Behaviour of dolomite, olivine and alumina as primary catalysts in air–steam gasification of sewage sludge

Abstract

ARTICLE INFO ABSTRACT Keywords:Primary catalyst Sewage sludge gasification Bubbling fluidised bed Tar contentSewage sludge gasification assays were performed in an atmospheric fluidised bed reactor using air and air-steam mixtures as the gasifying agents. Dolomite, olivine and alumina are three well known tar removal catalysts used in biomass gasification processing. However, little information is available regarding their performance in sewage sludge gasification. The aim of the current study was to learn about the influence of these three catalysts in the product distribution and tar production during sewage sludge gasification. To this end, a set of assays was performed in which the temperature (750-850 °C), the inbed catalyst content (0,10 and 15 wt.%)and the steam-biomass ratio (SB) in the range of 0-1 were varied with a constant equivalence ratio (ER) of 0.3. The results were compared to the results from gasification without a catalyst. We show that dolomite has the highest activity in tar elimination, followed by alumina and olivine. In addition to improving tar removal, the presence of water vapour and the catalysts increased the content of H 2 in the gases by nearly 60%.

Tar Removal From Biomass Gasification Streams: Processes and Catalysts

“…Tem menor atividade catalítica que a dolomita, necessitando de elevadas temperaturas reacionais (acima de 850 °C), mas tem elevada resistência mecânica, por isso é amplamente estudada como suporte. [65][66][67][68][69][70] Uma questão importante no uso da olivina é que o material não é estável nas condições de gaseificação, pois é suscetível à decomposição em elevadas temperaturas, formando uma mistura de olivina e fases livres 3 ) e pirita (FeS 2 ) são menos ativos que a dolomita, desativando rapidamente na ausência de hidrogênio. As zeólitas possuem custo relativamente elevado quando sintéticas, e apresentam como desvantagens rápida desativação e baixa atividade catalítica quando comparadas com a dolomita.…”

“…38 Outra preocupação é o grande acúmulo de coque, já que o mineral é apenas ativo em temperaturas elevadas, que proporcionam a formação de coque devido às reações de craqueamento, sendo que esse coque pode ser minimizado através do emprego de catalisadores mais básicos. 38,65,76 Estudos comparativos com dolomita, magnesita e calcita, empregadas como leito de guarda do reator de reforma a vapor, evidenciaram que a dolomita foi mais ativa nas condições de reação. As condições favoráveis para uma vida mais longa da dolomita são temperaturas acima de 840 °C, pequeno diâmetro de partícula (< 1,9 mm) e altos tempos espaciais (> 0,17 kg(dolomita)h/m 3 ).…”

Sustainability of Domestic Sewage Sludge Disposal

“…The need for supplemental fuel, emissions of sulfur oxides, nitrogen oxides, heavy metals, and fly ash, and the potential production of dioxins and furans, which may be produced during incineration as a consequence of the oxidizing atmosphere [4], are avoided by sewage sludge gasification. A main advantage of sewage sludge gasification is that a high-quality flammable gas may be obtained, so it can be directly used for electricity generation or for supporting the drying of sewage sludge [5] and also may be employed as raw material in chemical synthesis processes [6]. Indeed, as for biomass gasification, a main difficulty about sewage sludge gasification is the presence of tar and dust in the synthesis gas produced, which may cause problems in process equipment and/or in turbines and engines for gas distribution [7][8][9][10][11].…”

“…The Scientific World Journal Theory on sewage sludge gasification and a description of the process were reported by Dogru et al [13] and also by Fytili and Zabaniotou [1] in their review on thermal processing of sewage sludge. Since Garcia-Bacaicoa et al [14] first published a work on sewage sludge gasification, encouraging results have been reported, mainly during the last decade [3,5,6,[9][10][11][15][16][17][18]. However, as recently highlighted by de Andrés et al [6], comparatively with the large number of references that can be found in scientific literature regarding biomass gasification, experimental works on sewage sludge are relatively scarce.…”

Air gasification of oil palm waste over dolomite in a fluidized bed

“…Dolomite has proved its ability to avoid or reduce the formation of agglomerates, especially in feedstocks with high alkali contents (Gusta et al, 2009). Moreover, in situ catalytic reactions promoted by dolomite positively affect the cracking of tar and enhance the quality of the producer gas (Narvaez et al, 1996;Olivares et al, 1997;Xie et al, 2010;de Andrés et al, 2011). It has been reported that the presence of 20-30 wt% dolomite in the gasifier bed significantly improves the quality of the producer gas and prevents bed agglomeration (Gil et al, 1999).…”