Electric and Steam System for LNG Boil-Off Gas Management
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Solution Overview
Problem
Liquefied natural gas (LNG) storage tanks on LNG carrier vessels are not designed to withstand significant internal pressure, leading to natural boil-off gas (NBOG) generation, which must be constantly managed to ensure vessel safety, and existing systems lack efficient methods to utilize this gas as a fuel source effectively.
Innovation Solution
A gas turbine-based electric and steam system that utilizes a portion of the boil-off gas (BOG) to fuel an electrical generator assembly and oxidizes excess BOG in a gas combustion unit, with the exhaust gases from both systems being channeled through a crossover duct to a heat recovery steam generator, allowing for efficient energy capture and utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If NBOG is vented overboard to ambient, then safety is maintained, but energy is wasted and environmental impact increases
Solution Approach 1:
The patent converts the harmful waste product (NBOG vented to ambient) into a beneficial resource by routing it through a heat recovery steam generator (HRSG) to generate steam and electricity. The NBOG that would otherwise be wasted is combusted to produce useful energy, simultaneously maintaining safety through controlled combustion and eliminating energy waste.
Solution Approach 2:
The system uses the NBOG itself as the fuel source to generate the steam and electricity needed for ship operations. The waste gas serves its own disposal function while simultaneously providing energy services, making the system self-sufficient regarding NBOG management.
2Loss of energy
If NBOG is used as fuel source, then energy utilization improves, but system complexity increases
Solution Approach 1:
The HRSG serves multiple functions: it acts as a combustion chamber for NBOG, a heat exchanger for steam generation, and a driver for power generation through the turbine-generator set. This multi-functionality consolidates what would otherwise require separate systems, managing complexity while maximizing energy utilization.
Solution Approach 2:
The patent merges the NBOG combustion process with the steam generation process. Instead of separate combustion and steam generation systems, the HRSG combines these functions, allowing NBOG to be burned while simultaneously producing steam for both process needs and power generation.
3Productivity
If excess NBOG is combusted in GCU, then energy management improves, but heat recovery efficiency decreases
Solution Approach 1:
The patent converts what would be wasted heat from GCU combustion into useful steam by routing the GCU exhaust through the HRSG. The heat that would otherwise be lost is now recovered to generate additional steam, turning an energy loss into a beneficial contribution.
4Loss of substance
If storage tanks are refrigerated and pressurized, then NBOG generation is reduced, but capital cost and operational complexity increase
Solution Approach 1:
Instead of investing in complex refrigerated and pressurized storage tanks to prevent NBOG generation, the patent accepts NBOG as an inevitable byproduct and converts it into a useful fuel source. This approach trades capital expenditure on complex tank systems for operational energy production.
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 system provides a cost-effective and environmentally friendly method to manage NBOG, improving the economics of LNG shipping while reducing environmental impact by utilizing a clean-burning fuel source and maintaining power reliability across varying ship operations.
Implementation Method 1
an electrical generator assembly configured to receive a first portion of a flow of a boil off gas (BOG)
Implementation Method 2
channel the first and second flows to an inlet of a heat recovery steam generator
Implementation Method 3
a steam turbine generator (STG) configured to receive a flow of exhaust gas from the HRSG
Data Source
AI summary
An electric and steam system includes an electrical generator assembly configured to receive a first portion of a flow of a boil off gas (NBOG). An oxidizing unit is configured to receive a second portion of the flow of the boil off gas (NBOG), the second portion being an excess of the flow of the boil off gas (NBOG) that the electrical generator can process, and a crossover duct configured to receive a first flow of exhaust gas from the electrical generator assembly and a second flow of exhaust gas from the oxidizing unit and channel the first and second flows to an inlet of a heat recovery steam generator.