火灾环境下CNG长管拖车气瓶不同结构泄压装置的响应规律

由于天然气在储运过程中存在着潜在的泄漏和爆炸风险,一旦发生事故就有可能造成人民生命财产的重大损失。因此国内外有关标准法规均要求安装泄压装置,以保证CNG气瓶在超温、超压工况下能安全泄放,降低事故风险。但由于国内外标准对泄压装置设计计算方法和计算公式不同,导致不同的泄压装置在火灾工况下的动作响应规律存在着差异。为此,针对不同结构型式、不同泄放面积的泄压装置,开展了大容积钢质无缝气瓶整体火烧工况的分析研究,以获取CNG长管拖车气瓶在受火工况下温度压力的变化规律,以及不同泄压装置在火烧环境下的响应规律。研究结果表明:(1)大容积钢质无缝气瓶按照API 521-2014、CGA S-1.1和GB 16918—1997设计的泄压装置均能够满足大容积钢制无缝气瓶整体受火安全泄放的要求,考虑到可能引起二次灾害的CNG气体,推荐使用API 521-2014或CGA S-1.1计算最小泄放面积;(2)在火焰被钢板隔绝的情况下,泄压装置的热传导受阻,单爆破片结构往往比爆破片+易熔合金的组合结构先动作;(3)大容积钢质无缝气瓶在火灾环境下,泄放装置开启后,气体温度变化规律受泄放面积的影响较大。结论认为,该研究成果可以为CNG长管拖车气瓶泄压装置的标准制订和选型提供技术支撑。

Response laws of pressure relief devices with different structures on the cylinder of CNG long tube trailer in fire environments

Natural gas is susceptible to leakage and explosion during storage and transmission. Any of such incidents may induce great personal and physical losses. Therefore, installation of pressure relief devices is mandatory under relevant industry standards and codes to ensure the safe pressure release of CNG cylinders under over-temperature and over-pressure conditions, so as to reduce the accident risks. However, the calculation methods and formulas for the design of pressurerelief devices under such standards and codes are different, so the pressure relief devices provide different responses under fire conditions. In this paper, the case that a large-capacity seamless steel cylinder is totally in fire was analyzed to figure out the temperature and pressure changes of the CNG cylinder on the trailer and the responses of pressure relief devices with different structural styles. The following results were obtained. First, the pressure relief devices designed according to API 521-2014, CGA S-1.1 and GB 16918-1997 can satisfy the requirements on safe pressure release of large-capacity seamless steel cylinder. Considering that CNG may induce secondary damage, it is recommended to calculate the minimum relief area according to API 521-2014 or CGA S-1.1. Second, when the flame is isolated by the steel plates, the heat conduction of pressure relief devices is hindered and a single bursting disc structure usually responds earlier than a composite structure of bursting disc and fusible alloy. Third, when a large-capacity seamless steel cylinder is in fire, the change of gas temperature is much more affected by the relief area after the pressure relief device is started. In conclusion, the research results provide a technical support for the standard preparation and type selection of pressure relief devices on the CNG tube trailers.