Determination of Langmuir-Hinshelwood gasification kinetics from integral drop tube experiments Florian Keller, Felix Küster, Bernd Meyer 1
I. Motivation & Background II. Gasification experiments III. Description of gasification reactivity IV. Determination of gasification kinetics V. Summary & Outlook 2
I. Motivation & Background Project ibi Central German lignite Production Processing Extraction Montan wax LT-Conversion Olefins HT-Conversion Syngas 3
II. Gasification experiments Gasification equipment GMEQ Gasification Measurement Equipment Drop tube furnace reactor L heated = 1,75 m T max = 1300 C p max = 6 bar m char,max = 1.2 kg/h for CO 2 and steam gasification 4
II. Gasification experiments Gasification equipment M Fuel feeder (char) N 2 Char Preheater Preheater Reactant gases N 2 Steam CO 2 CO H 2 N 2 Ar Evaporator Electric heaters Reaction tube (AlO-ceramics) Shell space Gas analyzer GC N 2 Solids separator Reaction gases Filter Condenser Gas treatment equipment Container for solid residues 5
II. Gasification experiments Experiment overview Char preparation Central German Lignite Pyrolysis in rotary kiln at 600 C Crushed to particle size below 200 µm Gasification experiments 66 experiments Mixtures of steam, CO 2, CO, H 2 6 bar total pressure 900 to 1100 C p CO2 p H2O p CO p H2 V Gas X C [bar] [bar] [bar] [bar] [l(stp)/h] - min 0.00 0.00 0.27 0.26 246 6% max 3.74 3.91 1.77 1.61 543 71% 6
III. Description of gasification reactivity Reaction gas composition Reaction gas composition Reactant gas partial pressure Surface saturation (CO 2, steam) Inhibition (CO, H 2 ) Langmuir-Hinshelwood rate equation dx C dt = r LH RPM η LH rate expression without inhibition 1 r LH = k 11p CO2 1 + k 12 p CO2 + k 21p H2O 1 + k 22 p H2O LH expression of shared active sites 2 k 11 p CO2 + k 21 p H2O r LH = 1 + k 12 p CO2 + k 13 p CO + k 22 p H2O + k 23 p H2 LH expression of separated active sites 2 r LH = k 11 p CO2 1 + k 12 p CO2 + k 13 p CO + k 21 p H2O 1 + k 22 p H2O + k 23 p H2 1 N. M. Laurendeau, Progress in Energy and Combustion Science, 4(4):221 270, 1978. 2 S. Umemoto et al., Fuel, vol. 103, pp. 14 21, Nov. 2013. 7
III. Description of gasification reactivity Particle structure change Reaction gas composition Langmuir-Hinshelwood rate equation Particle structure change Initial increase of reactive surface area Random Pore model dx C dt = r LH RPM η Random Pore Model 3 RPM = 1 X C 1 Ψ ln 1 X C 3 S. K. Bhatia and D. D. Perlmutter, AIChE J., vol. 26, no. 3, pp. 379 386, 1980. 8
III. Description of gasification reactivity Pore diffusion Reaction gas composition Langmuir-Hinshelwood rate equation Particle structure change Random Pore model Pore diffusion Reaction rate limitation at higher temperatures Pore Effectiveness Factor dx C dt = r LH RPM η Pore Effectiveness Factor 4 η = 1 φ 1 tanh 3φ 1 3φ Thiele modulus 4 C r(c AsDe As φ = L P α r α dα 2 0 1 2 ϕ = L P m char,0 V Gas x c,char,0 R T 1 k 12 p CO2 1 k M c 2D 11 ea 1 + k 12 p CO2 + k 13 p CO k 12 p CO2 1 + k 13 p CO ln(1 + k 12 p CO2 + k 13 p CO 4 K. Bischoff, AIChE J., vol. 11, no. 2, pp. 351 355, 1965. 9
IV. Determination of gasification kinetics Advantages of drop tube furnace experiments Single particle behavior Problems for determination of kinetic expressions Linear regression not possible Changing gas composition CO 2 and steam gasification Impact of gas phase reaction on gas composition Fitting concept Modeling of gasification process Determination of deviation between model and experiments Minimization of deviation by adjustment of kinetic parameters 10
