Effect of biomass ash on preventing aromatization of olefinic cracking products in dual fluidized bed systems

Abstract

In this work, the effect of ash activated olivine on olefinic products cracking and aromatization was assessed. The experiments were carried out in the Chalmers 2–4 MWth dual fluidized bed gasifier, where the feedstock was cracked using steam as fluidization agent, at a reaction temperature of ca. 780–790 °C. Three activation states of the olivine, representing three consecutive days of the campaign, were evaluated. The changes of the permanent gas composition along with the reduction in aromatic species with the time of exposure to biomass ash demonstrate a clear effect of the ash activated olivine on the conversion of olefinic cracking products. The ash activation of the olivine clearly promoted the reactions involving steam. As a consequence, higher yields of permanent gases, mainly H2, CO and CO2, were produced at expenses of the yields of the total aromatic compounds and C4 hydrocarbons and larger. It is concluded that the biomass ash activated olivine promotes the steam reforming path of the C4 and larger hydrocarbon fragments, while avoiding the alternative aromatization route. The results presented here provide useful insights on the opportunities and limitations of ash activated materials in DFB systems when steam cracking linear hydrocarbon feedstocks, e.g., polyolefin-based materials.