Double-Wall Turboexpander for sCO2 Power Cycles
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Solution Overview
Problem
Supercritical carbon dioxide power cycle equipment faces challenges in withstanding high temperatures and pressures, leading to material strength reduction and increased thickness requirements, which complicates design and increases costs due to the need for high-strength alloys and additional thermal management issues.
Innovation Solution
A double-wall turboexpander design is implemented, featuring an inner chamber for high-temperature/high-pressure process fluid surrounded by an outer chamber with a coolant or insulation barrier, reducing the differential pressure and temperature on the inner chamber wall, allowing for thinner, less expensive materials and improved thermal management through strategic coupling and flow enhancement features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-strength materials are used to withstand high pressure and high temperature, then the equipment can operate safely at extreme conditions, but the material cost increases and fabrication complexity increases
Solution Approach 1:
The equipment housing is divided into two distinct chambers: an inner chamber that directly contacts the high-temperature process fluid and an outer chamber that serves as the structural housing. This segmentation allows each chamber to be optimized for its specific functional requirements, with the inner chamber using high-temperature alloy and the outer chamber using lower-cost materials.
Solution Approach 2:
Different material properties are applied to different parts of the housing structure. The inner chamber wall uses high-temperature alloy material to withstand thermal exposure, while the outer chamber uses lower-cost materials that only need to handle mechanical pressure. This local differentiation of material quality reduces overall fabrication complexity and cost while maintaining safety.
2Reliability
If high-strength materials are used to withstand high pressure and high temperature, then the equipment can operate safely at extreme conditions, but the material cost increases
Solution Approach 1:
The housing is segmented into inner and outer chambers with different material requirements. Only the inner chamber, which is directly exposed to high temperatures, requires expensive high-temperature alloy material. The outer chamber can use lower-cost materials, significantly reducing overall material cost while maintaining the safety margin through the inner chamber's material selection.
Solution Approach 2:
High-cost high-temperature alloy material is applied locally only where thermally necessary (inner chamber), rather than throughout the entire housing structure. This localized material application maintains the required safety margin for heat resistance while minimizing material cost by using cheaper materials for the outer chamber that does not experience high temperatures.
3Strength
If the thickness of the equipment housing is increased to provide adequate safety margin at high temperature, then the strength and safety margin improve, but the stress induced by thermal gradients increases and fabrication complexity increases
Solution Approach 1:
The housing structure is segmented into an inner chamber and an outer chamber separated by an inner chamber wall. The inner chamber wall is the primary component exposed to thermal gradients, while the outer chamber serves as a protective enclosure. This segmentation allows the inner wall to be designed with appropriate thickness for thermal stress management, while the outer chamber can be thinner since it is protected from direct thermal exposure.
Solution Approach 2:
The inner chamber wall acts as an intermediary barrier between the high-temperature process fluid and the outer chamber. This intermediary structure absorbs and manages the thermal gradients, protecting the outer chamber from direct thermal exposure and reducing the overall thermal fatigue risk in the housing structure.
4Strength
If the thickness of the equipment housing is increased to provide adequate safety margin at high temperature, then the strength and safety margin improve, but the material cost increases
Solution Approach 1:
The housing is segmented into inner and outer chambers, allowing the inner chamber wall to bear the primary thermal and pressure loads with appropriate thickness for safety margin. The outer chamber can be thinner since it is protected from direct thermal exposure, reducing overall material usage and cost while maintaining the required strength and safety margin through the inner chamber's design.
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 design reduces material costs and fabrication complexity by using thinner high-temperature alloy for the inner chamber and lower-cost materials for the outer chamber, while enhancing heat transfer and flow efficiency, effectively addressing thermal fatigue and stress issues in high-pressure/high-temperature applications.
Implementation Method 1
an inner chamber wall that separates the inner chamber from the outer chamber
Implementation Method 2
the outer chamber to receive a coolant at an elevated pressure or an insulation barrier at an elevated pressure
Data Source
AI summary
The present disclosure is directed to systems and methods generating power using supercritical CO2 in a Brayton cycle that incorporates a double-wall turboexpander that includes an inner chamber housing the turbine and an outer chamber that includes a thermal attenuator that reduces the outer chamber wall temperature of the turboexpander. An inner chamber wall separates the inner chamber and the outer chamber within the double-wall turboexpander. In supercritical CO2 applications, the double-wall turboexpander operates at elevated temperatures and elevated pressures. By maintaining the thermal attenuator the outer chamber at an elevated pressure, the differential pressure across the inner chamber wall is reduced, requiring less high-temperature alloy material in the construction of the double-wall turboexpander when compared to a conventional turboexpander. By reducing the operating temperature of the outer chamber wall, a less costly lower-temperature alloy may be used to provide structural strength to the double-wall turboexpander.