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Strömningsteknisk modellering och konstruktion av pelletsbrännare och kaminer. Henrik Wiinikka 1 , Stefan Westerlund 1 , Roger Hermansson 2 , Lars Westerlund 2 , Ida-Linn Nyström 2 och Marcus Öhman 2. 1 Energitekniskt centrum, 2 Luleå Tekniska Universitet (Energiteknik).
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Strömningsteknisk modellering och konstruktion av pelletsbrännare och kaminer Henrik Wiinikka1, Stefan Westerlund1, Roger Hermansson2, Lars Westerlund2 , Ida-Linn Nyström2 och Marcus Öhman2 1Energitekniskt centrum, 2Luleå Tekniska Universitet (Energiteknik) STEM programkonferens 2009-10-20
Målsättning • Demonstrera CFD (Computational Fluid Dynamics) som praktiskt verktyg för förbränningsoptimering av småskalig pelletsteknik (brännare och kaminer) • Demonstrera generella konstruktionslösningar för småskalig pelletsteknik som möjliggör minimal skötsel (enkel askutmatning) och estetiskt tilltalande flamma som fortfarande ger låga emissioner
Industripartner Piteå Kaminen SWEBO Bioenergy
Numerical and Experimental Investigation of Ash Transport during Wood Pellets Combustion Stefan Westerlund (ETC) and Ida-Linn Näzelius (LTU) 5
Background • Furnaces does not have automatic ash removal • Leads to disposal issues • Is it possible to design the internal fluid flow for automatic ash removal? • CFD is a tool to investigate this. • Combined with experiments for validation 6
CFD model, geometry Insulated wall 30° slice Burner cup Total length: 1695 mm 8
CFD model, boundary conditions T = 600°C Periodic interface Ash trap Tertiary inlets Secondary inlet Primary inlet 9
CFD model, mesh 30° slice # of Nodes: 1 132 643 # of Elements: 5 649 458 10
Simulation cases • Parametric study = 7 cases • In order to determine the controlling parameters for particle carryover • One-way coupled particles introduced at the grate 11
Simulation conditions • Simulations are performed with two different settings for the particle introduction: • Zero slip velocity; particles are given the initial velocity equal to the gaseous phase. • Fixed velocity particles are given higher initial velocity than the gaseous phase (5 m/s). 12
Global Reactions (Jones-Lindstedt) Mathematical Models Tar Modeling (Klason, Bai, 2007) 14
Mathematical Models • Combustion Model • EDCM (Magnusen and Hjerthager) • EDC coefficient A = 2.5 (default = 4) • Turbulence Model • k-epsilon • Radiation • P1 Thermal radiation model (Ansys) • Heat transfer • Thermal energy • Particles • Lagrangian particle transport, one-way coupled 15
General aerodynamics Streamlines Particle tracks Temperatures/Ignition 16
General aerodynamicsparticles Ash tray openings Grate 19
Results 20
Results 21
Results 22
Results Exp 23
Results Exp 24
Results Exp 25
Conclusions The simulation with no secondary air shows that no particles are trapped in the ash tray. Increased oxygen content in the flue gas result in improved performance of trapping particles in the ash tray. Particles trapped in the ash tray increases with increased power output. Simulation and experiments generally show the right trends 26