Thermodynamic investigation and hydrate inhibition of real gas flow through orifice during depressurization

A thermodynamic procedure has been proposed which can be used to predict the gas pressure, temperature and flow rate through orifice upon chock flow condition, using equation of state (EOS). The procedure applied for emergency depressurization operation incorporating the Peng-Robinson EOS and validated by comparing flow rates of a multi-component hydrocarbon gas mixture for thirteen experimental cases. The average absolute deviations of the predicted flow rates for orifice discharge coefficients of 0.85 and 0.9, are 7.36% and 2.03%, respectively. The corresponding error for API 520 (American Petroleum Institute Recommendation Practice 520) method is 6.91%. In this work, the hydrate formation temperature and hydrate inhibitor type and its required weight fraction for preventing the hydrate formation upon orifice and its upstream conditions are evaluated by the EZ-Thermo software using the Moshfeghian–Maddox method. The results qualitatively show that the hydrate prevention is essential for the safety of the operation due to low temperature condition.     

低浓度瓦斯安全输送新技术

阐述了瓦斯水合物合成的可行性,分析了水合物储存的稳定性,讨论了水合物固化储运的经济性.结果表明,应用固态水合物方式储运瓦斯具有安全、经济的特点.     

对天然气水合物预防管理保障安全生产的研究

为了保障陆上气田冬季天然气安全生产,防止因天然气水合物导致安全事故,采用鱼骨图法对陆上气田天然气水合物产生的原因进行系统分析。分析显示,导致天然气水合物产生的根本原因,出现在天然气产能建设和日常生产管理各环节,以及单井、输气管道和集气站各生产场所,为防止天然气水合物产生,针对原因采用5W1H法进行管理,从而达到对冬季天然气生产主要安全风险进行有效控制的目标。     

Research on flow assurance of deepwater submarine natural gas pipelines: Hydrate prediction and prevention

The formation of hydrate will lead to serious flow assurance problems in deepwater submarine natural gas transmission pipelines. However, the accurate evaluation model of the hydrate blocking risk for submarine natural gas transportation is still lacking. In this work, a novel model is established for evaluating the hydrate risk in deepwater submarine gas pipelines. Based on hydrate growth-deposition mechanism, the mathematical model mainly consists of mass, momentum and energy conservation equations. Meantime, the model results are obtained by finite difference method and iterative technique. Finally, the model has been applied in the production of deepwater gas field (L Gas Field) in China, and the sensitivity analysis of relevant parameters has been carried out. The results show that: (a). The mathematical model can well predict the hydrate blockage risk in deepwater natural gas pipelines after verification. (b). Hydrate is easily formed at the intersection of horizontal pipeline and vertical riser, and the maximum blocking position often occurs in middle of the riser. (c). The hydrate blockage degree and length of hydrate formation region (HFR) decrease with the increase of gas transport rate. (d). The hydrate blockage degree and length of HFR decrease with the increase of gas transport temperature. (e). The hydrate blockage degree and length of HFR increase with the extension of horizontal pipeline. (f). Injecting inhibitors can effectively inhibit hydrate formation and blockage, but the improvement of transmission measures can significantly reduce the dosage of inhibitor. It is concluded that measures such as increasing gas transportation rate and temperature, shortening horizontal pipeline length, optimizing inhibitor injection point and injection rate can play a safe, economic and efficient role in hydrate preventing and controlling.     

