Fluidised bed combustion and ash fusibility behaviour of coal and spent coffee grounds blends: CO and NOx emissions, combustion performance and agglomeration tendency

Garcia, Eduardo; Mejía, Manuel F.; Liu, Hao

Abstract

The co-combustion of coal and waste biomass is an advantageous option for combined waste biomass disposal and energy production. However, co-firing coal with waste biomass has to overcome various ash-related operational problems, for example, ash agglomeration and bed defluidisation in fluidised bed boilers. Using spent coffee grounds (SCG) for energy generation via co-combustion is much more sustainable and environmentally friendly than SCG disposal in landfills. The research done so far on the co-combustion of coal and SCG is quite scarce and almost non-existing. Further research is needed to understand how the properties of SCG affect the co-combustion of coal and SCG in existing coal-fired boilers. This study investigates the combustion of a bituminous coal blended with SCG in a pilot-scale (30kWth) bubbling fluidised bed (BFB) combustor focusing on CO and NOx emissions, combustion performance, and agglomeration tendency. The BFB combustion tests were conducted at 900 °C and atmospheric pressure using silica sand as the bed material. For comparison purposes, combustion tests of the same coal in pure and blended with wheat straw pellets at the same blending ratio were also performed. Further, ash fusibility studies were performed to elucidate the interactions between the coal ash and SCG ash, and the effect of ash compositions on the fusibility temperatures. Samples of the used bed material collected from the combustor and cyclone ash were characterised by SEM-EDS and XRF. The BFB combustion test results revealed that SCG could reduce the efficiency loss of coal combustion under co-combustion conditions. Despite the higher K2O content in SCG compared to wheat straw, a reduced agglomeration tendency was observed with the BFB combustion of the coal-SCG blends. The results from the characterisation of the used bed material, cyclone ash, and ash fusibility studies confirmed this finding, which was attributed to the formation of high melting temperatures Mg- and Ca-bearing compounds.

Citation

Garcia, E., Mejía, M. F., & Liu, H. (2022). Fluidised bed combustion and ash fusibility behaviour of coal and spent coffee grounds blends: CO and NOx emissions, combustion performance and agglomeration tendency. Fuel, 326, Article 125008. https://doi.org/10.1016/j.fuel.2022.125008

• Journal Article Type: Article
• Acceptance Date: Jun 21, 2022
• Online Publication Date: Jun 28, 2022
• Publication Date: Oct 15, 2022
• Deposit Date: Jul 6, 2022
• Publicly Available Date: Jul 6, 2022
• Journal: Fuel
• Print ISSN: 0016-2361
• Publisher: Elsevier BV
• Peer Reviewed: Peer Reviewed
• Volume: 326
• Article Number: 125008
• DOI: https://doi.org/10.1016/j.fuel.2022.125008
• Keywords: Organic Chemistry; Energy Engineering and Power Technology; Fuel Technology; General Chemical Engineering
• Public URL: https://nottingham-repository.worktribe.com/output/8851943
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S0016236122018506?via%3Dihub