In Furnace Sampling, FEGT, HVT

ESA uses a High Velocity Thermocouple (HVT) Probe for temperature measurement and flue gas sampling in the primary furnace. By varying probe depth and location, temperature profiles and species concentrations can be mapped at various locations in the furnace. This information is very useful in diagnosis of operational problems and design of equipment for improving operation.

The HVT probe is constructed of 3 concentric tubes of stainless steel. The probe features a thermocouple protected by a porcelain radiation shield and an aspirating system to draw in the flue gas. This takes place in the innermost tube. The two outer tubes are occupied by cooling water which makes 2 passes. Probes with length in excess of 20 feet can be constructed for deep penetration into the furnace. The thermocouple allows easy recording of temperatures while the flue gas is pumped to ESA's gaseous analyzers.

Furnace exit gas temperatures are measured using an HVT probe. A high velocity flow is set up across the thermocouple by aspirating the flue gas through the inlet at the refractory tip. The main advantage of using an HVT probe is that temperature measurements are not affected by radiation losses. A thermocouple placed in the flue gas stream is heated by the flue gas by convection and simultaneously cooled by radiating heat to the relatively cool boiler tubes. The resulting equilibrium temperature is, therefore, lower than that of the flue gas. The refractory housing of the HVT probe establishes a high velocity flow across the thermocouple. This increases the convective heat transfer coefficient between the flue gas and thermocouple and decreases the radiative heat transfer coefficient, resulting in a thermocouple temperature closer to the true bulk gas temperature.

Temperatures in the main furnace can also be measured with an optical pyrometer.

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