液化气体的热分层及爆沸机理研究

发布时间：2018-02-07 10:19

本文关键词： 液化气体储罐热响应热分层爆沸　出处：《大连理工大学》2015年博士论文　论文类型：学位论文

【摘要】：液化气体储罐是液化气体储运过程中的核心设备和主要危险源。火灾热侵袭会引起储罐内部介质的温度与压力升高,罐体强度下降。一旦储罐破裂,可能引发危害性极大的沸腾液体膨胀蒸气爆炸(简称BLEVE)。对液化气体储罐的热响应及BLEVE的研究,可为液化气体储罐的事故预防及控制提供理论依据。国内外学者在这方面进行了大量研究工作,探讨了液化气体储罐的热响应过程,获得了一些很有价值的结论。然而,由于此过程涉及储罐与其内部介质的耦合传热及气液两相非平衡热力学传质问题,至今热分层及其消除机理以及BLEVE过程机理尚未形成一致结论,有待进一步研究。鉴于此,本文主要开展了以下几方面的研究工作： (1)建立了用于模拟液化气体热响应及BLEVE过程的实验系统。该系统可对加热区域、热流密度、充装率、初始温度等参数进行控制,可监测热响应过程中的温度分布和介质的对流及沸腾现象,并可记录快速泄压过程中的瞬态压力变化。 (2)进行了液化气体热分层实验,通过分析介质在受热条件下的温度响应和近壁面的两相流动,揭示了热分层的形成和发展机理。结果表明,单相浮升力驱动下的自然对流使热分层形成,壁面上出现的核态沸腾通过对液相区的扰动促使热分层消除。基于以上机理,重点研究了受热条件和介质条件对热分层发展过程的影响规律。在气、液相壁同时受热时,气相区向液相区传热,气相加热区域的增大会加大液相的热分层度及热分层的维持时间。介质的物性影响其对流传热及相变速率,从而影响输入热流的空间分布、分层区的扩展速度、气相升温速率、液相的沸腾强度与核化点分布,进而影响热分层度。 (3)通过介质的快速泄放实验模拟液化气体的BLEVE过程,并结合数值模拟方法研究了爆沸过程的机理。结果表明,快速泄压导致液体过热及爆沸,在储罐泄压和介质过热沸腾两种机制的耦合作用下,储罐内部压力呈现“降压—升压—降压”的响应过程。介质充装率为60%时产生最大的压力反弹幅度；泄放口径的增大会使得压力突降幅度、压力反弹幅度、压力突降速率、压力反弹速率均增大；液相的热分层影响液体的总能量与泄压后的能量释放速率,液体在热分层条件下的总能量较低,能量的释放速率较慢,导致压力反弹值降低。 (4)基于液化气体储罐的热响应规律及热分层对爆沸过程的影响机理,提出了一种液化气体储罐的安全装置,获取了国家发明专利。该装置通过维持热分层和冷却气相壁,降低介质的总能量和储罐破裂失效的概率,从而实现预防BLEVE事故的目的。
[Abstract]:Liquefied gas storage tank is the core equipment and main dangerous source in the process of liquefied gas storage and transportation. The thermal invasion of fire will cause the temperature and pressure of the internal medium of the tank to rise and the strength of the tank to decrease. The thermal response of liquefied gas storage tanks and the study of BLEVE, It can provide theoretical basis for accident prevention and control of liquefied gas tank. Scholars at home and abroad have done a lot of research in this field, discussed the thermal response process of liquefied gas tank, and obtained some valuable conclusions. Since this process involves the coupled heat transfer between the tank and its internal medium and the gas-liquid two-phase non-equilibrium thermodynamic mass transfer, the thermal stratification and its elimination mechanism and the mechanism of the BLEVE process have not reached a consistent conclusion, which needs further study. This paper mainly carried out the following research work:. An experimental system for simulating the thermal response of liquefied gases and the BLEVE process is established. The system can control the heating region, heat flux, filling rate, initial temperature and so on. The temperature distribution and the convection and boiling phenomena in the medium can be monitored during the thermal response, and the transient pressure changes during the rapid pressure relief can be recorded. (2) the thermal stratification experiment of liquefied gas was carried out. The formation and development mechanism of thermal stratification was revealed by analyzing the temperature response of the medium under heated conditions and the two-phase flow near the wall. Natural convection driven by single phase buoyancy causes thermal stratification, and nucleate boiling on the wall causes thermal delamination to be eliminated by disturbance in the liquid region. The influence of heating conditions and medium conditions on the development of thermal stratification is studied. When the wall of gas and liquid phase is heated simultaneously, the heat transfer from the gas phase region to the liquid phase region is obtained. The increase of gas heating region will increase the thermal delamination degree of the liquid phase and the maintenance time of the thermal stratification. The physical properties of the medium affect its convection heat transfer and phase transition rate, thus affecting the spatial distribution of the input heat flux, the spreading velocity of the stratified zone, and the gas phase heating rate. The boiling strength and nucleation point distribution of the liquid phase affect the thermal stratification. (3) the BLEVE process of liquefied gas was simulated by the rapid release experiment of medium, and the mechanism of explosion boiling process was studied with numerical simulation method. The results show that the rapid pressure relief leads to the overheating and explosion boiling of liquid. Under the coupling of the two mechanisms of tank pressure relief and medium overheating boiling, the internal pressure of the storage tank presents a response process of "depressurization-boost-pressure depressurization". The maximum pressure rebound is produced when the medium filling rate is 60. The increase of release caliber will increase the amplitude of pressure sudden drop, the range of pressure rebound, the rate of pressure sudden drop, the rate of pressure rebound, the thermal stratification of liquid phase affects the total energy of liquid and the rate of energy release after releasing pressure. Under the condition of thermal stratification, the total energy of the liquid is lower and the energy release rate is slower, which leads to the decrease of the pressure rebound value. 4) based on the thermal response of liquefied gas storage tank and the influence mechanism of thermal stratification on the explosion boiling process, a safety device for liquefied gas storage tank is proposed, and the national invention patent is obtained. The total energy of medium and the probability of tank failure are reduced to prevent BLEVE accident.
【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TE972;TQ086

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