LC-REFINING CONSIDERATIONS ON ENERGY EXPENDITURE

Transcription

1 KCL Refining Seminar November 15 th 2004, Espoo, Finland LC-REFINING CONSIDERATIONS ON ENERGY EXPENDITURE Tom Lundin

2 Presentation lay-out Background Principles Aims Low consistency refining (LCR) theories Energy expenditure ProLab TM refiner Idling power measurements Loadability trials (bar clearance, intensity) Conclusions 2

3 Background Licentiate thesis: LC-refining of softwood-bleached kraft pulps with special reference to pulp suspension rheology Åbo Akademi University 2002 Main Goal: To investigate the pulp flow conditions in LC-refining and to clarify their effects on the beating of reinforcement fibres Main objectives Effects of refining parameters (n, c, SEL, SEC) The role of flow conditions in the refining zone Floc-size modification by dispersion 3

4 Background D. Sc.(Tech.) thesis under construction: Mechanisms in LC-refining of pulp fibres (Åbo Akademi University 2005) Main Goal: To investigate the process of LC-refining pulp fibres for improved understanding of fundamental fibre treatment mechanisms Main objectives ear of refiner bars (smoothness & rounding) Energy expenditure in LC-refining Comparison of (contemporary) LCR-theories 4

5 LC-refining Introduction Fibre( floc)s are transported/collected by moving bars during shear and compressive action between opposing bar faces while mechanical energy is being transferred Main effects Fibre modification Cell wall delamination, internal fibrillation Hydration, swelling, flexibility, fibre-collapse Fibrillation External fibrils and fines-release Fibre (straightening) shortening Formation of secondary fines Improves fibre bonding potential resulting in enhanced paper sheet quality 5

6 hy LC-refining? At P&P mills the fibres are suspended for transportation to low-consistency a well-represented resource To modify the (various) fibres prior web-formation, for achievement of improved runnability (e.g. drainage, wetstrength, pressability) For enhanced fibre-fibre bonding capabilities Strong, long (unshortened) & straight fibres High average intrinsic fibre strength Improved fibre-fibre interaction (fibre-packing) Increased fibre flexibility At minimum expense of bulk and opacity 6

7 LCR-theories Jagenberg F. (1887) characterised the Hollander (α=0º) Beating pressure & bar contact area Edge length/s (fibre cutting action) Area (fibrillation action) Jagenberg crushing formula Beater z b zbbbl Kirchner E. (1906) expanded theory to inclined bars (α>0º) The actual bar length and contact area The number of crossing points Pfarr A. (1907) evaluated the probability of trapping fibres The single bar crossing point Total contact area Smith S. (1922) originator of the fibrage theory Bar edges collect fibres forming a fibrage Bar edge pressure = (contact force / total length of active bar edges) Beating pressure 1/fibre lenght p = FπD w 8

8 LCR-theories Milne S. (1927) described the Hollander beater et beating factor Q Cutting action - bar width: wider bars promote crushing ultsch F. & Flucher. (1958) used the number of rotor and stator bars for a more universal theory Pnet Pnet Defined Spezifische Kantenbelastung, B s Bs = = L n s Van Stipout (1964) equated frequency and intensity zr zsl 60 The probability of a fibre being caught in the refining gap The force acting on fibres The mass of treated fibres ( mean residence time) Brecht. & Siewert. (1966) defined SEL (equal to B s ) Demonstrated the dominant impact of the bar edge Introduced specific power consumption (SEC) Danforth D. (1969) attempted to describe the process with frequency and intensity Intensity x frequency = SEC 9

9 LCR-theories Leider P. and Nissan A. (1977) integrated fibre parameters Number of impacts per single fibre per refiner pass The probability of a fibre stapling on a bar The required intensity/fibre impact resulting in changed fibre characteristics Derived a term for SEC utilising intensity and number of impacts Kline S. (1978) related the net power to the refining area Treatment intensity = net power/effective refining area Treatment frequency = effective refining area/fibre mass flow Joris G. (1986) used the number and velocities of bar crossing points and the variation of bar cutting angles in his theory Prediction of refining result by key figures in conjunction with net power and fibre flow as based on fibre length data Lumiainen J. (1990) accounted the effects of bar width Defined SSL (from SEL) Treatment frequency = (edge length/s)/fibre mass flow 10

10 LCR-theories Kerekes R.J. (1990) introduced a C-factor measuring the capacity of a refiner to treat fibres Incorporation of fibre, process and machine parameters Impacts/fibre (N*), energy/impact (I) or impacts/s (C) Meltzer F. (1994) expanded the SEL to account for bar angle, widht and groove width Extended edge length Probability of a fibre treatment Defined MEL (Modified Edge Load) Musselman R. et al. (1997) assumed that the fibres only are stapled onto and carried by the rotor bars Exclusion of the stator bar width from the SSL-theory Defined MSSL (Modified Specific Surface Load) Lönnberg B. & Lundin T. (1998) modelled the refining action using power P, rotational speed n, consistency c and pulp flow m Refiner load (intensity) as function of pulp flow (or production) 11

