Analysis on the application of gas sensor in gas leakage accident

In recent years, the use of sensors has become more and more common, and it can be seen in industrial automation, factories and other industries. This article mainly introduces the application of gas sensors in actual leakage accidents.

1 Introduction

In recent years, there have been frequent gas explosion accidents in coal mines in China; a large amount of natural gas has been used after the west-to-east gas transmission; and the recycling of blast furnace gas and coke oven gas; Flammable, explosive and toxic gases will cause poisoning, fire and even explosion accidents during the production, transportation and use of leaks. Seriously endangering people's lives and property safety. Due to the diffusivity of the gas itself, the gas will diffuse along the ground surface under the action of external wind force and internal concentration gradient after the leak occurs, forming a flammable, explosive or poisonous danger zone at the accident site to expand the hazardous area. For example: In 1992, during the commissioning of a blast furnace gas generator set in a company, one person was killed and more than 30 people were injured due to gas leakage. In a short period of time, the work area was fully filled with blast furnace gas. Therefore, this type of accident has the characteristics of strong suddenness, rapid spread, large rescue difficulty and wide range of hazards. Once a leakage accident occurs, corresponding measures must be taken as soon as possible to reduce the accident loss to the minimum level, timely and reliable analysis of the content of certain gases in the air, the correct disposal method is to reduce the accident caused by the leakage and the lives of people And the necessary conditions for property loss, this puts higher requirements on gas detection and monitoring equipment. This article starts with the type of sensor and analyzes its application in early warning and accident disposal of gas leakage accidents To achieve the purpose that relevant departments attach importance to.

2. Overview of gas sensors

Foreign countries began to research and develop gas sensors in the 1930s. China has also made great progress in the research of gas sensors in recent years, and the technology is maturing. At present, the types of gases that need to be detected are also extended from the original reducing gases (H2, C4H, CH4) to toxic gases (CO, NO2, H2S, NO, NH3, PH3), etc.

There are many types of gas sensors. According to different gas-sensitive materials and gas-sensitive characteristics, they can be divided into semiconductor type, electrochemical type, solid electrolyte type, contact burning type polymer type and so on.

2.1 Semiconductor gas sensor

This kind of sensor mainly uses semiconductor gas-sensitive materials. Since the advent of semiconductor metal oxide gas sensors in 1962, it has been widely used due to its high sensitivity and fast response. It has become one of the most widely used sensors in the world. , According to the different ways of detecting gas-sensitive feature quantity, it is divided into electronic and non-electronic types.

Resistive semiconductor sensors work by detecting the changes in gas content accompanying gas content. Mainly use metal oxide ceramic materials. The characteristics and applications of this sensor are relatively wide. For example, the WO3 gas sensor can detect the concentration range of NH3 from 5PPM to 50PPM, and the ZNO-CUO gas sensor is very sensitive to 200PPM CO.

Non-electronic semiconductor gas sensors work by using the principle that the current or voltage of the gas sensor changes with the gas content, mainly including MOS diode type and junction diode type, and field effect tube gas sensor. The detection gas is mostly hydrogen, alkanes and other combustible gases.

2.2 Solid electrolyte gas sensor

Solid electrolyte gas sensors use solid electrolyte gas sensing materials as gas sensing elements. The principle is that the gas-sensitive material generates ions when passing through the gas, thereby forming an electromotive force, and measuring the electromotive force to measure the gas concentration. Because of its high conductivity, good sensitivity and selectivity, this gas sensor is widely used, second only to metal oxide gas sensors. Such as measuring YST-Au-WO3 of H2S, measuring NH4 + CaCO3 of NH3, etc.

2.3 Contact combustion gas sensor

Can be divided into direct contact combustion type and catalytic contact combustion type. Its working principle is: when the gas-sensitive material is energized, the combustible gas is oxidized or burned under the action of a catalyst, and the heat generated causes the heating wire to heat up, thereby changing its resistance value, and measuring the resistance change to measure the gas concentration . This sensor can only measure that combustible gas is not sensitive to non-combustible gas. For example, a sensor made by coating active catalysts Rh and Pd on pt wire has a broad-spectrum characteristic and can detect various combustible gases. The contact combustion gas sensor is very stable at ambient temperature and detects most of the flammable gases in the lower explosion limit. It is commonly used in the monitoring and alarming of flammable gases in petrochemical, coal mine, kitchen, etc.

2.4 Polymer gas sensor

Gas sensors using polymer gas-sensitive materials have been greatly developed in recent years. When a polymer gas-sensitive material encounters a specific gas, its physical properties such as resistance, dielectric constant, speed and frequency of sound wave propagation on the surface of the material, and weight of the material change. Mainly include phthalocyanine polymer, LB film, polyisobutylene, etc. Polymer gas-sensitive materials have easy operation, simple process, good selectivity at room temperature, low price, easy to be combined with microstructure sensors and surface acoustic wave devices, and have an important role in the detection of toxic gases and food freshness. . According to the gas-sensitive characteristics of the materials used, this type of sensor can be divided into: polymer resistance gas sensors that measure the gas concentration by measuring the resistance of the gas-sensitive material; according to the formation of a concentration battery when the gas-sensitive material absorbs gas, and the determination of the electromotive force Concentration battery gas sensor of gas concentration; surface acoustic wave gas sensor made according to the principle that the sound wave propagates on the surface of the material after the gas is absorbed by the polymer gas-sensitive material; and after the gas is absorbed by the polymer gas-sensitive material Quartz oscillator type gas sensor made by weight change, etc. The polymer gas sensor has high sensitivity to specific gas molecules, good selectivity, and simple structure, can be used at normal temperature, and can supplement the deficiencies of other gas sensors.

3. Application of gas sensor

Install the gas sensor in the flammable, explosive, toxic and hazardous gas production, storage, use and other places, detect the gas content in time, detect leakage accidents early, achieve early warning in case of minor leakage, so that personnel can be disposed of in time, and will The gas sensor is linked with the protection system, so that the protection system acts before the gas reaches the explosion limit, and the accident loss is controlled to a minimum. It can also be combined with computer technology to form an intelligent system. It can be detected when the gas concentration is very low, without having to go deep into the scene to avoid unnecessary damage caused by not knowing the situation. After the gas leakage accident, quickly analyze the nature of the gas, quickly and accurately provide information about the nature of the common gas stored in advance and the disposal plan, determine the warning area, and organize the evacuation of people in the dangerous area.

4 Conclusion

The power plant of Ansteel Group Xingang Company entrusted Zhengzhou University of Technology to design and manufacture a carbon monoxide detection system as early as 1995. This system designed 40 measurement points, distributed in the blast furnace gas transmission pipeline, evacuation of water, boiler explosion-proof membrane, plant The duty room and other places, although later withdrew because of the high damage rate of the electrochemical sensor and the damage of the detection host (diskless 286 machine). However, during the operation, early warnings were made for minor leaks many times, thereby avoiding the risk of accidents caused by the continued expansion of the leak.

With the continuous emergence of new gas-sensitive materials, the intelligentization of gas sensors has also developed rapidly. It is believed that in the near future, more mature intelligent gas sensor systems will come out. The current status of gas leakage accidents will be greatly improved.

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