张劲军，学者全讯担保网主页-全讯担保网

-statistics with the minimum of 29.568 are much higher than the corresponding t-quantiles with the maximum of 3.4995. the results also show that the larger value of the boundary box dimension represents the higher complexity and irregularity of the wax crystal morphology. the box dimension increases with decreasing oil temperature for each waxy crude oil. after the oil is beneficiated with a ppd, the box dimension increases at each given temperature. thus, it is feasible to use fractal dimensions to characterize the waxy crude oil microstructures. this helps to probe the theology–microstructure relation.

daqing oilfield is the largest oilfield in china. this crude oil is a typical waxy crude oil, with a wax content of 26% and a gel point of 32℃. flow behaviors of waxy crude oils at temperatures near the gel point/pour point are vital for both pipeline hydraulic calculation and evaluation on restartability of a shutdown pipeline. in this study, experimental simulation was conducted by using a stirred vessel with the energy dissipation of viscous flow as the shear simulation parameter. crude oil specimens were taken from the stirred vessel at different temperatures during flow simulation, and the dsc (differential scanning calorimetry) curves and rheological properties, such as viscosity, gel point, yield stress, and thixotropy, were measured. the viscosity under simulated pipelining conditions was found to be much less than that measured under quiescent cooling conditions, and the gel point decreased with decreasing temperature of sampling, i. e., the end temperature of the dynamic cooling process. the dsc curves of crude oil specimen captured at different sampling temperatures and from different positions such as the bulk of crude oil and the wall of the stirred vessel showed no difference, which indicated the depletion of wax due to wax deposition during the shear simulation was not responsible for viscosity and gel point reduction in the dynamic cooling measurement. therefore, this reduction is attributed to shear disturbance on the developing wax crystal structure, called the shear history effect. at sampling temperatures above 35℃, which is 3℃ above the gel point measured under quiescent cooling conditions, both the yield stresses and the thixotropic parameters showed little dependence on the shear history. however, at lower sampling temperatures, remarkable shear history dependence was found. empirical correlations were developed between the yield stress and the sampling temperature as well as the measurement temperature and between the thixotropic parameters and the sampling temperature. these correlations provide not only quantitative information on the shear history effect of waxy crude but also accurate rheological properties for assessment of the operation state and restartability of pipelines transporting this crude oil.

this paper deals with the separation and characterization of alkyl phenol formaldehyde resins demulsifier by infrared spectrometry and nuclear magnetic resonance spectroscopy after separation of the different surfactants and lowmolecular additives by adsorption chromatography. firstly, the types of surfactants are identified by methylene blue chloride–chloroform test method and the elemental analysis such as ca, k, mg, na, p, s and n. then, the different surfactants and low molecular components are separated by adsorption chromatography after parts of low molecular components are dried in an oven, and the molecular weight distribution is measured by gel permeation chromatography also. finally, the separated surfactants are determined by fourier transform infrared (ftir) spectrometry and nuclear magnetic resonance (nmr) spectroscopy. the distortion less enhancement by polarization transfer (dept), h, c correlated spectroscopy (h, c–cosy), h, h correlated spectroscopy (h, h–cosy) and heteronuclear multiple-bond correlation (hmbc) spectroscopy are applied to determine the molecular structures.

flow risk of a hot waxy crude pipeline mainly comes from restart failure, i. e. oil gelation resulted from prolonged pipeline shutdown, and unstable operation at low flow rate. once the unstable operation happens, the friction loss of the pipeline increases with decreasing flow rate and finally flow may cease if treated improperly. to avoid these flow risks, the pumping temperature of the crude is generally required to be kept above a minimum allowable temperature, and conventionally the pour point temperature is taken. this practice is effective but quite rough. obviously, to control the inlet temperature of a heating station at the pour point temperature implies different safety margin for winter and summer operation. for large throughput hot oil pipelines, reduction of the heating temperature even by a little bit may save a great amount of fuel. therefore, how to save fuel while ensuring safe operation has been a valuable topic for long time. on the other hand, many factors impacting the flow safety are stochastic and with uncertainty, so analysis without considering this feature can hardly yield convincible results, though this has been the common case for many years. in this paper, by taking the stochastic feature into account, a stable operation index (soi) and a pipeline restartability index (pri) were proposed to assess the flow safety of a pipeline concerning the low-flow rate stable operation and restartability after shutdown. combining these two indexes, a pipeline flow safety index (pfsi) was adopted to assess the flow risks of hot waxy crude pipelines. on this basis a new approach to quantitatively determining the safe pumping temperature was developed and illustrated by a case study. encouraging results show that this new approach has the potential to replace the simple rule of pour point as a guide to determining the safe pumping temperature of waxy crude pipelines.

the amount of precipitated wax is one of the key factors that governs the flow properties of waxy crudes. experimental results of 24 crudes have shown that approximately 2 wt% precipitated wax is sufficient to cause a virgin waxy crude gelling. accordingly, a correlation between the pour point and the temperature at which 2 wt% of wax has precipitated out from a crude oil; i.e., tc(2 wt%), and a correlation between the gel point and tc(2 wt%) have been developed. the proposed correlation of the pour point is in accordance with the correlation developed by letoffe et al. (1995) on the basis of 14 crudes from eight countries. the development of the gel point correlation and further verification of the pour point correlation indicate that there is a relationship between the gelling of virgin waxy crudes and the amount of precipitated wax. according to these correlations and the amount of precipitated wax, which can be determined only with a little sample by thermodynamic models or differential scanning calorimetry (dsc) experiment, the gel point and pour point of virgin waxy crude can be predicted even if the oil sample is very limited. heat treatment and chemical treatment can greatly improve flow behavior of waxy crudes, and more precipitated wax is present when the beneficiated (thermally beneficiated or ppd-beneficiated) crude oils gel. experimental results showed that approximately two or three times the amount of precipitated wax presents at the gelling temperature when the oils were in their beneficiated (thermally beneficiated or ppd-beneficiated) conditions.

