maintaince of heat exchangers

PRESENTATIONPRESENTATIONONON

MAINTAINCE OF HEAT MAINTAINCE OF HEAT EXHANGERSEXHANGERS

PRESENTED BY:PRESENTED BY:HAMMAD MAJEEDHAMMAD MAJEED

CHEM ENGG. DEP CHEM ENGG. DEP NFC IEFR FNFC IEFR FPAKISTANPAKISTAN

HEAT EXHANGERSHEAT EXHANGERS

Heat exchangerHeat exchanger is a device built for is a device built for efficient heat transfer from one medium efficient heat transfer from one medium to another. The medium may be to another. The medium may be separated by a solid wall, so that they separated by a solid wall, so that they never mix, or they may be in direct never mix, or they may be in direct contact. They are widely used in , contact. They are widely used in , industryindustry , ,refrigerationrefrigeration, , air conditioningair conditioning, , power plantspower plants chemical plantschemical plants, , petrochemical plantspetrochemical plants petroleum petroleum refineriesrefineries and and natural gas processingnatural gas processing. .

TYPESTYPES

Shell and tube heat exchanger Shell and tube heat exchanger

Plate type heat exchanger Plate type heat exchanger

Spiral tube heat exchangerSpiral tube heat exchanger

Co-centric tube heat exchangerCo-centric tube heat exchanger

Lamella type heat exchangersLamella type heat exchangers

Regenerative heat exchanger Regenerative heat exchanger

Plate fin heat exchanger Plate fin heat exchanger

SHELL N TUBE SHELL N TUBE EXCHANGERSEXCHANGERS

SHELL N TUBE SHELL N TUBE EXCHANGERSEXCHANGERS

Shell and tube heat exchangersShell and tube heat exchangers consist of a consist of a series of tubes. One set of these tubes series of tubes. One set of these tubes contains the fluid that must be either heated contains the fluid that must be either heated or cooled. The second fluid runs over the tubes or cooled. The second fluid runs over the tubes that are being heated or cooled so that it can that are being heated or cooled so that it can either provide the heat or absorb the heat either provide the heat or absorb the heat required. A set of tubes is called the tube required. A set of tubes is called the tube bundle and can be made up of several types of bundle and can be made up of several types of tubes: plain, etc. Shell and Tube heat tubes: plain, etc. Shell and Tube heat exchangers are typically used for high exchangers are typically used for high pressure applications (with pressures greater pressure applications (with pressures greater than 30 bar and temperatures greater than than 30 bar and temperatures greater than 260°C).260°C).

CONTD……CONTD……

CONTD…….CONTD…….There are several thermal design features There are several thermal design features

that are to be taken into account when that are to be taken into account when designing the tubes in the shell and tube designing the tubes in the shell and tube heat exchangers. These include ,heat exchangers. These include ,Tube diameter:Tube diameter:

Using a small tube diameter makes the Using a small tube diameter makes the heat exchanger both economical and heat exchanger both economical and compact. However, it is more likely for the compact. However, it is more likely for the heat exchanger to foul up faster and the heat exchanger to foul up faster and the small size makes mechanical cleaning of the small size makes mechanical cleaning of the fouling difficult. To prevail over the fouling fouling difficult. To prevail over the fouling and cleaning problems, larger tube and cleaning problems, larger tube diameters can be used.diameters can be used.


Tube thickness:Tube thickness:

The thickness of the wall of the tubes is The thickness of the wall of the tubes is usually determined to ensure: usually determined to ensure:

That flow-induced vibration has resistance That flow-induced vibration has resistance Axial strength Axial strength Availability of spare parts Availability of spare parts Hoop strength (to withstand internal tube Hoop strength (to withstand internal tube

pressure) pressure) Buckling strength (to withstand Buckling strength (to withstand

overpressure in the shell) overpressure in the shell)


