page_title: Flash-gas (petroleum)
section_title: Vapor Recovery Units
hierarchical_section_title: Flash-gas (petroleum) / Reduction of Flare Gas / Vapor Recovery Units
caption_attribution_description: English: Pueblo Chemical Agent-Destruction Pilot Plant Scrubber Tower The scrubber tower is part of the off-gas treatment system that will be used to filter air emissions from the Pueblo Chemical Agent-Destruction Pilot Plant.
context_page_description: 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.
  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.
context_section_description: Vapor Recovery Units (VRU’s) have commonly been used to capture vented gas and other waste gas (vapor recovery) during petroleum production, it was originally created to capture hydrogen sulfide from oilfield stock tanks. A VRU works by compressing the flash gas that is produced in storage tanks and other units to be put into a pipeline. A basic VRU is made up of a scrubber, compressor, and a switch. Once the pressure in the tank reaches the set-point, the switch kicks on the compressor and sends the vapor to a scrubber where the liquid portion is separated out. The gas portions can be used to fuel on-site operation, be transported to storage tanks for further separation, can be piped out directly to another facility, or be injected into a compressor; the liquid portions (NGLs) that commonly form are normally sent to the water tank. If they are sent to oil storage they will re-vaporize and go through the VRU, creating an endless cycle.
  VRU’s can create revenue through the resale and use of the captured vapors that would have been vented into the environment and lost. The revenue produced is dependent on the amount of vapor captured and sold into a pipeline. Analysis has been done to show the economic impacts from emission reduction and capture using VRU and other technology. These units also reduce the amount of emissions of VOCs associated with oil and natural gas production, again by preventing them from being vented directly into the atmosphere.
  There have been concerns raised about the efficiency of VRU’s. It has been pointed out that vapor recovery units (VRU’s) cannot recover lighter hydrocarbons that have been dissolved into the liquid phase because the units are designed to recover what is already in the vapor phase. Also, when the gas in put under high pipeline pressure, NGLs are condensed out and are returned to the water tank (in rare instances they are processed and sold as NGL’s).
caption: Pueblo Chemical Agent-Destruction Pilot Plant Scrubber Tower. The scrubber tower is part of the off-gas treatment system that will be used to filter air emissions from the Pueblo Chemical Agent-Destruction Pilot Plant.
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