Methane Extraction Column Cooling to Prevent Heat Exchanger Pinching

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Solution Overview

Problem

Existing methods for liquefying hydrocarbon streams enriched in methane, such as those from natural gas, often result in significant temperature differences between refrigerant streams and hydrocarbon vapors, leading to thermal stresses and internal pinching in heat exchangers, which can cause unstable cooling and damage.

Innovation Solution

A method and apparatus that pre-cool both the hydrocarbon stream and the main refrigerant stream, then indirectly heat exchange the methane-enriched vapor effluent with the pre-cooled hydrocarbon stream to match their temperatures within the extraction column's approach temperature, reducing temperature differences and minimizing thermal stress in subsequent heat exchangers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the gaseous overhead stream and main multicomponent refrigerant stream are cooled in an auxiliary heat exchanger against a pre-cooled refrigerant, then the cooling efficiency is improved, but the temperature difference between streams causes thermal stresses and internal pinching leading to unstable behavior and damage

Engineering Contradiction:

Improvecooling efficiencyVSAvoidheat exchanger stability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The invention applies preliminary cooling to the gaseous overhead stream before it enters the auxiliary heat exchanger. A pre-cooling heat exchanger is introduced that cools the overhead stream using a portion of the main refrigerant stream before both streams enter the auxiliary heat exchanger. This preliminary action reduces the temperature difference between streams in the auxiliary heat exchanger, preventing thermal stresses and internal pinching while maintaining cooling efficiency.

Inventive Principle:

Principle #10Preliminary action

2Power

If a large temperature difference exists between refrigerant streams and hydrocarbon vapors in heat exchangers, then heat transfer rate is improved, but thermal stresses and internal pinching occur causing unstable cooling and damage

Engineering Contradiction:

Improveheat transfer rateVSAvoidthermal stress

Core Design Contradiction:

PowerVSObject-affected harmful factors

Solution Approach 1:

The cooling process is segmented into two stages: a pre-cooling stage and a main cooling stage. The pre-cooling heat exchanger handles the initial temperature reduction of the overhead stream, while the auxiliary heat exchanger handles the subsequent cooling. This segmentation allows each heat exchanger to operate with more manageable temperature differences, maintaining adequate heat transfer rates while avoiding excessive thermal stresses.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention introduces an intermediary cooling stage using the pre-cooling heat exchanger and a portion of the main refrigerant stream. This intermediary step acts as a buffer between the hot overhead stream and the cold auxiliary heat exchanger, reducing the temperature shock and thermal stress on the auxiliary heat exchanger while maintaining overall heat transfer efficiency.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 ensures stable cooling processes by maintaining temperature differences within acceptable limits, reducing the risk of thermal stress and damage to heat exchangers, and enhances the efficiency of the liquefaction process.

Implementation Method 1

cooling at least a part of the hydrocarbon stream and a main refrigerant stream by indirect heat exchanging against a pre-cooling refrigerant

Methodology Applied

Scientific EffectHeat exchange: Heat Exchanger

Implementation Method 2

discharging an effluent stream, in the form of a methane-enriched hydrocarbon stream, from the extraction column via a vapour outlet arranged gravitationally higher relative to the first inlet into the extraction column

Methodology Applied

Scientific EffectGravity separation: Gravitation

Implementation Method 3

cooling both the effluent stream and the at least part of the pre-cooled main refrigerant stream in the further heat exchanger

Methodology Applied

Scientific EffectHeat exchange: Heat Exchanger

Data Source

PatentUS10215485B2Method of treating a hydrocarbon stream comprising methane, and an apparatus therefor

Publication Date: 2019.02.26 SHELL USA INC

AI summary

In a method and apparatus for treating a hydrocarbon stream having methane, at least a part of the hydrocarbon stream and a main refrigerant stream are cooled by indirect heat exchanging against a pre-cooling refrigerant. The pre-cooled hydrocarbon stream is passed to a first inlet of an extraction column, and an effluent stream is discharged from the extraction column. The effluent stream and at least a part of the pre-cooled main refrigerant stream are passed to a further heat exchanger, where they are both cooled thereby providing a cooled methane-enriched hydrocarbon stream and at least one cooled main refrigerant stream. The passing of the effluent stream to the further heat exchanger and the passing of the pre-cooled hydrocarbon stream to the first inlet of the extraction column includes indirectly heat exchanging the effluent stream against the pre-cooled hydrocarbon stream.