天然气水合物水力提升中继舱舱体沉积安全性分析

针对天然气水合物水力提升过程中中继舱部件的沉积安全性问题,为了避免中继舱因沉积过多而导致整个提升系统的瘫痪,利用流场模拟软件CFD,分析了不同结构对中继舱内部流场的影响,对比了正方体、球体和圆柱体3种不同中继舱结构下的颗粒沉积情况、内部流速分布、粗细颗粒以及海水体积分数分布情况,得出圆柱体结构的安全性要优于另外两种结构。研究了圆柱体结构在不同工况下的沉积情况与安全性。结果表明:增加粗颗粒浓度,粗颗粒直径以及粗颗粒的密度都会导致中继舱沉积厚度增加,安全性降低,而增加进口速度则会导致中继舱沉积厚度减小,安全性有所提高。     

湿天然气管道螺旋流水合物浆液安全输送研究

研究了天然气水合物浆液在气液两相螺旋管流中流动特性,分析了以气相为连续相、水合物颗粒为离散相的气固两相螺旋流的流动机理,通过对水合物颗粒受力分析和运动分析,结合螺旋流旋涡结构演化规律,推导出水合物颗粒平动、转动的判断条件,给出了颗粒各种受力的关联式,建立螺旋管流水合物颗粒运动模型,探讨了水合物颗粒的动力学行为。分析水合物浆液流动特性得到临界速度1即水合物浆液从固定床流动向悬浮流转化速度以及临界速度2即水合物浆液从移动床流动向固定床转化速度,为水合物浆液稳定流动提供了理论判据。     

Prediction of methanol loss in liquid hydrocarbon phase during natural gas hydrate inhibition using rigorous models

Methanol is the most widely used natural gas hydrate inhibitor and it is only effective as a hydrate inhibitor in the aqueous phase. Methanol is not regenerated in natural gas inhibition process due to its intermittent application in most cases. However, a significant cost is associated with the process because of methanol loss while utilizing this inhibitor. In this work, several intelligent models along with a new mathematical correlation are presented in terms of methanol concentration in aqueous phase and temperature to precisely forecast the methanol loss in the saturated hydrocarbons phase. An excellent match was noticed between the calculated results and literature data.     

深水测试地面流程节流油嘴段温压场研究

为对深水高压气井测试地面流程中的节流油嘴段的温压场及水合物生成情况进行研究,采用数值模拟的方式对整个节流管路进行气体流动特性分析.并利用P-T图回归公式法,得出不同温压场条件下的水合物生成情况,进行水合物生成范围对比.结果表明:针阀出口后端气体速度随着管路入口压力和针阀直径的增大而增大,随管路出口压力的增大而减小,而气...     

Prediction of methanol loss in vapor phase during gas hydrate inhibition using Arrhenius-type functions

Gas hydrate formation in natural gas and NGL systems can block pipelines, equipment, and instruments, restricting or interrupting flow leading to safety hazards to production/transportation systems and to substantial economic risks. The amount of hydrate inhibitor to be injected not only must be sufficient to prevent freezing of the inhibitor water phase, but also must be sufficient to provide for the equilibrium vapor phase content of the inhibitor. The vapor pressure of methanol must be high enough so that significant quantities will vaporize. Therefore to estimate methanol vaporization losses, it is necessary to develop a new predictive tool. In this work, a simple correlation, which is a mathematically compact and reasonably accurate equation containing few tuned coefficients, is presented here for the prediction of methanol vaporization loss and vapor pressures of aqueous methanol solutions as a function of temperature and methanol mass fraction in aqueous solutions using a novel and theoretically meaningful Arrhenius-type asymptotic exponential function and Vandermonde matrix. The proposed correlation predicts the vapor pressures of aqueous methanol solutions for temperatures up to 100 °C and methanol vaporization loss for temperature between ?16 and 16 °C. Estimations are found to be in excellent agreement with the reliable data in the literature where the average absolute deviation from data is less than 1.5%. The tool developed in this study can be of immense practical value for the engineers and scientists to have a quick check on the methanol vaporization loss and vapor pressures of aqueous methanol solutions at various conditions without opting for any experimental measurements. In particular, chemical and process engineers would find the approach to be user-friendly with transparent calculations involving no complex expressions.     

