Cascade Heat Exchangers for Methane Cold Recovery and CO2 Capture
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Solution Overview
Problem
Current methods for recovering cold from liquefied methane during its compression for natural gas distribution are inefficient, and there is limited utilization of this cold for CO2 capture from independent gas flows.
Innovation Solution
A refrigeration system with a cascade of heat exchangers that utilizes liquefied methane to transfer cold to a mixture of refrigerant fluids, allowing for independent control of methane and CO2 flow rates, and includes expanders and separators to adjust pressure and temperature, enabling efficient cold recovery and CO2 capture through frosting and defrosting cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If liquid methane is compressed to high pressure for distribution, then methane can be transported efficiently through the network, but the cold energy produced during compression is wasted and not utilized
Solution Approach 1:
The invention converts the previously wasted cold energy from methane compression into a useful resource for CO2 capture. The cold methane stream that was simply heating up during compression is now used to frost CO2 from flue gas, transforming an energy loss into a beneficial cooling source for carbon capture operations.
Solution Approach 2:
The invention merges two independent processes - methane compression for distribution and CO2 capture from flue gas - into a single integrated system. The methane compression process provides the cooling capacity needed for CO2 separation, combining what were previously separate operations into a synergistic system where waste cold from one process drives the other.
2Productivity
If the flow rate of methane is increased to improve distribution capacity, then more natural gas can be transported, but the ability to capture CO2 is affected since the flows were previously considered uncorrelated
Solution Approach 1:
The heat exchanger serves multiple functions simultaneously: it acts as a compression heater for methane, a cooler for the refrigerant cycle, and a CO2 capture unit. This multi-functionality allows the system to handle varying methane flow rates while maintaining CO2 capture capability, as the same equipment serves both methane distribution and carbon capture needs.
Solution Approach 2:
The system dynamically adapts to varying methane flow rates by adjusting the refrigerant circulation and heat exchanger operations. The coupled flows of methane and CO2-conveying gas are coordinated through the thermal interaction in the heat exchanger, allowing the system to maintain optimal performance across different operating conditions rather than requiring fixed flow rates.
3Ease of operation
If a simple heat exchanger is used to recover cold from methane, then the system is easy to operate, but it cannot simultaneously handle independent methane and CO2 flow rates effectively
Solution Approach 1:
The invention nests the CO2 capture process within the methane compression process by using the same heat exchanger for both functions. The refrigerant cycle is embedded within the methane compression system, with the evaporator serving as the CO2 capture unit. This nested structure allows independent flow rate control while maintaining operational simplicity through a unified system 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
The system effectively recovers cold from liquefied methane, reducing energy consumption in methane transport and enabling efficient CO2 capture by modulating cold recovery based on CO2 capture system needs, while also converting excess cold into mechanical energy.
Implementation Method 1
each of the heat exchangers (E1, E2, and E3) passes a cold-supplying flow (150) of liquefied methane
Implementation Method 2
a high-pressure flow (122) of a mixture of refrigerant fluids that condenses partially or completely; a low-pressure flow (100) of a mixture of the same refrigerant fluids, which evaporates
Implementation Method 3
an expander (60) placed at the outlet from the cascade (E1, E2, and E3)
Implementation Method 4
a separator (21) placed at the outlet from the partial condenser (200)
Implementation Method 5
a partial condenser (200) suitable for condensing, partially or completely, the mixture of refrigerant fluids (120) compressed by the compressor (10)
Implementation Method 6
a compressor (10) suitable for compressing the mixture of refrigerant fluids (120)
Implementation Method 7
the flow of a mixture of refrigerant fluids that condenses is also cooled in part by a fraction of the flow of the mixture of refrigerant fluids
Data Source
AI summary
A refrigeration system includes a plurality of heat exchangers (E1, E2, E3) in cascade, each of said heat exchangers including: a flow (150) of cold-producing liquefied methane; a high-pressure flow (122) of a two-phase mixture of refrigerant fluids giving up in heat and including refrigerant fluids having a low normal boiling temperature; and a low-pressure flow (100) of a cold-producing two-phase mixture of said refrigerant fluids.