Guide to Tube Bundle Assembly Methods for Heat Exchangers

 
The tube bundle is a critical component in heat exchangers, commonly used in shell-and-tube exchangers and similar equipment. The main components of a tube bundle include tube sheets, baffles, support plates, spacers, tie rods, and heat exchange tubes. Through thoughtful design and precise assembly, these parts form a compact and functional unit to ensure the efficient operation of the heat exchanger. The assembly method for the tube bundle can vary depending on the baffle diameter and specific equipment requirements, and it is tailored to different operating conditions and technical specifications.

Components of a Tube Bundle

 
Before delving into the assembly methods for tube bundles, it's essential to understand their key components. As a crucial element of heat exchangers, the tube bundle comprises several parts, each playing a significant role in the overall structure. Here are the main components of a tube bundle and their functions.

1. Tube Sheets

 
Tube sheets are the fundamental elements of a tube bundle, used to secure the heat exchange tubes. Typically, there are two tube sheets located at each end of the heat exchanger, providing sealing and supporting the weight and pressure of the heat exchange tubes.

2. Baffles

 
Installed between the tube sheets and distributed along the length of the heat exchange tubes, baffles alter the direction of fluid flow in the shell side to enhance heat transfer efficiency. They also provide structural support to prevent damage to the tubes from vibrations.

3. Support Plates

 
Generally located between baffles, support plates hold and stabilize the heat exchange tubes, preventing deformation due to thermal expansion or fluid impact during operation.

4. Spacers

 
Spacers maintain the fixed distance between baffles, ensuring uniform fluid flow paths and stable heat transfer performance.

5. Tie Rods

 
Tie rods connect the tube sheets and baffles, secured with nuts to form the skeleton of the tube bundle.

6. Heat Exchange Tubes

 
The core component of the tube bundle, heat exchange tubes facilitate the transfer of energy by exchanging heat between internal and external fluids. The material and dimensions of the tubes are selected based on the specific application needs of the heat exchanger.

Detailed Methods of Tube Bundle Assembly

 
Having established the essential components of a tube bundle, it's important to explore the various methods for assembling these components into a fully functional unit. Each assembly method is tailored to specific conditions and requirements, ensuring that the tube bundle is accurately constructed for optimal performance in heat exchangers. The following sections will provide a detailed explanation of the different assembly techniques, their procedures, and the scenarios in which they are best applied.

1. Visible Installation Method

 
For baffle diameters up to 1400mm, the "Visible Installation Method" is used for horizontal assembly of the tube bundle. This method involves assembling the tube bundle outside the equipment shell before inserting it, which facilitates easier handling and alignment. The process is as follows:
 
Install Tube Sheet and Tie Rods: Place one tube sheet vertically and secure it, then attach the tie rods to the tube sheet.
Install Spacers and Baffles: Sequentially slide the spacers, baffles, and support plates onto the tie rods, tightening with nuts while ensuring accurate relative positioning for a stable tube bundle framework.
Adjustment and Calibration: Check the relative positions of the components during assembly to ensure verticality and flatness, making adjustments as necessary.
Insert Heat Exchange Tubes: Insert each heat exchange tube through the holes in the tube sheets and baffles, ensuring proper alignment and avoiding deformation or damage.
Insert into the Shell: Place the entire tube bundle structure into the heat exchanger shell and install the second tube sheet at the other end.
Positioning and Welding: Align the tube sheet with the shell, ensuring welding gaps meet design requirements. Perform positioning welding to stabilize the bundle, followed by circumferential welding.
Connect Tube Ends: Finally, weld the ends of the heat exchange tubes to the tube sheets, ensuring sealing and structural integrity.

2. Hidden Installation Method

 
For baffle diameters of 1600mm and larger, the "Hidden Installation Method" is employed within the equipment shell. This approach involves assembling the tube bundle inside the shell rather than outside, allowing for precise fitting in tight spaces. It's particularly suited for large heat exchangers, ensuring accurate assembly and robust structural integrity. The process is as follows.
 
Position Tube Sheet and Shell: Align the first tube sheet with the equipment shell, ensuring accurate placement, and perform initial positioning welding.
Mark Baffle Locations: Mark the positions of the baffles on the shell according to the design drawings to ensure accurate subsequent assembly.
Install Baffles and Reference Tubes: Insert the baffles into the shell and simultaneously introduce reference tubes for positioning and support, ensuring accurate baffle installation.
Baffle Positioning: Ensure the spacing between baffles meets design specifications, securing them with spot welds to prevent movement during further operations.
Install Second Tube Sheet: Place the second tube sheet on the ends of the reference tubes and perform positioning welding to secure its position.
Insert Remaining Tubes: Insert the remaining tubes through the tube sheet holes and baffles, starting with the first row and ensuring proper placement.
Tube Positioning: To facilitate tube insertion, clean the tube sheet holes with compressed air to prevent obstruction.
Vertical Tube Insertion: Given the length of the tubes and the number of baffles, vertical tube insertion helps reduce bending and installation difficulty but requires adequate building height and equipment conditions.

3. Platform Assembly Method

 
The platform assembly method is used under specific conditions by pre-manufacturing several support plates to create an assembly platform.
 
Set Up the Assembly Frame: Construct an assembly frame with support plates and ensure the platform is level for accurate assembly.
Initial Tube Insertion: Insert all tubes through the assembly frame and into the left-side tube sheet of the heat exchanger.
Step-by-Step Baffle Installation: Place two baffles inside the shell, securing them with tie rods while pushing the tubes through the baffles one by one.
Repeat Operations: Continue installing baffles and pushing tubes until all baffles are installed.
Weld Right-Side Tube Sheet and Shell: Finally, weld the right-side tube sheet to the shell to ensure sealing and structural integrity.
Insert Tubes into Left-Side Tube Sheet: Complete the assembly by guiding the tubes into the holes of the left-side tube sheet.
Assembly of Dual-Tube Sheet Bundles
For tube bundles with dual tube sheets (without tie rods and spacers), the assembly method is simpler but requires high precision. The steps include:
 
Initial Positioning of the First Tube Sheet: Align one tube sheet with the shell and perform initial positioning welding to ensure accurate placement.
Install Reference Tubes and Second Tube Sheet: After inserting ten reference tubes, fit the second tube sheet onto the ends of these tubes and perform positioning welding at the joint between the tube sheet and shell.
Insert Remaining Tubes: Insert the remaining tubes from the first tube sheet side, guiding them through the internal space of the shell and into the holes of the second tube sheet.
Push Tubes into Place: Begin from the top row and progressively push the tubes into place, ensuring all tubes are correctly positioned.
Clean Tube Holes: Prior to insertion, clean the tube sheet holes with compressed air to prevent debris from obstructing tube insertion.
Choosing the appropriate tube bundle assembly method depends on factors such as baffle diameter, heat exchanger structure, and assembly environment. Regardless of the method, precise positioning and tight welding are essential to ensure the functionality and safety of the tube bundle. Proper application of these methods not only enhances the efficiency of the heat exchanger but also extends the equipment's service life.