SOEC Front-End for Ammonia Synthesis Gas With Partial Air Separation
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Solution Overview
Problem
Existing ammonia production processes rely heavily on fossil fuels and require energy-intensive air separation units for high-purity nitrogen, leading to high operating costs and CO2 emissions, with little attention given to sustainable production methods using solid oxide electrolysis cells (SOEC) and partial air separation.
Innovation Solution
A method combining partial air separation using membranes or PSA/TSA with SOEC stacks, where air is pre-separated to reduce oxygen content, allowing for endothermal operation and integrating steam production with ammonia synthesis, thereby reducing the need for large air separation units and minimizing CO2 impurities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If air separation is performed to high purity using conventional units, then nitrogen purity is improved, but energy consumption and operating costs increase
Solution Approach 1:
The patent applies partial air separation instead of complete high-purity separation. The air feed is separated to a moderate purity level (e.g., 30-70% oxygen removal) which is sufficient for the SOEC process requirements, avoiding the excessive energy consumption of conventional high-purity air separation units while still achieving the needed nitrogen concentration for ammonia synthesis.
Solution Approach 2:
The invention changes the purity parameter requirement from conventional high-purity standards to a lower threshold suitable for SOEC operation. By adjusting the separation degree parameter and matching it with the steam production requirements, the system achieves adequate nitrogen supply without the high energy penalty of producing ultra-pure nitrogen.
2Quantity of substance
If conventional steam methane reforming is used for hydrogen production, then hydrogen supply is improved, but CO2 emissions increase
Solution Approach 1:
The patent replaces the thermal chemistry-based steam methane reforming process with an electrochemical water electrolysis process using SOEC. This substitution eliminates the need for hydrocarbon feedstock and avoids CO2 generation from fuel reforming, while still providing sufficient hydrogen for ammonia synthesis through water splitting.
Solution Approach 2:
The invention changes the hydrogen production methodology from fossil fuel-based reforming to renewable electricity-based electrolysis. By altering the energy input parameter from thermal (natural gas combustion) to electrical (renewable sources), the system achieves the same hydrogen output quantity without the harmful CO2 emissions.
3Quantity of substance
If air is used directly for reforming processes, then nitrogen is introduced, but oxygen-containing species poison the catalysts
Solution Approach 1:
The patent applies preliminary air separation before the hydrogen production and ammonia synthesis processes. By removing a significant portion of oxygen from air upfront (achieving moderate nitrogen enrichment), the system prevents oxygen-containing species from reaching and poisoning the ammonia synthesis catalysts, while still providing the necessary nitrogen for the 3:1 H2:N2 ratio.
Solution Approach 2:
The SOEC process acts as an intermediary between air and the ammonia synthesis catalyst. The electrolysis cell selectively consumes hydrogen and water vapor while allowing nitrogen to pass through, effectively filtering out harmful oxygen species before they can contact and poison the downstream catalysts.
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
This approach achieves efficient, sustainable ammonia synthesis with reduced operating costs and lower CO2 emissions by optimizing the air feed to match steam production needs, simplifying the process layout and minimizing CO2 removal requirements.
Implementation Method 1
air separation step upstream the SOEC stacks. The air separation is ideally carried out by using a membrane
Implementation Method 2
or alternatively by using pressure swing adsorption (PSA)
Implementation Method 3
or temperature swing adsorption (TSA)
Implementation Method 4
synthesis gas for ammonia production is prepared by electrolysis using solid oxide electrolysis cell (SOEC) stacks
Implementation Method 5
electrolysis units are run in thermoneutral or endothermal mode
Implementation Method 6
The combustion of hydrogen and residual oxygen can take place inside the stacks or between separate stacks
Data Source
AI summary
In a method for generating ammonia synthesis gas by electrolysis, comprising the steps of compressing air and feeding it to an air separation process, in which the content of nitrogen is concentrated while the content of oxygen and CO2 is diluted, feeding a mixture of steam and the compressed and refined air into the electrolysis unit or into the first of a series of electrolysis units and passing the outlet from one electrolysis unit to the inlet of the next electrolysis unit, either together with air added after each electrolysis unit or only adding air after the last electrolysis unit, the electrolysis units are run in thermoneutral or endothermal mode and the nitrogen part of the synthesis gas is provided by burning the hydrogen produced by steam electrolysis by the refined air in or between the electrolysis units.