Energy analysis in pulp refining. Tom Lundin Åbo Akademi University Laboratory of Physical Chemistry

Transcription

1 Energy analysis in pulp refining Tom Lundin Åbo Akademi University Laboratory of Physical Chemistry

2 Outline Background Idea and data Theory Energy: definitions, forms and principles Energy breakdown, energy balance model Deformation characteristics Experimental Results Raw data, modelling, analysis Conclusions 2

3 Background Lab refining data with systematic trends T=f(t, c, SEC) Challenging topic... Lundin, T. (2008), D.Sc.-thesis, ÅA 3

4 What is energy? Energy describes the capability of a force performing work Different forms of energy: Potential (electric, gravity) Mechanical (kinetic, sound) Magnetic Electromagnetic (light, radiation) Thermal (heat) Chemical (bonding; structural) 4

5 Thermodynamic laws Energy principles: The internal energy of a system is constant E in E out [kj] Energy can be transferred as Work [kj/s = kw = kgm 2 /s 2 ] Mass [kg/s] E Heat [kj/s = kw] system Energy cannot be destroyed, only change into a less ordered form (e.g.: electric kinetic heat) 5

6 Model system Defined system boundary Energy, mass and heat flows M in [kg/s] U, E p, E k, H M out [kg/s] W in [kw] 6

7 Thermodynamics From the 1 st law: d ( U E p E k ) M ( H Ep Ek ) dt For this to apply we assume: [kj/s = kw] Incompressible suspension, constant T in a section, c p =c V both denoted c and constant The kinetic and potential components neglible Conductive heat losses ignored convective only We know that U m c p T [kj], m = total mass (water/fibres/metal) [kg] c P = specific heat (p. const) [kj/kg] T = system temperature [K] 7

8 Thermodynamics Applying the assumptions follows: ha( T T ) [kj/s = kw] Where: ha = overall convection coeff. (incl. surface area) [kj/s K] T = surrounding temperature [K] Considering the enthalpy we get: dt mc dt ha( T T ) Ptot M ( H in H out) [kw] 8

9 Thermodynamic modeling For an incompressible fluid we get: H in H out U in U out v( Pin Pout) c( Tin T) v( Pin Pout) Exclusion of the entalpy term provides: dt mc dt ha ( T T ) P tot [kj/s] Rearrangement and integration gives us: ha( T Tin ) P ln P tot hat mc tot That rearranged gives the final model: P tot T T in 1 e ha hat mc [-] [K] 9

10 Wood structure model 10

11 Rheology Deformation characteristics Native wood Ingenious organic composite structure: High dimensional strength at low density (30-40% solid) An effective natural viscoelastic motion damper effective at low frequencies (~ s -1 ) Difficult to modify effectively for paper applications Refer to mech. pulping TEC-requirements These properties remain even if 50% of the material is being removed: Kraft pulp fibres capable of withstand» High edge loads (SEL) and» energy inputs (SEC) 11

12 Rheology Deformation characteristics Water viscous (Newtonian) Total energy dissipation (h=f(t)) Fibre suspension plastic+thixotropic (Bingham) Energy dissipation proportional to amount viscous/plastic deformations Fibres with water-filled cavities viscous/plastic behaviour depending on the strain rate At higher frequencies (refiner >100 khz) the fibres behave more like elastic cushions momentarily damping the deformation forces 12

13 Pulp refining energy break-down 13

14 Experimental Series of trials was performed No-load: constant rpm: 2250 /min ( m/s), 1 mm refining gap Pulp consistencies 0, 2, 4 and 6 weight-% Finnish SW dry-lap reinforcement pulp Pine:spruce 40:60, ECF-bleached 2.44 mm, mg/m Refiner run empty + conventional refining trial 2250 rpm, 2.7 J/m, 4 % 14

15 Experimental ProLab TM refining station Power 30 kw Consistency 1-7 % Pulp flow L/min Feed pressure bar Conical fillings LM-type: 52 m/rev Rotor Ø min / max 46 / 130 mm Speed Rotational /min Peripheral 5-14 / m/s SEL * J/m SEC * kwh/t * Depending on fillings and type of pulp 15

16 Process energy balance area 16

17 Temperature ( C) Results raw data Refining system temperature development ProLab 2250 rpm, 100 L/min, FIC12=35% %, LM2-fillings (30,8 m/rev), 1.0 mm 2 % ECF2, LM2-fillings (30,8 m/rev), 0,5 mm 2 % ECF2, LM2-fillings (30,8 m/rev), 1,0 mm 4 % ECF2, LM2-fillings (30,8 m/rev), 1.0 mm 6 % ECF2, LM2-fillings (30,8 m/rev), 1.0 mm 0 0:00:00 1:12:00 2:24:00 3:36:00 4:48:00 6:00:00 Time 18

18 Tensile index, Nm/g Results pulp properties Pulp sheet strength 60 1, % 4 % 6 % 1,2 1,0 0,8 0,6 0,4 0,2 WRV, g/g 10 0, Beating degree, ºSR 19

19 Fibre curl, % Results pulp properties Fibre dimensions 18,0 17,5 17,0 16,5 16,0 15,5 15,0 14,5 2 % 4 % 6 % 8,0 7,5 7,0 6,5 6,0 5,5 5,0 4,5 Cell wall thickness, mm 14,0 4, Beating degree, ºSR 20

20 Tear index, mnm 2 /g Results pulp properties Fibre length sheet strength 60 2, % 4 % 6 % 2,50 2,45 2,40 2,35 2,30 2,25 Fibre length, mm 10 2, Beating degree, ºSR 21

21 Results The heat balance model fitted data well % data Temperature ( C) P tot T T in 1 ha e hat mc 2 % data 4 % data 6 % data 0 % model 2 % model 4 % model 6 % model Time (s) 22

22 Q (kj) Results energy break-down Energy estimation by contributors Refining system energy components Ideal system Measured Suspension Water Bearing losses Time (s) 23

23 Energy break-down 24

24 Conclusions The consumed energy in pulp refining is consumed as Copper losses (magnetic) Bearing losses (mechanical) Hydrodynamic losses (viscous) Fibre deformations (elastic/viscoelastic/plastic) providing Breakage of chemical bonds in fibres that delivers the desired and undesired changes in the final pulp A majority of the spent energy is converted into sensible heat A pulp refiner is an inefficient water boiler... 26

25 Conclusions It was possible to model a refining process using a thermodynamic model The model applied well for (continuous) batch processing The power level for a given shear rate was determined by the amount of water and fibre intraand interactions, and thus the pulp consistency. The no-load energy spent was totally converted into sensible heat The no-load power could be split into mechanical and viscous components 27

26 Acknowledgements My journal paper I co-authors: Especially Ms. Fernanda Wurlitzer is warmly recognised for her solid contributions: Performing the experiments with great care and Co-authoring the manuscript Metso Paper for technological and financial support The Research Institute of the Åbo Akademi Foundation for financial support I Lundin, T., Wurlitzer, F., Park, S.W. and Fardim, P. (2009): Energy analysis in low consistency refining of softwood. O Papel 70(10):