Abstract
Melina wood torrefied at 260 °C for 60 min was agglomerated with lean grade coal fines into composite briquettes using pitch as binder. Torrefied biomass (3%–20%) and coal fines (80%–97%) were blended together to produce the composite briquettes under a hydraulic press (28 MPa). The briquettes were cured at 300 °C. Density, water resistance, drop to fracture, impact resistance, and cold crushing strength were evaluated for the composite briquettes. The proximate, ultimate, and calorific value analyses were carried out according to different ASTM standards. Microstructural studies were carried out using scanning electron microscope and electron probe microanalyzer equipped with energy dispersive x-ray. Fourier Transform Infrared Spectrophotometer (FTIR) was used to obtain the functional groups in the raw materials and briquettes. The density of the composite briquettes ranged from 0.92 to 1.31 g/cm3 after curing. Briquettes with < 10% torrefied biomass has good water resistance index (> 95%). The highest cold crushing strength of 4 MPa was obtained for briquettes produced from 97% coal fines and 3% torrefied biomass. The highest drop to fracture (54 times/2 m) and impact resistance index (1350) were obtained for the sample produced from 97% coal and 3% torrefied biomass. The fixed and elemental carbons of the briquettes showed a mild improvement compared to the raw coal. The peaks from FTIR spectra for the briquettes shows the presence of aromatic C=C bonds and phenolic OH group. The composite briquettes with up to 20% torrefied biomass can all be useful as fuel for various applications.
Highlights
Coal fines are by-products that are inevitably produced when lump lean grade coal is being processed, transported or handled (Adeleke et al 2019a)
To produce briquettes from the lean grade coal, lower temperature range where the weight loss will be limited to bounded moisture and light volatile losses must be employed during its curing
To have a briquette with good mechanical integrity and a stable or improved combustion properties from lean grade coal, curing in the neighborhood of 300 °C under a protected environment that is deficient of oxygen was needed (Adeleke et al 2019a)
Summary
Coal fines are by-products that are inevitably produced when lump lean grade coal is being processed, transported or handled (Adeleke et al 2019a). Biomass has low density and high moisture than coal (Adeleke et al 2020a) and this makes its combustion without any pretreatment not favorable (Lasode et al 2014) Several pretreatment techniques such as torrefaction (Bach et al 2017), carbonization (Basu 2013) and pyrolysis (Basu 2010) have been employed to upgrade biomass. Mursito and Widodo (2020) characterized bio-coal briquettes blended produced from low quality coal and biomass waste treated with GarantÒ bio-activator. There is limited study on the physicomechanical characteristic of briquettes produced from lean grade coal fines and torrefied woody biomass (melina). The present study focuses on the use of up to 20% torrefied biomass aggregated with lean grade coal fines in developing composite briquettes with good physical and mechanical properties
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