Energy Densification via Hydrothermal Pretreatment (HTP) of Cellulosic Biomass

Transcription

1 Energy Densification via Hydrothermal Pretreatment (HTP) of Cellulosic Biomass S. Kent Hoekman, Amber Broch, Curt Robbins DRI Chuck Coronella, Wei Yan Univ. of Nevada, Reno Larry Felix Gas Technology Institute TCS 2010 Conference September 22-23, 2010 Iowa State University Ames, IA 1

2 Background and Introduction Lignocellulosic biomass is a promising feedstock for production of heat, chemicals, fuels, and electrical power Diverse biomass sources: Woods, agricultural wastes, grasses, and other Large diversity of biomass sizes, shapes, compositions, and other parameters creates difficulties in: Handling, transporting, and storing different materials Feeding different materials into a single thermal conversion unit 2

3 Purposes of Biomass Pre-Treatment Three main objectives: 1. Homogenize feedstocks Reduce handling difficulties Convert multiple materials into a single feedstock 2. Increase energy density Reduce oxygen content of raw biomass Higher energy density reduces transportation costs 3. Improve storage stability and logistics Address seasonality of some feedstocks Overall Goal: Convert biomass into biochar that resembles low grade coal 3

4 Biomass Pre-Treatment Processes Many different pre-treatment processes have been developed. Two are of interest here: 1. Torrefaction Mild form of pyrolysis Dry conditions, low O 2 levels HTP Process Gas 2. Hydrothermal Pretreatment (HTP) Also known as wet torrefaction and hydrothermal carbonization (HTC) Treatment in hot, pressurized water Produces gases, liquids, and biochar Solid Biomass H 2 O Pressure Vessel 260º Condensed Liquid Recovered Solid (Bio-char) to Gasifier or Pyrolyzer for Energy/ Fuels 4

5 HTP Laboratory Process 2-Liter Stirred Parr Pressure Vessel Process variables: Temperature: o C Hold time at temp.: 0-60 min. Water/Biomass ratio: 4 8 Feedstock size: ¼ - ½ inch 5

6 Temperature (C) Pressure (PSIG) Temperature and Pressure Profile HTP Treatment of Tahoe Chips at 235º C for 30 minutes Time (min) Wall Temp. Internal Temp. Temp. Set pt. Saturated Steam Curve Pressure 6

7 HTP Feedstocks and Products Woody Feedstock used: Tahoe Mix Typical thinnings from Tahoe Forest Roughly 2/3 Jeffery Pine; 1/3 White Fir Other feedstocks also being investigated Loblolly Pine before and after HTP Process Reaction Products Gas phase: mostly CO 2 Traces of CO, CH 4, others Aqueous-phase: Degradation of hemi-cellulose Sugars, furans, organic acids Biochar: Cellulose and lignin Adsorbed organic compounds Friable, brittle materials (suitable for pelletization) 7

8 Mass Balance of HTP Process Collect and quantify gaseous, water soluble, and solid products Product fractions vary with process severity Higher temperature more gas; less solid Higher temperature more water Accurate mass balance is somewhat difficult to obtain Process conducted in large excess of water Water itself is a product of reaction Typically 55% solid, 10% gas, 20% water, 15% water solubles 8

9 Percentage Starting Bone Dry Feedstock Effect of Temperature on HTP Mass Recovery Tahoe Mix Feedstock Water/biomass ratio of 8/1 Hold at temperature for 30-min. 70% 60% 50% Biochar 40% 30% Unidentified (including H 2 O) 20% Non-condensable gases 10% H 2 O Soluble Non-Volatiles 0% Temperature of Pre-treatment for 30 min (C) 9

10 Effects of Temp. on Biochar Properties Tahoe Mix Feedstock Hold at temperature for 30-min. 10

11 Atomic H/C Ratio Van Krevelen Diagram of Biochar Produced by HTP and Torrefaction of Woody Biomass Tahoe Chips 250 Biomass 275 Peat Lignite Loblolly pine Coal Raw Feedstock HTP of Tahoe Chips (30 min) Dry Torrefied Loblolly Pine (80 min) Anthracite Atomic O/C Ratio 11

12 % Starting Dry Feedstock Effect of Temperature on Sugar Recovery Tahoe Mix Feedstock Hold at temperature for 30-min. 1.6% 1.4% 1.2% 1.0% 0.8% 0.6% 0.4% 0.2% Others Glycerol Levoglucosan Mannosan Galactose Glucose/ Xylose 0.0% Reactor Temperature (ºC) for 30 min Residence Time 12

13 % Starting Dry Feedstock Effect of Temperature on Organic Acids Tahoe Mix Feedstock Hold at temperature for 30-min. 7% 6% 5% 4% 3% 2% 1% Other Acids Lactic Acid Acetic Acid Formic Acid 0% Reactor Temperature (C) for 30 min Residence time 13

14 Percentage Starting Bone Dry Feedstock Effect of Hold Time on HTP Mass Recovery Tahoe Mix Feedstock Reactor Temperature of 255 o C 60% 50% Biochar 40% 30% Unidentified (including H 2 O) 20% 10% 0% H 2 O Soluble Non-Volatiles Non-condensable gases Hold time (min) at 255 C 14

15 Energy Content (Btu/lb) C, O Content (%) Effect of Hold Time on Biochar Properties Tahoe Mix Feedstock Reactor Temperature of 255 o C BTU C O 0-10 Feedstock Reactor Hold Time (Temperature at 255ºC)

16 Atomic H/C Ratio Van Krevelen Diagram of Biochar Produced by HTP and Torrefaction of Woody Biomass Biomass Tahoe Chips Peat Lignite Loblolly min min 30 min Raw Feedstock Coal 60 min HTP of Tahoe Chips- 30 min HTP of Tahoe Chips at 255 C Dry Torrefied Loblolly Chips- 80 min Anthracite Atomic O/C Ratio 16

17 Conclusions HTP process is an effective way to increase the value of biomass feedstocks Can increase energy density > 40% Can be applied to wide variety of biomass types Optimum HTP conditions for woody biomass: Temps of o C; reaction times of times of 5-30 min. Tradeoff between time and temperature Expected ancillary benefits of HTP include: Improved storage and handling properties of solid fuels Pelletizing biochar and co-firing with coal Use of biochar for soils improvement and carbon sequestration Possible beneficial uses of water-soluble products 17

18 Acknowledgements DOE funding sources: DE-FG36-01GO11082 EE Parr reactor experiments: Eric Ceniceros Keri Noack Analytical laboratory analyses: Mark McDaniel Stephanie Smith Steve Kohl 18