The Dynamic Combustion Technique is superior to all other combustion techniques on the market when performing Total Sulfur, Total Nitrogen, or Total Chlorides analysis.  The explanation below uses sulfur analysis by chemiluminescence as the example case:

•   No 'coke' formation in the high temperature furnace:

  • This challenge is met by using a dual zone, high temperature furnace, which gives full control over the mixing of the sample with the gases.

  • To explain the above, we'll track back to the earlier analyzers that use a high temperature furnace to convert sulfur to detectable species like SO or H₂S.

    • Using the earlier design, the sample is injected into the hot region of the tube.

    • The liquid hydrocarbon sample (HC) will vaporize and expand 200-350 times in volume. This vapor pressure exerted by the sudden introduction of the sample will exert a backpressure on the incoming hydrogen gas.

    • The important requirement is that hydrogen gas must be in excess of the sample to avoid HC sample converting to coke. However, at the time that the sample is introduced, the vapor pressure momentarily stops the flow of hydrogen, causing hydrogen starvation, which results in some coke formation. (A pyrolyzer under these circumstances is nothing but a 'coke-factory' if a HC sample is injected in the absence of hydrogen.) 

    • If one uses air or oxygen instead of hydrogen, the HC sample will combust to form carbon dioxide, water and the oxides of sulfur. However, if the ratio of HC sample and air is not correct, there will be incomplete combustion and coke will still be formed.

  • The challenge to have no coke formation in the high temperature tube was met by C.I. Analytics as follows:

    • C.I. introduced a dual-zone electrical furnace. The first zone mixes the sample with excess air. In the case of sulfur analysis, the products of combustion at 1180ºC are carbon dioxide, water and oxides of sulfur (mainly SO₂).

    • These products pass via a capillary tube and enter the second zone. In this zone, referred to as the reductive zone, the oxides of sulfur are converted to mainly SO, H₂S and other unknown species that take part in the chemiluminescence reaction. 

    • The liquid sample is injected using the GC liquid valve, and the small amount of liquid sample passes through the vaporizer. Here, the sample is vaporized, and flows through the heated 1/8" tube to the oxidative side of the dual zone furnace. The expansion of the sample is at the vaporizer and not inside the tube.

    • After evaporation, the sample is mixed with excess of air. The 1/8" tubing that is heated acts as a mixing chamber for the air and the sample prior to introduction into the first zone of the dual-zone electrical furnace. These steps assure that there is no air starvation in the first zone.  

    • The products of combustion pass via another capillary tube, designed to control the proper mixing with the hydrogen. The hydrogen is introduced separately into this second zone, referred to as reductive zone. Again, this arrangement assures that there is no case of hydrogen starvation.   

    • By keeping the amount of sample to less than 0.5 :l for liquid HC samples, the chances of coking are minimized.  For parts-per-trillion analysis, the smart use of the GC-backflush system and/or the trap-technique, leads to a situation in which the amount of HC sample passed through the electrical furnace is kept small, even though the detection is in parts-per-billion level. 

    • In the first zone, oxidative zone, there will be formation of water and carbon dioxide. These do not interfere in the chemiluminescence reaction. The water is kept in vapor form by the low pressure in the reaction chamber by the vacuum pump.

• Complete conversion of organically bound compounds:

  • The Dynamic Combustion Technique, with the three-zone heated system, ensures equi-molar conversion of all organically bound elemental compounds in the hydrocarbon sample. Further, to avoid interference, all hydrocarbons are converted to water, CO, and CO₂.