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Assessment of flammability and explosion risks of natural gas-air mixtures at high pressure and high temperature

机译：评估天然气-空气混合物在高温高压下的易燃性和爆炸危险

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The flammability and explosion characteristics of natural gas (NG) and air mixtures at high pressure and high temperature are of great concerns for air injection IOR (improved oil recovery) process in oilfield and for natural gas combustion engines. In this study, an experimental setup is built up to measure the explosion limits (flammability limits) of methane and natural gas at elevated pressures and temperatures up to 20 MPa and 100 degrees C. The influences of pressure, temperature, and ignition energy and gas composition on the flammability limits, minimum oxygen content required for explosion (MinOC) and explosion energy have been investigated for methane and typical natural gas mixtures with air. High pressure and high temperature flammability limit models for natural gas-air mixtures have been proposed based on the experimental data. The experimental results show that the flammability limits of natural gas can be significantly extended at high temperature and high pressure, indicating a good flammability for combustion applications but high explosion risks in terms of the safety for the oilfield air injection process. At 100 degrees C and 20 MPa, the explosion limit range measured for methane in air is extended to 2.87%-64.40%vol, in contrast to the range of 4.95%-15.51%vol at the normal pressure and temperature (0.1 MPa and 25 degrees C), and the corresponding minimum oxygen content required for explosion can be reduced to as low as 5.74% from around 10% at the atmospheric conditions. The variation of the upper flammability limit (UFL) is more sensitive than that of the lower flammability limit (LFL) as pressure and temperature increase. Electrically heated tungsten wires were applied for the ignition, and it has been found that high ignition energy is required to ignite the gas mixtures at high pressure conditions. The peak explosion pressure (or explosion energy) is mainly depended on the composition of the flammable gas and oxygen, while it is slightly reduced at high temperature conditions and gradually increases with the initial pressure. Explosions with incomplete combustion reaction can occur at near UFL points with enormous amount of carbon black formed due to lack of oxygen, while the explosion energy can be significantly reduced at near LFL points because of lack of flammable gases. The increase of risk index at high pressure and high temperature indicates a larger explosion risk and safety concern.
机译：天然气（NG）和空气混合物在高压和高温下的易燃性和爆炸特性对于油田的空气注入IOR（提高采油率）过程以及天然气内燃机非常重要。在这项研究中，建立了一个实验装置，以测量在升高的压力和温度（最高20 MPa和100摄氏度）下甲烷和天然气的爆炸极限（易燃极限）。压力，温度以及点火能量和气体的影响根据易燃极限的组成，爆炸所需的最低氧气含量（MinOC）和爆炸能量，已对甲烷和典型的天然气与空气的混合物进行了研究。基于实验数据，提出了天然气-空气混合物的高压和高温可燃极限模型。实验结果表明，在高温和高压下，天然气的可燃性极限可以显着延长，这表明燃烧应用具有良好的可燃性，但就油田注气过程的安全性而言，爆炸的危险性很高。在100摄氏度和20 MPa下，空气中甲烷的爆炸极限范围扩大到2.87％-64.40％vol，而在常压和温度下（0.1 MPa和25时，则为4.95％-15.51％vol） ℃），爆炸所需的相应最低氧气含量可从大气条件下的约10％降低至5.74％。随着压力和温度的升高，可燃性上限（UFL）的变化比可燃性下限（LFL）的变化更敏感。将电加热的钨丝用于点火，并且发现在高压条件下点燃气体混合物需要高点火能量。峰值爆炸压力（或爆炸能量）主要取决于易燃气体和氧气的组成，而在高温条件下会略有降低，并随初始压力逐渐增加。燃烧反应不完全的爆炸会在UFL点附近发生，由于缺氧会形成大量的炭黑，而LFL点附近由于缺乏可燃气体会大大降低爆炸能量。在高压和高温下危险指数的增加表明更大的爆炸危险和安全隐患。

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