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Thermal conductivity analyzer selection

2022-07-22136

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Thermal conductivity analyzer

1. Introduction

The material thermal conductivity of each gas differs, and its thermal conductivity (or thermal conductivity) is related to its molar mass and temperature and has little effect on the gas pressure. When gases with different thermal conductivities are mixed, the thermal conductivity of the mixture depends on the concentration of its components. So the proportion of each component gas can be determined.

The principle of thermal conductivity measurement is particularly applicable when the gases to be measured have significantly different thermal conductivities and one of the following three conditions is fulfilled.

1. the gas mixture contains only two components. For example, the carbon dioxide content in nitrogen or the hydrogen content in nitrogen.

2. the gas mixture contains more than two components, but the concentration of only two components changes.

3. A gas mixture contains more than two components and the background gas contains two or more components but with similar thermal conductivity, which corresponds to two components mixture. For example, when measuring hydrogen or helium in oxygen/nitrogen.


2. Measurement principle

The sample gas flows through the thermal conductivity cell, which is heated to a constant temperature of 60°C and a thermistor above the film to a constant temperature of 130°C. This creates small cavities below and above the film into which the measurement gas can diffuse. The heat loss due to the thermal conductivity of the sample gas is compensated by heating, and the voltage required to maintain a constant temperature of the film is measured for the thermal conductivity of the measured gas.


3. Anti-corrosion protection

Some gases form compounds with moisture that can corrode with the sensor, thus damaging the measurement accuracy and eventually destroying the measurement capability. Therefore, MZD sensors use stainless steel and O-rings made of FPM or FFKM. And a 4µ thick protective coating of halogenated polymer layer is applied to the surface of the measurement sensor. This coating does not affect the excellent measurement performance of the sensing unit and effectively protects the sensor.

To strongly corrossive gas, measuring cell is made from Al2O3 , glass and quartz. It's can be used for high contents of Cl2 , HCl, H2S, SO2, etc.


4. Condensate and dust control

The sensor is protected with a sintered glass of µm pore size, through which gas molecules can pass, while liquid water molecules can not penetrate. In addition the sintered glass protection layer reduces the dependence on the gas flow, so that the sample gas flow can be 10 to 400 L/h through the thermal conductivity cell.

High temperature sensor with thermostat-controlled gas paths up to 180°C can be used for high dew points and/ or to avoid possible salification.


5. Built-in integrated flow meter

Built-in flow measurement with arithmetic compensation by gas composition.


6. Cross-sensitivity compensation

The presence of interfering components in the sample gas is an important factor in generating additional error, which is almost negligible for most gases when the concentration is low. Complex gas mixtures can be fully determined by cross-sensitivity modeling and other measurements. Even IR and humidity measurements can be used to compensate for the arithmetic, allowing for an integrated solution for determining homonuclear and rare gases in complex gas mixtures.


7. Built-in multiple gas measurement modes

The instrument has 16 built-in binary gas mixture measurement modes and calibration data, so that different gases and gas mixtures can be measured using the same instrument.


8. Measurement range

Measuring gas

Background Gas

Measurement range

Min. range 1

Min. range 2

Gas mixtures

Hydrogen(H2)

Nitrogen (N2) or air

0% – 100%

0% – 0.5%

98% – 100%

Yes

Hydrogen(H2)

Argon (Ar)

0% – 100%

0% – 0.4%

99% – 100%

Yes

Hydrogen(H2)

Helium (He)

20% – 100%

20% – 40%

85% – 100%


Hydrogen(H2)

Methane(CH4)

0% – 100%

0% – 0.5%

98% – 100%


Hydrogen(H2)

Carbon dioxide (CO2)

0% – 100%

0% – 0.5%

98% – 100%


Hydrogen(H2)

Oxygen(O2)

0% – 100%

0% – 0.8%

97% – 100%


Carbon dioxide (CO2)

Nitrogen (N2) or air

0% – 100%

0% – 3%

96% – 100%

Yes

Carbon dioxide (CO2)

Argon (Ar)

0% – 60%

0% – 10%

Yes

Argon (Ar)

Oxygen(O2)

0% – 100%

0% – 3%

96% – 100%

Yes

Argon (Ar)

Carbon dioxide (CO2)

40% – 100%

80% – 100%

Yes

Argon (Ar)

Xenon (Xe)

0% – 100%

0% – 3%

99% – 100%


Nitrogen (N2)

Argon (Ar)

0% – 100%

0% – 3%

97% – 100%

Yes

Nitrogen (N2)

Hydrogen(H2)

0% – 100%

0% – 2%

99.5%– 100%

Yes

Oxygen (O2)

Nitrogen (N2)

0% – 100%

0% – 15%

85% – 100%

Yes

Oxygen (O2)

Argon(Ar)

0% – 100%

0% – 2%

97% – 100%

Yes

Oxygen (O2)

Carbon dioxide (CO2)

0% – 100%

0% – 3%

96% – 100%

Yes

Methane (CH4)

Nitrogen (N2) or air

0% – 100%

0% – 2%

96% – 100%

Yes

Methane (CH4)

Argon (Ar)

0% – 100%

0% – 1.5%

97% – 100%

Yes

Neon (Ne)

Argon (Ar)

0% – 100%

0% – 1.5%

99% – 100%


Helium (He)

Nitrogen (N2) or air

0% – 100%

0% – 0.8%

97% – 100%

Yes

Helium (He)

Argon (Ar)

