understanding the nutsche filtration and drying process

Filtration and Drying Equipment

Typical Scope DDPS Filter/Dryers:

– efficiently perform filtration, washing, reslurry, and drying

– are designed for batch operation – handle multipurpose pharmaceutical

and fine chemical applications– are available in pilot, semi-works,

and production units• Sizes from 0.002m² to 16.0m²

Typical Scope DDPS Filter/Dryers:

– efficiently perform filtration, washing, reslurry, and drying

– handle multipurpose pharmaceutical and fine chemical applications

– are available in pilot, semi-works, and production units

• Sizes from 0.002 m² to 16.0 m²

Special designs are available, including:• cGMP• CIP• Aseptic• Sterile• Lethal service• Customization

for other special requirements

Filtration and Drying Process Steps

1. Filling/Charging2. Filtering3. Displacement Washing 4. Reslurry Washing5. Smoothing6. Drying/Cooling7. Discharging

Filling/Charging The first step involves charging

the product to be filtered, typically an aqueous or solvent based solid/liquid slurry, into filter from a primary location (reactor/vessel)

The filter is usually sized for solids volume.― Maximum solids = agitator stroke,

typically 12 - 20 inches.― Also limited by filtration rate.

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Filling/Charging The first step involves charging

the product to be filtered, typically an aqueous or solvent based solid/liquid slurry, into filter from a primary location (reactor/vessel)

The filter is usually sized for solids volume.― Maximum solids = agitator stroke,

typically 12 - 20 inches.― Also limited by filtration rate.

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Filter vessel volume does not have to equal reactor volume

Filtration Rate What controls filtration rate? ― Particle size― Particle shape― Cake porosity― Compressibility

Typically you cannot measure these factors directly, so testing must be done to measure their effect: 

― Pressure drop― Filtration rate― Cake depth

Tests should be conducted at anticipated cake depth, and more.

Higher temperature usually = faster filtration.

Filtration Constraints Minimum cake depth of 3 inches

―Note: This is pertaining to “deep bed filtration”, in which the filtration mechanism is particle bridging (not absolute filtration).

Minimum Filtration Rate―Typically 4 liter/min-M² (0.1 gpm/ft²)―Minimum cake buildup rate of 1-inch per hour

Filtering The second step involves the

use of pressure or vacuum to force liquid through the solid bed and filter media. The process is stopped when solids are visible, or can be continued until all the liquid is pushed out.

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Washing of the Filter Cake: Displacement

Here, fresh wash liquid is sprayed on top of the solid cake. The liquid is forced through with pressure or vacuum.

The purpose of this step is to: ― remove the previous liquid and its

impurities.― keep cake intact (do not disturb).― try to close cracks (if cake has any).― replace previous liquid with fresh

liquid.

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Washing of the Filter Cake: Reslurry

As an additional washing option, fresh wash liquid is added and mixed with the solids. The agitator is stopped and raised before filtering.

The reslurry process is used if:―extracting or dissolving

impurities―long contact time is needed―cake is severely cracked―displacement wash does not

work

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Washing of the Filter Cake: Reslurry

As an additional washing option, fresh wash liquid is added and mixed with the solids. The agitator is stopped and raised before filtering.

The reslurry process is used if:―extracting or dissolving

impurities―long contact time is needed―cake is severely cracked―displacement wash does not

work

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..Reslurry is unique to agitated nutsche filters.

Smoothing This next step may be used

after any filtration or wash, especially after the final wash, when gas is blowing through.

The agitator will close cracks and compress the cake to reduce residual moisture level.

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Smoothing This next step may be used

after any filtration or wash, especially after the final wash, when gas is blowing through.

The agitator will close cracks and compress the cake to reduce residual moisture level.

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The smoothing process may not be necessary or useful in some cases.

Vacuum Drying  Vacuum drying requires:

―Heated vessel surfaces (wall, base, agitator)

―Vacuum source―Agitation―Dust filter

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Vacuum Drying  Vacuum drying requires:

―Heated vessel surfaces (wall, base, agitator)

―Vacuum source―Agitation―Dust filter

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Vacuum drying is the most common drying method in filter/dryers, and the only method for dedicated dryers such as pan and spherical dryers.

Convection Drying• During the convection drying

phase hot, pressurized gas (usually nitrogen) can be blown down through solids and out of filtrate lines; this will eventually dry the solids.

• The vessel should be heated.• Solids may or may not be agitated.• Hot gas may or may not be

recirculated.

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Convection Drying• During the convection drying

phase hot, pressurized gas (usually nitrogen) can be blown down through solids and out of filtrate lines; this will eventually dry the solids.

• The vessel should be heated.• Solids may or may not be agitated.• Hot gas may or may not be

recirculated.

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This method of drying is applicable to filter/dryers only, because of their porous filter plate.

Stages of the Drying Process- Stage One: Removal of free moisture from the wet product.- Stage Two: Removal of moisture from pores of the wet product.- Stage Three: Removal of chemically bound moisture.

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100

1 2 3 4 5 6 7 8 9 10 11 12

Time

% M

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Dry

ing

Rat

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Stage One:Constant Rate

Stage Three:Diffusion Rate

Stage Two:Falling Rate

Critical Point

Rate of DryingPercent Moisture

Discharging Discharge is accomplished through

the valve/port located on the vessel sidewall.

  The agitator is used to move

product to the side discharge valve―Agitator is slowly lowered until

product is removed. 

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Discharging Discharge is accomplished through

the valve/port located on the vessel sidewall.

  The agitator is used to move

product to the side discharge valve―Agitator is slowly lowered until

product is removed. 

...The vessel and

product may need to be cooled to an ambient temperature prior to discharge.

Process Support Capabilities Fully supported by in-house

process engineers. Filtration testing with 0.002m²

“Pocket” Filter―Ensures the acceptability of the filter

for the specific customer processes. Allows for process optimization,

while limiting product losses and production down time.

Filter/Dryer Advantages Totally enclosed and pressure tight (rated to 50 psig/FV at a minimum)

― No operator or environmental contact with the product― Ideal for high purity, toxic, or flammable materials

No live load associated with the filter― Low RPM agitator (8 – 20 rpm typical)― Lower installation cost

Low maintenance and operational costs― No high speed components― Low motor HP by comparison to other types of equipment (e.g. Centrifuge)― Agitator only used during drying, smoothing, reslurry washing, and discharge

(whereas a centrifuge motor is always in operation).

Filter/Dryer Advantages (cont’d) Efficient cake washing

― Extended residence time during displacement washing― Capable of reslurry washing― Reduced wash fluid

Possible increased capacity― Units typically sized to handle entire batch solids load

Flexible discharge― Can discharge dry solids, wet solids, slurries, or liquid

Drying capability― Less than 0.1% final product moisture― Vacuum or blow through drying― Completely dry material out of the filter

Example – Production Unit (1.0m2 units)

Example – Production Unit (1.0m2 units)

Additional Resources– Filtration Webpage– Filtration Questionnaire– Contact Us– Call 908.317.2585 to speak with a DDPS

representative

Thank you