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Biofilm in heat exchanger

Johan Guldbj?rnsen johanag at online.no
Mon May 10 01:32:39 EST 2004

not at home.com ("GS") wrote in message=20
news:<c7j03q$luo$1 at hercules.btinternet.com>...
 > "Johan Guldbj?rnsen" <johanag at online.no> wrote in message
 > news:a2b656d2.0404290354.6aa63e44 at posting.google.com...
 >  > > approx 0,2 g/l Ca(OH)2 is added and  approx 200L 75% H3PO4 i added.
 >  >
 >  > In the heat exchangers the process water is cooled from 40-48 C to
 >  > 30-34 C, the cooling water has a temperature approx 4C in the winter
 >  > increasing to approx 20 C in the summer.
 >  > Move the dosing location of Ca(OH)2 and H3PO4 to after the heat
 >  > exchangers
 > You don't mention the pH of the process water. At neutral pH at least,=
 > will probably get precipitation of relatively insoluble calcium=

The pH after adding Ca(OH)2 is approx 6 - 6.5. I have done some
calculation on the crystallisation of calcium with ortophosphates and
the concentrations are below the saturation points. Furthermore the
water is cooled in teh exchabgers so solubility will be increased.

 > Another possible factor is if there is any alginate present in the water=
 > produced by the organisms growing on the heat exchanger - add calcium to
 > alginate and you will produce a relatively rigid gel. Either way, if you=
 > move the calcium addition downstream of the heat exchanger it may help.

In the papermaking process river water is used -> micro organisms.

The reject water from biomass after pressing the biomass form the HCR
reactors are sent to the pre sedimentation loop -> microorganisms

Moving the calcium downstream will hopefully be done soon, but the
velocity in the exchangers are too low, so we are working on that too.

Thank you for the reply.

-Johan Guldbj=F8rnsen

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