Fuel Cell System Dew Point Control for Condensed Water Recovery
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Solution Overview
Problem
Fuel cell systems face challenges in generating a sufficient quantity of condensed water, especially when operated at low S/C ratios, leading to an imbalance in latent heat and sensible heat ratios, which affects water self-sustaining states and efficiency.
Innovation Solution
A fuel cell system incorporating a reforming unit, combustion unit, hot water storage tank, heat exchanger, and control device that adjusts dew point temperature by controlling the supply of reforming raw materials, oxidizer gas, and reforming water to enhance water vapor condensation and recovery, ensuring a necessary and sufficient quantity of condensed water is produced.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the fuel cell system is operated at a low S/C ratio to achieve high efficiency, then power generation efficiency is improved, but the latent heat/sensible heat ratio becomes smaller and insufficient condensed water is generated
Solution Approach 1:
The control device changes the dew point temperature parameter of the combustion exhaust gas by adjusting the supply quantities of reforming raw material, oxidizer gas, and reforming water. This parameter change allows the system to maintain high efficiency operation at low S/C ratios while generating sufficient condensed water by optimizing the thermal conditions in the heat exchanger.
Solution Approach 2:
The control device implements feedback control by monitoring the water self-sustaining state and adjusting the dew point temperature accordingly. When insufficient condensed water is generated, the system increases the dew point temperature through adjusted gas and material supplies, creating a closed-loop control that ensures both efficiency and water generation requirements are met.
2Quantity of substance
If the dew point temperature is increased to generate more condensed water, then condensed water quantity is improved, but the heat exchange capability may be limited by the exhaust heat recovery water inlet temperature
Solution Approach 1:
The system dynamically adjusts the dew point temperature target value based on the actual exhaust heat recovery water inlet temperature. By making the dew point temperature adjustable rather than fixed, the system can optimize condensed water generation while respecting the thermal constraints imposed by the heat exchanger's water inlet temperature, allowing flexible adaptation to varying operating conditions.
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 recovers latent heat and reduces combustion exhaust gas outlet temperature, ensuring a stable water self-sustaining state and efficient power generation by adjusting dew point temperature, even in conditions with a small latent heat/sensible heat ratio.
Implementation Method 1
a heat exchanger that performs heat exchange between the combustion exhaust gas and the stored hot water, condenses water vapor contained in the combustion exhaust gas, and produces condensed water
Implementation Method 2
a dew point temperature increase control unit that increases the dew point temperature of the combustion exhaust gas in the heat exchanger
Data Source
Figure 1
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Figure 4
AI summary
A fuel cell system (1) includes: a fuel cell (34) that generates power by fuel and oxidizer gas; a reforming unit (33) that generates the fuel from a reforming raw material and reforming water and supplies the fuel to the fuel cell; a combustion unit (36) that introduces combustible gas containing unused fuel from the fuel cell thereinto, burns the combustible gas using oxidizer gas, and leads out the combustion exhaust gas; a hot water storage tank (21) that stores stored hot water; a heat exchanger (12) that performs heat exchange between the combustion exhaust gas and the stored hot water, condenses water vapor contained in the combustion exhaust gas, and produces condensed water; a stored hot water circulation line (22) for circulating the stored hot water between the hot water storage tank and the heat exchanger; and a control device (15) that integrally controls the fuel cell system.