The influence of temperature and steam on the yields of tar and light hydrocarbon compounds during devolatilization of dried sewage sludge in a fluidized bed

The influence of temperature and steam concentration over the yields of tar and light hydrocarbon compounds generated during devolatilization of batches of dried sewage sludge in a laboratory fluidized bed reactor was investigated. Tests were conducted in the temperature range of 600–900 °C with gas residence time of 1.5 s. Thirty-six aromatic tar compounds (from benzene to perylene) were analyzed by GC/MS and light hydrocarbons (CH4, C2H6, C2H4, C2H2, C3H8 and C3H6) by GC/thermal conductivity. The content of C, H, N and S in the gravimetric residue of the tar sample (that obtained after vacuum distillation of the original sample) was also analyzed. It was found that increasing the steam concentration (up to 30% molar) did neither modify the aromatic tar composition nor the yield of light hydrocarbons, only slightly affecting the yield of gravimetric tar. Detailed analyses of tar composition and light hydrocarbons enabled us to relate the yields of these compounds at different temperatures, shedding light on the mechanisms of tar conversion into light hydrocarbon species. It also provides shortcut methods for the estimation of tar mixture properties, such as the yields of heavy aromatic compounds and the aromaticity of the tar mixture, from light hydrocarbon measurements at different temperatures.