Multistage Nitrogen Removal in LNG Liquefaction Feed Streams

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Solution Overview

Problem

High nitrogen concentrations in natural gas feed streams complicate liquefaction, increasing compressor horsepower requirements and leading to lower quality LNG and higher operational costs due to inefficient nitrogen removal processes in LNG facilities.

Innovation Solution

A process involving multiple refrigeration cycles and a multistage separation vessel to enhance nitrogen removal, where the nitrogen mole fraction of the vapor stream is increased relative to the feed stream, utilizing a separation-enhancing stream to facilitate efficient nitrogen separation and reduction in LNG facilities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional nitrogen removal units process large volumes of methane-containing intermediate process streams, then nitrogen can be removed from the natural gas stream, but the overall cost of nitrogen removal increases due to processing larger volumes of more nitrogen-dilute process streams

Engineering Contradiction:

Improvenitrogen removal effectivenessVSAvoidcost of nitrogen removal

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent applies preliminary action by performing nitrogen removal at an earlier stage in the liquefaction process, before the natural gas stream is fully processed. By removing nitrogen from the feed stream or intermediate streams with higher nitrogen concentrations, the system avoids the need to process large volumes of nitrogen-dilute streams later in the process, thereby reducing the overall cost and complexity of nitrogen removal while maintaining effectiveness

Inventive Principle:

Principle #10Preliminary action

2Productivity

If natural gas with high nitrogen concentration is subjected to liquefaction, then the natural gas can be converted to LNG, but compressor horsepower requirements increase and liquefaction efficiency decreases

Engineering Contradiction:

Improveliquefaction throughputVSAvoidcompressor horsepower requirements

Core Design Contradiction:

ProductivityVSUse of energy by moving object

Solution Approach 1:

The patent applies the extraction principle by removing nitrogen from the natural gas stream before liquefaction. By extracting the harmful nitrogen component from the feed stream or intermediate streams, the system reduces the nitrogen concentration in the stream undergoing liquefaction, thereby decreasing compressor horsepower requirements and improving liquefaction efficiency without sacrificing throughput

Inventive Principle:

Principle #2Taking out (Extraction)

3Reliability

If conventional nitrogen removal processes are used, then nitrogen can be removed from the natural gas stream, but operational costs increase and profit margins decrease

Engineering Contradiction:

Improvenitrogen removal effectivenessVSAvoidoperational costs

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent applies self-service by integrating nitrogen removal functionality into the existing liquefaction process streams, allowing the system to remove nitrogen using its own process materials and energy flows. By utilizing intermediate process streams and existing equipment capabilities, the system achieves nitrogen removal without requiring separate, expensive dedicated removal units, thereby reducing operational costs while maintaining removal effectiveness

Inventive Principle:

Principle #25Self-service

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 process effectively reduces nitrogen levels in LNG, improving liquefaction efficiency, reducing compressor demands, and lowering operational costs by optimizing nitrogen removal in LNG facilities.

Implementation Method 1

cooling at least a portion of the natural gas stream in a first heat exchanger of a first upstream refrigeration cycle via indirect heat exchange with a first pure-component refrigerant

Methodology Applied

Scientific EffectIndirect heat exchange: Heat Exchanger

Implementation Method 2

cooling at least a portion of the cooled natural gas stream in a cooling pass of a second heat exchanger in an open-loop methane refrigeration cycle

Methodology Applied

Scientific EffectHeat exchange: Heat Exchanger

Implementation Method 3

separating at least a portion of the cooled predominantly methane stream in a multistage separation vessel to thereby provide a predominantly vapor stream and a predominantly liquid stream

Methodology Applied

Scientific EffectVapor-liquid separation: Phase Change

Implementation Method 4

passing at least a portion of the predominantly vapor stream through a warming pass of the second heat exchanger to thereby accomplish at least a portion of the cooling of step (b)

Methodology Applied

Scientific EffectHeat exchange: Heat Exchanger

Data Source

PatentUS9528759B2Enhanced nitrogen removal in an LNG facility

Publication Date: 2016.12.27 CONOCOPHILLIPS CO

AI summary

An LNG facility employing an enhanced nitrogen removal system that concentrates the amount of nitrogen in the feed stream to a nitrogen removal unit (NRU) to thereby increase the separation efficiency of the NRU. In one embodiment, the nitrogen removal system comprises a multistage separation vessel operable to separate nitrogen from a cooled natural gas stream. At least a portion of the resulting nitrogen-containing stream exiting the multistage separation vessel can be used as a refrigerant, processed to a nitrogen removal unit, and/or utilized as fuel gas for the LNG facility.