Cold Box Refrigeration Integration for Natural Gas Liquid Recovery
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Solution Overview
Problem
Natural gas liquid recovery systems face inefficiencies in energy consumption and heat recovery due to limitations in existing refrigeration and separation processes, particularly in achieving the required low temperatures and high purity of natural gas liquids.
Innovation Solution
A natural gas liquid recovery system incorporating a cold box with a mixed hydrocarbon refrigerant composition of 61% to 69% C3 hydrocarbons and 31% to 39% C4 hydrocarbons, which includes a chill down train, de-methanizer column, gas and liquid dehydrators, and a refrigeration system with a primary refrigerant that undergoes compression, condensation, and expansion cycles to achieve efficient cooling and separation of methane from heavier hydrocarbons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional refrigeration and separation processes are used, then natural gas liquid recovery can be achieved, but energy consumption is high and heat recovery is inefficient
Solution Approach 1:
The patent combines the refrigeration system and separation process into an integrated system where the refrigerant cycle and hydrocarbon separation occur in close thermal coupling. This merging allows waste heat from the refrigeration condensation process to be directly utilized for heating feed gas or pre-heating purposes, eliminating the need for separate utility heating systems and significantly improving overall energy efficiency.
Solution Approach 2:
The patent converts the waste heat generated during refrigerant condensation, which would normally be discarded to the environment, into a useful resource for heating process streams. The condensation heat that was previously a loss is now captured and used to pre-heat feed gas or provide process heating, transforming an harmful thermal pollution into a beneficial energy source and reducing total energy consumption.
2Reliability
If mixed hydrocarbon refrigerant is used, then cooling efficiency is improved, but system complexity increases
Solution Approach 1:
The patent utilizes parameter changes by adjusting the composition ratios of C3 and C4 hydrocarbons in the mixed refrigerant to optimize cooling performance for specific temperature ranges. By varying the refrigerant composition parameters, the system can be tuned to achieve maximum cooling efficiency at different operating conditions while managing the inherent complexity through systematic composition control.
Solution Approach 2:
The patent employs a composite refrigerant system using a mixture of C3 and C4 hydrocarbons rather than a single component. This composite approach allows the refrigerant to operate effectively across a broader temperature range and provides better heat transfer characteristics, improving cooling efficiency while the complexity is managed through the predictable behavior of hydrocarbon mixtures.
3Manufacturing precision
If multiple separation stages are implemented, then natural gas liquid purity is improved, but process complexity increases
Solution Approach 1:
The patent divides the separation process into multiple stages, with each stage targeting specific hydrocarbon components for removal. This segmentation allows for progressive purification where each stage focuses on extracting particular fractions, achieving high overall purity through cumulative effect rather than requiring a single complex separation step, thus managing complexity through modular staged processing.
Solution Approach 2:
The patent implements separation stages that may remove slightly more than the minimum required components at each step, ensuring that the cumulative effect achieves the target purity specification. This partial or excessive action at intermediate stages prevents the need for overly complex final polishing steps, as the systematic over-removal at earlier stages simplifies the overall process complexity while maintaining high purity output.
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 produces sales gas with at least 98.6 mol% methane and natural gas liquid with at least 99.5 mol% hydrocarbons heavier than methane, reducing energy consumption and operating costs by optimizing heat transfer and refrigeration processes.
Implementation Method 1
a refrigeration system with a primary refrigerant that undergoes compression, condensation, and expansion cycles
Implementation Method 2
the primary refrigerant that undergoes compression, condensation, and expansion cycles
Implementation Method 3
optimizing heat transfer and refrigeration processes
Implementation Method 4
achieve efficient cooling and separation of methane from heavier hydrocarbons
Implementation Method 5
gas and liquid dehydrators
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
This specification relates to operating industrial facilities, for example, crude oil refining facilities or other industrial facilities that include operating plants that process natural gas or recover natural gas liquids.