Study On Water Quality Characteristics Of Two Large-Quantity Crude Oil Electric Desalting Inlet And Outlet In A Refinery

In recent years,refineries often use a variety of crude oil blending processing methods to cope with the current phenomenon of more types of crude oil,which will lead to large fluctuations in the quality of electric desalting sewage and complex composition,while the impact of different crude oil blending on pollutant composition and load is not clear.This paper starts from the dissolving trend of the organic matter in the mixed crude oil of Napo and Sandy,and combines with the water quality characteristics of the mixed crude oil electric desalting influent and effluent to determine the source of the characteristic organic pollutants in the electric desalting effluent,and then explores the impact of the mixing of Napo and Sandy crude oil on the sewage quality of electric desalting by means of macro-analysis,organic pollution and inorganic pollution composition analysis.The main research contents and results include:（1）The characteristics of dissolved organic matter of mixed crude oil under the condition of adding/not adding demulsifier were compared and studied.When 20 mg/L demulsifier was added,COD,SCOD,total oil and UV₂₅₄ were reduced by 34.2%,41.0%,34.1%and 22.9%.With the addition of demulsifier,the solubility of non-aromatic organic compounds containing C=C and C=O double bonds in the mixed crude oil decreased significantly,and SUVA₂₅₄ increased by 63.3%.The dissolved organics in the mixed crude oil are mainly aromatic hydrocarbons,and the demulsifier reduces the organic acids and aldehydes and ketones dissolved organics in the mixed crude oil.（2）Take the steam stripping purified water as the injected water,and comprehensively analyze the water quality variation characteristics of the inlet and outlet water of the mixed crude oil electric desalting.The pollution load of the electric desalting effluent mainly comes from the stripping purified water.COD,total oil and NH₄⁺-N in the electric desalting effluent increased by 6.2 mg/L,8.7 mg/L and 5.6 mg/L,respectively,compared with the water injection.The relative content of phenolic compounds（such as phenol,p-cresol）in the electro-desalted effluent decreased significantly,while the content of nitrogen-containing compounds（such as 9-octadecenamide）increased.（3）The influence of the proportion of Napo and sand heavy mixed crude oil on the quality of electric desalting sewage was studied.The conductivity and pollution load of electric desalted sewage increase with the increase of the specific gravity of Napo crude oil.The increase of specific gravity of Napo crude oil increased the relative abundance of monoaromatic and polyphenolic compounds,fluorescent compounds and organic compounds with molecular weight of 100-200 Da.The relative content of alcohol non-polar/weakly polar organics in electric desalting wastewater was significantly negatively correlated with the blending ratio of Napo crude oil（p<0.001）.The main polar organics in the electric desalting wastewater of the mixed crude oil from Napo and Sandy are O_Xand O_XS₁,and the relative abundance of ester and aliphatic polar organics increases with the increase of the proportion of Napo.