Oil produced in most of oil fields is accompanied by water and dissolved salts, mainly NaCl, which can cause considerable operational problem. Therefore, desalting and dehydration plants are often installed in crude oil production units to remove water soluble salts from an oil stream. This paper investigates experimentally the effect of five parameters (demulsifying agent concentration, temperature, wash water dilution ratio, settling time and mixing time with wash water) on performance of the desalting/dehydration process. The performance was evaluated by calculating the Salt Removal Efficiency (SRE) and the Water Removal Efficiency (WRE) based on the five process parameters. In order to investigate the effect of these parameters on desalting/dehydration efficiencies a 26-1 fractional factorial design with five other experiments at the center of the design for analysis of variance was applied. Based on the statistical analysis, SRE was expressed by a model for the whole range of variables while WRE was expressed with two models, each is valid in a part of variable domains. The models were satisfactorily evaluated with plant experimental data. For the SRE, the optimum values of demulsifying agent concentration, temperature, wash water dilution ratio, settling time and mixing time with wash water were found to be 15 ppm, 77 oC, 10%, 3 min and 9 min respectively. As a result, the optimum value of 93.28% salt removal efficiency was found. This value was 94.80% and 89.57% for water removal proposed models.

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