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GSG™ Graduated Straightening Grid

Fuel Tech Air Pollution Control TechnologiesGSG™ Graduated Straightening Grid

Patented GSG Graduated Straightening Grid Technology Applied to Areas in the Power Plant from the Economizer to the Air Heater

GSG Graduated Straightening Grid - Fuel TechThe turning vanes were tuned to achieve an even velocity distribution, while the straightening grid below straightened the flow direction. This system requires exact spacing and angling of turning vanes during SCR construction to ensure required flow distributions are met. This traditional solution is also extremely sensitive to changes in the upstream flow distribution since any changes to the system require remodeling and retuning of the vanes to maintain the required distributions.


Until Now, the Traditional Solution Used Many, Large Turning Vanes With a Straightening Grid Immediately Above the Catalyst

After years of research and development using scale and computational modeling, GSG technology has been thoroughly tested and now successfully deployed in the field. The GSG system combines the turning vanes and straightening grid into a single sloped grid. By greatly increasing the number of turning elements, it is theorized that the flow is not broken up, but is caused to turn with a minimum of detachment and recirculation, which can be seen when using large turning vanes. GSG systems have resulted as an extremely robust flow corrective solution. It is much less sensitive to upstream flow distributions than traditional solutions so that the catalyst and catalyst performance are protected even when the unit is not running at optimum design conditions (such as economizer bypass) or if boiler or ductwork changes are made in the future. The GSG’s simple design also makes precise spacing and angling of turning vanes unnecessary.


Fuel Tech's Unique GSG Provides the Following Advantages:

  • Improving velocity distribution and flow direction

  • Reducing problems associated with:

    • Dust accumulation

    • Erosion

    • Uneven catalyst loading

  • Extended catalyst Life

Velocity Statistics

Traditional Turning Vane VelocityGSG velocity model Distribution at Catalyst Face Statistics  

  • 62% of velocities within 10% of average

  • 93.9% of velocities within 20% of average

GSG Velocity Distribution at Catalyst Face 

  • 95% of velocities within 10% of average

  • 100% of velocities within 20% of average





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