超临界CO2埋地管道泄漏土壤形貌及温度研究

为探究CO2埋地管道泄漏对土壤区热力特性的影响,依托DN250、长260 m的工业级试验管道,搭建了 DN100规格埋地管道泄漏试验装置,通过设置4个不同孔径和开孔方向的泄漏孔,对超临界CO2埋地管道泄漏时的土壤形貌及土壤区温度变化情况进行了分析.结果表明:土壤区会形成冻土球,由外向内分为冻土层和干冰球两部分;干冰球内部存在冲击空腔,其外表面布满凹坑;3 mm孔径泄漏生成干冰球体积是1 mm孔径泄漏的5.5倍;水平和顶部泄漏试验生成干冰球体积接近,约为底部泄漏的1.9倍;总结了干冰球增长过程,干冰球高度与时间满足正弦函数和指数函数关系;3 mm泄漏土壤区温降起始时刻比1 mm泄漏早,前者温降速度是后者的50倍.     

卷烟膨胀烟丝生产线冷端CO_2泵装置的优化改进

为解决干冰膨胀烟丝生产线冷端液体工艺泵因机械密封长期超压和气缚现象造成损坏发生CO2泄漏而导致紧急停机抢修的问题,对干冰膨胀线冷端工艺罐系统进行了优化改进。在工艺泵吸口前管路引一根气相平衡管至工艺罐顶部,当泵吸口前管路有CO2液体时,输送管路内气化的CO2气体通过气相平衡管线释放回工艺罐内,不会进入工艺泵体内。应用结果表明,工艺泵内的憋压和气缚现象消失了,机械密封受到保护。改造前机械密封平均一个季度更换一次,改造后机械密封使用5年未损毁,达到保护干冰膨胀线冷端工艺泵机械密封的目的。     

基于流体动力学的放空管应力分析

根据放空管内流体流动特性,利用ANSYS流体-固体有限元分析软件,建立放空管流体动力学和结构应力学模型,利用多物理场耦合得到放空管在流体压力下的应力分析：同时探讨了蒸汽压力以及支撑架与固定管道的距离对放空管支反应力的影响。     

超临界二氧化碳泄漏减压模型构建及泄漏量分析

为了解决超临界二氧化碳管道泄漏风险评估问题,基于工业规模超临界二氧化碳小孔泄漏试验结果,提出分别构建超临界泄漏阶段、气液两相泄漏阶段、气相泄漏阶段的理论模型,并通过确定各阶段的传递参数,实现二氧化碳减压过程的理论建模。采用MATLAB软件编制了模型求解程序。通过试验数据验证了理论模型的可靠性。基于理论模型计算结果定量探讨了初始压力、初始温度和泄漏口径对泄漏减压过程压力及质量流量的影响。结果表明：初始压力在8～9.5 MPa变化时,对减压过程压力及泄漏质量流量影响较小;初始温度在33～39℃变化时,压力降至临界值的时间逐渐增加;泄漏口径减小,压降时间显著变长;在泄漏减压初期,泄漏质量流量均出现波动,随后随压力降低而逐渐降低。构建的理论模型能够实现超临界二氧化碳泄漏质量流量预测。     

三通管支管位置对爆炸火焰传播影响分析*

为研究分支管道位置对丙烷爆炸火焰传播的影响规律,通过多组数值模拟与已有实验数据对比,分析不同工况下三通管内火焰传播形态变化特征及温度变化。结果表明:向右传播的爆炸气流在支管左侧形成湍流旋涡,火焰受到拖拽及壁面制约,贴支管右侧壁面呈尖刀状传播;封闭管道中,火焰传播受主管道高速前驱压力波回波影响更显著,垂直支管中火焰与高温风险更大;实验支管位置距离点火源5.6 m时岔口处监测点温度高达2 214.08 K,支管位置增加至5.71 m时,支管处湍流旋涡拖拽火焰,使火焰出现中断,支管移至5.825 m后高温火焰无法传播至支管口,支管中的爆炸风险显著降低。研究结果为工业生产三通管支管位置的选择和支管内二次爆炸风险预测提供科学参考。     

