Inhibiting Salt Formation and Corrosion Treatment

Although crude oils delivered from production fields are desalted, a small portion of water and salt always remains in the crudes.  Sodium, calcium, and magnesium chlorides and sulfates can have detrimental and costly effects on corrosion of oil processing equipment. Common problems are corrosion, erosion or sedimentation of salts in product lines, furnace tubes, pumps, valves and impaired heat transfer due to salt deposits in heat exchangers. Loss of heat-transfer by deposits of salts and corrosion products causes higher energy costs, which contribute negatively to higher CO2 emissions and increase in greenhouse gases.

To prevent salt formation, the operating temperature should be above the sublimation temperature. Unfortunately, this cannot always be achieved or controlled in practice. Ammonium salts are very corrosive to most metals if the salts themselves are wet. White, thick ammonium salt layers often indicate fouling and severe corrosion problems.

Ammonium salt fouling

Many refiners reduce the top temperature of the crude distillation column or FCC main fractionator column. Besides several benefits, reducing the top temperature also bears some risks. Depending on the concentration of certain components in the liquid going up to the top of the column, a lower temperature on the column top trays may lead to deposition of solids like ammonium salts or to development of free water. The formation of salts can cause severe fouling and plugging of valves, loss of separation efficiency, and problems with product quality, increased pressure drop, energy losses and ultimately an unreliable operation of the column. In most cases the only salt deposit mitigation strategy is to implement regular water wash of the column top section which will cause a reduction in unit throughput. Neutralising amines are used as corrosion inhibitors to prevent or at least slow down corrosion. However, the neutralising amine salts formed from the reaction with acidic components are usually also corrosive themselves and can cause damage if they are not removed.

Kurita`s ACF Technology is a very effective way to prevent such situations of corrosion or formation of ammonium salt deposits.  ACF products are formulations of a very strong organic base. The organic base ACF provides the full base strength of the hydroxide ion. They are about 10 - 100 times stronger than typical organic neutralising amines.  This opens up the possibility of both dissolving ammonium salt deposits and, at the same time, also dissolving and removing unwanted deposits of precipitated neutralising amine salts. 

ACF completely avoids the negative consequences of inorganic cations like sodium and potassium that would be introduced with caustic solutions. According to the chemical laws of nature, the strong base ACF displaces the weaker base ammonium (NH3) from its salts. ACF salts have a very low corrosion potential with a neutral pH of 7. The formed liquid salts absorb humidity and have a high tendency to stay in the water phase without precipitation. Although ammonium salts dissolve very well in water, a pure water wash does not always have the expected success in practice. The combination of ACF together with washing water often shows significantly better results that cannot be achieved with a pure water wash.