Size-Segregated Particulate Matter from Gasification of Bulgarian Agro-Forest Biomass Residue

• Main Authors: Ricardo Ferreira, Tsvetelina Petrova, Ana F. Ferreira, Mário Costa, Iliyana Inaydenova, Stela Atanasova-Vladimirova, Bogdan Ranguelov
• Format: Article
• Language: English
• Published: MDPI AG 2021-01-01
• Series: Energies
• Subjects: gasification; rapeseed; sunflower husk; softwood; particulate matter; syngas
• Online Access: https://www.mdpi.com/1996-1073/14/2/385

The main purpose of the present work was to evaluate the efficiency of the gasification process of three different types of agro-forest biomass residue (rapeseed, softwood, and sunflower husks) along with the characterization of size-segregated particulates’ emissions. The experiments were carried out in a drop tube furnace (DTF), using two different gasifying agents (O₂/N₂ and O₂/N₂/CO₂) at atmospheric pressure and a constant temperature of 1000 °C. In focus was the effect of biomass and the gasifying agent on syngas composition (CO, H₂, CH_4, and CO₂), cold gas and carbon conversion efficiency, and on the emissions of by-products, such as particulate matter (PM), known for having negative environmental and health impacts. The collected particulates were characterized by SEM/EDS and XPS analysis. The results reveal that: (i) the introduction of CO₂increased the production of CO and CH₄ and syngas’ lower heating value (LHV), thus leading to higher cold gas and carbon conversion efficiency; (ii) CO₂ decreased the production of H₂, leading to lower H₂/CO ratio (between 0.25 and 0.9). Therefore, the generated syngas is suitable for the synthesis of higher hydrocarbons, (iii) CO₂ lowered the emissions of char (cyclone) particles but increased the overall PM_10–0.3. Submicron size PM was the dominant fraction (PM_1–0.3) in O₂/N₂ and (PM_1.6–0.3) in O₂/N₂/CO₂. Unimodal PM size distribution was observed, except for sunflower husks gasification in O₂/N₂/CO₂; (iv) the SEM/EDS and XPS analysis confirmed that submicron-sized PM_1–0.3 contain above 80% of carbon associated to soot, due to incomplete oxidation, whereas in cyclone (char) particles, carbon decreased to about 50%. The SEM/EDS results showed that K and Cl are typical constituents of the submicron size PM, whereas the alkaline earth metals were detected mainly in fine and coarse particulates. Detailed analysis of the XPS (C1s) spectra showed that the most common oxygen-containing groups on the PM₁ surface were carbonyl and carboxyl.