What Is Methane Gas?
- Methane is a colourless, tasteless, odourless gas and has the chemical formula CH4 – methane is the main component of natural gas. It is made up of one atom of carbon and four atoms of hydrogen.
- Methane is produced naturally by the process of methanogenesis and is found under the ground and in seabed locations – it is commonly used in chemical industries and also for electricity generation.
- Methane is non-toxic but highly explosive
- Production of Methane gas occurs naturally in many industries including waste disposal, mining, oil and gas, petrochemical and the energy sector.
Where is Methane Gas Used?
- Methane gas is commonly used in chemical industries and is used to refine petrochemicals. It is also used as a fuel and is burned in gas turbines or steam generators to produce electricity.
- Methane is widely used domestically for heating and cooking in homes
- Methane is the main component of Liquefied Natural Gas (LNG) and Compressed Natural Gas (CNG). Methane is generated by the decomposition of biodegradable solid waste as well as animal and human waste. It is therefore commonly present in landfill sites and sewage treatment works.
- As Methane is an incredibly potent, hazardous greenhouse gas it is important to not only manage storage and production but also re-use and recycle the gas. Methane emissions represent a profitable solution to global climate change.
- The most common anthropogenic sources of methane gas are agriculture, mining, landfills and natural gas oil activities.
Why Is Methane Gas Dangerous?
- Methane is not generally considered a toxic gas however, it is extremely flammable even in low concentrations when mixed with other chemicals – it is also an asphyxiant as it will displace oxygen. This is particularly dangerous in confined spaces working.
- In order to create a fire/explosion, you need three things:
- An ignition source and
- A fuel
- Take away the oxygen and you remove the risk of explosion – in contrast, high levels of oxygen will cause fuels to burn faster and more vigorously. For an explosive atmosphere to exist, a certain ratio of oxygen and fuel must exist. The ratio differs depending on the fuel.
In the gas detection industry, such ratios are known as lower explosion limits (LEL) and upper explosion limits. (UEL) in %Vol
Methane Gas: LEL & UEL
- LEL (Lower Explosive Limit) is defined as “the minimum concentration of a particular combustible gas necessary to support its combustion in air.” Concentrations below this level will not burn. The UEL (Upper Explosive Limit) is defined as “the highest concentration (percentage) of a gas or a vapor in air capable of producing a flash of fire in presence of an ignition source.”
- The range between LEL and UEL is referred to as the flammable range and as the name suggests is when fire/explosions will occur.
- As can be seen from the table, the LEL for methane(HC) is 5% Vol and UEL is 15% Vol. Concentrations of 9% Vol are thought to be the most volatile. It may sound strange but concentrations above 15% Vol will not be explosive as the air is too saturated with methane. However, this is when asphyxiation can be just as hazardous.
- Our MSR sensor is calibrated on LEL scale i.e. 0-5% Vol = 0- 100% LEL therefore we prefer to set a alarm level or actuate exhaust fan at 25% LEL, which = 1.25% Vol (HC)CH4
- Asphyxiation becomes a risk when there are high concentrations of methane. This is because the methane displaces the oxygen. We need approximately 18% Vol oxygen to breath, levels below 16% Vol can be dangerous and levels below 10% Vol can cause immediate loss of consciousness and inevitably death. Working in confined spaces can be extremely dangerous if exposure to methane (or any other gas for that matter) is considered a risk.
Sensor Technology Used
- There are two technologies used to manufacture Methane Sensors, Catalytic Bead and Infrared sensor technologies.
- Catalytic Bead Sensors, infrared sensors, and are prone to being poisoned by silicone, lead, sulfur and halogenated compounds. They also require frequent calibration and although less costly than an Infrared sensor, require replacement on a more frequent basis. Because they are lower in cost, some end users still prefer to use Catalytic Bead Sensors as a Methane Sensor, especially where there could be other combustible solvent vapors present that the Catalytic Bead Sensor will detect, while an Infrared sensor would not.
- As a Methane Sensor, Infrared sensor technology has now become the dominant Methane Gas Sensor in a fixed gas detection system for combustible detection of hazardous levels of methane in air. Because an Infrared Methane Sensor does not require oxygen to operate, Infrared Methane Sensors can also be used in a 0-100% by LEL methane or other hydrocarbon gas process gas environment, such as in natural gas pipelines, utility applications and bio gas applications.
- A Catalytic Bead Methane Sensor works as a simple Wheatstone bridge circuit, where an active and reference filament wound from platinum wire with a palladium based catalyst changes the proportional resistance between the active and reference bead of the methane sensor in proportion to the amount of methane detected in a background of air.
- Infrared Gas Detection instruments that use infrared methane sensors often use two wavelengths of infrared energy, with one active wavelength used for gas absorption, and the other as a reference wavelength to compensate the output signal of the Infrared Detection system for the effects of temperature and humidity.