Water Tank Sizing

[landrover77]

I am designing a plant in which i have two pumps collecting water from a tank and then cirulating it through two condensers to recieve heat before passing through a heat exchnager connected indirecrtly to a coolign tower before returning the water to the same tank.

The pump flows are both around 120m^3/hr. pipe/condenser system volume ~ 4-5m^3.

I have looked with success to find an guidance / eqns relating to sizing the tank.

I presume there are some guidlines based on flow rate in and out of the tank and the volume of water in the entire system. can anybody help me in finding these?

many thanks in advance

 

[landrover77]

The Tank is situtated on a concrete base and effectively open to atmoshpere. Thus there is no vent. Whilst our current tank is glass fibre.

i don't have access to API 650 is anybody able to provide the typical equations

 

[MJCronin]

creed...

While bigger is usually better, there is no code or guideline to help you size the tank. This is a matter of design preference

If indeed this is a closed system and your only losses are evaporation, I would suggest 3 to 5 minutes pump capacity. (~360-600 m^3).

My opinion only

-MJC

 

[sshep]

In many closed loop cooling systems, the tank is simply a pressized vessel, often called an expansion drum, which is used to take up thermal expansion of water in the system. Pressurized suction reduces the circulating pump head to friction losses rather than pump design based pumping from atmospheric to desired pressure at highest point. Such ab expansion tank is often only connected by equalization line to the process flow- the flow returns to the circulating pump suction and doesn't even go through the tank. Such a tank is usually very small relative to system inventory. Level indication on the tank is included to detect if there are water leaks, and make-up water provision is included.

In your case, your system sounds pretty small, although the condenser duties were not stated which will determing the system volume via pipe and exchanger size. Because the circulating water will include some treatment chemicals for corrosion, you might be able to use your tank to save your treated water when the system is shut down. Therefore: the tank can be sized to hold the complete inventory of hot water in the circulating loop, plus level (or elevation design) to keep the pump suction flooded, and some small extra inventory to allow a few days between make-ups in the event of a small system leak and evaporation from your tank (a loss rate of 100liters/hr *2days =5cum). The water can't really go anywhere else except if there is a leak (or someone drains water), so the usual rules about how much reaction time is needed between normal and low (or high) level is not very important. You will still have the option to run the tank at a higher level when the system is in operation.

This is what I think anyway, others may have a different view.

best wishes,
sshep