Tank Battery Vapor Recovery & NSPS Compliance
Light crude: 35-45, Medium: 25-35, Heavy: <25
Typical: 4-12 psia. Higher RVP = more flash gas.
Understand flash gas generation, VRU compressor selection, emissions calculations, and NSPS compliance requirements
A vapor recovery unit (VRU) is a compression system that captures hydrocarbon vapors from storage tanks, loading operations, and process vessels that would otherwise be vented to the atmosphere or flared. The VRU compresses the vapors and routes them to a sales gas line, fuel gas system, or back into the process. VRUs typically achieve 95-98% vapor recovery efficiency and are required at many oil and gas facilities by EPA NSPS OOOO/OOOOa regulations.
Under EPA NSPS Subpart OOOO (2012) and OOOOa (2016), storage vessels with potential VOC emissions of 6 tons per year or more must reduce emissions by 95% through a VRU, combustion device, or equivalent control. NSPS OOOOb (2024) further expanded requirements. State regulations like Texas TCEQ and Colorado AQCC may have stricter thresholds. A VRU is the preferred control because it recovers product revenue rather than destroying the vapors.
Flash gas generation from a storage tank is calculated using the Vasquez-Beggs correlation or API MPMS Ch. 19.4. The key inputs are oil throughput (BPD), API gravity, Reid vapor pressure (RVP), separator pressure, and tank pressure. Higher RVP and higher separator pressure produce more flash gas. Typical flash gas rates for Permian Basin crude are 200-800 SCF/bbl, depending on the crude oil characteristics and upstream separator conditions.
Three main compressor types are used in VRU service: rotary vane (most common for small-medium VRUs, 5-100 HP, simple operation), rotary screw (medium-large VRUs, 50-500 HP, higher efficiency), and ejector (no moving parts, uses motive gas, suitable for remote locations). Rotary vane compressors dominate the upstream oil and gas market due to their tolerance of liquid carryover and simple maintenance.