Almost all combustible gases can be detected using sensors based on the catalytic combustion principle.
In locations with multiple combustible gases, the selection of a combustible gas alarm should prioritize safety and cover the most stringent conditions. It is recommended to prioritize a general-purpose catalytic combustion sensor alarm that can respond to multiple combustible gases, using the gas with the lowest lower explosive limit (LEL) as the calibration and alarm threshold setting benchmark to ensure timely warnings for all combustible gases. Here, the lower explosive limit refers to the LEL concentration corresponding to the lower explosive limit of the measured gas; for example, 5% VOL for methane corresponds to 100% LEL, and 4% VOL for hydrogen corresponds to 100% LEL.
The working principle of a catalytic combustion sensor: Combustible gas enters the sensor and undergoes a flameless combustion reaction with oxygen in the air and the catalyst inside the sensor. This reaction generates heat, causing the temperature of the detection element to rise, thus affecting the resistance value of the platinum wire. This resistance change is directly proportional to the concentration of the combustible gas. In other words, this sensor outputs a resistance change signal based on the concentration of the corresponding combustible gas, thus deriving a standard curve.
What are some common combustible gases?
1. Liquefied Petroleum Gas (LPG): Obtained from petroleum processing or oil and natural gas extraction, its main components are propane, propylene, butane, and butene. Gaseous LPG is heavier than air, with a specific gravity 1.5-2 times that of air.
2. Natural Gas: Natural gas is a gaseous hydrocarbon produced from the long-term underground deposition of ancient biological remains, undergoing slow transformation and metamorphic cracking. It is flammable and is often found alongside crude oil extraction in oil fields. Natural gas is stored in porous rock layers at depths of approximately 3000-4000 meters. Its main component is methane, and it also contains small amounts of ethane, butane, pentane, carbon dioxide, carbon monoxide, and hydrogen sulfide.
3. Methane (Gas): Primarily composed of methane, a flammable gas, colorless and odorless, sparingly soluble in water, less dense than air, and prone to explosion when mixed with oxygen or air at a certain temperature in a confined space.
4. Toluene: Toxicity: Classified as low toxicity. Toluene is tested for both toxicity and flammability (specific testing objectives must be confirmed with the client).
5. Coal Gas: Primarily composed of carbon monoxide, hydrogen, alkanes, alkenes, and aromatics. Coal gas is toxic because CO and aromatics can bind to hemoglobin in the blood, causing oxygen deficiency, leading to unconsciousness or even death. Even at low concentrations, it can cause dizziness, nausea, and collapse.
Note that some catalytic combustion sensors cannot detect flammable gases such as diesel and acetylene. The main components of the flammable gas must be specified before purchase.