hydraulics for a FOG vortex separator

[RRichardson]

I have this idea to adapt what is common in storm water practice (vortex separation), to fats, oils and grease screening before being pumped into anaerobic digesters. The only difference is that I have no intention of capturing the volatile stuff, the FOG. The vortex will be used to capture heavy particles, which I suspect will be better than the existing rock baffle.

So I've been pouring over lots of vortex equations trying to size the vertical column pipe. Trucks will empty tanks at about 250 gpm into a 6-inch pipe that will enter tangentially into a vertical column pipe. The 6-inch pipe will be about mid-way. If the vertical pipe is 4 feet in diameter with about 8 feet in elevation head between the truck and vortex separator, I'm estimating the strength of the vortex to be about 0.008 ft^2/s with an elevation difference between the center and outside radius about 1.3 feet. Am I doing this right? Is there a better way to size this column?

 

[RRichardson]

As a follow-up to my previous post, I figured out what parameters are actually needed to design this vortex separator: angular velocity and settling velocity. The whole purpose of the vortex is to allow heavy debris to settle. So I found a technical article on the ASCE library that will allow me to calculate the steady state condition.

Angular Velocity Formula for Turbulent Vortex Chamber Flows

http://ascelibrary.org/doi/abs/10.1061/(ASCE)HY.1943-7900.0000547

Unfortunately, I have not been able to reproduce the results they obtained using the empirical formulas they provided. The dimensional analysis does not appear to be correct... but I'm still trying with the thought that I'm making some error along the way.

 

[bimr]

One would not expect what you have described to work. "Trucks will empty tanks at about 250 gpm into a 6-inch pipe that will enter tangentially"

For best results, you would have to esablish a steady state flow condition which will not happen with a periodic truck dumping scenario.

Most of the vortex systems that I have witnessed all have some type of paddle device to maintain the vortex. One unit called grit king does not have a paddle.

http://www.hydro-int.com/UserFiles/downloads/UK_Grit_King_Leaflet.pdf

In regards to storm water systems, I have noticed that manufacturers of various gadgets are making treatment claims without independent verification. It is a buyers beware situation.