Re-hardening

The re-hardening filters are used on board ships to remove solid particles and contaminants and to adjust Ph value of desalinated water to 7.0…8.5 in order to reduce corrosion of pipes, heat exchangers, hydrophores etc. to a minimum.

Design and working principle of re-hardening water filters of different manufacturers (JOWA, HANSUN, etc) in general same. Below presented models of JOWA F-75 and HANSUN FIL-1.5 re-hardening water filters.

The filter tank 9 (capacity 75 l) of the re-hardening water filter JOWA F-75 contains special filter sand 11 and pH-adjusting material 10 for the removal of solid particles as well as alteration of the pH-value. The filter is equipped internally with a feed-pipe with a strainer 3 at the top as well as at the bottom (bottom strainer doesn’t show in figure below). During normal filter operation water coming through bottom 3-way valve 2 going inside pipe up to the top 3-way valve 4 then passes top strainer 3, filter material 10, 11 and outgoing from the bottom 3-way valve 2.

General design of the re-hardening water filter JOWA F-75

1 – lower manhole, 2 – bottom 3-way valve, 3 – strainer, 4 – upper 3-way valve, 5 – upper manhole, 6 – 2-way valve, 7 – safety valve (6 bar), 8 – pressure gauge (0-10 bar), 9 – filter tank (75 l), 10 – pH adjusting media, 11 – filter sand

Flow diagram of the re-hardening water filter JOWA F-75 presented in paragraph "Re-hardening filter and mineralizer maintenance".

The HANSUN re-hardening water filter FIL-1.5 can remove solid particles, alga and other foreign particles without changing water tastes. Special filtering media also can increase water hardness and mineral, meanwhile the PH value can be adjusted in middle, which cause no damage to pipe and sanitary system onboard, and inhibits corrosion occur.

The filter tank is made in stainless steel, inner piping and distributors arranged inside, and the filter material has been filled accordingly in the tank. The unit equipped with safety valve, vent valve, drain valve and three-way valve etc, which arranged for performing filtering and back-flushing purpose.

To the main particulars of re-hardening filters commonly belongs: capacity (m³/h), volume (L), weight (kg), Filter sand weight (kg), PH adjusting media weight (kg), working pressure (MPa), PH value, dimensions (l×b×h mm), pressure drop (bar).

Re-hardening water filter HANSUN FIL-1.5 design drawing

1 – distributor, 2 – bottom strainer, 3 – top strainer, 4 – pressure gauge, 5 – gauge valve, 6 – air vent valve, 7 – safety valve, 8 – upper manhole, 9 – o-ring, 10 – flange joint, 11 – top 3-way ball valve, 12 – pipe, 13 – filter tank, 14 – bottom 3-way ball valve, 15 – lower manhole 

In the figure above depicted design of the HANSUN re-hardening water filter FIL-1.5 under normal operation status (both handles downward).

PH adjusting media is a half-calcined dolomite produced by calcinating pure dolomite at a temperature of about 850 °C. Compared with dolomite a partial decomposition to CaCO₃ * MgO and carbon dioxide took place.

PH media de-acidizing water and hardens it up. Moreover, it is used as a carrier of reagents in desulphurisation of waste gases.

Filter sand is quartz grain produced by crushing of quartz. It is a silicate material with hard texture, abrasion resistant and chemical stabilization. The main component is SiO₂.

Filter sand can remove solid particles, alga and other foreign without changing tastes. Meanwhile it can prevent incompact PH media clogging the distributor when it is lower than PH media.