SNOWPURE, LLC, 2005-2018
VERSION 3.5 (XL+EXL)
–FEBRUARY 2018
PAGE 36
Power Supply: DC power is the source for generating the potential across the EDI
module that drives the deionization process. Should be current limiting, and be capable
of being shut off by the system controller or directly through an interlock system. To
protect the EDI module(s), power should be shut off if flow to any of the EDI module
streams is below a set point.
Pressure Relief Valve: Protects against excessive pretreatment pressure fluctuation.
EDI Module(s)
: Act as a polisher by means of SnowPure’s electrodeionization
technology. It splits the RO product flow into two streams, EDI product and EDI
concentrate. There is a small (0.05 gpm) EDI electrode stream that goes to drain. EDI
modules may be operated in parallel for greater flow.
The EDI concentrate may be diverted back to the RO feed (option 1) or it may
be reclaimed for other uses, or sent to drain (option 2). There is no need to
recirculate the concentrate
—one time through makes for a simple system.
The pressure of the EDI product should be higher than the EDI concentrate to
prevent back-leakage and loss of quality. It is recommended to use
(diaphragm or needle) valves and rotameters upstream of the EDI module to
control concentrate and electrode outlet flows. Upstream valves minimize
downstream outlet pressure. When set properly these controls help
maximize efficiency. It is very important to remember that any back pressure
will have an effect on product quality and if too great, damage may occur.
Gas Vent: Note that the electrode waste stream contains water and gas. The gases
include Cl
2
(mostly dissolved), H
2
, and O
2
. These must be vented safely. This is the
responsibility of the OEM and customer. Note that the LEL (lower explosion limit) of H
2
gas is 4% (v/v) so the gases must be dispersed with proper dilution. Normal margin of
safety is 25% of the LEL, or under 1% (v/v).
P&ID Designation for an EDI Module
The symbol for an EDI module in a P&ID has not been defined to date. The symbol
below is proposed. This is similar to an RO module symbol yet reflects the several
plumbing connections and the electrical nature of the EDI module.
This symbol would be connected in the following manner in a P&ID:
+
+
Main Feed
Elec Feed
Conc Feed
Product
Elec Waste
Concentrate