In an oil and gas production, flash-gas is a spontaneous vapor that is produced from the heating or depressurization of the extracted oil mixture during different phases of production. Flash evaporation, or flashing, is the process of volatile components suddenly vaporizing from their liquid state. This often happens during the transportation of petroleum products through pipelines and into vessels, such as when the stream from a common separation unit flows into an on-site atmospheric storage tank. Vessels that are used to intentionally "flash" a mixture of gas and saturated liquids are aptly named "flash drums." A type of vapor-liquid separator. A venting apparatus is used in these vessels to prevent damage due to increasing pressure, extreme cases of this are referred to as boiling liquid expanding vapor explosion (BLEVE).
The composition of the gas that is flashed is dependent on many factors, therefore it is suggested that all extractions be analyzed to determine accurate compositional values. As a generality, this definition applies to the nature of flashing hydrocarbons (HC) that make up oil and natural gas, "If the saturated liquid is a multi-component liquid (for example, a mixture of propane, isobutane and normal butane), the flashed vapor is richer in the more volatile components than is the remaining liquid". Although the flashed portion will be primarily components with higher volatilities (lighter HC), heavier HC will also flash into the vapor phase to some extent. Composition of flash gas is highly dependent on temperature and pressure and can therefore be manipulated using these control variables to become a usable resource (natural gas, natural gas liquids (NGL's), alternative fuels, etc.) if proper infrastructure and sponsorship is in place.
The production of flash-gas and its release into the atmosphere, via venting and improper handling during production, is of concern to environmental efforts due to the presence of Hazardous Air Pollutants (HAP), Greenhouse Gases (GHG), and Volatile Organic Compounds (VOC) which have been suggested to have harmful long-term environmental impacts. Various efforts by organizations around the world have been made to develop appropriate guidelines for handling flash gas as well as tools for evaluating flash emissions through model based calculations.
Natural Gas Liquids/Liquid Petroleum Gas
Natural gas liquids (NGL) are the fraction of the hydrocarbons, primarily having 2-8 carbon atoms,International Energy Agency. Natural Gas Liquids Supply Outlook, 2008-2015. Paris: International Energy Agency, 2010. Print that are present in the flash gas during oil production or as liquids in natural gas production. In other words, NGL is the liquids removed from natural gas such as ethane and heavier products.GPSA Engineering Data Book. S.l.: GSAP, 2004. Print. Components of NGL's have varying states during production, meaning that some will exist solely as a liquid or vapor, and some will be a mixture of the two depending on the current temperature and pressure. Therefore, it is necessary that components of NGL are distinguished as either natural-gas condensate, heavier components (C5+), or "other NGL", lighter components that typically remain in the vapor phase during production. NGL is not to be confused with its subcategory LPG, liquefied petroleum gas, described as "hydrocarbon mixtures in which the main components are propane, iso and normal butane, propylene and butylenes."
Capturing NGL's has shown an uptick in their economic share of U.S. production levels the past few years,"U.S. Energy Information Administration - EIA - Independent Statistics and Analysis." What are natural gas liquids and how are they used? - Today in Energy - U.S. Energy Information Administration (EIA). Web. 26 Mar. 2017. sparking interest for advancement in recovery techniques for petroleum extraction. Uses of NGLs vary, from other combustible fuels like autogas and natural gasoline, to the manufacturing of plastics. The apparent value of these materials has put the level of products developed from NGLs at an all-time high in the United States in 2015. Despite its value and use, many of the components that make up NGL and LPG become considered "waste gas" during production and are flared on-site or vented into the atmosphere as flash gas.Peterson, J.; Cooper, H.; Baukal, C.: Hydrocarbon processing, 2007, 111-115. This can be due to a lack of infrastructure to capture and store and/or transport these liquids to market. Profitability under current models is highly dependent on the access to pipeline infrastructure, gas volume produced, and the number of/distance between production facilities (batteries).Johnson, M.R.; Coderre, A.R.: Canada, International Journal of Greenhouse Gas Control. 2012, 8, 121–131.
Environmental Concerns
Flash gas is the emissions from flash evaporation, breathing emissions, and working emissions. Breathing, or standing emissions, occur naturally as liquid sits in a vessel and undergoes normal evaporation into the atmosphere. Working emissions are created when the liquid is agitated, such as during transportation, emptying/filling of tanks, sampling, etc. Contained within all of these emissions are materials that have been deemed hazardous to humans and the environment by regulatory agencies and scientific bodies worldwide.Sources:Sources: The complex nature of chemical interactions in flare, flash, and other production vapors have spawned many efforts to describe and control how these hydrocarbons interact with other materials in the atmosphere to create air pollution.Sources: The study of these interactions is encompassed by the field of atmospheric chemistry.
