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Detailed Chemical Kinetic Modelling of Pollutant Conversion in Flue Gases from Oxycoal y Plant R.K. Robinson and R.P. Lindstedt Thermofluids Section, Department of Mechanical Engineering, Imperial p College g London,, Exhibition Road,, London SW7 2AZ Outline Motivation Model Development Calculation of Thermodynamic Data Results, Sensitivities and Product Distributions Conclusions Future Work and Acknowledgements Motivation Carbon Capture and Storage (CCS) aims to capture CO2 emissions from large scale energy generators. Strongly corrosive impurities such as oxides off nitrogen it and d sulphur l h need d tto b be separated t d ffrom other th exhaust h t gases. Experimental methodologies to remove these impurities have been developed[1,2]. However the chemistry behind these processes is poorly understood. The current work outlines computational methods that attempt to model the relevant conversion processes and the distribution of subsequent products in flue gases. 1. White V. and Allam R.J., Purification of Oxyfuel-Derived CO2 for Sequestration or EOR, Proceeding of the 8th International Conference on Greenhouse Gas Control Technologies, Trondheim, Norway, (2006). 2. Allam R.J., White V. and Miller J., Purification of Carbon Dioxide, US Patent 7,416,716. Background The sulphur p chemistry y is based on detailed high g temperature p chemical kinetics obtained from the following studies: F.G. Cerru, A. Kronenburg and R.P. Lindstedt “A systematically reduced mechanism for sulphur oxidation” oxidation Proc. Proc Combust Combust. Inst Inst. 30 (2005) 1227-1235 1227 1235. F.G. Cerru, A. Kronenburg and R.P. Lindstedt “Systematically reduced chemical mechanisms for sulphur oxidation and pyrolysis” Combust. Flame 146 (2006) 437-455. The nitrogen chemistry is based on the following studies: Lindstedt, R.P., Lockwood, F.C. and Selim, M. A., “Detailed Kinetic Modelling of Chemistry and Temperature Effects on Ammonia Oxidation” Combust. Sci. and Technol., 99 (1994), 253-276. Lindstedt, R.P., Lockwood, F.C. and Selim, M.A., 'Detailed Kinetic Study of Ammonia Oxidation', Combust. Sci. Technol., 108, (1995) 231-254. In both cases subsequent updates have been performed and validated in combustion applications. Background Work has taken p place in 3 key y areas: Current kinetic models of combustion involving both sulphur and nitrogen species have been extended to low temperature ranges via th addition the dditi off key k species i and d reactions. ti An aqueous phase mechanism has been developed to model reactions occurring in solution solution. A mass transfer coefficient has been estimated to allow movement of species between the gaseous and aqueous phases. Accurate quantum mechanical methods have been used to update thermodynamic data for species involved in the model and to calculate new data for aqueous species by taking into account the enthalpy of dissolution. Model Development The original Sulphur mechanism featured 12 sulphur containing species and 70 reversible reactions. The nitrogen mechanism featured 21 species and 95 reversible chemical reactions. The above mechanisms are here combined with hydrocarbon chemistry for C1-C2 species that permit the additional interactions with burnt gas products such as CO, CO2 and H2O as well as any remaining hydrocarbon fragments. 16 additional reactions for nitrogen and sulphur gas phase chemistry. 