Hydrogen-rich producer gas from air- and steam-blown co-gasification of waste polypropylene pyrolysis oil and cashew nut shell in a two-stage downdraft gasifier

Abstract

The co-gasification of waste polypropylene pyrolysis oil (WPPO) and cashew nut shell (CNS) was investigated in a two-stage downdraft gasifier to produce hydrogen-rich, low-tar gas. Experiments were conducted under air (ER = 0.3) and steam (S/C = 2.5) conditions, with selected runs incorporating activated carbon (AC) in the secondary reactor. Steam gasification achieved a maximum hydrogen concentration of 77.9 vol%. The WPPO/CNS mixing ratio affected performance, with the 1:1 blend increasing CGE from 70.3 to 89.7% to 108.9% and CCE from 68.2 to 71.5% to 83.9%, along with enhanced gas yield. The use of AC reduced gas-phase tar, and a downstream dried AC impinger further decreased tar concentration to 0.45 mg/Nm3. In contrast, the composition of condensed tar showed a shift toward heavier species during steam gasification. GC–MS analysis at a WPPO/CNS ratio of 1:1 indicated that steam gasification promoted the formation of heavier PAHs due to enhanced thermal cracking and subsequent polymerization of aromatic intermediates.