Limit Controls on chemical storage tanks

[bp99]

The AHJ has required an additional means of limit controls during filling(in addition to alarms and overflow pipe at top of tank)for large chemical tanks used for drinking water treatment. The AHJ basically wants a physical device to prevent the chemical from spilling out of the tank. To meet this requirement, we have designed a motorized valve (at the tank fill hook up) which is hardwired to automatically close during emergency situations when the tank high level alarm is initiated. Some engineers have opposed this design arguing that we are creating a more hazardous situation for the truck fill guy due to the back pressure in the truck hose when the valve closes. Does anyone have any other design ideas???

 

[jay165]

You could limit the speed at which the valve closes, which would avoid a pressure surge. Set the LSH level low enough on the tank so that the valve will be competely closed before a spill. You could also put the SDV on the outlet of the overflow line and allow the tank to dampen the pressure waves. Of course you have to ensure that the truck's pump won't overpressure the tank via a relief device of some sort.

 

[quark]

1. If you don't want to have any spills either from the tank or from the truck discharge pipe, take a branch from the truck discharge pipe, fix an auto on/off valve(normally closed) and put it back into the truck tanker( what I mean is a bypass arrangement). You can use one signal to close the filling line valve and the bypass valve.

2. If your supplier can supply less than full truck load, just get the required volume which can safely be accomodated in your tank.

3. If full truck load is compulsory, manage your inventory programme to get a truck when you have safe level in the tank. Don't laugh, this is the way I do it with fuel oil storage.

Regards,

 

[bp99]

Thanks for the suggestions! The limit control devide needs to be on our end of the system rather than on the truck side since we use different bulk carriers whose trucks are different. Our chemical suppliers charge us for full truck loads (44,000lbs ~4000 gal minimum), so we typically wait until there is a low level in the tank before calling in a new truckload.

I like the idea of limiting the speed of the motorized valve to avoid pressure surges. We currently have about 12 inches of "unusable" space below the overflow line and the high level limit. This would allow about 80 more gallons to pass through the closing valve before the tank overflows.