Gas subcooled process conversion to recycle split vapor for recovery of ethane and propane

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Solution Overview

Problem

Conventional cryogenic expansion processes for recovering ethane and propane from natural gas suffer from significant losses of C2 components due to incomplete separation, resulting in reduced recovery efficiency and revenue, as they operate largely as stripping columns without adequate reflux to absorb these components from rising vapors.

Innovation Solution

The Recycle Split Vapor Process introduces a second smaller demethanizer tower and a residue reflux stream to enhance separation, allowing for additional rectification and polishing of the product streams, thereby improving the recovery of ethane and propane by bringing rising vapors into contact with a significant quantity of liquid containing minimal C2 components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a conventional single demethanizer tower is used, then the process simplicity is maintained, but the recovery efficiency of C2 components is reduced due to insufficient reflux

Engineering Contradiction:

Improverecovery efficiency of C2 componentsVSAvoidnumber of fractionation towers

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The single fractionation tower is divided into two separate towers: a first fractionation tower for initial separation and a second fractionation tower for enhanced rectification and polishing. This segmentation allows each tower to perform specialized functions, with the second tower providing additional theoretical stages specifically for C2 component recovery, thereby resolving the contradiction between recovery efficiency and device complexity.

Inventive Principle:

Principle #1Segmentation

2Manufacturing precision

If the demethanizer operates as a stripping column without adequate reflux, then the process complexity is reduced, but the separation precision deteriorates due to C2 component losses

Engineering Contradiction:

Improveseparation precision of C2 componentsVSAvoidreflux system configuration

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

A reflux system is implemented where liquid from the top of the second fractionation tower is returned to the tower to contact rising vapors. This feedback mechanism provides continuous rectification, allowing the system to achieve high separation precision by absorbing C2 components from the vapor phase into the liquid reflux, thereby resolving the contradiction between separation precision and device complexity.

Inventive Principle:

Principle #23Feedback

3Productivity

If additional rectification stages are added to improve C2 recovery, then the recovery efficiency is improved, but the capital cost increases

Engineering Contradiction:

Improveethane and propane recoveryVSAvoidcapital cost of additional equipment

Core Design Contradiction:

ProductivityVSEase of manufacture

Solution Approach 1:

Instead of adding extensive stages to a single tower, the system segments the fractionation function across two towers of appropriate size. The second tower is specifically designed with the necessary theoretical stages for C2 recovery, providing cost-effective additional rectification capacity without requiring excessive capital investment in a single oversized tower.

Inventive Principle:

Principle #1Segmentation

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 significantly enhances ethane and propane recovery to 99.98% and 100% respectively, increasing revenue by an estimated 9.7 MM$ per year at a 200 MMSCFD FEED rate, while maintaining flexibility and efficiency across varying flow rates.

Implementation Method 1

cooling the gaseous second stream under pressure sufficiently to partially condense, separating the partially condensed second stream to thereby provide a vapor stream and a condensed stream

Methodology Applied

Scientific EffectPartial condensation: Condensation

Implementation Method 2

expanding the vapor stream to a lower pressure... at which additional liquids are condensed as a result of further cooling of the stream

Methodology Applied

Scientific EffectJoule-Thomson effect: Joule-Thomson Effect

Implementation Method 3

cooled to substantial condensation by heat exchange with other process streams

Methodology Applied

Scientific EffectHeat exchange: Heat Exchanger

Implementation Method 4

the expanded stream, comprising a mixture of liquid and vapor, is fractionated in a distillation (demethanizer) column

Methodology Applied

Scientific EffectDistillation: Distillation

Implementation Method 5

reflux capable of absorbing the C2 components and heavier components from the vapors

Methodology Applied

Scientific EffectAbsorption: Absorption (physical)

Data Source

PatentUS11473837B2Gas subcooled process conversion to recycle split vapor for recovery of ethane and propane

Publication Date: 2022.10.18 UOP LLC

AI summary

A design is provided to convert a gas subcooled process plant to a recycle split vapor process for recovering ethane and propane from natural gas. When in operation, the recovery of ethane and propane can exceed 97 to 99 wt. % of the stream being processed. A second smaller demethanizer column is added to the gas subcooled process plant as well as the addition of several cryogenic pumps.