Understanding Removable Bundle Types of Shell and Tube Heat Exchangers
Shell and tube heat exchangers are widely used in industries for transferring heat between two process fluids. The most critical component of heat exchangers is the tube bundle, which typically consists of tubes, tube sheet (s), baffles, tie-rods, and spacers. A removable bundle design allows for easier cleaning and maintenance of the heat exchanger, especially on the shell side (outside tube surface area), making it a preferred choice in certain applications. Let’s review some of the types of removable tube bundles for heat exchangers and how to choose the right one.
The Tubular Exchanger Manufacturers Association (TEMA) has established a set of standards for the design and construction of shell and tube heat exchangers. These standards include TEMA-type designations, which indicate the configuration of a heat exchanger and the type of removable bundle used. The TEMA designations for removable bundle types are U, S, T, and W. W-Type exchangers are not permitted per API 660, so their use in petrochemical applications is limited and we won’t cover them here.
Removable Bundle Types
U-tube bundles are the most common and economical type of removable bundle used in shell and tube heat exchangers. In a U-tube design, a single tubesheet at one end serves for both inlet and outlet tube side flow, with U-shaped tubes running the full length of the exchanger and back. Typical TEMA configuration is AEU, BEU, or CEU, and the shell will have an integral welded 2:1 SE cover. The U-type bundle is ideal for applications with low-fouling on the tube-side process. They are also excellent with high differential temperatures between tubeside and shell side processes as the tube bundle is free to expand and contract within the shell.
S-Type removable bundles utilize straight tubes with a floating rear tubesheet, split backing ring, and a bolted floating head cover. Due to its inherent configuration, a removable shell cover is required for assembly and disassembly. S-type bundles allow for differential thermal expansion of the tubes and permit easier cleaning of the inside of the tubes (no bends). Typical TEMA configurations are AES and BES. Compared to U-tube configurations, S-Type exchangers are considerably more expensive due to the additional tubesheet and body flanges.
T-Type removable bundles are similar to the S-Type with the main difference being that the bundle can be removed from the shell without disassembling the shell cover and floating head. This is accomplished by making the rear floating tubesheet flanged (bolt-through) instead of using a split backing ring for bolting the floating head cover. The major downside to a T-Type exchanger is that the bundle OTL (outer tube limit) is greatly reduced by the flanged tubesheet, so the exchanger will require a larger shell diameter for a similar surface area and performance relative to an S-Type. For this reason, T-Type (AET, BET) exchangers cost more than S-Type and are less common.
Differential Thermal Expansion
Stresses due to differential thermal expansion occur in heat exchangers when the tubes and shell expand at different rates due to different metal temperatures and/or different metallurgies. Stainless steels, nickel alloys, copper, brass, and carbon steel all have different coefficients of thermal expansion, so differential thermal expansion stresses must be considered in the selection of metallurgy and overall exchanger design. The thermal expansion stresses primarily impact the tubes and tubesheet joints, which can lead to leaks and other failures. To avoid this, free expansion of the tube bundle relative to the shell must be permitted either via a shell expansion joint (bellows or flanged & flued), or a removable bundle with U, S, or T-type rear head.
Get Removable Tube Bundles For Your Heat Exchanger From Altex
At Altex, we offer a wide range of removable tube bundles for shell and tube heat exchangers. Our bundles are designed to meet TEMA standards and can be customized to meet your specific requirements. Contact us to learn more about our bundle replacement and re-tube services.