IV. Determination of gasification kinetics Considered reactions Heterogeneous water gas reaction C f + H 2 O CO + H 2 Boudouard reaction C f + CO 2 2 CO Homogeneous water gas reactions CO + H 2 O CO 2 + H 2 CO 2 + H 2 CO + H 2 O 11
IV. Determination of gasification kinetics Gasification process model Isothermal 1D plug flow gasification model 2 x dx C,i dt 4 x d n i dt 1 x dl dt Langmuir-Hinshelwood model Random pore model Effectiveness factor Heterogeneous gasification reactions Homogeneous gas phase reaction Gas velocity Particle sinking velocity (Stokes) (CO 2, H 2 O) (CO 2, CO, H 2 O, H 2 ) 2 x η i Thiele modulus approach (CO 2, H 2 O) Differential algebraic equation system with 9 equations and 14 kinetic constants Solved in MATLAB Initial condition: experimental conditions Termination criterion: length of reaction tube 12
Total gas volume flow [l(stp)/h] IV. Determination of gasification kinetics Example model course Reaction gas partial pressure [bar] CO 2 CO H 2 O H 2 Ar N 2 Initial gas flow [l (STP) /h] Temperature [ C] 2.10 1.12 1.15 0.34 0.33 0.96 507.4 1100 80% 800 Gas vol. fraction / carbon conversion X C 70% 60% 50% 40% 30% 20% 10% 700 600 500 400 300 200 100 X C x (CO2) x (CO) x (H2O) x (H2) Gas flow 0% 0.0 0.2 0.4 0.6 0.8 1.0 1.2 0 Reactor length [m] 13
IV. Determination of gasification kinetics Fitting procedure Design (14 constants) Validation of Effectiveness Factor Experimental results Gasification Model (MATLAB) for 66 experiments Average deviation (CO 2, CO, H 2 ) Optimization Algorithm (ModeFRONTIER) Optimized Design 14
IV. Determination of gasification kinetics Results Optimization results Kinetic expression: LH with inhibition > LH without inhibition > n-th order Concept of active carbon site competition has no significant effect Effectiveness factor does not improve fitting quality dx C dt = 1 X C 1 Ψ ln 1 X C k 11 p CO2 + k 21 p H2O 1 + k 12 p CO2 + k 13 p CO + k 22 p H2O + k 23 p H2 Relative mole flow deviation CO 2 H 2 CO C 16,6% 18,4% 7,5% 4,4% 15
Vol.-fraction CO IV. Determination of gasification kinetics Results 80% 70% Experiments Simulation 900 C 1000 C 1100 C 50% Experiments Simulation 900 C 1000 C 1100 C Carbon conversion X C 60% 50% 40% 30% 20% Vol.-fraction CO 2 40% 30% 20% 10% 10% 0% 0 10 20 30 40 50 60 70 Experiment number 0% 0 10 20 30 40 50 60 Experiment number 60% Experiments Simulation 900 C 1000 C 1100 C 70% Experiments Simulation 900 C 1000 C 1100 C 50% 60% Vol.-fraction H 2 40% 30% 20% 50% 40% 30% 20% 10% 10% 0% 0 10 20 30 40 50 60 Experiment number 0% 0 10 20 30 40 50 60 Experiment number 16
V. Summary & Outlook Example model course Summary Gasification experiments with lignite char in PDTF at 6 bar, up to 1100 C in atmosphere of steam, CO 2, H 2, CO Isothermal 1D plug flow gasification model Determination of kinetic parameters by model fitting Outlook Comparison of DTF kinetics to TGA derived kinetics Method application under more sever reaction conditions Integration of methanation reaction, film diffusion 17
Thank you for your attention! Acknowledgment: The ibi project was supported by the Federal Ministry of Education and Research (BMBF) (project ID: 03WKBZ06C) 18