Best way to filter cooling water

[StoneCold]

We have a cooling water system that contains about 2500 gallons of water total. The water is pumped from a "cold well" tank out to the plant at a rate of 300 gpm. The water returns to a "hot well tank" where it is pumped from the hot well tank through a "Lakos filter" Which is kind of a cyclone that concentrates solids and takes 10% of the water and solids as a side stream. The sludge flow is filtered through a bag filter and returned to the inlet of the hot well pump. Once the water makes it through the filter it then goes through a cooling tower. The water gravity feeds back to the hot well.

The problem with the system is filtering off the solids. We have had the "Lakos filter" for about three years and it's ability to remove the particles in our system is marginal. The bag filter plugs in about 8 hours. It appears to blind off with scale and biological material. Increasing the biocide in the system did not seem to help much. I installed four single can cartridge filters to replace the bag filter but they are plugging quickly right now and I don't know if that situation is going to improve after a few days of catching up on the solids.

I am at a loss as to what to do next. I have looked at the Orival self cleaning filters but they only filter down to about 75 microns and I would like to clean the water up down to about 10 microns if possible.
I have thought about making my own sand filter but I am not sure that would work any better.

What is everyone else doing?

Thanks
StoneCold

 

[orenda1168]

StoneCold:

A couple of thoughts about your cooling water........

1) Have you considered bag filters of varying micron retentions in a series alignment to ease the blinding off of only one low micron filter.

2) To my experience, sand filters have a nominal retention of about 30 microns without use of a filter aid such as cellulose. I suspect that cartridge filters will continue to give you the same pluggage as you've seen to date. A better bet may be diatomaceous earth filtration which should routinely pull out 5 micron or smaller particulate.

3) You indicate that much of the plugging material is scale and organic residue. Is it appropriate to revisit whatever chemical treatment program is in place for the cooling water to find a way to minimize both residues?

Orenda

R. J. Kersey

http://www.orenda-tech.com

 

[StoneCold]

Orenda1168
Thankyou for your response. We are looking into changing our biocide treatment to help decrease the amount of biological material we have to filter.
I will look into the diatomaceous earth filters.
I have not messed with more bag filters. I have considered pleated filters to try to get the surface area up.

Thanks
StoneCold

 

[katmar]

I have seen plenty of sparkling clean cooling towers using sand filters, but also some dirty ones. If a properly operated sand filter does not keep the tower clean then there is something wrong with your chemical treatment, or maybe a leak from the process into the CW.

A sand filter is so much easier to clean that I would certainly use them in preference to anything else. If you must go for a finer filtration, then install cartridges as polishing filters after the sand filter.

 

[cub3bead]

All of the ones I have installed were dual media gravity filters with integral backwash storage tanks and air scour capabilities. Nominal sizing criteria is 3% of the CW circulation rate. Nominal performance is 10 NTU or better in the CW. Filter effluent overflows back to the tower basin.

 

[rzrbk]

Cleaning the tanks and tower basin at the next opportunity might help, as there can be a large amount material that accumulates over time on the bottom. This can get periodically stirred up and sent down the line and would overwhelm filters.

If the cooling tower has a water deck which is exposed to sunlight, I have seen some success in cutting bio growth by installing a shade over the deck.

Also, 10 microns sounds like a very small partical to worry about. Unless this is required for the downstream equipment it might be worthwhile to check on filtering larger particles and let the small ones circulate. This would allow a smaller overall filter housing size.

 

[StoneCold]

cub3bead
What do you mean by a "dual media gravity filter"? Are you talking about sand and diatomatious earth?

Thanks
StoneCold

 

[cub3bead]

Anthracite and sand media.

Pressure filters can be used but the tanks are more expensive because they need to be ASME code stamped for operation above 15 psig.