Tube length:Tube length: Heat exchangers are usually cheaper Heat exchangers are usually cheaper

when they have a smaller shell diameter when they have a smaller shell diameter and a long tube length. Thus, typically and a long tube length. Thus, typically there is an aim to make the heat there is an aim to make the heat exchanger as long as physically possible exchanger as long as physically possible whilst not exceeding production whilst not exceeding production capabilities. However, there are many capabilities. However, there are many limitations for this, including the space limitations for this, including the space available at the site where it is going. available at the site where it is going. etcetc


Tube pitch:Tube pitch:

when designing the tubes, it is when designing the tubes, it is practical to ensure that the tube pitch practical to ensure that the tube pitch (i.e., the centre-centre distance of (i.e., the centre-centre distance of adjoining tubes) is not less than 1.25 adjoining tubes) is not less than 1.25 times the tubes' outside diameter. A times the tubes' outside diameter. A larger tube pitch leads to a larger larger tube pitch leads to a larger overall shell diameter which leads to a overall shell diameter which leads to a more expensive heat exchangermore expensive heat exchanger

PLATE TYPE HEAT PLATE TYPE HEAT EXCHANGEREXCHANGER

CONTD…..CONTD…..The plate and frame heat exchangerThe plate and frame heat exchanger was one was one

of the first compact exchangers to be used in of the first compact exchangers to be used in the UK process industries, being originally the UK process industries, being originally introduced in 1923; the first plates were made introduced in 1923; the first plates were made of gunmetal. It is currently second to the shell of gunmetal. It is currently second to the shell and tube heat exchanger in terms of market and tube heat exchanger in terms of market share. The most common variant of the plate share. The most common variant of the plate and frame heat exchanger consists of a number and frame heat exchanger consists of a number of pressed, corrugated metal plates compressed of pressed, corrugated metal plates compressed together into a frame. These plates are provided together into a frame. These plates are provided with gaskets, partly to seal the spaces between with gaskets, partly to seal the spaces between adjacent plates and partly to distribute the adjacent plates and partly to distribute the media between the flow channels. The most media between the flow channels. The most common plate material is stainless steel.common plate material is stainless steel.

FLOW PATTRENFLOW PATTREN

PROS N CONSPROS N CONS

Gas keted units may be used in refrigeration and heat Gas keted units may be used in refrigeration and heat pump plants pump plants Extensively used in the processing of food and drinks, Extensively used in the processing of food and drinks, In the chemicals sector, a substantial list of heating In the chemicals sector, a substantial list of heating andand

cooling applications includes cooling iso paraffin, cooling applications includes cooling iso paraffin, sulphuric acid, salt solutions, hexane andsulphuric acid, salt solutions, hexane andkerosene. kerosene. Heating glycerine and condensing ethanol are other Heating glycerine and condensing ethanol are other routine uses. The offshoreroutine uses. The offshoreCare should be taken in locating the gaskets during Care should be taken in locating the gaskets during reassembly, as imperfect sealing is the main reassembly, as imperfect sealing is the main disadvantage of the plate and frame heat exchangerdisadvantage of the plate and frame heat exchanger..

SPIRAL TUBE HEAT SPIRAL TUBE HEAT EXCHANGEREXCHANGER

SPIRAL TUBE HEAT SPIRAL TUBE HEAT EXCHANGEREXCHANGER

A spiral heat exchanger (SHE),A spiral heat exchanger (SHE), may may refer to a helical (coiled) tube refer to a helical (coiled) tube configuration, more generally, the term configuration, more generally, the term refers to a pair of flat surfaces that are refers to a pair of flat surfaces that are coiled to form the two channels in a coiled to form the two channels in a counter-flow arrangement. Each of the two counter-flow arrangement. Each of the two channels has one long curved path. A pair channels has one long curved path. A pair of fluid ports are connected tangentially to of fluid ports are connected tangentially to the outer arms of the spiral, and axial the outer arms of the spiral, and axial ports are common, butports are common, but optional. optional.

