Methane Rejection Process Using LNG Recycle for High-CO2 Natural Gas
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Solution Overview
Problem
Existing processes for purifying methane from feedstocks with high concentrations of carbon dioxide are economically unviable due to the large size and high operating costs of amine systems, which also pose safety hazards from handling toxic and corrosive solvents.
Innovation Solution
A simplified apparatus that uses liquid natural gas (LNG) to condition the feedstock, reducing the need for consumables and cycling it back into the process, thereby reducing capital and operating expenses while effectively removing CO2 and producing high-quality methane vapor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If amine systems are used to treat high concentration CO2 feedstock, then CO2 removal capability is improved, but capital expenses and device complexity increase significantly
Solution Approach 1:
The patent changes the operating parameters by using refrigerated conditions (low temperature) and pressure swing operations instead of chemical absorption. The feedstock is cooled to approximately -100°F to -150°F, causing CO2 to preferentially condense and separate from methane, eliminating the need for large amine treatment systems
Solution Approach 2:
The patent replaces the chemical absorption mechanism (amine systems) with a physical separation mechanism based on temperature and pressure control. The mechanical refrigeration system and phase separation process substitute for the chemical reaction-based amine treatment, reducing both capital expenses and operational complexity
2Reliability
If amine systems are used to treat high concentration CO2 feedstock, then CO2 removal capability is improved, but operating expenses increase due to electrical power consumption and consumables
Solution Approach 1:
The patent employs periodic pressure swing operations where the system alternates between high-pressure separation mode and low-pressure regeneration mode. During high pressure, CO2 is separated; during low pressure, the adsorbent or separation medium is regenerated. This periodic cycling reduces continuous energy input requirements compared to constant operation of amine systems
Solution Approach 2:
The refrigeration system is designed to be self-sufficient by using the cold LNG product as a heat sink for the refrigeration cycle. The LNG provides the cooling capacity needed to maintain low temperatures, reducing or eliminating the need for external electrical power input for refrigeration
3Reliability
If amine systems are used to treat high concentration CO2 feedstock, then CO2 removal capability is improved, but safety hazards increase due to toxic and corrosive solvents
Solution Approach 1:
The patent extracts and eliminates the harmful amine chemicals from the process entirely. By using physical separation methods based on temperature and pressure, the system removes CO2 without requiring toxic and corrosive chemical solvents, thereby eliminating the associated safety hazards and environmental concerns
Solution Approach 2:
The patent creates an inert operating environment by using cold temperatures and pressure-controlled conditions that enable physical separation without chemical reactions. This inert approach avoids the use of reactive chemical solvents, eliminating corrosion and toxicity issues inherent in amine-based systems
4Reliability
If amine systems are used to treat high concentration CO2 feedstock, then CO2 removal capability is improved, but capital expenses increase due to larger equipment requirements
Solution Approach 1:
By changing the operating parameters to low temperature and high pressure conditions, the patent enables compact equipment design. The refrigerated separation vessels and heat exchangers required for this process are significantly smaller and less expensive than the large amine treatment towers, pumps, and associated infrastructure
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 achieves cost-effective and safe methane vapor production with lower capital expenses and operating costs, producing high-quality methane and liquefied CO2, suitable for LNG and industrial applications, without the need for hazardous solvents.
Implementation Method 1
contacting a first feedstream comprising liquid natural gas (LNG) with a feedstock comprising methane
Implementation Method 2
liquefying the first overhead product to form a liquefied product
Data Source
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AI summary
A process that is configured for treating natural gas mixed with carbon dioxide (CO2) in high concentrations of 30% mole by volume or more. In one embodiment, the process comprises contacting a first feedstream comprising liquid natural gas (LNG) with a feedstock comprising methane to form an overhead product comprising methane vapor and a bottom product comprising carbon dioxide (CO2). The embodiment can also comprise liquefying the methane vapor to form a LNG product and using the LNG product as the liquid natural gas (LNG) in the first feedstream.