Dual-Loop Rankine Cycle Waste Heat Recovery
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Solution Overview
Problem
Current Rankine cycle systems for waste heat recovery from fuel combustion activities are limited in efficiency, as much of the thermal energy from waste heat sources remains unutilized, necessitating further enhancements to improve energy conversion and recovery.
Innovation Solution
A dual-loop Rankine cycle system with two closed loops, each comprising a working fluid stream, heat exchangers, heaters, expanders, condensers, and pumps, where heat is transferred and expanded to produce mechanical energy, and additional heat is extracted through a second heater and combiner to enhance energy recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-loop Rankine cycle system is used for waste heat recovery, then the system structure is simple, but the energy recovery efficiency is limited and much thermal energy remains unutilized
Solution Approach 1:
The single-loop Rankine cycle system is divided into two separate closed loops: a high-temperature loop and a low-temperature loop. Each loop operates independently with its own working fluid, heat exchangers, expanders, and condensers. This segmentation allows the system to extract energy at multiple temperature levels from the waste heat source, thereby improving overall energy recovery efficiency while maintaining manageable system complexity through modular design
2Loss of energy
If a dual-loop Rankine cycle system is implemented to improve energy recovery, then the energy recovery efficiency is enhanced, but the system complexity increases with additional components
Solution Approach 1:
The dual-loop system merges the high-temperature and low-temperature Rankine cycles through a shared heat exchanger network where the condensed working fluid from the high-temperature loop serves as a heat source for the low-temperature loop. This merging allows thermal energy that would otherwise be wasted in the high-temperature loop to be utilized in the low-temperature loop, improving energy recovery efficiency while reducing the need for separate external heat sources
Solution Approach 2:
The heat exchangers in the dual-loop system serve multiple functions: they act as condensers for the high-temperature loop, evaporators for the low-temperature loop, and enable heat transfer between the two loops. This multi-functionality reduces the total number of separate components needed and simplifies the overall system architecture while maintaining the benefits of the dual-loop configuration
3Power
If heat is transferred from the first working fluid stream to the second working fluid stream, then the mechanical energy output is improved, but the thermal energy available in the first stream is reduced
Solution Approach 1:
The system performs preliminary heat extraction in the high-temperature loop before the working fluid is condensed. The heated second working fluid stream is then used to provide additional thermal energy to the first working fluid stream in the evaporator, ensuring that the first loop operates at optimal temperatures for maximum mechanical energy output while efficiently utilizing the thermal energy cascading from the second loop
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 thermal energy from waste heat into mechanical energy, with improved power output and efficiency compared to standard configurations, as demonstrated by experimental and simulation data, showcasing enhanced energy recovery capabilities.
Implementation Method 1
a heater configured to transfer heat from a first waste heat-containing stream to a first working fluid stream to produce a vaporized first working fluid stream
Implementation Method 2
produce a vaporized first working fluid stream
Implementation Method 3
a first closed loop thermal energy recovery cycle comprising a first working fluid stream... a first expander configured to receive the vaporized first working fluid stream and to produce therefrom mechanical energy
Implementation Method 4
a first heat exchanger configured to transfer heat from the first working fluid stream to the second working fluid stream; wherein the second heat exchanger is configured to transfer heat from the second working fluid stream to the first working fluid stream
Implementation Method 5
a first expander configured to receive the vaporized first working fluid stream and to produce therefrom mechanical energy and an expanded first working fluid stream
Implementation Method 6
a first condenser configured to cool a heat depleted first working fluid stream and to produce therefrom a chilled first working fluid stream
Implementation Method 7
a pump configured to pressurize the chilled first working fluid stream
Data Source
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AI summary
A Rankine cycle system useful for the conversion of waste heat into mechanical and/or electrical energy is provided. The system features a novel configuration in which a first closed loop thermal energy recovery cycle comprising a first working fluid stream and a second closed loop thermal energy recovery cycle comprising a second working fluid stream interact but do not mix. The two thermal energy recovery cycles interact thermally via heat exchangers, a first heat exchanger configured to transfer heat from the first working fluid stream to the second working fluid stream, and a second heat exchanger configured to transfer heat from the second working fluid stream to the first working fluid stream. In one or more embodiments, the Rankine cycle system is adapted for the use of supercritical carbon dioxide as the working fluid.