FLOW PATTRENFLOW PATTREN

Spiral Flow/Cross FlowSpiral Flow/Cross Flow One fluid is One fluid is in spiral flow and the other in a cross in spiral flow and the other in a cross flow. Spiral flow passages are welded flow. Spiral flow passages are welded at each side for this type of spiral at each side for this type of spiral heat exchanger. SHE’s are generally heat exchanger. SHE’s are generally smaller than other types of heat smaller than other types of heat exchangers.exchangers.

The display or the pattern view is in The display or the pattern view is in the next slidethe next slide

CONTD….CONTD….


The main advantage of the SHE is its The main advantage of the SHE is its highly efficient use of space highly efficient use of space

The SHE is good for applications such The SHE is good for applications such as dry milk products,as dry milk products,

In heat recovery, pre-heating and In heat recovery, pre-heating and effluent cooling. effluent cooling.

For sludge treatmentFor sludge treatment, ,

CONTD…..CONTD…..

FoulingFouling occurs when a fluid goes through occurs when a fluid goes through the Spiral heat exchanger, and the the Spiral heat exchanger, and the impurities in the fluid precipitate onto the impurities in the fluid precipitate onto the surface of the tubes. Precipitation of surface of the tubes. Precipitation of these impurities can be caused by:these impurities can be caused by:Frequent use of the heat exchanger Frequent use of the heat exchanger Not cleaning the heat exchanger regularly Not cleaning the heat exchanger regularly Reducing the velocity of the fluids moving Reducing the velocity of the fluids moving through the heat exchangerthrough the heat exchanger

CO CENTRIC TUBE HEAT CO CENTRIC TUBE HEAT EXCHANGERSEXCHANGERS

CO CENTRIC TUBE HEAT CO CENTRIC TUBE HEAT EXCHANGERSEXCHANGERS

Co centric tube heat exchangersCo centric tube heat exchangers also known as double pipe also known as double pipe exchangers widely used in industry exchangers widely used in industry for the exchange of heat.for the exchange of heat.

There are two main flow pattern in There are two main flow pattern in double pipe heat exchangers double pipe heat exchangers

Co currentCo current

Counter currentCounter current

FIGFIG

CONTD…CONTD…

Both of these patterns follow in Both of these patterns follow in the same heat exchangerthe same heat exchanger

In b/w stem and cold water there In b/w stem and cold water there is a co flowis a co flow

In b/w hot water n cold water In b/w hot water n cold water there is a counter current flowthere is a counter current flow..

LAMELLA HEAT LAMELLA HEAT EXCHANGEREXCHANGER

LAMELLA HEAT EXCHANGERLAMELLA HEAT EXCHANGER

The lamella heat exchangerThe lamella heat exchanger is an efficient, is an efficient, and compact in size, heat exchanger. The and compact in size, heat exchanger. The principle was originally developed around principle was originally developed around 1930 by the company Ramens Patenter1930 by the company Ramens Patenter

Normally consists of a cylindrical shell Normally consists of a cylindrical shell surrounding a number of heat transferring surrounding a number of heat transferring lamellas. The design can be compared to a lamellas. The design can be compared to a tube heat exchanger but with the circular tube heat exchanger but with the circular tubes replaced by thin and wide channels, tubes replaced by thin and wide channels, lamellaslamellas. .

FIGFIG


Lamella exchanger is widely used for Lamella exchanger is widely used for small scalesmall scale

Have an extensive use for sensitive Have an extensive use for sensitive fluids.fluids.

Less pressure drop then others.Less pressure drop then others.

No baffles in it so turbulence is small.No baffles in it so turbulence is small.

As no baffle so rate of H.T is low.As no baffle so rate of H.T is low.

