Integrated LNG and CO2 Liquefaction With Shared Refrigeration
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Solution Overview
Problem
The existing natural gas liquefaction and CO2 purification processes require separate cold production systems, leading to high capital expenditures and inefficient thermal integration, particularly due to the need for dedicated refrigeration cycles and the challenge of removing heavy hydrocarbons and aromatic derivatives like benzene during liquefaction.
Innovation Solution
A thermal integration method that couples the natural gas liquefaction unit with the CO2 purification/liquefaction unit, utilizing a shared refrigeration cycle and heat exchanger system to provide the necessary cold temperatures, thereby eliminating the need for a dedicated CO2 refrigeration unit and optimizing the use of existing machinery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate cold production systems are used for natural gas liquefaction and CO2 purification, then each process can be optimized independently, but capital expenditures increase and thermal efficiency decreases
Solution Approach 1:
The patent combines the natural gas liquefaction system and CO2 purification system into a single integrated process where the CO2 purification unit is thermally coupled to the natural gas liquefaction unit. The cold production system serves both processes simultaneously, eliminating the need for separate refrigeration cycles and reducing capital expenditures while maintaining process reliability.
Solution Approach 2:
The cold production system is designed to perform multiple functions: it provides cooling for natural gas liquefaction and simultaneously supplies cold temperatures for CO2 purification and liquefaction. This multi-functional approach eliminates redundant equipment and optimizes thermal efficiency across both processes.
2Manufacturing precision
If a dedicated refrigeration cycle is installed for CO2 purification, then CO2 can be purified to food-grade specifications, but the system complexity and investment costs increase
Solution Approach 1:
The CO2 purification unit is merged with the natural gas liquefaction unit through thermal coupling. The same cold production system and heat exchanger network serve both processes, eliminating the need for a dedicated refrigeration cycle while achieving food-grade CO2 purity through integrated temperature control and phase separation.
Solution Approach 2:
The integrated system uses the cold temperatures generated during natural gas liquefaction to automatically provide cooling for CO2 purification without requiring additional active refrigeration equipment. The system serves itself by utilizing waste cold from one process to enable another process.
3Manufacturing precision
If heavy hydrocarbons and aromatic derivatives are removed during liquefaction, then the quality of liquefied natural gas is improved, but the process complexity increases
Solution Approach 1:
The washing column is positioned in the process flow to remove heavy hydrocarbons and aromatic derivatives before the natural gas enters the main liquefaction process. This preliminary purification prevents freezing issues during liquefaction and eliminates the need for additional complex separation equipment downstream, simplifying the overall process while ensuring LNG 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
This approach reduces the investment in cold production systems, enhances thermal efficiency, and ensures the removal of heavy hydrocarbons and aromatic derivatives, such as benzene, while maintaining high efficiency in liquefying natural gas and producing high-purity CO2.
Implementation Method 1
Amine scrubbing separates CO2 from the feed gas by scrubbing the natural gas stream with an amine solution in an absorption column
Implementation Method 2
refrigerant streams are used to produce cold at different levels of a main heat exchanger by vaporizing against the stream of hydrocarbons to be liquefied
Implementation Method 3
refrigerant streams are used to produce cold at different levels of a main heat exchanger by vaporizing against the stream of hydrocarbons
Implementation Method 4
The CO2-enriched amine solution is recovered from the bottom of this absorption column and is regenerated at low pressure in a distillation (or stripping) column
Data Source
Figure 1
AI summary
A method of producing liquefied natural gas (27) and carbon dioxide (liquid CO2 (29) from a natural gas feed gas (1) containing carbon dioxide and rich in hydrocarbons comprising at least 10 ppm molar hydrocarbons having at least six carbon atoms, comprising at least the following steps: - Step a): separation of a feed gas (1) from natural gas, containing hydrocarbons and carbon dioxide in a unit treatment (2), into a CO2-enriched gas stream (4) and a natural gas stream (3); - Step b): Cooling of said natural gas (3) in a heat exchanger (2'); - Step c) Purification of compounds containing at least six carbon atoms of the partially liquefied gas in step a); - Step d): At least partial condensation of said gas stream (9) from step c) to form a two-phase stream (15); - Step e): Separation of said two-phase stream (15) from step d) to form a gaseous stream (17) and a liquid stream (18); - Stage f): Use of a first part (18') of the liquid stream (18) resulting from stage e) as reflux at the head (8) of the washing column (5); - Step g): Condensation of the gas stream (17) from step e) to form a liquefied gas (21) containing less than 5 ppm by volume of compounds containing at least six carbon atoms. - Stage h): Liquefaction of the gas stream enriched in CO2 (4) resulting from stage a) with a part (18") of the liquid stream (18) resulting from stage e).