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Pharos University جامعه فاروس Faculty of Engineering كلية الهندسة Petrochemical Department قسم البتروكيماويات. LECTURES (5-8) Ammonia Production Process by steam reforming of Natural Gas. 2-Steam reforming Process:.
Pharos University جامعه فاروس Faculty of Engineering كلية الهندسة Petrochemical Department قسم البتروكيماويات
Ammonia Production Process by steam reforming of Natural Gas
The primary reformer is a furnace in which a multiplicity of tubes of high-nickel chromium alloy filled with nickel-containing reforming catalyst in a big chamber (Radiant box) with burners to provide heat.
The composition of gas leaving the reformer is given by close approach to the following chemical equilibrium:
CH4 + H2O ↔ CO + 3H2 ∆H = 49.2 kcal/mol
CO + H2O ↔ CO2 + H2 ∆H = -9.8 kcal/mol
The flue gas leaving the radiant box has temperature in excess of 900°C, after supplying the high level heat to the reforming process.
The process gas is mixed with the air in the mixing chamber of secondary reformer then passed over a nickel catalyst that is supported by a ring-shaped arch made of high-alumina bricks.
A- Water-gas shift reaction :
CO + H2O ↔ CO2 + H2 ∆H = -41 kJ/mol
A conventional water-gas shift reactor then uses a metallic catalyst in a heterogeneous gas-phase reaction
with CO and steam.
The process gas from the secondary reformer contains 12-15% CO (dry gas bases) and most of the CO is converted in the shift section according to the reaction:
CO + H2O ↔ CO2 + H2
There is tendency to use copper containing catalyst to increase conversion. The gas from the HTS is cooled and passed through the low temperature shift (LTS) converter.
The main advantage of potassium carbonate solution is lower heat requirements for stripping the CO2 from the solvent
When the solution pressure is reduced to about atmospheric pressure, part of the CO2 and water vapor escape. CO2 release is assisted by steam stripping.
K2CO3 + CO2 + H2O ↔ 2KHCO3
During absorption, the reaction proceeds from left to right and during regeneration from right to left. The heat of reaction amounts to 340 kcal/Nm3 CO2.
It could also be permanently poisoned by sulfur, arsenic, phosphorus, chlorine, and heavy hydrocarbons; oxygen-bearing compounds will cause temporary poisoning, which may be reversed if the exposure was only for a short while.
The “inerts” consist mainly of methane, argon, and sometimes helium if the natural gas feedstock contains the element.
The gas leaving the converter will contain 12%-18% NH3, depending mainly on the pressure; conversion per pass increases with pressure.
The purge gas is scrubbed with water to remove ammonia before being used as fuel or before being sent to hydrogen recovery unit.