Effect of Pressure and Heating Rates on Biomass Pyrolysis and Gasification Pradeep K. Agrawal School of Chemical and Biomolecular Engineering Georgia Institute of Technology June 15, 2012 Auburn University Workshop on Lignocellulosic Biofuels Using Thermochemical Conversion
Strategies for production of fuels from lignocellulosic biomass Cellulosic Biomass Gasification SynGas (CO + H 2 ) Fischer-Tropsch Methanol, Water-Gas Shift Alkanes, Methanol Liquid Fuels Hydrogen Hydrolysis Aqueous sugar Fermentation, Dehydration Aqueous-Phase Processing Ethanol Aromatic Hydrocarbons Liquid Alkanes or Hydrogen Lignin Lignin Upgrading Liquid Fuels Pyrolysis or Liq. Bio-oils Zeolite Upgrading Hydrodeoxygenation Liquid Fuels Characteristics of Gasification Huber et al., Catal. Today 2006, 111, 119. Pyrolysis and Char gasification proceed sequentially Pyrolysis pressure and temperature affect char reactivity Char reactivity depends on temperature, gas composition, porosity, ash contents, and transport effects Langmuir-Hinshelwood kinetic models suggested in the literature for biomass/char gasification High pressure gasification has particular significance Sutton et al., Fuel Processing Technology, 73 (2001) 155-73 Di Blasi,, Progress in Energy & Combustion Science 35 (2009) 121-140 Cetin, Gupta, and Moghtaderi, Fuel, 84 (2005) 1328-1334
Impact of Pressure on Gasification Carbon gasification rate slow step in conversion of biomass to syngas (CO + H 2 ) C + H 2 O CO + H 2 C + CO 2 2 CO Rate catalyzed by alkali metals Langmuir-Hinshelwood type kinetics CO and H 2 inhibit gasification Devolatilization impacts amount of carbon to be gasified and gas composition, including tar and hydrocarbon formation
Alkali Catalyzed Carbon Gasification * + CO 2 <-> *(CO 2 ) *(CO 2 ) <-> *(O) + CO * + H 2 O <-> *(O) + H 2 *(O) + C * + C(O) C(O) CO r C 1 k 1 ap p H CO 2 2 O k bp 2 H p 2 CO 2 cp r 1 r 1 CO P ap CO CO k' P H a' P k 2 2 H 2 O bp CO Need to Obtain Rate Data Including Impacts of All Relevant Species 4
Biomass Gasification Background Biomass gasification is a combination of two series processes pyrolysis (devolatilization) and char gasification. Char gasification activity is affected by the pyrolysis conditions (heating rate, temperature, and pressure), ash content and composition, and gasification conditions. The challenge is to develop experimental protocols that would allow collecting experimental data at conditions that most likely mimic the heating rate, temperature, pressure, residence time, and transport effects likely to be encountered in a commercial gasifier.
Goals/Objectives Quantitative understanding of the gasification and pyrolysis along with an improved understanding of the catalytic effect of inorganics present in biomass Role of particle morphology in mass transport effects as well as the char reactivity Identifying process conditions where synergistic effects of biomass-coal blending are observed. This will include effect of particle size, residence time and proximity of the two feed types Building mathematical models based on science and engineering principles that would predict the biomass gasification rate at a given pressure, temperature and feed composition. Quantify the effect of pressure and temperature on the formation of tars and light hydrocarbons.
Methods Experiments in two complementary reactors: Pressurized entrained-flow reactor (PEFR) at Georgia Tech Pressurized thermogravimetric apparatus (PTGA) at NREL Differences in heating rate, reaction time Mass/heat transfer limitations Three biomass types: Loblolly pine Switch grass Corn stover Innovation for Our Energy Future
PEFR Vs. PTGA REACTOR PEFR PTGA Pressure Up to 80 bar Up to 100 bar Temperature Up to 1500 C Up to 1200 C Mode Co-current flow Semi-Batch Sample size ~1 g/min 10-100 mg Heating Rate ~10,000 C/s ~10 C/min Residence time Up to 10 s Up to hours Kinetic Control >1000 C ~800 C Limit Gas analysis FTIR, GC MS, FTIR
