Multi-Stage CO₂ Compression with Bypass Subcooling for Inlet Stability
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Solution Overview
Problem
Existing pressure increasing systems face challenges in stabilizing the temperature and pressure of carbon dioxide at the inlet of the final stage compressor, leading to potential excessive cooling and unsuitable conditions for compression, especially when aiming for a final pressure of 10 MPa.
Innovation Solution
The system incorporates multiple stages of compressors, intermediate coolers, a subcooler, a bypass line with a flow rate adjusting valve, and a control unit to regulate the temperature and pressure at the inlet of the final stage compressor, using the gas as a refrigerant to maintain stability and prevent physical property changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If carbon dioxide is additionally cooled using carbon dioxide as a refrigerant after cooling with an intercooler, then the cooling effect is improved, but the temperature may be excessively lowered and enter the transition zone which is not suitable for compression
Solution Approach 1:
The control unit continuously monitors the temperature and pressure of carbon dioxide at the inlet of the final stage compressor and adjusts the degree of opening of the flow rate adjusting valve based on these measurements. This feedback mechanism ensures that the cooling effect is optimized while preventing the temperature from dropping into the unstable transition zone, thereby maintaining compression stability.
Solution Approach 2:
The system dynamically changes the flow rate parameter of the refrigerant carbon dioxide by adjusting the degree of opening of the flow rate adjusting valve. This parameter change allows precise control over the cooling intensity, ensuring that the temperature remains within the stable compression region while achieving the desired cooling effect.
2Temperature
If the temperature of carbon dioxide is excessively lowered to achieve sufficient cooling, then the cooling performance is improved, but the physical properties change in the transition zone making stable compression difficult
Solution Approach 1:
The control unit uses real-time temperature and pressure measurements to adjust the flow rate adjusting valve, creating a closed-loop feedback system. This ensures that cooling performance is maximized while preventing the carbon dioxide from entering the transition zone where physical properties are unstable, thus maintaining composition stability.
Solution Approach 2:
The system dynamically adjusts the degree of opening of the flow rate adjusting valve based on real-time conditions. This dynamic adjustment allows the system to adapt to changing conditions and maintain stable physical properties while achieving sufficient cooling performance.
3Reliability
If a flow rate adjusting valve is added to regulate the refrigerant flow, then the temperature and pressure control is improved, but the device complexity increases
Solution Approach 1:
The system uses the carbon dioxide itself as the refrigerant, eliminating the need for separate refrigerant circulation systems. The flow rate adjusting valve directly controls the refrigerant flow using the working fluid itself, simplifying the overall system architecture while maintaining precise temperature and pressure control.
Solution Approach 2:
The carbon dioxide serves multiple functions: it is both the working fluid being compressed and the refrigerant for cooling. The flow rate adjusting valve controls this dual-purpose fluid, reducing the need for separate control systems and simplifying the overall device complexity.
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 allows for stable and sufficient cooling of carbon dioxide to a suitable state for compression, reducing the motive power required for the final stage compressor and preventing surging, while also serving as a recycling operation without additional heating or cooling units.
Implementation Method 1
a subcooler that is provided between the final stage compressor and a compressor in a stage before the final stage and cools the gas
Implementation Method 2
a flow rate adjusting valve which is provided on the bypass line and by which the extracted gas is depressurized upstream from the subcooler
Implementation Method 3
a control unit configured to regulate a degree of opening of the flow rate adjusting valve so that at least one of a temperature and a pressure of the gas in the inlet of the final stage compressor remains constant
Implementation Method 4
a plurality of stages of compressors configured to compress a gas to a target pressure higher than a critical pressure
Data Source
AI summary
A pressure increasing system includes a plurality of stages of compressors configured to compress carbon dioxide to a pressure higher than a critical pressure; intermediate coolers cooling the carbon dioxide discharged from a compressor in a preceding stage; a subcooler provided between a seventh stage compressor in the final stage and a sixth stage compressor in a preceding stage and cools the carbon dioxide; a bypass line through which the carbon dioxide in the inlet of the seventh stage compressor is extracted, depressurized and supplied to the subcooler as a refrigerant; a flow rate adjusting valve provided on the bypass line; and a control unit configured to regulate a degree of opening of the flow rate adjusting valve so that at least one of a temperature and a pressure of the carbon dioxide in the inlet of the seventh stage compressor remains constant.