Liquid Tank Design: Design Solution for 100gpm Flow & 10min Retention

[mr_jeffo]

I have 2 locations of approx 80”w x 80”l x 112”h to install a tank(s). The tank must meet the following criteria:
1. Influent: 100gpm continuous flow of ground water dosed with 12% sodium hypochlorite to eliminate ammonia
2. 10 minute minimum verifiable retention time in the tank during continuous flow before discharge

Any thoughts on designing this? There are no other restrictions in terms of baffling, tank materials, etc. It must fit in the space alloted, so I can't just create a large tank. I must be able to prove the 10 minute minimum time in the tank via a dye tracer test or similar (of the flow mass center). Plug flow or other theories can be assumed but only if the retention time can be field verified.

 

[Unrest]

What happens if you start by assuming any simple velocity profile through a pipe with the same volume as the tank and see what dimensions the pipe needs to have? That should give a first guess at the geometry of any baffles. Or just use a pipe.

Having a rough idea of the geometry would then allow you to check other things like diffusion, Reynolds number, back-pressure, etc.

 

[mr_jeffo]

Chlorine Contact Tank

As I see it, the available footprint is awkward for application, so I can't do with one tank in allotted footprint and would need two vertical tanks plumbed in series.My initial thought is two custom, baffled chlorine contact tanks for series operation where I direct size. Currently I currently have a single 64" tank 112" high with 1100 gal capacity. it is short circuiting in about 3.5 min at 25 gpm. Again I need 10 min at 100gpm. Through testing the current tank baffling is about 30% efficient.

By my calcs for the new system:
Contact Time = Theoretical Detention Time X Baffling Factor
10 min X 1.5 (minimum factor of safety by user) * (0.5 efficiency for baffles provided near inlet and along tank axis)
Ergo, TDT = 30 minutes
Q = 100 gpm = 13.4 cfm (assumes this is maximum flow capable of being pumped to the vessel)
V/Q = V/13.4 = 30 minutes
V = 402 cf = 3007 gal

Looks like 1500 gallons in each vertical tank in SHELL LENGTH. Can’t allow diameter to length ratio to get too weird on a custom job, or I’ll need to bump the 1.5 safety factor used above.

I'm looking for creative solutions in terms of baffling to extend the current retention time or a new design in limited space.