10 mass transfer rates added to allow movement of species between gaseous and aqueous phases. 8 aqueous phase h reaction ti used d tto create t a basic b i aqueous phase h mechanism. Model Development Additions to reaction Mechanism rates taken from NIST Chemical Kinetics Database or CAPRAM Aqueous Mechanism for Troposheric chemistry or extrapolated there from. Gaseous Phase Additions with rates shown in modified Arrhenius form PRODUCTS NH3 NO2 NO2 O2 N3 N3 O2 NO2 NO2 NO2 NO N2O3 N2O5 NO2 H2O SO3 + + + + + + + + + + + + + + + + REACTANTS NO2 N3 N3 N3 O N3 NO O O NO3 NO2 H2O H2O NO2 NO H2O + M + NO2 = = = = = = = = = = = = = = = = HNO2 N2O N2 N2O N2 N2 NO3 NO3 NO3 N2O5 N2O3 HNO2 HNO3 N2O4 HNO2 H2SO4 + + + + + + A NH2 N2O NO NO NO N2 + M + HNO2 + HNO3 + HNO2 ; ; + NO ; ; ; + N2 ; ; ; ; ; ; ; ; ; ; ; n 2.4510E-03 3.410E+00 1.2040E+08 0.000E+00 3 3.6130E+08 6130E+08 0 0.000E+00 000E+00 3.6130E+01 0.000E+00 6.7450E+09 0.000E+00 9.0330E+08 0.000E+00 3.4030E-16 -1.750E+00 4 4.0990E-07 0990E 07 -1.500E+00 1 500E+00 3.5240E+09 0.240E+00 3.7300E+07 0.600E+00 1.6050E+06 0.000E+00 1.2900E+07 0.000E+00 5 5.1000E-05 1000E 05 0.000E+00 0 000E 00 6.0220E+05 0.000E+00 5.1530E-10 0.000E+00 7.2270E+05 0.000E+00 Ea 1.250E+05; 0.000E+00; 0 0.000E+00; 000E+00; 0.000E+00; 0.000E+00; 0.000E+00; 0.000E+00; 0 0.000E+00; 000E+00 0.000E+00; 0.000E+00; 0.000E+00; 3.717E+04; 0 0.000E+00; 000E 00 0.000E+00; 0.000E+00; 0.000E+00; Model Development Mass Transfer Rates between Gaseous and Aqueous Phase taken to be 0.01 kmol m-3 s-1 after sensitivity analysis performed. Basics Aqueous Phase Mechanism with rates shown in modified Arrhenius form PRODUCTS REACTANTS SO2 = SO2(A) ; NO2 = NO2(A ; NO = NO(A) ; HNO3 = HNO3(A) ; HNO2 = HNO2(A) ; NO3 = NO3(A) ; N2O5 = N2O5(A) ; N2O3 = N2O3(A) ; N2O4 = N2O4(A) ; H2SO4 = H2SO4(A) ; SO2(A) + H2O(L) = H2SO3(A) ; NO2(A + NO2(A + H2O(L) = HNO2(A) + HNO3(A) ; HNO2(A) + HNO2(A) + HNO2(A) = HNO3(A) + NO(A) + NO(A) + H2O(L); N2O5(A) + H2O(L) = HNO3(A) + HNO3(A) ; N2O4(A) + H2O(L) = HNO2(A) + HNO3(A) ; HNO2(A) + OH(A) = NO2(A + H2O(L) ; NO(A) + NO2(A + H2O(L) = HNO2(A) + HNO2(A) ; NO2(A + NO2(A + NO2(A +H2O(L)= HNO3(A) + HNO3(A) + NO(A) ; A 0.010E+00 0.010E+00 0.010E+00 0.010E+00 0.010E+00 0.010E+00 0.010E+00 0.010E+00 0.010E+00 0.010E+00 0 010E+00 6.270E+04 1.000E+08 6.000E+00 5.100E-05 5.100E-05 5.100E 05 1.000E+09 1.000E+08 1.000E+08 n 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0 000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 Ea 0.000E+00; 0.000E+00; 0.000E+00; 0.000E+00; 0.000E+00; 0.000E+00; 0.000E+00; 0.000E+00; 0.000E+00; 0.000E+00; 0 000E+00 0.000E+00; 0.000E+00; 0.000E+00; 0.000E+00; 0.000E+00; 0.000E+00; 0.000E+00; 0.000E+00; Calculation Method for Thermodynamic data Molecular Mechanics Mi i i ti and Minimisation d Conformational Analysis used to locate starting structure Program locTorsion ran to locate all internal rotations and create input files Program polyScript ran to harvest data from G3B3 and scanCalc log files, files calculate Enthalpies of Formation and Moments of Inertia, and produce input for next stage High Accuracy Q Quantum t Mechanics G3B3/G3MPB3 Energy Calculation DFT Quantum Mechanics used to scan and analyse Internal Rotations Statistical Mechanics Package PAC 99 used to calculate thermodynamic values from 200K to 6000K Atomization Energies, E th l i and Enthalpies d