This is an EPA background sheet, provided for the Dot Earth blog, on imaging of methaneand other emissions from oil and ga...
Table 1: Emissions from tank calculated using   Table 2: Emissions from tank calculated using  E&P Tank program while assu...
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Why Infrared Cameras Can Spot Leaking Methane Gas (EPA)

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This is background from the Environmental Protection Agency explaining why infrared imagery can be useful in spotting leaks or stray emissions of methane from natural gas wells, oil tanks or other infrastructure.
Related Dot Earth posts here:
http://j.mp/dotgasleaks
EPA background here:
http://www.epa.gov/gasstar/tools/recommended.html

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Why Infrared Cameras Can Spot Leaking Methane Gas (EPA)

  1. 1. This is an EPA background sheet, provided for the Dot Earth blog, on imaging of methaneand other emissions from oil and gas facilities:Summary - The IR camera detects methane and other light hydrocarbons that include butane, propane and pentane. - Gas evolving from stock tanks and compressor station condensate tanks is a mixture of methane and other light hydrocarbons. - We agree with the statement that methane would be “boiling at ambient conditions if any significant amount of methane were still in the liquid”, and this is in fact the major source of the vented methane emissions. Crude is transferred from containment (i.e. pipeline) at a high pressure to containment (i.e. storage tank) at low pressure. Crude at high pressure is highly saturated with methane, the saturated methane flashes out of the crude as soon as it is transferred into storage tanks that are at ambient conditions. - Based on the last bullet, the composition of the gas mixture evolving out of stock tanks and compressor station condensate tanks is usually dominated (by volume) by methane.Detailed response The three major sources for losses of light hydrocarbons are flash losses, working lossesand standing losses. Emissions from a tank vary based on numerous factors including thefrequency of cycling, duration of time within tank, temperature, pressure and the API gravity.The composition of the emitted vapor varies; however; the largest component (by volume) ismethane (between 40 and 60 percent)1. “Other components include more complex hydrocarboncompounds such as propane, butane, and ethane; natural inert gases such as nitrogen and carbondioxide; and HAP like benzene, toluene, ethyl-benzene, and xylene (collectively these four HAPare referred to as BTEX)”Error: Reference source not found. During storage, these components“flash out” of the crude and collect in the space between the liquid and the fixed roof. This vaporis oftentimes vented into the atmosphere. A variety of components including methane, ethane, butane, propane, pentane as well asother hydrocarbons chains, benzene, toluene, methanol and various other components can bedetected by an IR camera. While it is true that the IR camera can detect components other thanmethane, the emission composition exiting from production stock tanks and compressorcondensate tanks are primarily methane. These tanks typically have a high pressure inletgas/condensate which flashes bringing the inlet stream to tank conditions. When the streamflashes, a significant amount of methane is emitted. Conversely, tanks that house crude oil whichwas previously at atmospheric conditions will not have significant quantities of methane in theiremissions. Tanks which receive crude at high pressure (i.e. crude experiences high pressuredrops) will have more methane emissions. All tank emissions will include a range of vapors from methane to pentane plus. In acouple of simulations done using geographic data and the simulation software E&P tank, notedin the results listed below. It is clear that at standard industry operating conditions, the majorityof emissions are methane by mole percent.1 http://www.epa.gov/gasstar/documents/ll_final_vap.pdf
  2. 2. Table 1: Emissions from tank calculated using Table 2: Emissions from tank calculated using E&P Tank program while assuming an API E&P Tank program while assuming an API crude oil gravity of 20. crude oil gravity of 45. Composition Composition Inlet to Tank Emissions Inlet to Tank EmissionsComponent mol% wt% mol% wt% Component mol% wt% mol% wt% C1 0.2 0.0 51.9 25.8 C1 1.8 0.2 62.1 35.0 C2 0.2 0.0 13.7 12.8 C2 0.6 0.1 11.8 12.5 C3 0.8 0.2 14.0 19.1 C3 1.3 0.4 10.8 16.7 C4 2.1 0.8 11.9 21.4 C4 2.5 1.1 7.6 15.4 C5 3.4 1.7 5.9 13.2 C5 3.7 2.1 3.4 8.6

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