Comparing Continuous Fluid Bed Dryers

GEA Process Engineering

Comparing Continuous Fluid Bed Dryers: Vibrating vs Static


Jim Schak, GEA Process Engineering Inc. North America (GPNA)Sales Manager for Chem System Division of GPNAInstructor for University of Wisconsin Drying Technology Course Email: [email protected] Phone: 973-316-2499

Ananta Islam, GEA Process Engineering Inc. North America (GPNA)Sales Engineer for Chem System Division of GPNAEmail: [email protected] Phone: 410-997-6621

Presented by

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Comparing Continuous Fluid Bed Dryers: Vibrating vs Static

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Webinar Outline:1. Introduction 2. Fluid Bed Drying Principle3. Static Fluid Bed Design4. Advantages of Static Fluid Bed(SFB) Design5. Vibrating Fluid Bed Design6. Advantages of Vibrating Fluid Bed(VFB) Design7. Hybrid Static Fluid Bed Design 8. Fluid bed with Integral Bag Collector9. Closed Cycle Drying 10. Fluid Bed as a Second Stage Dryer11. Design Table comparison(SFB/VFB) for air flow, energy,

capacity, bed area and retention time.12. Summary


Introduction: There are two types of continuous fluid bed dryer: Vibrating or Static.

Overlapping applications for both types, It is important to understand the capabilities and shortcomings of each.

SFB is first choice.

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Fluid Bed Drying Principle

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Advantages of a Static Fluid Bed(SFB) Design:

* Bed depth is usually in 5 to 10+ times the bed depth of a VFB * A backmix zone allows the handling of a wide range of feed moistures. * The SFB does not need to be vibrated and has less moving parts than VFB. * There are no flex connections required that may limit operating temperatures. * Internal heat panel design reduces the amount of air exhausted. * Special directional air plate aids in directing the flow of product.* In a closed cycle SFB dryer the heat panels minimizes the amount of heat and

cooling required.

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Video Clip

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Static Fluid-bed Dryer System

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Static Fluid-bed Dryers w/ Internal Heat Panels

Heating Coils to add Heat without using more Air

High Heat and mass transferdue to wet material always in

contact with the drying medium

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Can accept non-fluidizablefeed

Can only dry off surface moisture

Static Fluid Bed Dryer: Back Mix Zones

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Glass Fluid Bed Bench Top Test Unit

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Calculating Retention Time in a Fluid Bed Dryer

Retention Time = Volume of bed/Flow RateExample: 6 cu.meters / 3 cu.meters/min = 2 minutes

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Feed Rate: 3 cu.meters/min

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Special Feed Distributor Designs to spread the feed evenly in the backmix zone

Feed Distributor

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Can only accept fluidizablefeed.

Can dry interstitially bound moisture.

Static Fluid Bed Dryer: Plug Flow Zone

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Static Fluid Bed Dryer: Back Mix & Plug Flow Zones

Combination of back-mix and plug flow fluid bed

Provided with or without heating panels.

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Static Fluid-Bed Dryers w/ Heat Panels

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VFB Advantages: The VFB is a vibratory conveyor that has a holes in the pan to allow air to bubble up through the holes and contact the wet feed solids. Distribution of particle size The VFB relies on the vibrating action to

conveying the product, so the air velocity can be adjusted without greatly affecting the conveying action of the VFB.

Particle Shape - The vibrating action will minimize the air channeling(rat holing) effect of long L/D shapes

Small Particle Size The VFB can handle a smaller particle size than a SFB since air flow is independent of transport.

Plug Flow Design The vibrating action is a more positive force that aids in first in first out design..