11 Energy expenditure Energy consumption in LC-refining: Frictional heat losses in Motor (electrical) and Bearings (frictional) Losses due to fibre suspension rheology Suspension flow (shear and turbulence) Energy dissipation in the suspension (LC-refining = an inefficient way of heating the suspension) Pressure losses Repeated fibre stress, (unknown) part of which result in Fibre modification 12

12 Theory Adapted bar clearance at a specific intensity: Direct indication (physical measure) of fibres at shear Is the fibre-conformation in V I dependent on Rotational speed, n Pulp consistency, c or Cutting length cl? 13

13 Theory Identified parameters related to the rheological behaviour of a fibrous suspension: Fibre concentration (flocculation and viscosity) Fibre morphology Fibre length (average and distribution) Fibre aspect ratio Fibre coarseness Fibre-to-fibre surface friction Fibre flexibility Degree of shear (fibre flocculation) 14

14 Theory Pulp transportation volume V T (in grey) Refining area x bar clearance = impact transfer volume V I Bar clearance determined physically by: Floc size Consistency Fibre length (aspect ratio) Network strength Refining intensity Bar width P/n torque Cutting length Cutting angle Shear rate Fibre mat V >> V T I 15

15 ProLab TM refiner Specifications : Pulp suspension volume V: : L Fibre concentration c: : 2-7% 2 Pulp temperature T: : C Pulp flow V: : L/min Feeding pressure p: : bar Rotational speed n: : r/min (5-35 m/s), pumping/non-pumping Refining energy SEC: : kh/t, kh/t per passage Refining intensity SEL: : J/m 8 fillings (3 cutting lengths; 7 soft- and 1 hardwood fillings) 16

16 Loadability trials Experimental Refiner power determined at Pulp consistencies 0, 1, 2, 3, 4, 5 and 6% Rotational speeds rpm Bar clearances (2 mm to minimum) at 600, 1500, 2250, 3000 and 4000 rpm (sequentially) increasing SEC ECF-bleached softwood reinforcement pulp (2.2 mm) Cutting lengths (30.8 and 52.0 m/rev) 17

17 52.0 m/rev, 6% Experimental Pulp Temperature [C]

18 Idling power P [k] 5000 V= L/min p in = bar gap>0.8 mm 6% 5% 4% 3% 2% 1% 0%(water) Loss n [rev/min] 19

19 Idling power m/rev V= L/min p in = bar Refiner Power [k] 6% 5% 4% 3% 2% 1% 0% Bar Clearance [mm] 20

20 Hydraulic volume LM-fillings (52.0 m/rev) V hydraulic [dl ] Impact Transfer Volume Hydraulic Volume V I V T Bar clearance [mm] 21

21 Idling power bar clearance 12 Power (k) y = 2E-10x 3-4E-07x x R 2 = 1 y = 2E-10x 3-5E-07x x R 2 = 1 y = 8E-11x 3-9E-09x x R 2 = 1 ater 6% ( mm) 6% ( mm) n (1/min) 22

22 Idling power SEC SEL 3.0 J/m SEC (kh/t) ater 6% ( mm) 6% ( mm) n (1/min) 23

23 Results ProLab 1500 rpm m/rev 30.8 m/rev Consistency [%] Refine r Power [k] Bar Clearance [mm] Bar Clearance [mm] 24

24 Results ProLab 3000 rpm 52.0 m/rev 30.8 m/rev Refine r Power [k] Consistency [%] Bar Clearance [mm] Bar Clearance [mm] 25

25 Results 26

26 Results 27

27 Results The minimum bar clearance required for refining energy transfer (P tot >P 0 ) Critical Bar Clearance C.B.C. [mm] Min (1%) Max (6%) Rotational Speed [1/min] 28

28 Results Number of fibres between bars ProLab 3000 rpm, 3 J/m Minimum fibre diameter (2xCT) # fibres Maximum fibre diameter (fibre width) Pulp consistency [%] 29

29 Conclusions Idling power Increased with consistency Depend on the active hydraulic volume Refiner loadability Increased with consistency (thicker fibre mat) Thinner fibre mat at higher n (more effective deflocculation) The critical bar clearance Increased with consistency (c>2% cons.) 5-20 fibres between rotor and stator bars depending on consistency (3000 rpm, 3 J/m) 30

30 Acknowledgements PAPSAT is acknowledged for financial support 31