3 replies to this topic

HI:

THIS IS MUHAMMAD RIZWAN, CHEMICAL ENGINEER AT AMMONIA PLANT.
IF ANY BODY HAS WORKED ON AMMONIA SYNTHESIS CATALYST, PLEASE HELP ME REGARDING EFFECT OF CARBON MONOXIDE UPON AMMONIA SYNTHEISIS CATALYST.
I HAVE A PROBLEM OF HIGH CARBON MONOXIDE CONCENTRATION IN SYNTHESIS GAS DUE TO TUBE LEAKAGE IN DOWNSTREAM EXCHANGER OF METHANATOR. THIS IS A GAS TO GAS EXCHANGER AND DP ACROSS THE STREAMS IS NOT SO HIGH. DUE TO ABOVE LEAKAGE CO AND CO2 IN SYN GAS HAVE REACHED AT 40 TO 50 PPM. WHAT COULD BE THE PROBABLE EFFECTS OF THIS HIGH CONCENTRATION ON PERFORMANCE AND LIFE OF AMMONIA SYNTHESIS CATALYST. PRESENTLY WE ARE USING IRON BASED CATALYST ( MAGNETITE, POTASSIUM, ALLUMINA, CALCIUM OXIDE ETC)




REGARDS,
MUHAMMAD RIZWAN

[Satyajit]

Hi Rizwan,

Your ammonia synthesis catalyst would have got partially poisoned; you can observe in reduction of delta T across the bed, increase of syn loop pressure. The extent of poisoning depends on amount of CO and CO2 present in Synloop.

As you know, the limit is less than 10ppm.

Run your bed inlet temperature 5-10degree C higher for few days, increase purge from synloop, catalyst will regain the activity.

Good Luck,
Satyajit

[pawan]

Yes rightly pointed out by Satyajit.
CO & CO2 both can be permanenet posions also for
Syn Cat if prolonged operation is there in such condition.

Active Iron forms Carbonyls & carbonates with these two.
U will soon observe a sudden drop in catalyst activity in terms of Pressure, Conversion (Delta T across beds) bcoz till now U might be gaining due to margins considered in desing.

The cost economics is always in favor of immediate stoppage & repair of tubes in a short shutdown AND NOT in favor of spoiling the cat & replace it which is a very very costly affair due to longer shutdown required & very high cost of catalyst.

The above is true unless U r near EOL operation of the catalyst.
So go for immediate repair of leaky exchanger.

[Pronab]

In addition of the above two reply,CO and CO2 will make ammonium carbamate and will deposit in the piping at cold section of ammonia synthesis loop. After some days of operation you will see make -up flow in Synthesis compressor will come down. Don't delay to repair the tube leak and tell us what is going on .