Commercial Steam Reforming Catalysts To Improve Biomass Gasification with Steam−Oxygen Mixtures. 2. Catalytic Tar Removal

Abstract

Eight different commercial catalysts, nickel based, for steam reforming of naphthas and of natural gas are tested in biomass gasification for hot gas cleanup and conditioning. They were manufactured by BASF AG, ICI−Katalco, UCI, and Haldor Topsøe a/s. The catalysts were tested in a slip flow after a biomass gasifier of fluidized bed type at small pilot-plant scale (10−20 kg of biomass/h). The gasifying agent used is steam-oxygen mixtures. A guard bed containing a calcined dolomite is used to decrease the tar content in the gas at the inlet of the catalytic bed. Main variables studied are catalyst type, bed temperature, H2O + O2 to biomass feed ratio, and time-on-stream. All catalysts for reforming of naphthas show to be very active and useful for tar removal and gas conditioning (in biomass gasification). 98% tar removal is easily obtained with space velocities of 14 000 h-1 (n.c.). No catalysts deactivation is found in 48 h-on-stream tests when the catalyst temperature is relatively high (780−830 °C). Using a simple first-order kinetic model for the overall tar removal reaction, apparent energies of activation (of around 58 kJ/mol) and preexponential factors are obtained for the most active catalysts.

Stability and Regeneration of Catalysts for the Destruction of Tars from Bio-mass Black Liquor Gasification

“…The reactor was operated at temperatures between 500°C and 800°C. The reactor effluent stream was analyzed using on-line FTIR for CO, CO 2 , CH 4 , and other hydrocarbons (including the reactant benzene), as well as sulfurcontaining compounds.…”

“…Of these, catalytic approach is the most promising alternative to destroy tar compounds since it can convert tar to gaseous fuels at moderate temperatures. Several different catalytic materials have been tested for biomass tar destruction, including dolomite, nickel and cobalt based catalysts (3)(4)(5)(6)(7)(8). The rapid deactivation of catalysts in the fuel gas presents a major challenge.…”

Tar Removal From Biomass Gasification Streams: Processes and Catalysts

“…Apesar dos excelentes resultados alcançados com catalisadores comerciais, com conversão para alcatrão superior a 97%, a vida útil dos catalisadores é afetada pelos seguintes fatores: 1-alto teor de alcatrão na entrada do reformador; 2-natureza química do alcatrão; 3-envenenamento por enxofre e metais alcalinos; 4-formação de coque. [34][35][36][37][38] Muitos estudos publicados na década de 90, oriundos das universidades espanholas, como Universidade de Zaragoza, empregavam minerais como calcitas, magnesitas, dolomitas e olivinas no leito do gaseificador, usando madeira como matéria-prima. [34][35][36][37][38] Esses minerais continuam sendo estudados, porém com foco na gaseificação de outras matérias-primas, como lodo de esgoto, resíduo da indústria papeleira e bagaço-de cana.…”

“…46,47 Vários catalisadores comerciais de reforma a vapor já foram reportados na literatura para a reforma do alcatrão. [34][35][36][37][38] Cabe reforçar que os catalisadores comerciais para reforma a vapor de nafta se mostraram mais adequados do que os catalisadores para reforma do gás natural.…”

“…Como os catalisadores de reforma a vapor são fornecidos na forma de anéis (1 cm altura × 1 cm diâmetro), estes tiveram que ser moídos e peneirados, obtendo-se um tamanho médio de 1,2 mm, obtendo--se conversão para o alcatrão no reator de reforma igual a 98%. 34,35 Resultados publicados evidenciaram que os catalisadores usados para reforma a vapor de nafta foram mais ativos que os catalisadores comerciais empregados para a reforma de gás natural. 9 Deve-se destacar que a maioria dos estudos apresentados não emprega injeção de vapor no reator de reforma, já que aproveita o vapor d'água presente na corrente produzida na gaseificação.…”