Chemical sediments control

[JuanMC]

Hi!

There are several titanium-plates heat exchangers in our facility. By one side of the exchanger (cool fluid) runs non-treated water, taken directly from a little dam. By the other side runs treated water that cools an electric generator.
Due to the level variation in the dam, sometimes we have a sediment clogging in the exchangers, reducing the total heat transfer.

The manufacturer suggests to use sodium hydroxide or sodium carbonate, for biological growth, or nitric, sulfamic, citric or phosphoric acid to control all the other sediments.
However, we discharge the non-treated water to a river, i'd like to have a quick guideline to choose a treatment and control the chemical wastes. ¿Does anybody know where could i find something like that?

Thanks,

JuanMC

 

[bimr]

The ususal practice is to use a filter to remove the sediment and then to periodically chlorinate the filtration system for control of biological foulants.


The following methods will not work, get better advice:
"The manufacturer suggests to use sodium hydroxide or sodium carbonate, for biological growth, or nitric, sulfamic, citric or phosphoric acid to control all the other sediments."

 

[JuanMC]

I won't say the name of the manufacturer... i'll just say that it's name has a greek character and it produces heat exchangers around the world.
The mentioned methods are specified on the heat exchanger's manual.

Regards,

JuanMC

 

[bimr]

Improved filtering protects plate heat exchangers against fouling

http://www.engineerlive.com/europea...s-plate-heat-exchangers-against-fouling.thtml

Water sources are becoming more and more polluted, says Bernoulli System AB. This demands improved filter capacity to protect process equipment from fouling and clogging and subsequent lower output and higher operating costs.

Early tests showed clearly that surface deposits could not be prevented by over sizing of the heat exchangers.
Attempts were made with a simple back flushing systems (flow reversal) combined with chlorination to protect the sensitive plate heat exchangers from fouling. Chlorination is environmental reasons prohibited in Europe today.
It was discovered that solids could not settle on the plate surface if the shear rate was sufficiently high. The required shear rate corresponds to about 0.8 bar pressure drop for a normal plate type.
One problem remained -- the narrow gap between the plates makes them sensitive to clogging.
The modern philosophy for designing cooling plants using any natural water such as sea or river waters is: Use automatic filters such as Bernoulli Filters with filtration of 20--50percent of the plate gap, and locate them close to the exchangers. Design plate heat exchangers for a minimum pressure drop of 0.8bar, corresponding to approximately 70Pa shear stress. Operate the heat exchanger at full flow rate. Use the same standby philosophy for pumps, filter or heat exchangers.
The fouling rate in a heat exchanger operating in natural waters can be limited to insignificant values if a shear stress of 70kPa can be maintained during operation.
Blockage in exchanger inlet is prevented by the use of Bernoulli Filters, for example.

 

[sbush]

Bimr is correct. Chemical treatments alone cannot prevent the build-up of sediments from forming. I've seen this firsthand at a paper mill where two separate heat exchangers fed from the same source were becoming fouled with sediment. There is also evidence of localized pitting of the stainless interior occurring in area with sediment build up. The chemical supplier for the mill recommended that a filtration system be installed on the feedwater, and that is why I was called in. We are currently designing an 800 gpm pressure sand filter system with a chemical coagulant filter aid.

S. Bush

http://www.water-eg.com