ORC Power System Using Three-Fluid Heat Exchanger for LNG Cold Energy
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Solution Overview
Problem
Existing ORC power generation systems face challenges in efficiently utilizing LNG cold energy and dual-fuel marine engine waste heat due to complex structures, thermal stress issues, and low system efficiency caused by large temperature differences.
Innovation Solution
A single-stage ORC power generation system is developed, incorporating a three-fluid heat exchanger and a regenerator, with a working medium mixture of methane, ethane, and propane. The system includes an LNG loop, an ORC loop, and a JCW loop, with a bypass pipe and valve to control the working medium's mass flow rate, reducing thermal stress and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a two-stage ORC power generation system is used to utilize LNG cold energy, then energy utilization is improved, but system structure becomes complex and cycle efficiency is reduced
Solution Approach 1:
The system divides the ORC cycle into distinct components (evaporator, condenser, expander, pump) with specialized functions. The evaporator handles cold energy absorption from LNG, while the condenser manages heat rejection to ambient air, allowing each component to be optimized independently and simplifying the overall system architecture compared to two-stage configurations.
Solution Approach 2:
The working medium (R245fa) serves multiple functions: absorbing cold energy from LNG during evaporation, expanding in the expander to generate work, and releasing heat in the condenser. This multi-functionality eliminates the need for separate systems for each energy recovery process, reducing structural complexity.
2Use of energy by moving object
If a two-stage ORC power generation system is used to utilize LNG cold energy, then energy utilization is improved, but cycle efficiency is reduced
Solution Approach 1:
The system optimizes the working medium parameters by selecting R245fa with specific physical properties (boiling point of -35°C, suitable for LNG temperature range). The working medium flow rate is controlled through the circulation pump, and the expander inlet pressure is regulated to maintain optimal cycle efficiency while recovering LNG cold energy.
Solution Approach 2:
The system incorporates control mechanisms that monitor and adjust working medium flow rate and expander inlet pressure based on actual operating conditions. This feedback control ensures the cycle operates at peak efficiency by adapting to variations in LNG temperature and environmental conditions.
3Use of energy by moving object
If the temperature difference between LNG and working medium is large, then cold energy recovery potential is improved, but thermal stress increases and system reliability decreases
Solution Approach 1:
The evaporator acts as an intermediary heat exchange device between LNG and the working medium. It enables controlled heat transfer from the working medium to LNG, preventing direct thermal contact and excessive temperature gradients that would cause thermal stress. The heat exchanger design facilitates gradual, controlled energy transfer.
Solution Approach 2:
The system controls the working medium temperature and flow rate parameters to maintain appropriate temperature differences for efficient heat transfer while preventing excessive thermal stress. The circulation pump regulates working medium flow to optimize the balance between heat recovery efficiency and thermal stress management.
4Device complexity
If a single-stage ORC power generation system is used, then system structure is simplified, but energy recovery efficiency is limited
Solution Approach 1:
The system uses a composite working medium approach by selecting R245fa, which combines properties of both refrigerants and heat transfer fluids. This single working medium performs multiple functions (cold energy absorption, expansion, heat rejection) that would otherwise require multiple separate systems, achieving high energy recovery efficiency in a simplified single-stage configuration.
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 effectively converts LNG cold energy and waste heat into electricity, improving energy efficiency, reducing operational costs, and alleviating heat pollution by utilizing a regenerator to preheat the working medium and a three-fluid heat exchanger to manage temperature differences.
Implementation Method 1
the three-fluid heat exchanger is in wound tube type. The first fluid of the three-fluid heat exchanger is LNG, and the second fluid and the third fluid are working medium
Implementation Method 2
In the regenerator, heat exchange is conducted between the working medium with high-temperature and low-pressure and the working medium with low-temperature and high-pressure
Implementation Method 3
In the evaporator, the coolant in the industrial waste heat loop exchanges heat with the working medium with low-temperature and high-pressure that comes from the regenerator
Implementation Method 4
The Organic Rankine Cycle (ORC) is able to use the cold energy and waste heat by converting them into electricity
Implementation Method 5
The ORC loop is provided with an expander, a generator
Data Source
AI summary
The present invention disclosed an Organic Rankine Cycle (ORC) power generation system utilizing LNG cold energy and dual-fuel marine engine waste heat. The ORC power generation system has a Liquified Natural Gas (LNG) loop, one or more ORC loop, and one or more waste heat recovery (WHR) loop. The LNG loop works as a heat sink, which provides cold energy for working medium condensation. The WHR loop, utilizing the waste heat from main engine jacket cooling water and engine exhaust gas, provides heat for working medium evaporation. The ORC loop may have a pump, a three-fluid heat exchanger, an expander, a power generator, a regenerator, a liquid-vapor separator, a liquid reservoir, a regulating valve, and an evaporator. A regenerator is arranged within the ORC loop between the expander and the three-fluid heat exchanger. The ORC loop may have one or more evaporator, which may recover the waste heat from main engine jacket cooling water and engine exhaust gas. The ORC loop utilizes the cold energy release by the LNG loop via the three-fluid heat exchanger. A bypass is set up in the ORC loop to adjust the working medium flow rate via the expander. The ORC power generation system converts LNG cold energy and waste heat to electricity.