| With the property of high pressure, flammable and explosive of liquefied petroleum gas(LPG), there is a huge potential safety hazard in the pipage process. Once the pipeline was damaged, it is likely to cause fire even explosion. It is a prerequisite of accessing the accident quickly and accurately for carrying out the emergency rescue measures correctly and timely. In concequense, this paper regards propane and n-buttane as the research object, which are the main components of LPG. The purpose is to establish the pipeline leakage mathematical model about the source type of no momentum injection, programme the LPG pipeline release computational software using Borland C++ Builder programming language programs, create a DEGADIS interface to calculate the diffusion parameters. On the basis of the established model, the mechanism and effects about the leakage and diffusion process has been analyzed, and the main conclusions are as follows.1. Based on the research of the essence and mechanism about propane and butane pipeline, it can conclude that the pipeline leakage is time-varying, nonlinear and multivariable, which is a more complex flow process. The releasing process can be divided into three stages, including the initial liquid leakage stage, gas-liquid flow leakage stage and gas flow leakage stage. Among these three stages, the first stage lasts shorter, while the latter two stages costs longer time, that is the principal part of the leaking process.2. Establishing the propane and butane pipeline mathematical model. By studying the mechanism of the pipeline leakage and simplifying governing equations, including the energy conservation equation, momentum equation, continuous equation, and state equation, etc., this paper has established the pipeline leakage mathematical model. The LPG pipeline release-diffusion compute software has been programmed on the basis of the mathematical model.The mathematical model covers six calculation module, such as pressure calculation, release mass calculation, compressibility factor calculation, fanning friction factor calculation, critical two-phase flow calculation and diffusion calculation, which is verified by the Isle of Grain LPG pipeline test.3. The LPG pipeline release-diffusion compute software was used to simulate the behaviors and rules of the pipeline leakage, analyzing the influence of the pipeline structure, operating parameter and orifice features on the releasing process. The results shows that the releasing time is comprehensively determined by the length of the pipeline, operating temperature and equivalent aperture, while the relase flow rate is affected by operating temperature, operating pressure, flow rate and equivalent aperture. It indicates that the releasing time and release mass increase with the increasing of the pipeline length, and most of the releasing process stays in a steady stage. The operating pressure has larger effect on the initial release flow rate. The releasing time, the initial flow release flow rate and the cumulative release mass dearese due to the rising of the operating temperature. The increasing equivalent aperture result in that the releasing time reduces obviously and the release flow rate increases remarkably.4. The diffusion process of propane in the wide area where the obstacle is not obvious was investigated by using DEGADIS and ALOHA models including its impact factors. It indicates that the longer the pipiline, the more dangerous areas, and the distance between source and is eventually flattened after increasing. Increasing with the orifice area, the maximum of the dangerous area and concentration of the certain position rises; with the increase of wind speed, the diffusion speed and danger area increased; when the pipeline is longer, the dangerous area in the downwind is increased as the temperature goes up, but in crosswind has little variation. In the condition of the shorter length of the pipeline, with the increase of the atmospheric stability level, the release medium spreads nearer. |
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