Influence of super-absorbent polymer on the growth rate of gas hydrate

The growth rate of hydrate and morphology of methane hydrate formation were studied in a visual pressure cell at 5.5 MPa. The gas hydrate formation was carried out (coal mine methane (CMM) + tetrahydrofuran (THF) + sodium dodecyl sulphate (SDS) + H₂O) with and without SAP. Experimental data on the hydrate growth rate and induction time were obtained for three different CMM samples. The influence of SAP on hydrate growth rate was determined. Results showed that after the addition of SAP, with the methane concentration increased in CMM, the induction time was reduced by 9 min, 10 min and 3 min, and the growth rate was shortened by 0.56 × 10⁻⁶/m³ min⁻¹, 0.53 × 10⁻⁶/m³ min⁻¹ and 1.42 × 10⁻⁶/m³ min⁻¹, respectively. This study could be useful for the recovery of methane from CMM by forming hydrate in the chemical and mining industry.     

盐穴地下储气库事故统计及风险分析

借鉴输气管道和二氧化碳地下封存设施的风险评价方法,结合盐穴地下储气库的事故统计分析,对储气库系统中的潜在风险因素进行12大类、35小类的初步分类,并归纳总结了盐穴地下储气库的3种主要事故类型。采用事故树分析的风险评价方法,对13种主要风险因素进行风险识别。在此基础上,提出定量风险评价的重要工程模型,其包括气体水合物模型、盐穴稳定性评价模型以及气体泄漏模型。该风险分析方法和工程模型有助于定量评价盐穴地下储气库的主要风险因素,为储库的安全稳定运行提供了科学依据。     

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。     

大气污染物质的干性沉着及其计测

在分析了大气污染物质干性沉着特点的基础上，重点讨论了干性沉着短期计测的扩散管法和4段滤纸法以及求算气体流束F的涡相关法，倾度法和热平衡法，这对我国进一步开展大气污染物质干性沉着机理的解明及其对环境影响的把握研究具有重要意义。     

Explosibility and thermal decomposition behavior of nitrile rubber dust in industrial processes

The formation of nitrile rubber (NBR) dust clouds during processing can lead to a potential dust explosion under certain conditions. However, the potential explosion hazard posed by NBR dust is usually overlooked by enterprises. In this paper, the explosive properties of NBR dust are investigated using a Hartmann tube, a G-G furnace, and a 20 L explosion chamber. The results showed that NBR dust could cause explosions severe enough to be classified as St-1. In addition, the thermal decomposition behavior of NBR dust under combustion conditions was investigated using a combination of thermogravimetric analysis coupled with Fourier transform infrared spectroscopy (TGA-FTIR). The results indicated that in the early stage, NBR dust mainly undergoes self-thermal decomposition to produce a large amount of combustible gas, which combines with oxygen to form a mixed gas and cause a gas-phase explosion. In addition, the participation of oxygen could lower the initial temperature of NBR dust thermal decomposition. As a result, decomposition occurred more quickly and a large amount of combustible gas was produced, thus expanding the range of dust explosions. Furthermore, these combustible gases exhibit varying degrees of toxicity, seriously affecting the life and health safety of relevant personnel. This work provides theoretical guidance for the development of safe procedures to prevent and address problems during NBR dust processing in enterprises.     

采用高压水射流技术清洗炼油催化装置油汽管线

炼油厂催化裂化装置沉降器至分馏塔之间的油气管线,在生产过程中容易结焦而影响装置的正常运转。通过几种方案的分析对比,选择并采用高压水射流技术进行清洗。结合多年的清洗实践,提出了该工况条件下,高压水射流清洗工装的设计设置、清洗装备器材的选配、清洗工艺参数的确定、清洗方案实施的业绩以及清洗作业的安全措施要点。指出了采用高压水射流技术清洗油气管线结焦是行之有效的方法。     

A CART technique to adjust production from longwall coal operations under ventilation constraints

