The
need for
Disinfection
Many
industries
today
use
large
quantities
of water
for
process
cooling
and
applications
needing
disinfected
water. Power
generation
plants,
chemical
plants,
refineries,
LNG
facilities,
paper
mills,
steel
works
etc. In
addition
in many
areas of
the
World
desalination
of
seawater
and
brackish
water by
flash
evaporation,
distillation
or
membrane
process
is
commonplace.
In most
case the
presence
of biofouling
such as
molluscs,
algae or
slime,
cause
numerous
problems
for
downstream
plant
and
equipment.
Fouling
can
adversely
affect
system
hydrodynamics,
restricting
flow,
increasing
pumping
pressures
and
accelerating
corrosion
potential.
Such
problems
will
shorten
the life
of
pumps,
screens,
heat
exchangers,
condensers
and
other
plant
items as
well as
increase
the
operation
and
maintenance
costs.
The
treatment
of
biofouling
problems
is
generally
acceptably
controlled
by the
addition
of a
disinfection
process
into the
system.
Commonly
gas
chlorination
or
commercially
available
bulk
hypochlorite
has been
the
historic
choice.
Increasingly
a more
efficient
and
environmentally
sustainable
technology
is being
chosen....
Electrochlorination
also
known as
hypochlorination.
Electrochlorination
is the
‘onsite’
instantaneous
production
of
sodium
hypochlorite
solution
at a
safe,
dilute
concentration
suitable
for
direct
injection
into
process.
The
elimination
of
transportation
and
storage
of
chlorine
gas or
other
disinfection
chemicals
means
electrochlorination
is now a
more
viable,
cleaner,
safer
technology
for
today’s
industries.
PANCLOR™
and
ELCHLOR™
systems
have
demonstrable
benefits
in terms
of safe,
reliable,
economic
and
maintenance
free
operation
at
hundreds
of
installations
throughout
the
World.
Electrolytic
Hypochlorite
Generation
The
electrolysis
of
seawater
or
artificial
brine in
an
electrochemical
cell
produces
sodium
hypochlorite
by a
combination
of
electrochemical
and
chemical
reactions.
As
seawater
passes
through
the
cell,
the
addition
of
direct
current
will
produce
certain
chemical
reactions,
at the
anode,
the
oxidation
of
chloride
ions to
produce
chlorine
takes
place;
2Cl →
Cl2 +
2e−
At the
cathode
the
reduction
of water
to
produce
hydrogen
takes
place
together
with the
corresponding
formation
of OH−
ions;
2H20 +
2e− → H2
+ 2OH−
The
electrolysis
takes
place in
an
undivided
cell
with
slightly
alkaline
pH so
that as
soon as
chlorine
is
liberated
at the
anode it
immediately
reacts
with
water to
produce
hypochlorite;
Cl2 +
H20 →
HOCl +
H+ + Cl−
The
overall
process
therefore
can be
summarised
as the
reaction
of salt
with
water
according
to;
NaCl +
H20 →
NaOCl +
H2
Chemical
and
electrochemical
side
reactions
also
occur
simultaneously
such as
the
decomposition
of
hypochlorite
to
chloride,
the
oxidation
of
hypochlorite
to
chlorate
and the
evolution
of
oxygen.
In
addition
certain
cations
present
in all
seawater
will
form
hydroxides
and
carbonates
and
whilst
most of
the
suspended
solids
are
transported
out of
the cell
naturally
by the
seawater
flow,
some
will
inevitably
deposit
at the
cathode
surface.
These
deposits
can be
easily
removed
using
weak
acid
solution.
In
standard
seawater
applications
using
PANCLOR™
and
ELCHLOR™
systems,
the
available
chlorine
concentration
in the
produced
hypochlorite
is
typically
in the
range
1000 –
2000 ppm.
Hypochlorite
is a
powerful
biocide
and
although
it
eventually
decomposes
back to
chloride
ions and
oxygen
it has
the
advantage
over
other
biocides
in that
it is
relatively
stable.
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