Main Heat Exchanger Flow Rebalancing for Uniform Tube Exit Temperature
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Solution Overview
Problem
Larger coil-wound heat exchangers face challenges in maintaining even heat transfer and efficiency due to uneven distribution of shell side fluids, leading to temperature imbalances and reduced efficiency in liquefaction processes, particularly in liquefying methane-rich feeds to produce LNG.
Innovation Solution
The process involves adjusting mass flows to subsets of individual tubes within the heat exchanger to equalize exit temperatures by measuring and comparing exit temperatures of different mass flows, using temperature sensors and a controller to adjust mass flows through plugging or restricting tubes, ensuring balanced heat transfer across the tube bundle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If larger coil-wound heat exchangers are used to increase processing capacity, then productivity increases, but heat transfer uniformity deteriorates due to uneven distribution of shell side fluids
Solution Approach 1:
The tube bundle is divided into multiple subsets of individual tubes, with each subset receiving a controlled mass flow of tube side stream. This segmentation allows independent flow management across different regions of the heat exchanger, enabling uniform heat transfer distribution even in large-scale configurations.
Solution Approach 2:
Different mass flows are provided to different subsets of tubes based on local requirements. The system adjusts the mass flow of tube side stream to each subset individually, creating local quality variations that compensate for the uneven distribution of shell side fluids in larger heat exchangers.
2Productivity
If mass flow is increased to improve productivity, then processing capacity increases, but temperature balance deteriorates due to uneven heat transfer distribution
Solution Approach 1:
The system dynamically adjusts the mass flow rate to each subset of tubes based on real-time temperature measurements. By continuously monitoring exit temperatures and modifying mass flow distribution accordingly, the system maintains temperature balance even at high productivity levels.
Solution Approach 2:
Temperature sensors monitor the exit temperature of tube side stream from each subset of tubes, and this feedback is used to control the mass flow rate to each subset. This closed-loop control ensures that temperature uniformity is maintained across all tube subsets, preventing pinching and optimizing heat transfer efficiency.
3Device complexity
If shell side fluid distribution is left uncontrolled, then device complexity remains low, but heat transfer efficiency deteriorates due to temperature imbalances
Solution Approach 1:
The heat exchanger system performs self-diagnosis and self-adjustment by monitoring its own exit temperatures and automatically modifying mass flow distribution to correct imbalances. This self-service capability maintains high heat transfer efficiency without requiring external intervention or complex external control systems.
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
This approach enhances the efficiency of the heat exchanger by maintaining balanced temperature profiles across the tube bundle, preventing pinching and improving overall liquefaction efficiency, thereby optimizing the production of liquefied natural gas.
Implementation Method 1
evaporating a refrigerant stream on the shell side to provide cooling to the first mass flow and the second mass flow
Implementation Method 2
evaporating a refrigerant stream on the shell side to provide cooling to the first mass flow and the second mass flow whereby the tube side stream becomes a liquid
Implementation Method 3
a wall defining a shell side within which is arranged a coil-wound tube bundle
Data Source
Figure 1
Figure 2
AI summary
A process for liquefying a tube side stream in a main heat exchanger is described. The process comprises the steps of: a) providing a first mass flow to the warm end of a first subset of individual tubes, b) providing a second mass flow to the warm end of a second subset of individual tubes, c) evaporating a refrigerant stream on the shell side; d) measuring an exit temperature of the first mass flow; e) measuring an exit temperature of the second mass flow; and, f) comparing the exit temperature of the first mass flow measured in step d) to the exit temperature of the second mass flow measured in step e), the process characterized in that at least one of the first and second mass flows is adjusted to equalise the exit temperature of the first mass flow with the exit temperature of the second mass flow.