Elemental Composition of Biomass Feed Element Loblolly Switchgrass Cornstover Pine C 52.4% 48.3% 43.7% H 6.3% 6.1% 5.9% N 0.07% 0.36% 0.59% O 40.9% 44.7% 45.3% Ash 0.3% 2.2% 6.1% Volatile Matter 79.1% 77.6% 74.4% Fixed Carbon 12.8% 12.4% 12.6%
Elemental Analysis of Feed Biomass (ICP) Element Loblolly Pine Switchgrass Cornstover Ca 490 1790 1900 Fe 38 20 437 K 358 4980 8675 Mg 203 1540 1325
Approach Investigate high temperature pyrolysis of biomass - effect of pressure and temperature on char morphology and reactivity towards gasification Gasification kinetics of chars generated from pyrolysis (individual chars, blend pyrolysis chars, and blending of chars generated individually) Catalytic effect of inorganics (ash) on char gasification Transport effects and mathematical models
Pressurized Entrained Flow Reactor
Pressurized Entrained Flow Reactor
Pressurized Thermobalance (PTGA) 1000 100 900 90 800 80 Temperature, C 700 600 500 400 300 70 60 50 40 30 Mass, % 200 20 100 10 0 0 0 50 100 150 200 250 300 350 Time, min Pine, 30 bar, 33% CO 2
Effect of Pressure and Heating Rate on Loss of Mass in PTGA Pyrolysis -dm/dt, mg/min 10 5 0-5 Loblolly Pine, 5C/min 0 200 400 600 800 Temperature, C 5 bar 30 bar -dm,dt, g/min 50 40 30 20 10 0-10 Loblolly Pine, 25C/min 0 200 400 600 800 Temperature, C 5 bar 30 bar
Effect of Pressure on Residual Char 30% Loblolly Pine, Final T 900C Char Yield 20% 10% 0% 0 10 20 30 40 Pressure, bar
FTIR vs. Mass Spectrometer in PTGA CO 2 MS (44) vs. FTIR (2319 cm -1 ) absorbance 0.3 0.25 0.2 0.15 0.1 0.05 0 8.E-10 6.E-10 4.E-10 2.E-10 0.E+00 0 50 100 150 200 time (mins) peak height 1.E-11 8.E-12 6.E-12 4.E-12 2.E-12 0.E+00 1 11 21 31 41 51 61 71 81 91
Effect of Pressure on Gas Species Evolution 4.0E-09 3.0E-09 2.0E-09 1.0E-09 0.0E+00 0 20 40 Pressure, bar H2 (2) CH4 (16) CO (28) CO2 (44) 3.0E-10 2.0E-10 1.0E-10 0.0E+00 0 20 40 Pressure, bar C2H5 (29) C2H6 (30) 2.0E-11 2.0E-10 C2H2 (26) 1.5E-11 1.0E-10 0.0E+00 0 10 20 30 40 Pressure, bar C2H3 (27) Benzene (78) 1.0E-11 5.0E-12 0.0E+00 0 20 40 Pressure, bar Acetic acid/ Formaldehyde (60)
Effect of Pressure on Gas Species Evolution Major Gas Species (5 bar) Major Gas Species (30 bar) 5.E-11 4.E-11 3.E-11 2.E-11 1.E-11 0.E+00-1.E-11 Pine, 10C/min CO 2 (44) H 2 (2) CH 4 (16) CO (28) 0 50 100 150 Time, min 7.E-11 6.E-11 5.E-11 4.E-11 3.E-11 2.E-11 1.E-11 0.E+00-1.E-11 CO 2 (44) CO (28) CH 4 (16) Pine, 10C/min H 2 (2) 0 50 100 150 Time, min Light Hydrocarbons (5 bar) Light Hydrocarbons (30 bar) 6.E-12 5.E-12 4.E-12 3.E-12 2.E-12 C 2 H 3 (27) C 2 H 3 (30) C 2 H 5 (29) C 2 H 2 (26) 6.E-12 5.E-12 4.E-12 3.E-12 2.E-12 C 2 H 5 (29) C 2 H 3 (30) C 2 H 3 (27) C 2 H 2 (26) 1.E-12 1.E-12 0.E+00-1.E-12 0 50 100 150 Time, min 0.E+00-1.E-12 0 50 100 150 Time, min
Effect of Pressure on Minor Gaseous Products 1.2E-12 1.0E-12 8.0E-13 6.0E-13 4.0E-13 Benzene, Oxygenated Species at 5 bar Furan (68) Benzene (78) Acetic acid/ Hydroxyacetaldehyde 2.5E-12 2.0E-12 1.5E-12 1.0E-12 Benzene, Oxygenated Species at 30 bar Benzene (78) Acetic acid/ Hydroxyacetaldehyde(60) Furan (68) 2.0E-13 5.0E-13-1.0E-15-2.0E-13 0 50 100 150 Time, min 0.0E+00-5.0E-13 0 50 100 150 200 Time, min Benzene, Methanol at 5 bar Benzene, Methanol at 30 bar 4.50E-12 3.50E-12 2.50E-12 1.50E-12 CH 3 O - (31) Benzene (78) 3.50E-12 2.50E-12 1.50E-12 5.00E-13 CH 3 O - (31) Benzene (78) 5.00E-13-5.00E-13 0 50 100 150 200-5.00E-13 0 50 100 150 200 Time, min Time, min
Morphology Studies Effect of Temperature at Constant pressure 600 C 800 C 1000 C Char generated in LEFR
Effect on Pressure at constant temperature 1 bar 5 bar 10 bar 600 C
Effect on Pressure at constant temperature 1 bar 5 bar 10 bar 800 C
Effect on Pressure at constant temperature 1 bar 5 bar 10 bar 1 bar 1000 C