0% – 100%

0% – 0.5%

98% – 100%

Yes

Krypton (Kr)

Argon (Ar)

0% – 100%

0% – 2%

96% – 100%


Deuterium gas (D2)

Nitrogen (N2) or air

0% – 100%

0% – 0.7%

96% – 100%


Deuterium gas (D2)

Helium (He)

0% – 100%

0% – 5%

70% – 100%


Sulfur hexafluoride (SF6)

Nitrogen (N2) or air

0% – 100%

0% – 2%

96% – 100%


Nitrogen Dioxide (NO2)

Nitrogen (N2) or air

0% – 100%

0% – 5%

96% – 100%


Extinguishing gas (R125)

Nitrogen (N2) or air

0% – 100%

0% – 5%

98% – 100%


 

10. Typical applications

Thermal conductivity gas analyzers are an effective method for measuring a component of two gas mixtures (with very different thermal conductivities). It is mainly used to measure the content of hydrogen (H2), carbon dioxide (CO2), argon (Ar), etc. Some typical applications are listed below. 

- Measurement of hydrogen (H2) content in synthesis gas of ammonia plant

- Hydrogen (H2) purity measurement in hydrogenation plants

- Measurement of hydrogen (H2) in pure hydrogen (O2) and hydrogen (H2) in pure oxygen (O2) in the process of hydrogen and oxygen production by electrolysis of water

- Measurement of hydrogen (H2) content in hydrocarbon gases

- Monitoring of hydrogen (H2) and carbon dioxide (CO2) content in hydrogen-cooled generator sets 

- Measurement of hydrogen (H2) in chlorine gas (Cl2) in chlorine production processes

- Measurement of carbon dioxide (CO2) content in the combustion flue gas of the furnace cellar 

- Argon (Ar) content measurement in air separation units

- Monitoring of pure gas production, e.g. helium (He) in nitrogen (N2), argon (Ar) in oxygen (O2)

- Measurement of sulfur dioxide (SO2) content in sulfuric acid and phosphate fertilizer production processes



Application case list:

No.

Industry

measurement tasks

Measurement

Measurement Range

Carrier gases

1

Chemicals

Hydrogen as impurity

H2

0-0,5%

Ar, N2, O2

2

Chemicals

Hydrogen production by electrolysis

H2


O2

3

Chemicals

Ammonia (NH3) production

H2


NH2, Air

4

Chemicals

Fertilizer production methanation furnace and ammonia (NH3) converter export

H2

50-100%

N2, CH4, NH3, Ar

5

Air Separation, Chemicals

Hydrogen purity

H2

99-100%

N2, O2, HC, Air, SIH4

6

Air Separation, Chemicals

Argon refining process

H2


Ar

7

Metallurgy

Annealing furnace H2, N2 anti-oxidation

H2


N2, ppm O2

8

Metallurgy

Blast furnace gas

H2

0-20%

N2, CO, CO2, H2O

9

Metallurgy

Blowing Oxygen Furnace (BOF) 

H2

0-10%

N2, O2, H2O, O2, CO, CO2, Fuel gas

10

Metallurgy

Pig iron for steel plants

H2


11

Metallurgy

Heat treatment H2, N2

H2

0-5% ; 10%; 20%

N2, ppm O2

12

Metallurgy

Protective Gas

H2


Air, N2

13

Metallurgy

Hydrogen removal, monitoring of H2 discharge from the metal melt

H2


N2

14

Chemical & Pharmaceutical

Quality Inspection

Impurity


Ar

15

Glass production

Flat glass production

H2

0-10%

N2

16

Food & Beverage, Medical Technology

Gas Mixing




17

Semiconductor Industry

Monitoring Process

H2

0-8%

Ar

18

Power plant

Turbine Generator

H2

0-100%

CO2 or Ar

19

Power plant

Turbine Generator

Air

0-100%

CO2 or Ar

20

Power plant

Turbine Generator

H2

90-100%

Air

21

Power plant

Turbine Generator

H2

90-100%

Air

22

Power plant

Turbine Generator

H2


Air

23

Nuclear Power

Nuclear energy, monitoring deuterium in the air (D2)

D2

0-5%

D2, Air

24

Nuclear Power

Nuclear power plant, vacuum dragging reconstructor after condenser

H2

0-5%

N2, O2

25

Nuclear Power

Nuclear power plants, hydrogen propagation analysis to avoid flammable atmosphere

H2

0-20%

Air

26

Petrochemical

Acetone, phenol, isopropylbenzene production

H2

50-100%

N2, CH4

27

Petrochemical

H2 production from isocyanate in feed gas

H2

0-1Vol%

CO

28

Petrochemical

Aromatic lift gas tube, N2 header and regulator hopper

HC, H2

0-15% 0-1%

НС

29

Petrochemical

Caprolactam production H2 purity

H2

70-100%

N2, ppm NH3, ppm CO

30

Petrochemical

Hydrocracker unit cycle gas compressor

H2

50-100%

Hydrocarbons

31

Petrochemical

Hydrocracker make-up gas

H2

50-100%

Hydrocarbons

32

Petrochemical

Hydrocracker downstream collection point

H2

50-100%

Hydrocarbons

33

Electrical industry

Welding

H2


N2

34

Life Sciences & Medical Applications

Nitrous oxide anesthetic dose N2O

N2O


N2

35

Automotive, Power Generation, Renewable Energy

Fuel Cell

H2


O2, N2





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