Fate of phosphorus in pulverized fuel co-combustion of sewage sludge and agricultural residues. (1st March 2023)

• Record Type: Journal Article
• Authors: Häggström, Gustav; Karl Hannl, Thomas; Holmgren, Per; Broström, Markus; Skoglund, Nils; Öhman, Marcus
• Is Part Of: Fuel. Volume 335(2023)
• Publication Date: 2023-03-01
• Subjects: Sewage sludge -- Phosphorus -- Combustion -- Ash recovery -- Powder combustion -- Suspension firing; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2022.127059
• Languages: English
• ISSNs: 0016-2361

Abstract

Graphical abstract: Highlights: EFR powder combustion of sewage sludge and mixtures with agricultural residues. Melt formation on the deposition probe at both 1000 °C and 1400 °C. Precipitation of Ca-P-rich phases and Fe-oxide from the formed melts. TECs suggest that immiscible melts support formation of P-rich and Si-rich phases. <5% of fuel-P was found in particulate matter (PM1) of the flue gas precipitates. Abstract: The fate of phosphorus concerning its distribution in the thermal process and chemical speciation was studied during the co-combustion of sewage sludge with wheat straw and sunflower husks in powder combustion conditions. Co-combustion experiments were performed in a lab-scale entrained flow reactor (EFR) at 1000 °C and 1400 °C. SEM-EDS and ICP-OES analyses were used for studies of deposits collected on a probe, bottom ash, and particulate matter samples collected during experiments. Deposition probe samples were further studied and interpreted using powder X-ray diffraction (XRD) and thermochemical equilibrium calculations (TECs). The inorganic material in the different fuel particles mainly interacted through a molten phase observed on deposition probes. Crystalline P was mainly identified in β -Ca3 (PO4 )2 whitlockites. TECs support the experimental findings and suggest that a mostly homogenous melt occurs at 1400 °C, whereas Fe-oxides and Ca-phosphates precipitate during the cooling of the formed deposits. It was found that <5 % of incoming P was collected in fine particulate matter (<1 µm), indicating that the majority of P can be found in deposits and bottom ash. This outcome implies that P recovery efforts should be focused on these ash fractions.