Abstract:
In ammonia plants purge gas is extracted from the ammonia synthesis loop to maintain
the inert gases (like Argon, Methane) level in the loop and maximize the conversion in
the ammonia converter. Purge gas contains Hydrogen, Nitrogen, Ammonia, and traces of
other inert gases Argon and Methane. Although the percentage of Ammonia in the purge
gas is less but it is safe and economical to recover it from the purge gas. Ammonia
emissions can lead to air and water pollution. Burning of purge gases in the boiler cause
NOx formation to higher extent that exceeds the environmental regulations ranges set by
the government. The main cause of NOx formation is the presence of Ammonia in the
purge gas, so industry wants to recover ammonia from the purge gas. For the hydrogen
recovery it is also necessary to first recover ammonia.
The recovery of Ammonia from the Purge gas is essential to keep the overall NOx
emissions of the plant within safe environmental regulations ranges (400mg/l) under
Punjab Environmental Quality Standards and to increase the production of Ammonia (~
15 MTPD).
One of the FFC plant needs Ammonia Recovery Unit (ARU) for the removal of ammonia
from the purge gas in order to make the ammonia production process more efficient,
environment friendly and economical. Different methods of ammonia recovery from the
purge gas including Membrane Separation, Pressure Swing Adsorption (PSA) and
Absorption-Stripping process had been studied in order to select the most feasible
method.We choose “Absorption and Stripping Process” because of its unique advantages
as compared to other two processes. Due of high efficiency and cost effectiveness this
method is widely used in several fertilizer industries for ammonia recovery from Purge
gas as well as from the off gases.
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