Clarification of gasification behavior of solid fuel char prepared under CO 2 atmosphere

Transcription

1 3rd Oxyfuel Combustion Conference Ponferrada, Spain Technical session 3c Clarification of gasification behavior of solid fuel char prepared under CO 2 atmosphere Tokyo Institute of Techonology Kiyomi SHIMOMURA* Kiyomi SHIMOMURA, Hirotatsu WATANABE, Ken OKAZAKI

2 Today s contents 2 Background Research purpose Experiment Sample and setup Experiment condition Result and Discussion Pyrolysis experiment Char gasification experiment Conclusion

3 Today s contents 3 Background Research purpose Experiment Sample and setup Experiment condition Result and Discussion Pyrolysis experiment Char gasification experiment Conclusion

4 Background 4 Air combustion Fuel Air Boiler Flue gas treatment N 2 CO 2 13% H 2 O O 2 N 2 2 O 2 /CO 2 combustion 2 2 Flue gas composition N 2 Fuel CO 2 95% Boiler Flue gas H 2 O Air O O treatment CO 2 ASU 2 2 N 2 Flue gas composition Flue gas recycling (Mainly CO ASU : Air Separation Unit 2 ) Easy to treat/handle CO 2 (Eg. Carbon capture & Storage)

5 Research purpose 5 Because CO 2 is highly concentrated in O 2 /CO 2 combustion The pyrolysis y process of solid fuel undergoes in CO 2 atmosphere. The mechanism of production of char in pyrolysis process is considered to be different, which causes the difference of char property. Possible changes: Reaction between CO 2 and alkali metal (Influence on catalytic effect of alkali metal [1] ) Increase of specific surface area [2] (enhancement of gasification reaction) Research purpose Investigate the influence of these properties on char gasification Clarify the effect of CO 2 in char gasification [1] McKee, D. W, Marcel Dekker, New York, 1981, 16, [2] Renu Kumar Rathnam et. al., Fuel Processing Technology,2009,6,

6 6 Background Research purpose Experiment Sample and setup Experiment condition Result and Discussion Pyrolysis experiment Char gasification experiment Conclusion

7 Sample & Setup 7 Table: proximate analysis & ash contents (ICP AES) Alkali lignin [wt%] Volatile matters 46.4 Fixed carbon 23.1 Water 11.8 Ash 18.2 flowmeter CO 2 Reaction tube Pt cell Ash Na 55.0 thermobalance [mg/g] K 1.03 Ar Air compressor sample heater Thermometric point Pressure meter Alkalilignin lignin was employed to extract the effect of alkali metal in CO 2 environment PC Vacuum pump Fig. Thermobalance

8 Experiment method (Pyrolysis) 8 Pyrolysis exp. Gas CO 2 or Ar Gas flow rate 08l/min 0.8 Heating rate 1 K/s Final temp. 700 o C Sample mass 40mg The chars were analyzed by FT-IR, N 2 BET analysis and SEM images to investigate the influence of CO 2 on char properties.

9 Experiment method (Char gasification) Energy Phenomena Laboratory 9 Pyrolysis Gasification Gas CO 2 or Ar Switching Air Gas flow rate 0.8 l/min 0.8 l/min CO 2 or Ar Heating rate 1 K/s - Final temp. 700 o C pyrolysis swithcing gasification Air 700 o C, 750 o C,800 o C, 850 o C, 900 o C, 950 o C, 1100 o C,1150 o C, 1200 o C [mg] Weight Pyrolysis (700 o C) and Gasification (900 o C) char Time [sec] Temperat ture [ o C] dx / dt dw X W i / dt =gasification rate X:Char conversion ratio W:Weight Arrhenius plot (X=0.5)

10 10 Background Research purpose Experiment Sample and setup Experiment condition Result and Discussion Pyrolysis experiment Char gasification experiment Conclusion

11 Result and Discussion (Pyrolysis) Energy Phenomena Laboratory 11 Reaction between CO 2 and alkali metal FT IR 1450 cm cm -1 lignin char Ar = lignin char made in Ar lignin char CO 2 = lignin char made in CO 2 Na 2 CO 3 Int tensity [a.u u.] Wavelength [cm -1 ] Wavelength of 1450cm 1 and 880cm 1 are assigned to the peaks for carbonate ion [1]. Carbonate was formed in lignin char which was prepared in CO 2 atmosphere. This result matches 500 with our previous research [3]. [1] McKee, D. W, Marcel Dekker, New York, 1981, 16, [3] Watanabe, H. et al., Proceedings of the Combustion Institute, 2013, 34,

12 Result and Discussion (Pyrolysis) Energy Phenomena Laboratory 12 Surface area of char SEM 10μm N 2 BET analysis Specific surface area [m 2 /g] lignin char CO lignin char Ar Lignin char CO 2 Lignin char Ar Drastic development of pores in lignin-char-co 2 is considered to be caused by char-co 2 reaction. The char prepared in CO 2 atmosphere has more porous surface and larger surface area than that prepared in Ar atmosphere

13 13 Background Research purpose Experiment Sample and setup Experiment condition Result and Discussion Pyrolysis experiment Char gasification experiment Conclusion

