Algae Buildup In a Heat Exchanger 1

[Murdul]

We have two plate heat exchangers. They have approximately 50 plates each. They are continuing to get an algae buildup inside which must be cleaned by dissasembling the heat exchangers. We have Bromicide in the tanks, but the algae builds up anyway. The algae is a orange brown color.

The tanks are used as a quench at the end of continuous steel sheet paint line ovens. One being a primer quench and the other a finsh paint quench. The temperature of the water is around 95oF into the heat exchanger, and 85oF out. Cooling water comes in at 66oF and out at 74oF.

Is there a fast effective way of killing and removing algae? A solution we could just run through the heat exchanger instead of taking them apart?

 

[orenda1168]

Murdul:

I suspect that the deposit in the exchangers is not an algae, which among other things requires nutrients such as phosphates and nitrates, as well a light, to flourish. More likely, it is a biological slime formed from whatever bacteria may be present.

I would suggest your consideration of a VERY healthy dose of a quaternary amine based biocide with recirculation in the exchangers for several hours if possible, as the surfactancy of these products will fairly well remove the existing deposits and kill off the biological cause.

Orenda

 

[DYV1973]

Try to increase velocity, as this create a higher shear rate and more turbulence. This might reduce the problem.

When (re)circulating over the PHE´s, try to flush backwards.
How often doe you need to clean the PHE plates.

 

[Murdul]

Currently we have to take the heat exchangers apart every month. The time interval between taking them apart is not so bad, but the amount of work and time it takes is.

We are also looking into doubling the plates that we have to increase cooling. This is why I am looking more into the problem now so hopefully we can spend less time dealing with the plates and let them run.

 

[DYV1973]

Why do you want to double the amount of plates?
If you require a higher volume to be cooled, you might need to double the amount of plates. But if you do, please make sure that you choose plates which create more tubulence (and therefore higher HTC, less fouling).

If you require the fluid to be cooled further down, then it might be better to add an extra "pass" to the PHE. You will have then plates in series as well. When you put more plates parallel, when you try to cool further down, you will increase the fouling problem. Adding an extra pass, might require changing the back plate of the PHE, but this can be done.

When you are changing the piping anyway, you might want to install the possibility to flush (or run) backwards.

 

[chief]

I will not speculate on the cause or the cure for your algae build up. But I have had lots of experience of cleaning plate type heat exchangers. One fast method, which is possible if there is a back pressure on your discharge outlet is to back flush the heat exchanger to a drain.
This is possible if you have flush valves fitted after the inlet valves, or remove an inlet spool. This method literally takes minutes.