Sandtrap design Does anybody hav 4

[Joe591]

Sandtrap design

Does anybody have any type of guideline for the design of sandtraps? Much like what is pictured:

Perhaps flowrate and sand particle size and level of entrainment can be inputs and then various dimensions of the trap can be outputs. Maybe it can be very sophisticated, maybe it can be a bit rougher...

We have a boilerhouse with a ash conveyor that messes a lot. The sand trap ys just to catch all that rubbish from that. The blowdown already has its iwn solution so wont affect the sand trap at all.

 

[dik]

Why would you not build the interior wall less high, rather than put a hole in it?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Joe591]

Because holes in the intermediate walls can get blocked. I suppose if the sandtrap is being cleaned daily this probably not as big of an issue. The ones that ive seen have usually had progressively shorter walls.

Also the guys that do the cleaning are equiped with shovels. Shovel doesnt really fit through a hole so a hole will progessively fill up until its blocked. This is a third world country and the labour does not give a damn. Work ethic? Whats that?

 

[swazimatt]

I did a proposal for one once but never got the job. I think the theory was to reduce the flow in the first section to less than a certain velocity for a certain depth to allow sediment to drop out before it reaches the wall
(sorry for the fairly useless post, but keeps it active!)

 

[hydrae]

I remember seeing a chart that had particle size verses drop velocity for particles with specific gravity of 2.65 (silt/sand/pebbles in water) but I do not remember where that was.
So, targeting the particle size you wish to capture, then ensure flow across the bay is has a Reynolds number
less than 2000 after entry and exit effects. That would calculate the size of the box. The size of the box could be reduced
by providing inlet flow splitting system system that would shorten the inlet effect.
Since you say the box is cleaned daily, I assume it is drained for the cleaning. If so, sloping the bottom towards the drain can aid in cleaning
and a steep enough slope and high draining velocity; it can be self cleaning by opening the valve.

 

[zelgar]

You can probably find a lot online searching for settling basin design.

 

[1503-44]

Its Stokes law for settling velocity

You want longitudinal velocity in the trough slow enough that the longitudinal travel time <= the particles vertical travel time down to the tank bottom. You must calculate settling velocity.

http://personal.kent.edu/~amoore5/FST_L_11.pdf

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[Joe591]

Thanks, for all the replies. This is certainly enough to get something done.

@Zelgar: Settling basin design is definitely bearing better fruit than anything else I've tried so far.
@1503-44: stokes settling definitely got me some good results. The only problem is just trying to figure out what the max and min particle size is, but I'll try a few things and see what happens.

 

[LittleInch]

Or fit a cyclone?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Haydre is on the right track. Try bracketing the density, not so much the size.
Should work something like this.

Particles that float will never drop, so you have to skim those, which is why you have holes and not a weir. You can skim everything with sg<1

Lite particles have a big Cd/density ratio, so they don't settle as fast as they run. You'll need a screen over the holes to catch those that run out the trough length before they can settle.

Plot trajectories (or actually only the angles of them) verses densities.

Cd is proportional to diameter, ie volume and drop velocity is proportional to weight, resulting in Vx, being proportional to trough velocity and Vy proportional to density, both Vx and Vy form a particle velocity vector. Vr, the resultant velocity vector, and its vector angle, Ø will be >= to the same angle formed by the height and length of the trough for all particles that settle in the trough. The angle will be less (a flatter trajectory) for those that do not settle.

Cd-x is proportional to the square of Vx, so keep trough velocity as small as possible.




--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[GeoEnvGuy]

Hi there, call the precast concrete product suppliers in your area for a septic or sewage holding tank.