1 Christer Haugland, Modeling and Control of fertilizer granulation process Christer Haugland Supervisors: Sigurd Skogestad Vidar Alstad (Yara Technology Center) Modeling and Control of Fertilizer Granulation Process

2 Outline Fertilizer and granulation Process description Modeling –New crusher model Control –Re-tuned recycle mass flow controller –Added particle size controller

3 Fertilizer A major product in the world’s chemical industry Keep up with the increasing food demand in the world One important process step in making fertilizer is granulation.

4 Granulation Granulation consist of solidifying fertilizer melt into small granules which can be used in the agriculture. Solid granule particles are about 3 mm in diameter.

5 Process description Feed: Slurry melt Atomizing air Spherodizer: Drying Granulation Screen Separation based on size Crusher Crush oversize particles

6 Spherodizer

7 Recycle mass flow controller Split range controller

8 Modeling Old crusher model New crusher model Based on work done by Yara in MATLAB Extended with new crusher model

9 Control Re-tuning of recycle mass flow controller Based on open loop step response in model

10 Re-tuning of recycle mass flow controller Two model approximations: First order plus delay: Pure delay:

11 Re-tuning of recycle mass flow controller Gain variations in split range controller valves. k 2 = -670 k 1 = -295

12 Process gain variations in MV’s: –Gain scheduling control (one controller for each MV) –Changing the split in the split range controller (usually set at 50%) Gain scheduling: Re-tuning of recycle mass flow controller

13 Comparing the two with a ”trial and error” approach: Re-tuning of recycle mass flow controller

14 Re-tuning of recycle mass flow controller First order plus delay model: Not a good approximation! SIMC rules:

15 Re-tuning of recycle mass flow controller Comparing the two model approximations: Pure delay best!

16 Particle size control Added another PI controller to control particle sizes in granulator loop. Vibration in screen as MV, D50 out of granulator as CV. –But the MV saturated!!

17 Particle size control Recycle mass flow controller

18 Thank you!