Relationships Between Coal Relationships Between Coal Chemistry and Decomposition Chemistry and Decomposition ProductsProductsThomas H. FletcherChemical Engineering DepartmentBrigham Young UniversityGCEP MeetingMarch 15, 2005Provo, UTOutline• What is coal?• Simple descriptions of coal reaction• Coal chemistry• Lattice models• Secondary reactions• Light gas• Nitrogen evolutionCoal DecompositionCoalVolatilesheatCharTarLight gasSootPrimary Devolatilization Secondary DevolatilizationDefinition: Tar = Volatiles that condense at room T and P0.100.080.060.040.020.00H/CRatio0.50.40.30.20.10.0O/C Ratio1507lignite1445subbitum.1451hvabitum.1508lvbitum.1493hvbbitum.CoalificationGraphitelignitesubbituminousbituminouslv bituminousanthraciteModerate Temperature Pyrolysis0.100.080.060.040.020.00H/C Ratio0.50.40.30.20.10.0O/C Ratio1507 lignite1445 subbitum.1451 hva bitum.1508 lv bitum.1493 hvb bitum.Early Char Combustion 0.100.080.060.040.020.00H/C Ratio0.50.40.30.20.10.0O/C Ratio CCL, 0% post-flame O2, 47 ms CCL, 6% post-flame O2, 47 ms CCL, 6% post-flame O2, 72 ms1507 lignite1445 subbitum.1451 hva bitum.1508 lv bitum.1493 hvb bitum.Coal StructurePyrrolic NitrogenPyridinic NitrogenBridge StructuresSide ChainLoop StructureAromatic ClusterMobile Phase GroupBi-aryl BridgeHCH2HO CH2NRCROHSH2OHCH2H2 OHH2OHCH2OOCH3COHORCH2NHHHHHHH2H2H2OH2OCH3CHH2OHH2CHHHHPrimary Coal PyrolysisHNROHCCH3H2H2H2RCH3HOCHHCH3SOCCH3OH2 OHH2H2H2NCH3HHTarRCO2H2OH2OCO2CH3TarLattice Devolatilization Models• Coal molecule description–13C NMR spectroscopy• Rates of bridge breaking– Aromatic clusters remain intact– Kinetics are coal independent• Lattice statistics– Amount of liberated fragments• Vapor-liquid equilibrium– Light fragments vaporize• Crosslinking– Stable bridges form, making charTypes of LatticesHONEYCOM B LATTICE TRIGONAL BETHE LATTICEDI AMOND L ATTICETETRAGONAL BETHE LATTICEA. Coordination number = 3B. Coordination number = 4Lattice Statistics•45% bridges broken,•~10% fragments liberated•Fragments include monomers,dimers, trimers, etc.•20% bridges broken,•0.3% fragments liberatedClosed-Form Solution of Percolation Lattice Statistics1.00.80.60.40.20.0Fraction of Finite Clusters1.00.80.60.40.20.0Fraction of Intact Bridges (p)4126σ + 1 = 3Vapor-Liquid Equilibrium and CrosslinkingFinite Fragments (Metaplast) Infinite Coal Matrix Tar Vapor Reattached Metaplast Crosslinking Vapor-Liquid Equilibrium Labile Bridge Scission MWfMWfMWfGeneralized Hydrocarbon Vapor Pressure Correlation for the CPD Model0.010.1110100VaporPressure(atm)3.02.52.01.51000/Temperature (K-1)110MW = 315 285258218237212188158140127116(500 K)(667 K) (400 K) (333 K)()TMWccPcivapi/exp321−=Data taken from Gray et al. (Ind. Eng. Chem. Process Des. Dev., 1985) for12 narrow boiling point fractions of coal liquids from a Pittsburgh seam coalInput Parameters Required by the CPD Model• Number of attachments per cluster (σ+1) (i.e., coordination number)• Fraction of attachments that are bridges (p0) (bridges/bridges+side chains)• Molecular weight per aromatic cluster (Mcl)• Molecular weight per side chain (Mδ)Measured with 13C NMR Spectoscopy• Fraction of bridges that are stable (c0)Not measuredDo Structure