art_'s tema designations

7/28/2019 Art_'s TEMA Designations

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Art Montemayor September 30, 2005

Rev: 0

A E L

B F M

C G N

N H P

D J S

device (split-ring)

Divided shell flow

Channel integral with tubesheet

& removable cover.

Double split flow Outside, packed floating head

Special, high-pressure closure Floating head with backing

Channel integral with tubesheet& removable cover.

Shown: Removable Tube

Bundle

Split Flow Shell Fixed tubesheet; like "C"stationary head.

Stationary head.

Bonnet (Integral Cover) 2-pass shell with longitudinal

baffle

Fixed tubesheet; like "B"stationary head.

DESIGNACIONES TEMA

Shell TypeFront End Stationary Head Rear End Stationary Head

Channel and removable cover One-pass shell Fixed tubesheet; like "A"

Page 1 of 4FileName: 139904612.xls.ms_office

WorkSheet: Designaciones TEMA


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Rev: 0

K T

Other popular rear end head types employed:

U

W

Some examples of the TEMA designation for Heat Exchangers are shown below:

Front bonnet (Intergral Cover), with one-Pass Shell and a Fixed Tubesheet rear Bonnet

Fixed tubesheet heat exchanger. This is a very popular version as the heads can be removed to clean the inside

of the tubes. The front head piping must be unbolted to allow the removal of the front head, if this is undesired

this can be avoided by applying a type A front head. In that case only the cover needs to be removed. It is not

possible to clean the outside surface of the tubes as these are fixed inside the shell. Chemical cleaning can be

used in the shell side. Shown is a version with one shell pass and two tube passes. This is probably the least

expensive of the shell-and-tube designs.

Kettle type of reboiler Pull-through floating head

U-tube bundle design

Packed floating tubesheet with

lantern ring

BEM




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Rev: 0

This is the same type of heat exchanger as shown above, except it has but with one tube pass

Channel with Removable Cover, One Pass Shell, Fixed Tubesheet Bonnet

This is almost the same type of heat exchanger as the first BEM, the removable cover allows the inside of the

tubes to be inspected and cleaned without unbolting the piping. However, as can be expected, the tradeoff isthat this convenient feature makes it more expensive.

The maintenance feature of having a removable tube bundles requires an exchanger as the following:

Channel and Removable Cover, One Pass Shell, Floating Head with Backing Device

A floating head heat exchanger is excellent for applications where the difference in temperature between the

hot and cold fluid causes unacceptable stresses, in the axial direction, between the shell and tubes. The

floating head can move, i.e. it provides the ability to allow tube expansion in the axial direction.

Note that the bundle can not be pulled from the front end. For maintenance both the front and rear end head,

including the backing device, must be disassembled. If pulling from the front head is required a typeAET

should be selected.

However, it is wise and prudent to be aware of the inherent trade-offs in this design. Note that the tube-side

fluid can leak through the internal floating head cover gasket and mix (or contaminate) the shell-side fluid.

It is very difficult -and sometimes impossible to mitigate or compensate for the internal bolts tightening the

internal bonnet to remain under constant, steady torque. Hot fluid temperatures make the bolts expand and

the result is a reduction in bolt torque and subsequent leaks through the bonnet gasket. Additionally, it is a

common and expected occurance for maintenance crews to find the internal bolts badly rusted or corroded to

the point where they have to be burned or sawed off in order to extract the "removable" tube bundle.

The chemical engineer has other options to apply when requiring mechanical expansion of a heat exchangertube bundle. Various rear head design also exist that allow for tube bundle expansion. Among these are the

popular (and inexpensive) "U" tube bundle design. A "P" and "W" rear head design will also contribute this

feature without the hazard of internal mixing (or contamination) of the two fluids.

BEM

AEM

AES




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Rev: 0Also, be aware that any TEMA shell and tube design with a removable tube bundle feature has - by nature - a

larger shell diameter (& increased cost) due to the need to be able to pull the rear tubesheet the length

of the exchanger's shell. A larger diameter shell can sometimes also present problems in a lower Reynolds

number (yielding a lower heat transfer) and internal by-passing of the shell fluid around the baffles (this also

reduces the effective heat transferred. All these effects eventually lead to a bigger heat exchanger (more area

and more tubes) in order to do a heat transfer operation.

Longitudinal Baffles - their application and inherent problems

The employment of longitudinal baffles in heat exchangers - such as the "F", "G", and "H" shell types - can

often resolve both heat transfer and fluid flow problems within the shell and tube exchanger used.

Their application can significantly increase the shell-side Reynolds Number and lead to more efficient shell-side

heat transfer coefficients with a subsequent increase in heat transfer. Additionally, these type of baffles permit

the engineer to incorporate counter-flow heat transfer. True counter-current heat transfer is as efficient

a heat transfer configuration as an engineer can obtain. In some heat recovery applications, this is highly sought.

By splitting the shell-side flow, some applications can actually have a significant reduction in shell-side pressuredrop. This is especially true in partial vacuum process operations where a minimum of pressure drop can be

tolerated.

However, the application of longitudinal baffles should be always carefully scrutinized and used sparingly. There

are, as would be expected, some very important trade-offs involved in the application of longitudinal baffles.

Firstly, if a longitudinal baffle is a process necessity, the baffle should be seal-welded against the inner shell

wall in order to ensure that there will be no internal, by-pass leakage. This positive step negates the possibility

of having a removable tube bundle. Additionally, the welding necessity requires a minimum shell diameter

and this winds up being applicable only to relatively large streams.

By the basic need to establish effective shell-side flow around a longitudinal baffle, one has to accept the

obvious fact that a minimum of shell-side clearances can be tolerated. Once having said and applied these facts,

one then has to also accept that the required, small baffle clearances mean extraordinary fabrication techniques

and resultant super-human maintenance efforts to extract a removable tube bundle. In far too many actual

field cases, it has been found that the removable tube bundle with a longitudinal baffle is a non-practical device.

Field results have shown that in most cases the tube bundle has resulted in being destroyed in order to remove it.

This extraordinary and desperate maintenance act labels such a design as non-practical.



art_'s tema designations

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