Optimization Of Corrosion And Scale Inhibitor And Biocide-algaecide For Circulating Water Treatment In Dushanzi Refinery

Problems such as corrosion, scale, and microorganism growth in circulating water system of Dushanzi petrochemical company limit the effective use of water resources and economic benefits of enterprises. Thus, it is necessary to raise the repeating utilization factor for water and ensure the good operation of circulating water system. Water from circulating water system in Dushazi refinery was first analyzed. Moreover, corrosion inhibitor as well as scale inhibitor was selected for circulating water and interactions between them were evaluated systematically. Consequently, formulation of composite corrosion and scale inhibitor was optimized by orthogonal experiment and the performance of the inhibitor was evaluated. What’ more, biocide-algaecide was selected for circulating water system and optimized scheme of biocide-algaecide was proposed based on characters of water in Dushazi refinery.Water characterization indicated that the stability index is 6.86 when the concentration ratio is 1, which implies water is corrosive to metal. In other words, the addition of corrosion inhibitor to water is considered. On the other hand, the stability index decrease to 4.2 when the concentration ratio correspond to 4, which shows the great scale tendency for water.Therefore, the addition of corrosion inhibitor as well as scale inhibitor to water is considered.PBTCA shows greater inhibitory performance than HPAA and HEDP. Furthermore,compared for one inhibitor, greater inhibitory performance exhibits in PBTCA + zinc acetate inhibitors, HEDP + zinc acetate inhibitors, PBTCA + HEDP + zinc acetate inhibitors. There is a significant cooperative effect between PBTCA and HPMA, PBTCA and AMPS, while this effect don’ indicate between AMPS and HPMA.Optimized formulation of composite corrosion and scale inhibitor by orthogonal experiment are shown as follows: PBTCA 15 mg/L、HEDP 25 mg/L、zinc acetate 2 mg/L and AMPS 25 mg/L. The corrosion rate, inhibitive efficiency and scale inhibiting ratio of optimized formulation is 0.0126 mm/a, 98.65% and 93.52% respectively. The optimized formulation shows excellent inhibitory performance. More importantly, it is low phosphorus content, low zinc content and environmental formulation.For non-oxidized biocide-algaecide, isothiazolinone shows better performance than quaternary ammonium salt and for composite biocide-algaecide. There almost no difference between isothiazolinone and composite biocide-algaecide. Sodium hypochlorite indicates great performance in oxidized biocide-algaecide. The selected biocide-algaecide is compatible with corrosion and scale inhibitor, which has no influence on the corrosion and scale for inhibitor. The optimized scheme of biocide-algaecide is mainly based on sodium hypochlorite,which is continuous added to water. In addition, non-oxidized biocide-algaecide is also intermittent added to water and isothiazolinone and composite biocide-algaecide were used interchangeably.