掺氢天然气组分的超声监测方法研究

Blending hydrogen into natural gas offers efficiency benefits for the large-scale usage of wind energy and solar energy and is one of the fundamental steps toward the goal of building the energy internet. However, few practical sensory technologies are available to measure the compositions of hydrogen compression nature gas (HCNG) in real-time, at low-cost, with high reliability, and easily maintained over a long period of time. It demonstrates the aforementioned advantages that accurate measurements of the speed of sound can be used to predict the methane concentration in a representative sample of 6700 gases from across the United States of America at a high predictive confidence level. This project is aimed at developing an acoustic gas detection technology and proposing a real-time ultrasonic sensing method for HCNG. There are four main objectives in this project: 1) establish a theory concerning acoustic multi-relaxation in a gas media, which is made up of molecular rotational relaxation processes and vibrational relaxation processes, 2) propose an ultrasonic propagation model in HCNG to predict the acoustic relaxation absorption spectrum and the sound speed dispersion spectrum as a function of frequencies, 3) tackle the problem that the necessary measuring acoustic frequencies would be very lower than the effective relaxation area, which is result from the high pressure in natural gas pipeline, 4) develop a practical ultrasonic sensing method of the compositions of HCNG by using the proposed ultrasonic propagation model. The successful completion of this project would lead to a real-time sensing method for monitoring the compositions in HCNG, which itself could be turned into an emerging industry for the advancement of the energy internet in the near future.

天然气掺入电解氢被认为是解决我国大规模风电、光电消纳问题的有效途径之一，是我国建立能源互联网的基础步骤之一。然而，当前尚缺乏一种实时强、寿命长、维护低、价格低的掺氢天然气组分监测方法。在美国广泛应用的声速天然气浓度传感技术为本项目的研究指出了方向。本项目提出的掺氢天然气组分超声监测方法，首先研究将分子转动弛豫归入振动弛豫的气体声弛豫理论；进而得到掺氢天然气及其组分（特别是缺乏结果的轻烃气体）的超声传播理论模型；重点研究各组分的弛豫幅值强弱特性、弛豫频率强弱特性、声速强弱特性，提出一种联合声弛豫、声吸收和声速的掺氢天然气组分监测方法；并解决因天然气管道内气压增大等效于声工作频率变小，造成测量频点低于声弛豫作用区的问题，最终获得掺氢天然气组分的可实用化超声监测方法。本项目的实现不仅将为我国新兴的掺氢天然气产业链，提供一套可影响其定价权的实时监测技术，更可为我国建立能源互联网提供基础传感技术。

天然气掺入电解氢是利用再生能源解决即将枯萎的化石能源的有效途径。获得一种实时强、寿命长、维护低、价格低的掺氢天然气组分超声监测方法，是本项目的核心研究目标。.本项目首先建立了氢气转动声弛豫的复合有效热容随声频率变化的解析形式，其结果与实验数据一致性好；然后获得了氢气转动声弛豫的解耦合模型，与项目组已有的气体振动声弛豫解耦合模型联立统一，建立了一种转动弛豫与振动弛豫相结合的掺氢天然气声弛豫理论模型，以氢气、甲烷、二氧化碳、氮气、氧气等各种混合气体为目标，获得了声弛豫吸收谱和声速频散谱，且与众多国外学者的实验数据相吻合；还获得了一种基于声速频散分解的气体分子声弛豫快速测量方法，为缺乏量子物理弛豫参数的天然气中烃类气体，如乙烷，找到了一种简单快速的声学测量方法，为全面建立掺氢天然气的超声传播模型奠定了理论和实验基础。.基于已建立的掺氢天然气超声传播理论模型，本项目获得了多种掺氢天然气的超声监测方法，包括：1）基于单频率点声速频散和弛豫声吸收测量值的掺氢天然气监测方法；2）基于声速频散强度变化率的掺氢天然气成分探测方法；3）基于声速谱拐点的掺氢天然气探测方法；4）基于声弛豫+深度学习的掺氢天然气组分检测方法。另外，本项目还获得了基于改进的弛豫谱峰值作用区和基于有效热容分解的两种低品质天然气超声监测方法。这些方法，对掺氢天然气即可进行快速简单的定量监测，还可突破性的进行定性探测。.同时，本项目建立了一套可承受30个大气压的掺氢天然气超声监测系统原型，内含7组不同频率的超声波换能器测量模块，获得了多种混合气体的声吸收谱和声速频散谱实验数据，为本项目的理论研究成果提供了有力的支持，并获得了发明专利“一种基于超声波换能器的通用气体测量方法及装置”的授权。.综上所述，本项目顺利完成了申请时的预期研究目标：建立了掺氢天然气的超声传播理论及模型，获得了掺氢天然气的超声监测方法，并研制了传感系统原型。