOILERS, FURNACES & OXIDIZERS The emissions from natural gas-fired boilers, furnaces and oxidizers include nitrogen oxides (NOx), carbon monoxide (CO), and carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), volatile organic compounds (VOCs), trace amounts of sulfur dioxide (SO2), and particulate matter (PM). Natural gas is mainly methane (CH4) which is the simplest of the hydrocarbons. Even though natural gas is cleaner than oil, gasoline or coal, it does convert to CO2 when burned. In the combustion process, almost all of the carbon in the natural gas converts to CO2 as combustion adds oxygen to the methane. Due to impurities present during the natural gas refining process, traces of sulfur, nitrogen and other hydrocar- bons are also emitted when natural gas is burned. PROPANE BOILERS & FORKLIFTS Propane itself is not a direct GHG when released into the air. Unlike fuels such as natural gas, propane vapor is removed from the atmosphere faster than it takes for it to become well-mixed and impact the global climate. In addition to propane fired boilers, more than 600,000 pro- pane forklifts operate in factories and warehouses across the United States. Although they have less GHG emissions than gas or diesel powered counterparts, when propane is used as a fuel, it does generate small amounts of GHGs. Propane does emit CO2 and much lesser amounts of N2O and CH4. REFRIGERANTS Many commonly used refrigerants are chemicals referred to as hydrofluorocarbons (HFCs), which are important GHGs. Small amounts of HFCs leak from refrigerators and air con- ditioners (including in vehicles). Any of these units that your company has control over need to be included in Scope 1 of a carbon footprint. INK & SOLVENT OXIDATION The Clean Air Act requires certain printers to reduce volatile organic compound (VOC) emissions which result from the use of solvent inks, coatings, adhesives and cleaners. To do this, VOC emissions are often combusted in an oxidizer. Oxidizers are typically fueled with natural gas, which must be included in Scope 1 of a carbon footprint. However, the com- bustion of the VOCs is often overlooked as another source of CO2. SCOPE 2 EMISSIONS The Scope 2 emissions of a facility are indirect greenhouse gas (GHG) emissions from the generation of purchased electricity that is consumed in owned or controlled equipment or operations. Three types of GHGs are released when fossil fuels are combusted to generate electricity -- carbon dioxide (CO2), and to a lesser extent, methane (CH4) and nitrous oxide (N2O). For any company, purchased electricity will represent one of the largest sources of GHG emissions and the most significant opportunity to reduce emissions from a facility. The vast majority of electricity is produced by the com- bustion of fossil fuels. More than 84 percent of the energy consumed in the United States (on a Btu basis) is produced through the combustion of coal, natural gas and oil, all which generate GHGs. The remaining 16 percent come from other energy sources, such as hydropower, biomass, nuclear, wind and solar energy. Energy-related activities from fossil fuel combustion, ac- count for the vast majority of CO2 emissions worldwide. In the United States, electricity generation presents 40 percent of total CO2 emissions from all CO2 emissions sources across the country. Reducing scope 2 emissions has the greatest potential to impact total CO2 emissions worldwide. CH4 and N2O account for a much smaller portion of emis- sions from electricity generation. In fact, some reporting pro- grams consider CH4 and N2O insignificant and do not require that they are included in the calculation, thereby simplifying the calculations. If they are not included, be sure to make note of that for future comparisons. To begin to calculate Scope 2 emissions, a facility must know the amount of electricity it uses. Electricity use is typical- ly reported on a facility 's monthly utility bill in kilowatt-hours (kWh). To determine the total carbon emissions from Scope 2, including the emissions of CO2 and the CO2 equivalent (CO2e) from CH4 and N2O, it is necessary to know how much of each gas is generated from the production of one kilowatt-hour of electricity by your specific utility. Across the world these numbers will vary as utilities generate power using different 12 Sustainable FLEXO FALL 2011 www.flexography.org
Spring Summer 2009
Year End 2011