Application analysis of toxic gas detector in industry
According to the hazards, we divide toxic and harmful gases into two major categories, flammable gases and toxic gases. Due to their different nature and hazards, their detection methods are also different. The first is the classification and principle of toxic and harmful gas detectors: the key component of the gas detector is the probe.
The combustible gas detector is the most dangerous gas encountered in industrial occasions such as petrochemical industry. It is mainly organic gases such as alkanes and certain inorganic gases: such as carbon monoxide. There must be certain conditions for a flammable gas to explode, that is: a certain concentration of flammable gas, a certain amount of oxygen, and sufficient heat to ignite their ignition source. These are the three elements of an explosion, which is indispensable, that is, lack of any of them. Conditions will not cause fire and explosion. When combustible gas (steam, dust) and oxygen are mixed and reach a certain concentration, it will explode when it meets a fire source with a certain temperature.
We refer to the concentration of a flammable gas as it explodes when exposed to a fire source, referred to as the explosive concentration limit, referred to as the explosive limit, and is generally expressed in%. In fact, this mixture does not explode at any mixing ratio but requires a concentration range. When the concentration of flammable gas is lower than the LEL (lowest explosive limit) (the concentration of flammable gas is insufficient) and its concentration is higher than the maximum explosive limit of UEL) (the lack of oxygen), no explosion will occur. Different flammable gases have different LELs and UELs. This must be taken into account when calibrating the instrument. To be on the safe side, we should generally issue an alert when the flammable gas concentration is between 10% and 20% of the LEL. Here, the 10% LEL says. As a warning alarm, 20% LEL is called a danger alarm. This is why we call the combustible gas detector the LEL detector.
It should be noted that 100% displayed on the LEL detector does not mean that the concentration of the flammable gas reaches 100% of the volume of the gas, but that it reaches the LEL formula 100%, which is equivalent to the lowest explosive limit of flammable gas. % LEL = 4% volume concentration (VOL). In work, the detector that measures these gases by LEL is our common catalytic combustion detector.
Its principle is a two-way bridge (commonly called Wheatstone bridge) detection unit. One of the platinum wire bridges is coated with a catalytic combustion substance. No matter what kind of flammable gas, as long as it can be ignited by the electrode, the resistance of the platinum wire bridge will change due to temperature changes. This resistance change is the same as The concentration of flammable gas is a certain proportion. The concentration of flammable gas can be calculated by the instrument's circuit system and microprocessor.
Thermal conductivity detectors that directly measure the volume concentration of combustible gases are also available on the market. At the same time, there are already LEL / VOL combined detectors. The flammable detector is particularly suitable for measuring the volume (VOL) concentration of combustible gases in an oxygen-deficient (oxygen-deficient) environment. Toxic gases can exist in production raw materials, such as most organic chemical substances (VOC), or in by-products in various stages of the production process, such as ammonia, carbon monoxide, hydrogen sulfide, and so on. They are the most dangerous risk factors for workers. Such hazards include not only immediate harm, such as physical discomfort, illness, death, etc., but also long-term harm to the human body, such as disability, canceration, and so on. The detection of these toxic and harmful gases is an issue that our developing countries should begin to pay full attention to.
Detection of toxic gases Depending on the type of gas, for the detection of specific toxic gases, we use the most specialized probes. It can include the above. All probes listed include the photoionization detectors described in the previous two chapters. Among them, the most common method for detecting inorganic gases, the technology is relatively mature, and the best comprehensive index is the potentiostatic electrolytic method, which is often referred to as the electrochemical probe. The composition of the electrochemical probe is: two reaction electrodes-a working electrode and a counter electrode, and a reference electrode are placed in a specific electrolyte, and then a sufficient voltage is applied between the reaction electrodes to make the transmission coated with a heavy metal catalyst The gas to be measured in the film undergoes a redox reaction, and then the current generated during the gas electrolysis is measured by the circuit system in the instrument, and then the microprocessor therein calculates the concentration of the gas.
Currently, electrochemical probes that can detect specific gases include: carbon monoxide, hydrogen sulfide, sulfur dioxide, nitrogen monoxide, nitrogen dioxide, ammonia, chlorine, hydrogen cyanic acid, ethylene oxide, hydrogen chloride, and so on. The VOC detector can be used with the photoionization probe described in the previous chapter. Oxygen is also a factor that requires great attention in industrial environments, especially in closed-loop environments. Generally, we call the oxygen content over 23.5% as excess oxygen (enriched oxygen), and it is easy to explode at this time; while the oxygen content below 19.5% is oxygen deficiency (hypoxia), at this time it is easy for workers to suffocate and comatose To death. The normal oxygen content should be around 20.9%. The oxygen detector is also a type of electrochemical probe. At present, we pay more attention to the detection of gases that can cause acute poisoning, such as hydrogen sulfide, cyanohydrin, etc., but we do not pay enough attention to the detection of gases that can cause chronic poisoning, such as aromatic hydrocarbons and alcohols. The health and safety hazards of workers are not inferior to the gases that can cause acute poisoning! They can cause cancer and other invisible conditions, affecting workers' life and health. In addition to the reasons for this phenomenon, the lack of suitable organic gas detectors that can detect lower concentrations on the market was also an important reason. With the development of scientific and technological standards and the improvement of people's health awareness, people are no longer satisfied with merely "happily going to work and going home safely", but are pursuing a higher quality of life and living conditions. People are not only concerned about today's work, but also about tomorrow-life after retirement. Therefore, we must continuously introduce new ideas and new ideas in the work of industrial health and industrial safety in order to not only avoid the immediate dangers, but also pay attention to avoid future tragedies, all of which need to pass regulations and improve the quality of people Continuously improved and enhanced. The above is an analysis of the application of toxic gas detectors in the industry.