Mixed Refrigerant Drain-Down Subsystem to Reduce LNG Shutdown Losses
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Solution Overview
Problem
Natural gas liquefaction facilities face significant losses of mixed refrigerants during shutdowns due to the volatility of heavier light hydrocarbons, leading to over-pressurization and potential explosions, which results in costly venting and flaring of refrigerant, necessitating methods to conserve the mixed refrigerant during drain-down operations.
Innovation Solution
Implementing a drain-down subsystem with a high-pressure holding tank and a low-pressure drum, where the mixed refrigerant is pumped into the high-pressure tank and optionally transferred to the low-pressure drum, and using a backfill gas to maintain system pressure, allowing for the conservation of mixed refrigerant during shutdowns by managing pressure drops across valves to prevent over-pressurization and facilitate safe storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the mixed refrigerant is drained during shutdown to prevent over-pressurization, then safety is improved, but refrigerant loss increases due to venting and flaring
Solution Approach 1:
The patent introduces an intermediary storage system consisting of a high-pressure holding tank and a low-pressure drum to capture and temporarily store the drained refrigerant. The high-pressure holding tank receives refrigerant directly from the refrigeration system at elevated pressure, then gradually transfers it to the low-pressure drum, preventing direct venting to atmosphere and enabling refrigerant recovery when the system is back online
Solution Approach 2:
The patent utilizes parameter changes in the refrigerant's physical state, specifically exploiting the pressure-temperature relationship of the mixed refrigerant. By controlling pressure differentials between the high-pressure holding tank and low-pressure drum, the system enables phase changes and controlled flow of refrigerant without requiring additional energy input, allowing the refrigerant to self-regulate its transfer based on thermodynamic properties
2Loss of substance
If the refrigerant is stored in high-pressure holding tank, then refrigerant conservation is improved, but system complexity increases
Solution Approach 1:
The patent segments the refrigerant storage function into two distinct pressure zones: a high-pressure holding tank for immediate capture of drained refrigerant and a low-pressure drum for gradual discharge and long-term storage. This segmentation allows each component to operate within optimized pressure ranges, simplifying the design requirements for each individual component while achieving the overall goal of refrigerant conservation
Solution Approach 2:
The system is designed to be self-regulating, using the inherent pressure differential between the high-pressure holding tank and low-pressure drum to automatically control refrigerant flow. The refrigerant itself provides the driving force for transfer between storage vessels through pressure equalization, eliminating the need for external pumps or complex control systems during the transfer process
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 method effectively conserves mixed refrigerant by storing it at safe pressures and temperatures, reducing losses and costs associated with venting and flaring, while ensuring safe operation during shutdowns and startup processes in natural gas liquefaction facilities.
Implementation Method 1
draining down at least a portion of a mixed refrigerant in one or more components of the refrigerant distribution subsystem into a high-pressure holding tank of a drain down subsystem, wherein draining down to the high-pressure holding tank is achieved by pumping the mixed refrigerant from the refrigerant distribution subsystem to the high-pressure holding tank
Implementation Method 2
The mixed refrigerant being used in components of the natural gas liquefaction facility warms and increase in pressure
Data Source
AI summary
A method of operating, during an at least partial shutdown of a refrigerant distribution subsystem in a natural gas liquefaction facility, can include: draining down at least a portion of a mixed refrigerant in one or more components of the refrigerant distribution subsystem into a high-pressure holding tank of a drain down subsystem, wherein draining down to the high-pressure holding tank is achieved by pumping the mixed refrigerant from the refrigerant distribution subsystem to the high-pressure holding tank or backfilling the refrigerant distribution subsystem with a backfill gas; and optionally, transferring at least a portion of the mixed refrigerant into a low-pressure drum from the high-pressure holding tank.