Vapor Recovery of Natural Gas Using Non-Mechanical Technology

Abstract

Abstract There are approximately 250,000 tank batteries in the United States1. These tanks store crude oil and condensate prior to transportation to sales via pipeline, barge or trucking. The sources of the vent gases from tanks are from flash, standing and working losses. There are approximately 8,000 to 10,000 mechanical vapor recovery units (VRUs) installed at oil production sites with four tanks typically connected to each VRU2. Most of these tanks are fixed-roof storage tanks. This project demonstrated the use of an alternative method for handling low-pressure natural gas that is typically vented to the atmosphere, flared or recovered with a mechanical compressor by oil and gas production facilities. This application used a venturi jet ejector as a device to compress natural gas from crude oil/water storage tanks to an intermediate pressure for use at the location or ultimate injection into the sales pipeline. Upon injection of the oil into the storage tanks, lower molecular weight hydrocarbons dissolved in the crude oil come out of solution or "flashes" when the pressure drops as the oil enters the tank. The storage tanks are typically downstream of a low-pressure vessel such as a two or three phase separator or heater treater. The hydrocarbons that flash include methane, ethane, volatile organic compounds and hazardous air pollutants. These gases collect in the plenum of the fixed roof storage tanks that are typically used in oil and gas production operations.