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Table 2 Essential feedstock and solid fuel characteristic

From: Densification of agro-residues for sustainable energy generation: an overview

Classification Properties Descriptions Methods/equations/equipment References
Physical Bulk densitya Density of feedstock. It influences the economics of storage collection and transportation Ratio of measured mass (using any analytical balance) and calculated volume of feedstock Lestari et al. (2017), Goulart and Maia (2013), Zhang et al. (2012)
Green densityb The density of the solid fuel immediately after ejection from the mold Ratio of mass to volume; measuring the mass and calculating the volume of the briquettes/pellet Oladeji et al. (2016), Lestari et al. (2017), Goulart and Maia (2013)
Relaxed densityb The density of the solid fuel after drying. It is the density of the fuel when it had achieved a stable weight Ratio of mass to volume of the briquettes/pellet Oladeji et al. (2016), Lestari et al. (2017), Goulart and Maia (2013)
Water-resistance/porosity index (PI)b The quantity of water the fuel will be able to absorb when exposed to a humid environment. Porosity affects the heat and mass transfer, airflow velocity, which in turn influences the heat conductivity, conversion efficiency, emissions and burning rate It is calculated using the following expression:
\({\mathrm{PI}}= \frac{\mathrm{MW}}{\mathrm{MF}}\times 100\) (1)
where \({\mathrm{MW}}\) is the mass of water absorbed while \({\mathrm{MF}}\) is the mass of fuel sample
Tuates et al. (2016b), Oyelaran and Tudunwada (2015), Zhang et al. (2012)
Particle distributiona The particle size distribution influence the heat, diffusion, flowability, bonding and reaction rate It is determined by performing sieve analysis Tuates et al. (2016b), Zhang et al. (2012)
Mechanical Compressive strengthb Measure the resistance of the solid fuel to squeezing and pressing forces It can be determined using universal testing machine (UTM) in accordance with established standards Paper and Luttrell (2012)
Durability/shatter indexb Measure the degree of fuel breakage and shattering tendency under sudden forces It can be determined by performing a drop test. Fuel with known weight and dimensions would be dropped on the concrete floor from a height of 1 m
Calculate the shatter index (SI) after 4 drops
\(\% {\text {weight loss}}= \frac{{w}_{1}-{w}_{2}}{{w}_{1}}\) (2)
\({\mathrm{SI}}=100-\% {\text{weight loss}}\)
\({w}_{1}\) and \({w}_{2}\) are the weight of the fuel before and after shattering, respectively
Paper and Luttrell (2012)
Impact/attrition resistanceb Measure the resistance of the solid fuel to impact and grinding forces Tumbler could be employed to determine attrition resistance. A fuel of known weight is placed in a tumbler rotating at about 12 revolutions per minute for about 4 min. After the tumbling process, fuels are taken out and weighed. The expression used for the shatter resistance will be adopted to calculate the abrasive resistance Paper and Luttrell (2012)
Combustion/thermal Proximate analysisa This analysis will reveal the feedstock moisture (MC), volatile matter (VM), ash (AC), and fixed carbon (FC) contents The MC, VM, AC, FC can be determined following the procedures of ASTM E1871-82 (2006), E872-82 (2006) E1755-01 (2007) and E1756-08 (2008), respectively Ikelle et al. (2014), Ajimotokan et al. (2019b), Chou et al. (2009), Young and Khennas (2003), Ghaffar et al. (2015), Shuma and Madyira (2019)
Thermogravimetric analyses (TGA)a Provide information on the thermal breakdown profile of feedstock. It measures the fuel percentage weight loss as a function of temperature and presents a peculiar shape as the resulting thermogram for fuel materials Determine using thermogravimetric analyzer Raj, et al. (2015), Anukam et al. (2017)
Calorific valuea Reveals the feedstock energy potential It is determined using bomb calorimeter or calculated from the results of proximate and ultimate analyses Ikelle et al. (2014), Ghaffar et al. (2015), Shuma and Madyira (2019), Djatkov et al. (2018)
Energy density/thermal efficiencyc Describe the amount of energy stored per unit volume. Thermal efficiency is the percentage of fuel energy available for power generation It is usually measured by performing a water boiling test Odusote and Muraina (2017)
  Ignition timec Ignition time is the average time taken to achieve steady glowing fire while burning the fuel Fuel ignition time is determined by burning a known quantity of the fuel in a charcoal stove Oyelaran and Tudunwada (2015), Odusote and Muraina (2017)
Combustion rate (CR)c It is the time taken to burn a known mass of fuel completely \({\mathrm{CR}}= \frac{\text{Total mass of burnt sample}}{\text{burning time}}\)(3) Oyelaran and Tudunwada 2015, Odusote and Muraina (2017)
Chemical Ultimate analysisa Reveal the contents of hydrogen, nitrogen, sulfur, chlorine, oxygen, and carbon in the feedstock Hydrogen, nitrogen, and carbon may be determined using an elemental analyzer, while sulfur may be determined using an atomic emission spectrometer Thulu et al. (2016), Lestari et al. (2017), Gado et al. (2013)
Chemical bonds and constituents and crystalline nature of feedstocka Estimate the quality and quantity of the chemical constituents and crystalline nature of feedstock used for fuel production. Identification of the chemical bonds in the molecule and generate an infrared retention range of the compounds These can be determine using Fourier transform spectroscopy (FTIR) Onukak et al. (2017), Raj, et al. (2015), Anukam et al. (2017)
Analysis of surface morphologyb It is used in portraying and distinguishing minerals and material formed together with surface components. SEM is used for viewing the surface morphology solid fuel to establish the suitability of fuel for a given application Scanning electron microscope (SEM) Promdee et al. (2017), Onukak et al. (2017)
Elemental compositiona Used for quantitative and qualitative determination of elemental composition feedstock X-ray fluorescence Promdee et al. (2017)
  1. aCharacteristic of biomass feedstock
  2. bCharacteristic of densification product
  3. cCharacteristic of both biomass feedstock and densification product