The Effect Of Ppd Modification Methods On Flowability Of Mixed Oil

In the actual production and operation,it is common for crude oil pipelines to transport mixed crude oil,including the introduction of high-pour-point oil in branch line into low-pour-point oil in trunk line.When the low-pour-point oil is blended with the high-pour-point oil,its flowability deteriorates and it may be modified with the pour point depressant(PPD).Therefore,there are three possible blending modification methods:(1)high-pour-point oil and low-pour-point oil were mixed in advance and then PPD was added to modify;(2)PPD-benefited high-pour-point oil was blended with low-pour-point oil at the same/normal temperature;(3)PPD-benefited high-pour-point oil at a high temperature was blended with low-pour-point oil at normal temperature.According to the characteristic temperature of mixed oil,such as wax appearance temperature,apex temperature of wax precipitation,and combined with the evaluation results of the susceptibility of PPD,this paper studied the effect of PPD modification methods on flowability of mixed crude oil.Considering the relationship between the crude oil components and the PPD,the ideal method is “blending first and then adding PPD” method.If it is considered from the actual engineering,it is better to modify high-pour-point oil with PPD and then blending.This paper studied the flowability,high-speed shear stability and reheating stability of the mixed crude oil.The results show that,in terms of flowability of the mixed crude oils,for modification method(2),when the temperature after blending(the final temperature of dynamic cooling)is lower than the wax appearance temperature of high-pour-point oil,the flowability of mixed oil will deteriorate compared with modification method(1).The deterioration is the most serious as the temperature is near the apex temperature of wax precipitation.This is attributed to the adverse effect of shear effect during dynamic cooling on the PPD modification effect.For modification method(3),when the temperature after blending is lower than the wax appearance temperature of the high-pour-point oil,the flowability of mixed oil will deteriorate.This is attributed to the adverse effect of quenching on the PPD modification effect.In terms of modification effect stability,improper high-speed shear and reheating will deteriorate the modification effect,and the average size,coefficient of variation,and fractal dimension of wax crystals will become smaller.Once the oil temperature is lower than the wax precipitation point,the adverse effects of high-speed shear on modification effect will appear.When the temperature of reheating is near the apex temperature of wax precipitation,the PPD modification effect will even be completely lost.The bigger the proportion of high-pour-point oil occupies and the lower the initial temperature before reheating is,the more serious the deterioration will be.Finally,four kinds of pour point prediction models including Liu,Li,Chen and Qian model were used to predict the pour point of PPD-benefited mixed oil,and the predicted results were compared with the measured results.It is found that the pour point of PPD-benefited mixed oil is also consistent with predicted results from the existing pour point prediction models.The shearing,reheating and quenching during the blending process will cause changes in the pour point of the high-pour-point oil and the low-pour-point oil.Therefore,when using the mixed oil point prediction models to predict the pour point of mixed oil,the pour points under the mixed conditions were used.