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PRESENTATION
ON
MAINTAINCE OF HEAT EXHANGERS
PRESENTED BY:
HAMMAD MAJEED
CHEM ENGG. DEP
NFC IEFR F
PAKISTAN
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HEAT EXHANGERS
Heat exchanger is a device built for efficientheat transfer from one medium to another. The
medium may be separated by a solid wall, so
that they never mix, or they may be in direct
contact. They are widely used in , industry
,refrigeration, air conditioning, power plants
chemical plants, petrochemical plantspetroleum refineries and natural gas
processing.
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TYPES
Shell and tube heat exchanger
Plate type heat exchanger
Spiral tube heat exchangerCo-centric tube heat exchanger
Lamella type heat exchangers
Regenerative heat exchangerPlate fin heat exchanger
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SHELL N TUBE EXCHANGERS
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SHELL N TUBE EXCHANGERS
Shell and tube heat exchangersconsist of a series oftubes. One set of these tubes contains the fluid thatmust be either heated or cooled. The second fluid runsover the tubes that are being heated or cooled so thatit can either provide the heat or absorb the heatrequired. A set of tubes is called the tube bundle andcan be made up of several types of tubes: plain, etc.Shell and Tube heat exchangers are typically used for
high pressure applications (with pressures greaterthan 30 bar and temperatures greater than 260C).
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CONTD
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CONTD
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CONTD.
There are several thermal design features that are to betaken into account when designing the tubes in theshell and tube heat exchangers. These include ,
Tube diameter:Using a small tube diameter makes the heat exchangerboth economical and compact. However, it is morelikely for the heat exchanger to foul up faster and thesmall size makes mechanical cleaning of the fouling
difficult. To prevail over the fouling and cleaningproblems, larger tube diameters can be used.
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CONTD
Tube thickness:The thickness of the wall of the tubes is usuallydetermined to ensure:
That flow-induced vibration has resistance
Axial strength
Availability of spare parts
Hoop strength (to withstand internal tube pressure)
Buckling strength (to withstand overpressure in theshell)
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CONTD
Tube length:Heat exchangers are usually cheaper when
they have a smaller shell diameter and a long
tube length. Thus, typically there is an aim tomake the heat exchanger as long as physicallypossible whilst not exceeding production
capabilities. However, there are manylimitations for this, including the spaceavailable at the site where it is going. etc
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CONTD
Tube pitch:when designing the tubes, it is practical to
ensure that the tube pitch (i.e., the centre-
centre distance of adjoining tubes) is not less
than 1.25 times the tubes' outside diameter. A
larger tube pitch leads to a larger overall shell
diameter which leads to a more expensive heat
exchanger
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PLATE TYPE HEAT EXCHANGER
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PLATE TYPE HEAT EXCHANGER
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CONTD..
The plate and frame heat exchanger was one of thefirst compact exchangers to be used in the UKprocess industries, being originally introduced in1923; the first plates were made of gunmetal. It is
currently second to the shell and tube heatexchanger in terms of market share. The mostcommon variant of the plate and frame heatexchanger consists of a number of pressed,corrugated metal plates compressed together into a
frame. These plates are provided with gaskets, partlyto seal the spaces between adjacent plates andpartly to distribute the media between the flowchannels. The most common plate material isstainless steel.
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FLOW PATTREN
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PROS N CONS
Gas keted units may be used in refrigeration and heat pumpplants
Extensively used in the processing of food and drinks,
In the chemicals sector, a substantial list of heating and
cooling applications includes cooling iso paraffin, sulphuricacid, salt solutions, hexane and
kerosene.
Heating glycerine and condensing ethanol are other routine
uses. The offshoreCare should be taken in locating the gaskets duringreassembly, as imperfect sealing is the main disadvantage of
the plate and frame heat exchanger.
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SPIRAL TUBE HEAT EXCHANGER
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SPIRAL TUBE HEAT EXCHANGER
A spiral heat exchanger (SHE), may refer to ahelical (coiled) tube configuration, more
generally, the term refers to a pair of flat
surfaces that are coiled to form the two
channels in a counter-flow arrangement. Each
of the two channels has one long curved path.
A pair of fluid ports are connected tangentiallyto the outer arms of the spiral, and axial ports
are common, but optional.
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FLOW PATTREN
Spiral Flow/Cross Flow One fluid is in spiral flowand the other in a cross flow. Spiral flow
passages are welded at each side for this type
of spiral heat exchanger. SHEs are generallysmaller than other types of heat exchangers.
The display or the pattern view is in the next
slide
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CONTD.
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PROS N CONS
The main advantage of the SHE is its highly
efficient use of space
The SHE is good for applications such as dry
milk products,
In heat recovery, pre-heating and effluent
cooling.
For sludge treatment,
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CONTD..
Fouling occurs when a fluid goes through theSpiral heat exchanger, and the impurities in thefluid precipitate onto the surface of the tubes.
Precipitation of these impurities can be causedby:
Frequent use of the heat exchanger
Not cleaning the heat exchanger regularlyReducing the velocity of the fluids movingthrough the heat exchanger
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CO CENTRIC TUBE HEAT
EXCHANGERS
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CO CENTRIC TUBE HEAT EXCHANGERS
Co centric tube heat exchangers also known asdouble pipe exchangers widely used in industry
for the exchange of heat.
