低压煤气储气罐采用可变喉部截面引射器引射利用研究

为结合上海市重大工程项目建设,进一步改善天然气引射调峰装置性能,围绕低压煤气储气罐在天然气榆配调峰中的应用问题开展低压煤气储气罐配套可变喉部截面引射器系统用于天然气储气调峰的模拟研究,为低压煤气储气罐的改造利用提供技术支撑。     

Numerical modeling of two-phase supersonic ejectors for work-recovery applications

An ejector is a fluid pumping device that uses the energy of a high pressure motive fluid to raise the pressure of a secondary lower-pressure fluid. Motive pressure is converted into momentum through a choked nozzle creating a high velocity jet which entrains the surrounding low-momentum suction flow. The two streams mix and finally pressure is recovered through a diffuser. There has been little progress on high fidelity modeling of the expanding supersonic two-phase flow in refrigerant expansion work recovery ejectors due to rather complex physics involving nonequilibrium thermodynamics, shear mixing, and void fraction-dependent speed of sound. However, this technology can be applied to significantly increase the efficiency of space cooling and refrigeration devices. The approach developed in this study integrates models for real-fluid properties, local mass and energy transfer between the phases, and two-phase sonic velocity in the presence of phase change into a commercial CFD code. The intent is to create a practical design tool with better fidelity than HEM CFD models yet with tractability lacking in current boundary tracking phase change CFD models. The developed model has been validated through comparison of key performance metrics against test data under certain operating conditions.     

Modelling and optimization of two-phase ejectors for cooling systems

A one-dimensional compressible flow model, which is based on the control volume approach, has been formulated to model and optimize one and two-phase ejectors in steady-state operation with particular reference to their deployment in a jet cooling system. The working fluid can be both single-component (NH₃) and two-component (NH₃–H₂O). The developed model takes into account the duct effectiveness, wall friction, momentum loss, ejector geometry, shock waves as well as the acceleration of the induced flow in the conical part of the mixing section. Neither the usual assumption of mixing at constant pressure over the mixing chamber cross section nor that of a constant mixing chamber cross section were made. A comparison with other computation methods as well as with available experimental data from the literature is presented. The performance is significantly influenced by the ejector geometry.     

Numerical simulation of natural gas flows in diffusers for supersonic separators

Diffusers play a vital role in the supersonic separator to convert kinetic energy into pressure energy. The natural gas flows in diffusers were numerically calculated using the navier-stokes equations with the RSM (reynolds stress model). The behavior of gas dynamic parameters was analyzed under conditions of shock waves and boundary layers. The results show that the conical diffuser with high pressure recovery performance is a good choice for the supersonic separator. The shock waves appear as bifurcation structures as a result of the interaction between the shocks and the boundary layer in the conical diffuser. When the swirling flow goes into the diffuser, the strength of the swirl changes the shock positions and the static pressure. The strong swirl results in the shift forward of the shock and the non-uniform distributions of the static pressure.     

An experimental investigation of natural convection in mercury at low grashof numbers

This paper presents the results of an experimental investigation of natural convection from a uniformly heated, vertical flat plate immersed in mercury. Data were obtained at low Grashof numbers particularly.     

Design optimization of ejectors using ANN and GA

Ejectors are devices that are based on the principle of momentum transfer. A primary fluid passes through a nozzle that is usually of converging–diverging cross-section so that the flow reaches supersonic velocity at the exit. Consequently, a low-pressure region is created just outside the nozzle exit. This pressure gradient draws out the secondary fluid, into the ejector through the annular space—a phenomenon known as entrainment. This paper attempts to design and optimize an ejector with 1,1-dichloro-1-fluoroethane as the working fluid. The governing equations that accurately predict the behavior of the working fluid, are solved using the finite volume method after the discretization of the flow domain, using ANSYS Fluent. A database is created over 1008 similar computational fluid dynamics simulations by recording the input parameter values and the corresponding output parameter values. It is then used to define a function that can precisely predict the output for an unknown set of input parameters. This is achieved through the implementation of artificial neural networks—a surrogate modeling technique. The accuracy of the model is determined from the coefficient of correlation. The objective function thus obtained is optimized with the help of a genetic algorithm (GA)—a nature-inspired optimization technique. The optimal design of the ejector for a set of operating conditions is obtained as the output of the GA.     

