Hot gas cleaning for biomass gasification for clean gas production

Transcription

1 Institute of Chemical Technology Prague Dep. of Gas, Coke and Air Protection Czech Republic Technická 5, Prague 6 Hot gas cleaning for biomass gasification for clean gas production Skoblja S., Malecha J., Koutsky B., Buryan P. International Freiberg Conference on IGCC & XtL Technologies TECHNISCHE UNIVER SITÄT, BERGAKADEMIE FREIBERG June 17, 2005 General gas composition and equipment requirements: biomass Gasification medium gas + impurities Impurities: strongly depends on reactor type, operation condition (dust, tar) independent on reactor type, operation condition (S, Cl, Alkali) main impurities gas quality requirements raw gas motors turbines fuel cells (MC, SO) Tar, mg.m <5 (50) <0,1 (1) <0,1 Dust, mg.m <5 (50) <0,1 <0,1 H2S, ppm <1 <0,1 HCl, ppm <100 <0,5 <0,1 alkaline metals, mg.m <0,1 <0,1 max. el. eff., %

2 Temperature windows for separate process: gas generators el. energy production updraft fluid downdraft motors turbines MCFC SOFC dust H 2 S HCl water quenching fabric filtr ZnO Fe,Mn oxide CaCO3 Na2CO3 ceramic filtr granular bed filtr dolomite alkali removal tar water organic Char coal prereformin Ni reforming Ni dolomite Optimal process temperature, C 3 Hot temperature Hot cyclones (low dp, high T, low efficiency ) Barrier filter Ceramic filter (corrosion, pore cleanup, thermal shock) Metallic filter Granular bed filter Changing surface and filter material Solve the problem with filter clogging Granular material could be used for gas cleaning Principe of granular bed filter (internal impact, agglomeration, diffusion) dp, Pa A dp o inner B surface C 0 0 time, min clogging point A B C Clean bed Surface cake Routing-cake (poor efficiency) (high efficiency) 4

3 Hot temperature granular filters inner M B F surface P B F normal mode dp, Pa dpo clogging point 0 0 time, min filter parameter M B F P B F bed material size (d p ), mm 2-5 0,2-0,5 superficial velocity -1 (Us), cm.s P kpa ,5-2,0 efficiency % >97 >99,5 pulse cleaning mode 5 Catalytic tar removal Limestone (CaCO3) dolomite (MgCO3. CaCO3) low activity: 750 C, conversion 80% ; >850 C conversion 95-98% resistance to deactivation (fluidized and fix bed) Nickel catalyst high activity deactivation at lower H 2 O/C ratio (H 2 O/C >2, depends compounds type), temperatures (<650 C), sensitivity to poison (H 2 S) application: methanation 250 C <T<350 C pre-reforming 350 (450) C <T<550 C steam (CO 2 ) reforming T > 550 (650) C CO + H2O CO2 + H2 CO + 3H2 CH4 +H2O tar + C x H y + H 2 O + CO 2 CO + H 2 + CH 4 6

