Removal of urea and ammonia from exhaust gases

• US 10,640,428 B2
• Filed: 01/31/2017
• Issued: 05/05/2020
• Est. Priority Date: 09/16/2009
• Status: Active Grant

• Current Assignee: Stamicarbon B.V. (Maire Tecnimont SpA)
• Original Assignee: Stamicarbon B.V. (Maire Tecnimont SpA)
• Inventors: Meessen, Jozef Hubert, Orfanidis, Pantelis
• Primary Examiner(s): Nassiri-Motlagh, Anita
• Application Number:
  US15/421,265
• Publication Number:
  US 20170137330A1
• Time in Patent Office: 1,190 Days
• Field of Search: None
• CPC Class Codes: B01D 2251/506 Sulfuric acid
• CPC Class Codes: B01D 2257/406 Ammonia
• CPC Class Codes: B01D 2257/70 Organic compounds not provided for in groups B01D2257/00 - B01D2257/602
• CPC Class Codes: B01D 53/54 Nitrogen compounds
• CPC Class Codes: B01D 53/58 Ammonia
• CPC Class Codes: B01D 53/80 Semi-solid phase processes, i.e. by using slurries
• CPC Class Codes: C01C 1/12 Separation of ammonia from gases and vapours as part of the ammonia synthesis process C01C1/04
• CPC Class Codes: C01C 1/22 Sulfites of ammonium
• CPC Class Codes: C05C 3/00 Fertilisers containing other salts of ammonia or ammonia itself, e.g. gas liquor
• CPC Class Codes: C05C 3/005 Post-treatment
• CPC Class Codes: C05C 9/00 Fertilisers containing urea or urea compounds
• CPC Class Codes: C07C 273/16 Separation; Purification

Abstract

The invention relates to a method for recovery of urea dust and ammonia from a gas stream by contacting said gas stream with an aqueous sulphuric acid solution, thus forming an acid solution of ammonium sulphate and urea, characterized in that the acid solution is concentrated to a melt comprising less than 5 wt % of water, which melt is subsequently transferred into solid particles comprising urea and ammonium sulphate.

Claims

1. A method for converting urea dust and ammonia from a waste air stream comprising urea dust and ammonia into particles comprising urea and ammonium sulphate which method comprises

(i) scrubbing said waste air stream comprising air, urea dust and ammonia with an aqueous sulphuric acid solution, thus forming an acidic solution of ammonium sulphate and urea;

(ii) adding ammonia to the acid solution, thus forming a neutralized solution of urea and ammonium sulphate in water;

(iii) concentrating the neutralized solution of (ii) to a melt comprising less than 5 wt % of water, and

(iv) transforming the melt into solid particles comprising urea and ammonium sulphate;

wherein the waste air stream is from urea granulation or urea prilling; and

wherein step (iv) is performed in a pelletizer.

2. The method of claim 1, wherein the concentrating of the neutralized solution from step (ii) in step (iii) is performed by vaporization of at least part of the water phase, thus forming water vapor and said melt comprising less than 5 wt % of water.

3. The method of claim 2, wherein the vaporization is performed in more than one step.

4. The method of claim 1, wherein the melt is mixed with an additional amount of ammonium sulphate.

5. The method of claim 1 wherein the neutralized solution of step (ii) is mixed with an additional amount of ammonium sulphate before said concentrating of step (iii).

6. The method of claim 1, wherein said pelletizer comprises a feeding device, a belt and a device to remove the formed pellets from the belt, whereby droplets of the urea/ammonium sulfate comprising liquid are dosed to the belt, whereon the urea/ammonium sulfate-comprising droplets solidify;

and

removing the formed urea/ammonium sulfate comprising particles from the belt.

7. The method of claim 1, wherein said solid particles obtained in step (iv) are a solid UAS fertilizer product.

8. The method of claim 1, wherein the scrubbing of step (i) is carried out in a scrubber that circulates said acidic solution of ammonium sulphate and urea over the scrubber, and make-up water is provided to the scrubber, wherein cleaned air from said waste air stream leaves the scrubber.