Scrub Column Reflux Configuration for LNG Heating Value Control
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Solution Overview
Problem
Existing LNG liquefaction plants face challenges in producing LNG with varying heating values to meet different market specifications, particularly due to limitations in NGL recovery, especially at high pressures, which leads to excessive refrigeration costs and operational inflexibility.
Innovation Solution
A flexible NGL recovery system is implemented using a scrub column with a second C3+ enriched reflux stream generated by expanding the C5+ depleted vapor fraction, allowing for efficient separation and liquefaction without external refrigeration, by operating at high pressures and utilizing a turbo-expander system to control C3 recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If deep removal of NGL components is implemented to meet low heating value specifications, then heating value control is improved, but plant complexity and cost increase due to requiring additional NGL recovery units
Solution Approach 1:
The cryogenic exchanger is designed to serve dual functions: its primary function of heat exchange for LNG liquefaction and a secondary function of NGL removal through selective condensation. By optimizing the exchanger configuration and operating conditions, lighter NGL components (C1-C4) are removed alongside the heavy NGL components, enabling heating value control without adding separate NGL recovery units.
2Adaptability or versatility
If NGL recovery units are added to existing LNG plants, then heating value flexibility is improved, but capital cost and economic viability worsen, particularly for smaller plants
Solution Approach 1:
The invention utilizes the existing cryogenic exchanger in LNG plants to perform both its original heat exchange function and an additional NGL removal function. By adjusting operational parameters such as pressure, temperature, and feed composition, the system can flexibly control heating value output without requiring capital-intensive additions to the plant infrastructure.
3Manufacturing precision
If C3+ component removal is increased at high pressure, then heating value reduction is improved, but separation difficulty increases making the process less economical
Solution Approach 1:
The system exploits phase transition differences of hydrocarbon components at high pressure within the cryogenic exchanger. By controlling temperature and pressure conditions, components are selectively condensed or vaporized based on their phase behavior, enabling effective separation of C3+ components from lighter gases without requiring complex separation equipment.
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 enables flexible and economical NGL recovery, achieving C3 recovery rates from 40% to 80% without external refrigeration, simplifying control over heating value specifications and reducing costs, making it suitable for both new and retrofitted plants.
Implementation Method 1
a first portion of the C5+ depleted vapor fraction is cooled using refrigeration generated by expansion of a C3+ depleted vapor stream
Implementation Method 2
contacting the cooled natural gas stream in a scrub column with a first and a second reflux stream to thereby produce a C3+ enriched bottoms product and a C5+ depleted overhead product
Data Source
AI summary
NGL recovery from natural gas is achieved by processing the natural gas in a scrub column that operates at high pressure. A C3+ depleted vapor stream is generated from the vapor portion of partially condensed scrub column overhead and expanded to provide refrigeration for the vapor portion to so form a second reflux stream and the C3+ depleted vapor stream. The C3+ depleted vapor stream is then combined with another vapor portion of partially condensed column overhead to produce a lean liquefaction feed stream.