Hazardous Air Pollutants (HAP) The environmental impact of emissions can be quantified in terms of the amount of hazardous air pollutants (HAP) they contain. HAPs, also known as toxic air contaminants, are defined by the EPA as "those known to cause cancer and other serious health impacts".Hazardous Air Pollutants. (2017, March 17). Retrieved April 11, 2017, from https://www.epa.gov/haps In the United States, legislation known as the Clean Air Act mandated the EPA to regulate appropriate levels of HAP emissions from source categories such as industrial and mobile.Rules and Implementation. Retrieved April 11, 2017, from https://www3.epa.gov/ttn/atw/eparules.html
There are currently 187 different chemical compounds that are classified as HAP which are declared in the National Emissions Standards for Hazardous Air Pollutants (NESHAP).What are Hazardous Air Pollutants? (2017, February 09). Retrieved April 11, 2017, from https://www.epa.gov/haps/what-are-hazardous-air-pollutants Oil and natural gas production is known as a stationary source and is therefore required by the Clean Air Act to follow guidelines put forth by NESHAP, New Source Performance Standards (NSPS), and Control Techniques Guidelines to reduce the amount of emissions the industry produces.National Air Toxics Assessment. (2016, May 18). Retrieved April 11, 2017, from https://www.epa.gov/national-air-toxics-assessment
The EPA, as of 2015, has public record of two [2005/2011] National Air Toxics Assessments (NATA) which present the effects of air toxic emissions on a national-scale.GHGRP and the Oil and Gas Industry. (2017, March 12). Retrieved April 11, 2017, from https://www.epa.gov/ghgreporting/ghgrp-and-oil-and-gas-industry In addition to identifying and prioritizing air toxins, the assessment determines specific locations that are at risk so that corrective measures may be implemented. Reports also go into detail about potential cancers and health problems associated with the level of reported toxins.
Greenhouse Gases (GHG) Greenhouse gases are classified by their ability to absorb and emit radiation energy in atmosphere. This process of energy capture and release is what allows for the greenhouse effect, when energy trapped within the gas causes a resulting warming of the atmospheric temperature. Greenhouse gases are necessary for keeping our atmosphere warm enough to sustain life but also serve as a medium for over-heating to occur, a phenomenon referred to as global warming. GHGs are produced both directly and indirectly during many production phases of the oil and gas industry.Emissions from oil and gas production operations. Retrieved April 11, 2017, from http://petrowiki.org/Emissions_from_oil_and_gas_production_operations
It is estimated that 90% of GHG emissions from fossil fuels is due to its combustion.Blasing, T. Recent Greenhouse Gas Concentrations. Carbon Dioxide Information Analysis Center (CDIAC) Datasets. As of 2009, energy-related CO2 emissions made up more than 80% of total U.S. greenhouse gas emissions.Emissions of Greenhouse Gases in the United States 2009. Retrieved April 11, 2017, from https://www.eia.gov/environment/emissions/ghg_report/pdf/0573(2009).pdf Flare and flash gas both contain GHGs and therefore contribute to their release into the atmosphere, estimates of their emission levels during petroleum production vary due to largely unmeasured release of flash gas and other forms of fugitive emissions.
One study estimated a 40% increase in the atmospheric concentration of the GHG carbon dioxide (CO2) is due directly to human activities since 1750.Team, E. W. (2005, October 01). ESRL Global Monitoring Division - Global Greenhouse Gas Reference Network. Retrieved April 11, 2017, from https://www.esrl.noaa.gov/gmd/ccgg/trends/global.html GHGs other than CO2 which are produced during petroleum operations are also a concern to the environment. On average, 43.6% of waste gas from a typical plant is methane.United States, EPA, Air Quality. (1994). Control techniques for volatile organic compound emissions from stationary sources. Rockville, MD, Oklahoma: Government Institutes, Inc. Methane has 28-36 times the amount of global warming potential (GWP) as CO2 because of its ability to absorb more radiation energy.Understanding Global Warming Potentials. (2017, February 14). Retrieved April 11, 2017, from https://www.epa.gov/ghgemissions/understanding-global-warming-potentials) Nitrous oxide has a GWP of 265-298 times that of CO2 and is known to also be released during flaring and combustion of fossil fuels.Sources:
Sangsaraki, M.E.; Anajafi, E.: International Conference on Chemical, Food and Environment Engineering (ICCFEE'15), Dubai (UAE), January 11–12, 2015. Rahimpour, M.R.; Jokar, S.M.: Journal of Hazardous Materials, 2012, 204-217, Ezersky, A.; Lips, H.: Characterisation of refinery flare emissions: assumptions, assertions and AP-42, Bay Area Air Quality Management District (BAAQMD), 2003.
Volatile Organic Compounds (VOC)
Volatile organic compounds (VOCs) are organic chemicals, some of which occur naturally in oil and gas, that have high vapor pressure at ordinary room temperature. As a result, these chemicals exhibit an ease of transition from the liquid to the vapor state under atmospheric (ambient) conditions. In general chemistry terms, VOCs are organic molecules with low molecular weights, boiling points below 200 ˚C, and low to medium solubility in water. The EPA defines VOC's as, "Any compound of carbon, excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates and ammonium carbonate, which participates is atmospheric photochemical reactions, except those designated by the EPA as having negligible photochemical reactivity."Code of Federal Regulations, 40: Chapter 1, Subchapter C, Part 51, Subpart F, 51100, and EPA's Terms of Environment Glossary, Abbreviations, and Acronyms.