Ammonia cracking process
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Solution Overview
Problem
Existing processes for producing hydrogen from ammonia are inefficient in terms of energy consumption and hydrogen recovery, and they often require the combustion of fossil fuels, leading to inefficiencies and increased nitrogen presence that reduces the efficiency of vehicle fueling systems.
Innovation Solution
A method involving pressurizing and heating liquid ammonia, cracking it into hydrogen and nitrogen using catalyst-filled reactor tubes, followed by purification with a PSA device, and utilizing PSA tail gas for heating, with optional secondary cracking to enhance hydrogen recovery, including the use of membrane separators to further purify and recycle ammonia.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If PSA is used to purify cracked gas for vehicle fueling, then hydrogen purity is improved, but nitrogen is compressed along with hydrogen, increasing power consumption and storage volume
Solution Approach 1:
The invention extracts nitrogen from the cracked gas stream before the PSA purification step by using a nitrogen-selective membrane separator. This removes the harmful diluent nitrogen that would otherwise be compressed with hydrogen, thereby reducing power consumption and storage volume requirements while maintaining high hydrogen purity.
Solution Approach 2:
The nitrogen-selective membrane separator acts as an intermediary device between the cracking reactor and the PSA system. It selectively separates nitrogen from the cracked gas, allowing hydrogen and other valuable components to proceed to PSA purification while nitrogen is removed, thus avoiding the energy penalty of compressing nitrogen.
2Temperature
If electrical heating is used in small scale crackers, then temperature control is improved, but energy consumption increases
Solution Approach 1:
The invention merges the cracking reactor with a heat exchanger system that recovers heat from the PSA tail gas and flue gas. This integration allows the endothermic cracking reaction to be sustained using recovered process heat rather than external electrical heating, thereby reducing energy consumption while maintaining effective temperature control.
Solution Approach 2:
The heat exchanger system enables continuous heat recovery from the PSA tail gas and flue gas streams, providing sustained thermal energy to the cracking reaction. This continuous heat supply replaces intermittent electrical heating, reducing overall energy consumption while maintaining stable operating temperatures.
3Device complexity
If PSA tail gas is vented to atmosphere, then process simplicity is maintained, but hydrogen recovery is reduced
Solution Approach 1:
The invention implements a feedback loop where PSA tail gas is not vented but instead routed through a heat exchanger to recover heat, then through a nitrogen membrane separator to remove nitrogen, and the resulting hydrogen-rich stream is recycled to the cracking reactor or combined with fresh cracked gas. This feedback approach recovers hydrogen that would otherwise be lost while adding manageable complexity to the process.
Solution Approach 2:
Instead of discarding the PSA tail gas to atmosphere, the invention recovers valuable hydrogen from this stream using a nitrogen-selective membrane separator. The nitrogen is removed and discarded, while the hydrogen-rich permeate is recovered and reused, thereby improving overall hydrogen recovery while maintaining reasonable process complexity.
4Temperature
If fossil fuels are combusted to heat reactor tubes, then cracking temperature is achieved, but energy efficiency is reduced and nitrogen presence increases
Solution Approach 1:
The invention converts the harmful hot flue gas from fossil fuel combustion into a beneficial heat source by routing it through a heat exchanger that recovers thermal energy. This recovered heat is then used to sustain the endothermic cracking reaction, thereby improving energy efficiency by utilizing what would otherwise be waste heat, while also reducing the amount of fossil fuel needed for heating.
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 process achieves higher hydrogen recovery rates, reduces energy consumption, and minimizes the need for fossil fuel combustion, resulting in a more efficient production of hydrogen suitable for vehicle fueling systems.
Implementation Method 1
cracking it into hydrogen and nitrogen using catalyst-filled reactor tubes
Implementation Method 2
purification with a PSA device
Implementation Method 3
including the use of membrane separators to further purify and recycle ammonia
Implementation Method 4
heating (and optionally vaporizing) the liquid ammonia by heat exchange with one or more hot fluids
Implementation Method 5
combusting a fuel in a furnace to heat a first set of catalyst-containing reactor tubes
Data Source
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AI summary
Ammonia cracking process in which cracked gas is purified in a PSA system are improved by converting residual ammonia in the first cracked gas into further hydrogen and nitrogen by feeding PSA tail gas, or a gas derived therefrom, to a secondary cracking reactor and further processing the second cracked gas.