Hydrocarbon stop valve

[ER_Azza]

Hi All

The bunded jetty I am working at has draining system for rainwater to a storage tank.
(The jetty has fuel import facility, so some traces of hydrocarbon initially)
There is a bypass valve to drain to the sea.

Normally during rain, it will initially drain to the tank.
After 10 min at least, with no trace of hydrocarbon, a manual (bypass) valve is opened to direct the rainwater to the sea.

I was thinking of replacing the manual valve with an "automatic" valve.

Anyone knows any product to suit this task?

 

[LittleInch]

Your issue is how to detect what might be very small amounts of hydrocarbon. Anything which has a "sheen" will be visible and lead to accusation you are dumping contaminated water into the sea. Draining water from a bunded area direct into the sea or water courses has risks and hence it is normally a manual operation when someone can confirm there is no visible contamination. what do you do when there is contamination?

Normally to do this automatically you need to install an oil /water interceptor able to result in oil in water in the region of 5ppm.

But they cost money and you need to prevent them being subject to excess flow in a rain storm so still need some sort of holding tank / area.

Or you could pump the water through a cyclone filter which removes any oil.

What is the driver behind changing something which works?

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

 

[ER_Azza]

Hi LittleInch

Currently, it is a manual operation as what you have stated on the potential of carry over, even a minute amount.

The drivers for the change are:

1. The manual operation of the valve only happen on dayshift. On nights, heavy rain, either it will go to the holding tank (there is a sump pump), and/or jetty gets flooded. No operators at night to divert water to the sea.

2. Current holding tank (65kL) not big enough to cope with the heavy rain. Can't put any bigger tank due to space constraint.

 

[LittleInch]

How does the water get out of the tank?

Gravity or pump?

Either way so long as you can control the flow you need to run it through an interceptor.

Places like garage forecourts have a similar issue and use fairly cheap devices.

Things like this

https://www.kingspan.com/gb/en/products/water-management/fuel-oil-separators/forecourt-separators/

Search forecourt oil separators.

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

 

[ER_Azza]

HI LittleInch

I have attached a schematic.

This is a bunded jetty with fuel transfer facilities, so the occasional (seldom & very minor) spill from hoses connection and disconnection.
Potentially small amount of hydrocarbon on the jetty surface.

During rain, rainwater is drained from the bunded jetty via the under jetty pipe and goes to the sump pump. The pump pushed the rainwater to the holding tank.
If water draining to the tank is clear, the valve to the sea might be open, manually.
Tank is drained via a vac truck.

Issue one: Tank could not cope due to heavy rain
Issue two : And/Or no one on night shift to operate the valve.
Issue Three: Minute amount of oil + 99.9% rainwater that goes to the tank (65kL) will be removed by the vac truck to be separated at an external facility. Very expensive exercise (based on the total volume).

Your proposal using Aquaoil forecourt separator seem to be an option. But not sure if the design is suitable for the heavy rainwater flow rate.
I have attached a 2nd schematic with the separators at both ends. What's your thought?

With the propose Aquaoil forecourt separator

 

[LittleInch]

I think you are better off going via the tank to the interceptor so that you have a buffer storage for heavy rain. Plus if there is any large oil spill you have somewhere to store it as the interceptors can get overwhelmed / fill up and pass over a large spill into the drain. The more sophisticated interceptors have level alarms etc which close the outlet valves.

A lot of systems don't have this so people end up having a large separator to deal with high rain flow, but if you have a buffer tank then you can probably have a smaller unit.

You really need to do a design based on good rainfall data including peak rain for 15mins for your catchment area etc to size your system accordingly.

There always need to be some compromise about the heaviest rain and flow capacity of the interceptor, but having your tank helps a lot and if a bit of ponding in the bund is acceptable then max flow is based on your sump pump.

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

 

[ER_Azza]

Thanks mate. Appreciate the input and suggestions.

Wondering out there, what is piping material used in this situation.
The draining system uses PVC, as mostly would be rainwater.
It's very wet in winter and normally very dry in other seasons.
I am not sure - I thought they design this way because they do not want stagnant water in the pipework - (can't drain fully, and therefore corrosion).

 

[LittleInch]

PVC is fine.

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