Distributed gas sensing using hollow core optical fibre

分布式光纤传感器可以沿着光纤绘制测量图，并在商业上部署用于测量物理参数，如温度、应变和声发射。它们被用来监测大型结构，如管道、风力涡轮机、石油和天然气井、地下电缆，以及用于碳捕获和储存的地质地点。光纤可以沿着结构或围绕结构安装，测量数据由连接在一端的单个询问箱读取。可以监测大量的传感路段，例如沿着100 - 1公里的长度每1米。在空间和时间上绘制测量图的能力提供了丰富的信息来源，彻底改变了对大型工程结构的理解和操作。分布式测量目前还不能用于化学参数。我们的愿景是开发一种新的分布式传感器，可以沿光纤长度检测、定位和量化气体浓度。该传感器将激光光谱气体测量的性能优势与分布式传感丰富的信息量相结合。加工工业有完善的传感器来检测潜在的爆炸性碳氢化合物，包括甲烷。对于传统的逐点传感，英国健康与安全执行局建议每个传感器之间的距离不应超过5米。如果应用于整个站点，将需要数千个传感器，因此覆盖范围仅限于安全关键区域。挑战包括在难以进入的区域进行常规校准、维护和更换传感器。在100年的时间里，甲烷的温室效应是二氧化碳的32倍。甲烷作为天然气和沼气的主要成分，是垃圾填埋场厌氧过程和废水处理的产物，是一个持续存在的重要问题。减少工业场所的逸散性甲烷泄漏被认为是减少温室气体排放的早期目标，但这需要在测量范围上进行一步改变。现场调查可能会漏掉偶发的泄漏；要尽量减少排放，就需要一种永久可用的解决方案。目前这一代的点传感器可能会遗漏逸散性泄漏，这些泄漏可能来自整个站点，并且足够大，需要缓解，但可能低于现有可燃气体传感器的检测阈值。许多泄漏只能在源头下风几米内检测到，因此需要大量的点传感器来覆盖整个现场。目前可用的替代方案包括气体泄漏的被动热成像（存在量化/故障安全问题，需要清晰的视线）和声发射传感器（只能发现高压泄漏，难以在嘈杂环境中使用）。使用开路光学（通常是激光）光束的现场周边传感可以很好地工作，但需要清晰的视线，并且提供的泄漏位置信息有限。需要一项新的战略来补充这些措施。分布式光纤气体传感器具有解决上述问题的潜力；由于气体可以沿着传感器的整个长度测量，没有明显的间隙，泄漏不太可能被遗漏。最近的技术发展使分布式气体传感器成为一种诱人的可能性。克兰菲尔德大学的研究小组开发了一种新型的询问仪器，用于沿纤维在多个传感区域进行气体检测，具有高灵敏度。南安普顿的研究人员开发了新的空心纤维（HCFs）；通过沿着纤维长度钻出微小的侧孔，气体可以进入核心，光可以探测到气体的存在。我们的目标是共同开发一个可以在模拟气体泄漏中进行现场测试的工作演示器。

Distributed optical fibre sensors can map measurements along an optical fibre, and are commercially deployed for the measurement of physical parameters such as temperature, strain and acoustic emission. They are used to monitor large structures such as pipelines, wind turbines, oil and gas wells, underground electricity cables, and geological sites used for carbon capture and storage. The fibre can be installed along or around the structure, and measurements read by a single interrogator box connected at one end. A large number of sensing sections can be monitored, e.g. every 1 m along a 100m - 1km length. The ability to map measurements in space and over time provides a rich source of information that has revolutionised the understanding and operation of large engineering structures.Distributed measurement is not currently available for chemical parameters. Our vision is to develop a new distributed sensor that can detect, locate and quantify gas concentrations along the length of an optical fibre. The sensor will combine the performance advantages of laser spectroscopic measurement of gas with the rich information content of distributed sensing. The process industries have well-established sensors for detection of potentially explosive hydrocarbons, including methane. For conventional point-by-point sensing, the UK Health and Safety Executive recommends that there should be no more than 5m between each sensor. If applied across an entire site, this would require thousands of sensors, therefore coverage is limited to safety-critical areas. Challenges include routine calibration, maintenance and replacement of sensors in difficult to access areas. Methane has a greenhouse warming potential of 32x that of carbon dioxide over a 100 year period. As the main constituent of natural gas and biogas, and a product of anaerobic processes within landfill sites and wastewater treatment, methane emission is an ongoing and significant problem. Reduction of fugitive methane leaks from industrial sites is recognised as an early target to reduce greenhouse emissions, but this requires a step change in measurement coverage. Site surveys can miss episodic leaks; to minimise emission requires a permanently available solution. The current generation of point sensors can miss fugitive leaks, which can originate from all over a site and be large enough to require mitigation, but may be below the detection threshold of existing flammable gas sensors. Many fugitive leaks are only detectable within a few metres downwind of the source, therefore an impractically large number of point sensors would be required for full site coverage.Currently available alternatives include passive thermal imaging of gas leaks, which has quantification / fail safety issues and requires a clear line of sight, and acoustic emission sensors, which can only find high-pressure leaks and are difficult to use in noisy environments. Site perimeter sensing using open-path optical (usually laser) beams can work well, but requires a clear line of sight and provides limited information on leak location.A new strategy is needed to complement these measures. Distributed optical fibre gas sensors have the potential to address the above issues; because gas can be measured along the sensor's entire length, with no significant gaps, leaks are less likely to be missed. Recent technology developments make a distributed gas sensor an enticing possibility. The Cranfield team has developed a novel interrogation instrument for gas detection in multiple sensing regions along a fibre, with high sensitivity. Southampton researchers have developed new hollow core fibres (HCFs); by drilling tiny side holes along the fibre length so that gas can enter the core, light can detect its presence. Together, we aim to develop a working demonstrator that can be field tested on simulated gas leaks.