The Experimental Study On The Cleaning And Prevening Of Sulfate Crystal In Bittern Transportation Pipeline Endophragm

In this paper, studies were carried out on the problem of CaSO4 crystal in pipeline endophragm and impeller of bittern transfer pump which was difficultly to be removed with conventional chemical and physical methods in the bittern transportation process of the Jiangsu Oilfield Bittern Extraction and Transportation Management Department. According to the characters of bittern extraction, transportation, and follow-up Ammonia-soda industry of Jiangsu Oilfield, we studied the Synthetic methods and conditions of scale inhibitors PASP and LZ-06. In this study, two methods were adopted to synthesize polyaspartic acid, i.e. the aqua ammonia-maleic anhydride thermal polymerization–hydrolysis and ammonium salt-maleic anhydride thermal polymerization-hydrolysis. The optimal conditions for the former were as follows: 1.2～1.3 of the molar ratio of aqua ammonia and maleic anhydride, and 2 hours at 200℃of the polymerization reaction time. On these conditions, the output rate of PASP was 90.3 % and its viscosity average molecular weight was about 6000. The optimal conditions for the latter were the molar ratio of ammonium ion and maleic anhydride is 1.2～1.3, and the time for polymerization reaction was 80 minutes at 180～200℃. On these conditions, the output rate of PASP was 92.3 % and the viscosity average molecular weight of PASP was in the range of 3000～4000. LZ-06 was synthesized with poly-amino compounds AE, phosphorous acid and formaldehyde as raw materials. The optimal conditions for LZ-06 synthesis were feeding the raw materials with the molar ratio of AE:phosphorous acid:formaldehyde = 1:6:6.5 in the order of H2O+AE→H3PO3→CH2O, and keeping the reaction last two hours at 100～105℃. The conversion rate of phosphorous acid was 96.9 %. The structure of products was identified by infrared spectrum. Thorough researches had been done on the scale-inhibition of PASP, LZ-06 and PASP/LZ-06 to CaSO4, the corrosion-inhibition of PASP/LZ-06 and the compatibility between PASP/LZ-06 and PAC. The experimental results indicated that: The scale-inhibition effect of the combination of PASP and LZ-06 at the mass ratio of 1:2 was better than that of either PASP or LZ-06 alone; PASP/LZ-06 had good corrosion-inhibition to A3 steel and favorable compatibility with PAC. The research were done by Digital-Photo, SEM and XRD on CaSO4 crystal cell dimension before and after the addition of PASP/LZ-06 and the discussion about scale inhibition mechanism indicated that the scale inhibition effect of PASP/LZ-06 to CaSO4 could be achieved through complexing increased solubility, electrostatic repulsion, crystal lattice aberration and threshold effect.