Biomass
Characterization
Prof. Shushil Kumar
Characterization of Biomass
Structural composition
• Biomass contains varying amounts of cellulose, hemicellulose,
lignin, and small amounts of lipids, proteins, simple sugars, and
starches.
• Biomass also contains inorganic constituents and a fraction of
water.
• Among these compounds, cellulose, hemicellulose, and lignin
are the three main constituents.
• The structural analysis of biomass is particularly important in
the development of processes for producing other fuels and
chemicals and in the study of combustion phenomenon.
• https://www.sciencedirect.com/science/article/pii/S136403211
1000578
Structural composition
Proximate analysis
• A crucial method for characterizing biomass
• It provides detailed information on moisture, volatile matter, fixed
carbon, and ash content.
• Understanding these parameters helps in comparing different biomass
types and determining the best methods for their utilization or
pretreatment to enhance efficiency.
• Essential for comparing fuels, guiding industrial decisions, and
facilitating the use of agroforestry residues that might otherwise be
discarded.
Moisture
• Evaluated by following the ASTM E871-82 standard
• A sample was put into a preweighed ceramic crucible
and placed in an oven at a temperature of 105 °C for 2
h. The samples were reweighed after cooling.
• 𝑀𝑜𝑠𝑖𝑡𝑢𝑟𝑒 𝑐𝑜𝑛𝑡𝑒𝑛𝑡 =
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒−𝑀𝑎𝑠𝑠 𝑜𝑓𝑑𝑟𝑖𝑒𝑑 𝑠𝑎𝑚𝑝𝑙𝑒
𝑥100 %
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒
• Moisture affects combustion efficiency
• High moisture content lowers the calorific value by
requiring additional energy to evaporate the water
before effective combustion can occur.
Volatile matter (VM)
• Refers to the gases released during the
initial stages of combustion and is directly
linked to the fuel's ease of ignition and
combustion stability
• A higher VMC generally indicates that the fuel
is easier to ignite and requires less energy for
ignition.
• However, fuels with higher VMC emit less heat,
as a significant portion of their mass is
released as volatiles.
Volatile matter (VM)
• The conversion of the volatile fraction in biomass into
gaseous species begins at around 225 to 300 °C and is
mostly complete by 500 to 600 °C
• Before combustion, biomass undergoes an initial stage of
instantaneous pyrolysis and gasification, during which the
volatile matter is released
• Volatile matter constitutes a significant portion of biomass,
making its calculation crucial
Volatile matter (VM)
Proximate analysis in biomass: Standards, applications and key characteristics,Results in Chemistry, Volume 12, 2024,101886,
Volatile matter (VM)
𝑉𝑜𝑙𝑎𝑡𝑖𝑙𝑒 𝑚𝑎𝑡𝑡𝑒𝑟
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝑑𝑟𝑦 𝑠𝑎𝑚𝑝𝑙𝑒 − 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑓𝑖𝑛𝑎𝑙 𝑠𝑎𝑚𝑝𝑙𝑒
= 𝑥100 %
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝑠𝑎𝑚𝑝𝑙𝑒
Fixed carbon
• The portion of the fuel remaining after moisture and
volatiles have been removed.
• Fixed carbon refers to the carbon content of
biomass, not as pure carbon, but as part of organic
compounds formed with other elements.
• Closely linked to the calorific value and serves as a
key indicator of the biomass's energy potential.
• The amount and quality of fixed carbon impact
combustion efficiency, with biomass high in fixed
carbon being more effective at heat production.
Fixed carbon
• In gasification, fixed carbon plays a crucial role as it represents the fraction
of biomass carbon that does not volatilize during the process.
• This fixed carbon is vital for syngas production, providing the raw material
for carbon monoxide and hydrogen, the main components of syngas.
• The amount and composition of fixed carbon can affect the process’s
efficiency, as well as the quality and quantity of the gas produced
• In pyrolysis, fixed carbon is critical in determining the products formed
during this thermal transformation.
• The thermal decomposition of fixed carbon produces gases, liquids, and
residual char.
Fixed carbon
• During torrefaction, fixed carbon helps transform biomass into a
torrefied product with enhanced properties.
• As fixed carbon stabilizes and the proportion of volatile elements
decreases, the resulting product has a higher energy content and
greater chemical stability.
• The fixed carbon content influences the extent of torrefaction and the
final properties of the product, such as carbon content, bulk density,
and combustion characteristics.
Fixed carbon
• Fixed carbon is the solid fuel portion of biomass, and most standards,
such as ASTM D Standard 3172–73,
• Calculated by subtracting the ash, volatile matter, and moisture content
from the Initial weight of the biomass sample
• 𝐹𝑖𝑥𝑒𝑑 𝑐𝑎𝑟𝑏𝑜𝑛 = 100 − 𝑚𝑜𝑖𝑠𝑡𝑢𝑟𝑒 % + 𝑣𝑜𝑙𝑎𝑡𝑖𝑙𝑒 𝑚𝑎𝑡𝑡𝑒𝑟% + 𝑎𝑠ℎ %
Ash
• Ash, the inorganic residue left after combustion
• Ash-forming constituents include elements such as Si, Ca,
Mg, K, Na, P, S, Cl, Al, Fe, Mn, as well as heavy metals (e.g.,
Cu, Zn, Co, Mo, As, Ni, Cr, Pb, Cd, V, Hg) and nitrogen.
• One of the primary challenges with using biomass as a fuel
is the corrosive nature of the resulting ash, which tends to
damage furnaces and boilers.