14 Result and Discussion (Char gasification) Energy Phenomena Laboratory 14 Gasification rate of lignin char lignin-char-co 2 = lignin char made in CO 2 lignin-char-ar = lignin char made in Ar.5 [s -1 ] ln dx/dt x= o C Zone II Zone I Zone I = Kinetic controlled region Zone II = Internal diffusion controlled region 950 o C lignin char CO 2 lignin char Ar 700 o C /T [K -1 ] dx / dt dw X W i / dt =gasification rate X:char conversion ratio W:Weight Fig. Arrhenius plot of ligninchar gasification in air environment

15 Result and Discussion (Char gasification) Energy Phenomena Laboratory 15 Gasification rate of lignin char lignin-char-co 2 = lignin char made in CO 2 lignin-char-ar = lignin char made in Ar.5 [s -1 ] ln dx/dt x= o C Zone II Zone I Zone I = Kinetic controlled region Zone II = Internal diffusion controlled region 950 o C lignin char CO 2 lignin char Ar 700 o C /T [K -1 ] dx / dt dw X W i / dt =gasification rate X:char conversion ratio W:Weight Fig. Arrhenius plot of ligninchar gasification in air environment

16 Result and Discussion (Char gasification) 16 Zone I (Kinetic controlled region): We eight [mg] Pyrolysis Gasification lignin-char -CO 2 lignin-char-ar Time [s] Gasification reaction at 700 o C o C] Temp perature [ At the temperature lower than 750 o C, lignin char prepared in CO 2 (lignin char CO 2 ) didn t gasify, while the lignin char prepared in Ar (lignin char Ar) gasified. Carbonate formation in ligin char prepared in CO 2 inhibited char gasification at lower temperature (<750 o C).

17 Result and Discussion (Char gasification) 17 Zone I (Kinetic controlled region): How the carbonate inhibit gasification reaction? P. J. van Eyk et al. [4] reported that Na works as a catalyst by repeating the following redox reaction. ( CNa)+1/2O 2 ( CONa) oxidation ( CONa)+C ( CNa) +CO reduction ( CNa) plays important role in char gasification reaction. In pyrolysis y in CO 2 environment, it can be assumed that Na reacts with CO 2 to form Na 2 CO 3 so that Na cannot act as the specie which can contribute to the catalytic reaction shown above, especially at lower temperature. [4] van Eyk, P. J. et al., Combustion and Flame, 2011, 158,

18 Result and Discussion (Char gasification) Energy Phenomena Laboratory 18 Gasification rate of lignin char lignin-char-co 2 = lignin char made in CO 2 lignin-char-ar = lignin char made in Ar.5 [s -1 ] ln dx/dt x= o C Zone II Zone I Zone I = Kinetic controlled region Zone II = Internal diffusion controlled region 950 o C lignin char CO 2 lignin char Ar 700 o C /T [K -1 ] dx / dt dw X W i / dt =gasification rate X:char conversion ratio W:Weight Fig. Arrhenius plot of ligninchar gasification in air environment

19 Result and Discussion (Char gasification) Energy Phenomena Laboratory 19 Zone II (Internal diffusion controlled region): Lignin char made in CO 2 had higher gasification rate than that of char made in Ar. SEM 10μm ligninchar CO 2 ligninchar Ar During pyrolysis in CO 2, both micro and macro pores of char developed more drastically. It makes gasification agents to diffuse more easily. More porous morphology and larger specific surface area of char made in CO 2 enhanced gas transport leading to increase of gasification rate.

20 20 Background Research purpose Experiment Sample and setup Experiment condition Result and Discussion Pyrolysis experiment Char gasification experiment Conclusion

21 Conclusion Energy Phenomena Laboratory 21 Properties of lignin char in CO 2 : The lignin char prepared in CO 2 environment contained carbonate and it had more porous surface and larger specific surface area. Char gasification behavior of lignin char: Zone I (Kinetic controlled region): Carbonate formation inhibited char gasification, by changing Na form in char. Zone II (Internal diffusion controlled region): More porous morphology and larger specific surface area of char due to char CO 2 gasification enhanced gas transport leading to increase of gasification rate. CO 2 in pyrolysis of lignin plays different roles in char gasification process, according to the rate limiting factors.

22 Thank you for your kind attention

23 Characteristics of lignin Energy Phenomena Laboratory

24 Lignin (proximate & ultimate analysis) 24/14 Ultimate analysis lignin [wt%] C 46.5 H 4.49 N 0.08 S 2.51 O Ash 18.2 Proximate analysis lignin [wt%] Volatile matters 46.4 Fixed carbon 23.1 Water 11.8 Ash 18.2 Ash composition of lignin [mg/g] (ICP-AES) Lignin Ion-exchanged lignin Na K

25 Pyrolysisexperiment i Energy Phenomena Laboratory

26 Result (Pyrolysis) Energy Phenomena Laboratory 26 Pyrolysis of lignin (biomass) FTIR analysis 1440 cm cm -1 Weight 10%UP.u.] tensity [a. Int Temperature [ o C] Wavelength [cm -1 ] ligninchar-co 2 = lignin char made in CO 2 ligninchar-ar = lignin char made in Ar Na 2 CO 3 Lignin char i prepared in CO 2 contains carbonate

