EFFECT OF GAS-PHASE ALKALI ON TAR REFORMING CATALYST

Transcription

1 EFFECT OF GAS-PHASE ALKALI ON TAR REFORMING CATALYST Pouya Haghighi Moud 1), Klas Engvall 1) and Klas J. Andersson 2) 1) Dept. of Chemical Engineering and Technology, KTH, Stockholm Sweden 2) Haldor Topsøe A/S, Kongens Lyngby, Denmark

2 CHALLENGE OBJECTIVE Unknown effects of gas phase alkali on tar reforming catalyst Investigations of interactions between tar reforming catalyst and gas phase alkali at realistic conditions 2

3 Outline Background Experimental Results so far Gas composition Tar measurements Sulfur uptake Chemical eq calculation K adsorption Summary On-going work 3

4 Background Preprocessing of biomass Gasification Gas clean-up & reforming Gas utilization Tar removal Reforming of the syngas/catalysis Syngas Tar Tar removal Biomass Gasifier Application Gasifying agent Gas clean-up Downstream cleaning (Tar, particulates,alkali, S, etc) 4

5 Background Gasifier Hot gas filter Tar reformer Gasifier High temperature hot gas filter Tar reformer Clean tar reforming Gasifier Tar reformer Hot gas filter Dusty tar reforming 5

6 Background Alkali promotion* Surface carbon gasification Decrease in intrinsic activity of the nickel in traditional steam reforming Type of support influences the alkali interaction *Ref: Concepts in Syngas Manufacture, Jens Rostrup-Nielsen Lars J.Christiansen 6

7 Background Deactivation of the catalyst Fouling/coking Sintering* Temperature, ph 2 O, and ph 2 (mobile Ni(OH) 2 species) Activity suppression by sulfur* Under reforming conditions all the sulfur compounds are converted into H 2 S H 2 S+ Me-> Me-S + H 2 Stable saturation uptakes of sulfur 10x10-6 < H 2 S/H 2 < 1000x10-6 Metal (Ni) surface area/g catalyst => surface saturation by S *Ref: Concepts in Syngas Manufacture, Jens Rostrup-Nielsen Lars J.Christiansen 7

8 EXPERIMENTAL 8

9 Experimental Setup Excess gas Gas analysis N 2 Dry alkali salt particles Biomass feeder Atmospheric fluidized bed (A) Gas analysis - Permanent gases - Tar -others 850 C (A) Filter vessel Gas pre-heater (A) Catalytic reactor 850 C 850 C N 2 O 2 H 2 (A) Product gas Nibased Haldor Topsøe catalyst 9

10 Experimental Setup Excess gas Gas analysis N 2 Dry alkali salt particles Biomass feeder Atmospheric fluidized bed (A) Gas analysis - Permanent gases - Tar -others 850 C (A) Filter vessel Gas pre-heater (A) Catalytic reactor 850 C 850 C N 2 O 2 H 2 (A) Product gas Nibased Haldor Topsøe catalyst Alkali and hydrogen sulfide is added after the filter. 10

11 Experimental Tests Test campaign 1 st test campaign 2 nd test campaign Alkali species KCl, KNO 3 KCl Addition of H 2 S No addition ppm 11

12 Catalyst characterization Surface area of catalyst (BET) K content (AAS) Carbon/coke formation (TPR) Cl content(ic) S and C content (FTIR, SEM) Particle size distribution (SMPS) AAS Atomic Absorption Spectroscopy TPR Temperature Programmed Desorption IC ION Chromatography FTIR Fourier Tranform Infrared Spectroscopy SEM Scanning Electron Miccroscopy SMPS Scanning Mobility Particle Sizer 12

13 RESULTS 13

14 Gas composition Methane (KCl) 9 8 Methane content (%) KCl 1 ppm H 2 S 10 ppm Time (minute) Significant decrease in methane conversion already after one hour 14

15 Gas composition 10 9 Methane (KCl+hydogen sulfide) Methane (KCl) Methane content (%) Time (minute) KCl 1 ppm H 2 S 10 ppm KCl 1 ppm H 2 S 50 ppm At extended exposure time, higher H 2 S addition results in lower methane 15 conversion

16 Gas composition 10 9 Methane (KCl+hydogen sulfide) Methane (KCl) Methane content (%) Time (minute) KCl 1 ppm H 2 S 10 ppm KCl 1 ppm H 2 S 50 ppm At extended exposure time, higher H 2 S addition results in lower methane 16 conversion

17 Tar measurement SPA method and online GC Tar (Excluding Benzene) Naphthalene KCl 1 ppm H 2 S 50 ppm Tar Reduction (%) Time (hour) Decrease in tar reduction for both light and heavy hydrocarbons A trend is observed: Initial activation drop 17

18 Sulfur effect 1,2 S content S/S capacity 1 0,8 0,6 0,4 KCl 1 ppm H 2 S 50 ppm KCl 1 ppm H 2 S 10 ppm 0, Time on stream(hour) Increase in S content of the catalyst: Initial activation drop Higher H 2 S addition: S saturation coverage is more rapidly reached 18

19 K adsorption Methane (KCl+H2S) Methane (KCl) K adsoption on catalyst Methane content (%) KCl 1 ppm H 2 S 50 ppm Time (minute) 0,3 0,25 0,2 0,15 0,1 0,05 K adsorption on catalyst(mg K/ g Catalyst) Comparing S and K uptake, initial activity suppression is dominated by S. Therefore important to perform experiments with S coverage equilibrated Ni 19 surface.

20 Summary so far There is a trend in gas composition/tar reduction behavior After first hours of run Methane conversion is stable (constant catalytic activity) S content of the catalyst reaches its maximum meaning the surface is equilibrated How do we isolate the effect of gas phase alkali on the catalyst in realistic conditions? Pre-sulfidation Ageing (High T and high steam content) 20

21 Tests Test campaigns 3 rd test campaign Alkali species KCl (0.1, 0.5, and 1 ppm) Addition of sulfur H 2 S/H 2 corresponding to surface coverage of 0.9 Pre-treatment Pre-ageing and Pre-sulfidation Results of pre-treatment indicates: 1. BET surface area is constant from start 2. Sulfur content of the catalyst is constant from start 21

22 Thermodynamic consideration Chemical eq. calculations* for KCl ppm (850 C) 1 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0 reference 0.5 ppm KCl 1 ppm KCl KCL KCl KOH K K2CO3 KCN At current conditions of experiment,molecular KCl is the main alkali compound present in the gas phase at different concentrations *NASA computer program 22

23 Experimental K adsorption data K adsorption (µg/bet surface area) ppm excess KCl Experimental value ppm excess KCl Time on stream (hour) 23

24 Future work Experimental value K adsorption (µg/bet surface area) ppm excess KCl 0.5 ppm excess KCl Speculated value No excess KCl ppm KCl Decay time for adsorbed KCl Time on stream (hour) Following the uptake of K at different concentrations, it is possible to observe if the catalyst reaches an equilibrium coverage. More data points are needed. 24

25 Summary Pre-ageing and pre-sulfidation : isolate the effect of gas phase alkali on tar reforming catalyst Initial uptake of K is different at different gas phase concentrations of KCl Following the uptake of K at different concentrations, it is possible to see if the catalyst reaches an equilibrium coverage. As the result of the objective of this project, we were able to develop a methodology for investigation of gas phase alkali on tar reforming catalyst 25

26 On going work Extended test plan Longer exposure times Different KCl concentrations Decay time of adsorbed K 26

27 Acknowledgment SFC 27