Torrefaction as a Valorization Method Used Prior to the Gasification of Sewage Sludge

Abstract

The gasification and torrefaction of sewage sludge have the potential to make the thermal utilization of sewage sludge fully sustainable, thus limiting the use of expensive fossil fuels in the process. This includes sustainability in terms of electricity consumption. Although a great deal of work has been performed so far regarding the gasification of sewage sludge and some investigations have been performed in the area of its torrefaction, there is still a gap in terms of the influence of the torrefaction of the sewage sludge on its subsequent gasification. This study presents the results from the torrefaction tests, performed on a pilot scale reactor, as well as two consecutive steam gasification tests, performed in an allothermal fixed bed gasifier, in order to determine if torrefaction can be deemed as a primary method of the reduction of tar content for the producer gas, from the aforementioned gasification process. A comparative analysis is performed based on the results obtained during both tests, with special emphasis on the concentrations of condensable compounds (tars). The obtained results show that the torrefaction of sewage sludge, performed prior to gasification, can indeed have a positive influence on the gas quality. This is beneficial especially in terms of the content of heavy tars with melting points above 40 °C.

Torrefaction of Straw from Oats and Maize for Use as a Fuel and Additive to Organic Fertilizers—TGA Analysis, Kinetics as Products for Agricultural Purposes

“…One result of such an analysis is a kinetics model which correctly corresponds to the nature of experimental data under varied temperature conditions [29]. Use of the kinetic model helps to predict a chemical system's behavior under user-defined temperature conditions [30]. Alternatively, this kind of model could be used for process optimization.…”

“…Isoconversion analysis was first to be performed. This allows us to calculate the activation energy without knowing the reaction model [30]. Results of TGA analysis for the maize and oat straws are shown in The torrefaction process was conducted in a resistance electric oven PR-45/1350M in a carbon dioxide atmosphere.…”

“…Isoconversion analysis was first to be performed. This allows us to calculate the activation energy without knowing the reaction model [30]. Results of TGA analysis for the maize and oat straws are shown in After performing TGA analysis on maize and oat straws using 3 heating ratios, 5, 10, and 20 K/min the kinetic analysis was done using NETZSCH Kinetics Software.…”

Torrefaction of oat straw to use as solid biofuel, an additive to organic fertilizers for agriculture purposes and activated carbon – TGA analysis, kinetics

“…In addition, it can be seen that oat straw torrefaction process at this temperature range of 250-350°C has enhanced the solid biofuel qualities of maize and oat straws by the decrease of the O/C ratio and the increase of HHV [16][17][18]. It was concluded that kinetic analysis methods using multiple heating rate experiments are more efficient compared to the use of a single heating rate [19][20]. The best fit for the experimental data for the oat straw sample was obtained for the n-order reaction model for n = 3.4235.…”

Toward an Efficient and Sustainable Use of Energy in Industries and Cities

“…The topic of the different possible utilisation of biomass for the reduction of primary energy consumption is also diffusely investigated in this SI. Pawlak-Kruczek et al [119] analyse gasification and torrefaction processes. In particular, they focus on sewage sludge that is a residue of wastewater processing.…”