200 MW燃气流风洞高压氧气系统安全操作分析

为保证200 MW燃气流风洞高压氧气系统安全运行,从初始能量出发,对高压氧气系统充气、供气、排气时管道内的激波管流动、绝热压缩等过程进行安全分析,并提出针对性安全措施。结果表明:对于充气管道内存在的激波管流动,当驱动气体压力为20 MPa、被驱动气体压力为0.1 MPa时,激波反射后末端气体温度远远高于200 ℃,通过减小阀门开启速度,对阀前管道进行充气以减小上下游压差,可避免因绝热压缩产生的高温;供气管道充填时,管道内最高温度为73 ℃,通过控制充填速度,可进一步降低管道内氧气温度;通过高压排气、低压排气2种模式,可满足国标中对氧气流速的要求。研究结果可为氧气管道远程安全操作提供参考。     

超临界CO2气爆致裂规律实验研究

针对我国低渗透性煤层增透困难的现状,研发了可控超临界二氧化碳气爆发生装 置,对不同强度的模拟煤体进行了不同温压条件下的超临界CO2气爆实验,结合孔内窥 镜观测和外观测量手段,对爆后宏观裂隙数目和长度等爆破响应信息进行统计分析。结 果表明:气爆裂纹起裂所需的最小爆破压力与介质的抗拉强度呈指数式增长的关系,主 要是固体材料在动力载荷作用下强度增大引起的;超临界二氧化碳气爆后产生宏观裂隙 的数目和累计长度与爆破压力满足Logistic函数关系,是裂隙面积超线性增加所消耗能 量也超线性增加的结果;超临界CO2对温压条件敏感,爆破有降温作用,是良好的物理 爆破原料,使用超临界二氧化碳作为爆破原料的爆破效果优于空气爆破效果。     

大规模埋地CO_2管道泄漏过程中的温度场变化

化石燃料燃烧产生温室效应明显,为解决这一问题,提出碳捕集利用(CCS)技术。CO_2管道运输在CCS技术链中占有重要地位,研究埋地管输安全是重中之重。基于大规模CO_2埋地泄漏试验装置开展了高压CO_2的泄漏试验。测量了CO_2在泄漏口径为1 mm、3 mm时,泄漏过程中的埋地管道壁面温度、土壤温度分布、干冰球和冻土球的大小。分析了干冰球和冻土球体积增大的过程。结果表明,泄漏过程中泄漏口附近有椭球形的冻土球生成,冻土球内包裹着干冰球。泄漏口径增大,干冰球和冻土球的体积增大,体积增大的速率加快。在泄漏过程中管壁温度先上升后下降最后稳定。泄漏口附近的土壤温度经历了恒定、缓慢下降、温度快速下降和稳定4个阶段。越靠近泄漏口温度越低,泄漏口径越大低温区域越大。     

贫氧环境对煤低温氧化特性影响研究

浅埋藏煤层开采过程中,由于地表裂隙导致的漏风,使其经常处于变化的氧浓度场中。针对这一实际情况,利用煤氧化动力学测定系统,对煤样在21%,18%,14%,10.5%,5%,3%氧浓度下,进行程序升温试验。测得了不同温度下指标气CO,C2H4,C2H6,C3H8浓度,并分析了其随温度变化规律,测量并计算了不同氧浓度下交叉点温度以及升温速率;对氧浓度大小影响指标气产量和其随温度变化幅度原因,以及温度特征影响效果进行必要的机理分析。结果表明:不同氧浓度下指标气CO,C2H4,C2H6在70 ℃左右有明显产量变化,分别在120 ℃,125 ℃,120 ℃处开始大量释放,C3H8则在温度达到125 ℃左右开始大量释放;120 ℃前,各氧浓度下煤样温度按相同规律变化,120 ℃后,氧浓度越大则对应的升温速率越大,温度也越高;氧浓度不同影响了煤中脂肪烃侧链氧化产生-OH的过程,继而造成指标气产量与温度变化差异。     

