Cascade CO2 Compressor Stages with Annular Gap
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Solution Overview
Problem
The CO2 flow reaching the impeller of the first compressor in a supercritical CO2 cycle often enters in a multiphase status due to local acceleration, leading to a sonic region that limits the compressor's operating range and reduces efficiency.
Innovation Solution
A compressor system with two cascade compression stages and an annular gap in-between, where the first compressor stage has a lower number of blades to minimize shock waves and maintain supercritical conditions, and the second stage provides a higher pressure ratio to ensure efficient compression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the CO2 flow is compressed close to the critical point to reduce compressor work, then the thermal efficiency of the sCO2 cycle is improved, but the CO2 flow enters a multiphase status due to local acceleration, causing a sonic region that limits the compressor operating range
Solution Approach 1:
The compression process is divided into multiple stages with an intercooler between them. The first compressor stage compresses CO2 to a pressure slightly above saturation pressure, then the intercooler removes heat to return the CO2 to supercritical conditions before the second compressor stage. This segmentation prevents the CO2 from entering multiphase status during compression while still achieving the desired pressure ratio and thermal efficiency.
Solution Approach 2:
The intercooler acts as an intermediary device between the two compressor stages. It removes the heat of compression and returns the CO2 to supercritical conditions, preventing phase change and sonic region formation in the second compressor stage. This intermediary step enables the system to maintain both high efficiency and wide operating range.
2Stress or pressure
If numerous compressor blades are used at the inlet stage to increase compression capability, then the pressure ratio is improved, but the local flow acceleration increases, promoting phase-change phenomena that reduce compressor efficiency
Solution Approach 1:
The total pressure ratio is segmented across two compressor stages rather than achieving it in a single stage. The first stage uses a moderate number of blades to compress CO2 to slightly above saturation pressure, while the second stage completes the compression after the intercooler has reset the CO2 to supercritical conditions. This avoids excessive local acceleration and phase-change phenomena in any single stage.
Solution Approach 2:
The temperature and pressure parameters of the CO2 are changed between compressor stages through the intercooler. By removing heat and returning the CO2 to supercritical conditions, the physical state parameters are optimized for the second compression stage, reducing compressibility effects and preventing phase change even with multiple blades.
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 configuration enhances the compressor's operating range and efficiency by maintaining supercritical conditions and minimizing losses, thereby improving the overall thermal efficiency of the CO2 cycle.
Implementation Method 1
When a fluid flowing at a given pressure and temperature passes through a constriction, the fluid velocity increases. At the same time, the Venturi effect causes the static pressure, and therefore the density, to decrease at the constriction.
Implementation Method 2
the fluid is compressed by one or more compressors, heat is introduced into the cycle by a first heat exchanger, the fluid is expanded by one or more expanders
Data Source
AI summary
The compressor is used for processing a CO2 flow; a first compressor stage has a first row of blades with a first number of blades and a second compressor stage, downstream the first compressor stage, has a second row of blades with a second number of blades; the number of blades of the first compressor stage is less than the number of blades of the second compressor stage; there is an annular gap between the first row of blades and the second row of blades; the first compression stage (200) is designed so to assure that the CO2 flow is in supercritical condition, preferably close to CO2 critical point, at its outlet, and so that the second compressor stage process CO2 in supercritical condition.