Amine filtration in oil refineries, hydrocarbon gas plants and ammonia plants.
Background:
Amine is a term referring to aliphatic ammonia derivatives that when mixed with water, form an aqueous solution. This solution is used to purify hydrocarbon gas streams by removing two acid gases, hydrogen sulfide (H2S) and carbon dioxide (CO2). Amines used could be any of the following:
MEA - Monoethanolamine MDEA - Methyldiethanolamine
DEA - Diethanolamine DGA - Diglycolamine
TEA - Triethanolamine DIPA - Diisopropanoloamine
Of the above MEA, DEA and MDEA are the most commonly used amines to remove acid gases by absorption and reaction. Amine selection is the end use of the gas and the economics of treatment in relation to the required purity. Natural gas for residential and commercial users must have CO2 (reduces heat value) and H2S (toxic in high concentrations) removed. Plant gas which is a byproduct in refineries, is used to fire heaters or boilers. Government regulations require that the H2S be removed form the gas for plant use. However, it is not economical to remove CO2 from the gas for plant use.
Since amines are corrosive, especially the reactive ones, the generated solids can cause a variety of problems in amine units. Solids entering the units can include:
- Pipe scale, rust, iron sulfide and down hole sand
- Mineral precipitates from makeup water
- Charcoal fines from carbon filters
Iron sulfide particles and other solids can contribute to foaming in towers which can be a major concern due to various side reactions in downstream processes.
Media:
Wound Cartridge (polypropylene) Bag Filter Media (polypropylene)
Melt Blown Cartridge XLH Bag Filter Media
Poly-Mate Cartridge
Recommendations:
Placement of a filter on the rich side protects fouling of the flash tank, lean/rich exchangers, stripper and re-boiler. However, the filter housings at this location should be flushed with water prior to filter media change out to drive out any hydrogen sulfide gas. This location is also on the cool side of the process and therefore better suited for polypropylene filter media.
Filters should also be placed ahead of the charcoal filters to prevent fouling of the bed and after the charcoal filter to trap on carbon fines that may migrate from the bed.
Two other areas in the process below may also benefit from filtration. First, after the gas leaves the primary amine unit, it enters a tail gas unit. These units also use amine solutions that may benefit from filtration. Secondly, make-up water for the amine unit may be a significant source of solids and therefore require filtration.
