Leakage sensor Gas sensor is a commonly used gas detection equipment, with accurate measurement, the use of flexible, wide range of measurement and other advantages, is widely used in coal, underground, petroleum, chemical, Electronics, machine tools and other fields. Gas sensors in the gas leakage accident also played a crucial role, the following Xiaobian to specifically introduce it
Leakage sensor In recent years, China's coal mine gas explosion accidents; West-East gas after a large number of natural gas applications; and blast furnace gas, coke oven gas recycling and so on; to produce life and bring high efficiency at the same time also brought insecurity, Flammable, explosive, toxic gases in the production, transportation, use the process in the event of leakage will lead to poisoning, fire or even explosion. Seriously endangering people's lives and property. Due to the existence of the existence of the gas itself, after the occurrence of leakage in the external wind and internal concentration gradient under the action of the gas will spread along the surface in the accident site to form a flammable, explosive or toxic areas to expand the area of danger. For example: In 1992, a company in a blast furnace gas generator commissioning process, because the gas leak, causing one person died, more than 30 people were injured, in a very short period of time all the work area filled with blast furnace gas. So this kind of accident has the sudden strong, the rapid spread, the difficulty of the rescue and so on. In the event of a leak, it is necessary to take appropriate measures as soon as possible in order to reduce the accident loss to a minimum level, timely and reliable analysis of certain gases in the air content, the correct disposal method is to reduce the accident caused by leakage and people's lives And the necessary conditions for the loss of property, which put forward the higher requirements for gas detection and monitoring equipment. This paper starts from the type of sensor, analyzes its application in the early warning and accident disposal of gas leakage accident, The use of the relevant departments to achieve the purpose of attention.
2, gas sensor overview
Foreign from the 30's began research and development of gas sensors, China's gas sensor in recent years has also been a great development, technology matures. At present, the types of gases that need to be detected are also extended from the original reducing gas (h2, c4h, ch4) to toxic gases (co, no2, h2s, no, nh3, ph3).
A wide range of gas sensors, according to the use of gas-sensitive materials and gas-sensitive characteristics of different, can be divided into semiconductor, electrochemical, solid electrolyte, contact combustion polymer and so on.
2.1 Semiconductor gas sensor
This sensor is mainly used in semiconductor gas-sensing materials, since the advent of semiconductor metal oxide gas sensor in 1962 since the high sensitivity, fast response and other characteristics, has been widely used, has become the world's largest production of the most widely used sensor , According to the detection of gas-sensitive features of different ways divided into electronic and non-electronic two.
Leakage sensor The resistive semiconductor sensor is operated by detecting the change of the gas-sensitive element with the gas content. The main use of metal oxide ceramic materials. The characteristics and application of this sensor is relatively wide. For example, the wo3 gas sensor can detect nh3 concentration range of 5ppm-50ppm, zno-cuo gas sensor is very sensitive to 200ppm co.
Non-electronic semiconductor gas sensor is the use of gas-sensing components of the current or voltage with the gas content of the principle of change, mainly mos diode and junction diode, and field effect tube gas sensor. Detection of gas mostly hydrogen, alkanes and other combustible gases.
2.2 Solid electrolyte gas sensor
Solid electrolyte gas sensors use solid electrolyte gas-sensing materials for gas-sensing components. 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 this gas sensor has high conductivity, good sensitivity and selectivity, it is widely used, only after the metal oxide gas sensor. Such as measuring h2s yst-au-wo3, measuring nh3 nh4 + caco3 and so on.
2.3 contact with the combustion gas sensor
Can be divided into two kinds of direct contact combustion and catalytic contact combustion. Its working principle is: the gas-sensitive material in the state of electricity, combustible gas oxidation combustion or oxidation of the catalyst under the action of the combustion, the heat generated so that the heating wire temperature, so that its resistance value changes, measuring resistance changes to measure the gas concentration The This sensor can only measure combustible gases that are insensitive to incombustible gases. For example, the pt filament coated with active catalyst rh and pd made of the sensor, with a broad spectrum of characteristics, both can detect a variety of flammable gases. The contact combustion gas sensor is very stable at ambient temperature, and the vast majority of the lower explosive limit of flammable gas detection, commonly used in petrochemical, coal, kitchen and other flammable gas monitoring and alarm.
2.4 Polymer gas sensor
Leakage sensor Gas sensors using polymer gas-sensitive materials have been developed in recent years. Polymer gas-sensitive materials in the face of a specific gas, the resistance, dielectric constant, the material surface acoustic wave propagation speed and frequency, material weight and other physical properties change. Mainly phthalocyanine polymer, lb film, polyisobutylene and so on. Because of its easy operation, simple process, good room temperature selectivity, low cost, easy combination with microstructure sensor and surface acoustic wave device, it has important role in the detection of toxic gases and food freshness. The According to the gas-sensing properties of the materials used, such sensors can be divided into: by measuring the resistance of gas-sensing materials to measure the gas concentration of the polymer resistance of the gas sensor; gas-based materials to absorb gas when the formation of concentrated batteries, measuring the electromotive force to determine Gas concentration of the battery gas sensor; according to the polymer gas-absorbing material to absorb gas after the sound wave in the material surface propagation speed or frequency changes in the principle of the surface acoustic wave gas sensor; and according to polymer gas-absorbing material to absorb gas Weight changes made of quartz oscillator gas sensors and so on. Polymer gas sensor with a specific gas molecules with high sensitivity, good selectivity, and simple structure, can be used at room temperature, can supplement the lack of other gas sensors.
3, gas sensor applications
The gas sensor installed in the flammable, explosive, toxic and harmful gas production, storage, use and other places, the timely detection of gas content, early detection of leaks, in a slight leak to reach early warning, so that personnel can be disposed of, and Gas sensor and protection system linkage, so that the protection system in the gas reaches the explosion limit before the action, the accident loss control to a minimum. Can also be combined with computer technology to form intelligent systems. In the gas concentration is very low when you can detect, without having to go deep into the scene, in order to avoid the situation and cause unnecessary harm. In the gas leak accident after the rapid analysis of the nature of the gas, quickly and accurately provide the nature of pre-stored common gas and disposal plans and other information to determine the alert area, the organization of dangerous areas of the evacuation of the masses.
4, concluding remarks
Leakage sensor As early as 1995 commissioned by the Zhengzhou University of Technology designed and manufactured a set of carbon monoxide detection system, the system designed 40 measuring points, distributed in the blast furnace gas pipeline, drain water, boiler explosion-proof membrane, plant duty room, etc., although later because Electrochemical sensor damage rate is too high and the detection of the host (diskless 286 machine) damage and exit operation. But during the operation, many times on the slight disclosure of the success of the early warning, thus avoiding the disclosure continue to expand the risk of accidents.
With the new gas-sensitive materials continue to appear, the gas sensor intelligence has also been rapid development, I believe that in the near future, there will be more mature intelligent gas sensor system come out. When the gas leakage accident disposal situation will be greatly improved.