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.

Bernoulli System AB is based in Lund, Sweden. www.bernoulli.se