Versatility

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VFB Flow Diagram & Commercial Size Unit

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Vibrating Fluid Bed Dryer Schematic

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Vibrating Fluid Bed Dryer (Quick Clean)

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Vibrating Fluid Bed Technology

Vibro-Fluidizer1990

Air Distribution plate

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Rice Fluidization - With & Without Vibration

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Air Directional Plates

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Barrier Gas Design

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Advantages of Integrated Bag Filter Design

Full thermal treatment of fines

Compact design

Reduced pressure drop lower power consumption

Lower dust emission and no waste water compared to a wet scrubber

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Fluid Bed Dryer with an Integral Baghouse Design

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Whatever you put in,you have to take out

Closed Cycle Fluid Bed Dryer

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Using a Fluid Bed Dryer as a Secondary Dryer

Static Fluid Bed

Vibrating Fluid Bed

Cyclone

Exhaust Fan

Fines Recirculation

Baghouse

Feed Tank:

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GEA Process Engineering28

Spray Granulator Static Fluid Bed

Spray Nozzles

Spray layers of coatings on a particle like onion peels 0.5-5 mm pellets are achievable The larger the particle the higher the

air flow the higher the evaporative rate.

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The data shows how the design factors vary for a standard static fluid-bed dryer and vibrating fluid-bed dryer when drying wet organic salt crystals from 5 percent to 1 percent moisture at the same production rate.

Table 1

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The data in Table II shows how the design of a hybrid static fluid-bed dryer with conductive heat panels. The data is based on drying polyvinyl chloride (PVC) powder from about 26 percent to less than 2 percent moisture at the same production rate.

Table 2

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In Summary

It seems to be clear that a SFB has many technical design advantages over a VFB but its applications are very limited.

The versatility of the VFB gives a bigger window of operation.

Feasibility, laboratory, pilot plant testing and a good understanding of the design limitations will be important in the final determination of equipment selection and scaleup.

Thank You for Your Interest.


Do you need a feed rotary airlock to minimize air inleakage?

Question

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Answer OK, I am glad that you brought this point up. First of all let me say that the feed entry point in

a dryer is usually the most problematic area. Great attention should be made concerning the feed. If you can get a uniform consistent feed without large lumps into the dryer usually you are able to dry the material successfully. So Hopefully you have this consistent feed and now you want to make sure that you are not sucking in a lot of air which can rob you of heated drying air going through the burner. There are different ways to minimize air inleakage at the feed entry point. One is using a rotary air lock. Rotary airlocks can be a problem though. If the material is sticky or pasty, you can have some buildup issues in the pockets of the valve. You can go to a larger valve with smooth shallow pockets to try to avoid buildup, but in any case there is some air leakage in all rotary airlocks. When dealing with an abrasive material it is difficult not to have leakage.

Another is to balance the fans and zero point the inlet as mentioned above. Maybe the best way is to use a screw feeder and fill up the screw flights with material to create a seal to prevent air from passing back the screw flights. An intermeshing co-rotating twin screw with a wet material should be enough to achieve this air lock. This design has a positive conveying action that will promote the flow into the dryer. The multiple screw design has many discharge points so there is less plopping of the wet free which can translate to less fluctuations of the product moisture.

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Why dont we use a closed cycle dryer with no exhaust on every dryer?

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OK There are some engineers that think that in 15-20 years from now that you will not be able to exhaust anything into the air, so why not start now. I do have one company that does not need a closed cycle system since he is using water, and wants to go to a closed cycle system. Maybe eventually we will have to go in that direction, but there is a high premium for going to a closed cycle system. Cooling BTUs are more expensive then heating btus. Refrigeration can get very expensive especially if you need to go to low air temperatures to condense out the solvent. It is sometimes tough enough to justify the money to build a plant on its own merits, putting on an additional cost could break the bank.

Answer

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What is an underflow weir?

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Most fluid beds use an overflow weir especially at the end of the dryer. It is basically a dam. The weir is to aid in controlling the bed depth in the dryer. If you are dealing with a heat sensitive material like a food product, you can buildup some of the large particles at the base of the weir and may degrade over a period of time. In these cases you can have a plate timed to rotate up off the bed to allow possible buildup of material to flow under it. This reduces the possibility of off spec material.

Answer

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Do you need an air directional holes in a Vibrating fluid bed?

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OK, Do you need gill type holes in a VFB? Not necessarily. In a SFB it becomes more important but in the VFB, you do have the vibrating conveying action to promote the flow of the material, but you usually still have a residue of material in the dryer. The air directional gills due aid in the cleanout and does it faster. It may also help in getting difficult to flow feeds to convey at the feed entry point.

Answer

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Comparing Continuous Fluid Bed Dryers