In-line particle sizing probe in continuous fluidized bed

Application

Direct in-line measurement in a fluidized bed granulator.

Customer

A leading German detergents manufacturer.

Product

 Several components of detergents and washing powders, Dv50 is about 700μm. 

Process type

The fluidized bed granulator has a circular design of the air distribution plate which effects nearly ideal mixing of the fluidized product. It continuously classifies appropriate sized granules through a central discharge pipe. A separate adjustable classifying airflow is fed to this pipe and particles which are heavy enough and whose terminal falling velocity is higher than the gas velocity insides the discharge pipe are discharged as product. Smaller particles and dust are blown back to the fluidized bed and exposed to the growth process once again.

Plant equipment

Granulator Type AGT, produced by Glatt. Loading of product in fluidized bed is 1.5 tons.
Height of fluidized bed is about 1.5 m from the base of the sieve. 

Customer objectives 

• Use of IPP 70-SE's predecessor IPP 50-SE (explosion proof version ) to provide the operator assistance in controlling the process.
• Monitoring of process to see real time change in particle size, and hence gain information on the stability of the fluidized bed and how much of the product is within specification.
• Improvement in stability of production process (particularly the fluidised bed).
• A final goal was to reduce the amount of circulating “off-spec”-material.

Customer benefits

• Greater process transparency helps the operator to see if anything goes wrong within the fluidized bed in real time.
• To see problems as they develop enables the operator to take corrective action and make the appropriate process adjustments.
• Reduction of off-spec material. 

Process conditions

Temperatures:

• Air inlet to granulator more than 250°C
• Fluidized bed up to 110° C in the measurement zone
• Wall of granulator 85°C
• Probe (electronic housing) 45°C
• Very high loading and density inside fluidized bed
• Movement of fluidized bed causes vibration of the probe
• Ambient atmospheric pressure
• High humidity

Measurement equipment

• IPP 50-Se with Flow Cell SZ 20-4 and pulse option
• Software V5.60
• Cable length 30m (Ex zone)
• PC in control room

IPP 50-Se's successor IPP 70-Se in a different application

Measurement position

• Measurement position is about 1m from the base of the sieve.
• Measurement takes place about 15 cm from the wall inside the granulator. The Granulator is thermally insulated so the probe could not be installed any deeper into the vessel (it is not a problem because of the homogeneity of the particles in the fluidized bed).
• Installation was made through the Glatt-standard-port, which are available in all AGT-machines at 3 or 4 different heights. 

Modifications for high temperature up to 120°C

1. Additional air-cooling for electronics housing (compressed air, about 10 l/min is put in the housing, pipe DN 4 mm) outlet temperature of this air is about 43°C.
2. Additional air-cooling for probe pipe (compressed air is put into the 25mm probe pipe) outlet temperature of the air is about 54°C.
3. Insulation plate to protect from heat radiating from the granulator surface.
   
   

Modifications of the probe to better meet the conditions in a highly loaded fluidized bed

1. An additional pipe with diameter of 40mm in combination with a flange DN 80 (3,5 inches) is mounted. to protect the probe from high mechanical stress, caused by the vertical movement of the product in the fluidized bed. The pipe is welded to the flange and gives more stability.
2. An air purge “Lance” (4 mm steel pipe) is added to blow away lumps and powder that may block the entrance of the flow-cell SZ 20-4. It works with air pulses only.
   
   

Software parameters

• Loading is very variable pulsating between 10% …100%, therefore the maximum loading parameter is set to 30%, all measurements at loadings between 30 % and 100% are filtered out.
• Sampling rate = 400kHz, low particle velocity.
• Adjust Factor = 0.7 (find out empirically, in comparison to customer sieving analyses) Adjust Offset = 0.
• Coincidence Level = 3%, Probability of Stay = OFF.
• Particle buffer = 5000 (small for statistics but provides the fastest reaction time to any process changes).

Cleaning of the probe 

Customer reports that clearing blockages from the probe of lumps or large agglomerates is required 1-2 times per shift (product dependant ), and that this is effected automatically by the additional air pulse from the “Lance” modification.