Young Nam Chun*, Seong Cheon Kim and Kunio Yoshikawa
The Journal of Mechanical Science and Technology, vol. 26, no. 1, pp.241-250, 2012

Abstract : For energy and resource utilization of dried sewage sludge, an integrated system with in-line connection of pyrolysis gasifier, plasma reformer, and fixed bed adsorber was developed. The plasma reformer was set to improve producer gas yield by destructing tar released from the pyrolysis gasifier. The fixed bed adsorber filled with the sludge char produced from the pyrolysis gasifier was installed for adsorption of un-treated tar. The pyrolysis gasifier produced sludge char, tar and gas. The sludge char showed 98.1 m2/g of specific surface area and 63.49 Å of mean pore size, which had a good distribution of micropore and mesopore with superior adsorption rate of light PAH tar. The concentrations of gravimetric tar and total light tar were 26.3 g/Nm3 and 10.9 g/Nm3, respectively. The analyzed light tar was in the order of benzene, naphthalene, benzonitrile, benzeneacetonitrile, anthracene and pyrene. Produced gas was composed of hydrogen, carbon monoxide, methane, and carbon dioxide. The plasma reformer displayed 83.2% of removal efficiency with 4.4 g/Nm3 of gravimetric tar at the outlet due to tar cracking and steam reforming reaction. The total amount of light tar was 1.3 g/Nm3. Among the reforming gas, the concentration of hydrogen, carbon monoxide, and methane was increased. Gravimetric tar at the outlet of the adsorber was 0.5 g/Nm3, which was 88.6% of removal efficiency. The total amount of light tar was 0.39 g/Nm3. Gas analysis results at the exit showed 50.5% H2, 21.9% CO, 10.5% CH4, 7.7% CO2 and 0.1% C2H2 with a higher heating value of 13,482 kJ/Nm3. Therefore, sewage sludge can be converted into energy and resource by pyrolysis and gasification since the producer gas and sludge char could be utilized in a heat engine and adsorption tower for tar removal, respectively.

Keyword : Pyrolysis gasification; Sewage sludge; Sludge char; Produced gas; Tar generation