Demethanizer Reflux Configuration for High C2 Recovery
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Solution Overview
Problem
Conventional cryogenic expansion processes for natural gas liquids recovery face inefficiencies in recovering ethylene, ethane, propylene, and heavier hydrocarbons due to losses in the demethanizer column and issues with carbon dioxide icing, which increases capital and operating costs.
Innovation Solution
A supplemental reflux stream is introduced in the upper rectification section of the demethanizer column, combining a recycled residue gas reflux with a side-drawn vapor stream from the lower portion of the tower, allowing for enhanced absorption of C2 and C3+ components, reducing carbon dioxide concentrations, and mitigating icing risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If conventional cryogenic expansion process is used, then natural gas liquids recovery is achieved, but C2 component recovery is insufficient and carbon dioxide icing occurs
Solution Approach 1:
The patent extracts the harmful carbon dioxide component from the gas stream by introducing a supplemental reflux stream that selectively absorbs C2 and C3+ components, leaving carbon dioxide behind. This separation prevents carbon dioxide from reaching conditions where it would form ice, while simultaneously recovering valuable C2 components that would otherwise be lost.
Solution Approach 2:
The patent changes the operational parameters of the demethanizer column by introducing a supplemental reflux stream with specific temperature and composition characteristics. This alters the absorption equilibrium conditions in the upper rectification section, enabling enhanced C2 component recovery while maintaining temperatures and concentrations that prevent carbon dioxide icing.
2Loss of substance
If demethanizer column is operated conventionally, then separation is achieved, but C2 component losses occur in the column
Solution Approach 1:
The patent applies preliminary action by introducing a supplemental reflux stream before the main separation process in the demethanizer column. This pre-conditioned reflux stream, drawn from the lower portion of the tower and combined with residue gas reflux, is prepared in advance to optimize absorption conditions in the upper rectification section, thereby preventing C2 component losses before they occur.
3Loss of substance
If C2 component recovery is increased, then ethane and ethylene recovery improves, but process complexity increases
Solution Approach 1:
The patent achieves multi-functionality by designing the supplemental reflux stream to simultaneously accomplish multiple objectives: it enhances C2 component absorption, maintains column temperature profiles to prevent carbon dioxide icing, and optimizes separation efficiency. This single supplemental stream performs what would otherwise require multiple separate process modifications.
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 achieves C2 component recoveries exceeding 97% with no loss in C3+ component recovery, while maintaining low capital investment and reducing the risk of carbon dioxide icing, thus improving the overall efficiency and safety of the process.
Implementation Method 1
enhanced absorption of C2 and C3+ components
Implementation Method 2
cryogenic expansion processes for natural gas liquids recovery
Implementation Method 3
The vaporization occurring during expansion of the liquids results in further cooling of the stream
Data Source
AI summary
A process for the recovery of ethane, ethylene, propane, propylene, and heavier hydrocarbon components from a hydrocarbon gas stream is disclosed. The stream is cooled and is thereafter expanded to the fractionation tower pressure and supplied to the fractionation tower at a lower mid-column feed position. A distillation stream is withdrawn from the column below the feed point of the stream and is then directed into heat exchange relation with the tower overhead vapor stream to cool the distillation stream and condense at least a part of it, forming a condensed stream. At least a portion of the condensed stream is directed to the fractionation tower at an upper mid-column feed position. A recycle stream is withdrawn from the tower overhead after it has been warmed and compressed. The compressed recycle stream is cooled sufficiently to substantially condense it, and is then expanded to the pressure of the fractionation tower and supplied to the tower at a top column feed position. The quantities and temperatures of the feeds to the fractionation tower are effective to maintain the overhead temperature of the fractionation tower at a temperature whereby the major portion of the desired components is recovered.