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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

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Outline

• Fertilizer and granulation• Process description• Modeling

– New crusher model

• Control– Re-tuned recycle mass flow controller

– Added particle size controller

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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.

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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.

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Process description• Feed:

• Slurry melt• Atomizing air

• Spherodizer: • Drying • Granulation

• Screen• Separation

based on size• Crusher

• Crush oversize

particles

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Spherodizer

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Recycle mass flow controller

• Split range controller

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Modeling

Old crusher model New crusher model

• Based on work done by Yara in MATLAB• Extended with new crusher model

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

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Re-tuning of recycle mass flow controller

• Two model approximations:

• First order plus delay:

• Pure delay:

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Re-tuning of recycle mass flow controller

• Gain variations in split range controller valves.

k2 = -670 k1 = -295

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• 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

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• Comparing the two with a ”trial and error” approach:

Re-tuning of recycle mass flow controller

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

SIMC rules:

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Re-tuning of recycle mass flow controller

• Comparing the two model approximations: Pure delay best!

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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!!

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Particle size control

• Recycle mass flow controller

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Thank you!