Segmented Cooled Tube Supports for Duct-Fired HRSG Heat Exchangers
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Solution Overview
Problem
Conventional once-through heat recovery steam generators face challenges with corrosion and mechanical stress due to increased heat levels from supplementary heating, which can shorten the lifespan of ferritic materials used in tube supports, and there is a need to manage thermal and mechanical stresses across vertically oriented tube supports.
Innovation Solution
A heat exchanger design featuring multiple cooled supports with a casing configured to direct a working fluid, including pairs of spaced supports with coolant carrying bodies and vertically spaced cross-supports that distribute the load and provide cooling to mitigate thermal expansion, allowing the use of ferritic materials in harsher environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If ferritic material is used for tube supports in conventional once-through HRSGs, then manufacturing cost is reduced and ease of manufacture is improved, but the lifespan is shortened due to corrosion and thermal stress in high-temperature environments with supplementary heating
Solution Approach 1:
The support structure is divided into multiple segments: outer supports made of ferritic material and inner supports made of austenitic material. This segmentation allows each material to be used where it is most effective - ferritic for structural support and austenitic for corrosion resistance in high-temperature zones - thereby extending lifespan while controlling manufacturing costs.
Solution Approach 2:
Different materials are used in different locations within the support structure. Austenitic material is placed in the inner supports where it directly contacts the harsh high-temperature, high-corrosion environment, while ferritic material is used in outer supports where mechanical strength is prioritized. This local differentiation optimizes both lifespan and manufacturing ease.
2Duration of action of stationary object
If austenitic material is used for tube supports to withstand high-temperature corrosive environments, then lifespan is extended, but material cost and manufacturing complexity increase
Solution Approach 1:
The support structure is divided into multiple segments: outer supports made of ferritic material and inner supports made of austenitic material. This segmentation allows each material to be used where it is most effective - ferritic for structural support and austenitic for corrosion resistance in high-temperature zones - thereby extending lifespan while controlling manufacturing costs.
Solution Approach 2:
Different materials are used in different locations within the support structure. Austenitic material is placed in the inner supports where it directly contacts the harsh high-temperature, high-corrosion environment, while ferritic material is used in outer supports where mechanical strength is prioritized. This local differentiation optimizes both lifespan and manufacturing ease.
3Device complexity
If single cross-support configuration is used in vertically oriented HRSGs, then device complexity is reduced, but thermal and mechanical stresses concentrate on specific tube supports causing shortened lifespan
Solution Approach 1:
The single cross-support is segmented into multiple cross-supports spaced vertically along the tube supports. This distributes the mechanical load and thermal stress across multiple points rather than concentrating it at one location, thereby extending the lifespan of the tube supports while maintaining relatively simple device complexity.
Solution Approach 2:
The support structure transitions from a single-point support to a distributed multi-point support system along the vertical dimension. This dimensional distribution of support points reduces stress concentration and improves thermal management along the length of the tube supports.
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 design extends the lifespan of heat exchanger components by distributing load and thermal stress, reducing the need for costly austenitic materials and simplifying manufacturing, while enabling operation in hotter environments with supplementary heating.
Implementation Method 1
at least one of the upstream support and the downstream support includes a coolant carrying body configured to direct a coolant therethrough
Implementation Method 2
provide cooling to mitigate thermal expansion
Implementation Method 3
a heat exchanger section in the casing, each HE section including a pair of spaced supports... and a plurality of tube positioners suspended from each of the first and at least one second cross-support, each tube positioner positioning a plurality of heat exchange tubes extending across at least a portion of a working fluid path through the casing
Data Source
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AI summary
A heat exchanger (108) includes a casing (140) configured to direct a working fluid (142, 144) therethrough, and at least one heat exchanger (HE) section (168) in the casing (140). Each HE section (168) includes a pair of spaced supports (170). The spaced supports (170) include: an upstream support (172U) and a downstream support (172D) with at least one of them including a coolant carrying body (182) configured to direct a coolant (184) therethrough. A first cross-support (174) couples to and extends between respective upstream and downstream supports (172U, 172D); and at least one second cross-support (176) couples to and extends between the respective upstream and downstream supports (172U, 172D). Cross-supports (174) are vertically distanced from adjacent cross-supports (174). A plurality of tube positioners (180) coupled to each cross-support (174) position a plurality of heat exchange tubes (146) extending across a working fluid path (164) through the casing (140). The segmented support of the tube positioners (180) and the cooling of the cross-supports (174) allows ferritic material to be used for once-through, duct-fired HRSGs (148).