Vibration Frequencies produced in G3B3 log file Program scanCalc ran to harvest internal rotation data fit data, V = ½ ∑Vn(1 – cos(nθ)) and calculate IR symmetry numbers and Moments of Interia 7 Term JANAF Polynomials produced by regression of calculated data Examples of NOx Thermodynamic Data Thermodynamic data calculated for species where data were not available or required updating and fitted to 7 term JANAF polynomials. For aqueous species enthalpy of dissolution were taken into account by modifying the enthalpy of formation at 298K. NO2(Aq)Calculated Data N2O3 Calculated Data ∆fH298 22.6 kJ/mol ∆fH298 81.7 kJ/mol S298 239.9 J/mol/K S298 317.0 J/mol/K Cp298 36 9 kJ/mol 36.9 Cp298 69 2 kJ/mol 69.2 HNO2(A) 200K-6000K REF : R.ROBINSON 03-Dec-08 5.83337654E+00 3.92942470E-03 -1.49885436E-06 2.43940583E-10 -1.45404150E-14 -1.64746315E+04 -3.02996870E+00 4.73508766E+00 6.07796919E-03 -2.03586709E-06 -9.22492080E-10 6.38649372E-13 -1.61106404E+04 2.90221746E+00 N2O3 200K-6000K REF : G3B3 R.ROBINSON 16-Dec-08 8.75695849E+00 3.70515651E-03 -1.41680841E-06 2.34798620E-10 -1.42777213E-14 6.73047701E+03 -1.35522821E+01 4.90534181E+00 1.63782898E-02 -2.10621083E-05 1.70161360E-08 -5.97183185E-12 7.79013682E+03 6.09886939E+00 Examples of NOx + SOx Thermodynamic Data HNO2 Calculated Data HNO2(Aq) Calculated Data ∆fH298 -76.7 kJ/mol ∆fH298 -120.1 kJ/mol S298 249 3 J/mol/K 249.3 J/ l/K S298 249 3 J/mol/K 249.3 J/ l/K Cp298 45.4 kJ/mol Cp298 45.4 kJ/mol SO2 Calculated Data SO2(Aq)Calculated Data ∆fH298 -296.8 296 8 kJ/mol kJ/ l ∆fH298 -323.8 323 8 kJ/mol kJ/ l S298 248.2 J/mol/K S298 248.2 J/mol/K Cp298 39.9 kJ/mol Cp298 39.9 kJ/mol Results : Experiment 1 - Conversion Evolution Conditions : Pressure - 2.7 2 7 Atmospheres Species ppm % SO2 9 81E+02 9.81E+02 0 10% 0.10% 09 0.9 NO 3.22E+02 0.03% 0.8 NO2 3.58E+01 0.00% 0.7 O2 5.50E+04 5.50% 0.6 CO 2.00E+02 0.02% CO2 8.34E+05 82.35% NH3 1.00E+04 1.00% N2 9.00E+04 9.00% 0.2 H2O 1.00E+04 1.00% 0.1 H2O Liquid 1.00E+04 1.00% Temperature - 300 K % Conversion 1 0.5 0.4 0.3 SO2 NOx Experimental SO2 Experimental NOx 0 0 50 100 Time (s) 150 200 250 % Conve ersion Results : Experiment 1 – Mass Transfer Sensitivity 1 0.9 0.8 0.7 0.6 0.5 04 0.4 0.3 0.2 0.1 0 SO2 Mass Transfer x5 SO2 Mass Transfer 0.01 kmol3 m3 s-1 SO2 Mass Transfer x 0.2 % Conversion 0 50 100 Time (s) 150 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0 3 0.2 0.1 0 200 250 NOx Mass Transfer x5 NOx Mass Transfer 0.01 kmol3 m3 s-1 NOx Mass Transfer x 0.2 0 50 100 Time (s) 150 200 250 Results : Experiment 1 – NOx Ratio Evolution The Ratio of NO to NO2 is known to change from approximately 9:1 to 3:1 after the compressor/receiver the current model reproduces this affect. 1 0.9 0.8 % Conversion 0.7 0.6 NO NO2 Experimental NO Experimental NO2 0.5 0.4 0.3 0.2 0.1 0 0 50 100 Time (s) 150 200 250 Results : Experiment 1 – NOx Ratio Sensitivity NO2 is more readily absorbed into the aqueous phase due its larger negative enthalpy of dissolution, therefore the ratio of NO to NO2 influences conversion time for NOx. 1 09 0.9 0.8 % Conversion 0.7 0.6 0.5 0.4 0 0.3 0.2 90%-NO 10%-NO2 0.1 75% NO 25%-NO2 75%-NO 25% NO2 50%-NO 50%-NO2 0 0 50 100 Time (s) 150 200 250 Results : Experiment 1 – Pressure Sensitivity NOx conversion also pressure dependent as higher pressures lead to greater conversion from NO to NO2 in the gaseous phase. 