Corrosion protection of equipment is the most important task of ensuring the smooth operation of oil refineries. Effective protection of technological installations can significantly reduce the cost of their repair, increase the duration of the overhaul run.
The main sources of corrosion are water, chloride salts and organochlorine compounds present in crude oil.
Crude oil supplied to refineries contains water up to 1% and chloride salts up to 500 mg/l. The high water content in the oil supplied to the atmospheric and vacuum distillation units leads to a violation of the technological operation mode, an increase of the pressure in the apparatus and a decrease in their productivity, as well as the consumption of additional heat for the oil heating. The chloride salts contained in oil have even more negative effect on the operation of the plants. Chlorides of alkaline-earth metals are hydrolyzed to form hydrochloric acid, that determines the potential corrosive effect of oil during its distillation. Chlorides are removed at the electrodesalting stage, where the crude oil is washed with fresh water. The resulting oil-water emulsions are destroyed by the combined action of temperature, an electric field in electric dehydrators and a demulsifier. The effectiveness of oil washing with water and the complete destruction of the resulting oil-water emulsions depends on a number of technological factors, and one of the main ones is the use of an effective demulsifier. The role of the demulsifier is to reduce the mechanical strength of the protective shells formed on the surface of water globules in an oil-water emulsion. However, even the most effective demulsifier is not able to completely remove water and salts from the refined oil. In addition, in the process of distillation, hydrolysis of organochlorine compounds presented in crude oil occurs, that increases the corrosiveness of the column top product. A complex of two reagents is used to prevent corrosion of the top of the columns as well as the condensation and refrigeration equipment of the atmospheric and vacuum distillation units: a film-forming corrosion inhibitor and a neutralizing amine.
As a film-forming corrosion inhibitor nitrogen-containing compounds with a long hydrocarbon chain capable of forming an adsorption protective film on a metal surface are used. To create optimal conditions for the formation of a protective film (pH = 5-6), neutralizers are used that interact with acidic components (naphthenic acid, HCl) of the top product of the column, thereby maintaining the neutrality of the medium.
Thus, the proper selection and complex use of all three reagents is one of the most important components of the corrosion protection of primary oil distillation plants.