冲缝筛管结垢速率模拟研究*

为对防砂过程中因地层物性影响而导致冲缝筛管出现结垢问题进行准确的过程分析,基于FLUENT平台利用现场数据建立流道中的化学反应和沉积结垢的数值模型,评估管道缝宽、环境压力、温度、离子浓度与流速对冲缝筛管结垢速率的影响规律。结果表明:筛管结垢速率与管内温度和离子浓度成正相关,与管内流体流速成负相关,但环境压力影响不大,同时结垢主要产生在冲缝台阶以及冲缝套与打孔基管的接触面上,对产液的过流面积存在较大影响;结合正交分析得到4个敏感因素的主次顺序为:管内温度、管内流速、反应物浓度、环境压力,并确定最小结垢的组合方案;通过DPM模型探究CaCO3颗粒的沉积规律,得到管内的沉积情况,并建立多因素垢层厚度的计算模型。在实际生产中为降低筛管结垢对油井产能的影响,可以通过降低管内的温度、离子浓度及适当地增大流速来抑制结垢过程的发生。     

Fracture criterion and control plan on CO2 pipelines: Theory analysis and full-bore rupture (FBR) experimental study

Pressurized pipelines are the most reliable and cost-effective option for the long-distance transportation of CO₂ from an emitter to an onshore storage site. Propagating or unstable factures are considered catastrophic pipeline failures, resulting in a massive escape of inventory within a short period of time. The decompression curve for CO₂ exhibits a large drop in decompression wave speed at the phase transition pressure, leading to a higher driving force for crack propagation. The study of fracture control plans is very important for assessing the possibility of fracture propagation and preventing unstable fracturing along CO₂ pipelines. Three full-bore rupture (FBR) experiments were performed using an industrial-scale (258 m long, 233 mm inner diameter) CO2 pipeline with initial CO2 states of gaseous, dense and supercritical phases, respectively. The relation between the decompression velocity and the pipeline fracture propagation velocity was analyzed during the process of buried CO2 pipeline release. A fracture propagation criterion was established for the buried CO₂ pipeline. For the gaseous CO₂ leakage, the pressure plateau corresponding to the decompression wave velocity only appeared near the closed end of the pipeline. For the dense CO₂ leakage, the pressure plateau corresponding to the decompression wave velocity was observed near the saturation pressure after rapid decompression. For the supercritical CO₂ leakage, the pressure plateau corresponding to the decompression wave velocity was observed in the stage when the supercritical CO₂ transformed into the two phases of gas and liquid. Compared with the gaseous and dense CO₂, for the supercritical CO_2, the initial decompression wave velocity was the smallest, and the requirement of the pipeline safety factor was the highest.     

Study of dry ice formation during blowdown of CO₂-CH₄ from cryogenic distillation column

Cryogenic distillation columns are generally subjected to high-pressure loadings during the natural gas purification process. The high-pressure conditions inside the column cause safety risk e.g. rupture. When an emergency arises, blowdown is a typical way of minimizing the failure hazard. However, blowdown at the cryogenic conditions involves dry ice formation due to the rapid decrease in temperature driven by the Joule-Thomson effect. The dry ice formation intensifies the failure hazard due to the orifice blockage. Therefore, optimization of blowdown parameters is necessary to avoid the dry ice formation. So far, very limited studies are available in the literature for the blowdown of CO₂-CH₄ mixture, especially at the cryogenic conditions. In this study, a computational investigation followed by the experimental validation is accomplished to analyze the dry ice formation during blowdown of CO₂-CH₄ binary mixture from the cryogenic distillation column. The composition of mixture, orifice size, and initial conditions inside vessel have a high impact on blowdown path. A 3.00 mm orifice is the most suitable size for the blowdown at cryogenic conditions as it doesn't promote solidification and discharges the inventory quickly. Based on the experimental observation, an empirical correlation is also developed to instantly find out the optimum blowdown parameters.     

