>Date: Mon, 29 Jun 1998 06:28:42 -0400
>From: Paul Wilson <[log in to unmask]>
>Subject: GEN: DI Water System Capacity
>
>Technet:
>
>.... Looking for a good number cruncher to explain options available.
----------<Anti-sales stuff deleted>------------
----------<Which one of you technical people out there developed plasma,
plotters, black hole, quad drills, solder leveling, automated plating
lines, inline tab plates (Hi Charlie), dry film solder mask, photoresist
(liquid and dry), pick and place, epoxy adhesives, inline chip carriers,
etc. Your world is driven by vendor inovations. Multilayers were only
possible once some vendor figure out how to do it. It is a joint effort
between vendors and shops, we would still be using paper, wire and a Sears
hand drill if it wasn't for vendors figuring out a better mouse trap... and
selling it> !:-) Now lets talk about reps...
>Suppose you have a tandem cation-anion system filled with resin with a
>=capacity of 90 cubic feet each. Flow rates of 10 gal per minute are
>typi=cal or slightly less.
>How many gallons throughput are expected with 400ppm TDS input before >reg=
>eneration?
>How many gallons regenerants are needed for regeneration?
>How many gallons of water are needed for backwash?
>What is the expected lifespan between regenerations?
>What quality of water is expected to be maintained (2 Megohm or 6 >
>Megaohm=
etc...
Paul,
Check out the home pages of Resintech, Pureolite and Sybron, Bayer,Dow and
R&H. They are resin manufacturers and have full data sheets. One of them
has a form you can fill out and get back a suggested configuration.
In general -
Regeneration frequency is base partly on ion distribution,
monovalent,divalent etc. You need a better water analysis to determine the
actual frequency of regeneration. If you have a pure copper sulfate
solution, you can run much longer between regenerations with a high
resistance reading, Sodium and Chloride bleed out sooner and ... but,
Copper is divalent and will take up two sites and sodium is monovalent and
will take up one so you really need to know the ratio then look it up on
the chart (one of about 6) to determine the capacity of the resin then look
at the monovalent to divalent ration to determine the next parameter etc...
So everyone on just ballparks it and if it isn't exactly right, you just
live with it or fix it. You guarantee a certain capacity and water quality
by oversizing the columns.
Resin columns are not equal. Anion columns are usually larger than cation
as the capacity of the resin differs. With low pH water, the anion must be
MUCH larger to take out the extra anions.
To generalize. Anion resins, 14kgr/cu.ft. Cation resins, 18-22 kg/cu.ft.
I think its 17.1 ppm /kg. Actual capacity depends on regenerate used
(4,6,8,or 10 lb/cu.ft) and ion mix.
Rinsing, 3 bed volumes per rinse and 1 hour slow rinse at the end to get to
lowest TDS out (wastes lots of water). One half hour for Cation regenerant
and one hour for anion regenerant.
I think most recycling system operators are generally happy with less then
20 ppm out of the system once reality has set it. For pure water
applications, they polish with a mixed bed service from Culligan.
We have some capacity calculations on our website below (no salesman will
call) and if it's a waste treatment application, see Circuitree, May 98.
If you're building your own, get tight with a resin manufacturer, they can
help you a lot. If you are putting in a dual system, you don't have to
worry about regeneration frequency or time as they switch back and forth
(Assume 4 hours minimum for regeneration).
At 400 ppm tds, for waste, look at a chelated resin for no recycling and DI
for people who like to be stressed all the time and work weekends. For
incoming water, RO is the only way to go at 400 ppm tds. Dow did a
cost-benefit study many years ago on DI vs RO and the break point was 70
ppm and RO's have come down in cost significantly since then.
If you are recycling, make sure you have enough water capacity to cover a
missed regeneration cycle (4-6 hrs).
In general, if you haven't the faintest idea what you are putting in the
system, no one can tell you how long it will last nor will you be able to
predict accurately what the water quality is comming out. You can get some
ball park numbers but they are guesses. Ion exchange is chemistry, if you
want numbers out, you have to put numbers in (lots of them). They are
still writing papers on how to figure the calculations of ion exchange
capacity with various ion combinations.
Best Regards
Bob Mesick
Remco Engineering
Water and Wastewater Treatment Systems
www.remco.com
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