| Natural gas will become one of the energy troika needed for driving the global economy development in the middle of this century. Domestic utilization of natural gas has made significant progress in recent ten years, but there is still a large gap with the world's average level, which can be treated as both challenge and opportunity. With enhancement of economic strength and increase of urbanization rate, city gas has developed to current urban gas in China, then to universal gas in the future. In this process, the urban natural gas pipeline network continuously expands, contacts, connects, that covering urban agglomerations comes into being gradually and presents a trend of sustainable development. As to this frontier phenomenon, this paper has carried out the research on planning and design theory of urban agglomerations natural gas pipeline network.Firstly, according to the generalization of natural gas pipeline network construction at home and abroad, especially, its attempts or planning achievements emerging in similar urban agglomerations of China in recent years, the looming phenomenon of natural gas pipeline network in urban agglomeration is abstracted to one new engineering concept, natural gas regional pipeline network. It describes the functions and composition. Its various characteristics are analyzed. the location and boundaries of natural gas regional pipeline network in the natural gas pipe network chain are determined. Meanwhile, the formation mechanism of natural gas regional pipeline network is discussed.Next, that planning and design of natural gas regional pipeline network should be adapted to its sustainable development system was put forward. This system contains the characteristics of three aspects. One is the synthesizing of two kinds of planning and design on our country existing natural gas pipeline. Another is the three levels of modern system, namely, the legal system level complying with national and local laws and regulations, the longitudinal system level taking the construction administrative management system as the core, the planning and design work system level constituted by the government planning and the enterprise design. The last one is planning and design theory system in line with natural gas regional pipeline network characteristics.Thirdly, the planning theory of natural gas regional pipeline network is established, mainly including prediction model and methods suitable for calculating regional gas supply scale, complex pipe network structure and planning form, pipe network layout planning method represented by important node connection method, confluence method and midpoint method, multiple pressure levels and range planning mode containing ultrahigh pressure(6.0 MPa), planning and layout principles involving multiple gas sources and peak-shaving and gas storage, etc. The decision of natural gas regional pipeline network planning goal should attach importance to the function value of its regional energy infrastructure, be conducive to fully perform function and role promoting regional economic development and urban and rural resources sharing.Fourthly, the design theory of natural gas regional pipeline network is explored, mainly including natural gas pipeline flow theory based on the three laws, strength theory based on different application conditions, security theory based on intrinsically safe and other various elements, pipeline design optimization theory based on multiple factors and targets, etc. Meanwhile, individuality characteristics of gas transmission and distribution piping systems are analyzed and universality judgment principles to divide them by pipeline transmission efficiency are put forward. Further, three kinds of natural gas regional pipe flow features are summarized when having transmission, storage and distribution functions. Dimensionless equation is derived to reveal multi-factors coupling and comparison between pipeline actual flow condition and its design flow condition, then to be used for calculating and analyzing impact level of multi-factors variation coupling effect on design flow condition.Fifthly, the flow characteristics in natural gas regional pipeline are explored. The concept of potential energy factor is put forward. Moreover, containing this concept, natural gas non-horizontal pipe flow basic equation, practical equation and engineering calculation formula are deduced. The formula can be not only applied to natural gas regional pipe, but also to natural gas transmission pipeline and town gas pipeline with no more than 6.0 MPa pressure. Meanwhile, it may replace two formulas of non-horizontal pipe and horizontal pipe, being easy to use.Finally, storage capacity universally existing in natural gas regional pipeline is studied. Concepts and definitions refer to flow pipe storage and retention ratio, storage performance and efficiency and so forth are put forward. As pipe storage and retention ratios in the first and second working conditions are deemed as the characteristic parameters, their storage performance and efficiency mathematical expressions are given. Further, their combination is extended as the third working condition and its mathematical expression is obtained. It's demonstrated that primary flow pipe with combination of various pressure levels and adjacent pressure level has the maximum storage performance and efficiency. Pipe flow minimum load factor is proposed and then the ways and means to increase pipe storage performance are analyzed based on this.This research results indicate that the natural gas regional pipeline network clear characteristics on functional value, role, structure, layout, flow conditions, construction conditions, etc, which are determined by its gradually discovered unique properties. Meanwhile, with deep analysis and research on natural gas regional pipeline network engineering characteristics and flow characteristics in transmission, storage and distribution functions, it has scientific significance for exploring natural gas regional pipeline network features, description, comprehending its operation rule and enriching natural gas pipeline network engineering theory. Planning and design theory establishment of natural gas regional pipeline network will provide strong technical support and reference for its future construction in our country. |
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