Energy Efficient Fibrillation of Cellulose Fibers using an Ultrasound Reactor

Contact: Taraka Pamidi (Taraka.pamidi@ltu.se)Örjan Johansson (orjan.johansson@ltu.se), Torbjörn Löfqvist(torbjorn.lofqvist@ltu.se) Funded by:

Motivation• Minimizing electrical energy use by 50% is essential for a

cost efficient and competitive operation of modern pulp &paper mills.

• Hydrodynamic and acoustic cavitation has the potentialto be an energy efficient alternative to modify theproperties of cellulose fibers.

Results

Future Work• Increasing flow rates, process temperature and static

pressure in an up-scaled reactor• Find optimal balance between process parameters related

to the fiber suspension characteristics and flow inducedcavitation.

Problem Description• Swedish paper mills combined consumes about 19 %

of the Swedish industry’s total energy use.• In the refining process, fibrillation is one of the essential

unit operation that count for up to 80% of the total energyuse.

Effect on fibers due to cavitation“Development of an energy efficient flow reactor for

treatment of cellulose fibers”• Separate the wood fibers from each others• Retain or reduce fiber length• Swelling and shrinking occurs• The fibers will be delaminated (internal fibrillation)• Fibrillation of the secondary wall (external fibrillation)• Creation of fines occur

MethodsAcoustic modeling coupled to structural interaction andCFD are used to optimize an ultrasound controlled reactorusing FEM, CFD.and experimental investigation

Scanning Electron Microscopy images of untreated and ultrasound treated cellulose fibers

Background

Micro jets and shockwaves effects the fiber surfaceFrequency dependent bubble size –– Optimized with respect

to pulp characteristics

Taraka Pamidi, Örjan Johansson, Torbjörn LöfqvistEngineering Acoustics

Experiment have been performed on both mechanical andchemical pulp fibers. The fibers did not receive any pre-treatment prior to ultrasound exposure. After ultra-sonication the samples was characterized with respect tomodification of fiber properties and the energy supplementby sonication. Test 4 and 3b give the best results.

The reactor is driven with nine sonotrodes mounted radiallyon the reactor wall. Three in the center, top and bottompositions at 120° spacing. The sonotrodes are excited withdouble frequencies, at 22.6 and 38.8 kHz. Both bottom upand top down flow through a venturi nozzle to initiatebubbles give a significant impact on fiber properties.

(a) Fiber absorption properties (b) fiber mean length with distribution