Shell-and-Tube Heat Exchanger for LDPE Off-Gas Cooling
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Solution Overview
Problem
Conventional heat exchangers used in high-pressure low-density polyethylene (LDPE) production systems face issues such as high pressure drop, space inefficiency, leakage due to welding points, and corrosion, leading to increased production costs and safety risks.
Innovation Solution
A shell and tube heat exchanger system with tubes extending through a tube sheet to collector conduits, made of corrosion-resistant duplex stainless steel, and a cleaning tool for easy maintenance, reducing leakage and corrosion risks while improving accessibility for cleaning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If double pipe heat exchangers are used, then heat exchange function is provided, but pressure drop is high and space requirement is large
Solution Approach 1:
The heat exchanger is divided into multiple tube bundles arranged in parallel within the shell, allowing the process fluid to be split into multiple streams. This segmentation reduces the flow velocity and pressure drop in each individual tube while maintaining the overall heat exchange capacity through the combined surface area of all tubes.
Solution Approach 2:
The invention transitions from a double-pipe configuration to a shell-and-tube configuration, adding spatial dimensions by arranging multiple tubes within a shell volume. This three-dimensional arrangement increases the heat exchange surface area within a compact space, improving heat transfer efficiency while reducing pressure drop compared to series double-pipe exchangers.
2Reliability
If double pipe heat exchangers are used, then heat exchange function is provided, but space requirement is large
Solution Approach 1:
The heat exchange surface is segmented into multiple tubes of smaller diameter rather than using fewer large-diameter pipes. This allows the total heat exchange area to be packed more efficiently within the shell volume, reducing the overall footprint and space requirement of the heat exchanger.
Solution Approach 2:
Multiple tubes are nested within the shell, with tube bundles arranged in a compact configuration. The tubes are positioned closely together in a nested arrangement that maximizes the use of shell volume, achieving high heat exchange capacity in a compact package that requires less space than double-pipe configurations.
3Strength
If tubes are welded to tube sheet, then structural support is provided, but leakage risk increases
Solution Approach 1:
The tubes are extracted from the welded configuration and instead passed through expansion holes in the tube sheet. This removes the welding operation entirely, eliminating the source of welding-induced stresses and potential leakage paths at the weld joints, while still providing secure structural support through mechanical expansion.
Solution Approach 2:
The welding mechanism is replaced with a mechanical expansion system. Tubes are inserted through the tube sheet and then expanded mechanically using expansion tools that deform the tube outer surface to create a tight interference fit with the expansion hole, providing structural support and sealing without thermal welding.
4Reliability
If conventional tubes are used, then heat exchange function is provided, but cleaning difficulty increases
Solution Approach 1:
The tube ends are extracted from the shell and extended beyond the tube sheet to accessible locations. This allows cleaning tools and procedures to be applied to the tube interiors from the outside, making maintenance and cleaning operations straightforward without requiring shell disassembly or special access procedures.
Solution Approach 2:
The tube design incorporates features that facilitate self-cleaning or easy access for cleaning. The extended tube ends and smooth internal surfaces allow process fluids to flush through the tubes effectively, and enable routine maintenance personnel to access and clean tubes using standard tools without requiring specialized equipment or complex procedures.
5Ease of manufacture
If carbon steel tubes are used, then cost is reduced, but corrosion resistance decreases
Solution Approach 1:
The heat exchanger employs composite construction with corrosion-resistant alloy tubes (such as stainless steel) installed within a carbon steel shell. This composite structure provides the corrosion resistance needed for the process fluid contact surfaces while utilizing the cost-effective carbon steel for the shell and non-contact components, achieving an optimal balance between durability and cost.
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 system minimizes pressure drop, reduces space requirements, and enhances safety by eliminating welding-related leaks and corrosion, while facilitating easy cleaning and maintenance, thus improving the efficiency and longevity of the heat exchanger.
Implementation Method 1
Heat is transferred from the off-gas to the cooling water, thereby cooling the off-gas
Implementation Method 2
The nozzle is aligned with the plugged tube and a fluid stream is passed through the nozzle to impact the interior of the tube at a pressure sufficient to remove the plug
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
Improved heat exchanger systems and processes for cooling recycled off-gas in high pressure low-density polyethylene production. A system for exchanging heat between a first material and a second material can include a shell for containing the first material therein, a plurality of tubes disposed within the shell for containing the second material therein, a tube sheet disposed at an end of the shell for restricting flow of the second material to the shell, and at least one collector conduit disposed exterior to the shell for receiving at least one end of the plurality of tubes, wherein at least one of the plurality of tubes extend through the tube sheet to the collector conduit. A cleaning tool can be disposed within the collector conduit for cleaning the tubes. A process for cooling a gas stream can include introducing the gas stream to the heat exchanger system provided herein.