Cascade CO2 Compressor With Unequal Blade Counts for Supercritical Flow

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Solution Overview

Problem

The efficiency of supercritical CO2 cycles is limited by shock waves and reduced operating range due to the fluid's proximity to its critical point, causing phase-change phenomena and inefficiencies in turbomachinery design.

Innovation Solution

A compressor system with two cascade compression stages, where the first stage has fewer blades than the second, ensuring the CO2 flow remains supercritical at the outlet, and an annular gap between stages maintains constant pressure, avoiding sonic regions and shock waves.

Engineering Contradictions & Design Principles

VSEngineering 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 enhanced, but the fluid enters a multiphase status causing sonic regions and limitation of compressor operating range

Engineering Contradiction:

Improvecompressor workVSAvoidcompressor operating range

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The compression process is divided into two distinct stages: a first compression stage that compresses the CO2 flow to near-critical conditions, and a second compression stage that further compresses the fluid to supercritical conditions. This segmentation allows each stage to operate in its optimal range, avoiding the multiphase region while achieving the desired pressure ratio and thermal efficiency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first compression stage performs preliminary compression of the CO2 flow to near-critical conditions before the second stage completes the compression to supercritical conditions. This preliminary action prepares the fluid in a controlled manner, preventing premature entry into the multiphase region and ensuring stable operation throughout the compression process.

Inventive Principle:

Principle #10Preliminary action

2Productivity

If numerous compressor blades are used at the inlet stage to handle high flow, then the compression capacity is increased, but local flow acceleration promotes phase-change phenomena and reduces compressor efficiency

Engineering Contradiction:

Improvecompression capacityVSAvoidcompressor efficiency

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The compressor is divided into two stages with different blade configurations. The first stage uses fewer blades optimized for near-critical flow conditions, while the second stage uses more blades optimized for supercritical flow conditions. This segmentation allows each stage to be independently optimized, preventing phase-change phenomena in the first stage while maintaining high compression capacity in the second stage.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each compression stage is designed with locally optimized blade characteristics appropriate for its specific operating conditions. The first stage blades are designed for near-critical flow with lower blade counts to avoid flow acceleration issues, while the second stage blades are designed for supercritical flow with higher blade counts to maximize compression capacity. This local optimization ensures high efficiency throughout the entire compression process.

Inventive Principle:

Principle #3Local quality

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

Enhances cycle efficiency by operating away from the critical point, reducing losses and maintaining high pressure ratios, thus improving overall thermal efficiency.

Implementation Method 1

a first compression step is used for compressing said CO2 flow to a supercritical condition through a first compressor stage (200) so to generate a supercritical CO2 flow, and a second compression step is used for compressing said supercritical CO2 flow through a second compressor stage (300)

Methodology Applied

Scientific EffectCompression: Compression

Implementation Method 2

an annular gap between stages maintains constant pressure, avoiding sonic regions and shock waves

Methodology Applied

Scientific EffectPressure equilibrium:

Implementation Method 3

the CO2 flow reaches the impeller of the first compressor in a multiphase status because of local acceleration upstream and across compressor impeller leading edge... the CO2 flow is in supercritical condition at the outlet of the first compressor stage

Methodology Applied

Scientific EffectPhase transition: Phase Change

Data Source

PatentUS20250283472A1Compressor for co2 cycle with at least two cascade compression stages for assuring supercritical conditions

Publication Date: 2025.09.11 NUOVO PIGNONE TECH SRL

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 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.