人工煤气管道萘颗粒沉积规律研究

针对萘在人工煤气管道中沉积会造成管道堵塞,影响管道的安全运行的这一问题,以昆明人工煤气管道为例,运用计算流体动力学软件Fluent,选用离散相模型和雷诺应力模型,对水平直管、水平弯管和三通管进行萘颗粒沉积的数值模拟,对于不同的管径、弯曲比、管径比,分别分析萘颗粒直径、入口速度、温度及压力对萘颗粒沉积的影响。研究结果表明:水平直管、水平弯管、三通管中的萘颗粒沉积率与颗粒粒径成正相关关系,而与气流入口速度、压力成负相关关系;萘颗粒在人工煤气管道中的沉积率主要受颗粒直径、气流入口速度的影响;萘颗粒的沉积率随着水平直管的管径增大而增大,随着水平弯管的弯曲比增大而增大,随着三通管的管径比增大而先增大后减小;可通过适当增大管内煤气输送速度、压力,降低温度来降低萘颗粒在人工煤气管道中的沉积速度,进而减少萘颗粒沉积的发生。     

无烟煤对超临界态CH4-CO2气体吸附特性研究*

为探究无烟煤对超临界态CH4-CO2混合气体的吸附特性,采用重量法开展无烟煤对纯CH4与纯CO2气体、3种体积浓度CH4-CO2混合气样的超临界等温吸附实验,应用过剩吸附理论和Langmuir单层吸附理论,通过校正绝对吸附量、计算吸附相密度、煤的比表面积以及测定吸附平衡后游离态气体组分,探究由亚临界状态到超临界状态下无烟煤吸附纯CH4、纯CO2以及混合气体的吸附相密度变化特征、混合气吸附特征以及吸附分子层数。研究结果表明:煤对纯CH4与纯CO2、混合气体过剩吸附量随着压力增大呈现出先增大后减小的峰值型曲线;CH4绝对吸附量随吸附压力增大不断增大,接近CH4临界压力时,绝对吸附量缓慢增加并趋于稳定。低压下CH4在煤颗粒中以单层吸附为主;超过临界压力后出现表面局部2层吸附的现象;1~3 MPa 时,CO2在煤颗粒中即表现出2层吸附为主的现象,随压力增大甚至出现局部4层吸附的现象,煤颗粒对CO2有更大的吸附能力。     

连续起伏管道投产过程中的气相运移研究*

为应对山区液体管道在投产过程中可能出现的气阻、超压问题,从气相运移角度出发,建立液顶气模型,研究在1个U型单元内积气形成、压缩和破碎的全过程,在此基础上,提出连接各个U型单元的气相的传递函数,探讨背压累积因素下,连续起伏管道投产过程中各个U型管段的积气情况和压力的变化,进行动态的建模和计算。以国内某原油管道的现场投产数据与模型结果进行比对。结果表明:可以更加准确地预测山区液体管道投产过程中的气相传递和压力变化过程,能为未来连续起伏大落差液体管道投产的安全稳定运行提供理论指导和技术支持。     

天然气管道直管段结垢速率数值模拟研究

为了探究天然气集输管道运行中结垢速率的影响因素,基于FLUENT软件建立了天然气集输管道结垢速率数值模拟模型。结合川西北天然气管网的实际运行参数,定量分析了管道压力、温度、垢粒子浓度和流速对结垢速率的影响。结果表明,管道压力、介质流速与结垢速率呈负相关关系,介质温度、粒子浓度与结垢速率呈正相关关系。在实际生产过程中,可以通过适当增大气田采出水的压力和流速,降低介质温度来达到抑制结垢发生的目的;并且还分析了CaCO3颗粒在直管段处的生成与沉积规律。     

