On Safe Operation Of Nanyang Mixed Oil Pipeline

It is a remarkable improvement of an oil pipe's transport efficiency to blend several types of crudes into a pipe,which is,however,also leads to a series of problems.For instance,if heavy or inferior oil is added into the original light crude,the fluidity will be worse than the original light crude,and also,the cloud point will become higher,which leads to more probability of solid precipitation.Thus,all these changes cause the increasing risk of blockage.There was the blockage of filter,tank and stuff like that caused by precipitate appeared in Nanyang pipeline after mixing with dewaxing oil.To solve this problem,the precipitation law of Nanyang mixed crude is studied in this paper by means of experimental test,theoretical analysis and numerical model,and several measures to prevent blockage and ensure the safety are put forward.The main research contents are shown as follows:(1)Several experiments were conducted.First,the viscosity of oil samples including dewaxing oil,SJ oil and mixed oil was tested and the viscosity-temperature curve of each oil sample was fitted.Second,the gas chromatography-mass spectrometry(GC-MS)and thin layer chromatograph evaluating the fraction of saturates,aromatics,resin and asphaltene were carried out;the fraction distribution of each oil was analyzed;and the Whitson method was used to characterize the plus fraction of the dewaxing oil as well as SJ oil based on the experimental results of GC-MS and thin layer chromatograph.Finally,the DSC(Differential Scanning Calorimeter)of dewaxing oil,SJ oil and oil samples under different mix proportion were measured,and the cloud point and the precipitates amounts of each sample were calculated based on the results obtained from DSC.(2)Based on the simplified perturbed chain statistical associating fluid theory equation of state(sPC-SAFT EOS),a thermodynamic model predicting wax as well as asphaltene precipitation including gas,liquid,wax-rich and asphaltene-rich phases is established,accounting for the liquid-solid phase equilibrium condition of mixed oil and the precipitation law of asphaltene as well as wax in crudes.In this model,a characterization method for oil mixture containing both asphaltenes and waxes is proposed,and a correlation is developed for prediction of binary interaction parameter based on experiment data of binary solid solubility.Besides,the universal quasi chemical activity coefficient(UNIQUAC)model is used to account for the non-ideality of wax-rich phase.In this thesis,the cloud points and the precipitate amounts of Nanyang mixed oils under different blending ratios are estimated,the absolute average relative error of cloud point is only 0.12%,and of precipitates amount is 15.04%.(3)With the consideration to the factors of molecular diffusion,shear stripping and aging in the process of oil flow,the kinetic model predicting the growth of gel deposit on pipe wall is established,and the numerical simulation of the model is carried out based on OLGA.According to the operating parameters of Nanyang pipeline,the process parameters in the heating,pumping station and soil physical property parameters along the pipe are tuned so that the hydraulic and thermodynamic results calculated by the model are corresponding to the actual operating parameters.According to the model,the gel deposition rate under different blending ratios in winter and summer is analyzed.The results show that the maximum deposition rate of mixed oil with dewaxing oil and SJ oil blending ratio of 1:1.5 is 0.15 mm/month in winter,0.09 mn/months in summer,and the maximum deposition rate of the mixed oil with blending ratio of 1:1.75 and of 1:2 is 19.64%and 29.98%less than that of 1:1.5 respectively.(4)To solve the problem of blockage in Nanyang pipeline,three measurements including adding naphtha,infusing asphaltene dispersant and modifying process are put forward.According to the results of DSC carried out on the mixed oils with naphtha and dispersant,the cloud point of oil adding 10%naphtha and 0.1%dispersant decrease from 58.82oC to 58.11?and 52.45? respectively.Besides,these methods are compared with each other and analysed synthetically with consideration to the investment cost,operating cost,anti-plugging effect,process complexity and environmental influence,and the results show that it is feasible to add dispersant and transform the process for Nanyang pipe.