SpecialReport: Gas Compression & Vapor Recovery FIGURE 2 Storage Tank Vapor Recovery Process Flow Suction Line to VRU Scrubber One Inch Sensing Line or Transducer Pressure/Vacuum Relief VRU Suction Scrubber Bypass Line Butterfly or Gate Valve Storage Tank Storage Tank Drip Pot on VR Sensing Panel VRU: Vapor Recovery Unit Scrubber Drain Pump Condensate Return rules now in place, the focus for EPA and state regulatory agencies has shifted to active enforcement. The expectation is that EPA will continue to make storage tank emissions a priority in enforcement inspections. Implementing best practices can enhance compliance and improve negotiations with regulators should an operator have a compliance issue to resolve. All new and existing facilities must be designed and operated to comply with the new rules, although facilities that existed prior to the applicability dates of NSPS OOOO/OOOOa are "grandfathered in" and have fewer emission control requirements. These grandfathered facilities can be opportunities to use voluntary options to reduce VOC and methane emissions. Also, many companies have GHG emission reduction goals that are used to voluntarily reduce fugitive emissions in their operations. Best Practices Specific engineering and maintenance best practices for recovering flash gas from liquids storage tanks identified by EPA include: · Reducing liquid pressure prior to transferring the liquid to atmospheric storage vessels; · Using adequate diameter piping for vent lines to emission control devices; · Preventing liquids collection in vent lines; · Eliminating unintentional natural gas carry-through; · Ensuring proper maintenance and set points for pressure relief valves; · Minimizing venting from thief 64 THE AMERICAN OIL & GAS REPORTER hatches; and · Adequately sizing emission control devices. Operators should use multiple stages of separation to reduce flash gas volumes and peak vent gas flow rates during separator dumps of oil and produced water to storage vessels. This allows the system to operate with a smaller pressure drop between the last stage of separation (lowpressure separator/heater treater) and an atmospheric tank. Of course, to reduce air emissions, the gas liberated by the in- termediate stages of separation must be recovered by a VRU and used either as fuel or sent to the sales pipeline rather than vented to the atmosphere. Infrared optical imaging video cameras routinely are used to survey production sites to identify gas being vented to the atmosphere that is invisible to the human eye, validating volumes being lost. Infrared cameras also can be used to assess an oil and gas process to optimize pressure drops to atmospheric tanks and reduce flash emissions. Vent piping between storage tanks and emission control devices must have a sufficient diameter to handle the potential instantaneous peak flow of vent gas (including flash gas) during separator dumps. If the piping is inadequate, a portion of the gas will not be collected by the VRU. This will increase the chance of creating backpressure on the storage tank and result in venting to the atmosphere at the thief hatches and/or pressure relief valves. Adequately sized vent piping should be a standard design criteria when sizing VRUs for a tank facility (Figure 3). With respect to preventing liquids collection in vent lines, the efficiency of vent gas control systems will be reduced if rich gas in the vent line between the tank and emission control device condenses and collect in vent lines, especially in low spots along the path. An effective FIGURE 3 Vapor Recovery Unit in Single-Tank Application