Benefits:

• Improves furnace O2 balance (reduces excess O2).
• Reduces CO emissions at furnace exit.
• Reduces water wall corrosion.
• Reduces slagging.
• Helps determine applicability of SNCR by measuring exit gas temperatures.
• Reduces NOx emissions.
• Improves steam temperature balances.

How it works:
All in-furnace measurements are taken with a high velocity traverse (HVT) probe (also known as a suction pyrometer). Up to 25 feet long, this probe functions by aspirating furnace gases to be measured through the array CEM equipment, enabling the sampling of any number of gas species. HVT traverses incrementally across the furnace exit. Cooling, service water of approximately 15 gpm protects the HVT equipment in the furnace environment.

To ensure accuracy, exit gas temperatures use shielded thermocouples that prevent measurement bias from flame radiant heat levels.

A gas sample is then drawn over the tip of the thermocouple at a full flow velocity of 500 fps. Once the thermocouple reaches a stable temperature, it is recorded (T max). The velocity is then reduced to one-fourth the flow of the full flow measurement. Once again, the thermocouple is stabilized and the temperature is recorded (T 1/4). Finally, the flow is shut off across the thermocouple tip, providing a zero flow reading (T 0). This tells us the efficiency of the suction pyrometer. Once that is known, the actual gas temperature can be obtained by adjusting the T-max temperature that was measured at full flow conditions.

Uses of in-furnace measurements:
These measurements can be used to determine and diagnose combustion-related problems that may cause uneven steam temperatures, uneven metal temperatures, an imbalance in O2 or unusual furnace temperature. They can also diagnose slagging problems and aid in reducing water wall corrosion.

Typical adjustments which can be made:

• Adjustments to burner air shrouds for balancing airflow.
• Overfire air port adjustments to reduce high CO levels at furnace exit and improve mixing.
• Fan damper adjustments to balance secondary airflow from side-to-side and back-to-back.