SNOWPURE, LLC, 2005-2018
VERSION 3.5 (XL+EXL)
–FEBRUARY 2018
PAGE 35
Gas Removal Module: For the highest quality resistivity, gases should be removed from
the EDI feedstream. Of particular importance is removal of CO
2
. Lower levels of CO
2
will allow the EDI module to remove silica (SiO
2
) more efficiently. The gas removal
module may be a gas-transfer membrane unit such as Liqui-Cel
. Best placed after the
RO, but may be before. These can be purchased as an option from SnowPure.
Reverse Osmosis System: Removes the bulk of dissolved salts and organics. When
properly maintained, an RO system can reject up to 98-99% of the ions and TOC.
Proper RO pretreatment is critical for low-maintenance EDI operation. The membranes
will most likely be high-rejection thin film composite (TFC). Reverse osmosis splits the
RO feed water into two streams
—product water and concentrate water. Only the
product water is fed into an EDI module. The RO concentrate has too much hardness
and other impurities.
Pressure Regulators: Used to regulate the applied pressure to the reverse osmosis
membrane, and to the EDI module.
Pressure Gauges: Measure the operating pressures of the RO and EDI streams. See
specifications for minimum and maximum operating pressure.
Sample Valves: Small labcocks allow the sampling of system water during normal
operation and when troubleshooting. It is recommended to sample both product and
concentrate streams, ideally the concentrate of each module in a multiple module
system.
Flow Meters: Measure the flow rates of the various streams. May send signals to a
controller.
Flow Switches: Ensures that the EDI unit receives power only when water flow is
present. If too little or no water is flowing to the EDI module, the flow switch would
cause the system to shut down. This can be done directly with the power supply
interlock system or through a controller. See SnowPure for detailed schematics.
Conductivity Monitors: Measure and display the quality of the product from the RO and
EDI components. The RO product is typically measured in conductivity (
μS/cm) or total
dissolved solids (ppm), and the EDI product is typically measured in resistivity (MΩ.cm).
The monitor may interface with the controller as part of the system’s protection
mechanism. These meters may be purchased as options from SnowPure.
Controller: Optional system to control startup and automatic operation. The controller
may control the power supply directly, this may include EDI control algorithms to
optimize EDI performance, should include protection schemes to shut down power if any
of the EDI flows are low, should alarm if RO conductivity rises above a set point(or if EDI
resistivity drops below a set point). In AutoFlush mode, it should divert the RO product
to drain until initial conductivity quality is attained
—this prevents the EDI from being
overloaded with ions and reduces EDI maintenance. It may have other safeguards
based on customer need, and finally, it may communicate with a master factory
controller.