Vapor recovery systems are designed to recover vapors from gasoline or other fuels so that these gases do not escape into the atmosphere. They are used in the chemical process and petroleum industries to recover escaped vapors for either reuse or destruction (usually by combustion)
Types of Vapor Recovery Systems
Vapor recovery systems can capture target compounds in a gas stream through multiple processes. These include condensation, activated carbon, lean oil absorption, and jet ejector systems.
- Condensation systems chill a gas stream to a temperature where the target pollutants or compounds condense out of the stream. Since most streams contain water vapor which can plug the coils when it freezes, most systems implement a multi-stage cooling system. The cooling liquids used depend primarily on the compounds being targeted and the emission limits required.
- Activated carbon systems utilize activated carbon’s ability to adsorb certain molecules from gaseous mixtures. Adsorption of target molecules onto the carbon’s surface is encouraged by low temperatures, high pressures, and high concentrations of target gas. The process continues until the carbon is either fully saturated and removed, or regenerated in-situ for reuse.
- Lean oil absorption systems implement an absorbent oil or liquid which is forced to make close contact with the contaminated vapor stream, usually in a column. Trays, spray nozzles, or packing materials are used to enhance the contact. The liquid may be re-circulated until it is saturated with the target compound.
- Jet ejector systems are closed loop processes that use a venturi jet ejector to compress target gases. By utilizing a high-pressure motive gas, the system entrains target compounds out of low pressure streams. The combined discharge gas then exits at an intermediate pressure and can be injected into a compressor for further handling or reentered into the process stream.
Some modern vapor recovery systems implement multiple techniques in combination for complex or specialized gas streams.
Selecting a Vapor Recovery System
The type of vapor recovery system required depends largely on the type of compounds being captured. The most common vapor pollutants are hydrocarbons, which can be removed in most system types. The most important factor in selection is finding a system which meets the capture requirements to attain the desired emission limits.
Other critical factors in system selection include operating and maintenance costs, which tend to be higher when utilizing high pressure compressors, low temperature condensers, or when a system requires frequent or constant attention. Cyclical systems and those with no moving parts are generally preferred because they require little maintenance and are less inclined to fail.
At filling stations, vapor recovery systems are used as safety and anti-pollution devices to reduce noxious and potentially-explosive fumes. Vapor recovery systems are also used in the oil and gas industry to recover natural gas vapors that can then be made into a usable and profitable product.
In addition to their applications with gasoline fuel pumps and fuel storage tanks, mechanical and non-mechanical vapor recovery systems are used with industrial equipment, chemical storage tanks, chemical mixers, reactors, and automobiles (cars, trucks, and buses).