Thermocouple with a Gas-tight Sapphire Protective Tube

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Emerson Process Management has introduced a Rosemount thermocouple with a gas-tight sapphire protective tube for use in gasification reactor applications. The thermocouple offers an extended operating life in difficult process conditions, where temperatures up to 3200°F, pressures up to 110 bar and aggressive gases often lead to the premature failure of standard thermocouples.

The Rosemount insulated thermocouple is enclosed within a protective tube manufactured from commercially grown sapphire, which is corrosion resistant and impermeable to gases. The improved design enables accurate and reliable measurements over an extended sensor life of 6,000 to 18,000 hours (depending on the application). This is typically three times the life of a standard thermocouple. By reducing the number of unplanned shutdowns due to sensor failure, production output is increased. Lifetime costs are also reduced since the longer operating life reduces the number of replacement sensors that are required.

A feature of the Rosemount design is the hermetic sealing of the sapphire protecting tube to the supporting bushing. In the event that the probe breaks, there is a redundant seal system that prevents toxic emissions from being released from the reactor. All of the seals are pressure tested with Nitrogen at 110 bar before delivery. The connection housing is made from forged steel, which avoids the leakage of hydrogen containing gases from the reactor.

The high-temperature thermocouple assembly can be used with the Rosemount model 3144P temperature transmitter for critical control and safety applications. The predictive thermocouple degradation diagnostics contained within the transmitter can further improve plant availability by providing an alarm when the resistance of the thermocouple changes. This enables maintenance staff to plan the change out of the thermocouple prior to an unplanned shutdown, minimizing cost and plant downtime.

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