1 reply to this topic

[sam1111]

Hi All

 

We have found what we believe to be ammonia converter catalyst in equipment downstream of our ammonia converter. This was discovered after we removed the flow control valve on a high pressure direct line to the associated urea plant. This particular flow control valve was operating very erratically and was not passing the usual amount of flow. We are currently awaiting results of lab analysis to confirm it is catalyst, but visual observation leads us to believe it is.

 

Can anyone share their experiences with a similar situation, where catalyst particles are passing from a reactor vessel and travelling through pipework, exchangers and valves entrained in a liquid flow. 

 

How do we quantify the risk associated with potential erosion of the pipework, thermowells, heat exchanger tubes etc? 

 

What approach has other people taken when this situation has been observed? Shutdown or keep running after accepting and understanding the risk to plant?

 

So far, we have not noticed any changes in operation of the ammonia converter. Pressure drop is the same, NH3 conversion is the same and temperature profile is the same.

 

The catalyst itself is 1.5mm-3mm irregular iron based particles. 

 

We are working with the converter OEM along with the catalyst supplier. However, it would still be helpful to gain some insight from other people in the industry.

 

I can provide more specific information if required, but general comments, what approach other plants have taken and what similar situations have been seen are what I would like to hear about if possible.

 

Regards

Sam

[Satyajit]

Hi Sam,

             I have experienced similar incidents in one of plant couple of years ago. Many such problems had also been reported in the past. Please refer to AICHE ammonia safety symposium papers on it.

The curiosity is to know :  is it happening after you have replaced your catalyst or after many years of operation ?

If the sample you have collected is only dust, then it may not be a big issue. But if you are sure, the sample collected is catalyst , then this could be the beginning of a big trouble.  As you have mentioned that all operating parameters are stable, it shows ok now but could change anytime you have an upset in the plant.

 

Migration of catalyst and dust  could happen due to following:

1. catalyst dust which was not removed before catalyst loading except pre-reduced catalyst are slowly migrating.

2. catalyst migration through leak in  converter basket screen ( Johnson screen) due to failure of mechanical integrity .

 

Other than mechanical manufacturing defects, rupture or damage of  converter basket screen is  possible due to following mal-operation.

1. Rapid depressurisation after shut down of synloop.

2. Fas pressurisation during start up.

3. Heating of converter at much higher rate than recommended by licensor.

 

My suggestion would be to investigate  and correct plant operating procedures , start up and shut down procedures if there are some deviations and communicate to operating staff. Try to observe other control valves particularly from ammonia separator to downstream ammonia product pump, product pump strainers etc. If the situation worsens, plan for replacement of catalyst basket and the catalyst which will take atleast one year to get in site.

There is a safety concern too. Keep the dust and catalyst particles under water as these are reduced catalyst and will catch fire once exposed to air.

 

Kind regards,

Satyajit