Thursday, November 27, 2014

CALCULATION OF GREENHOUSE GASES EMITTED FROM GAS COMPRESSOR STATIONS



CALCULATION OF Greenhouse Gases EMITTED FROM GAS COMPRESSOR STATIONS



Some gases in the atmosphere affect the Earth’s heat balance by absorbing infrared radiation.  These layers of gas in the atmosphere can prevent the escape of heat in much the same way as glass in a greenhouse.  Thus, global warming is often referred to as the “greenhouse effect.”  The gases most responsible for global warming are referred to as greenhouse gases (GHG).  It is becoming more widely accepted that continued increases in GHGs will contribute to global warming, although there is uncertainty concerning the magnitude and timing of the warming trend.  Combustion of fossil fuels during a gas project construction and operation will result in the emission of the following GHGs: carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O).  Emissions of GHGs are typically expressed in terms of CO2 equivalents  (CO2e),  where  the potential of  each gas to  increase heating in the  atmosphere is expressed as a multiple of the heating potential of CO2, or its global warming potential.

GHG emissions, expressed in terms of CO2e, typically must be estimated for both compressor station operation and construction.  The proposed Project is not subject to the newly revised PSD regulations applicable to GHGs.  Known as the “Tailoring Rule”, this regulation sets a higher major source threshold than other pollutants.  Typically, the estimated potential GHG emissions are less than the threshold amount.

Another new regulation which specifically targets GHGs is the Mandatory Reporting Rule, codified under 40 CFR Part 98.  As a natural gas transmission compressor station, the station may potentially be applicable to Subpart C (stationary combustion) and Subpart W (Oil and Natural Gas Systems) of the rule.  Subpart C covers fuel combustion in the compressor turbines (the two Solar Centaur 50 turbines) and the fuel gas heater.  All compressor stations (at least the new ones) include emergency generators.  The emergency generator is not included in the emission calculations, as it is used as an emergency unit.  Subpart W covers venting of the compressor turbines, venting of condensate storage tanks, station blowdown venting, and equipment leaks from piping components.  The rule requires monitoring and reporting if an applicable source emits greater than actual emissions of 25,000 metric tons of GHGs from certain source categories.




Construction Emissions

Construction of the Gas Compressor Station will result in temporary increases in emissions of some pollutants due to the use of construction equipment powered by diesel or gasoline engines.  Construction activities will also result in the temporary generation of fugitive dust due to disturbance of the surface and other dust generating actions.  Indirect emissions during the construction period will be associated with delivery vehicles and construction worker commuting.

The quantity of fugitive dust generated depends on the size of area disturbed and the intensity of construction activity and also on the silt and moisture content of the soil, the wind speed, and the speed, weight, and volume of vehicular traffic.  Fugitive dust emissions will be mitigated, as necessary, by spraying water to dampen the surfaces of dry work areas.  Worst-case fugitive particulate matter emissions for PM10 and PM2.5 were calculated based on EPA AP-42 recommended emission factors for heavy construction activities along with estimates of the extent and duration of active surface disturbance.  The use of the heavy construction emission factor from AP-42 is meant to be general in nature to cover a wide range of construction operations.  This may overestimate potential fugitive dust generated by the proposed construction project.  The estimated emissions are summarized in tables and supporting calculations are provided in the appendices.

Emissions of NOx, CO, PM10, PM2.5, SO2, VOCs and Greenhouse Gases (GHGs) from construction equipment engines used during Project construction have been estimated based on the anticipated types of non-road and on-road equipment and their levels of use.  Emission factors for diesel and gasoline on-road vehicles were obtained using EPA’s MOBILE6.2 model (SO2) and from New York State Department of Transportation  (NYSDOT)  tables  developed  using  MOBILE6.2  (NOX,  CO,  VOC,  PM10,  PM2.5).



Emission factors for diesel and gasoline non-road equipment engines were obtained using EPA’s NONROAD model documentation.  Emission factors using Tier 2 diesel engine standards have conservatively been assumed to apply to construction equipment engines during 2012 and do not reflect the anticipated phasing-in of more stringent emissions and fuel standards.  A Table typically presents these emission estimates by major construction activity for the entire construction period for all construction activities, respectively.  The assumptions, data, and emission factors used to estimate emissions from construction equipment engines and vehicles are provided in Appendices, along with more detailed listings of emissions estimates.