Wenlong Jia

Application of Multi-hierarchy Grey Relational Analysis to Evaluating Natural Gas Pipeline Operation Schemes

In the condition of satisfying process requirement, determining the optimum operation schemes of natural gas pipeline network is essential to improve the overall efficiency of network operation. According to the operation parameters of natural gas network, the multi-hierarchy comprehensive evaluation index system is illustrated. This paper presents a multi-hierarchy grey relational analysis method which is suitable for evaluating the multi-hierarchy index system with combining the AHP and grey relational analysis. The comprehensive evaluating mathematic model for natural gas network operation schemes is built based on the method. Ultimately, the practical application shows that multi hierarchy grey relational analysis is effective to evaluate the nature gas pipeline network operation schemes.

Simulation of Shutdown and Restarting Process of Heated Oil Pipelines

During the operation process of heated oil transportation pipelines, shutdown accidents may be caused by some faults. In view of hydraulic and thermodynamic characteristics, the transient simulation model of heated oil pipelines is established based on hydrodynamic theories. The model is composed of quasilinear hyperbolic partial differential equations. Integration with the boundary conditions that are pressures, temperatures, flow rates and other factors which are obtained while shutdown and restart process, method of characteristic and finite difference method are applied to solve this model. The VB and Matlab hybrid programming technology which is based on COM technical is utilized to develop simulation software which is used to simulate the restarting process after shutdown. Then the safety time of shutdown and maximum transient pressure are determined. The results show the integration of mathematic model and computer simulation can simulate the restarting process successfully.

Transient Modeling and Simulation of Coal Bed Methane Transmission Pipeline

The coal bed methane is methane mainly and it has less heavier than conventional natural gas, thus coal bed methane has a slightly higher value than natural gas. Developing and utilization of coal bed methane is an important way to release contraction between supply and demand of natural gas in China. The pipeline is principle way of transporting the coal bed methane from sources to end-users. In view of the characteristics of coal bed methane, equation of state BW RS is used to calculate the thermodynamic parameters. Then based on continuity equation, momentum equation, characteristic equations of non-pipe elements and flow quantity balance equation, the transient simulation mathematic model of coal bed methane transmission pipeline is built. Considering the slow transient characteristic of gas flowing, the implicit central difference method is used to transform partial differential equations of the model into finite difference equations. Aiming at non- linear characteristics of differential equations, Newton iteration format is constructed and the models solution method is discussed. Finally, MS Visual C++ is utilized to develop a simulation software name coal bed methane pipeline emulation system, and the practical applications are carried out. The results show the mathematic model built in the paper and its solving method are both feasible. They provide technical supports for reasonable design and operation of the coal bed methane pipelines.

Water Hammer Analysis for Heated Liquid Transmission Pipeline with Entrapped Gas Based on Homogeneous Flow Model and Fractional Flow Model

Abstract —In view of the hydraulic transient problem in heated liquid pipeline with entrapped gas, water hammer analysis equations are built. The solve methods are discussed based on homogeneous flow model and fractional flow model. Then VC++ is utilized to develop a computer program to simulate the hydraulic transient behavior. Ultimately, this paper simulates the hydraulic transient behavior on the conditions which include different initial void fraction in liquid, a constant liquid level at upstream end and sudden closure of valve at downstream end of pipeline. The simulation results not only suggest higher void fraction in liquid lead to lager of water hammer wave response, lower of fluctuation frequency and quicker of pressure wave damping but also indicate small amount of gas in liquid can weaken pressure increasing caused by water hammer. At the same time, the differences between the two models’ simulation results are analyzed, the analysis shows that fractional flow model is better than homogeneous flow model if liquid column separation phenomenon occurs. The study results are benefit to guide the hydraulic transient problem in practical.

Analysis of Operation Optimization of Gas Pipelines Based on Adaptive Genetic Algorithm

A variety of processes are utilized for gas transmission. It is important to optimize the operation conditions of these processes to promote efficiency. The operation efficiency of pipeline systems is combined with the purchase and sale prices of gas, the quantity bought and sold of gas and the management costs. Aimed at the maximum operation efficiency, an operation optimization model of gas pipelines is established with consideration of quantity input (output) constraints of each node, operation pressure constraints of pipelines, compressor constraints, valve constraints and hydraulic constraints of the pipeline system. The model adapts to all kinds of pipeline structures and it is solved by the method of adaptive genetic algorithm because of its non-linear form. Based on this, a computer program is developed to optimize the operation conditions of gas trunk lines, gas gathering and distribution network. Finally, an application example is given.

