Cleaning regimes used in falling film plate evaporators
Following table is a list of all the methods tried by the author with a comment about the method.
Cleaning method
description
Time
Effectiveness
Comments
Caustic at 5%
2 to 4% is most
likely a high
enough
concentration for
two hours
1-48
hours
Organic scales were
often present, caustic
always turned black in
first hour
No noticeable improvements with long
caustic boils, diminishing return beyond 4
hrs. Both rising and falling film cleaning
modes were tried. In area where there were
complete plugs existed, caustic was able to
concentrate 'increasing embrittlement and
leaching effects.
Caustic at >10%
1-48
hours
No increase in
No advantage to high strength unless
effectiveness from lower recovery of the caustic is planned
strength
Caustic at 5% with
soda ash Added
1-48
Improves the dissolution Longer retention time may improve
of CaC2O4*H2O
dissolution, however as scale becomes
more porous acid
will remove the rest
Caustic with KEBO
at 2.5 to 5%
Definite improvements
in organic debris loosing
and being
removed
Increased effectiveness against the
organics including small amounts of "sugar
coal" more pieces of scale were present in
the blow down
Caustic with KABO
at 2.5 to 5%
Definite improvements
Generally same results as the KEBO
in organic debris loosing
and being
removed
Formic acid
3 to 8%
OK
Effective as an organic acid; compared
to sulfamic is equal, compared to HCL is
less favorable for scale removal but less
aggressive to the heat transfer
surfaces -·
Sulfamic acid
5%
By acid
strength:
titration
method,
Never
more
than 1
hour
Varied but an acid
cleaning is necessary
for the carbonates and
Sulphate, not as
effective as HCl
The layering of the scale may
have masked the effectiveness. Acid was
sometimes consumed in minutes and other
times we only broke it down as we hurried
to remove it from the vessel before it
converted to H2SO4 and create the
risk of Calcium Sulfate
Cleaning
method
description
Time
Effectiveness
Sulfamic acid 15%
No advantage, increase
risk
Nitric acid
Very effective cleaner
on most of the scales
including
the organics
Gluconic acid
Water boil
Mechanical drilling
In place high
pressure water
blasting
Out of vessel high
pressure water
blasting
20
minutes,
on/off
cycles
Effective for high
organic loads
Difficult with limit
success
Difficult with slight
improvements
Effective
Comments
Aggressiveness makes it dangerous, no
mild steel can be in the system without
problems
Similar to EDTA, appears to be good at
loosing up organic compounds
Requires rising film mode which can
damage internal components, large forces
were generated and
scale was removed
Nearing last resort over replacing plate
packs
If a flexible 8 mm hose can be fabricated
this could prove effective for the severely
fouled
units. There is progress being made in this.
Expensive and can be near the cost of
replacement.