onsuming for long-distance pipelines. a new method for predicting the viscosity variation during pipelining is presented in this article based on a mathematical model for predicting viscosity of ppd-beneficiated waxy crude oils at certain temperature after shear and a model for predicting non-newtonian viscosity of waxy crude oils as a function of temperature and precipitated wax. as verification, viscosity variations of five ppd beneficiated waxy crude oils during pipelining are predicted by using the presented method and compared with the measured data from experimental simulations. the predicted viscosities are in good agreement with the measured data, with an average absolute deviation of 14.1% for all 52 data points. comparisons between the measured or predicted viscosities during pipelining and viscosities obtained from the fast cooling experiment of ppd effectiveness evaluation demonstrate that the evaluation of ppd effectiveness for practical application should take the shear effect into consideration. the presented method provides a new way to evaluate the ppd’s effectiveness in pipelining application quickly and effectively.

waxy crude oil, theology, shear history effect, simulation, shear rate, energy dissipation, entropy generation abstract. flow properties such as viscosity and gel point of waxy crude oils, particularly the beneficiated waxy crude oils, are sensitive to shear history that the crude oil experienced, called the shear history effect. to understand quantitatively this shear history effect are necessary to oil pipeline design and operation. for experimental simulation of the shear process during pipelining, shear rates of turbulent pipe flow, and flow through centrifugal pumps and throttle valves are necessary. stirred vessels are usually used for shear simulation in laboratory, therefore shear rate in the stirred vessels has to be known before shear simulation. based on relationship between energy dissipation rate and the shear rate, approaches are developed and presented for calculation of shear rates in the above-mentioned specific flows. combined with the entropy generation due to viscous flow in the shear process, which has been proved to be a proper parameter for simulation of the shear history effect, the shear history effect on viscosity and gel point of the beneficiated waxy crude oils has been experimentally simulated accurately.

剪切作用是影响加剂原油流动性的主要因素之一。现场测试数据及实验室数据表明，剪切作用引起的加剂原油凝点上升幅度与剪切前加剂原油的降凝幅度 (加剂原油的凝点与空白原油凝点的差值) 之间有很好的相关性，基于对加剂原油剪切效应实验规律的分析，建立了对不同原油具有一定通用性并能较好地描述剪切后加剂原油凝点与剪切过程粘性流动熵产关系的数学模型。借助该模型，只须知道空白原油的凝点以及剪切前加剂原油的凝点，即可确定经过一定熵产的剪切后，加剂原油的疑点。对于加剂大庆原油，加剂新疆混合原油以及加剂中原原油的294组数据，模型计算结果与实验测结果偏差小于1℃的占50％，偏差小于2℃的占86.8％，平均偏差仅为1，12℃.该模型的建立为实现对管输过程中加剂原油流动性变化的数值模拟打下了基础。

flow properties such as viscosity and gel point of waxy crude oils, particularly the beneficiated waxy crude oils, strongly depends on shear history the oil experienced, called the shear history effect. to simulate this shear history effect accurately is vital to oil pipeline design and operation. shear rate is generally thought as a parameter for shear simulation. however, in many cases, shear rate is quite different from place to place in the flow field. based on experiments on over 10 waxy crude oils, it is demonstrated that entropy generation due to viscous flow in the shear process can be a proper parameter for shear simulation, and by using entropy generation as a parameter describing shear, the shear history effect on viscosity and gel point of the beneficiated waxy crude oils was successfully modeled.

the lu-ning pipeline in the eastern china, 655.37 km long and 720 mm o. d., transports viscous shengli waxy crude with a wax content of ca 15.24% (wt), a density of 922 kg/m3 at 20℃, a gel point of 24℃, and a viscosity of 3210 mpa·s at 25℃. it was designed as a hot oil pipeline. in the mid 1990’s, with decreasing of the crude throughput, the fuel consumption for pipelining per ton of crude increased dramatically. for reducing fuel consumption, the technology of pour-point-depressant (ppd) beneficiation was adopted. great success was achieved. with a ppd dosage of 50 ppm and a beneficiating temperature of 60℃ at the initial pumping station, the gel point of the crude was reduced by 16℃, and the viscosity at 25℃ was reduced by 87%. as a result, the crude temperature at the inlet of the intermediate heating stations was lowered from 34℃ to 27±1℃. this resulted in annual 17200 tons of fuel oil saving. thanks to improvement of the crude flow properties, running heating stations were reduced from twelve before using the ppd to only one (the initial station) in summer, seven in winter, and two to five in spring and autumn depending on ground temperature. this was the pipeline with the longest distance, the largest diameter, the largest throughput and the most running pumping stations in china that ever used the ppd beneficiation technology. we believe that experiences gained from this pipeline and other pipelines operated by the sinopec pipeline transport and storage company will be helpful to safe and economical operation of hot waxy crude pipelines.