Storm Water Treatment

[makeup]

I've just been involved in a FEED study for the treatment of storm water released from bunded areas. The final report recommended a pumped solution that is: Water would be gravity fed to a pump and then passed through a parallel plate separator before going to public drain. The pump offered total control over which water would leave the site. In short, the client hated the solution(cost) and wants a gravity feed solution only (no pump). Unfortunately the site is not flat and the bunds are at the top of a 30 degree slope. At the bottom of the slope is a public road, drain and a fence. OK in order to achieve gravity fed solution we must put the separator below the bund water levels. This puts the separator 5m from the fence and road. Now in this position calcs show that we can get water to the separator quicker than I can get water from it. Thus we must restrict the flow to the separator. This means that water will spend longer in the bund and the bund level may wet the bottom of the tanks (12000m^3 each). Can anyone tell me or point me in the direct of information that says whether this is an issue. To me this doesn't sound right, but the client seems to think that allowing water under the tanks is not a problem?????? Thanks for any assistance

 

[HeinrichK]

What volume of water are we talking about. Would a surge drum between bund and separator help you out?

Are they regular CS, atmospheric, ambient temperature storage tanks?

How often would you expect to have the tanks exposed to high rain water level? what level of rain water (above tank bottom) is it?

Corrosion might be a problem here if it occurs regularly. And if they are empty, they might start to float!

 

[makeup]

The tanks store hydrocarbon, they have floating roofs as far as I am aware. The client suggests that they never empty a tank completely? so floating is not an issue. Now that the client has rejested the pumped solution for removing storm water, we will be trebling the drianage time thus storing water for longer, thus potentialy wetting the bottom of the tanks more often. A surge drum would help albeit that space here is at an absolute premium and its an idea still to be considered. To give a better idea of the layout. Image standing with your back to a perimeter fence and looking up a 20 degree slope to the top of the bunds 35m away. Vertical height from where you 10m, bund depth 4m.

 

[IFRs]

Water under the tanks is undesirable, but it is the owner's choice to balance the cost/benefit.