1 0.9 0.8 % Conversion n 0.7 0.6 0.5 0.4 0.3 SO2 All Pressures NOx 1 Bar NO 3 B NOx Bar NOx 7 bar 0.2 0.1 0 0 50 100 Time (s) 150 200 250 Results : Experiment 2 - Conversion Evolution Conditions : Pressure - 5 Atmospheres p Species ppm % SO2 7.61E+02 0.08% NO 2.99E+02 0.03% NO2 3.32E+01 0.00% O2 5 50E+04 5.50E+04 5 50% 5.50% CO 2.00E+02 0.02% CO2 8.34E+05 83.37% NH3 0.00E+00 0.00% N2 9.00E+04 9.00% 0.2 H2O 9.98E+03 1.00% 01 0.1 H2O Liquid 9.98E+03 1.00% 0 Temperature p - 300 K 1 09 0.9 0.8 % Conversion 0.7 0.6 0.5 0.4 0.3 SO2 Nox Experimental SO2 Experimental NOx 0 100 200 300 Time (s) 400 500 Results : Experiment 2 – NOx Ratio Evolution The Ratio of NO to NO2 is known to change from approximately 9:1 to 3:1 after the compressor/receiver ,the current model reproduces this affect. 1 09 0.9 0.8 % Conversion 0.7 0.6 NO NO2 Experimental NO Experimental NO2 0.5 04 0.4 0.3 0.2 0.1 0 0 50 100 150 200 250 Time (s) 300 350 400 450 Results : Experiment 2 – Product Distribution 800 NO NO2 SO2 700 600 NO(A) NO2(A) SO2(A) 500 400 ppm 500 ppm 600 300 400 300 200 200 100 100 0 0 0 100 200 300 0 400 100 300 0.1 200 180 160 140 120 100 80 60 40 20 0 01 0.1 HNO2(A) HNO3(A) H2SO3(A) H2SO4(A) 0 100 200 Time (s) 300 400 400 N2O4 N2O4(A) N2O3 N2O3(A) 0.1 ppm ppm 200 Time (s) Time (s) 0.0 0.0 0.0 0.0 0.0 0 100 200 Time (s) 300 400 Conclusions The current work shows that detailed models based on chemical kinetics can be of significant help in interpreting experimental data. The approach of not heuristically fitting individual rate constants allows the separation of validation and simulation. Key sensitivities are also identified as part of the modelling process. SO2 and NOx conversion predominately occurs in the aqueous phase. NOx conversion residence times are highly dependent on the initial ratio of NO/NO2 and the pressure of system while the SO2 conversion is less pressure dependent. Anyy model needs to simulate both g gaseous and aqueous phases and the differing conditions of both the compressor and the receiver. Future Work and Acknowledgements Mass transfer rates need to be considered in more detail, and are likely to vary throughout the apparatus. Rates may be estimated from interfacial areas. Currently ionic species are modelled as molecules. molecules A detailed aqueous phase mechanism would include ionic species and the pH of the system. Expansion of the aqueous phase mechanism in line with current findings. We would like to thank Air Products and Doosan Babcock for their support. Also Dr. L.Torrente-Murciano and Prof. D.Chadwick, Imperial College, for the experimental data. Results : Experiment 3 - Conversion Evolution Conditions : Pressure - 5 Atmosphere Temperature - 300 K 1 ppm % SO2 6.22E+02 0.06% 09 0.9 NO 1.70E+01 0.00% 0.8 NO2 1.89E+00 0.00% 0.7 O2 5.50E+04 5.50% CO 2.00E+02 0.02% CO2 8 34E+05 8.34E+05 83 42% 83.42% NH3 0.00E+00 0.00% N2 9.00E+04 9.00% H2O 9.98E+03 1.00% H2O Liquid % Conversion Species 0.6 0.5 0.4 0.3 0.2 SO2 01 0.1 NOx 0 9.98E+03 1.00% 0 50 100 150 200 250 Time (s) 300 350 400 450 Results : Experiment 3 – Product Distribution 700 NO 600 NO2 SO2 500 ppm ppm 400 300 200 100 0 0 100 200 Time (s) 300 NO(A) NO2(A) ( ) SO2(A) 0 400 180 0.0 160 0.0 140 100 200 Time (s) 300 ppm 100 80 60 HNO2(A) HNO3(A) H2SO3(A) H2SO4(A) 40 20 0 400 N2O4 N2O4(A) N2O3 N2O3(A) 0.0 0 0 120 ppm 500 450 400 350 300 250 200 150 100 50 0 0.0 0.0 0.0 0.0 0.0 0 100 200 Time (s) 300 400 0 100 200 Time (s) 300 400