Model HTX

Thermocouple, Claus Sulfur Recovery Service, ATEX, IECEx

The Delta Controls Model HTX Thermocouple is designed to measure high temperatures under the extremely severe conditions of a Claus Thermal Reactor reliably and accurately for years without maintenance. The HTX is basically the same in form and function as the HTP but contains no welded components.


The HTX’s primary function is sensing the internal hot-face of the reactor lining to protect the vessel and its refractory lining from excessive temperatures.  The HTX design provides the best “up time” for plant operations and the lowest cost of temperature sensor ownership.

Claus Thermal Reactor 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 materials used in the HTX are chosen specifically to withstand this severe service.

This superior result is achieved by the mechanical design of the HTX which is the result of 40 plus years of evolutionary improvement. The thermocouple junction is maintained in a protected environment that subjects it only to the heat of the refractory. The thermocouple junction is isolated from the corrosive and invasive gases by using a constant, very low flow flush gas circulating past the junction. The flush gas is kept at a pressure higher than the maximum reaction vessel pressure to mitigate the migration of vessel gases through the primary well, body or seals. Any process gases that do enter are carried away by the flush gas. The flush gas flow has an insignificant effect on the accuracy of the temperature measurement.

All Delta HTX’s are built to meet each customer’s specific installation requirements, such as; thermocouple type, dry out/start up temperatures, nozzle size, insertion length, hazardous area classification and materials of construction. The HTX assembly is furnished complete with all necessary installation components including a HRW Refractory Well and HNP Nozzle Packing Kit. Installation tools are available (and recommended) to accurately produce the refractory aperture in the correct size and alignment needed by the Refractory Well and HTX thermocouple assembly. Nozzle insulation materials are made to meet the exact nozzle installation needs and dimensions.

Why HTX?

In Claus reactor service, typical industrial grade thermocouples have a reputation for failing shortly after start-up.  A Delta Controls thermocouple is designed to last from turnaround to turnaround and beyond by addressing the unique problems involved with temperature sensing in a Claus Thermal Reactor. 

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
  • 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
  • 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
  • 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)

Third Party Approvals

70131733Ex db IIB+H2 T2 Gb
Class I Zone 1, AEx db IIB+H2; T2 Gb
Certificate of Compliance
Sira 18ATEX1044XII 2G
Ex db IIB+H2 T2 Gb
EU Declaration of Conformity
IECEx SIR 18.0012XEx db IIB+H2 T2 GbIECEx Certificate of Conformity

Additional Information


Thermocouple, Claus Sulfur Recovery Service, ATEX, IECEx

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