Why is thermal conductivity principle very popular for Hydrogen measurement in analyzers?

 

It is popular because it is cheap and well known. It does however have the condition that the background stream MUST remain constant. If the background gas concentration can also change constituents, then the thermal conductivity of the stream will change and you will get an error in your Hydrogen purity reading. To be sure you are measuring Hydrogen only, will require use of a Gas Chromatograph to separate the hydrogen from the other gases in the stream.

Another option to using thermal conductivity for this type of measurement is to use the stream density, and one company makes a device that uses centrifugal energy as the basis for this measurement. Again the same limitations apply.

IR cannot be used to measure Hydrogen as the hydrogen molecule is NOT diatomic (Two different atoms in the same molecule).

Ian Verhappen
[email protected]

 

Hydrogen is supposed to be non reactive in natural environment except for the production of H2O. In any chemical reaction, heat is either adsorbed or released. Because Hydrogen is a simple molecule, and when it reacts, it is always complete combustion, the amount of heat released in this reaction is almost always the same.

Thermal conductivity principle is the most cheapest way of determining presence of H2 in air.

 

Hi..i would just like to ask. This is kinda confusing. From what I've learned hydrogen (H2) is one of the diatomic group (like O2).
Thank you and I hope to receive your reply..
Good day.

Best regards,
Yleana

 

But the two molecules are the same so they do not have a vibrational frequency that can be measured in the Infrared spectrum. They may be two molecules, but they are the same molecules, hence not considered diatomic.

Ian Verhappen
[email protected]

 

There are three companies that make a device that uses the tuning fork principle to measure gas density or SG. SG or density can be converted to gas concentration for a hydrogen percent measurement. These do not share the TCD requirement for reference gas, although they do have similar limitations on the gas stream composition. (ie. the gas stream must be binary or psudo-binary) to be species specific. Many reformers, cat crackers, hydrotreaters and FCC’s units have a gas stream composition that is close enough to a psudo-binary for an accurate measurement. Of course the H2 in air measurement in the power industry , H2 generation from PSA, or from cryogenic H2 production are a cake walk for this type of device.

It has distinct, documented advantages over the TCD unit in the area of oil resistance, thermal drift characteristics, warm up time, calibration time and response.

Jim Scott
Yokogawa
[email protected]

 

Why is thermal conductivity principle very popular for Hydrogen measurement in analyzers?

Thermal conductivity (often expressed as k, λ, or κ) refers to the intrinsic ability of a material to transfer or conduct heat. It is one of the three methods of heat transfer, the other two being: convection and radiation. Heat transfer processes can be quantified in terms of the corresponding rate equations. The speed equation in this mode of heat transfer is based on Fourier's law of heat conduction.
https://thermtest.se/