Model HTP

Thermocouple, Claus Sulfur Recovery Service

The Delta Controls Model HTP 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 HTP’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 HTP 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 HTP are chosen specifically to withstand this severe service.

This superior result is achieved by the mechanical design of the HTP which is the result of over 45 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 HTP’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 HTP 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 HTP thermocouple assembly.  Nozzle packing materials are made to meet the exact nozzle installation needs and dimensions.

Why HTP?

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.  These problems are:

  • Breakage due to shifting refractory – The wide refractory thermowell 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 thermowell. – A nitrogen purge effectively sweeps any diffusing gases away from the thermocouple junction. The low-level purge does not significantly affect the temperature reading.


  • Worldwide standard for protecting Claus reactors
  • Remains accurate under extreme conditions
  • Protects and extends the useful life of refractory and improves reactor up-time
  • Over 30 years of proven results in hundreds of installations worldwide
  • Keeps working accurately in sulfur service long after other thermocouple designs fail or read incorrectly
  • Safe; triple sealed. Block valve optional
  • Accuracy is continuously verified
  • Integral refractory dry out thermocouple reads accurately to 1°F (0.6°C)
  • Worldwide service and parts capability
  • Also used in process incinerators, POX units, and coal gasifiers
  • Special designs to 10,000 PSIG (70 MPa) or 4000°F (2200°C)
  • ATEX version available


  • Thermocouple Types: B, R, S,C, & T (others available)
  • Body/Flange Material: SA-516-70 Carbon 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)
  • Mounting Flange: ANSI 6”/150# (150mm) (Std.) 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 (1700°C) basic; 0 to 4000°F (2200°C) optional.


The Type HTP Thermocouple 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, acid gases, etc. Operating temperatures may be in excess of 3000°F and under pressure. Normal operating vibration will not cause sensor failure.

The most common application is to protect the refractory in Claus thermal reactors and sulfur burners in sulfur acid plants. Other applications include hydrogen burner systems, water gas generators, coal gassifiers and various kinds of POX units.

The design of the Model HTP was a result of careful attention to design detail, 30 years of experience, and many field installations. Materials used in the HTP are critical. For example, the ceramic parts exposed to the process are various blends of alumina, zirconia, MgO, and other materials. All conceivable care is taken during the application and fabrication of these units. The long service life and reliable operation of the HTP thermocouple sensor is a result of attention to detail.

Additional Information


Thermocouple, Claus Sulfur Recovery Service

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