Abhijay Awasthi Candidate for Shell-NWO CS Phd 2012

Abhijay AwasthiDept. of Mechanical Engineering25 Nov. 2013

DNS of particle laden flows in biomass co-firing power plantsOutlineBackgroundMotivationSolid fuel particle - chemistrySingle particle modelsDNS of channel flowGoverning equations and boundary conditionsFuture work

Biomass co-firingwood chips, saw dust, corn husks, wheat chaff

Environment and EconomicsCO2SOxNOxFuel processing costs (energy basis) = Transportation + Grinding etc.Vegetation (Biomass)PeatLigniteBituminousAnthraciteIncreasing C/OIncreasing C/HIncreasing Heating valueBiomass vs. CoalAnalysisBiomassCoalMoisture7.310.8Ash2.65.68Volatiles76.230.7Fixed Carbon13.952.8C46.954.9H5.24.33O37.823.32N0.10.76S0.040.34HHV (kJ/kg)1814026535Biomass has significantly higher volatile content as compared to coal

Biomass has lower heating value then coal

Differences in particle sizes biomass particles are larger

Sole firing of biomass not preferred due to operational problems

CO-FIRING with coal

Challenges in co-firingNeed to

- Optimize combustion time in co-firing solids with different sizes and compositions Reduce emissions of the power plants Determine optimum O2/fuel ratio for different blends

Solid Fuel Particle Gasification and oxidationDevolatilizationDrying

A solid fuel particle is composed of several chemical functional groups

Ash is an inert component in particle, does not react

Chemistry and Reactions C + O2 (2-2 )CO + (2-1)CO2C + CO2 2COC + H2O CO + H2C + 2H2 CH4CO + H2O H2 + CO2 CO + 3H2 CH4 + H2OCiHiOiNiSiA CHONSA + Volatiles (CO+H2O+H2+CO2+CH4+H2S+N2+NH3+Tar) (Raw solid fuel) (Char)Heterogeneous Solid-gas & Homogeneous gas phase reactionsCOS + H2O H2S + CO2

Pyrolysis Volatile combustion CharHeterogeneous reactions6vyzxBiomass co-firing : DNS of Turbulent channel flowEulerian Lagrangian approach Gas phase Eulerian Particles - LagrangianGas phase governing equations for compressible flow are based on conservation of momentum, mass and energy.

Mass conservation equations for individual gas species are solved apart from the total gas phase mass conservation.

Future work Addition of char combustion and volatile combustion reactions in the DNS of a turbulent channel flowBiomass onlyCoal only- Co-firing

Challenging due to differences in time scales of pyrolysis and combustion reactions

Identifying suitable time integration methods and spatial discretization schemes Sensitivity runs to determine the effects of parameters like particle size, volume fraction and particle composition

Particle-Particle interaction Particle of different size, composition (ash, volatiles and moisture) significant variations in particle surface temperatures Radiative heat transfer between particles to be includedQ&A

Thank you !

Numerical MethodTime integration : Low storage second order Runge-Kutta method

For j=1,2,3,4 where u(0) is a variable at time t and u(4) the variable at time t+dtSpatial discretization: Finite volume methodCentral differencingvyzxWall temperature constantNo-slip at the wallPeriodic boundary condition in streamwise(x) and spanwise (z) directionsBoundary conditions1283 control volumesUniform grid spacing in streamwise and spanwise directionsGrid points clustered near the walls in order to resolve boundary layersWork of Russo et al. Biomass pyrolysis in DNS of turbulent channel flow