Model HTX

Thermocouple, Claus Sulfur Recovery Service, ATEX

The Delta Controls Model HTX Thermocouple application is to protect the refractory lining in Claus thermal reactors and sulfur burners in sulfur acid plants. The HTX is functionally identical to the Model HTP but with ATEX compliance. The weld-free design of the model HTX reduces the regulatory documentation burden by eliminating welding inspection requirements and certifications.


The HTX  is designed to measure high temperatures under the extremely severe conditions of a Claus thermal reactor. The atmospheres to be measured may contain hydrogen, sulfur, sulfur oxides, chlorides, ammonia gases, etc. Operating temperatures may be in excess of 2500°F (1372°C) and under pressure. The construction of the HTX is to withstand the vibration and shifting refractory often encountered in the Claus reactor.

Materials used in the HTX are critical; for example, the ceramic parts exposed to the process are various blends of Alumina, Zirconia and MgO materials.

Why HTX?

In Claus reactors, some thermocouples have a reputation for failing shortly after start-up. Delta Controls thermocouples are designed to last for multiple thermal cycles.

By addressing the unique problems involved with temperature sensing in a Claus reactor, the Delta thermocouple design is a proven reliable instrument. 

A few problems addressed are:

  • Breakage due to shifting refractory – The large diameter refractory well provides room for moderate shifts in refractory that would otherwise break the thermocouple.
  • Contamination of the thermocouple due to diffusion of process gases into the element containing thermowell. A low-flow continuous nitrogen purge effectively sweeps acid gases away from the thermocouple junction. The metered flow does not significantly affect the temperature reading.


  • Worldwide standard for protecting Claus Thermal Reactors
  • ATEX Compliant flameproof design
  • Maintenance free
  • Remains accurate under extreme conditions
  • Protects and extends the useful life of refractory and improves reactor online time
  • Over 40 years of proven results in installations worldwide
  • Keeps working accurately in sulfur service long after other thermocouple designs fail or become inaccurate
  • Triple sealed isolation block valve: Optional
  • Accuracy is continuously verified; self-diagnostic.
  • Optional integral refractory dry out thermocouple reads accurately to 1°F (0.6°C).
  • Also used in process incinerators, POX units, and coal gasifiers.


  • Thermocouple Types: B, R, S (others available)
  • Body/Flange Material: SA-516-70 Carbon & Stainless Steel
  • Trim, Bolting, and Seats: Stainless Steel
  • Protective Well: Blended Alumina Ceramic See Document 00-HRW01
  • Certification: C.S.A., NRTL/C (U.S. and Canada)
    II d G/D, EEx d IIB+H2 IP65
  • Mounting Flange: ANSI 6”/150# (Standard) Other sizes, types, ratings available
  • Flush Gas: N2 or clean, dry air
  • Working Pressure: 150 PSIG (10 Bar) at vessel skin temperature of 500°F (260°C)
  • Working Temperature: 0 to 3100°F (1704°C)

Additional Information


Thermocouple, Claus Sulfur Recovery Service, ATEX

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