Shock wave in supersonic moist air jet for a low pressure ratio

In the present study,a computational fluid dynamics work was performed to investigate the occurrence of the shock wave by condensation in supersonic moist air jet.The unsteady,compressible axisymmetric Navier-Stokes equation is solved by TVD(Total Variation Diminishing) scheme in this study.The numerical simulations have been performed for low pressure ratio and various humidities.The results show the occurrence of the shock wave in supersonic moist air jet for a low pressure ratio when Mach disk does not occur,depending on humidity of the air.     

Full-scale experimental investigation on the shock-wave characteristics of high-pressure natural gas pipeline physical explosions

In this study, a series of full-scale high-pressure natural gas pipeline physical explosion experiments were performed, in which the overpressure of the shock waves was measured and analyzed. The concept of “physical explosion linear energy (PEXLE)” was proposed and a “PEXLE model” was established to evaluate shock waves in a cylindrical pipeline with high length–diameter ratio. Equations were fitted to describe the characteristics of peak overpressure, positive pressure duration and specific impulse. Results showed that peak overpressure of shock waves is not influenced by the length of pipeline. With the increase of the propagation distance, specific impulse first increases and then decreases. This indicates that the position of the maximum value of overpressure does not correspond with that of the specific impulse.     

An experimental and numerical investigation of natural convection melting

The melting of a vertical ice cylinder in water is investigated in this paper. The experiments were carried out in a water-filled cylindrical Perspex barrel with adiabatic walls for Rayleigh numbers of 0.22x10⁸ and 0.475x10⁸. The ice crystal is suspended in the water and experimental images of the natural convection melting process were obtained using both shadowgraphy and particle image velocimetry (PIV) techniques. This data is compared with a numerical model which attempts to capture the melt-front on a fixed computational grid. The numerical model takes into account the density inversion effects in the water. The results show the applicability of PIV to this type of flow and demonstrate a simple numerical model to effectively resolve the melting phenomenon.     

9FA燃气轮机的供气降压运行技术

9FA燃气轮机正常的天然气供气压力在4.0MPa及以上,那么在供气压力为2.0MPa时机组能否实现降压运行呢?通过对某厂9FA燃气轮机的供气降压运行实践证明,这种技术是可行的。9FA燃机的供气降压运行技术,拓宽了机组运行的供气范围,对某些天然气压力不足的地区有着现实的意义。     

Energy optimization for liquefaction process of natural gas in peak shaving plant

One of the most important sections in the gas peak shaving plant regarding the energy consumption is the liquefaction process of natural gas (NG). Thus, selection and development of this process with the lowest energy consumption, offer huge potential energy and cost benefits. Here, a single-stage mixed refrigerant (SMR) cryogenic cycle with two compression stages has been selected for producing Liquefied Natural Gas (LNG). Energy consumption of the process as an objective function is optimized by describing key variables of the design. The proposed process’s calculations of thermodynamic concepts and properties are applied in MATLAB software to generate the objective function; furthermore Genetic Algorithm (GA) is used as an optimization method. Concerning works done in this area, more key parameters – related directly to the objective function – are introduced in this paper. A low irreversibility is due to enhanced values of key parameters in the LNG heat exchanger observed under a low temperature difference between hot and cold composite curves. Finally, the exergy lost of equipments in the proposed process are evaluated and analyzed in details.     

利用文丘里引射装置回收利用高压天然气压力能

介绍引射器的基本工作原理及其特性,并对该项技术中的关键设备超音速引射器进行设计研究。工程应用表明,采用文丘里引射装置是以高压天然气引射低压人工煤气,不仅拓宽了天然气的应用领域,而且通过回收天然气管网压力能,可大幅度节省电耗,降低生产运营成本,提高城市燃气管网运行的可靠性。     

Numerical and experimental investigation of melting of ice involving natural convection

Two‐dimensional transient melting of ice in a rectangular enclosure was numerically and experimentally investigated. Natural convection in the liquid phase due to the temperature dependency of water density was considered in the numerical model. The implicit finite difference method with fixed staggered grid approach was utilized. The SIMPLER algorithm was followed for the solution of pressure and velocity fields in the liquid phase. The prediction of the model was found to be satisfactory through preliminary experimentation. Copyright © 2002 John Wiley & Sons, Ltd.     

An experimental investigation of incomplete combustion of gaseous fuels of a heavy-duty diesel engine supplemented with hydrogen and natural gas

This paper investigates the emissions of the unburned gaseous fuels of a heavy-duty diesel engine converted to operate under natural gas (NG)-diesel and hydrogen (H₂)-diesel dual fuel combustion mode. The detailed effects of the addition of H₂, NG, engine load, and engine speed on the exhaust emissions of the unburned H₂, methane (CH₄), and carbon monoxide (CO) were experimentally investigated. The combustion efficiencies of CH₄ and H₂ supplemented were also examined and compared.     

