For purifying return steam condensate, Condensate
polishing is employed. This is essential for meeting the quality
requirements of high pressure thermal cycles. It also minimizes
consumption of make-up water. Condensate polishing is applied in places
where the condensate is the major portion of the Boiler Feed Water. It
is also applied if the risk of contamination of return condensate is
persistent.
The Condensate Polishing removes following types of impurities:
Corrosive impurities
Oxides of iron, copper and nickel are the major corrosive products.
These products could be either in the form of particulate matter or in
solution. They are removed by filtration of the condensate. Cartridge or
precoat filters can be used for filtering these corrosive products.
Dissolved Salts
Sometimes due to leakage of cooling water the impurities caused by
dissolved salts arise. The use of ion exchange demineralizers these
impurities can be cleared. For low-contamination levels mixed-bed ion
exchangers are commonly used. Separate cation and anion exchangers can
be used only when there is higher level of mineral contamination.
Condensate Polishing Unit
In various manufacturing unit or plant steam is generated and released
for generating electricity. The steam after loosing its heat condensate
back into water. While condensing steam picks lot of impurities from the
environment which should be completely removed before using condensate
again. The polishing unit that is employed for this impurity is
condensate polisher that employs ion exchange resin bed to remove the
contaminants. After resin is exhausted it is regenerated.
On the basis of regeneration, condensate polishing systems can be of
following types :
- Mixed Bed External Regeneration
- Mixed Bed In-situ Regeneration
Ion Exchanged Resins Used In Condensate Polishing
Following resins can be used either independently or in combinations in
condensate polishing.
Strong Acid Cation Resins
Strong acid cation (SAC) resins are used for softening,
demineralization and dealkalization process. SAC resins are available in
different crosslinkage. Resin with 8% crosslinkage is commonly used for
electric utility condensate polishing applications where they remove
corrosion products (crud) from the utility's condensate.
Weak Acid Cation Resins
Weak acid cation (WAC) resins are also used for dealkanization and
demineralization processes. All cation that are held tightly to the
resin are removed by WAC resin. Normally these resins remove resins
remove only cations associated with alkalinity.
Strong Base Anion Resins
For various ion exchange demineralization processes, dealkanization,
organic trap applications etc. SBA is used.
Weak Base Anion Resins
Weak base anion (WBA) resins do dual function that is it absorbs acid
and functions as an ion exchanger. Only Strong acidic minerals are
remove by them. However they allow the ions of carbonate/bicarbonate and
silica to pass. It is due to this they are not used for
demineralization.
Required Properties of Resins for Condensate Polishing
The resins used in condensate polishing should have following features:
- It should have good physical strength in order to withstand
vigorous cleaning. It is also necessary for the rigorous of
hydraulic transfer during regeneration.
- For effective separation of resin's density should be precise.
- To prevent any flow restriction during operation, size and
kinetics of the resins is also important.
