AIR POLLUTION CONTROL Graduated Straightening Grid

Graduated Straightening Grid Technology (GSG)

Graduated Straightening Grid (GSG) technology is a significant step forward in SCR design. By improving velocity distribution and flow direction into the face of the first catalyst layer, problems of dust accumulation, erosion and uneven catalyst loading, which lead to shortened catalyst life, increased pressure loss and downtime, can be prevented.

Until now the traditional solution has been to use many large turning vanes along with a straightening grid placed immediately above the catalyst. The 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.

After two years of research and development using scale and computational modeling, the GSG has been thoroughly tested and now successfully deployed in the field. The GSG 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. The GSG has been shown to be 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.

We are very excited about this new patent pending technology, which has also been applied to air heaters and economizers.

Figure 1: Standard Vanes SCR Velocity Profile (CFD results)

Figure 2: GSG SCR Velocity Profile (CFD results)

Figure 3: Velocities Measured at Catalyst Face with Traditional Vanes
(Experimental Model)

Figure 4: Velocities Measured at the Catalyst Face with GSG
(Experimental Model)

Velocity Statistics

Traditional Turning Vane Velocity Distribution at Catalyst Face Statistics (Exp)
62% of velocities within 10% of average
93.9% of velocities within 20% of average

GSG Velocity Distribution at Catalyst Face Statistics (Exp)
95% of velocities within 10% of average
100% of velocities within 20% of average