Vapor recovery is the process of capturing escaped gas, often for injecting back into a process system or into a pressurized flare line, rather than venting. Vapor recovery is a broad term, but is often associated with entrained gas at atmospheric pressure coming off crude oil or produced water tanks.
Other applications that might be considered vapor recovery would be casing gas recovery, packing vent recovery, waste-gas, and overheads compression.
Increasing environmental regulations create more applications for vapor recovery units, where venting or flaring was the historical solution.
Common Themes with Vapor Recovery
The gas source is typically entrained in a liquid (oil or water), or pulled off a heated source. This means it’s often hot and saturated, and can have a high molecular weight.
The gas supply is usually not constant, and the flow-rate fluctuates drastically.
The theoretical maximum flow condition is often a rare combination of multiple factors such as ambient temperature, tank volumes and volatility, facility capacity, etc. Through the operating life of a VRU, it is very uncommon to see the max flow condition for any extended period of time.
VRU Compressor Solutions
Rotary Vane Compressors are designed to operate in saturated, hot, and corrosive gas streams. They are simple and effective, but can become costly with options like seal support systems in a 2-stage orientation.
Rotary Screw Compressors provide unmatched operating flexibility to accomodate massive flow changes. When properly designed to prevent lube oil contamination, they are extremely effective in VRU service.
Reciprocating Compressors are a less common solution for VRU service, but are found when discharge pressures exceed traditional vane or screw parameters.
Indirect Cooling prevents condensed liquids from freezing in an external process cooler in sub-zero temperatures.