Appendix; General Swro System Understanding With Isave; Instruction For Start And Stop Of The Swro With Isave Unit (180R9213); Prior To Start-Up - Danfoss iSave 40 Series Operation Manual

Operation guide | iSave 40

10. Appendix

10.1 General SWRO system understanding
with iSave
• Basically the permeate flow is the same as the
flow from the high-pressure pump.
• The HP concentrate flow into iSave HP-in and
HP seawater-out is determined by the rpm of
the iSave (See flow curve page 27).
• The iSave HP flow determines the recovery
rate (higher rpm on the iSave gives lower
recovery rate and vice versa).
• Flow on the low-pressure side of the iSave is
determined by feed pump and the pressure
control valve LP-out (not by the rpm of the
iSave).
• The flow on the low-pressure side must be at
least the same as on the high-pressure side of
the iSave (LP in flow = HP in flow; this is called
balanced flow).
• To minimize mixing, the flow on the low-
pressure side can be adjusted up to 10%
higher than the high-pressure flow.
10.2 Instruction for start and stop of the
SWRO with iSave unit (180R9213)
Below procedures are general guidelines for the
start-up and shut-down functions of SWRO-
systems with the Danfoss iSave energy recovery
device.
Procedure details may differ depending on the
system design.
The numbers marked in () refer to the diagram
on the next page.
10.2.1

Prior to start-up

Prior to initial start-up all piping connected with
the iSave unit must be thoroughly flushed to
ensure that no impurities enter the iSave.
Inadequate pre-flushing will strongly influence
the life of the iSave and might lead to breakdown
of the iSave.
1. Install all filter cartridges in the system.
2. With the iSave disconnected from the piping,
the system must be flushed in order to remove
possible impurities from the system (pipes,
hoses, membranes etc.).
Flushing must run until the system can be
ensured clean.
3. Connect the iSave to the pipework. The iSave is
now ready for start-up.
10.2.2

Starting up the system

1. Make sure that all valves are set in normal
operating positions.
2. Start the seawater supply pump (1).
3. Make sure all pipework is flushed with water.
Vent all air from the system through air valve
(8) and iSave unit (11). The iSave has ¼" plugs to
vent both the HP and LP side.
4. Start the iSave unit when the pipework is full of
water and the system and iSave unit has been
bled.
180R9239 | AQ299555093252en-001601 | iSave 40 | 09.2022
• Always start the iSave unit before
the high-pressure pump is started.
• The speed of the iSave unit must
be ramped up over a period of
3–15 seconds.
• If possible, run the iSave at maxi-
mum 750 rpm.
• When HP in is below 15 bars/217psig,
the maximum operation period is
10 minutes.
• Ensure the VFD/SoftStarter can
deliver 140% start torque since the
iSave starting torque can be higher
than nominal torque of the motor.
5. With a pressure control valve (15), adjust the
back pressure of the "LP-out" to a minimum of
1 bar/14.5 psig (14).
6. An "over flush" of the iSave can be done to
bleed any remaining air from the system.
Flush minimum 10% higher flow rate (12) at
"LP- in" compared to the flow rate on "HP-out".
Flush over a period of minimum 5 minutes.
7. Adjust the speed of the iSave unit to desired
flow (recovery rate). The speed is normally
controlled by a VFD.
8. Start the high-pressure pump (4), and the
system pressure (5) will rise until the permeate
flow (17) almost equals the flow (2) from the
high-pressure pump.
9. Adjust LP-in flushing flow:
There are two ways to check the optimal LP-in
flushing flow.
1. Check the low-pressure flow rates (12),
adjust flow with valve (15) or feed pump to
achieve balanced flow. It might be a benefit
to "over flush" the iSave with up to 10% to
lower mixing and HP pressure at mem-
brane.
2. Adjust low-pressure flow with valve (15) or
feed pump upwards slowly. Check HP
pressure at membrane, (the pressure will
fall with increased LP flow because of
decreasing mixing. Adjust upwards until the
HP pressure at the membrane does not fall
any more. (See mixing curve page 27).
10. Check that the pressure (14) of "LP-out" is at
least 1 bar/14.5 psig.
11. How to adjust system if LP-in flow or
pressure is too high/low:
1. If the "LP -in" flow (12) is too low and the
"LP-out" pressure (14) is higher than
1 bar/14.5 psig, increase flow and decrease
pressure by opening the pressure control
valve (15).
2. If the "LP-in" flow (12) is too low and
the "LP-out" pressure (14) is below
1 bar/14.5 psig, adjust the flow by raising
the flow from the seawater supply pump (1).
3. If the "LP-in" flow (12) is too high, reduce
flow by closing the pressure control valve
(15) or the flow from the seawater supply
pump (1).
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