Passion for Progress

Without verbal explanation the information on this document is incomplete

Fluidized-bed drying with superheated steam

Jochen Gaßmann, Mirko Löhn, Hartmut Hafemann

BMA Braunschweigische Maschinenbauanstalt AG Braunschweig, Germany

Steam drying

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…has been proven in a number of practical applications

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…takes place in a pressurized fluidized bed

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…uses superheated steam instead of hot air for fluidisation and drying

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…provides excess steam by evaporation of the product water

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…should be integreated into the energy system of a factory

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…is characterized by multiple use of primary energy

Operating principle

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Main components

(1) product feed system

(3) fuidized bed

(4) pruduct discharging system
(6) rotary dust separator

(8) vapour discharge
(9) heat exchanger
(10) fan 1 3 4 6 8 9 10

Integration into an energy system (pulp drying)

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Main processes
(1) steam generation
(2) power generation 1 2 3 4

(3) pressurized fluidized-bed steam drying
(4) utilization of the excess steam

Advantages

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The vapour produced during drying has a high energy content.

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This energy potential can be used for downstream processes.

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Because of the closed system emissions can be avoided.

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No air pollution by dust and odours.

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No loss of product.

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Oxygen-free steam atmosphere prevents oxidative reactions.

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Volatile substances can be removed and recovered by condensation.

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Optimum conditions for sterilisation prozesses.

New applications – Necessary investigations

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Assessment of the properties of the wet product before steam drying

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Investigation of flow characteristics

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Investigation of drying kinetics

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Assessment of product properties after the steam drying process In order to carry out such studies appropriate test equipment is

Test unit fluidized-bed steam dryer

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Parameter

batch-wise operating device
batch size: 0,5 to 2 kg

fluidized-bed: d = 200 mm

fluid velocity: up to 8 m/s

working pressure: up to 4,5 bar
process temperature: up to 210 °C

Technological principle test unit

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Main components

1

feeding lock system

2

dryer

3

fluidized bed with perforated plate

4

steam injection

5

discharge lock system

6

cyclone for dust separation

7

dust discharge

8

fan

Drying kinetics

Wheat stillage 120 130 140 150 160 170 180 190 200 0 60 120 180 240 300 Zeit [s] Zeit [s]Zeit [s] Zeit [s] T e m p e ra tu r [ ° C ] T e m p e ra tu r [ ° C ] T e m p e ra tu r [ ° C ] T e m p e ra tu r [ ° C ] Dampfeinlass Erweiterungsteil WS oben WS unten 120 130 140 150 160 170 180 190 200 210 T e m p e ra tu r [ ° C ] T e m p e ra tu r [ ° C ] T e m p e ra tu r [ ° C ] T e m p e ra tu r [ ° C ] Dampfeinlass Dampfeinlass Dampfeinlass Dampfeinlass Erweiterungsteil Erweiterungsteil Erweiterungsteil Erweiterungsteil WS o ben WS o ben WS o ben WS o ben WS unten WS unten WS unten WS unten eff. Dampftemp. eff. Dampftemp. eff. Dampftemp. eff. Dampftemp.

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Temperature profiles depend on the product characteristics

Results of steam drying tests

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Dried materials of different structures and

composition after drying (reference particle d=5mm)

Wood chips

200_°C, v=4 m/s, p=2 bar

Results of drying tests

Corn stillage 180°C 5 Min 1 bar 160°C 6 Min 1 bar 160°C 6 Min 2 bar 160°C 6 Min 3 bar 180°C 5 Min 2 bar 180°C 5 Min 3 bar 180°C 5 Min 4 bar 200°C 4 Min 3 bar 200°C 3 Min 4 bar 200°C 2 Min 4 bar Wheat stillage

Flow characteristics

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The flow test unit represents the elements of a real dryer

Flow characteristics

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to investigate the flow behavior during fluidization

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to investigate the efficiency of dust separation

Summary

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The aim of the fluidized-bed steam drying technology is the multiple use of primary energy and the reduction of CO₂ emissions.

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New applications require the possibility to conduct experiments.

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Investigations according real process conditions are necessary.

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The pressurized steam dryer is an highly efficient multiple utilisation system if integrated in combined plants or in energy networks

180 190 200

The installation of the pilot plant was co-financed by Deutsche Bundesstiftung Umwelt (DBU) as part of a research project (Ref.No.: 26568-24/2)