MAINTAINCE MAINTAINCE PROCEDUREPROCEDURE

MAINTAINCEMAINTAINCE

Minor maintenanceMinor maintenanceWhen the heat exchanger is isolated, When the heat exchanger is isolated,

minor maintenance such as clearing minor maintenance such as clearing blockages, cleaning, lubrication, and blockages, cleaning, lubrication, and oil level checks can be carried out in oil level checks can be carried out in accordance with the Standard accordance with the Standard Operating Procedures and the Permit Operating Procedures and the Permit To Work systemTo Work system


CleaningCleaningFor a heat exchanger to work For a heat exchanger to work

efficiently, the heat transfer surfaces efficiently, the heat transfer surfaces must be clean, and the flow passages must be clean, and the flow passages must be clear of obstruction.must be clear of obstruction.

A cleaning program should be put in A cleaning program should be put in place to help insure the continued place to help insure the continued optimal, or near optimal, performance optimal, or near optimal, performance of heat exchangers. of heat exchangers.


Mechanical cleaningMechanical cleaningMechanical cleaning requires opening the Mechanical cleaning requires opening the

exchanger. This involves the removal of exchanger. This involves the removal of the end covers and the tube bundle the end covers and the tube bundle (plates in the case of a plate exchanger), (plates in the case of a plate exchanger), then cleaning and then reassembly. then cleaning and then reassembly. Damage of the exchanger components, Damage of the exchanger components, particularly the tube bundle, is always a particularly the tube bundle, is always a risk and great care must be taken .risk and great care must be taken .


Chemical cleaningChemical cleaningWith chemical cleaning it is important to With chemical cleaning it is important to

identify the deposit in order to select the identify the deposit in order to select the correct method for its removal. Some of the correct method for its removal. Some of the common chemicals used to clean exchangers common chemicals used to clean exchangers are:are:

Mineral acidsMineral acids

Organic acidsOrganic acids

Alkaline agentsAlkaline agents

Organic solventsOrganic solvents

MINEARL ACIDSMINEARL ACIDS

Hydrochloric acid is most widely used Hydrochloric acid is most widely used because of its low cost. It dissolves because of its low cost. It dissolves calcium carbonate (limestone) scale calcium carbonate (limestone) scale deposits. (If sulphuric acid was used to deposits. (If sulphuric acid was used to remove calcium carbonate scale, remove calcium carbonate scale, calcium sulphate would form this is calcium sulphate would form this is another insoluble substance). another insoluble substance). Otherwise, this would result in the Otherwise, this would result in the formation of calcium sulphate, another formation of calcium sulphate, another equally insoluble substance.equally insoluble substance.

ORGANIC ACIDSORGANIC ACIDS

Citric and formic acids are widely Citric and formic acids are widely used - especially in shell n tube used - especially in shell n tube where chlorine ions would cause where chlorine ions would cause problems with austenitic steels. problems with austenitic steels. Citric acid is used, in the form of Citric acid is used, in the form of ammonium acid citrate, to ammonium acid citrate, to prevent the formation of prevent the formation of insoluble ferrous acid citratesinsoluble ferrous acid citrates..

ALKALINE AGENTSALKALINE AGENTS

These agents have a detergent These agents have a detergent action and are capable of action and are capable of neutralizing acids. Some neutralizing acids. Some examples are: soda ash, examples are: soda ash, caustic soda, sodium silicates caustic soda, sodium silicates and tri-sodium phosphatesand tri-sodium phosphates

ORGANIC SOLVENTSORGANIC SOLVENTS

These are used where fouling is These are used where fouling is due to waxes and tars. They due to waxes and tars. They include kerosene , diesel fuels include kerosene , diesel fuels and tri chloro -ethane. Organic and tri chloro -ethane. Organic solvents do not dissolve solvents do not dissolve mineral deposits mineral deposits

HOW TO CLEAN THE HOW TO CLEAN THE TUBESTUBES

When removing tube bundles from heatWhen removing tube bundles from heat

exchangers for inspection or cleaning,exchangers for inspection or cleaning,

exercise care to see that they are notexercise care to see that they are not

damaged by improper handlingdamaged by improper handling..

Do not handle tube bundles with hooksDo not handle tube bundles with hooks

or other tools which might damage or other tools which might damage tubes.tubes.

