Background
The Hydrogen generated by reforming of hydro-carbons is reacted with Nitrogen in the atmospheric air in the presence of a catalyst at higher pressure to synthesise Ammonia. The synthesis of Ammonia occurs in the Ammonia converters. The older Ammonia converters were all of axial type which required higher pressure and resulted in lower conversions. These have been replaced in some of the plants with radial type / axial-radial system with considerable benefits. A case study on the modernisation of the Ammonia converter basket taken up in a plant is described below.
Previous status
In a 357 TPD Ammonia plant, the Ammonia converter basket had a conventional axial type basket, as shown in the figure. This needed an operating synthesis loop pressure of 300 bar. The catalyst used was Topsoe supplied of 10 mm size with a pressure drop of 5 bar. The conversion per pass was around 16 %. In 1992, the bottom exchanger developed a leak, leading to further reduction of ammonia conversion and increased loop pressure. The total production loss was around 30 %.
Energy saving project
The converter basket was modified to a axial-radial type system. The modified system is indicated in the diagram.
Implementation methodology & time frame
The implementation of this project was taken up as part of the Revamping exercise and hence a separate stoppage of the plant was avoided. The implementation and consequently the operation did not pose any problem.
Benefits of the project
The replacement of the old axial type converter basket with the modern axial-radial system resulted in the following benefits:
Loop pressure reduced to 250 bar – reducing compression energy
Lower pressure drop in converter beds – 3 bar as against 5 bar before
Higher Ammonia production ( about 10 TPD )
The above benefits resulted in the reduction of energy consumption by 0.35 Gcal / MT of Ammonia.
Financial analysis
This amounted to an annual monetary saving (@ 1,00,000 MT production of Ammonia & Rs 1000 / Gcal) of Rs 20 million. The energy saving alone has been considered. The investment made was around Rs 50 million. The simple payback period for this project was 30 months.
Benefits of axial-radial type ammonia convertor basket
Lower loop pressure - reduces compression energy
Lower pressure drop in convertor beds (3 bar against 5 bar)
Higher Ammonia production by 2 to 3%
Cost benefit analysis
Annual Savings - Rs. 20 millionInvestment - Rs. 50 million
Simple payback - 30 months
No comments:
Post a Comment