IR Sensors for Methane Monitoring

Why an Infrared (IR) Sensor is the preferred option over other technologies for methane detection

as detectors that can detect and quantify industrial and environmental gases play a vital role in ensuring the safety and efficiency of a wide variety of processes and applications.

Natural gas, which mainly consists of methane, is widely used in power generation. However, methane is a greenhouse gas, extremely flammable, and can form explosive mixtures in air Methane leaks can have devastating results, so detecting leaks is vital during natural gas extraction transportation, and power generation.

In the chemical industry production of syngas, methanol, acetic acid and other commodity chemicals depend on methane gas sensors to ensure that processes are operating safely and efficiently Measuring atmospheric levels of methane is also becoming increasingly important for monitoring changing environmental conditions that may affect the environment and human health.

There are a wide range of commercially available methane gas detectors and sensors, all with their own advantages and disadvantages:

Flame ionised detectors (RDs)
FIDs use a hydrogen flame to ionise the methane gas.The ionised gas conducts an electrical current, which is measured to determine the gas concentration. Although FIDs are fast and accurate, they require the presence of a hydrogen source, an open flame, and a clean air supply As a result, FIDs are not suitable for some applications.

Catalytic Sensors
Catalytic sensors catalyse the reaction between methane and oxygen, resulting in heat generation and a change in resistance in the sensor, from which the methane concentration can be calculated. Although catalytic sensors are inexpensive and robust, they require the presence of oxygen to operate and are susceptible to poisoning, sintering, and contamination.As a result, regular calibration and replacement is required.

Semiconductor sensors
In a similar manner to catalytic sensors, semiconductor sensors react with methane, causing a change in resistance that is used to calculate the gas concentration. In common with catalytic sensors, semiconductor sensors are prone to contamination and poisoning.

Electrochemical sensors
Electrochemical sensors oxidise or reduce the methane at an electrode to produce a current, which is used to determine the gas concentration. Due to the contact between the atmosphere and the electrode, corrosion and chemical contamination can occur, and electrochemical sensors need frequent replacement.

Infrared sensors
IR sensors use an IR beam to detect and quantify gases present in the atmosphere. Although infrared sensors are slightly more expensive than some other sensors, they are robust and long-lasting. As a result, infrared sensors have become the dominant technology for detecting a range of gases.

A nondispersive infrared (NDIR) sensortypically consists of an IR source, a sample chamber, a light filter, and an IR detedorTypically, a second chamber containing a reference gas runs in parallel to the sampling chamber IR light is directed through the atmospheric sampling chamber to the detedorThe methane gas in the sampling chamber absorbs light at specific wavelengths. A filter in front of the detector blocks out light that is not at the desired wavelength, so the detector measures the attenuation at the specified wavelength only, which is used to determine the concentration of methane present.

IR sensors have several advantages over other gas detection technologies: IR sensors have a built-in failsafe system, which comes from the fact that small signals represent high concentrations of gas, while in other sensors small or no signal means zero or low gas concentrations. If the detector becomes obscured or fails, no IR radiation will register and an alarm will be raised.

Also, unlike other available types of sensors, IR detectors do not interact with the methane gas.The gas and any contaminants in the atmosphere only interact with a light beam As a result, the detector is protected from damage and has a long lifespan.

NDIR sensors are also able to be more specific than techniques that require the gas mixture to be burnt. In some cases, NDIR sensors even allow the detection of one flammable gas component in the presence of another However, this does produce a limitation that users cannot determine whether a gas mixture is flammable or not.

In common with other sensors, IR detectors provide fast response times and accurate results. While catalytic, semiconductor, electrochemical sensors, and FlDs all require the target gas to be present in concentrations below the lower explosion limit, IR sensors can accurately measure gas concentrations of zero to 100 per cent. In addition, IR sensors do not require oxygen or external gases to operate.

IR sensors have some disadvantages: they can be adversely affected by changes in temperature and pressure. However, advanced IR sensors now provide pressure and temperature compensation, resulting in reliable and durable sensors with few drawbacks. IR sensors have become the detection method of choice for methane and other industrially and environmentally relevant gases.

From an article by:

Edinburgh Sensors

October 2018


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