Improving supercritical water gasification of sludge by oil palm empty fruit bunch addition: Promotion of syngas production and heavy metal stabilization

The co-gasification of sewage sludge and palm oil empty fruit bunch(EFB) in supercritical water(SCW) was conducted at 400 °C with a pressure of over 25 MPa. This study aimed to investigate the influence of EFB addition on the syngas production and its composition. The heavy metal distribution and the leaching potential of the solid residue were also assessed. The results showed that syngas yield significantly increased with the addition of EFB into the feedstock. The cold gas efficiency(CGE) and carbon efficiency(CE) of co-gasification were higher than those of individual gasification. The actual syngas production from co-gasification of sludge and EFB was 45% higher than the theoretical total volume. The results indicated that the addition of EFB to sludge had the synergetic promotion effect on syngas production from sludge and EFB in supercritical water. This enhancement might be due to the dissolution of alkali metals from EFB and the adjustment of organic ratio. In addition, higher percentage of heavy metals were deposited and stabilized in the solid residue after SCWG. The leaching concentration of heavy metals from the solid residues was decreased to a level below the standard limit which enables it to be safely disposed of in landfill. In conclusion, the EFB addition has been proved to promote syngas production,as well as, stabilize the heavy metal in solid residues during co-SCWG.

Biochar and pyrolytic gas properties from pyrolysis of simulated municipal solid waste(SMSW)under pyrolytic gas atmosphere

Municipal Solid Waste(MSW)was converted into high-grade solid fuels(biochar)and gaseous product via thermal pyrolysis under pyrolytic gas atmosphere.The experiment was carried out in a packed-bed reactor at the temperature range of 600-800℃ in both atmospheres of N_(2) and pyrolytic gas.Gas,liquid,and solid products were analyzed by gas chromatograph and elemental analysis.Amount of biochar obtained from both atmospheres were not significantly different.CH_(4) and CO_(2) in pyrolytic gas promoted the release of volatile in the MSW,resulting in lower ratio of VM/FC,ca.0.13.The atomic ratios of O/C and H/C were around 0.02-0.11 and 0.005-0.035,respectively.These values were equivalent to anthracite coal type.On the other hand,the liquid fuel yield under pyrolytic gas condition was found to be higher,compared with that under N_(2) condition.In addition,the enhancement of H_(2) and CO production was accompanied by the decrease in CH_(4) and CO_(2) output.Overall,the operating condition at 800℃ or higher with reaction times longer than 4 min were recommended for production of biochar with fuel qualities approaching anthracite coal.