Air-steam gasification of sewage sludge in a bubbling bed reactor: Effect of alumina as a primary catalyst

Abstract

ARTICLE INFO ABSTRACT Keywords:Sewage sludge gasification Primary catalyst Bubbling fiuidised bed Gasifying agenteNumerous references can be found in scientific literature regarding biomass gasification. However, there are few works related to sludge gasification. A study of sewage sludge gasification process in a bubbling fiuidised bed gasifier on a laboratory scale is here reported. The aim was to find the optimum conditions for reducing the production of tars and gain more information on the influx of different operating variables in the products resulting from the gasification of this waste. The variables studied were the equivalence ratio (ER), the steambiomass ratio (SB) and temperature. Specifically, the ER was varied from 0.2 to 0.4, the SB from 0 to 1 and the temperature from 750 °C (1023 K) to850 °C (1123 K). Althoughit was observed that tar production could be considerably reduced (up to 72%) by optimising the gasification conditions, the effect of using alumina (aluminium oxide, of proven efficacy in destroying the tar produced in biomass gasification) as primary catalyst in air and air-steam mixture tests was also verified. The results show that by adding small quantities of alumina to the bed (10% by weight of fed sludge) considerable reductions in tar production can be obtained (up to 42%) improving, at the same time, the lower heating valué (LHV) of the gas and carbón conversión.

Sustainability of Domestic Sewage Sludge Disposal

“…Anyway, compared with sludge tested by other authors [6, 9-11, 15, 18], it can be observed that values in Table 1 are in the same order. Although ashes content is lower [6,[9][10][11] or similar [22] to that of some sewage sludge already used for gasification experimentation, it is high compared with that of biomass normally used for gasification. Volatiles content is in the range of the values found in the literature for sewage sludge to be used as fuel for gasification [10,13,22] while different biomass-based fuels used for gasification in the literature may have higher [23][24][25] or lower [26] volatiles content.…”

“…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]. In any case, gasification is considered a waste-to-clean energy technology [12].…”

“…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.…”

Development of a chemical kinetic model for a biosolids fluidized-bed gasifier and the effects of operating parameters on syngas quality

“…The authors found no published studies that reported kinetic data on individual reactions from biosolids gasification, but did find three experimental studies that reported on laboratoryscale sewage sludge bubbling fluidized-bed gasifiers (de Andrés, 2011;Kang et al, 2011;Manyà, 2006). The proximate and ultimate analyses of the sewage sludges used and the syngas produced in those studies are listed in Tables 5 and 6, respectively.…”

“…Following calibration of the model using the 18 data sets from literature (de Andrés et al, 2011;Kang et al, 2011;Manyà et al, 2006), the remaining 10 data sets from the same three experimental studies were used as independent data for final model performance validation, as seen in Figure 5. Using these data, statistical analysis was performed using the Ansari-Bradley method to compare the predicted gaseous compositions with the literature values.…”