Numerical analysis and experimental validation of high pressure gas quenching

Aided by the computational fluid dynamics package CFX-4 a transient flow model has been used to simulate the process of high pressure gas quenching of a large H13 die. The predicted temperature distributions, obtained under steady and transient flow conditions, together with experimental data have been compared, and a good agreement was obtained. This suggests that a steady state simulation can be effectively used in this type of study to achieve accurate simulated data with reduced computational time. This series of studies is seen as the precursor to the development of an overall simulation procedure for simultaneous distortion and heat transfer characterisation of the die leading to optimum heat treatment control.     

A multi-objective model for optimizing hydrogen injected-high pressure natural gas pipeline networks

The paper develops a statistical model for optimizing the Hydrogen-injected Natural gas (H-NG) high-pressure pipeline network. Gas hydrodynamic principles are utilized to construct the pipeline and compressor station model. The model developed is implemented on a pipeline grid that is supposed to carry Hydrogen as an energy carrier in a natural gas-carrying pipeline. The paper aims to optimize different objectives using ant colony optimization (ACO). The first objective includes a single objective optimization problem that evaluates the maximum permissible hydrogen amounts blended with natural gas (NG) for a set of pipeline constraints. We also evaluated the variations in operational variables on injecting Hydrogen into the natural gas pipeline networks at varying fractions. The study further develops a multi-objective optimization model that includes bi-objective and tri-objective problems and is optimized using ACO. Traditional studies have focused on single-objective optimization with minimal bi-objective issues. In addition, none of the earlier research has shown the effect of introducing Hydrogen to the NG network using tri-objective function evaluations. The bi-objective and tri-objective functions help evaluate the effect of injecting Hydrogen on different operational parameters. The study further attempts to fill the gap by detailing the modelling equations implemented through a bi-objective and tri-objective function for the H-NG pipeline network and optimized through ACO. Pareto fronts that show the tradeoff between the different objectives for the multi-objective problem have been generated. The primary objective of the bi-objective and tri-objective optimization problems is maximizing hydrogen mole percent in natural gas. The other objective chosen is minimizing compressor fuel consumption and maximizing delivery pressure, throughput, and power delivered at the delivery station. The findings will serve as a roadmap for pipeline operators interested in repurposing natural gas pipeline networks to transport hydrogen and natural gas blend (H-NG) and seeking to reduce carbon intensity per unit of energy-delivered fuel.     

燃机电厂天然气调压站配置探讨

天然气用于燃气轮机发电在我国越来越多,但燃气轮机对天然气的压力、温度等都有一定的要求。天然气调压站是天然气的主要处理系统,直接影响到燃气轮机的安全稳定运行。根据已投产燃气轮机的运行经验,对天然气调压站的系统设备配置作了分析探讨,对设备提出了经济合理地配置的建议。     

System optimization and cost analysis of plasma catalytic reforming of natural gas

Plasma reforming could provide advantages in hydrocarbon reforming especially in small-to-medium-scale plants and in plants with fast transients. The combination of a thermal plasma reformer operating in partial oxidation mode with a catalyst bed will be described. Reduced concentrations of CO (1–3% vol) can be achieved, with high hydrogen yields and minimal plasmatron electrical power requirements. A model for the cost of hydrogen production from natural gas has been developed. The model includes hydrogen cleanup utilizing a conventional pressure swing adsorption unit. The model uses experimentally determined conversion yields and operational parameters. The conditions that result in system optimization and cost minimization have been determined.     

Aerodynamic optimization for low pressure turbine exhaust hood using Kriging surrogate model

To further improve the pressure recovery capability of low pressure turbine exhaust hood, an aerodynamic optimization system has been developed on the Matlab platform. The shape optimization for a scale model of a low pressure exhaust hood is numerically performed to maximize the mass averaged pressure recovery coefficient while subjecting to geometric constraints. Two cubic Bezier curves are used to represent the flow guide and the bearing cone profiles, respectively. Evaluation of the aerodynamic performance of the model is carried out by the commercial CFD simulator CFX. The Kriging model is used as a surrogate, which establishes a global mapping between design variables and objective function. In order to seek a balance between local and global search, an adaptive sample criterion is employed. The optimal design exhibits a reasonable performance improvement compared with the original design.