Ammonia Cracking NOx Removal via PSA Tail Gas SCR
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Solution Overview
Problem
Current processes for producing hydrogen from ammonia are inefficient in terms of energy consumption, have lower hydrogen recovery rates, and generate NOx emissions due to the combustion of fossil fuels.
Innovation Solution
A method and apparatus that recover aqueous ammonia from PSA offgas and use it in a selective catalytic reduction (SCR) process to remove NOx from flue gas, while also using PSA tail gas as a fuel in the furnace to heat the catalyst-containing reactor tubes, thereby reducing energy consumption and NOx emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If ammonia is cracked using a furnace heated by fossil fuel combustion, then the cracking reaction can be sustained at required temperatures, but NOx emissions are generated and energy efficiency is reduced
Solution Approach 1:
The patent recovers ammonia from the PSA tail gas (which would otherwise be wasted) and uses it in an SCR system to reduce NOx emissions from the furnace. This converts a harmful byproduct into a beneficial resource for emissions control, simultaneously addressing both the temperature requirement and NOx reduction goal
Solution Approach 2:
The patent implements ammonia recovery from the PSA tail gas stream through absorption in water or acid, then utilizes the recovered ammonia for SCR denitrification. This prevents useful ammonia from being discarded and transforms it into a tool for reducing harmful emissions
2Manufacturing precision
If PSA is used to purify hydrogen from cracked gas, then hydrogen purity is improved, but ammonia is lost in the PSA tail gas
Solution Approach 1:
The patent captures ammonia that would otherwise be discarded in the PSA tail gas by absorbing it into water or acid, then recovers and reuses it for SCR emissions control. This eliminates the loss of valuable ammonia while maintaining the purification function
Solution Approach 2:
The patent creates a feedback loop where ammonia recovered from the PSA tail gas is fed back to the SCR system, which treats furnace emissions. This closed-loop approach maximizes resource utilization and eliminates waste
3Use of energy by moving object
If fossil fuels are combusted to heat the cracking reactor, then sufficient heat is provided for the endothermic reaction, but energy efficiency is reduced and NOx emissions increase
Solution Approach 1:
The patent converts the harmful NOx emissions and wasted ammonia into a beneficial resource by using recovered ammonia for SCR denitrification. This reduces the overall energy penalty associated with fossil fuel combustion and improves net energy efficiency
Solution Approach 2:
The patent changes the chemical composition parameter of the furnace atmosphere by introducing ammonia via SCR, which fundamentally alters the combustion chemistry to reduce NOx formation and improve energy utilization efficiency
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 enhances hydrogen recovery efficiency, reduces energy consumption, and significantly decreases NOx emissions by utilizing the recovered ammonia in the SCR process and minimizing the need for fossil fuel combustion.
Implementation Method 1
contacting the flue gas with a selective reduction catalyst in the presence of ammonia in a selective catalytic reduction (SCR) reactor to convert NOx to nitrogen gas and water
Implementation Method 2
purifying the cracked gas in a first PSA device to produce a first hydrogen product gas and a first PSA tail gas comprising ammonia
Implementation Method 3
supplying the heated ammonia to the catalyst-containing reactor tubes to cause cracking of the ammonia into a cracked gas containing hydrogen gas, nitrogen gas and residual ammonia
Implementation Method 4
combusting a fuel in a furnace to heat catalyst-containing reactor tubes and to form a flue gas comprising oxides of nitrogen (NOx)
Implementation Method 5
heating (and optionally vaporizing) the pressurized liquid ammonia by heat exchange with one or more hot fluids to produce heated ammonia
Implementation Method 6
compressing at least a portion of the first PSA tail gas to produce compressed PSA tail gas
Implementation Method 7
cooling the compressed PSA tail gas to produce cooled ammonia-depleted tail gas and an aqueous ammonia solution
Data Source
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AI summary
ΝΟx impurities in a flue gas generated in an ammonia cracking process may be removed from the flue gas by selective catalytic reduction (SCR) using an aqueous ammonia solution produced by cooling compressed tail gas from a hydrogen PSA device purifying the cracked gas.