DEM modelling of biomass packed bed combustion

Transkript

1 DEM modelling of biomass packed bed combustion Lehrstuhl and link für Energieanlagen with CFD und furnace Energieprozesstechnik models Dr.-Ing. Siegmar Wirtz 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013

2 Overview: Introduction The Diskrete Element Method Mechanical properties and behaviour Static Dynamic Heat transfer Conduction and radiation Convection Combustion Example of technical system: MSW incinerator 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 2

3 Introduction: Lehrstuhl für Energieanlagen und Energieprozesstechnik Combustion of solid biomass Some obvious statements: water content, calorific value and difficult mechanical properties intensive preparation is economically not feasible: burnt as delivered particles are large in comparison to conventional pulverized fuels particle shape is far from spherical, often unknown stoking of some kind (mechanical interaction) is required heating is strongly influenced by in particle heat conduction mechanical and thermochemical properties may vary from particle to particle -> simulation based on a discrete representation is required 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 3

4 The Discrete Element Method Lehrstuhl für Energieanlagen und Energieprozesstechnik solid particles multiple contacts (impacts) Beschreibung der Bewegung durch: v 2,ω ' ' 2 2 ' ' v,ω '' '' v,ω 2 2 '' '' v,ω 1 1 Newton (translational) 1 1 Euler (rotational) t F C δ n Fel n F diss t F st 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 4

5 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 5

6 move towards more realistic decriptions of the mechanical behaviour(dynamic/static) 1.) adhesion/cohesion model: -> use advanced force description 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 Outlook S. Wirtz 6

7 residence times and mixing on different grates backward acting grate, particle age 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 7

8 residence times and mixing on different grates backward PhD. Thesis, Björn Brosch, 2012 backward acting grate, mixing 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 8

9 residence times and mixing on different grates forward acting grate, mixing 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 9

10 this is a rather static situation dynamic angles of repose??? 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 10

11 drum diameter: D = 300 mm particle diameter: d = 5 mm filling : f = 20 % rotation: 3 rpm 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 11

12 32 drum diameter: D = 300 mm particle diameter: d = 5 mm 30 angle of repose [ ] d5_f20_versuch rotation [rpm] d5_f20_simulation d5_f10_versuch d5_f10_simulation st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 12

13 Is a more realistic particle geometry feasible??? clusters of spheres ellipsoidal objects, superquadrics, -> (smoothed) polyhedral definition 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 13

14 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 14

15 D. Höhner, S. Wirtz, V. Scherer: Experimental and numerical investigation on the influence of particle shape and shape approximation on hopper discharge using the discrete element method Powder Technology 235 (2013) st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 15

16 Silo Outflow of Wood Pellets 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 16

17 Forces in pellet transport with a screw feeder Hendrik Komossa 21st EU BC&E: IEA TASK 32 Copenhagen June 6th S. Wirtz 17

18 => dumping wood-chips from a tube: Florian Sudbrock 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 Introduction S. Wirtz 18

19 Heat transfer and transient heating 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 19

20 Heat transfer processes: Lehrstuhl für Energieanlagen und Energieprozesstechnik Conduction: 1. wall particle 2. particle particle 3. within the particles 4. wall gas particle 5. partikel gas particle 6. gas Radiation: 7. wall particle 8. partikel partikel 9. partikel gas 10.wall gas 11.gas Convection: 12.convection and mixing in gas 13.particle gas 14.wall gas 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 20

21 Total heat flux: Q P1 P 2 = R G R C T Inter-particle heat transfer: Conduction solid-solid (Hertz): 1 R C = 2 k S r C k S : conductivity particle r C = 3 1 γ2 F N r hm 2 E hm 1 3 Conduction particle-fluid-particle l G R G = A G k G k G : conductivity gas A G = 2 π r 2 2 P π r C l G = r P 2 1 π 4 r P r C + Radiation 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 21

22 Verification of the combined conduction/radiation model Comparison with measurements Yagi & Kunii (1957) Steady state situation: Q Ein = Q aus computing and comparing the effective heat transfer coefficient heating rod Q Ein spheres thermocouples Q out Q out insulation DEM-Simulation 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 22

23 Effective heat conduction, comparison to measurements Bastian Krause, LEAT 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 23

24 Convective cooling of cement clinker: Jens Wiese, LEAT 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 24

25 Bei Durchströmung der Schüttung: 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 25

26 well, then finally: combustion Doctorate Thesis, Björn Brosch, LEAT st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 26

27 Combustion of wood spheres Measurements by Forschungszentrum Karlsruhe in KLEAA device 1) ignition by radiation from the top primary air introduction from below constant downward reaction front velocity Electrically heated combustor Beechwood spheres Mass loss of beech spheres with diameters of 10 mm, 30 mm and 50 mm consideration of heat loss balance 1) Bleckwehl, S.: Doctorate Thesis, KIT / Univ.Stuttgart, 2010 primary air 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 27

28 Abbrand einer ruhenden Schüttung conversion rate: simulation vs. measurement Massenumsatzrate conversion [kg/(m2 [kg/(m² s)] s)] 0,04 0,03 0,02 0,01 0, Particle Partikeldurchmesser diameter [mm] [mm] Experiment Simulation 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 28

29 Coupling to a CFD code Lehrstuhl für Energieanlagen und Energieprozesstechnik CFD-model BC fom DEM to CFD (Gas) DEM-model 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 29

30 Basic Prof. Dr.-Ing. V. data, Scherer MSW incinerator, 57 MW th CFD-Model (Fluent, 3-dimensional, steady state solution(s)) Turbulence: k-ω SST Reaktion: Eddy Dissipation & Finite Rate Chemistry Radiation: P1 DEM-Model (3-dimensional, strip in the grate center, unsteady) Number of particles: ~8000 LHV: 10 MJ/kg Mass fraction wood: 15 % Mass fraction plastics: 15 % Mass fraction organic: 30 % Mass fraction inert: 20 % Mass fraction balance: 20 % 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 30

31 Conversion on the MSW grate Lehrstuhl für Energieanlagen und Energieprozesstechnik 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 31

32 Corresponding 3D simulation of the MSW furnace Secondary air Secondary air 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 32

33 Simulation eines Vorschubrosts 14 CO 2 above the grate 12 CO2-Anteil [Vol.-%] ,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 Relative Rostlänge [-] Messung Simulation 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 33

34 Simulation eines Vorschubrosts 30 H 2 O above the grate 25 H2O-Anteil [Vol.-%] ,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 Relative Rostlänge [-] Messung Simulation 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 34

35 Summary: Grate firing systems are strongly influenced by the interaction between the grate and the furnace atop. Correct representation of heat transfer mechanisms is required. DEM simulations allow the description of more and more mechanical details. DEM coupling with furnace codes is feasible. 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 35

36 The RUB-LEAT: Frederik Elskamp Jennifer Hold Dominik Höhner Bastian Krause Harald Kruggel-Emden Hendrik Komossa Tobias Oschmann Gerd Stein Florian Sudbrock Kevin Vollmari Jens Wiese Frank Wissing The financial support of DFG, AiF, Energie.NRW, Doosan Lentjes, is acknowledged 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 36

37 Thank you for your attention! 21st EU BC&E: IEA TASK 32 Copenhagen June 6th 2013 S. Wirtz 37