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Tema Standards
TEMA standards and the shell & tube heat exchanger design
This article aims to define the major TEMA constructions and identifies the advantages , limitations , and applications suitable for each type .
By Mihir M . Patel - Author of Mihir ’ s Handbook of Chemical Process Engineering
The shell and tube heat exchanger design is the most common in industry . Usually , exchangers are specifically designed and fabricated for each service ; very little heat exchange equipment can be purchased off the shelf . It is recommended that heat exchangers are designed through computer programming tools such as HTFS ( now Aspen EDR ) or HTRI . Certain specifications , such as exchanger type , tube length and size , and material preference are usually supplied by the end user . If the end user has no specific requirements , economics should dictate the unit chosen .
TEMA ( Tubular Exchangers Manufacturing Association ) is the preferred standard for the manufacture of shell and tube heat exchangers . The general descriptions of the three major TEMA classes are :
• TEMA C - General Service
• TEMA B - Chemical Service
• TEMA R - Refinery Service TEMA R is the most demanding standard , while TEMA C is the least . TEMA B and TEMA R are similar in scope , with TEMA R also mandating recessed flanges and tube sheets or spiral wound gaskets with ring construction . Additionally , TEMA R requires some components to have a greater minimum thickness . TEMA designations refer to the front head design , the shell design , and the rear head design . For example , a TEMA type BEM has a type B front head , a type E shell , and a type M rear head design . There are conditions such as with high vapor flows , high pressure , and temperature crossing where a combination of special TEMA feature is advantageous . For example , K type shells allow for proper vapor disengagement for reboilers , whereas J and H type shells accommodate high vapor flow .
TEMA types TEMA standards cover the heavy-duty heat exchangers ( TEMA R ) as well as the lighter duty heat exchangers ( TEMA C and TEMA B ). Refineries typically use only the TEMA R heat exchangers due to the generally severe requirements of petroleum applications ; however , more moderate process services may warrant consideration of TEMA B construction . Each TEMA heat exchanger consists of the following main parts : the front-end stationary head ( commonly referred to as the ‘ channel ’); the tube bundle ; the rear head , and the shell . Each part can be designed in several modifications , commonly referred to as ‘ types .’ Figure 1 depicts the five types of channels ( A , B , C , N , and D ), seven types of shells ( E , F , G , H , J , K , and X ), and eight rear end head types ( L , M , N , P , S , T , U , and W ) designated by the TEMA standard . The type of rear end head used determines if the tube bundle can be removed from the shell . Figure 2 provides details on parts within each exchanger type . In the following sections , you will find details of all tube types , along with advantages , disadvantages , and typical applications , as well as the distinguishing features of shell types .
Fig 1 : Shell & tube heat exchanger TEMA types ( Source : www . thermalproducts . com ).
Straight tube , fixed tubesheet - Types AEL , BEM , AEM , NEN This TEMA type is the simplest design and is constructed without packed or gasketed joints on the shell side . The tubesheet is welded to the shell and the heads are bolted to the tubesheet . On the NEN heat exchanger , the shell and the head are both welded to the tubesheet . Typically , a cover plate design is provided to facilitate tube cleaning .
28 Heat Exchanger World May 2023 www . heat-exchanger-world . com