LPG Recovery Process Using Sponge Absorber and Deethanizer

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Solution Overview

Problem

Current LPG recovery processes in hydrocracking units face challenges in reducing hydrogen sulphide (H2S) content below 10 wppm while maintaining high recovery rates and minimizing equipment and energy consumption, leading to increased costs and complexity.

Innovation Solution

A process involving a sponge absorber, deethanizer, and debutanizer column configuration, where a C3 stripped stream is mixed with the stripper overhead product to enhance H2S removal and LPG recovery, and stabilized naphtha is mixed with off-gas to improve absorption, allowing for flexible operation and reduced equipment needs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional sponge absorber and amine absorber configuration is used, then LPG recovery is achieved at 90-95%, but H2S content in LPG product remains at about 35 wppm or less which does not meet stricter environmental regulations

Engineering Contradiction:

ImproveH2S content specificationVSAvoidabsorber configuration

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The absorber is divided into distinct sections: a upper section for H2S removal using amine absorber and a lower section for LPG absorption using sponge absorber. This segmentation allows each section to perform its specific function efficiently, achieving low H2S content (below 10 wppm) while maintaining high LPG recovery without requiring multiple separate absorbers

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The absorber column performs multiple functions simultaneously: it acts as both an amine absorber for H2S removal in the upper section and a sponge absorber for LPG recovery in the lower section. This multi-functionality reduces the number of separate equipment units needed while achieving both H2S specification compliance and high LPG recovery

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Manufacturing precision

If amine absorbers treat the entire feed gas to remove H2S, then H2S content is reduced below 10 wppm, but equipment capacity and plot area increase

Engineering Contradiction:

ImproveH2S content specificationVSAvoidplot area

Core Design Contradiction:

Manufacturing precisionVSArea of stationary object

Solution Approach 1:

Instead of treating the entire feed gas through amine absorber, the H2S removal is localized to the upper section of the absorber where amine is introduced. The lower section then handles LPG absorption. This local application of H2S removal function reduces the required amine absorber capacity and associated plot area while still achieving H2S content below 10 wppm in the final LPG product

Inventive Principle:

Principle #3Local quality

3Manufacturing precision

If multiple separate absorbers are used for H2S removal and LPG recovery, then H2S content is reduced, but investment costs and equipment requirements increase

Engineering Contradiction:

ImproveH2S content specificationVSAvoidinvestment costs

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The amine absorber and sponge absorber functions are merged into a single integrated absorber column. The upper section handles H2S removal with amine while the lower section performs LPG absorption. This merging eliminates the need for multiple separate absorber units, reducing capital investment costs and simplifying the overall process configuration while achieving H2S content below 10 wppm and high LPG recovery

Inventive Principle:

Principle #5Merging (Combining)

4Productivity

If conventional single stripper configuration is used, then process is simple, but LPG recovery and H2S removal efficiency are insufficient

Engineering Contradiction:

ImproveLPG recovery efficiencyVSAvoidstripper configuration

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The absorber is segmented into functional zones with different operating characteristics. The upper section operates as an amine absorber for H2S removal while the lower section operates as a sponge absorber for LPG recovery. This segmentation enables high LPG recovery efficiency and effective H2S removal without requiring multiple completely separate processing trains

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 configuration achieves LPG recovery of 90-97% with H2S content below 10 wppm, reducing investment and operating costs, simplifying the process, and complying with stringent product specifications, while minimizing energy consumption and equipment requirements.

Implementation Method 1

passing a feed stream comprising a stripper overhead product through a sponge absorber (LPG absorber), and separating an off-gas stream from the top section of the sponge absorber and a light oil stream (LPG rich stream) from the bottom section of the sponge absorber

Methodology Applied

Scientific EffectPhysical absorption: Absorption (physical)

Implementation Method 2

fractionating the light oil stream into (i) an overhead vapour in the form of a C3 stripped stream comprising less than 20% butane or propane, without condensing and without recycling of condensed overhead vapour into this fractionating step, (ii) a LPG product stream and (iii) a stabilized naphtha stream

Methodology Applied

Scientific EffectDistillation: Distillation

Data Source

PatentUS11584891B2Process for LPG recovery

Publication Date: 2023.02.21 HALDOR TOPSOE AS

AI summary

Process and plant for recovering LPG in a refinery process combining the use of sponge absorber, deethanizer and debutanizer. The process and plant enable high LPG recovery and removal of hydrogen sulphide in the LPG product to low levels.