Danfoss iSave 21, Руководство пользователя

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User manual iSave 21
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180R9221 / 521B1174 / DKCFN.PS.003.A1.02
5.11 Flushing
RO membranes require periodic flushing to limit biological fouling.
There are two types of flushing: feed water (Seawater) flush and fresh water (Permeate)
flush.
Regardless of the flush water used, the water must be pre-filtered to the level described in
chapter 5.8. All parts of the iSave must be flushed, i.e. LP- and HP flow channels.
Feed water flushing is part of a normal shutdown sequence. After the HP pump has been
stopped, the permeate and concentrate production will continue until the high-pressure
drops below the osmotic pressure. Both the iSave and the LP seawater feed pump must run
until the conductivity measured at point (7) and (3) are satisfactory. See also P&ID in chapter
5.16.
Fresh water flushing is performed before every extended shutdown of the RO plant.
Permeate is simultaneously fed into the iSave at LP in (2), and either to the HP pump inlet
(1) or through some other injection point such as the CIP connections or full flow cleaning
connection. See also P&ID in chapter 5.16. Permeate may be produced during this flushing
process.
Special attention should be given to the pressure in the HP line (7) as the iSave may start to
cavitate when it runs at high speed and the pressure in the HP line (7) drops below 3 bars.
This can be avoided by reducing the speed of the iSave to about 750 rpm and keeping the
pressure in the HP line at the minimum of 1 bar. At this low pressure the iSave may only run
for a maximum of 10 minutes.
Failing to flush the iSave with fresh water before extended shutdowns may result in ex-
tensive biological growth and cause corrosion in the iSave and other equipment in the RO
system.
5.12 CIP or membrane cleaning
The purpose of membrane cleaning is to reduce scaling and fouling in the membranes. For
optimal performance specific chemicals are required, depending on the cause of the pollu-
tion. After chemical treatment the system must be flushed with fresh water.
The flush water coming out of the membranes may consist of a large amount of suspend-
ed inorganic particles. It is important to assure that these particles are not lead into the
iSave.
It is essential that the water used for the final pre-flush is pre-filtered to a level described
in chapter 5.8.
The iSave should not be exposed to chemicals that will damage the RO membranes
Also see instruction “Membrane cleaning of RO system with iSave unit” in appendix 10.2.
5.13 High pressure remains after shutdown
The HP line of the RO system equipped with an iSave can remain pressurised for a long time
after shutdown. Pressure decreases as water slowly leaks through the iSave. If more rapid
system depressurisation is required, the system should be bled through a suitable valve on
the HP concentrate line.
Always check the pressure in the high-pressure lines before making service in the HP lines
or pressurised equipment.
NB!