Views: 14 Author: Site Editor Publish Time: 2024-03-12 Origin: Site
Introduction
One end of the tube sheets at both ends of the floating head heat exchanger is fixedly connected to the shell with a flange, which is called the fixed end. Another type of end tube sheet is not connected to the shell, but can slide relative to the shell, which is called a floating head end. Since the floating head is located inside the shell, it is also called an internal floating head heat exchanger.
It is one of the most used heat exchangers specially designed to be completely stress-free to promote longer equipment life and virtually no maintenance.
This heat exchanger is widely used in situations where high temperatures between the shell and the tube bundle cause expansion problems. In terms of efficiency and maintenance, floating head heat exchangers are the best heat exchangers, but the cost is naturally higher.
Components
As the name suggests, this design has one end of the tube plate attached to the shell, while the other is free to "float" in the shell. It also consists of a removable tube bundle consisting of straight tubes, tube plates, tie rods and baffles.
Depending on the weight and length of the bundle, there may also be slides or wheel sets to facilitate removal of the tube bundle from the heat exchanger shell.
Depending on the requirements, the floating heads on floating heat exchangers can be of different types. To reduce thermal stress and provide a method of disassembling the tube bundle for cleaning, different floating heads were designed. Here are the four basic types.
Types
Split Back Ring Type, is a prevalent choice in various industries. This construction features a floating head attached to the tube sheet, positioned away from the channel. The floating head is secured by a split backing ring, allowing for easy dismantling. To facilitate removal, the floating tube sheet diameter is slightly smaller than the inner shell diameter.
A bonnet on the floating head side seals the shell, and the split-ring design incorporates the "pull-through" feature seen in pull-through bundle types. This configuration is particularly recommended for high-pressure applications involving non-hazardous process fluids.
Advantages:
1. Enables operation at high pressures.
2. Allows for differential expansion through the floating head.
3. Permits mechanical cleaning of the shell and tube.
4. Facilitates the removal of the entire tube bundle.
Disadvantages:
1. Gasket failure is not externally visible, potentially leading to undetected leakage for a period.
2)Pull through bundle type (TypeT)
In the pull-through bundle design, one of the tube sheets is intentionally smaller to allow it to be pulled through the shell. This facilitates internal access for inspection, maintenance, and cleaning purposes. However, due to the reduced number of tubes, heat transfer is slower compared to other designs. The limited tube count is primarily to accommodate the bonnet flange and bolt circle.
Pros:
1. Removability of both the tube bundle and individual tubes.
2. Differential expansion facilitated by the floating head.
3. Capability for mechanical cleaning on both shell and tube sides.
4. Feasibility of incorporating double tube sheets.
Cons:
1. The seal's visibility from the exterior is lacking, potentially leading to undetected leakage for a period.
2. This design typically incurs higher costs compared to other types.
This type employs individual packing to seal both the shell side and tube side streams, with separation achieved by a lantern ring. It represents the most economical option among floating head designs and is ideally suited for applications involving low pressure, low temperature, and non-hazardous fluids.
Pros:
1. Differential expansion between tubes is achievable through the floating head design, eliminating the need for an expansion joint.
2. Both the tube bundle and individual tubes are removable.
3. Enables mechanical cleaning on the tube side and shell side.
Cons:
1. Limited to a maximum of only two tube side passes.
2. Possibility of leakage on both the shell and tube sides.
3. The usage of these units is restricted to maximum temperatures of 375 degrees F and a maximum pressure of 300 psi, making them less suitable for higher pressure and temperature applications.
In this configuration, a skirt attached to the floating tube sheet extends through the back end of the shell. The space between the skirt and the shell is sealed using multiple layers of packing and a packing gland. Distinguished from the externally-packed lantern ring design, this version incorporates four tubes instead of two, resulting in faster heat transfer between mediums. It is recommended for applications involving low pressure, low temperature, and non-hazardous fluids.
Pros:
1. Accommodates high pressure on the tube side.
2. Both the tube bundle and individual tubes are removable.
3. Allows for mechanical cleaning on both the shell and tube sides.
4. More than two tube passes are possible, optimizing pressure drop utilization.
5. Packing failure is externally visible during operation.
6. Enables the use of a double tube sheet.
7. Differential expansion is facilitated by the packing.
Cons:
1. Unsuitable for hazardous materials on the shell side due to potential leakage.
2. The presence of packing limits shell fluids to temperatures below 300 degrees F and pressures below 150 psi.
3. This type lacks positive sealing, making it susceptible to potential leakage.
Application
This heat exchanger type finds extensive use across various industries, including petrochemical plants and chemical sectors. Its applications encompass:
1. General industrial settings where frequent cleaning is necessary.
2. Chemical processing applications involving toxic fluids.
3. Hydrocarbon fluid condensation processes.
4. Specialized gas aftercoolers and intercoolers.
5. Air pollution control systems.
6. Secondary heat recovery solutions to redirect heat to ovens, dryers, and kilns.
7. Building heating systems.
8. Original Equipment Manufacturer (OEM) energy recovery applications.
