Maintaince of Heat Ex Changers

8/3/2019 Maintaince of Heat Ex Changers

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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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Maintaince of Heat Ex Changers