Ammonia Cracking Flue Gas Steam Control Against Solid Nitrate
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Solution Overview
Problem
The formation of ammonium nitrite and ammonium nitrate in ammonia cracking processes poses an explosion risk due to the instability of ammonium nitrite, particularly when nitrogen oxides and ammonia are present in the flue gas, necessitating a method to prevent solid ammonium nitrate deposition.
Innovation Solution
Maintaining a specific steam content in the flue gas by adjusting the hydrogen content in the fuel gas and/or adding steam to the furnace, ensuring the steam partial pressure exceeds the equilibrium vapor pressure of water in ammonium nitrate solutions to prevent solid ammonium nitrate formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If ammonia is cracked in a furnace heated by combustion of fuel gas, then hydrogen is produced, but nitrogen oxides form during combustion which can react with ammonia to form explosive ammonium nitrate
Solution Approach 1:
The patent changes the chemical composition parameters of the flue gas by controlling the steam to air ratio during combustion and by adjusting the hydrogen content in the fuel gas. This modifies the partial pressures of water vapor, ammonia, and nitrogen oxides to prevent the formation of ammonium nitrate while maintaining hydrogen production efficiency
Solution Approach 2:
Water vapor acts as an intermediary substance that prevents direct contact and reaction between ammonia and nitrogen oxides. By maintaining sufficient steam content in the flue gas, the patent creates a protective atmosphere that inhibits the formation of explosive ammonium nitrate compounds
2Object-affected harmful factors
If steam content in flue gas is increased to prevent ammonium nitrate formation, then explosion risk is reduced, but combustion efficiency may be affected
Solution Approach 1:
The patent optimizes the steam to air ratio parameter during combustion to achieve the minimum necessary steam content for preventing ammonium nitrate formation. This allows maintaining combustion efficiency while providing sufficient protection against explosive compound formation
Solution Approach 2:
The patent applies partial action by introducing steam only to the extent necessary to prevent ammonium nitrate formation, rather than excessive steam addition. This is achieved by calculating and controlling the steam content to be just sufficient to maintain safe partial pressures, thereby minimizing impact on combustion 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
Prevents the formation of solid ammonium nitrate by dissolving it in the flue gas, thereby eliminating the explosion risk associated with its deposition in the furnace or downstream systems.
Implementation Method 1
the one or more tubes are heated by combustion of a fuel gas mixture to form a flue gas
Implementation Method 2
The ammonia cracking reaction is endothermic and may usefully be achieved by passing ammonia over a suitable catalyst in externally heated catalyst-containing reaction tubes
Implementation Method 3
cooling the flue gas to below 170° C.
Implementation Method 4
maintaining an amount of steam in the flue gas according to the following equation to prevent solid ammonium nitrate formation: where yH2O is the mol % of steam in the flue gas, p*H2O is the equilibrium vapor pressure of water in an aqueous solution of ammonium nitrate
Implementation Method 5
the presence of NH3 and NOx and H2O in the flue gas can result in the formation of ammonium nitrate or ammonium nitrite
Data Source
AI summary
A process for cracking ammonia to form hydrogen is described comprising the steps of (i) passing ammonia through one or more catalyst-containing tubes in a furnace to crack the ammonia and form hydrogen, wherein the one or more tubes are heated by combustion of a fuel gas mixture to form a flue gas containing nitrogen oxides capable of reacting with ammonia in the flue gas to form ammonium nitrate, and (ii) cooling the flue gas to below 170° C., characterised by maintaining an amount of steam in the flue gas according to the following equation to prevent solid ammonium nitrate formation: (I) where, yH2O is the mol % of steam in the flue gas, P*H2O is the equilibrium vapor pressure of water in an aqueous solution of ammonium nitrate, and p is the minimum operating pressure of the flue gas.