Reversible Heat Exchanger With Internal Bore Welding
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Solution Overview
Problem
Heat exchangers with tube bundles face issues of erosion and corrosion on the hot tubesheet due to high-speed gas flows and steam stagnation on the cold tubesheet, limiting their working life and requiring maintenance, especially in TLE exchangers for ethylene production.
Innovation Solution
Implementing Internal Bore Welding (IBW) for both ends of the tubes to both tubesheets, allowing the exchanger to be reversible and maintaining accessibility through a detachable shell section for alignment and welding, enabling the exchanger to withstand erosion and corrosion while allowing flow inversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If fillet-welding and strength-welding the tubes to the external face of the tubesheet is used, then the welding is convenient and economical to carry out, but the long welding bead is easily eroded by the high speed gas flow at the exchanger inlet
Solution Approach 1:
The harmful welding bead is extracted from the external face of the tubesheet and repositioned to the internal face, removing it from the erosion zone. The tube end is butted against the internal face and welded from inside the tube, so the welding bead faces away from the high-speed gas flow that causes erosion at the inlet.
Solution Approach 2:
The internal face of the tubesheet acts as an intermediary surface that protects the welding bead from direct exposure to erosive gas flow. By welding from the inside, the tubesheet structure itself shields the weld from the harmful external environment.
2Object-affected harmful factors
If butt welding with IBW is used for the inlet tubesheet, then the weld bead is no longer frontal to the fluid flow and does not experience direct impact, but exchanger asymmetry is generated which limits the working life by wear at the inlet
Solution Approach 1:
The exchanger is designed to be inverted after a certain period of operation. By inverting the exchanger, the inlet and outlet positions are swapped, allowing the previously outlet end (which has experienced less wear) to become the new inlet, thereby distributing wear more evenly and extending the overall working life.
3Duration of action of stationary object
If both ends of the tubes are fastened to the tubesheets by IBW, then the exchanger becomes reversible and working life is extended, but a detachable part of the shell must be provided to maintain accessibility for alignment and welding operations
Solution Approach 1:
The shell is segmented into a detachable part and a fixed part. The detachable portion allows access to the internal face of the tubesheet for alignment and welding operations, while the fixed portion maintains the structural integrity of the exchanger. This segmentation enables maintenance and assembly operations without requiring complete disassembly.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances the exchanger's resistance to erosion, corrosion, and steam stagnation, extends its working life by allowing flow reversal, and maintains structural integrity through complete reversibility and symmetry.
Implementation Method 1
both ends of the tubes in the tube bundle are fastened to the tubesheets by IBW (Internal Bore Welding)
Implementation Method 2
a tube bundle with exchanging tubes (18) between a first tubesheet (16) and a second, opposing, tubesheet (17)
Implementation Method 3
an ascending vertical motion of the flue gases within the tubes
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A heat exchanger (10) with a pressurised shell (11) and a tube bundle (18) with exchanging tubes between tubesheets (16, 17) has the tubes welded, at both ends, to the tubesheets via IBW (internal bore welding). At least one end of the exchanger shell has parts which are assemblable to allow inspection of and access to the tubes from the exterior during the IBW, when the tubes have already been welded to the tubesheet at the other end of the shell via IBW. In this way, the exchanger can also be reversible.