Cooling Tower Blowdown

[fdomin]

Blowdown from a cooling tower must be pumped to a 600 psig water pipeline.
Is there any disadvantage in locating blowdown (and pump suction) in the tower basin instead of placing it downstream of recirculating pumps?
It would be located opposite of make-up water inlet to avoid pumping fresh water.

 

[JeffHofacre]

I feel the best location for the blowdown is at the discharge from your condenser. This way the water is still under pressure and your blowdown pump can be sized slightly smaller and since the water is warm this reduces load on the cooling tower. (I realize this is very small.)

We have designs which can just dump straight from the cooling tower to a waste pond and others that take from the condenser discharge. If you are working on an existing plant I would look at what is the lowest cost option for installation. Do you really want to add a pump in your cooling tower basin? This may get in the way during basin cleaning or cooling tower maintenance.

Of course, your idea to put the inlet opposite your fresh water inlet is a good one. Ideally you will blowdown your highest concentrated water. To reduce blowdown try to use cooling water for uses such as running ashes. Especially if you are currently using fresh water to run ashes.

 

[DeltaCascade]

Of course, ensure that you do not overly complicate or loose control of blowdown rate...a key cooling water qulaity control parameter ...

 

[quark]

Placing of blowdown in the tank is OK. However fresh water shorcycling is a tricky thing. (though I also practise the same thing of opposite freshwater and blowdown, your make up is on the water surface and blowdown is from bottom. So there will be a good mixup of water before fresh water being drained out. Any comments anybody?)

5 cycles of concentration can be maintained without much damage to the system for blowdown.

Regards,

 

[aliansari]

It is better to discharge blowdown from the basin due the following facts, in my opinion.

1. If pumps are precisely sized to meet process cooling demand, downstream draw off could result in some kind of flow starvation at any specific process location.

2. If hot water is discharged, it may create problems in certain localities, having more strict environmental regulations. It is quite common to discharge water NOT MORE THAN 3 C, hotter than the receiving water streams.

Ansari

 

[matin]

put the transfering pump for the blowdown in cooling water return (to cooling tower)for following resons.
1- less pumping power you need. becuse of the positive pressure (CWR pressure)at the suction of your transfering pump.
2- since you are using pump to transfer the blowdown (600 psig), I believe, it would be for using the blowdown in another process or transfering to a long distance discharge area. however for both case cooling water return temp. is not a critical case, regarding the process or environmental regulations (in the case of discharge area, long distanse gives enough time for cooling the blowdown)
3- lowering the load on cooling tower
4- lowering chlorin consumption

 

[davefitz]

I think that the pump used to pressurize teh blowdown to 600 psig probably is a high speed pump with a significant NPSH requirement. This NPSH might not be available from the sump,and the extra 10-15 psi head available at the condenser outlet flange should provide adequate NPSH.