EFCE Working Party on Drying Advanced Drying Concepts

EFCE Working Party on Drying Advanced Drying Concepts: Superheated Steam and Adsorption TNO Environment, Energy and Process Innovation t Henk C. van Deventer

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 t Advanced drying concepts 11 April 2002 2

Advanced Drying Concepts • Drying with superheated steam • Drying with adsorptives, zeolites t Advanced drying concepts 11 April 2002 3

Superheated steam drying Energy recovery via heat exchanger Direct use of steam Recycled steam Fan Purged steam Superheater Closed steamdrying process t Advanced drying concepts Slightly superheated steam Removal of condensate 11 April 2002 4

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 t Advanced drying concepts 11 April 2002 5

Experimental set up t 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 Advanced drying concepts 11 April 2002 6

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 t Advanced drying concepts 11 April 2002 7

Example: Drying of Pigments • Better quality products • Faster drying • Prevention of emissions • No fire risc Stage: laboratory tests t Advanced drying concepts 11 April 2002 8

Example: Drying of Catalysts • Energy savings • Fluidised bed drying Stage: laboratory tests t Advanced drying concepts 11 April 2002 9

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 t Advanced drying concepts 11 April 2002 10

Example: Steam Drying of Potato’s and Vegetables • Fast drying • High quality products • Combination of drying and blanching Stage: laboratory tests t Advanced drying concepts 11 April 2002 11

Example: drying of cauliflower t Process variable Range of values Pressure 1. 1 - 1. 5 bar(a) Steam temperature 140 - 220 C Residence time 2 - 10 min. Advanced drying concepts 11 April 2002 12

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 t Advanced drying concepts 11 April 2002 13

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 Stage: laboratory tests t Advanced drying concepts 11 April 2002 14

Products for application of steam drying • Catalysts • Colouring agents • Inorganic chemicals • Chopped wood • Paper • (Coated) Textile • Vegetables • Potato fries • Herbs • Cacao beans t Advanced drying concepts 11 April 2002 15

Adsorption drying • Water adsorption by zeolites • Using adsorption heat • Low temperature drying • Fast drying • Direct or indirect t Advanced drying concepts 11 April 2002 16

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 t Advanced drying concepts 11 April 2002 17

Adsorption Drying product zeolite emission mixer regenerator separation device t Advanced drying concepts energy 11 April 2002 18

Regeneration of zeolites used in adsorptive drying processes • Thermal swing – Temperature increase 200 °C – 300 °C (4200 k. J/kg water) – Small stream of purge gas t Advanced drying concepts 11 April 2002 19

Zeolites for drying Energy aspects t Advanced drying concepts 11 April 2002 20

Zeolites for drying sludge or manure Raw material Pretreatment & Separation Liquid fraction Separation Product t Advanced drying concepts Fibrous Fract. Zeolite Drying Product 11 April 2002 21

Adsorption drying PFD t Advanced drying concepts 11 April 2002 22

Adsorption drying Pilot t Advanced drying concepts 11 April 2002 23

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 t Advanced drying concepts 11 April 2002 24

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 t Advanced drying concepts 11 April 2002 25

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 Advanced drying concepts 11 April 2002 26