Aenert. Research Laboratory news
Replacing fossil fuels with more sustainable products derived from biomass has been widely considered as an option to mitigate climate change as well as counteract future fuel shortages caused by dwindling fossil resources. As opposed to traditional fuels such as coal, natural gas and petroleum, biomass fuel is carbon-neutral, sustainable and has manageable pollutant emissions. However, its low density, high moisture absorption, and comparatively low heating values of biomass hamper efficient transportation, conversion, and combustion of biomass as solid fuels. To enhance both the volumetric density and energy density of biomass, densification such as briquetting and pelletizing is required. In this area, the use of plastics might help. Their good flowability, tensile strength, and hydrophobicity of plastics make them ideal binders for biomass and coal densification. However, the pollution caused by plastic wastes combustion has been widely considered as a problem.

Now (2023), scientists at University of Kentucky Research Foundation (Lexington, KY) have started a project where they will use a thermogravimetric analysis-mass spectrometer (TGA-MS), pyro-gas chromatography GC-MS, 1.5” drop tube furnace, 1 ton per day (TPD) coal gasifier, and a high-pressure extruder/pelletizer operated at University of Kentucky – Center for Applied Energy Research (UK CAER) to develop and study a coal/biomass/plastic blend fuel. The research is aimed at producing hydrophobic layer encapsulated biomass suitable for slurry with solid content greater than or equal to 60 wt% of blended coal/biomass and plastic suitable for oxygen-blown entrained flow gasification, complete lab-scale kinetic and gasification studies on the blended fuel as well as demonstrating practical operations in the commercially relevant, UK CAER 1 TPD entrained flow gasifier. As soon as a suitable production process and operating parameters have been stablished, 600 kilograms of pine wood-plastic fuel with and without coal will be analysed to determine grindability, slurryability, and slurry stability with a view to different gasification kinetics between plastic/biomass and coal. Ash and slag from the blended solid fuel will be studied to determine the gasification behaviour as well as fusion temperatures, chemical and mineral content, viscosity and potential interaction with the refractory. During the final gasification campaign, gasifier performance and the raw syngas composition will be measured, including the presence of species requiring removal, or that can be recovered for beneficial use.

Scientists have long tried to improve the properties of biofuels. In 2015, the effect of fuel composition on gasification process performance was anaylsed by carrying out mass and energy balances on a bubbling fluidized bed reactor containing mixtures of plastic waste, wood, and coal. The fuels containing plastic waste were found to produce less H₂, CO, and CO₂ and more light hydrocarbons than the fuels including biomass. The lower heating value (LHV) progressively increased from 5.1 to 7.9 MJ/Nm³ when the plastic waste was added. Higher carbonaceous fines production was associated with the fuel containing a large fraction of coal (60%). However, plastic waste gasification was found to produce the highest tar yield, 161.9 g/kgFuel, while woody biomass generated only 13.4 g/kgFuel. Wood gasification showed a carbon conversion efficiency (CCE) of 0.93. The tests with two fuels containing coal showed lowest CCE values. Plastic waste and wood gasification had similar cold gas efficiency (CGE) values (0.75 and 0.76, respectively), while that obtained during the co-gasification tests varied from 0.53 to 0.73.

Image: Schematic illustration of the pre-pilot bubbling fluidized bed gasifier



Source: Lucio Zaccariello, Maria Laura Mastellone/ Fluidized-Bed Gasification of Plastic Waste, Wood, and Their Blends with Coal/ Energies 2015(8):8052-8068, August 2015/ DOI: 10.3390/en8088052/ Open Source This is an Open Access article is distributed under the terms of the Attribution 4.0 International (CC BY 4.0)

In 2020, the characteristics of oil palm trunk and oil palm frond biomass were investigated for use as feedstock in thermochemical processes like gasification, pyrolysis, and combustion. The analysis carried out included: ultimate (CHNSO) and proximate (thermogravimetric) analysis, calorific value, field emission scanning electron microscopy (FESEM) and x-ray fluorescence (XRF). Both feedstocks exhibited potential for use as fuel in biomass thermochemical conversion. The CHNSO analysis showed the presence of sufficient carbon, hydrogen and oxygen elements in both feedstocks. The percentages of nitrogen and sulphur which need to be low in a fuel to be efficient were also obtained in low quantities for both fuels. The thermogravimetric analysis revealed that both feedstocks had high volatile matter 62.28%. Meanwhile, sufficient fixed carbon content of 26.18% in OPT and 25.68% in OPF with low ash content of 9.82% in OPT and 6.32% in OPF were found in the analysis. The EDX graph showed that carbon and oxygen were present in a higher amount while in the XRF analysis CaO and K₂O were found to be the major oxides present in both OPT and OPF, with a low amount of SiO making the feedstocks less prone to agglomeration during thermochemical conversion.

Image: Images of (a) oil palm frond and (b) oil palm trunk in drying process.



Source: Hadiza Aminu Umar, Shaharin Anwar Sulaiman, Shaharin Anwar Sulaiman, s. N.A. Tamili/ Characterisation of oil palm trunk and frond as fuel for biomass thermochemical/ IOP Conference Series Materials Science and Engineering 863(1), June 2020/ DOI: 10.1088/1757-899X/863/1/012011/ Open Source This is an Open Access article is distributed under the terms of the Attribution 3.0 Unported (CC BY 3.0)

There are many benefits to adding plastics to the biofuel blend: The efforts to generate experience for co-gasification of mixed solid feedstocks like biomass, coal, and carbonaceous mixed wastes such as plastics and municipal solid waste can make an important contribution to the advancement of clean hydrogen technologies. The data and experience provided in these projects facilitates the integration of pre-combustion carbon capture and storage (CCS) into gasification processes. Including biomass in the blended feedstock, the integration of CCS enables net-zero or net-negative carbon emissions. Similarly, blending other waste materials into the feedstock makes site remediation possible which promotes environmental justice that is needed in many communities around the world. Advancing co-gasification of blended feedstocks is important for reducing and eliminating carbon emissions from the electricity sector.

In view of the large amounts of plastic waste reaching landfills every day and the high fuel demands around the world, the utilization of plastics in fuel blends with biological feedstock can be a valuable contribution to reducing greenhouse gas emissions and waste.

By the Editorial Board