Abstract:
Ammonia is a highly irritating gas which is corrosive in nature and causes perilous
effects both on environment and human health if its amount increases the safe limit.
Upon contact with humans by either inhalation or ingestion, it causes damage to skin,
eyes and the respiratory system. It causes eutrophication, soil acidification and disturbs
the eco-system if discarded in environment. Therefore, its removal from the effluent
water streams of all industries is a pressing need.
Our aim is to reduce the amount of Ammonia from 800 to 20 ppm in the effluent water
stream of NP Plant of Pak-Arab Fertilizers. By doing so, the effluent water composition
matches the standards set by the Environment Protection Agency. Firstly, the dissolved
Phosphate and Fluoride impurities are removed by the addition of CaO in water, settling
of hence formed insoluble salts takes place in a set of clarifiers, sludge thickener and
filter press are installed to dewater the sludge and obtain a solid cake. A heat exchanger
is employed to increase the temperature of supernatant water stream, in order to meet the
desired stripper conditions. An air stripper, with counter-current flow type, reduces the
amount of ammonia in effluent water to 20 ppm. After that, the stripped ammonia moves
to an absorber column in which Sulphuric acid is used as an absorbent, resulting in a
lean solution of Ammonium Sulphate. The effluent air stream from absorber column has
12 ppm of Ammonia. Hence, by the use of this Ammonia removal and recovery process
the amount of ammonia in both effluent air and water streams meets the restriction of
EPA and falls well within the safe limits.
