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Revamp of Ammonia Plant

Customer:                                             Fertilizer industry.
Location:                                               Western India
Tower Name:                                       CO
2 Absorber and Regenerator.
Tower Diameter:                                 4900 mm; 2730-3940 mm.
Mass Transfer Equipment:               Tower Packing and Internals.


History:
Company is leading manufacturer of Ammonia, Urea, Di-methyl-formamide, Ammonium bicarbonate etc.

Process Overview:
Ammonia and Urea production unit generate their H2, N2 & CO2 feeds through a common reformer.

Outlet gases from the reformer are passed through the absorber, where Hydrogen along with other light gases are separated while the CO2 is removed through absorption in the solution. Hydrogen & other light gases along with slipped CO2 from the top of the absorber are passed to the methanation section. The methanator converts the residual COto methane to increase the catalyst life of the ammonia reactor.

The rich solution from the absorber is then stripped in the regenerator and the CO2 gas is used to produce Urea. The lean solution from the regenerator bottom is sent back to the absorber.

Customer Requirements:
In the existing condition, CO2 slippage from absorber was very high (~1200 ppm). This lead to an increase in the load on methanator and also simultaneously increasing the volume of purge stream from NH3 loop.

Customer wanted to revamp the system in order to
-  Reduce slippage of CO2.
-  Increase plant capacity without sacrificing absorber efficiency.

Problem analysis:
During the study of existing system it was noted that Pall rings were used as mass transfer media in the packed towers. The Pall rings inherently have a drawback of higher pressure drop and performance limitations for mass transfer. This was resulting in increased load on compressor, finally leading to slippage of excess carbon dioxide.

Solutions Provided:
Hydraulic rating of existing towers alongwith the tower internals was done using Medal-Pak and following results were noted:
-  The pressure drop was found to be appreciably lower than that of Pall rings.
-  The capacity could be increased by 20%.
-  Minor modification of the existing internals to handle higher loads  were also           suggested.

Also based on the process overview it was predicted that the slippage of CO2 would be in the range from ~ 1200 ppm.

Accordingly Medal-Pak tower packings were manufactured, supplied & installed. During the shutdown the internals were modified at site.

Results achieved:
-  After packing replacement COslip reduced to 500 ppm at higher capacity of          105%.
-  Steam consumption in re-generator reduced to 10%.
 
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