27 実験結果 :ligninチャー C123 東工大下村聖実 27 FTIR lignin-coi 2 lignin-ari Na 2 CO cm cm -1 coal-co 2 coal-ar 1440 cm cm -1 Intens sity [a.u.] Intensi ity [a.u.] Wavelength [cm -1 ] Wavelength [cm -1 ] lignin Coal [3] Watanabe, H. et al., Proceedings of the Combustion Institute

28 Gasification experiment Energy Phenomena Laboratory

29 Experiment method (Gasification) Energy Phenomena Laboratory 29 Pyrolysis CO 2 or 1K/s to 700 o C 700 o C for 3min. Switching gas CO 2 or Ar Air Gasification Air 700 o C 1200 o C Experiment condition Pyrolysis Gasification Gas CO 2 or Ar Switching Air Gas flow rate 0.8 l/min 0.8 l/min Heating rate 1 K/s - Final temp. 700 o C 700 o C, 750 o C,800 o C, 850 o C, 900 o C, 950 o C, 1100 o C,1150 o C, 1200 o C Sample mass 40mg -

30 Result: Gasification profile 30 lignin 700 o C(CO 2 ) 900 o C (Air) We eight [mg g] pyrolysis swithcing gasification W i Time [sec] Temp erature [ o C] W X 0. 1 W X 0. dw X / dt dt dx / dt dw X W i / dt =gasification rate X:char conversion ratio W:Weight At each temperature, gasification rate at X=0.5 was compared. 1

31 Advanced d discussion i Energy Phenomena Laboratory

32 Why carbonate inhibit gasification 32/14 The key reaction for Na to work as a catalyst in char gasification [4] ( CNa)+1/2O 2 ( CONa) oxidation ( CONa)+C ( CNa) +CO reduction When Na 2 CO 3 was formed in the pyrolysis process in CO 2 atmosphere, the Na loose chance to act as a catalyst COONa Pyrolysis y Ar CNa CO 2 NaN 2 CO 3 Gasification ( CNa) + 1/2O 2 ( CONa) ( CONa) + C ( CNa) + CO [4] van Eyk, P. J. et al., Combustion and Flame, 2011, 158,

33 Discussion 33 Zone I It has already revealed that carbonate (mainly Na 2 CO 3 ) is formed in the lignin char made in CO 2 (Ligninchar-CO 2 ). Lignin R-COONa NaCl, NaOH, CO 2 Lignincha r Na 2 CO 3, Different formations of Na seems to have different effects on gasification at temperature lower than 750 o C. s8 Analyze the formation of Na GOAL: To clarify the order of activeness as catalyst of gasification at lower temperature(-750 o C) with respect to the formation of Na.

34 Slide 33 s8 これを 図式化したほうがよかった 触媒の活性度を グラフみたいにして NaCl > Na2CO2 > NaOH とかみたいに shimomura, 18/06/2013

35 Background Energy Phenomena Laboratory

36 CO 2 separatation cost and energy 35/13 cost $55/tonne of CO 2 $35/tonne of CO 2 O 2 /CO 2 Air (by chemical absorption) O 2 /CO 2 Air energy ASU Power [MW e ] 86 - CO 2 Separation Unit Power [MW e ] Heat duty [MW th ] Cooling duty [MW th ] D. Singh et al. / Energy Conversion and Management 44 (2003)

37 Background:CCS 36 CCS: Carbon Capture and Storage Capture Storage Transport Compress Capture Compress Storage Transport Power Plant CO 2 Compress CO 2

38 Objective 37 How the enriched CO 2 affects oxyfuel combustion? Oxyfuel lcombustion Pyrolysis (Complicated to analyze) Emission of volatiles and formation of char Very important step, which also affects the following steps in combustion The effect of CO 2 in pyrolysis process of oxyfuel combustion is still unknown Gasification The char formed in pyrolysis process is gasified Gasification behavior of char strongly dependent on char property Objective: To clarify the effect of CO 2 in pyrolysis process by investigating char property and char gasification behavior

39 Background 38 Combustion phenomenon of coal particle Pyrolysis: Emission of volatile matters Formation of char Particle temperat ture Air+coal flame volatiles Ignition 1000~1700 Rapid increase of particle temperature JCOAL: shandbook/dlfiles/c3 4.pdf End of emission of volatiles Air Combustion of char fly ash Gasification: Gasification of char by gasifying agents (O 2,CO 2 ) pulverized coal Distance from burner

40 Background 39 Combustion phenomenon of coal particle Pyrolysis: Emission of volatile matters Formation of char Particle temperat ture Air+coal flame volatiles Ignition 1000~1700 CO 2 CO 2 2 CO 2 Rapid increase of particle temperature O 2 /CO 2 combustion End of emission of volatiles Air Combustion of char fly ash Gasification: Gasification of char by gasifying agents (O 2,CO 2 ) pulverized coal Distance from burner