System and method for re-liquefying ammonia boil-off gas of vessel
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Solution Overview
Problem
Conventional methods struggle to effectively reliquefy ammonia boil-off gas for ships, leading to fuel waste and potential pressure instability in storage tanks, which is critical as ammonia is a promising eco-friendly fuel but produces boil-off gas due to its higher boiling point compared to LNG.
Innovation Solution
A system and method involving multistage compression and cooling of ammonia boil-off gas using a compression unit, condenser, and heat exchangers to reliquefy the gas, with temperature regulation through partial diversion of ammonia in a temperature regulation line or side streamline, and pressure control via relief valves, ensuring efficient recovery and stable tank pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If ammonia is used as fuel in ships, then greenhouse gas emissions are reduced, but boil-off gas is generated due to ammonia's higher boiling point
Solution Approach 1:
The patent applies phase transition by compressing and cooling the boil-off gas to convert it from gaseous state back to liquid state, enabling it to be returned to the storage tank. The system uses compressors to increase pressure and condensers/heat exchangers to reduce temperature, transforming the ammonia from gas to liquid phase for recovery.
Solution Approach 2:
The patent converts the harmful boil-off gas (which would otherwise be wasted or vented) into a beneficial resource by reliquefying it and returning it to the storage tank. The system transforms what was previously a loss into recoverable fuel, improving overall fuel efficiency.
2Stability of the object's composition
If boil-off gas is vented to maintain storage tank pressure, then pressure stability is maintained, but fuel waste occurs
Solution Approach 1:
The patent implements a feedback mechanism where the reliquefied ammonia is returned to the storage tank, creating a closed-loop system. The boil-off gas is continuously compressed, cooled, and fed back into the tank, maintaining pressure stability while preventing fuel loss through automatic recovery.
Solution Approach 2:
Instead of discarding the boil-off gas, the system recovers it by compressing and cooling the gas back to liquid form, then returning it to the storage tank. This recovery process eliminates fuel waste while maintaining tank pressure.
3Loss of substance
If multistage compression and cooling is applied to reliquefy boil-off gas, then fuel recovery is improved, but system complexity increases
Solution Approach 1:
The patent segments the reliquefaction process into distinct stages: compression (first and second compressors), intermediate cooling (intercooler), and final condensation (condenser). Each stage handles a specific part of the thermodynamic transformation, making the complex process more manageable and efficient.
Solution Approach 2:
The patent introduces an intercooler as an intermediary component between the compression and condensation stages. This intermediate cooling device removes heat from the compressed gas before it enters the condenser, improving the overall efficiency of the reliquefaction process and reducing the workload on subsequent cooling equipment.
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
The system reduces greenhouse gas emissions by reliquefying ammonia boil-off gas, preventing fuel waste, and maintains storage tank pressure, enhancing heat recovery efficiency and reducing installation costs while meeting stringent regulatory standards.
Implementation Method 1
a first compressor receiving and compressing boil-off gas generated from ammonia
Implementation Method 2
a condenser cooling the boil-off gas compressed through the compression unit
Implementation Method 3
wherein a temperature of the boil-off gas in the compression unit is adjusted by partially diverting the ammonia from the reliquefied gas recovery line to be supplied to the compression unit
Data Source
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AI summary
A system and method for reliquefaction of ammonia boil-off gas for ships is disclosed. The ammonia boil-off gas reliquefaction system includes: a compression unit for multistage compression of boil-off gas, the compression unit including a first compressor receiving and compressing boil-off gas generated from ammonia in a storage tank provided to a ship, and a second compressor further compressing the boil-off gas compressed in the first compressor; a condenser cooling the boil-off gas compressed through the compression unit; and a reliquefied gas recovery line along which ammonia cooled and condensed in the condenser is delivered to the storage tank, wherein a temperature of the boil-off gas in the compression unit is adjusted by partially diverting the ammonia from the reliquefied gas recovery line to be supplied to the compression unit.