Biomass gasification gas cleaning by reforming Energy Lab 2.0 meets Neo-Carbon Energy Noora Kaisalo

Transcription

1 VTT TECHNICAL RESEARCH CENTRE OF FINLAND LTD Biomass gasification gas cleaning by reforming Energy Lab 2.0 meets Neo-Carbon Energy Noora Kaisalo

2 Biomass gasification Autothermal reforming Hot-filtration Oxygen Conditioning and ultra cleaning FT SNG H2 Steam reforming Heat Biomass Steam/Air/Oxygen For synthesis use, biomass gasification gas needs to be cleaned from light hydrocarbons and tar compounds reforming is an effective solution Pressurized or atmospheric process? 17/02/2017 2

3 Reforming of biomass gasification gas AIR (oxidizer) O2 N 2, CO, CO 2, CH 4, C x H y, H 2, H 2 O tar NH 3 /HCN H 2 S/COS HCl alkali metals heavy metals particulates ppm ppm ppm 1-10 g/m 3 n CATALYST C N 2, CO, CO 2, CH 4, CH 4, C x H y C x H y, H 2, H 2 O tar ~0 NH 3 /HCN ~equilibrium H 2 S/COS HCl alkali metals heavy metals particulates ppm 1-10 g/m 3 n 17/02/2017 3

4 Tar formation Non-condensable H 2 CO CO 2 Primary tar Small hydrocarbons C oxygenates 2 H 4 C 2 H 2 radicals 1,3-butadiene Condensable phenols benzene alkylated aromatics 2 ring PAH 3 ring 4 ring Solid biomass soot Severity of conditions (Increasing temperature, pressure, time) 17/02/2017 4

5 Effect of process conditions on tar formation Tar formation from small radicals affect cleaning of the gas at high temperatures Effect of reaction conditions on tar formation was studied with 5 vol-% of ethene in nitrogen Mixture of tar and light hydrocarbons was formed, tar mixture resembled that of high temperature fluidized bed gasification of forest residues Pressure increase increased the tar amount and shifted the composition towards heavier tar compounds Indicates challenges to reforming T=954 C Ref: Kaisalo, Koskinen-Soivi, Simell, Lehtonen: Effect of process conditions on tar formation from thremal reactions of ethylene, Fuel 2015, 153, /02/2017 5

6 Reducing the amount of tar in gasifier by using catalytically active bed materials Feedstock: Bark pellets Gasification temperature: 850 C Atmospheric pressure Air ratio: 0.22, Air/steam gasification conditions 75/25 vol-% air/steam Fluidising velocity: 0.30 m/s Tar concentration, mg/m3n (per dry gas) Heterocyclic 1-ring 2-ring 3-ring 4-ring or more Unknown Sand Dolomite Olivine B/kaolin MgO Ref: Tuomi, Kaisalo, Simell, Kurkela, Effect of pressure on tar decomposition activity 17/02/ of different bed materials in biomass gasification conditions, Fuel, 2015, 158,

7 Effect of pressure on activity of bed materials DRY GAS COMPOSITION (wet basis) CO vol-% CO 2 vol-% H 2 vol-% CH 4 vol-% N 2 vol-% C 2 H 4 vol-% NH 3 ppm-v H 2 S ppm-v Tar+benzene g/m 3 n H 2 O vol-% Total hydrocarbon conversion, % Dolomite Olivine A MgO Sand pressure, bar Ref: Tuomi, Kaisalo, Simell, Kurkela, Effect of pressure on tar decomposition activity of different bed materials in biomass gasification conditions, Fuel, 2015, 158, /02/2017 7

8 Tar load to reformer Tar formation by radicals is enhanced when pressure is increased Bed materials that are highly active in tar conversion at atmospheric pressure lose their activity at pressurized conditions Leads to higher tar load for the reformer, which means more challenges related to carbon formation on catalysts. Long-term testing of reforming catalysts (~500 h) Reforming experiments with different tar loads Steam reforming or autothermal reforming mode 17/02/2017 8

9 Staged reformer Reforming catalysts O 2 ZrO 2 Partial oxidation Precious metal Nickel Steam reforming catalyst Ref: WO 2011/ A1, WO A1, WO A1 Clean syngas from biomass-process development and concept assessment, Simell, Pekka; Hannula, Ilkka; Tuomi, Sanna; Nieminen, Matti; Kurkela, Esa; Hiltunen, Ilkka; Kaisalo, Noora; Kihlman, Johanna, Biomass Conversion and Biorefinery. Springer. Vol. 4 (2014) No: 4,

10 Reforming catalyst long-term testing Catalysts: commercial nickel and precious metal catalysts, around 3 mm particles Steam reforming mode: oven temperature 900 C Oxidative steam reforming: oven temperature 950 C Atmospheric pressure CO CO2 H2 CH4 O2 N2 C2H4 NH3 H2S Tar H2O Vol-% Vol-% Vol-% Vol-% Vol-% Vol-% Vol-% ppm ppm g/m3n Vol-% LH MH MH+O Ref: Kaisalo, Kihlman, Hannula, Simell: Reforming solutions for biomass-derived gasification gas - Experimental results and concept assessment, Fuel 2015, 147, /02/

11 Long-term experimental results Total hydrocarbon conversion, % Nickel MH+O2 MH LH time, h Total hydrocarbon conversion, % Precious metal MH+O2, PM1 MH+O2, PM2 MH, PM3 LH, PM time, h 600 Autothermal: slower deactivation Lower hydrocarbon load, lower deactivation rate Autothermal: slower deactivation Differences in catalysts 17/02/

12 Reforming catalyst long-term testing results Difference between precious metal and nickel catalyst in autothermal reforming An H 2 O/C HC ratio above 4 and O/C HC ratio above 8 are recommended for gasification gas reforming. 17/02/

13 Reforming when synthetic natural gas is a target product For SNG production, low methane conversion in the reformer is an advantage Tar is a complex mixture of aromatic hydrocarbons but benzene most stable and for synthesis purposes, it needs to be removed Design of the reformer can be based on benzene reforming in case of SNG In case of syngas production, design based on methane conversion 17/02/

14 Catalyst testing Experimental conditions Precious metal and nickel catalysts Activity of the catalysts compared by equal surface area ( cm 2 ) Atmospheric pressure Temperatures C Gas composition: CO CO 2 H 2 CH 4 N 2 C 2 H 4 NH 3 H 2 S Tar H 2 O in wet Dry gas vol-% vol-% vol-% vol-% vol-% vol-% ppm ppm g/m3n gas, vol-% MH /02/

15 Tar conversion 17/02/ Temperature in the bottom of the catalyst bed

16 Methane conversion Temperature in the bottom of the catalyst bed 17/02/

17 Conclusions of biomass gasification gas reforming Pressurized operation more challenging than atmospheric Tar formation from ethene Activity of bed materials reduced Catalytically active bed materials to obtain low tar load for reformer Dolomite, magnesium oxide Lower rate of deactivation in autothermal mode than in steam reforming mode Lower rate of deactivation if lower hydrocarbon load in inlet of the reformer. Methane reforming extent can be modified by catalyst choice and temperature and still keep the tar conversion to syngas high 17/02/

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