Water coming on shipboard from different sources is never pure and contains impurities, some suspended, and others dissolved in it apart from some living organisms like bacteria, viruses, etc.

The impurities in water must be removed, either partially or fully, to make it suitable for crew consumption or use in shipboard systems.

The most commonly used process aboard ships to remove the suspended impurities from the water is filtration.

Filtration is a physical separation process in which solid particles in a liquid or gaseous fluid are removed by the use of filter medium that has a complex structure and permits the fluid to pass through but retains the solid particles.

There are different types of water filters can be use in water systems on ships, for instance mechanical filters, absorption filters, sequestration filters, ion exchange filters, reverse osmosis filters, or in combination.

The materials used for filter media can be paper, textile fibers, synthetic or metal wool, sintered metal, sand, carbon etc. Commonly filter design consist of a casing with inlet and outlet pipe connections and filtering material inside (see figure beloow). The raw water coming to the filter from the inlet and leaves the filter from the outlet minus any suspended impurities left on the surface or in volume of the filter material inside casing. Nevertheless, the filters have some drawbacks, as very fine impurities in colloidal form cannot be separated by them.

The most practical, cheapest and basic type of water filtration is a carbon filter to clean water. With a carbon filter process, water passes through activated carbon which is porous, trapping certain particles that are attracted to the porous material.

The size of particles attracted depends on the size of the pores or micron rating. However, not all particles are attracted to the active carbon filter. And at some point it loses its ability to attract particulates and must be changed in order to be effective.

Filter effectiveness is measured in terms of size of particles they can separate. This is referred to as microns, with the higher number being the worst or least effective and the smallest number being the best. Carbon filters should not be confused with sediment or sand filters, which are effective in removing sand, soil, silt and other sediment. Also need to know that filters in general are helpless in reducing hard water.

To the main particulars of filters commonly belongs: casing and filter material capacity (L), micron rating, water flow (/h), working pressure (bar), design pressure (bar), hydraulic test pressure (bar), PH value, filter lifetime (months), connection sizes, etc.

In figure beow shown carbon filter flow diagram and drawing. The raw water coming to the filter from the inlet 1 passes filter material 3 (activated carbon) inside casing and then filtrate water leaves the filter from the outlet 7.

An automatic pressure relieving device 6 actuated by the static pressure upstream of the valve which opens in proportion to exceeding pressure compare with opening pressure.

 

 

                                            a                                                                       b

Carbon filter flow diagram (a) and drawing (b)

1 – water inlet flange, 2 – pressure gauge valve, 3 – filter material (activated carbon), 4 – filter casing, 5 – air vent valve, 6 – safety valve, 7 – water outlet flange, 8 – casing flange, 9 – filter frame, 10 – gasket, 11 – U-bolt, 12 – safety and drain pipe

Last modified: Wednesday, 22 March 2023, 4:24 PM