Move tube bundles on cradles or skidsMove tube bundles on cradles or skids..


Insert a soft wood filler board betweenInsert a soft wood filler board between

the bearing plate and tubes heat the bearing plate and tubes heat face to prevent damage to the face to prevent damage to the tube ends.tube ends.

A hardwood spreader block must beA hardwood spreader block must be

inserted between the cable and eachinserted between the cable and each

tube sheet to prevent damage to thetube sheet to prevent damage to the

tube ends.tube ends.


Lift tube bundles horizontally by Lift tube bundles horizontally by meansmeans

of a cradle formed by bending a of a cradle formed by bending a light gauge plate or plates into a light gauge plate or plates into a Ushape. Make attachments in the Ushape. Make attachments in the legs of the U for lifting.legs of the U for lifting.

Do not drag bundles, of tubes n coils Do not drag bundles, of tubes n coils of spiral plated to avoid any damage.of spiral plated to avoid any damage.


Extensive care is needed in the case of Extensive care is needed in the case of lamella b/c the lamella leafs are very lamella b/c the lamella leafs are very sensitive and not structurally strongsensitive and not structurally strong..

Do not attempt to clean tubes byDo not attempt to clean tubes by

blowing steam through individual tubes.blowing steam through individual tubes.

This overheats the individual tube andThis overheats the individual tube and

results in severe expansion strains andresults in severe expansion strains and

leaking tube-to-tube sheet jointsleaking tube-to-tube sheet joints..

SOME MORESOME MORE

TIGHTENING OF LEAKING TIGHTENING OF LEAKING FLANGESFLANGES

It is preferable, if possible, to replace It is preferable, if possible, to replace the gasket as the cost of the gasket the gasket as the cost of the gasket relative to the leak is minor. If a relative to the leak is minor. If a gasket needs to be replaced, the flow gasket needs to be replaced, the flow line will need to be depressured, line will need to be depressured, isolated and drained before work.isolated and drained before work.

If it is not possible to replace the If it is not possible to replace the gasket, the flange can be tightened gasket, the flange can be tightened by:by:


checking the alignment of the flange to checking the alignment of the flange to see that the two flange faces are parallelsee that the two flange faces are parallel

reducing the tension on the flange bolts reducing the tension on the flange bolts so that when the flanges are tightenedso that when the flanges are tightened

In shell n tube and double pipe rare and In shell n tube and double pipe rare and front ends bolts should be tighten front ends bolts should be tighten properly.properly.

In spiral tube the coils joints should be In spiral tube the coils joints should be checked and tighten properlychecked and tighten properly

TEMPRATURE SHOCKTEMPRATURE SHOCK

Temperature shock is one of the Temperature shock is one of the most failure cause in exchangers most failure cause in exchangers due to the exceeded pressure of due to the exceeded pressure of steam so steam valve should be steam so steam valve should be checked and maintained checked and maintained properly to avoid damageproperly to avoid damage..

SLUGISHNESSSLUGISHNESS

Do not thread rods or cables throughDo not thread rods or cables throughtubes of a heat exchanger equipped tubes of a heat exchanger equipped

wit ITT Standard Amatran® tubes, or wit ITT Standard Amatran® tubes, or any with internal fins.any with internal fins.Do not remove channel covers, shell Do not remove channel covers, shell covers, floating head covers or covers, floating head covers or bonnets until all pressure in the heat bonnets until all pressure in the heat exchanger has been relieved and exchanger has been relieved and both shell side and tube side are both shell side and tube side are completely drained.completely drained.

MAINTAINCE CIRCLE FOR “P MAINTAINCE CIRCLE FOR “P T E”T E”

The most important part in plate type The most important part in plate type exchanger is the gaskitexchanger is the gaskit

If there is a problem with it then If there is a problem with it then whole process damaged.whole process damaged.

Replacement circle for gas kit is…Replacement circle for gas kit is…

maintaince of heat exchangers

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