Fixed-tubesheet exchangers

The fixed-tubesheet exchanger is the most common, and generally has the lowest capital cost per ft of heat-transfer surface area. Fixed-tubesheet exchangers consist of a series of straight tubes sealed between flat, perforated metal tubesheets. 

The third element is a three-letter code indicating the type of front end, shell, and rear end, in that order. For example, a fixed tubesheet exchanger (the tubesheet does not expand and contract as it heats and cools) with removable channel and cover, single-pass shell, 23K-in, inside diameter with tubes 16 ft long is denoted as SIZE 23-192 TYPE AEL. 

A useful application is for tank and vessel heating, with the heater protruding into the vessel. Bayonet heat exchangers are used in place of reactor jackets when the vessel is large and the heat transfer of a large mass of fluid through the wall would be difficult or slow, because the bayonet can have considerably more surface area than the vessel wall for transfer. Table 10-43 compares bayonet, U-tube, and fixed-tubesheet exchangers. ... 

The bonnet (Fig. 11-35B) bolts to the shell. It is necessary to remove the bonnet in order to examine the tube ends. The fixed-tubesheet exchanger of Fig. 11-36 has bonnets at both ends of the shell. 

Tensile stress in tubes T T Important in a fixed tubesheet exchanger. 

A fixed tubesheet exchanger in a refinery precondenser service for a vacuum tower is a throwaway item. One of my clients just engaged in this exercise. Replacement for the 60-inches ID shell, as per my specs above, was 1,300,000 (in 2013). Not a happy situation. 

Fixed Tubesheet—The advantage of a fixed tubesheet exchanger is that it is a true countercurrent flow exchanger and no reduction of the log mean temperature difference (LMTD) is required for non-true counter-current flow between the shell-side fluid and the tube-side fluid. However, it s impossible to mechanically clean the shell side, as the bundle cannot be extracted from the shell. When such an exchanger fouls on the tube side, it can easily be cleaned. When it fouls on the shell side, you can throw the entire exchanger away. 

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