| Liquefied gas is short for liquefied petroleum gas (LPG), also known as liquid hydrocarbon. It is an inflammable liquid separated from the liquefaction the gaseous hydrocarbon produced in gas-field exploitation, oilfield exploitation, or the process of petroleum refining with removal of dry gas. It is a clean, efficient, low-cost, and high-quality energy. Except as chemical raw material and fuel for power generation, it has been widely used in the field of industry and for civil use. Along with the development of the world industrial progress, various countries are paying more attention to the reserve of petrochemical energy as a national strategic energy, and all kinds of oil and gas storage caverns have been built around the world, with the their types changing gradually from aboveground at first to underground. The underground space has been a widely recognized resource in the industry. On the basis of related planning and research, much study has been conducted on how to make full use of this type of resource to build underground storage cavern. And one of the main utilization patterns is to use existing space or space dug out by hand. Most of large storage caverns are used for oil and gas reserve.The purposes of oil and gas storage include national strategy purpose, commercial storage purpose and personal storage purpose. Strategic reserve of oil and gas refers to a certain quantity of crude oil, refined oil and natural gas possessed and controlled by the central government through means of direct investment or other methods, which is an important means to ensure energy security. In emergency period of war and wide embargo, oil and gas reserves can cope with volatility of international oil market, and cushion or shield its possible impacts on national economy.At present, there are few domestic liquefied gas storage caverns under construction, therefore no similar design or construction experience can be used for reference. We are still in the stage of exploration and test, with many technical problems to be deeply studied. Due to particularity of substances stored, a high requirement is posed on the physical design of underground cavern. During the excavation process and after excavation, initial ground stress inside the cavern will redistribute, changes of internal force and deformation of surrounding rock, especially quantitative analysis on the internal force and deformation of surrounding rock under complex geological conditions and working conditions (such as high water level and dynamic loading, etc.) will help make the right judgment on safety and stability of the surrounding rock and provide theoretical basis for physical design and scientific construction. Therefore, study of physical design parameters of water-sealed liquefied gas storage cavern under specific geological conditions is of important value for engineering application.The underground water-sealed liquefied gas storage cavern project in the relocating project of Yantai Wanhua Group is China’s first large-scale underground water-sealed liquefied gas storage cavern. In order to ensure the security, durability of the cavern and its reasonability of design, scientific research should be conducted on its underground physical design parameters. Based on the construction of underground water-sealed liquefied hydrocarbon cavern in the relocating project of the old Yantai Wanhua Factory, this paper uses numerical simulation test and physical model test to make computational analysis on parameters such as buried depth, depth-span ratio and spacing of the cavern, providing reliable structure parameters for the engineering design of underground water-sealed cavern and theoretical guidance for its design and construction.The characteristics of underground water-sealed liquefied gas storage cavern DECide that its safety and stability can only be ensured with a full dependence and use of the natural geological environmental conditions in cavern area. Based on the research of basic theory of gas storage in the cavern and principle of physical model tests, this paper relies on the Yantai Wanhua underground water-sealed liquefied gas storage cavern project to make a series of photoelastic test models with epoxy resin, and conducts photoelastic tests by Type409-2polariscope. Due to the defects of the factory-fresh polariscope, it has been upgraded before conducting the test. Meanwhile, we’ve also studied the structure parameters of the underground cavern with the method of numerical simulation test. The comprehensive analysis of physical model and numerical simulation results in reasonable structure parameters, which can be used as the basis and reference for the design and construction of the cavern.As a kind of basic chemical raw material and new type fuel, LPG has drew more attention from people. Boasting of its advantages of high calorific value, no dust, no carbon residue and convenient operation and use, the fuel of LPG has been widely used in life field. It is also used to cut metal, bake agricultural products and roast industrial kilns, etc. Chapter Two of this paper introduces storage mode of LPG cavern proceeding from its physical characteristics, illustrates the storage principle of water-sealed LPG cavern, discusses on the necessary geological conditions of constructing an LPG cavern, and illustrates the advantages of underground water-sealed liquid gas storage cavern. With many advantages of land saving, small investment, small pollution, environmental protection, steel saving and long service life, the construction of underground oil and gas storage cavern is an important measure to ensure national energy security, and also the most effective way to ensure safe and stable gas supply.Chapter Three gives a study on the basic principles of photoelastic test. This test is a rapid, accurate, economic and effective stress analysis method, with its main characteristic of strong intuitive. Through the test, you can get whole field information and can directly observe the stress distribution of stressed model, especially for the components with complicated shapes and load and difficult for theoretical calculation, it shows superiority. It can determine the stress concentration factor of component quickly and accurately, which provides experimental basis for improving structure design and structural performance. Photoelastic test has a history of over one hundred years, with its test technology becoming increasingly mature and perfect. At present, this test and analysis method has been widely used