Methane emissions in longwall coal mines can arise from a variety of geologic and production factors, where ventilation and degasification are primary control measures to prevent excessive methane levels. However, poor ventilation practices or inadequate ventilation may result in accumulation of dangerous methane-air mixtures. The need exists for a set of rules and a model to be used as guidelines to adjust coal production according to expected methane emissions and current ventilation conditions.In this paper, hierarchical classification and regression tree (CART) analyses are performed as nonparametric modeling efforts to predict methane emissions that can arise during extraction of a longwall panel. These emissions are predicted for a range of coal productivities while considering specific operational, panel design and geologic parameters such as gas content, proximate composition of coal, seam height, panel width, cut height, cut depth, and panel size. Analyses are conducted for longwall mines with and without degasification of the longwall panel. These models define a range of coal productivities that can be achieved without exceeding specified emissions rates under given operating and geological conditions.Finally, the technique was applied to longwall mines that operate with and without degasification system to demonstrate its use and predictive capability. The predicted results proved to be close to the actual measurements to estimate ventilation requirements. Thus, the CART-based model that is given in this paper can be used to predict methane emission rates and to adjust operation parameters under ventilation constrains in longwall mining.     

水平弯管内硫沉积数值模拟研究

元素硫在集输管道中沉积会引起堵塞和腐蚀问题,而弯管是集输管道中较易出现硫沉积的部位之一。为此,采用数值模拟的方法研究水平弯管内的硫沉积问题,首先利用雷诺应力模型对流场进行模拟,其次采用Lagrange颗粒轨道模型对硫颗粒进行模拟追踪,研究不同因素对硫颗粒在弯管中沉积率的影响。结果表明:弯管内壁会出现负压区和低速区,气流速度和弯曲比会对流场产生影响;硫颗粒在弯管中的沉积率随流速、粒径和弯曲比的增大而增大;硫颗粒沉积是重力和离心力共同作用的结果,其中离心力是导致弯管中沉积率增大的重要原因。     

A new approach for layout optimization in maintenance workshops with safety factors: The case of a gas transmission unit

In this study, an Integrated Simulation-Data Envelopment Analysis (DEA) approach is presented for optimum facility layout of maintenance workshop in a gas transmission unit. The process of repair of incoming parts includes various operations on different facilities. The layout problem in this system involves determining the optimum location of all maintenance shop facilities. Layout optimization plays a crucial role in this type of problems in terms of increasing the efficiency of main production line. Standard types of layouts including U, S, W, Z and straight lines are considered. First, the maintenance workshop is modeled with discrete-event-simulation. Time in system, average waiting time, average machine utilization, average availability of facilities, average queue length of facilities (AL) and average operator utilization are obtained from simulation as key performance indicators (KPIs) of DEA. Also, safety index and number of operators are considered as other KPIs. Finally, a unified non-radial Data Envelopment Analysis (DEA) is presented with respect to the stated KPIs to rank all layouts alternatives and to identify the best configuration. Principle Component Analysis (PCA) is used to validate and verify the results. Previous studies do not consider safety factor in layout design problems. This is the first study that presents an integrated approach for identification of optimum layout in a maintenance workshop of gas transmission unit by incorporating safety and conventional factors.     

球阀处硫颗粒运移沉降规律数值模拟研究

元素硫在集输管道中沉积会引起堵塞和腐蚀问题,球阀处是集输管道中较易出现大量硫沉积的部位之一。为此,采用数值模拟的方法研究高含硫天然气中析出的硫颗粒在球阀处的运移沉降规律,选用雷诺应力模型模拟球阀处的流场,选用Lagrange颗粒轨道模型追踪硫颗粒在球阀处的运动轨迹,探讨影响硫颗粒在球阀处沉积的因素。结果表明:气流进入球阀内将会出现压力损失和流动分离,气流进口速度和球阀开度会对流场产生影响;硫颗粒在球阀处的沉积率随气流流速和颗粒直径的增大而增大,随球阀开度的增大而减小;重力和离心力是造成硫颗粒在球阀处出现大量沉积的重要原因。     

提高转炉OG效率的对策

对武钢第一炼钢厂100t转炉OG系统设备存在的问题进行了分析、研究，结合生产实际进行了一系列的技术改进和工艺参数调整，提高了OG系统效率。