Parameters Correlate?6.56.05.55.04.54.03.5Coordination Number ( σ+1)10090807060%C in daf coal1.00.90.80.70.60.50.40.3Fraction of Intact Bridges (P0)10090807060%C in daf coal7006005004003002001000Molecular Weight per Cluster10090807060%C in daf coal806040200MW per Side Chain (Mδ)10090807060%C in daf coalLattice Model CapabilitiesCan Predict:• Tar yield– MW distribution• Light gas yield– Speciation• Char yield– Elemental compositionAs a Function of:• Coal type– Coal structure• Residence time– Kinetic rates• Particle heating rate– Distributed activation energies– Competing reactions•Temperature– Kinetic rates• Pressure– Vapor-liquid equilibriumUsing Correlations for Coal Structure Parameters6050403020100% Yield (daf)95908580757065% Carbon (daf)limit of data used to make correlations CPD mass release measured mass release CPD tar yield measured tar yield 17 non - U.S. coals, 3000 K/s to 1037 K, (Xu & Tomita) No 13C NMR data available, from Genetti et al., E&F 1999Light Gas Speciation is EmpiricalFrom Solomon et al., E&F, 1988.All E’s are distributed!19 species, needing yield factors and rate coefficients!Sample Predictions of Gas Species1.00.80.60.40.20.0Light Gas Composition95908580757065Percent Carbon in Parent Coal (daf)WaterCarbon dioxideMethaneCarbon monoxideOther gases0.950.900.850.800.750.700.650.600.55H/C Molar Ratio0.280.240.200.160.120.080.040.00O/C Molar Ratio121068397541211 Coals Studied by Solomon et al. Coals Studied by ChenInterpolation matrix for gas species(based on coalification diagram)Application to Xu and Tomita data(non-U.S. coals)From Genetti et al., E&F (1999)Nitrogen Release• All nitrogen in coal is contained in the aromatic structure– Pyridinic, pyrrolic, and quartenary¾ Nitrogen release highly dependent on tar releaseArgonne Premium Coals, XPS data from Kelemen et al. (1993), XANES data from Mitra-Kirtley et al. (1993)100806040200% of Nitrogen in Parent Coal959085807570% Carbon (daf) in Parent CoalPyrrolicPyridinicOther Forms XPS XANESTar Does Not Contain All PyrolyzedNitrogen, Especially for Low Rank CoalsPulverized coal particles in a radiant drop tube reactor (Chen, Stanford University, 1991)0.60.50.40.30.20.10.0Coal-N fraction in tar/oils0.60.50.40.30.20.10.0Coal-N fraction released Dietz subbituminous Illinois No. 6 hv bituminous Pittsburgh #8 hv bituminous Lower Kittanig lv bituminousNitrogen Release Models• Initial N release w/tar• Subsequent N release from char as HCN at higher T• Secondary tar reactions– Soot formation from tar– Light gas formation (HCN and then NH3)• Additional N release at extremely high T’s– 100% nitrogen release possible! stablechar Ncoal N+light gas Nsoot Nlight gas NT<1000 K T<1600 Ktar NT>1600 K (long residence times)tar Nlight gas N++char N+C (slow)B (fast)AFrom S. Perry, PhD Dissertation, BYU, 1999Sample Nitrogen Release Predictions50403020100Mass Release (% of daf coal)200015001000500Temperature (K)1.00.80.60.40.20.0 Fraction N Retained in CharPohl BYU Mass Release N remaining in charE4=75 kcal/mol, σE4=3 kcal/molCPD modelA. Flat-flame burner (high T and dT/dt) • matches volatiles yield and• nitrogen release)B. High temperature crucible data• volatiles reaches