| High sour natural gas purification plants own numerous process equipment and complicated process conditions, its treatment medium contains high concentrations of H2S and CO2and are usually treated under high temperature and pressure, which is combustible and corrosive and highly toxic. All these characteristics make the plants easy to catch serious gas leak and even explosion catastrophic accidents, and threaten the surrounding environment, people’s lives and property tremendously. Gas detector is able to detect the gas leak quickly and accurately, which is one of the most important protection means for safe production in high sour natural gas purification plants. Therefore, in order to improve the high-sulfur gas purification plants’safe operation and management level, it is important to identify the potential leak sources and risk level of flammable and toxic gas in each process unit first, then, the leakage characteristics and diffusion law of combustible and toxic gas are to be analyzed, at last, a risk-based optimization methods of gas detectors is established, which mean to make all types of leaks detected efficiently, reliably and accurately, as well as providing timely leakage alarm information. The method will be of great practical significance in improving the safety operation level and protecting the public safety around the station. In this regard, the paper carried out the research work in the following areas:(1) Based on analysis of media components, pressure and other characteristics of each process unit in high-sulfur gas purification plants, selection proposals of high sulfur gas purification plant gas detector are proposed through comparing and analyzing work principles and applicable scopes of existing categories of flammable and toxic gas detectors.(2) Based on on-site survey and statistical data analysis, the potential leakage source identification for each process unit of high sour natural gas purification plants is carried out. Each process unit and some equipment in purification plants are identified whether to be potential leak sources based on field survey data. Risk evaluation is made for each processing unit and some important equipment by adopting Dow Chemical fire and explosion index method. Results show that1) the desulfurization unit, dehydration unit and sulfur recovery unit are the main leakage process units, the flange, pipeline and valve leakage are the main leakage places, Leak happened mainly for small form, medium and big forms occurred in fewer;2) the fire and explosion danger levels for Desulfurization units, filtration separation, dehydration unit and sulfur recovery unit are lighter, medium, lighter, lighter and lighter, respectively; the fire explosion index of wet purge gas separator, MDEA absorber, MDEA regeneration in the desulfurization unit are mild, moderate and lightest, respectively.(3) A two-dimensional leakage and diffusion numerical model for high-sulfur gas is established based on FLUENT14.0software platform. The diffusion and leakage law of high sulfur gas, the transformation rule of effective detection range for CH4and H2S gas detectors are analyzed. Results show that:1) the valid detection range of combustible gas turns greater as the wind speed enlarges, turns bigger as the leaking source intensity increases, and nearly stay steady along with the H2S mole fraction changes larger, the strongest influence factor is the leakage source among them.2) the effective detection range of toxic gas detection range decreases gradually following larger wind speed, and enlarges and tends to be stable with the leakage source intensity increasing gradually as well as the rising of H2S content increases. And the biggest influence factor is the medium component.(4) The minimum sum of the product of all the potential leakage scene’s leakage risk and its corresponding required detection response time are taken as the optimization objective function, and the location and quantity of gas detectors are taken as optimization variables. An optimization mathematical model of gas detector was established, and the greedy dropping heuristic algorithm are used to solve the optimization model, the full layout optimization steps of gas detectors were given based on CFD simulation of gas leakage and the detection of response time.(5) Taking the desulfurization unit of a purification plant in WanZhou as an instance,72potential leakage scenarios and216candidate point sensor locations are determined through analysis. The leakage risk value of each leak scenario is obtained by expert scoring method. Three-dimensional CFD numerical simulation models are established for each leak scenario and numerical simulations are conducted respectively, the candidate leak detection point and its corresponding detection response time of each scene are obtained. The optimization configuration and layout program of gas detectors in desulfurization unit are given by adopting a risk-based optimization mathematical model and its solving method. The analysis conclusions show that the desulfurization unit in this purification plant had better to configure nine CH4detectors and11H2S detectors, and the defection efficiency is98.6%and detection time is5.22s. While, the detection efficiency is only63.9%and the detection time is11.29s for the present layout plan. When placing as many detectors as the present plan used in the plant, the detection efficiency is84.7%and the detection time is6.82s. Comparison and analysis shows that:the risk-based optimization method proposed in the paper detector can be of more effectiveness and reliability.
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