Troubleshooting of liquid carryover problem

Background
Customer operates one of the largest integrated ammonia-urea fertilizer plant in India, comprising 900TPD ammonia and 1500TPD urea facility.

Process Overview
Ammonia and urea production units generate the required hydrogen (H₂), dinitrogen (N₂) and carbon dioxide (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 carbon dioxide is removed through absorption in the solution. Hydrogen and other light gases along with slipped CO₂ from the top of the absorber are passed to the methanation section. The methanator converts the residual CO₂ to 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 used to produce urea. The lean solution from the regenerator bottom is then sent back to the absorber.

Customer Requirements
The customer was facing serious problems of liquid carryover in the CO₂ stream from the regenerator top which was following the downstream heat exchangers.

Problem analysis
After studying the system in order to optimise operation for an increased capacity it was noted that:

• The absorber was functioning normally
• The regenerator column was experiencing severe liquid carryover along with the CO₂
• The feed inlet nozzle was directing the inlet mixed phase feed onto the clear liquid residing on the Flash Feed Gallery deck thereby creating turbulence and causing the liquid carryover problem

Solutions provided
After studying entire equipments in the CO₂ removal section and conducting a detailed hydraulic check for increased capacity, the following was recommended:

• Option1 Increase the Flash Feed Gallery vertical wall height, which would entail hot work


• Option 2 Decrease the open area thereby increasing the Flash Feed Chamber deck area. Modify the inlet feed arrangement to facilitate lateral release of liquid along the column peripheryl and then onto the Flash Feed Gallery

The customer chose option 2 along with modification of the inlet feed arrangement.

Accordingly, the equipment was mechanically designed, manufactured and installed without any hot work to the column.

Results achieved
The problem of carryover is solved. The CO₂ removal section now runs at increased load of 1350 MTPD.