Why takes it so long to get conductivity down after resin regeneration?
Demin water after regeneration contains polyanionic Building Blocks. These are not sufficiently desorbed during regeneration of strong base anion.
Why do we have a premature release of cations from cation filter?
Cation feed water contains acid-precipitable humic acids, these slowly convert the cation filter into an anion filter. Pre-treatment is in sufficient.
Why is steam condensate cation conductivity in excess of 0.2 µS/cm?
Make-up water contains biopolymers and LMW neutrals which are cracked into organic acids. Drum type: Lowered pH in drum allows carry-over of acids into the steam. Benson type: Organics are cracked into acids in the superheater.
Why do we have such problems with our UF-module at site X?
Your biopolymers include molecular sizes which may act as pore blockers.
Examples
Quite a few sites have difficulties to meet the 0.2 µs/cm target value for steam condensates.
The reason is the combination of surface raw water and conventional demineralisation. Biopolymers and LMW Neutrals break through and are cracked to organic acids in the water steam cycle.
With LC-OCD the situation can be diagnosed and strategies can be developed how to overcome the problem. The addition of an RO unit is only one of several options.
Ideally, no precursors for organic acids should be present in the make-up water.
This is illustrated in this real case situation:
DOC of make-up is less than 20 ppb and no organic acids are found in the condensates, not even in the drum water. Cation conductivity is < 0.1 µS/cm.
The presence of biopolymers and LMW-neutrals in make-up water does not necessarily lead to elevated cation conductivities for condensates.
Biopolymers may accumulate in the drum and organic acids as cracking products, may accumulate in the drum, still, in the present example, no organic acids are carried over in the steam.
If pre-treatment and/or service operation is not sufficient the strong base anion filter may suffer organic fouling.
Indicative for this is the presence of biopolymers in circulation waters. Although biopolymers are ”neutral” they carry some charge.
Charge density is too low however to get adsorption by ion exchange. Adsorption is governed by numerous hydrogen bonds which can develop if ”random coils” align to resin surfaces.
The presence of (anionic!) humics, building blocks and LMW acids is secondary and reflects material released together with the biopolymers.
Reversed Osmosis (RO) is certainly a very effective barrier to remove DOC. In rare cases however, in particular if technical waste waters are recycled, RO may fail to remove specific LMW neutral compounds.
Amines are an attractive strategy to overcome DOC-related issues as amines are considered to create more homogeneous alkalisation conditions at different pressure/temperature regimes.
Under specific conditions, amines are, however, prone to decompose to acids and glycol, leading to elevated cation conductivities. It is a matter of debate whether these acids are harmful as long as alkalisation conditions are sufficiently stable.
