1. Used for combustible gas monitoring and alarm
At present, the development of gas-sensitive materials has made gas sensors with high sensitivity, stable performance, simple structure, small size, and low price, and has improved the selectivity and sensitivity of the sensor. Existing gas alarms mostly use tin oxide plus precious metal catalyst gas sensors, but the selectivity is poor, and the accuracy of the alarm is affected due to catalyst poisoning. The sensitivity of semiconductor gas-sensitive materials to gas is related to temperature. The sensitivity is low at room temperature. As the temperature rises, the sensitivity increases, reaching a peak at a certain temperature. Since these gas-sensitive materials need to achieve the best sensitivity at higher temperatures (generally greater than 100°C), this not only consumes additional heating power, but can also cause fires.
The development of gas sensors has solved this problem. For example, a gas sensor made of iron oxide-based gas-sensitive ceramics can create a gas sensor with high sensitivity, good stability, and a certain selectivity without adding a noble metal catalyst. Reduce the working temperature of semiconductor gas-sensitive materials, greatly improve their sensitivity at room temperature, so that they can work at room temperature. At present, in addition to the commonly used single metal oxide ceramics, some composite metal oxide semiconductor gas sensitive ceramics and mixed metal oxide gas sensitive ceramics have been developed.
Install the gas sensor in places where flammable, explosive, toxic and harmful gases are produced, stored, transported, and used to detect the gas content in time and find leakage accidents early. The gas sensor is linked with the protection system, so that the protection system will act before the gas reaches the explosion limit, and the accident loss will be kept to a minimum. At the same time, the miniaturization and price reduction of gas sensors make it possible to enter the home.
2. Application in gas detection and accident handling
2.1 Detection gas types and characteristics
After a gas leakage accident occurs, the handling of the accident will focus on sampling and testing, identifying warning areas, organizing the evacuation of people in dangerous areas, rescuing poisoned persons, plugging and decontamination, etc. The first aspect of disposal should be to minimize the damage to personnel caused by the leakage, which requires an understanding of the toxicity of the leaked gas. The toxicity of gas refers to the leakage of substances that can disrupt the normal reactions of people’s bodies, thereby reducing the ability of people to formulate countermeasures and reduce injuries in accidents. The National Fire Protection Association divides the toxicity of substances into the following categories:
N\H=0 In the event of a fire, apart from general combustibles, there are no other dangerous substances in short-term exposure;
N\H=1 Substances that can cause irritation and cause minor injuries in short-term exposure;
N\H=2 High concentration or short-term exposure can cause temporary disability or residual injury;
N\H=3 Short-term exposure can cause serious temporary or residual injury;
N\H=4 Short-term exposure can also cause death or serious injury.
Note: The above toxicity coefficient N\H value is only used to indicate the degree of human damage, and cannot be used for industrial hygiene and environmental evaluation.
Since toxic gas can enter the human body through the human respiratory system and cause injury, safety protection must be completed quickly when dealing with toxic gas leakage accidents. This requires accident handling personnel to understand the type, toxicity and other characteristics of the gas in the shortest time after arriving at the accident site.
Combine the gas sensor array with computer technology to form an intelligent gas detection system, which can quickly and accurately identify the type of gas, thereby detecting the toxicity of the gas. The intelligent gas sensing system is composed of a gas sensor array, a signal processing system and an output system. A plurality of gas sensors with different sensitivity characteristics are used to form an array, and the neural network pattern recognition technology is used for gas recognition and concentration monitoring of the mixed gas. At the same time, the type, nature, and toxicity of common toxic, harmful, and flammable gases are input into the computer, and accident handling plans are compiled according to the nature of the gas and input into the computer. When a leakage accident occurs, the intelligent gas detection system will work according to the following procedures:
Enter the site→adsorb gas sample→gas sensor generate signal→computer identification signal→computer output gas type, nature, toxicity and disposal plan.
Due to the high sensitivity of the gas sensor, it can be detected when the gas concentration is very low, without having to go deep into the accident site, so as to avoid unnecessary harm caused by ignorance of the situation. Using computer processing, the above process can be completed quickly. In this way, effective protective measures can be taken quickly and accurately, the correct disposal plan can be implemented, and accident losses can be reduced to a minimum. In addition, because the system stores information about the nature of common gases and disposal plans, if you know the type of gas in a leak, you can directly query the nature of the gas and the disposal plan in this system.
2.2 Find leaks
When a leakage accident occurs, it is necessary to quickly find the leakage point and take appropriate plugging measures to prevent the accident from further expanding. In some cases, it is more difficult to find leaks due to long pipelines, more containers, and hidden leaks, especially when the leak is light. Due to the diffusibility of gas, after the gas leaks from the container or pipeline, under the action of external wind and internal concentration gradient, it begins to diffuse around, that is, the closer to the leak point, the higher the gas concentration. According to this feature, the use of smart gas sensors can solve this problem. Different from the intelligent sensor system that detects the gas type, the gas sensor array of this system is composed of several gas sensors with overlapping sensitivity, so that the sensitivity of the sensor system to a certain gas is enhanced, and the computer is used to process the gas. The signal change of the sensitive element can quickly detect the gas concentration change, and then find the leak point according to the gas concentration change.
At present, the integration of gas sensors makes the miniaturization of sensor systems possible. For example, an integrated ultrafine particle sensor developed by the Japanese ** company can detect hydrogen, methane and other gases, concentrated on a 2 mm square silicon wafer. At the same time, the development of computer technology can make the detection speed of this system faster. Therefore, a smart sensor system that is small and easy to carry can be developed. Combining this system with appropriate image recognition technology, using remote control technology can make it automatically enter hidden spaces, poisonous and harmful places that are not suitable for people to work, and find the location of leaks.
3. Concluding remarks
Develop new gas sensors, especially the development and improvement of intelligent gas sensing systems, so that they can play the role of alarm, detection, identification, and intelligent decision-making in gas leakage accidents, greatly improving the efficiency and effectiveness of gas leakage accident handling. Safety plays an important role in controlling accident losses.
With the continuous emergence of new gas-sensitive materials, the intelligence of gas sensors has also been rapidly developed. It is believed that in the near future, smart gas sensing systems with more mature technologies will come out, and the current situation of gas leakage accident handling will be greatly improved.
Post time: Jul-22-2021