2 replies to this topic

[tarafdar]

Hi,

 

Our Natural Gas composition is such that CO₂ & NH₃ is produced almost as required in our Urea plant.  Feed NG is about 97-98% CH4.  Excess NH₃ produced is about 0.5-1%.  To utilize this NH₃, in our 3 old plants we have a CO₂ recovery plant where CO₂ is recovered from the flue gas of a package boiler in the utility plant.  MEA is used as the CO₂ absorbent.  Our latest plants don't have any CO₂ recovery plant.

 

Now we have a proposal for CO₂ recovery from the flue gas of our Primary Reformer.  We don't like the idea for the following reasons:

 

1) Primary Reformer furnace control will be complicated.

2) CO₂ recovery plant (of stainless steel) is not viable now a days.

3) Small XS ammonia may be sold as refrigerant for cold storage.

4) If we have to build one,it is better to recover CO₂ from utility package boiler as in earlier plants.

 

Like to hear from forum members.  Do you have similar plants?

 

Tarafdar

Edited by Art Montemayor, 03 March 2015 - 09:55 AM.
spelling, grammar, composition

[Art Montemayor]

Tarafdar:

 

I believe what you are trying to describe is that you are short of CO₂ supply for your Urea production, as fixed by your ammonia production.  This would be a normal situation for an ammonia-urea complex.  Therefore, you need an additional supply of CO₂ and someone (presumably within your organization) is suggesting that you employ the flue gas from one of your existing Primary Reformers as a source for CO₂ by incorporating a CO₂ absorber and a solution (presumably MEA) regeneration system.  The low pressure CO₂ gas recovered would be scrubbed, compressed, dried, liquefied, and stored for use as incremental feed to your urea converter.  Am I correct?

 

I agree with you that the idea - while attractive - is not a very good one.  My experience tells me:

• The reformer flue gas would be subject to being at a stable, steady, constant flow with almost complete combustion and a minimum of oxygen content.  You cannot ensure this type of reformer flue gas because of varying process firing controls you have on the reformer in order to ensure proper tube temperatures and reformer reaction in accordance with varying operational needs.  You either operate the reformer as an efficient reactor or you operate it as an efficient flue gas producer.  You can’t have both; it’s either on or the other, and the reaction needs to dominate.
• For efficient CO₂ removal you will inevitably have to employ MEA.  This ensures a maximum of CO₂ absorption in a 15% wt. solution (max.) and like all amines, it is susceptible to degeneration when exposed to oxygen or carbon monoxide.  That is why you require a close, tightly controlled combustion with little or no excess oxygen.
• The regeneration section will require low pressure steam and this will impose an additional load on your present steam generation production.  While you may be co-generating steam with your reformers, you may not have sufficient.
• An independent low pressure, packaged steam generating package can easily produce a complete, balanced, and correct combustion for producing 50 psig steam and a correct flue gas for CO₂ absorption.  The steam produced can easily be dedicated solely to amine reboiler use with gravity return to the boiler with no condensate pumps employed.  This type of independent CO₂ production can be simultaneously operated by one operator during urea operations or during turn-downs, filling a liquid CO₂ storage tank that can serve as a surge tank for steady or incremental urea production of any one of your urea units - as needs be.  This gives you as much flexibility as possible in your operations.

[Pronab]

MHI (Mitsubishi Heavy Industries) design a CO2 recovery plant from  Ammonia reformer ( Haldor Topsoe design Ammonia plant) flue gas that I worked in Malaysia in 1999. I didn't face any problem from an operational point of view.  MHI have their proprietary solvent, KS-1. However due to corrosion nature in flue gas, they might be used SS.