Heat-exchanger

Looking Inside...
Plate-Fin versus Coil-Wound Heat Exchangers

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Contents.
3 5 6 Introduction Overview Plate-fin heat exchangers
Features

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Coil-wound heat exchangers Plate-fin versus coil-wound heat exchangers
Outlook

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Attachments
Plate-fin heat exchanger structure (Attachment A) Plate-fin heat exchanger fabrication (Attachment B) Brief comparison (Attachment C)

3Introduction.
The fabrication facility of The Linde Group is the Engineering Division, a competent and well-known supplier of two special types of cryogenic heat exchangers with an emphasis on LNG production and cryogenic gas processing. Plate-fin as well as coil-wound heat exchangers are fabricated at Linde´s facility in Schalchen. Here, in the south-east of Germany, some 700 highlyqualified people are employed. Heat exchangers have been produced in various forms here for decades. The specific technical features are outlined and a technical comparison of coil-wound and plate-fin heat exchanger is provided.

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A brazed plate-fin heat exchanger is a stack of alternating flat and corrugated plates.

Plate-fin heat exchanger

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Coil-wound heat exchanger

Overview.Plate-fin and coil-wound heat exchangers are key components of cryogenic process plants worldwide. With more than one century of experience Linde is one of the major players in this business. Linde is the only company fabricating both types of heat exchangers in its own facilities. As of today, approx. 5000 plate-fin heat exchanger blocks and some 1000 coil-wound heat exchangers have been fabricated byLinde for a wide range of applications. Due to a dearth of available information about plate-fin and coil-wound heat exchangers, these items frequently have the status of black boxes in process plants. The objective of this paper is to open these black boxes and to have a look inside. Furthermore this paper aims to provide a brief comparison of the two types of heat exchangers in order tofamiliarize plant owners with the typical features.

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Plate-fin heat exchangers.
General arrangement A brazed plate-fin heat exchanger is a stack of alternating flat and corrugated plates. The corrugations (fins) form the flow channels for the diverse process fluids. Each process stream occupies a certain number of passages within the stack. These are collected by half-pipe headers and nozzles tosingle point connections on the inlet and the outlet of the respective process stream. In this way, up to 10 process fluids can exchange heat in only one heat exchanger block. Fig.1 is a sketch of the various types of fins. Materials and design temperature Usually this type of heat exchanger is made of aluminium alloys 3003 (blocks) and 5083 (all attachments). It is important to know that withthese standard materials the upper design temperature is limited to +65°C due to code requirements. Fins In order to meet the required performance, Linde can select the appropriate fin out of about 50 different fin types. In general a distinction is made between perforated fins and serrated fins. Serrated fins have higher heat transfer coefficients than performated fins. However, serrated fins aremore prone to fouling and result in higher pressure drop. Fabrication In order to bond the loose stack of plates and fins to a rigid block, vacuum brazing is used. This sophisticated process means spanning the loose stack together and heating it in a vacuum furnace up to a temperature of about 600°C. It should be understood that this temperature is very near the melting point of the aluminium basematerials. The filler material is clad by rolling on both sides of each parting sheet. The fins however are pure aluminium alloy without any cladding. After the vacuum brazing the blocks are completed by welding all the attachments such as half-pipe headers, nozzles, support brackets and lifting trunnions to the block. Please refer to Attachment B on page 13). Benefits Vacuum brazed plate-fin...