in aviation, shipbuilding, machinery, petrochemical, water conservancy and civil construction. This paper introduces basic principles of optics including plane-polarized light, circularly polarized light, interference of light and birefringence, demonstrates theorem of plane stress-optical and photoelastic effect of plane-polarized light, makes a detailed analysis on the principle of isochromatics and isoclinic, and describes the reading method of the features of isochromatics and series of isochromatics in the white light line. It analyzes the similarity of models on the basis of introducing model similarity theorem.Photoelastic materials is the key to photoelastic stress analysis. Only good materials can fully show the photoelastic effect, and therefore work as the basis for analyzing various mechanical problems. More than a century ago, photoelastic effect was found, and gradually evolved into the photoelastic principle. Due to the then insensitive material, it was difficult to process a model, leading to slow development of photoelastic experiment. Since epoxy resin material appeared in the twentieth century, polymer of epoxy resin has gradually become the basic raw material of photoelastic materials, which greatly promotes the development of the photoelastic method. After the research into construction principle of water-sealed cavern and principle physical model test, Chapter Four bases on Yantai Wanhua underground water-sealed liquefied hydrocarbon cavern, makes a series of photoelastic test models with epoxy resin for physical model test. It gives a detailed introduction of the project profile, basic geological conditions of the research area and the stress of cavern area, laying foundation for the processing and manufacturing of cavern physical models and photoelastic experiment in later period. It illustrates the method of selecting the model of Yantai Wanhua and the processing progress of making the model with epoxy resin on the basis of the principle of selecting the cavern model.12pieces of models have been made in total, including6pieces of single cavity and6pieces of multiple cavities.Photoelastic test is an experimental stress analysis method to measure the stress field of model using the stress-optical effect and optical theories of special transparent materials. It is a kind of whole field stress measurement method with features such as strong intuitive and high reliability, which is especially good for analyzing stress field in a complex structure and stress concentration, and is widely used in civil engineering, mechanical engineering and other fields. The study of physical model test uses the Type409-2polariscope. As the factory-fresh polariscope is mainly used in teaching demonstrative experiments, some components of the polariscope need to be transformed in design in order to be applied to the study of cavity. Chapter Five introduces the Type409-2polariscope used in tests and its beam path diagram, and puts forward the defects to realize the target device. Aimed at the defects, the loading system of the factory-fresh Type409-2polariscope has been upgraded and transformed according to related theory of mechanical design and manufacturing. After transforming, it consists of load frame part and hydraulic transmission part, and can be used for cavity model and physical model tests. There are many methods to study underground structure design parameters, of which the currently widely used are theoretical analysis method, physical simulation method, numerical simulation method, engineering geological analogy method, block theory method, etc. Physical simulation test is based on similarity theory and dimensional analysis, using model that is designed similar to its prototype to study the prototype indirectly. Simulation test develops with the development of production and science and technology, and has become one of the basic methods for human to understand and change the world. Commonly used methods of physical simulation include model test (similar material method) and photoelastic test (photoelastic method). In Chapter Six, the paper conducts research into aspects such as cavity depth, cavity depth-span ratio and cavern spacing, etc, uses optical method to measure the stress state of various points on the stressed model made of birefringent transparent material, imposes external force on the model, puts it into polarized light field and then observes fringe patterns related to the stress state. The fringe pattern is associated with stressed model boundary and its internal stress. The main stress difference and stress direction of various points on the model can be determined according to the principle of photoelastic.The underground physical design of water-sealed liquefied gas storage cavern belongs to the category of engineering mechanics, many problems of which can be classified to large-scale linear equations through numerical analysis method and be solved, such as differential equation and multiple unknown variables. Especially in recent years, numerical analysis method enjoys a great boom. The main reason for this is the rapid development of computer pushes forward the development of this method. Chapter Seven uses numerical simulation to study the design parameters of underground structure of water-sealed liquefied gas storage cavern, researches the cavity depth, cavity depth-span ratio and cavern spacing by means of FLAC software, and comes to the scientific design parameters of underground structure after comparison with photoelastic test and comprehensive analysis.There are three innovative points of this paper:(1) Make a comparative study of design parameters of underground structure of water-sealed liquefied gas storage cavern through physical model test and numerical simulation, obtain the scientific and reliable design parameters including cavity depth, cavity depth-span ratio and cavern spacing, and lays a theoretical foundation for physical design and scientific construction of underground water-sealed liquefied gas storage cavern.(2)Aimed at the defects, the loading system of the factory-fresh Type409-2polariscope has been upgraded and transformed according to related theory of mechanical design and manufacturing. After transforming, it can be used for cavity model and physical model tests.(3)Analyze the stress state and deformation characteristics of underground cavern by means of photoelastic test, and provide a theoretical basis for obtaining the accurate underground structure design parameters. |
PDF Full Text Request