水平管分层流下微孔泄漏特性数值模拟和实验分析

在油气田开发过程中,通常采用气液相混输模式,管道受腐蚀等因素影响容易出现穿孔而发生两相流泄漏。为分析两相流泄漏特性,对管内常见流型分层流下的微孔泄漏特性进行数值和实验分析;采用VOF耦合Level set算法分析了不同影响因素下的气液两相泄漏特性,设计了1种管道泄漏收集装置,进行室内两相流泄漏实验,并验证了数值预测模型的准确性。研究结果表明:气液两相流经过管壁泄漏口时会发生相分离,泄漏特性受小孔方位、管路内外压差、气液相流速影响较大;泄漏口位于管路侧壁时的泄漏特性与其他角度下的泄漏特性有所不同,可用泄漏影响区内的气液分布进行解释;当泄漏口位于管路底部时,存在临界液相分流系数,当液相分流比小于此临界值时,泄漏流体为单相液体。VOF耦合Level set算法的数值方法可为管路泄漏量预测和相分离特性分析提供参考。     

The influence of impurities on the transportation safety of an anthropogenic CO2 pipeline

Transportation safety is a key aspect of carbon capture and storage (CCS), which is a major technology used to reduce greenhouse gas emissions. Supercritical CO₂ pipelines have been certified as an optimised choice for CO₂ transportation. The results of this study show that the Peng–Robinson (PR) equation of state is recommended for analysis of the properties of supercritical CO₂. The influence of nonpolar and polar impurities on the two-phase region and the location of the sharp discontinuity in the density are found by analysing the ternary phase equilibrium and physical parameters using the PR equation of state. A transitional area between the supercritical phase and the dense phase, where the density changes abruptly, is defined as the quasi-critical region. This study describes the functional relation between the temperature and the pressure that defines the quasi-critical line by calculating the partial derivative equations and then determines the effect of impurities on the quasi-critical region of transported CO₂. Operational recommendations for pipeline transportation of flue CO₂ are developed using a pipeline operated by Sinopec as an example, demonstrating the influence of impurities in flue CO₂ on saturation pressure for control and prevention of fractures in CO₂ pipelines.     

基于元胞自动机数学模型的瓦斯抽采管道漏点定位研究

为了解决普通数学模型难以准确描述瓦斯抽采管道内流体的流动状态问题，提出了以元胞自动机模型为基础的瓦斯抽采管道漏点定位模型。根据元胞自动机在空间和时间上离散化的特性来演化管道流体在时空上的连续变化，将管径变化、管壁粗糙度、管构异件种类和数量以及温度等参数沿管道进行离散化，利用元胞自动机理论以及管道两端的信号对管道沿线压力和流量等参数变化进行预测，以判断泄漏的发生和漏点定位。通过实验验证，该方法能提高漏点定位精度。     

Release and dispersion behaviour of carbon dioxide released from a small-scale underground pipeline

The development of carbon capture and storage (CCS) brings challenges for safety issues regarding carbon dioxide (CO₂) transmission pipelines. Once a pipeline is punctured or full-bore ruptured, the leaked CO₂ is hazardous to personnel and the environment. Small-scale devices were established with the aim of studying the release and dispersion behaviour of gas and liquid CO₂ from a punctured underground pipeline. A sandbox was built to simulate the underground conditions. The parameters of the sand used in the experiments were tested. CO₂ concentrations on the ground and temperatures around the release orifice in the sand were analysed. The results indicate that in the CO₂ gas release experiments, the CO₂ concentration on the sand surface decreases with increasing horizontal distance in the form of a power function. CO₂ concentrations in upward release are slightly larger than those in horizontal release at the same location but are obviously bigger than values in downward release. The temperature-drop region is much smaller than that in air. A frozen ice ball can be generated near the release orifice during the gas phase of the CO₂-release process. In the liquid phase of CO₂-release experiments, a large amount of dry ice is generated near the release orifice. Dry ice can only be generated in the area close to the release orifice, especially in the near-field area.