Advantages of adding filters in cooling tower 1

[Brian2903]

What're the advantages or disadvantages to add filters in cooling towers?
And why some cooling towers have no filters?

 

[TD2K]

Cooling towers process a large volume of air and all the solids in the air get scrubbed out by the liquid.

That gets circulated through your cooling system and can contribute to fouling of heat exchangers.

Major disadvanage of filters off the top of my head would be the loss in circulation if you have a slipstream filter back to the sump (what water goes through the filter doesn't go through the system) or the pressure loss if it's an inline filter on the supply/return header, either full or partial flow. I think most filters are partial flow, full flow would be very large and expensive.

 

[bimr]

Sidestream cooling towers are used to remove suspended matter. The bane of cooling towers, with relation to efficient heat transfer is suspended solids. These solids can originate in the raw water, in the process, in the piping, from the atmosphere or from internal biological growth.

The suspended matter will concentrate in the cooling tower in direct proportion to the cycles of concentration.

The cooling tower manufacturer will specify a maximum suspended solids concentration in the cooling tower. A typical maximum is approximately 50.

So if you have 5 mg/l in the raw water, you can operate with 10 cycles of concentration.

If you have 25 mg/l in the raw water, you can operate for only 2 cycles unless you want to add a sidestream filter.

It is usually less expensive to use a sidestream treatment approach than to try to treat the entire makeup stream to the cooling tower.

 

[cub3bead]

bimr is right, keeping the tower TSS levels down is important, especially with the modern film fills. This type of fill is prone to cold end depositition which consists of a mixture silt and biofouling. The deposit restricts air flow through the fill. the net result is increased tower outlet water temperature.

Manual cleaning of fouled film fill is not fun nor inexpensive.

The rule of thumb is to size the sidestream filters for 2-3% of the circulating water flow rate. All of the towers that I have applied sidestream filters to have been able to keep the circulating water at less than 10 NTU. These towers were operating at 6-10 cycles. I like to use gravity dual media filters with air scour and integral backwash storage tanks for this service. Size them for about 5 gpm/ft^2 and cover the storage compartment.

If you don't cover the storage compartment UV will degrade the chlorine and let algae grow there. the algae then fouls the filter media, degrading filter performance and increasing backwash frequency.

You can use pressure filters but the cost of the code stamp for them adds $$$$.

 

[Brian2903]

So, we well water with low TSS is used. Side-stream filter may not be helpful, as chloride and hardness wiil be the limiting factor to the cooling tower

 

[25362]

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[cub3bead]

Not necessarily Brian2903.

If your tower is located in an area that is prone to windstorms with high levels of entrained solids you may need sidestream filters to prevent the porblems I mentioned earlier. I recall seeing a tower at a powerplant in SE New Mexico which had scrubbed enough sand out of the air that the solids were about 2' below the top of the basin. that tower used well water with less than 1 ppm TSS for makeup. The only thing that saved that tower was it was a cross flow with splash fill.

 

[Brian2903]

That means in a clean area like Iowa, and using good qulity well water(but mid-level hardness), filter shouldn't be very effective, right?

I was talking to a filter vendor last week, and they said filter won't help in cycles and chemicals reduction, so if I put enough chemicals to the tower, why I still need a filter?

Thanks guys, I'm very confuse on that.

 

[cub3bead]

I guess it depends on whether you are a belts and suspendeds type guy.

Do they do any farming near your plant site? If they do you can expect increased ambient particulate loads while the farmers are plowing and during harvests.