Gas-Filled Pockets Formed at High Pressures Pine Char Formed at 15 bars and 1000 C
Gas Composition during Pyrolysis Species Gas Composition (mole%) at 5 bars 600 o C 800 o C 1000 o C CO 45.2 41.2 61.0 CO 2 16.7 16.9 12.1 H 2 8.9 24.5 21.9 CH 4 21.1 16.6 4.75 C 2 H 6 1.42 C 2 H 4 5.70 0.52 0.10 C 2 H 2 0.09 0.22 0.15 C 3 H 8 0.03 C 3 H 6 0.66 C 4 H 10 C 4 H 8 C 4 H 6 0.14
Gas Composition during Pyrolysis Species Gas Composition (mole%) at 15 bars 600 o C 800 o C 1000 o C CO 39.4 37.5 65.3 CO 2 17.7 17.7 5.9 H 2 17.4 29.0 26.0 CH 4 21.7 15.6 2.84 C 2 H 6 0.1 C 2 H 4 3.40 C 2 H 2 0.20 0.16 C 3 H 8 C 3 H 6 C 4 H 10 C 4 H 8 C 4 H 6 0.03
BET Surface Area of Switchgrass Chars generated in PEFR Reference: Switchgrass feed BET area 0.8 m 2 /gm 600 o C m 2 /gm 800 o C m 2 /gm 1000 o C m 2 /gm 1 bar 1.8 2.9 75 5 bars 3.0 187 321 10 bars 3.3 175 278 15 bars 5.2 108 198
Mass Transfer Limitations in Thermobalances Mass transfer: - from bulk gas to surface of sample holder - from surface of sample to bottom of sample -from surface of particle to center of particle Georgia Institute of Technology Innovation for Our Energy Future
Impact of Heating Rate Chars prepared in PEFR (high heating rate) and PTGA (low heating rate) gasi fied in PTGA A PEFR 600C 5 bar B PEFR 1000C 5 bar C PEFR 600C 15 bar D PTGA 900C 5 bar 100% 80% Mass 60% C D 40% 20% B A 0% 130 140 150 160 170 180 190 200 Time (min) Georgia Institute of Technology 900C, 5 bar, CO 2 Innovation for Our Energy Future
Testing for Mass Transfer Limitations 100% 80% 25 mg 51 mg 100% 80% 29 mg 54 mg Mass 60% 40% Mass 60% 40% 20% 20% 0% 0% 125 130 135 140 145 150 200 220 240 260 280 Time (min) Time (min) 1000 C 900 C 100% 80% 25 mg 48 mg 100% 80% 25 mg 50 mg Mass 60% 40% Mass 60% 40% 20% 20% 0% 110 130 150 170 190 210 Time (min) 850 C 0% 100 150 200 250 300 350 400 Time (min) 800 C Georgia Institute of Technology Innovation for Our Energy Future
Loblolly Pine Gasification in PEFR Residence Time Percent carbon remaining in the char Residue Pressure 5 bars Pressure 15 bars 3 sec 50.4 % 52.9 % 6 sec 40.0 % 10 sec 24.5 % 32.0 % Gasification Conditions: 10% CO 2, 2% H 2 O, 0.3% H 2, 1.72% CO, 86% N 2 900 o C particle size 180-250 µm Georgia Institute of Technology
Cornstover Gasification in PEFR Residence Time Percent carbon remaining in the char Residue Pressure 5 bars Pressure 15 bars 3 sec 21.5% 29.7% 6 sec 20.3% 24.0% 10 sec 13.2% 18.6% Gasification Conditions: 10% CO 2, 2% H 2 O, 0.3% H 2, 1.72% CO, 86% N 2 900 o C particle size 106-180 µm Georgia Institute of Technology
Conclusions Pyrolysis pressure and temperature greatly affect char yield and char morphology. High heating rates in PEFR produce char that mimick commercial gasifier operation. PEFR can provide useful kinetic information on biomass conversion, but it will have limitations due to the need to run integral operation. PTGA operation is similar to a semi-batch reactor, which makes it possible to build the kinetic model. Caution is needed to ensure that results are not masked by the transport effects. Both PTGA and PEFR have limitations if used alone. However, when combined together, the two are complementary and would provide a basis for building a reliable mathematical model. Georgia Institute of Technology
Future Work Characterization of Chars ICP EA, Nitrogen physisorption, SEM, NMR (?), FTIR, C,H,N,O Analysis carbon balance Effect of pyrolysis conditions on the formation of tars and light hydrocarbons- tar characterization Kinetics of char gasification (L-H models) Catalytic role of recycled ash and inorganic species in char gasification Mathematical modeling (transport effects)
Acknowledgements Kristiina Iisa (NREL) Carsten Sievers Scott Sinquefield Steve Lien Pranjal Kalita Gautami Newalkar Paige Case Taylor Donnell Kathryn Black U.S. Department of Energy (Golden, Co; Morgantown, WVa)