Due to presence of solid particles in boosted seawater and considering sensitivity of electrolysers as the plant heart, it is required to purify the inlet water from any solid particle that may cause damages for the electrolyzers in filtration section; based on our extensive experiences in supplying EC package in Iran, normally it is required to remove all solid particles bigger than 500 micron. In normal cases, 2 self-cleaning filters are applied to remove solid particles of seawater; 1 in operation and 1 in stand-by. The stand-by filter is isolated manually by closing relevant inlet/outlet manual valves. If that is the case, the Manufacturer recommends emptying the filter completely; fill and then empty it with fresh water, in order to remove last traces of salts contained in seawater, and, finally, leave filter empty until it is placed in use.

 

Auto-backwash filter in seawater applications contains filtering elements normally constructed in Duplex or Supper Duplex SS. The filtering elements are mounted as a tube sheet, without moving clearances. During filtration, the raw seawater enters the filter shell and the inner tubes. Solids are left behind on the inner walls of the filtering elements, while the seawater passes through the filtering mesh towards the filtered seawater compartment and hence to the outlet nozzle.

 

As soon as the differential pressure across the duty clogged filter reaches the set point of the high-pressure (normally 50 kPa), the backwash sequence is activated. The filter motor starts to rotate backwash assembly and the automatic on/off backwash outlet valve is opened.

 

The backwash assembly is therefore positioned in a consecutive manner under the raw seawater opening of each element. Due to the differential pressure between the filtered sea water compartment and the atmospheric pressure downstream the backwash valve, a reversal flow is established across the filtering elements, so that the seawater removes and carries the solids out of the filter to drain.

 

After completion of this cycle provided that pressure loss value is lower than the pre-fixed one the motor-reducer is deactivated and the blow-down valve is closed.

 

It is noticeable that during the backwash sequence, approximately 10% inlet flow is discharged through the flush out valve, while the outlet pressure slightly decreases, but this will not cause any problem to the electrolyzers because the flow indicators and controllers maintains constant seawater flow-rate to each Generator.

 

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