High Pressure Ammonia from Synthesis Loop directly to Urea plant

Post Reply
muthukumar
Posts: 16
Joined: Tue Aug 29, 2017 1:57 am
Contact:

High Pressure Ammonia from Synthesis Loop directly to Urea plant

Post by muthukumar »

In any ammonia plant Ammonia produced in the synthesis loop at high pressure (~190 kg/cm2) is reduced to around 20kg/cm2 to increase the purity ( to separate the dissolved gases mostly hydrogen and nitrogen less than 5% by weight) and is sent to urea plant where it is again pumped to high pressure of 230 kg/cm2 . Can we just send the ammonia at 190 kg/cm2 directly to urea plant so that the pumping cost can be reduced. if not what are the constraints behind it?
bedmonds
Posts: 36
Joined: Thu Apr 06, 2017 10:52 am
Contact:

Re: High Pressure Ammonia from Synthesis Loop directly to Urea plant

Post by bedmonds »

Hi,
The issue is the dissolved H2 in the ammonia feed to urea and the passivation air in the CO2 which are both "inerts" in the urea process and concentrate a great deal in the HP scrubber. To avoid an explosive mixture it is important to reduce H2 in the ammonia and CO2. For the CO2 H2 is reduced to roughly 100 ppm using a Pt catalyst in a hydrogen removal reactor. For the ammonia H2 is reduced by flashing at lower pressure but the ammonia feed is typically the main source of H2. If there was a way to catalytically oxidize the O2 to water in the liquid ammonia it would resolve the problem but I don't know if such a step is practically possible due to low temperature. If there is a way it would possibly be a bit of a breakthrough.
vpattabathula
Posts: 10
Joined: Mon Sep 28, 2020 10:18 pm
Contact:

Re: High Pressure Ammonia from Synthesis Loop directly to Urea plant

Post by vpattabathula »

Some folks have tried this modification feeding HP ammonia directly to urea and caused inerts to build up in urea synthesis thereby reducing conversion in urea reactor in addition to the potential for an explosive gas mixture between H2 & passivation air. Hence, it's not considered the best practice to feed HP ammonia from the NH3 plant to the urea reactor. Otherwise, EPC companies would have done it a long time ago.
vpattabathula
Posts: 10
Joined: Mon Sep 28, 2020 10:18 pm
Contact:

Re: High Pressure Ammonia from Synthesis Loop directly to Urea plant

Post by vpattabathula »

Some folks have tried this modification feeding HP ammonia directly to urea and caused inerts to build up in urea synthesis thereby reducing conversion in urea reactor in addition to the potential for an explosive gas mixture between H2 & passivation air. Hence, it's not considered the best practice to feed HP ammonia from the NH3 plant to the urea reactor. Otherwise, EPC companies would have done it a long time ago.
Post Reply