Weak Acid Cation Dealkalization (http://www.culligan.ca/wacproc.html)
Frederick J Sparber
fjsparb at sprintmail.com
Fri Jun 12 18:43:17 GMT 1998
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Fundamentals of Weak Acid Cation Dealkalization
A WAY TO DE-ASH MANURES BY
REVERSING THIS PROCESS? FJS
Dealkalization processes reduce alkalinity, principally =
carbonate and bicarbonate anions. An advanced method of dealkalization =
is weak acid cation dealkalization. This process requires the use of =
acid during regeneration and degasification and repressurization =
following dealkalization.=20
The weak acid cation exchange process features excellent =
dealkalizing capability combined with finite softening capability. =
Provided that the hardness-to-alkalinity ratio exceeds 1, weak acid =
cation dealkalization will remove alkalinity and hardness in equal =
amounts, leaving the balance of the hardness in the water. A weak acid =
cation dealkalizer removes the carbonate and bicarbonate ions associated =
with alkalinity and the calcium and magnesium ions associated with =
hardness.=20
The weak acid cation dealkalizer uses carboxylic cation =
exchange resin regenerated with either hydrochloric acid or sulphuric =
acid leaving hydrogen ions on the exchange sites. When water containing =
alkaline anions and hardness cations passes through the resin, the =
resin's exchange sites take on the alkaline and hardness ions and give =
up their hydrogen ions. Hardness fouling is not of concern because of =
the resin's ability to remove hardness ions as well as alkaline ions. =
The water coming out of the weak acid cation dealkalizer contains the =
residual (non-exchanged) hardness ions and carbon dioxide (equivalent to =
approximately 88% of the raw water alkalinity). This carbon dioxide =
should be removed by degasification because of its potentially corrosive =
affect on piping systems and downstream equipment.=20
A weak acid cation dealkalizer consists of a pressure tank =
partially filled with weak acid cation exchange resin, an acid storage =
tank to provide hydrogen ions (preferably in the form of hydrochloric =
acid) for regenerating the resin, and hydraulic controls to direct the =
flow of water through the dealkalizer during service and regeneration. =
Other system components include a degasifier to remove the carbon =
dioxide generated by the ion exchange process, a repressurization pump, =
and a softener to remove residual hardness. The regeneration process of =
a weak acid cation dealkalizer is similar to a softener's. First, an =
upflow backwash loosens the resin and flushes sediment from it. Then =
concentrated acid is drawn from a storage tank and diluted to the proper =
concentration. As the acid passes through the resin bed its hydrogen =
ions reoccupy the exchange sites. A slow rinse step follows to flush =
spent acid and ions from the resin, and a final fast rinse purges all =
remaining acid from the tank.=20
The ion exchange capacity of each cubic foot of weak acid =
cation resin depends upon several key factors. Number one is the ratio =
of hardness-to-alkalinity in the influent water - a ratio above 1 is =
desirable. The other two lesser factors are water temperature and =
flowrate. Regeneration of the resin with hydrochloric acid is preferred, =
as single-step acid introduction is possible, with 1% to 5% diluted acid =
reaching the resin bed. Alternatively, sulphuric acid can be used, but =
multi-step acid introduction is required.=20
=20
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References | Copyright=20
=20
=20
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<H2><FONT color=3D#00004a>Fundamentals of Weak Acid Cation=20
Dealkalization</FONT></H2>
<H2><FONT color=3D#00004a>A WAY TO DE-ASH MANURES =
BY</FONT></H2>
<H2><FONT color=3D#00004a>REVERSING THIS PROCESS? =20
FJS</FONT></H2>
<P><FONT size=3D+1>Dealkalization processes reduce =
alkalinity</FONT>,=20
principally carbonate and bicarbonate anions. An advanced =
method of=20
dealkalization is weak acid cation dealkalization. This =
process=20
requires the use of acid during regeneration and =
degasification and=20
repressurization following dealkalization.=20
<P>The weak acid cation exchange process features excellent=20
dealkalizing capability combined with finite softening =
capability.=20
Provided that the hardness-to-alkalinity ratio exceeds 1, =
weak acid=20
cation dealkalization will remove alkalinity and hardness in =
equal=20
amounts, leaving the balance of the hardness in the water. A =
weak=20
acid cation dealkalizer removes the carbonate and =
bicarbonate ions=20
associated with alkalinity and the calcium and magnesium =
ions=20
associated with hardness.=20
<P>The weak acid cation dealkalizer uses carboxylic cation =
exchange=20
resin regenerated with either hydrochloric acid or sulphuric =
acid=20
leaving hydrogen ions on the exchange sites. When water =
containing=20
alkaline anions and hardness cations passes through the =
resin, the=20
resin's exchange sites take on the alkaline and hardness =
ions and=20
give up their hydrogen ions. Hardness fouling is not of =
concern=20
because of the resin's ability to remove hardness ions as =
well as=20
alkaline ions. The water coming out of the weak acid cation=20
dealkalizer contains the residual (non-exchanged) hardness =
ions and=20
carbon dioxide (equivalent to approximately 88% of the raw =
water=20
alkalinity). This carbon dioxide should be removed by =
degasification=20
because of its potentially corrosive affect on piping =
systems and=20
downstream equipment.=20
<P>A weak acid cation dealkalizer consists of a pressure =
tank=20
partially filled with weak acid cation exchange resin, an =
acid=20
storage tank to provide hydrogen ions (preferably in the =
form of=20
hydrochloric acid) for regenerating the resin, and hydraulic =
controls to direct the flow of water through the dealkalizer =
during=20
service and regeneration. Other system components include a=20
degasifier to remove the carbon dioxide generated by the ion =
exchange process, a repressurization pump, and a softener to =
remove=20
residual hardness. The regeneration process of a weak acid =
cation=20
dealkalizer is similar to a softener's. First, an upflow =
backwash=20
loosens the resin and flushes sediment from it. Then =
concentrated=20
acid is drawn from a storage tank and diluted to the proper=20
concentration. As the acid passes through the resin bed its =
hydrogen=20
ions reoccupy the exchange sites. A slow rinse step follows =
to flush=20
spent acid and ions from the resin, and a final fast rinse =
purges=20
all remaining acid from the tank.=20
<P>The ion exchange capacity of each cubic foot of weak acid =
cation=20
resin depends upon several key factors. Number one is the =
ratio of=20
hardness-to-alkalinity in the influent water - a ratio above =
1 is=20
desirable. The other two lesser factors are water =
temperature and=20
flowrate. Regeneration of the resin with hydrochloric acid =
is=20
preferred, as single-step acid introduction is possible, =
with 1% to=20
5% diluted acid reaching the resin bed. Alternatively, =
sulphuric=20
acid can be used, but multi-step acid introduction is =
required.=20
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size=3D-1><A=20
href=3D"copyrght.html">Copyright</A></FONT>=20
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