Three-Stage Shaft Seal for Supercritical CO2
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional shaft-sealing devices fail to maintain reliable sealing performance over a long period when handling supercritical carbon dioxide due to high load on sliding sections and leakage issues, particularly with carbon dioxide leaking into atmospheric air.
Innovation Solution
A three-stage shaft-sealing device is implemented, featuring a contact-type mechanical seal on the inner and outer sides and a contactless mechanical seal in the middle, with seal fluid under higher pressure than the machine fluid to reduce load and prevent leakage, and coolant circulation to recover and manage seal fluid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single contact-type mechanical seal is used, then the structure is simple, but the load on the sliding section is large causing considerable abrasion and short service life
Solution Approach 1:
The seal is divided into multiple sliding sections (first, second, and third sliding sections) with different pressure characteristics. The first sliding section handles high-pressure fluid, the second sliding section handles intermediate pressure with seal fluid, and the third sliding section handles low-pressure seal fluid. This segmentation distributes the load and prevents any single section from bearing excessive abrasion.
2Reliability
If seal fluid under higher pressure is introduced to prevent fluid leakage, then sealing performance improves, but a large amount of seal fluid may be discharged to the exterior
Solution Approach 1:
The second sliding section acts as an intermediary barrier between the high-pressure fluid and the external environment. By positioning this sliding section in the intermediate pressure zone and maintaining it in a non-contact state, the system prevents direct discharge of large amounts of seal fluid to the exterior while still achieving reliable sealing.
3Use of energy by moving object
If a contactless mechanical seal is used for the intermediate stage, then power consumption is reduced and service life is extended, but the structure becomes more complex
Solution Approach 1:
The seal is segmented into three sliding sections with different contact characteristics. The second sliding section is designed as a contactless mechanical seal to reduce power consumption and wear, while the first and third sliding sections use contact-type seals. This segmentation allows the system to benefit from reduced energy consumption in the critical intermediate zone without requiring all sections to be complex contactless designs.
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 extends the service life of mechanical seals, reduces power consumption, prevents fluid leakage, and ensures reliable sealing of supercritical carbon dioxide by distributing load effectively and utilizing higher-pressure seal fluid and coolant circulation.
Implementation Method 1
an intermediate second stage seal has a contactless mechanical seal structure in which the rotational seal element and the stationary seal element are kept by dynamic pressure so as not to be in contact with each other
Implementation Method 2
seal fluid under higher pressure than the pressure of fluid inside the machine is supplied into a first annular space surrounded by that portion of the seal case extending from the first-stage seal to the second-stage seal
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A shaft sealing device in which a load acting on a sliding section of the device is reduced to extend the life of the device and which permits no leakage of fluid in a machine to an atmospheric air to eliminate the need of recovery of the fluid. The shaft sealing device has seals arranged in three stages in the axial direction between a seal case and a rotating shaft passed through the inner periphery of the seal case. Of the seals of the three stages, a first-stage seal on the machine's inner side and a third-stage seal on the machine's outer side have a contact type mechanical seal structure in which a rotational sealing element and a stationary sealing element are in close sliding contact with each other. Further, of the seals of the three stages, the intermediate second-stage seal has a contactless mechanical seal structure in which a rotational sealing element and a stationary sealing element are kept by dynamic pressure so as not to be in contact with each other. A high-pressure sealing liquid is supplied by the pressure of fluid in the machine to an annular space surrounded by that portion of the seal case which extends from the first-stage seal to the second-stage seal.