4 Pre-reforming reforming nickel catalyst application Adiabatic pre-reforming of higher hydrocarbons for H 2 production in ammonia plant Pre-reforming LPG, naphtha, and liquid fuels for MCFC Catalytic tar removal Model tar removal (naphthalene) NTNU downdraft gasifier, 5.8 kg.h -1 quartz glass reactor (0,3 g cat 0.5-1,0 mm.+0.3 g. quartz glass) model granular bed filter 1 ID= 85mm, 57cm ml.min -1, SV=9700 h -1,8,9%H 1 th 2, 21,0 % CO 2, 70,1 % N 2, : 250 ml olivine sand dp=0,351 mm 24,4 g.m -3 H 2 O 2 th : 250 ml G56A (1-2) mm 1,0 530 C, 1,0 nm 3.h -1 GHSV=4700 Tar <1,0 g.m -3 n, Add. H 2 O 131 g. h -1.m -3 n naphthalene conversion 0,8 0,6 0,4 0,2 0,0 G 56A 450 C; C 10 :1,5 g.m -3 + H 2 O 450 C; C 10 :1,5 g.m -3 * 500 C; C 10 :1,5 g.m C; C 10 :3,0 g.m -3 + H 2 O 500 C; C 10 :3,0 g.m C; C 10 :3,0 g.m -3 + H 2 O 470 C; C 10 :3,0 g.m -3 * time on stream, min time, min gas content, % vol. H2 18,00 16,40 25,04 24,25 25,69 N2 45,76 47,56 41,31 43,21 40,12 CO2 9,09 7,46 16,65 16,08 17,15 CO 24,66 26,57 14,42 14,12 14,42 methane 2,03 1,58 2,58 2,34 2,61 ethane 0,024 0, ethylene 0,338 0,307 0,002 0,002 0,003 acetylene 0,022 0, benzene 0,050 0,045 0,001-0,001 toluene 0,007 0, Desulphurization Available adsorbents: >650 C: limestone (CaCO 3 ), dolomite (MgCO 3.CaCO 3 ) C min (H 2 S) > 150 ppm (T, CO 2, H 2 O) C: ZnO(ZnO-TiO 2 ), MnO 2 (MnO), Fe 2 O 3 (Fe 3 O 4,Fe),CuO(Cu), NiO(Ni) C min (H 2 S) = 0,1-5 ppm (T, H 2 O) MeO + H2 S MeS + H2O CaO + H2 S CaS + H2O H2S [mg.m -3 ] ,5 vol.% H2O t [ C ]

5 Proposal of Hot Gas Cleaning process 9 Acknowledgements This work was supported by the Grant Agency of the Czech Republic in the frame of the Grant No. 104/04/0829 and by the Ministry of Education, Youth and Sport of the Czech Republic in the frame of the research project MSM Thanks for your attention Questions? 10

6 Nickel surface reaction 1. adsorption C m H n +2 C n H y α-cleavage C n H y - 2 C 1 H x - + C n-1 H z dehydrogenation C 1 H x - C- +H x - 4. dissolution in Ni C - [C,Ni] whisker carbon 7. gum formation C n H y - 2 CH 2 CH 2 - gum 5. water adsorption H 2 O+ 2 O- + H 2 6. gasification C 1 H x - +O- CO +H x - C- +O- CO hydrogen adsorption H H- where: is a nickel active surface site Rostrup-Nielsen, J.R. Catalytic Steam Reforming, Springer-Verlag Berlin, Type of carbon deposition Whisker carbon Encapsulating polymers Pyrolytic carbon formation diffusion of C(s) through Nicrystal, whisker growth with Ni-crystal at top Slow polymerisation of CnHm radicals on Ni-surface, into encapsulation film thermal cracking of hydrocarbons, deposition o C-precursors on catalyst No deactivation of Nisurface, break-down of catalyst and increasing p Effects Progressive deactivation Encapsulating of catalytic particles, deactivation and increasing p temperature range, o C > 450 < 500 > 600 Critical parameters Low H2O/CnHm,No enhanced H2O adsorption, Low activity aromatic feed low temperature, low H2O/CnHm, low H2/CnHm, aromatic feed High temperature, high void fraction, low H2O/CnHm, hig pressure acidity of catalyst (support) 12

7 Carbon formation and carbon free operation temperature: 450 C<T op <550 C H 2 O/C n H m : >2.0 TGA study Ni/MgO catalyst (H 2 O/C=2; 0.1 MPa, 500 C)* Temperature Windows for free carbon operation** *Rostrup-Nielsen, J.R. Catalytic Steam Reforming, Springer-Verlag Berlin,1984 ** Rostrup-Nielsen, J.R. Christensen,T.S., Dybkjaer, Ib. Steam Reforming of Liquid Hydrocarbons. Studies in Surface Science and Catalysis. 1998,113, High temperature desalinization c H2S [ mg.m -3 ] C / 16 % H 2O C / 14 % H 2O C / 7 % H 899 C / 12 % H 2O 2O C / 10 % H 2O 750 C / 9 % H 2O gas volume [ l ] (50 l.h -1, C input (H 2 S)=760 (843) mg.m -3 ) Remaining H 2 S concentration in dependence on temperature and water contents 14