t tno environment, energy and process innovation henk c. van deventer advanced drying concepts:...

Henk C. van Deventer

t

TNO Environment, Energy and Process Innovation

Advanced Drying Concepts: Superheated Steam and Adsorption

EFCE Working Party on Drying

11 April 2002Advanced drying concepts 2t

Challenges Remaining on Drying Processes

• Decrease product degradation• Reduce high energy uses• Emissions control:

– Odours– Solvents– Volatiles– Dust

• Drying in controlled atmosphere– Oxygen free– Fire prevention– Explosion prevention

• Intensify drying• Combining processes


Advanced Drying Concepts

• Drying with superheated steam

• Drying with adsorptives, zeolites


Superheated steam drying

Closedsteamdrying

process

Fan

Removal ofcondensate

Energy recoveryvia heat exchanger

Direct useof steam

Purgedsteam

Slightly super-heated steam

Recycled steam

Super-heater


Potential benefits of superheated steam drying

• Latent heat comes available as slightly superheated steam, energy recovery on a relatively high temperature level

• Energy saving potential: 50 to 75 %

• No emission of odours, dust or hazardous components; pollutants in condensate

• Evaporation rates can be higher; increasing drying speed

• Product temperatures dependent on pressure

• No oxygen, qualitative benefits for the product

• Explosion and fire protection

• Additional processing: sterilising, blanching, fixation


Experimental set up

Process variable Range

Steam temperature 100 - 400 C

Steam flow rate 100 - 400 kg/h

Pressure 0.1 - 5 bar(a)

Evaporation capacity

100 kg/h


Feasibility studies

• Experimental:– product qualities

– drying rates

– additional processing

• Model calculations:

– validated Micro- and macro scale models

– heat and mass transfer in products

– Quality influences


Example: Drying of Pigments

• Better quality products

• Faster drying

• Prevention of emissions

• No fire risc

Stage: laboratory tests


Example: Drying of Catalysts

• Energy savings

• Fluidised bed drying



Example:Superheated steam drying of biomass, chopped wood

• Energy from biomass

• Drying before burning

• Better quality fuel

• Lower overall energy uses

• No emissions to the air

• Pollutants in condensate

Stage: pilot scale tests


Example: Steam Drying of Potato’s and Vegetables

• Fast drying

• High quality products

• Combination of drying and blanching



Example: drying of cauliflower

Process variable Range of values

Pressure 1.1 - 1.5 bar(a)

Steam temperature 140 - 220 C

Residence time 2 - 10 min.

0

20

40

60

80

100

120

140

160

180

200

0 2 4 6 8 10 12 14

Drying time [min]

Te

mp

era

ture

[d

g C

]

1

1,2

1,4

1,6

1,8

2

2,2

2,4

2,6

2,8

3

Pre

ss

ure

[b

ar(

a)]

Product temperature

Steam temperature

Pressure


Example: Sterilising / Drying of Herbs

• Alternative for steam sterilising, followed by drying

• No pressure differences

• Odours and flavours in circulation

• No odour emission Stage: industrial tests, superheating steriliser


Example: Drying and fixation

• Samples of cotton cloth, printed with various kinds of dye

• Best results for reactive dyes: drying and fixated in one step



Products for application of steam drying

• Catalysts

• Colouring agents

• Inorganic chemicals

• Chopped wood

• Paper

• (Coated) Textile

• Vegetables

• Potato fries

• Herbs

• Cacao beans


Adsorption drying

• Water adsorption by zeolites

• Using adsorption heat

• Low temperature drying

• Fast drying

• Direct or indirect


Adsorption drying using Zeolites

• Ideal drying process

– Low temperature

– Short duration

– Free of oxygen

– Good controlled process conditions

– Predictable final moisture

– Low energy consumption

– No emissions

– Compact equipment


Adsorption Drying

mixer

separationdevice

emission

energy

product zeolite

regenerator


Regeneration of zeolites used in adsorptive drying processes

• Thermal swing

– Temperature increase 200 °C – 300 °C (4200 kJ/kg water)

– Small stream of purge gas


Zeolites for dryingEnergy aspects

50 100 150 200 2500

10

20

30

40

50

60

70

80

90

100

temperatuur ingaande droge lucht (C)

kglu

cht

/ kg

wat

er

RV = 1

RV = 0.7

RV = 0.5

10 20 30 40 50 60 700

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

product temperatuur (C)

ener

gie

verli

es(M

J/kg

wat

er)

RV = 0.7

RV = 1

RV = 0.5

Zeoliet-drogen


Zeolites for drying sludge or manure

Raw material

Pretreatment &Separation

Liquid fraction Fibrous Fract.

Separation Zeolite Drying

ProductProduct


Adsorption drying PFD


Adsorption dryingPilot


Applications of Adsorption drying

• Slurries

• Lactic acid derivatives

• Manure

• Starch drying with a low energy consumption

• Milk powder drying in a oxygen-free environment

• Herbs

• Fast drying of cocoa cake

• Wheat flour with a low moisture content


Further developments on steam drying

Challenges remaining:

• Feasibility studies:– Product qualities– Quantify advantages

• Equipment development– Different types and throughputs

• Continuous operation

• Steam tight in and output devices

• Energetic process integration


Further development of Adsorption drying

• Feasibility studies:– Product qualities– Quantify advantages

• Zeolite crushing strength and erosion resistance

• Integration of unit operations

• Regenerator optimisation

• Different adsorbentia

• Equipment development

t tno environment, energy and process innovation henk c. van deventer advanced drying concepts:...

Documents

drying slide

drying processes

drying prevention of

drying combining processes

steam sterilising

fixation slide

bara steam temperature

high energy