A new method for evaluating the sewage sludge pyrolysis kinetics

Thermal decomposition of sewage sludge under N2, CO2 and air: Gas characterization and kinetic analysis

Thermochemical valorisation processes that allow energy to be recovered from sewage sludge, such as pyrolysis and gasification, have demonstrated great potential as convenient alternatives to conventional sewage sludge disposal technologies. Moreover, these processes may benefit from CO₂ recycling. Today, the scaling up of these technologies requires an advanced knowledge of the reactivity of sewage sludge and the characteristics of the products, specific to the thermochemical process. In this study the behaviour of sewage sludge during thermochemical conversion, under different atmospheres (N₂, CO₂ and air), was studied, using TGA-FTIR, in order to understand the effects of different atmospheric gases on the kinetics of degradation and on the gaseous products. The different steps observed during the solid degradation were related with the production of different gaseous compounds. A higher oxidative degree of the atmosphere surrounding the sample resulted in higher reaction rates and a shift of the degradation mechanisms to lower temperatures, especially for the mechanisms taking place at temperatures above 400 °C. Finally, a multiple first-order reaction model was proposed to compare the kinetic parameters obtained under different atmospheres. Overall, the highest activation energies were obtained for combustion. This work proves that CO₂, an intermediate oxidative atmosphere between N₂ and air, results in an intermediate behaviour (intermediate peaks in the derivative thermogravimetric curves and intermediate activation energies) during the thermochemical decomposition of sewage sludge. Overall, it can be concluded that the kinetics of these different processes require a different approach for their scaling up and specific consideration of their characteristic reaction temperatures and rates should be evaluated.

Investigation on thermochemical behavior of co-pyrolysis between oil-palm solid wastes and paper sludge

The pyrolysis characteristics of oil-palm solid wastes, paper sludge and their blends were studied via thermogravimetric analysis. Blends ranging from 10 wt.% to 90 wt.% on dosage ratio were prepared to investigate their co-pyrolysis behavior and kinetics. There was a synergistic interaction at low temperature during co-pyrolysis between oil-palm solid wastes and paper sludge. The synergistic interaction would improve thermochemical pyrolysis reactivity of the blends, which could be attributed to the hydrogenation role and the potential mineral catalytic effects on paper sludge pyrolysis. The value of average activation energy obtained by Starink and Friedmen methods did not gradually decline with the increasing proportion of oil-palm solid wastes in the blends. The lowest average activation energy was achieved when the percentage of oil-palm solid wastes was 70%, which was 152 kJ/mol by Starink and 149 kJ/mol by Friedmen, respectively.

Microwave Pyrolysis (MP) of Sewage Sludge: Profile of Bio-Fuel Production

This paper mainly focused on the characteristics of pyrolysis temperature and the bio-fuel production, and the energy recovery efficiency of sludge by MP was also explored.The results show that the final temperature of sample added carbonaceous residue (CR) is above 700°C and the maximum heating rate is up to 1.783°C/s. While the maximum heating rate of sludge with activated carbon (AC) is 1.084°C/s. The caloric value of the oil production can reach 41.57MJ/kg, and the content of PAHs is less than 4.54%. The volume fractions of H2 and CO in the gas production are higher than 54%, and the caloric values are higher than 9 540kJ/m3. The oil and gas production can use as the bio-fule.The energy of total bio-fuel obtained sample with CR is 6.99MJ/kg, and the energy recovery ratio is up to 45.63%. The MP is a potential method for the energy recovery of sludge.

Co-gasification of wet sewage sludge and forestry waste in situ steam agent

The co-gasification of wet sewage sludge (80 wt.% moisture, WSS) and forestry waste (FW) blends was studied. The thermogravimetric analysis showed that weight loss and the maximum weight loss rate of the sample increased with the increase in FW content. The co-gasification process was performed in a lab-scale fixed bed gasifier to investigate the effects of WSS content and reactor temperature on product yields, gas composition and gasification performance. The results indicated that steam generated from the moisture content in WSS took part in the gasification with char. The gas yield decreased with the increasing WSS content. And the concentrations of H(2) and CO reached the maximum when the WSS content was 50%. The LHV of fuel gas ranged from 11.89 MJ/Nm(3) to 12.72 MJ/Nm(3) when the reactor temperature increased from 700 °C to 900 °C.