Operation Optimization of Natural Gas Transmission Pipelines Based on Stochastic Optimization Algorithms: A Review

Operation optimization of natural gas pipelines has received increasing attentions, due to such advantages as maximizing the operating economic benefit and the gas delivery amount. This paper provides a review on the most relevant research progress related to the steady-state operation optimization models of natural gas pipelines as well as corresponding solution methods based on stochastic optimization algorithms. The existing operation optimization model of the natural gas pipeline is a mixed-integer nonlinear programming (MINLP) model involving a nonconvex feasible region and mixing of continuous, discrete, and integer optimization variables, which represents an extremely difficult problem to be solved by use of optimization algorithms. A survey on the state of the art demonstrates that many stochastic algorithms show better performance of solving such optimization models due to their advantages of handling discrete variables and of high computation efficiency over classical deterministic optimization algorithms. The essential progress mainly with regard to the applications of the Genetic Algorithm (GA), Particle Swarm Optimization (PSO), Ant Colony Optimization (ACO), Simulated Annealing (SA) algorithms, and their extensions is summarized. The performances of these algorithms are compared in terms of the quality of optimization results and the computation efficiency. Furthermore, the research challenges of improving the optimization model, enhancing the stochastic algorithms, developing an online optimization technology, researching the transient optimization, and studying operation optimization of the integrated energy network are discussed.

Experimental Study and Method for Predicting the Viscosity of Water-In-Super Heavy Oil Emulsions

We used five samples of super heavy oils collected in China to prepare 15 water-in-oil emulsions, with water cuts 10%, 20%, and 30%. We determined the viscosity of the emulsions at 30°C-75°C. Generally the viscosity of the studied emulsions is in the range 401-75200 mPa·s. Based on the experimental data, we propose a new rheological model for water-in-super heavy oil emulsions based on the Kalra model, introducing a term characterizing the dependence of the relative error on the water cut in the emulsion. The absolute average error in predictions according to the proposed model was 17.36%, which is 6.37% lower than in the original Kalra model.

Operation Optimization of Heated Oil Transportation Pipeline

Waxy, high pour point and high viscosity oil is transported by the heated oil pipeline. The power and fuel cost account for large proportion in total cost. Long distance heated oil transportation pipeline contains many pump stations and heating stations. In the condition of satisfying transportation amount required, the operators can formulate many operation schemes which are composed of different hydraulic and thermodynamic parameters. Determine optimal scheme is important to improve the economic returns and social benefits. Aimed at minimum power and heating cost, this paper proposes a heated oil pipeline operation optimization model with consideration of thermodynamic constraints, hydraulic constraints, pipeline strength constraints, pump characteristic constraints, temperature and pressure constraints at outlet and inlet of pump stations and heating stations along the pipeline. The model is solved by the combination of linear approximation method and simplex method. Based on theory research, computer program is developed. Finally, the practical application shows energy saving of the optimal operation scheme obtained is significant. The method and program are of widespread usage.

Water Hammer Characteristics of Glass Reinforced Plastic Oil Transportation Pipeline

Glass reinforced plastic (GRP) pipeline has good characteristics of anti-corrosion, anti-scaling and it is widely used in the oil transportation pipeline. Analyze the water hammer characteristics of GRP pipeline is essential to ensure the safety operation of the pipeline. The water hammer mathematic model for GRP pipeline is built through combing the general water hammer mathematic model and prosperities of GRP pipeline. The solving method of the model is discussed based on the method of characteristic. Ultimately, the simulation results show the GRP pipeline can reduce the peak pressure and pressure fluctuation frequency as well as increase the low pressure caused by water hammer compared with steel pipeline. The GRP pipeline has a better capability to reduce the harms brought by water hammer than steel pipeline.

New Approach to Calculation of Water Solubility in Oil Containing Asphaltenes

The degree of water dissolution in oil affects the flow behavior of oil—water mixtures in reservoirs and pipes. A multiphase flash algorithm was used to calculate the solubility of water in oil containing asphaltenes at various temperatures and pressures. A cubic-plus-association equation of state was used to simulate the formation of H-bonds between water molecules and polar asphaltene molecules. Experimental water solubilities in four oil samples validated that the method assumptions were accurate. The results demonstrated that the average absolute deviation between the experimental and calculated mole fractions of water in oil was less than 0.04673 in the range 452-557 K. Also, this method could explain the smooth transition from solubilized water at high temperatures to emulsified water at lower temperatures.