Heat Engine System Using Carbon Dioxide for Waste Heat Recovery and Cooling
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Solution Overview
Problem
Industrial processes that generate high-temperature waste heat often lack feasible methods for recycling this energy due to unfavorable conditions, and existing thermodynamic cycles using non-hydrocarbon working fluids do not integrate effectively with cooling circuits.
Innovation Solution
A heat engine system that incorporates a working fluid circuit with a waste heat exchanger, expander, recuperator, pump, and integrated cooling circuit, utilizing carbon dioxide as the working fluid to convert waste heat into mechanical and electrical energy while also functioning as a refrigerant in the cooling circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If traditional Rankine cycles use water or lower boiling-point hydrocarbon working fluids, then thermal energy conversion efficiency is improved, but issues arise regarding thermal instability, toxicity, flammability, and production cost
Solution Approach 1:
The patent changes the chemical composition parameter of the working fluid from traditional water or hydrocarbons to non-hydrocarbon fluids with superior thermal stability and safety profiles. Specifically, it uses fluids with high breakdown temperatures (e.g., HFC-134a with 760°C breakdown temperature versus 200-400°C for hydrocarbons) while maintaining appropriate boiling points for heat engine operation.
Solution Approach 2:
The patent employs working fluids that are inexpensive, environmentally benign, and readily available, such as HFC-134a, which can be obtained as waste refrigerant from discarded refrigeration systems. This approach eliminates the need for expensive, specialized fluids while ensuring continuous supply and reducing environmental impact.
2Reliability
If non-hydrocarbon working fluids are used in Rankine cycles, then safety and environmental compatibility are improved, but integration with cooling circuits remains ineffective
Solution Approach 1:
The patent makes the working fluid serve dual functions: as the heat engine working fluid for power generation and as the refrigerant for cooling circuit applications. By selecting fluids like HFC-134a that possess both appropriate thermodynamic properties for heat engine cycles and suitable refrigeration characteristics, the system achieves multi-functionality without requiring separate fluid systems.
Solution Approach 2:
The patent merges previously separate systems (heat engine cycle and cooling circuit) into a unified system by using the same non-hydrocarbon working fluid in both applications. The working fluid circulates through both the heat engine components (heat exchanger, expander, compressor) and the cooling circuit components (evaporator, condenser, expansion device), creating an integrated dual-purpose system.
3Ease of operation
If industrial processes exhaust high-temperature waste heat into the environment, then operational simplicity is maintained, but energy waste increases
Solution Approach 1:
The patent converts the harmful waste heat exhaust into a beneficial resource by using it as the heat source for the heat engine cycle. The high-temperature waste heat stream (e.g., from industrial processes at 50-150°C or higher) drives the non-hydrocarbon working fluid through the heat engine, generating useful mechanical or electrical power while simultaneously removing the waste heat from the environment.
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
Efficiently converts thermal energy from waste heat streams into valuable mechanical and electrical energy while providing cooling for external fluid streams, leveraging the properties of carbon dioxide as a non-hydrocarbon working fluid and refrigerant.
Implementation Method 1
a waste heat exchanger configured to be in fluid communication and in thermal communication with a heat source stream, and to transfer thermal energy from the heat source stream to the working fluid
Implementation Method 2
an expander disposed downstream from and in fluid communication with the waste heat exchanger and configured to convert a pressure drop in the working fluid to mechanical energy
Implementation Method 3
a pump disposed upstream of and in fluid communication with the recuperator and configured to pressurize and circulate at least a first portion of the working fluid within the working fluid circuit
Implementation Method 4
a recuperator configured to receive the working fluid from the expander and the first portion of the working fluid from the pump, and to transfer thermal energy from the working fluid received from the expander to the first portion of the working fluid received from the pump
Implementation Method 5
The evaporator may be further configured to receive a second portion of the working fluid from the working fluid circuit and to transfer thermal energy from the fluid stream to the second portion of the working fluid
Data Source
AI summary
A heat engine system and a method for cooling a fluid stream in thermal communication with the heat engine system are provided. The heat engine system may include a working fluid circuit configured to flow a working fluid therethrough, and a cooling circuit in fluid communication with the working fluid circuit and configured to flow the working fluid therethrough. The cooling circuit may include an evaporator in fluid communication with the working fluid circuit and configured to be in fluid communication with the fluid stream. The evaporator may be further configured to receive a second portion of the working fluid from the working fluid circuit and to transfer thermal energy from the fluid stream to the second portion of the working fluid.