1.
Plate Cleaning
A:
Gross Fouling
Gross
fouling is fouling by seaweed, wood chips, fibers, mussels, barnacles and other
substantial fouling
Gross
Fouling Cleaning Techniques:
a)
Soft brush and running water
b)
High pressure hose
c)
Back flushing of the unopened heat exchanger can sometimes be sufficiently
effective.
Note:
Be
careful not to damage gaskets. Under no
circumstances should hydrochloric acid be used with stainless steel
plates. Water of more than 300 ppm Cl
may not be used for the preparation of cleaning solutions. It is very important that carrying bars and
support columns in aluminum are protected against chemicals.
B:
Biological Growth – Slime
Biological
growth is from bacteria, nematodes and protozoa.
Biological
Growth Cleaning Techniques:
a)
Soft brush and running water
b)
High pressure hose.
c)
Chemical cleaning using alkaline cleaning agents:
- sodium hydroxide
- sodium carbonate
- Cleaning effect
can be considerably increased by the addition of small quantities of
hypochlorite or agents for the formation of complexes and surfactants.
Note:
Be
careful not to damage gaskets. Concentration
max of 4%. Temperature max of 80 degrees
C. Under no circumstances should
hydrochloric acid be used with stainless steel plates. Water of more than 300 ppm Cl may not be used
for the preparation of cleaning solutions.
It is very important that carrying bars and support columns in aluminum
are protected against chemicals.
C:
Incrustation – Scaling
Incrustation
is caused by calcium carbonate, calcium sulphate and silicates.
Incrustation
Cleaning Techniques:
a)
Soft brush and running water
b)
High pressure hose.
c)
Chemical cleaning on opened unit by using:
- Nitric acid
- Citric acid
- Sulfamic acid
- Phosphoric acid
- Complexing agents (EDTA, NTA)
- Sodium polyphosphates
Note:
Be
careful not to damage gaskets.
Concentration max of 4%.
Temperature max of 60 degrees C.
Under no circumstances should hydrochloric acid be used with stainless
steel plates. Water of more than 300 ppm
Cl may not be used for the preparation of cleaning solutions. It is very important that carrying bars and
support columns in aluminum are protected against chemicals.
D:
Sediment
Sediment
is caused by corrosion products, metal oxides, silt, alumina, diatomic
organisms and their excrement of various colors.
Sediment
Cleaning Techniques:
a)
Soft brush and running water
b)
High pressure hose.
c)
Chemical cleaning on opened unit by using:
- Nitric acid
- Citric acid
- Sulfamic acid
- Phosphoric acid
- Complexing agents (EDTA, NTA)
- Sodium polyphosphates
Note:
Be
careful not to damage gaskets.
Concentration max of 4%.
Temperature max of 60 degrees C.
Under no circumstances should hydrochloric acid be used with stainless
steel plates. Water of more than 300 ppm
Cl may not be used for the preparation of cleaning solutions. It is very important that carrying bars and
support columns in aluminum are protected against chemicals.
E:
Oil Residues, asphalt and fats
Oil
residues, asphalt and fats are a byproduct of the heat exchange process that
includes oil, asphalt and fat.
Oil,
Asphalt and Fat Cleaning Techniques:
a)
Hydrocarbon-based deposits may be removed by using a soft brush and a
PARAFFINIC or NAPHTA-BASED solvent (e.g. KEROSINE)
Note:
Gaskets in natural, butyl and EPDM rubber swell in these media. Contact time should be limited to 0.5 hour.
The
following solvents should not be used:
- Ketones (acetone, methyletylketone,
methuylisobutylketone)
- Esters (Ethylacetate, Butylacetate)
- Halogenated
hydrocarbons (Chloro-thene, Carbon tetrachloride, Frenons)
- Aromatics (Benzene, Toluene)
b)
Dry with a cloth or rinse with water.
Be
careful not to damage gaskets.
Concentration max of 4%.
Temperature max of 60 degrees C.
Under no circumstances should hydrochloric acid be used with stainless
steel plates. Water of more than 300 ppm
Cl may not be used for the preparation of cleaning solutions. It is very important that carrying bars and
support columns in aluminum are protected against chemicals.
2. Regasketing
There
are two types of glue to be used in regasketing plates.
A.
EPDM, NBR (rubber based)
-
Single component rubber based solvent adhesive.
-
Normally used for repair work in an uncured condition
-
Can be used for operating temperatures below 95 degrees C
-
For operation temperatures above 95 degrees C and oil coolers / heaters the
glued joints should be cured at 120 degrees C for one hour.
-
Future removal of the gasket can usually be carried out without heating of the
cement joint.
-
Storage life at room temperature is about two years. This period can be extended after checking
the glue.
B.
Viton and Silicon
- A two component, cold curing epoxy glue which
gives a strong joint for higher temperatures.
- Future removal of gaskets usually requires
heating or freezing of the joint.
-
The shelf life is limited to approximately 1 year when stored at room
temperature but can be prolonged when kept in a refrigerator.
C.
Clip in gasket (glue free)
- The clip in gasket is attached to the plate
by two gasket prongs which slip under the edge of the plate to hold the gasket
securely in alignment in the gasket groove.
- The prongs are situated at regular intervals
around the periphery of the plate.
- When the plate heat exchanger is then
assembled and tightened, the gasket provides a tight seal around the plate.
3. Fault Detection
A. Leakage between plate pack and frame
- Mark the area where the leakage seems to be
and open the heat exchanger.
-
Investigate the gasket condition of the end plate and the connection if
applicable. Look for dislocation,
foreign objects, scars and other damage to the gasket surfaces.
- Check the surface of the pressure plate for
unevenness, foreign objects etc., that might spoil the joint between the gasket
and the adjacent surface.