alkanolamine, amine, carbonate, carbon dioxide, contamination, degradation, foam, gas treating, heat-stable salts, hydrogen sulfide, impurities, purification.
potassium carbonate solutions in gas treating units removing carbon dioxide, hydrogen sulf ?de, or both are contaminated by impurities in the feed gases and makeup water and by the products of the degradation and oxidation of amines occurring in the units themselves. Feed gas impurities include oxygen, carbonyl sulfide, carbon monoxide, hydrogen cyanide, ammonia, brine, solid particles, heavy hydrocarbons, sulfur dioxide, hydrochloric acid, organic acids, and pipeline corrosion inhibitors. Impure makeup water contains sulfate, chloride, alkali metal, and alkaline earth ions (hardness). Reactions causing contamination in the units include oxidation of hydrogen sulfide to sulfate and thiosulfate, oxidation of amines Lo formic acid and other products, and degradation of amines by carbon dioxide. The resulting heat-stable salts and polymers reduce the gas absorbing capacity- of a kanolamine solutions and increase their corrosiveness. Similar problems occur in potassium carbonate solutions, except that degradation products of amine activators are too dilute to be harmful. Contaminants art? removed by inlet gas separation, charcoal and mechanical filtration, neutralization of heat-stable salts, reclaiming at both atmospheric and reduced pressure, upstream washing of the feed gas, electro dialysis, use of antioxidants, ion exchange, and blowdown and dumping of the solution.
INTRODUCTTON: SYMPTOMS AND DIAGNOSIS
Potassium carbonate is indestructible in gas treating service except by heat-stable acids, while amines are vulnerable to many contaminants. Therefore, the emphasis of this article will be on alkanolamines used as solvents or as activators for potassium carbonate. Initially, a contaminated gas treating solution may exhibit few symptoms. One exception is foam, which usually requires little contamination. Ti may be caused by heavy hydrocarbons or pipeline corrosion inhibitors in the feed, suspended solids, or excess antifoam. Darkening of the amine solution may indicate chemical degradation of the solvent if the dark material is soluble. Insoluble dark material may be a corrosion product from within the unit or extraneous matter brought in with the feed gas, and may plug filters or equipment and foul heat transfer surfaces. If the dark solids are fine enough, they are difficult to distinguish from dark soluble contaminants, which are generally products of thermal degradation of amines. Heat-stable salts are generally invisible and detectable only by analysis, and they have myriad causes, including oxygen, carbon dioxide, and other contaminants discussed below. Contamination which causes degradation of alkanolamines may eventually reduce the treating capacity of the unit and cause corrosion of piping and equipment . Yost symptoms of solution contamination have multiple causes, an( their diagnosis may require a number of tests.
