Gas and Vapor Recovery and Conveying

Vapor recovery can be achieved through many apparatus, such as pressure swing adsorption, absorption, temperature manipulation, and vacuum pressure. These methods allow for vapor to be recovered in an efficient manner, but vacuum is of the more efficient processes of the multitude.

Besides losses during manufacturing processes, storage of volatile material also builds up gasses that are eventually lost. This is especially true in the case of crude oil storage tanks, where flammable volatile substances build pressure within the tank, increasing risk of explosion and huge losses before fractionation. Vapor loss is also an issue when collecting, storing, and purifying methane for use as a fuel source. In the cases where gasses build up or create an opportunity for losses, vapor recovery units (VRU) are used.

Generally, a VRU consists of receiver tanks and a vacuum pump. The recovered vapors run through the piping, drawn through the negative pressure generated by the vacuum pump that creates a large pressure differential within the system. The vapor runs through tanks that hold the mechanism to separate the constituents of the gasses and extract the gas to be collected. The rest of the gas is drawn out of the tank towards the vacuum pump, where it is collected or discharged into the atmosphere.

Tail gas includes various greenhouse gasses such as hydrocarbons and carbon oxides, which contribute greatly to global warming and the general detriment of the global ecosystem. Nitride and sulfuric compounds that are harmful when inhaled or ingested are also included as tail gasses that factories produce as a byproduct of manufacturing processes. The obvious need for regulation and research on elimination of the production and disposal of these harmful byproducts has led to the development of tail gas conveying and treatment, which transports the tail gas to be decomposed or stored for use in another application.

One form of tail gas conveying and treatment, sulfur recovery via the Claus process, conveys the tail gas using a vacuum conveyor through a catalytic reactor. The sulfur compounds and carbon dioxide, the two most common and abundant kinds of tail gasses, are removed through the acid gas removal (AGR) process with carbon capture.

Through a series of thermal and catalytic stages, the hydrogen sulfide and carbon dioxide are isolated and removed from the solvent and water. The result is elemental sulfur and water. The tail gasses of this process are sent through the Shell Claus Off-Treatment (SCOT) unit, which applies further catalytic amines and solvents for even finer extraction of sulfur through its own thermal and catalytic stages.

Gas recovery can be seen in aerobic and anaerobic digestor systems as well. Aerobic digestor tanks primarily generate carbon dioxide, which can be captured, recycled, and used for anything from dry ice to polymerization. Anaerobic digestor tanks primarily generate methane, which is an invaluable ingredient for fuel, antifreeze, and fertilizer.