Integrated cascade process for vaporization and recovery of residual LNG in a floating tank application

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Solution Overview

Problem

Conventional methods for vaporizing and recovering residual liquefied natural gas (LNG) from offshore storage tanks face challenges due to limited space constraints and inefficiencies in recovering vaporized LNG, particularly in floating LNG facilities, where the last few feet of residual LNG are difficult to vaporize and evacuate, leading to increased inspection and maintenance costs.

Innovation Solution

A method and system for vaporizing LNG involve heating a portion of the LNG to produce a boil-off gas stream and a liquid quench stream, routing them through a quench system to cool the boil-off gas, and then compressing the resulting quenched stream, which can be integrated with existing LNG facilities, including cascade and mixed refrigerant systems, to efficiently vaporize and recover residual LNG.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of time

If conventional vaporization methods are used to remove residual LNG from storage tanks, then the vaporization process can be completed, but the time required is excessive and vaporized LNG cannot be recovered

Engineering Contradiction:

Improvevaporization timeVSAvoidvaporized LNG recovery

Core Design Contradiction:

Loss of timeVSLoss of substance

Solution Approach 1:

The patent combines the vaporization process with the LNG recovery process into a single integrated system. The vaporized LNG is not vented to atmosphere but is instead captured and condensed back to liquid form, merging two separate operations (vaporization and recovery) into one efficient process that eliminates time loss and prevents substance loss.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

Instead of discarding the vaporized LNG to the atmosphere as in conventional methods, the patent implements a recovery system that captures the vaporized gas and converts it back to liquid form. This transforms a waste disposal process into a resource recovery process, eliminating both time delays and substance loss.

Inventive Principle:

Principle #34Discarding and recovering

2Temperature

If heating is applied to vaporize residual LNG, then vaporization occurs, but energy consumption increases and vaporized LNG is lost

Engineering Contradiction:

ImproveLNG temperatureVSAvoidheating energy

Core Design Contradiction:

TemperatureVSUse of energy by moving object

Solution Approach 1:

The patent converts the harmful effect of energy consumption during vaporization into a beneficial outcome. The energy used to vaporize the LNG is not wasted because the vaporized gas is subsequently condensed back to liquid, recovering the energy investment and transforming a potentially wasteful process into an efficient cycle.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent utilizes phase transitions (liquid to vapor during heating, then vapor back to liquid during condensation) as the core mechanism. By controlling these phase changes in a closed loop system, the process efficiently manages energy consumption while achieving complete vaporization and recovery of the LNG.

Inventive Principle:

Principle #36Phase transitions

3Ease of operation

If space constraints in floating tanks are considered, then inspection and maintenance become more difficult, but tank safety and reliability are compromised

Engineering Contradiction:

Improveinspection accessibilityVSAvoidtank safety

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent implements preliminary vaporization and recovery of all LNG from the tank before inspection or maintenance activities begin. By completely emptying the tank of LNG in advance, the tank becomes safe for human entry and inspection, while the recovered LNG is stored elsewhere, maintaining operational reliability without compromising safety or accessibility.

Inventive Principle:

Principle #10Preliminary action

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 reduces the time required to vaporize and evacuate LNG before inspection or maintenance, allows for the recovery of vaporized LNG back into the main liquefaction process, and minimizes flaring, thereby reducing costs and improving operational efficiency.

Implementation Method 1

the quench system cools the boil-off gas stream to provide a quenched stream

Methodology Applied

Scientific EffectCondensation: Condensation

Implementation Method 2

heating at least a portion of the LNG to provide a boil-off gas stream and a liquid quench stream

Methodology Applied

Scientific EffectEvaporation: Evaporation

Data Source

PatentUS9835373B2Integrated cascade process for vaporization and recovery of residual LNG in a floating tank application

Publication Date: 2017.12.05 CONOCOPHILLIPS CO

AI summary

Methods and systems for vaporizing and recovering LNG are provided. One method includes: a) heating at least a portion of the LNG to provide a boil-off gas stream and a liquid quench stream; b) routing the boil-off gas stream and the liquid quench stream to a quench system, wherein the quench system cools the boil-off gas stream to provide a quenched stream; and c) compressing the quenched stream to provide a compressed quenched stream.