Fuel Cell Exhaust Condensation with Cryogenic Water Augmentation
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Solution Overview
Problem
Existing gas turbine engines waste a significant amount of thermal energy in the exhaust, limiting the energy recovery capability of bottoming cycles due to the limited heat acceptance capability of the working fluid.
Innovation Solution
Incorporating a cryogenic fuel system and a bottoming cycle that utilizes a cryogenic fuel as a heat sink, with components like a fuel/working fluid heat exchanger and a recuperation heat exchanger to recover and conserve thermal energy, and utilizing fuel cell exhaust water for steam injection and intercooling to enhance engine efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional bottoming cycle is used with limited heat acceptance capability, then the system is simpler to operate, but a large amount of thermal energy is wasted in the exhaust flow
Solution Approach 1:
The cryogenic fuel serves multiple functions: it acts as both the primary fuel for the gas turbine combustor and as a heat sink for the bottoming cycle working fluid in the fuel/working fluid heat exchanger. This multi-functionality allows the system to recover thermal energy without adding separate cooling infrastructure, resolving the contradiction between energy recovery and system complexity.
Solution Approach 2:
The fuel/working fluid heat exchanger acts as an intermediary device that transfers thermal energy from the bottoming cycle working fluid to the cryogenic fuel. This intermediary mechanism enables efficient heat recovery while maintaining system manageability, addressing the contradiction between energy recovery capability and operational complexity.
2Loss of energy
If the working fluid is cooled more effectively to increase heat acceptance, then energy recovery improves, but the system requires more complex cooling infrastructure
Solution Approach 1:
The cryogenic fuel system is utilized for dual purposes: supplying fuel to the combustor and serving as the cooling medium for the bottoming cycle working fluid. This eliminates the need for separate cooling infrastructure, achieving effective heat recovery without increasing cooling system complexity.
Solution Approach 2:
The cryogenic fuel naturally absorbs heat from the working fluid as it is routed through the fuel/working fluid heat exchanger, utilizing its inherent low temperature properties. This self-service cooling mechanism reduces the need for active cooling systems and infrastructure, resolving the contradiction between heat recovery efficiency and cooling system complexity.
3Productivity
If fuel cell exhaust water is utilized for steam injection and intercooling, then engine efficiency increases, but the system complexity increases
Solution Approach 1:
The fuel cell exhaust water is diverted to perform multiple functions: steam injection into the combustor and intercooling of the compressor. This multi-functional utilization of waste water improves engine efficiency without requiring separate water treatment or management systems, addressing the contradiction between productivity gain and system complexity.
Solution Approach 2:
The fuel cell exhaust water naturally provides both steam for combustion enhancement and cooling for the compressor through its thermal properties. This self-service approach to water utilization achieves efficiency improvements while minimizing the need for additional water management infrastructure.
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
Enhances engine efficiency by recovering waste heat and water from the fuel cell exhaust, increasing shaft power generation and reducing the energy required by the compressor, thereby improving overall propulsion system performance.
Implementation Method 1
a fuel/working fluid heat exchanger for cooling the working fluid with the cryogenic fuel flow
Implementation Method 2
a first heat exchanger that provides thermal communication between the fuel cell exhaust flow and the working fluid of the bottoming cycle
Implementation Method 3
an evaporator where water within the fuel cell exhaust flow is transformed into a steam flow for injection into the combustor of the core engine
Implementation Method 4
a second heat exchanger where the cryogenic fuel flow is heated by the exhaust gas flow from the core engine prior to being injected into the combustor
Data Source
Figure 1
AI summary
An aircraft propulsion system (20) includes a bottoming cycle (60) where a working fluid is heated and expanded through a bottom turbine to generate shaft power. A first heat exchanger (44) provides thermal communication between a fuel cell exhaust flow and the working fluid of the bottoming cycle (60). The working fluid is cooled by a cryogenic fuel flow (56) in a fuel/working fluid heat exchanger (54).