Revamp of Phosgene Absorber

Customer:	Petrochemical Company.
Location:	Western India.
Tower Name:	Phosgene absorber.
Tower Diameter:	630 mm.
Mass Transfer Equipment:	High Capacity Valve Tray.

History:
The company has a joint venture with Swedish Co., & is into manufacture of petrochemicals since 1989. Its main product includes Aniline, Nitrobenzene, TDI etc.

Process Overview:
Toluene di-isocyanate is obtained by reaction of Meta-toluene diamine and phosgene in ODCB solvent. The un-reacted gases containing phosgene are then sent to the absorber to be absorbed in ODCB for reuse in the process and to prevent the emission of highly poisonous phosgene in the atmosphere.

Customer Requirements:
Since the column was not performing to its capacity with very high pressure drops and bottom temperatures, the column was opened & inspected, the trays were found to be terribly corroded.

Client requested KEVIN to work on SOS basis & provide a permanent solution along with increased capacity to handle maximum load. Problem analysis:

KEVIN specialist 'performed the study & analysis, During hydraulic rating of existing valve trays it was noted that the jet flood & pressure drop were quiet high & were contributing to the problem. Since the pressure drop was high, the client had to maintain a very high pressure at the bottom of the column. The high pressure drop was resulting in higher column temperatures and corrosion. We decided to replace these trays with high performance high capacity valve trays.

On studying the hydraulics of the existing trays, it was found that they were running at 130% jet flood giving very high-pressure drop. Due to this the temperature at the bottom was very high resulting in corrosion. We decided to replace these trays with high performance valve trays. Solutions provided:
After study & analysis of the problems KEVIN recommended replacement of valve trays with high capacity valve trays. High capacity valve provide maximum open area & thereby reduce pressure drop. Also these trays could efficiently handle fouling services. Accordingly 30 High capacity valve trays were designed to suit the existing tray attachments, manufactured & installed within 48 hours. This resulted in
- Fitment on existing attachments thereby eliminating hot work.
- lowering the pressure drop.
- lowering column temperature.
- Reducing pressure requirement at bottom of the column.
- Reducing corrosion.
- Increased capacity.

Results achieved:
After installation of High capacity valve traystemperature was maintained and capacity increased by 40 % than the actual. The plant is running satisfactorily. The client was satisfied with overall performance and planned for further modification in other column under guidance of KEVIN. .