高含硫天然气集输系统硫沉积熔解特性研究

发布时间：2018-09-05 08:13

【摘要】：高含硫气体从气藏进入集输系统时,气体温度和压力降低,溶解在天然气中的硫元素由于过饱和开始析出成为小颗粒,进而沉积在管道和设备的内部表面,造成硫堵,影响集输系统安全生产。本文采集了普光气田集输系统中的沉积物并开展了化验分析。对沉积物进行了元素分析,发现其含有的主要元素为S和C,分别占65%和20%左右。在扫描电镜下放大观察,沉积物内含有形状不规则的固体颗粒,固体颗粒外包裹着粘稠混合物;经分析,固体颗粒为地层和管道中的杂质,粘稠混合物是硫单质与管道缓蚀剂的混合物。将沉积物置于甲苯中充分溶解,对不溶物质进行X射线衍射分析,对可溶物进行PID色谱分析,发现不溶物为S8晶体,可溶物为现场缓蚀剂。沉积物是一种非牛顿流体,具有剪切触变性。其粘度随温度的升高而降低,在75℃后,升高温度对其粘度的降低效果开始减慢;粘度随转子转速增大而减小。进行了热重-差热分析,沉积物出现重力损失较大的位置在220℃至260℃,差热曲线存在两个吸热峰,一个是硫单质的熔点(113℃),另一个是现场缓蚀剂沸点(220℃)。测量了沉积物的熔化温度,在65℃时就表现出流动性,而其中的无机成分熔化温度为113℃。本文对水平管道中的硫颗粒进行了受力分析,得到了颗粒的运动方程。基于能量损失的原理,获得了气体携带硫颗粒的临界速度。运用FLUENT中的离散相模型模拟了硫颗粒在水平直管和弯管中的沉积行为,开展了沉积速率影响因素敏感性分析,其中硫颗粒粒径范围为0.003mm~0.03mm,质量流量范围为0.01kg/s~0.1kg/s,气体流速范围为0.5m/s~25m/s。模拟结果发现,在直管段中,气流速度越大或者颗粒直径越小,气流对颗粒携带作用越强,硫颗粒在管壁上的沉积通量越小;而颗粒流量的增加会使管内颗粒分布浓度增大,沉积通量增大。在弯管中,弯头后易产生漩涡,使弯头后部的管段比弯头前部管段更易发生沉积。受重力作用影响,管道下壁面沉积量大于上壁面,且粒径越大重力效应越明显。此外,沉积速率随湍动能和颗粒流量的增大而增大。应用FLUENT软件中的VOF多相流模型和凝固/熔化模型对沉积硫在外加热条件下的熔解过程进行了模拟。改变气体流速、输送温度以及外加热温度,模拟环状沉积硫在管道内的温度场、相场分布特征。模拟表明,沉积硫与气体发生对流换热,同时与管壁产生热传导换热;沉积硫受热后温度升高,粘度降低,流动性变好,达到一定粘度后,开始沿管壁向下流动,最终全部流至管道底部。本文自主研发了由玻璃油浴、加热系统、搅拌系统、测量控温系统组成的沉积硫外加热解堵模拟装置。实验研究了外加热条件下管道内沉积硫环的熔解行为,结果表明,因现场沉积硫组成复杂,使沉积硫样品产生流动性的温度不必达到单质硫的熔点。开展了引压管加热熔解特性实验,发现对于小直径引压管的沉积硫堵塞,因与环境之间单位热损失大,在相同加热条件下更难以脱除。开展了气流和加热协同作用下管道堵塞的解堵实验,研究表明达到临界压力时,沉积硫首先中心失稳,而不是沿管壁整体滑移。开展了有效降低解堵压力峰值的预测评价,可为集输系统沉积硫加热解堵提供科学依据。
[Abstract]:When high-sulfur gas enters the gathering and transportation system from the gas reservoir, the temperature and pressure of the gas decrease. The sulfur dissolved in the natural gas begins to precipitate into small particles due to supersaturation, and then deposits on the inner surface of the pipeline and equipment, causing sulfur blockage and affecting the safety of the gathering and transportation system. Chemical analysis was carried out on the sediments. Element analysis showed that the main elements contained in the sediments were S and C, accounting for 65% and 20% respectively. The mixture is a mixture of sulfur and pipeline inhibitor. The sediment is fully dissolved in toluene, the insoluble material is analyzed by X-ray diffraction, and the soluble material is analyzed by PID chromatography. It is found that the insoluble material is S8 crystal, and the soluble material is in-situ corrosion inhibitor. The sediment is a non-Newtonian fluid with shear thixotropy property. The results of thermogravimetric-differential thermal analysis show that there are two endothermic peaks in the differential thermal curve, one is the melting point of sulfur (113 C) and the other is the field slowing down. The melting temperature of the deposit is measured at 65 C, and the melting temperature of the inorganic component is 113 C. In this paper, the force acting on the sulfur particles in the horizontal pipeline is analyzed, and the motion equation of the particles is obtained. The discrete phase model of FLUENT was used to simulate the deposition behavior of sulfur particles in horizontal straight pipe and elbow pipe. Sensitivity analysis of the factors affecting the deposition rate was carried out. The particle size ranged from 0.003 mm to 0.03 mm, mass flow ranged from 0.01 kg/s to 0.1 kg/s, and gas velocity ranged from 0.5m/s to 25 m/s. The larger the velocity of flow or the smaller the diameter of particles, the stronger the effect of air flow on particles, the smaller the deposition flux of sulfur particles on the pipe wall; and the increase of particle flow will increase the concentration of particles in the pipe and the deposition flux. In addition, the deposition rate increases with the increase of turbulent kinetic energy and particle flow rate. The VOF multiphase flow model and solidification/melting model in FLUENT software are used to simulate the melting process of deposited sulfur under external heating. The simulation results show that the convective heat transfer occurs between the deposited sulfur and the gas, and the heat conduction heat transfer occurs with the pipe wall. After the deposited sulfur is heated, the temperature increases, the viscosity decreases, and the fluidity becomes better. After reaching a certain viscosity, the deposited sulfur begins to flow along the pipe wall. In this paper, a simulation device for plugging removal of deposited sulfur by external heating is developed, which consists of a glass oil bath, a heating system, a stirring system and a temperature control system. It is found that the plugging of small diameter suction pipe is more difficult to remove under the same heating condition because of the unit heat loss between the environment and the deposited sulphur. The plugging removal experiment under the synergistic action of air flow and heating is carried out. The results show that when the critical pressure is reached, the sulfur deposit will lose its center stability first, not slip along the pipe wall as a whole.
【学位授予单位】：中国石油大学(华东)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE863

【相似文献】