There are two main flow pattern in double pipe
heat exchangers
Co current
Counter current
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FIG
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CONTD
Both of these patterns follow in the same
heat exchanger
In b/w stem and cold water there is a coflow
In b/w hot water n cold water there is a
counter current flow.
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LAMELLA HEAT EXCHANGER
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LAMELLA HEAT EXCHANGER
The lamella heat exchanger is an efficient, andcompact in size, heat exchanger. The principle was
originally developed around 1930 by the company
Ramens PatenterNormally consists of a cylindrical shell surrounding
a number of heat transferring lamellas. The design
can be compared to a tube heat exchanger butwith the circular tubes replaced by thin and wide
channels, lamellas.
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FIG
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FIG
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PROS N CONS
Lamella exchanger is widely used for small
scale
Have an extensive use for sensitive fluids.
Less pressure drop then others.
No baffles in it so turbulence is small.
As no baffle so rate of H.T is low.
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MAINTAINCE PROCEDURE
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MAINTAINCE
Minor maintenanceWhen the heat exchanger is isolated, minor
maintenance such as clearing blockages,
cleaning, lubrication, and oil level checks can
be carried out in accordance with the Standard
Operating Procedures and the Permit To Work
system
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CONTD
CleaningFor a heat exchanger to work efficiently, the heat
transfer surfaces must be clean, and the flow
passages must be clear of obstruction.
A cleaning program should be put in place to
help insure the continued optimal, or near
optimal, performance of heat exchangers.
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CONTD
Mechanical cleaningMechanical cleaning requires opening the
exchanger. This involves the removal of the end
covers and the tube bundle (plates in the case
of a plate exchanger), then cleaning and then
reassembly. Damage of the exchanger
components, particularly the tube bundle, isalways a risk and great care must be taken .
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CONTD
Chemical cleaningWith chemical cleaning it is important to identify the
deposit in order to select the correct method for its
removal. Some of the common chemicals used toclean exchangers are:
Mineral acidsOrganic acidsAlkaline agentsOrganic solvents
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MINEARL ACIDSHydrochloric acid is most widely used because of
its low cost. It dissolves calcium carbonate
(limestone) scale deposits. (If sulphuric acid
was used to remove calcium carbonate scale,calcium sulphate would form this is another
insoluble substance). Otherwise, this would
result in the formation of calcium sulphate,another equally insoluble substance.
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ORGANIC ACIDSCitric and formic acids are widely used -
especially in shell n tube where chlorine
ions would cause problems with austenitic
steels. Citric acid is used, in the form of
ammonium acid citrate, to prevent the
formation of insoluble ferrous acidcitrates.
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ALKALINE AGENTSThese agents have a detergent action and
are capable of neutralizing acids. Some
examples are: soda ash, caustic soda,sodium silicates and tri-sodium
phosphates
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ORGANIC SOLVENTS
These are used where fouling is due to
waxes and tars. They include kerosene ,
diesel fuels and tri chloro -ethane.Organic solvents do not dissolve
mineral deposits
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HOW TO CLEAN THE TUBES
When removing tube bundles from heat
exchangers for inspection or cleaning,
exercise care to see that they are not
damaged by improper handling.
Do not handle tube bundles with hooks
or other tools which might damage tubes.Move tube bundles on cradles or skids.
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CONTD
Insert a soft wood filler board between
the bearing plate and tubes heat face to
prevent damage to the tube ends.
A hardwood spreader block must be
inserted between the cable and each
tube sheet to prevent damage to thetube ends.
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CONTD
Lift tube bundles horizontally by means
of a cradle formed by bending a light gauge
plate or plates into a Ushape. Make
attachments in the legs of the U for lifting.
Do not drag bundles, of tubes n coils of spiral
plated to avoid any damage.
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CONTD
Extensive care is needed in the case of lamella
b/c the lamella leafs are very sensitive and not
structurally strong.
Do not attempt to clean tubes by
blowing steam through individual tubes.
This overheats the individual tube and
results in severe expansion strains and
leaking tube-to-tube sheet joints.
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SOME MORE
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TIGHTENING OF LEAKING FLANGESIt is preferable, if possible, to replace the
gasket as the cost of the gasket relative to the
leak is minor. If a gasket needs to be replaced,
the flow line will need to be depressured,isolated and drained before work.
If it is not possible to replace the gasket, the
flange can be tightened by:
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CONTD
checking the alignment of the flange to see
that the two flange faces are parallel
reducing the tension on the flange bolts so
that when the flanges are tightened
In shell n tube and double pipe rare and front
ends bolts should be tighten properly.
In spiral tube the coils joints should be checked
and tighten properly
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TEMPRATURE SHOCKTemperature shock is one of the most
failure cause in exchangers due to the
exceeded pressure of steam so steamvalve should be checked and maintained
properly to avoid damage.
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SLUGISHNESS
Do not thread rods or cables through
tubes of a heat exchanger equipped wit ITTStandard Amatran tubes, or any with internal
fins.Do not remove channel covers, shell covers,floating head covers or bonnets until allpressure in the heat exchanger has beenrelieved and both shell side and tube side arecompletely drained.
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MAINTAINCE CIRCLE FOR P T E
The most important part in plate type
exchanger is the gaskit
If there is a problem with it then whole process
damaged.
Replacement circle for gas kit is
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