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  1. 1. 1Challenge the future COMPUTATIONAL MODELLING OF A MICRO-GASIFIER COOKSTOVE MSc thesis presentation Anoop Asranna I.P. Supervisors Dr. Paul van der Sluis, Philips Research Dr.Ir. Prof. Benediks Boersma, TU Delft
  2. 2. 2Challenge the future Contents • Biomass as a cooking fuel – consequences • Philips woodtsove – Operating principles , constructional features • Motivation and objective • Methodology, results and conclusion
  3. 3. 3Challenge the future Open fire cooking
  4. 4. 4Challenge the future 2.7 billion people rely on direct biomass burning for their cooking needs Cooking -90% of total household energy consumption The Cooking Conundrum 52% of total population in developing countries using biomass
  5. 5. 5Challenge the future Climate Health Land usage • 500g equivalent CO2 • 2% of total global emissions • 21% of black carbon emissions • 4.3 million annual deaths • Biggest killer more than HIV, TB and malaria combined • Women & children, most vulnerable • Leading cause of deforestation in developing countries The Impact
  6. 6. 6Challenge the future Solutions? • Elimination of Household Air Pollution needs transition away from solid fuels • Transition to LPG, electric stoves will reduce emissions • Significant share of population reliant on biomass until 2030
  7. 7. 7Challenge the future Philips Woodstove ‘For biomass cooking, only gasifier stoves (such as Philips) approach the emission levels of LPG and hold the potential to impact the deadliest HAP (household air pollution) linked illnesses’ (World Bank, 2013) • Biomass burning micro-gasifier cookstove. • Highest efficiency, lowest emissions among wood burning cookstoves.
  8. 8. 8Challenge the future MICRO-GASIFICATION
  9. 9. 9Challenge the future Primary air Secondary air Exhaust gases Producer gases Secondary combustion zone •Gas combustion •Flame •Pollutant formation Primary combustion zone •Fuel bed •Drying, pyrolysis •Sub-stoichiometric combustion Heat transfer zone •Convective heat transfer to the vessel Fuel bed Vessel
  10. 10. 10Challenge the future Constructional Features
  11. 11. 11Challenge the future Top view
  12. 12. 12Challenge the future Performance parameters Performance indicator Value Fuel use Thermal efficiency (high power)   38.4%-39.4% Emissions CO emissions (g/MJ delivered) 0.98-2.71 PM 2.5 emissions (mg/MJ delivered) 62.3-147.3 Indoor emissions CO emissions 0.08-0.21 g/min   PM 2.5 emissions 4.70 -9.09 mg/min Output Firepower   4 -5 kW
  13. 13. 13Challenge the future • Experimental design • Knowledge gaps –inadequate characterization of design parameters • Traditional workflow – physical prototypes, time consuming and expensive. • Local measurements of airflows, temperatures not possible Design Philosophy SIMULATIONS!
  14. 14. 14Challenge the future • Develop a CFD model that enables an investigation into the steady state flow and temperature fields in the secondary combustion zone of the Philips woodstove. • Flaming mode operation, vessel on top • Mixing analysis • Aid and inform experimental design –qualitative validation Objective
  15. 15. 15Challenge the future Computational domain
  16. 16. 16Challenge the future Computational domain
  17. 17. 17Challenge the future Insulation tile - dimensions
  18. 18. 18Challenge the future Boundary conditions Inlet-2 Inlet-1 Volumetric heat generation T=373 K Outlet Ambient Surface to ambient radiation Central axis
  19. 19. 19Challenge the future Inlet 1- Annular chamber inlet Property Value Pressure (P) 30 Pa Turbulence intensity 5% Characteristic length (L) 7 mm Turbulence length scale 4.9 *10-4 m
  20. 20. 20Challenge the future Inlet 2 – Fuel bed top • Sub- stoichiometric combustion of volatiles with primary air Value Mass of volatiles/kg of wood 0.889 kg Wood consumption rate 16.8 g/min Producer gases (per segment) 0.541 g/min Temperature (Varunkumar,2012) 1200K
  21. 21. 21Challenge the future Heat source • Fire power of the stove - 4.5 kW • Flaming mode -70%, 3.15 kW • Net power in the domain = power generation + enthalpy of producer gases • Source term = 2.35 kW • Specified – 900W
  22. 22. 22Challenge the future Grid independence study
  23. 23. 23Challenge the future
  24. 24. 24Challenge the future Discretization order A) P1 elements B) P2 elements • Significant jump in DOF • Flow field better resolved
  25. 25. 25Challenge the future Annular chamber +nozzles • The preheating in the annular chamber is of the order of 100K. The average temperature of air at the nozzle inlet is 440K • Mass flow divided equally among the three nozzles • Nozzles-flow transforms into a jet, rapid heating • At the nozzle exit- Reynolds number =1000, Temperature = 580K
  26. 26. 26Challenge the future • Air jets suppress the producer gas flow • Collision of jets at the center to set up a zone of recirculation Combustion chamber
  27. 27. 27Challenge the future
  28. 28. 28Challenge the future Hotspot K K Fuel bed Vessel Nozzle • Existence of hotspots • Consequence of uniform heat generation • Not a realistic approximation • Massflows Combustion chamber- Temperature
  29. 29. 29Challenge the future   Experimental values Simulation Region Top (K) Bottom (K) Top (K) Bottom(K) Insulation tile holder 625-675 575-625 750 592 Inner shield 500-550 425 700 580 Outer shield 475-495 398 610 450 Housing 375-400 323 450 300 • Hotspot • Inclusion of design details
  30. 30. 30Challenge the future Mixing analysis • Mixture fraction analysis using passive scalars • Prerequisites- temperature and reactant concentration • Secondary combustion zone temperature -700°C • Reactant concentration- Combustion equation • Analysis conducted for two heights of the fuel bed.
  31. 31. 31Challenge the future Mixing analysis
  32. 32. 32Challenge the future Component Y (%) X (%) CO 10.8 9.6 CO2 23.5 13.3 CH4 2.5 3.9 H 0.8 10.0 H2O 15.6 21.6 O 0.8 0.6 N2 46.0 41.0 Stoichiometric molar air fuel ratio - 0.809 Combustion equation
  33. 33. 33Challenge the future Fuel rich wake Fuel bed Fuel bed Vessel Vessel A B Case A- Fuel mass fractions
  34. 34. 34Challenge the future Fuel bed Vessel Recirculation zone Vessel Fuel bed A B Case B- Flow pattern
  36. 36. 36Challenge the future Conclusions, Recommendations • Good tool for flow visualization • Uniform heat generation – hotspots • Establishing the secondary airflow rate • Influence of nozzle angle, diameter etc. • Reactive flow modelling