NOx Reduction Applications: Cracker Furnaces
Ethylene cracker furnaces are utilized in chemical process operations where heavier feedstocks, such as naphtha, are cracked to provide mainly ethylene and propylene. Gas burners provide the heat for the cracking operation, and the heat is then recovered downstream in a convection section to produce steam.

Application of Selective Catalytic Reduction (SCR) for NOx reduction from ethylene cracker furnaces presents unique challenges. Flue gas temperatures before the convection section are too high for SCR and installation at conventional SCR temperatures requires splitting the convection section, an expensive and often complex option, which also requires significant downtime.

The CRI low-temperature technology allows location of the SCR catalyst completely after the convection section, where temperatures are typically 320-450° F (160-230° C), which allows a simple installation with no impact on the existing furnace.

Two low-temperature locations are possible:

1. If space is available, the low-temperature SCR catalyst can be located directly on top of the furnace in the same duct space.

2. Alternately, the low temperature SCR catalyst can be installed in a separate reactor house further downstream.

Operating flexibility

Due to the broad SCR operating temperature range capability of the CRI catalyst technology, the full range of feedstocks can be cracked in the same furnace without impacting SCR performance, even when very low flue gas temperatures result.

Decoke

During decoke operation, flue gas temperatures can be significantly higher than normal operation. The CRI SCR catalyst is stable and active up to 750° F (400° C), which is above the highest decoke temperatures.

Minimum impact on existing equipment

The CRI SCR system can be designed for low-pressure drop which can allow use of the existing fan, saving a significant capital cost.