• These ashes can clog burners and reduce heat transfer in
boilers, thereby lowering efficiency
• These issues, make biomass with low ash content highly
desirable.
• The ash content of woody biomass is typically 1.5–2 %.
Ash
• These inorganic elements influence the combustion process by contributing
to gaseous and solid emissions, and by significantly affecting ash melting
behavior
• Ash can act as either a catalyst or an inhibitor in pyrolysis reactions, directly
affecting the composition and yield of liquid, gaseous, and solid products.
• The quantity and composition of ash can influence the formation of
undesirable by-products, such as tars and harmful gases, which require
management strategies to minimize their environmental impact
• Uses for ash: fertilizer or as a component in the cement industry
Ash
• ASTM E1755–01 standard
• Sample kept into preweighed ceramic crucibles before subjecting it to a
temperature of 730 °C for 5 h in a muffle furnace.
• The crucible lids were taken off before being placed in the furnace to
ensure clean/complete combustion.
• The samples were cooled for an hour. The ash mass was then evaluated
using below equation.
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑟𝑒𝑠𝑖𝑑𝑢𝑒 𝑙𝑒𝑓𝑡 𝑎𝑓𝑡𝑒𝑟 𝑐𝑜𝑚𝑏𝑢𝑠𝑡𝑖𝑜𝑛
• 𝐴𝑠ℎ 𝑐𝑜𝑛𝑡𝑒𝑛𝑡 = 𝑥100
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝑠𝑎𝑚𝑝𝑙𝑒
Ash
• https://www.sciencedirect.com/science/article/pii/S1364032111000578
Ash analysis
• The composition of biomass ash is strongly dependent on the species
and part of the biomass plant.
• The available nutrients, soil quality, fertilizers and weather conditions
have significant impact on the contents of potassium, sodium, chlorine
and phosphorus especially in agro-biomass ashes.
• Generally, biomass fuels can be divided into three groups on the basis of
their ash composition:
Ash analysis
• Biomasses with Ca, K rich and Si lean ash
• Generally the ash of woody biomass is typically rich in calcium (Ca)
and potassium (K),
Ash analysis
• Biomasses with Si rich and Ca, K lean ash
• Agricultural biomass e.g. Straw, Rice husk, bagasse
Ash analysis
• Biomasses with Ca, K and P rich ash
• Sunflower stalk, rapeseed expeller
Ash analysis
Ultimate analysis
• Ultimate analysis or elemental analysis (CHNS) is determined by a CHNS analyzer
• The CHNS Analyzer determine the percentages of Carbon, Hydrogen, Nitrogen,
Sulphur and Oxygen of organic compounds, based on the principle of "Dumas
method" which involves the complete and instantaneous oxidation of the
sample by "flash combustion".
• The combustion products (NO2,CO2, SO2, and H2O) are separated by a
chromatographic column and detected by the thermal conductivity detector
(T.C.D.), which gives an output signal proportional to the concentration of the
individual components of the mixture.
Ultimate analysis
• For analysis product gas mixture flows through
a silica tube packed with copper granules.
• This zone is held at about 500°C, and the
remaining oxygen is trapped inside, and
nitric/nitrous oxides are reduced. The leaving
gas stream includes the analytically important
species CO2, H2O and N2. Eventually SO2 is
absorbed at appropriate traps.
Ultimate analysis
• It helps to assess the percentage of N, and S to study the environmental
impact of biomass.
• It helps to estimate the heating value
https://www.sciencedirect.com/science/article/pii/S1364032111000578
Ultimate analysis
Calorific value
Heating value (or calorific value):
• It is the amount of heat released during the combustion of a specified amount of
it.
• It is measured in units of energy per unit of the substance, usually mass, such as:
kJ/kg, kJ/mol, kcal/kg, Btu/lb.
Higher heating value(HHV) or Gross calorific value (GCV):
• It is determined by bringing all the products of combustion back to the original
pre-combustion temperature, and in particular condensing any vapor produced.
Such measurements often use a standard temperature of 15 °C (59 °F; 288 K).
Calorific value
Lower heating value (LHV or LCV) or Net calorific value (NCV):
• It is determined by subtracting the heat of vaporization of the water
vapor from the higher heating value.
• This treats any H2O formed as a vapor. The energy required to vaporize
the water therefore is not released as heat.
A common method of relating HHV Where
Hv = Heat of vaporization of water
to LHV is:
nH2O,out = moles of water vaporised
n, fuel = number of moles of fuel
HHV = LHV + HV(nH2O, out/ n, fuel) combusted
Calorific value
Determination of heating value of solid and
liquid fuel
• A known amount of solid fuel is burnt in a
bomb.
• The generated heat is used to raise the
temperature of a certain volume of water kept
in a bucket.
• Heat gained by the water is equivalent to the
heat released by the fuel.
Calorific value
• Estimating the higher heating value of biomass
Calorific value
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Thermogravimetric analysis (TGA)
• For studying the thermal degradation behavior and composition of
biomass.
• Involves heating the biomass sample under a controlled atmosphere
(inert or oxidative) and monitoring its weight loss as a function of
temperature or time.
• Typical temperature range used is 40–900 °C, using various heating rates
• A constant flow rate of pure nitrogen gas for an inert atmosphere.
• Oxygen can be used for oxidative degradation.
Thermogravimetric analysis
• Moisture Content:
• Temperature Range: 25–150°C.
• Initial weight loss due to the evaporation of moisture.
• Volatile Matter:
• Temperature Range: 150–500°C.
• Represents the release of gaseous compounds (e.g., CO, CO₂, CH₄, and other light hydrocarbons) due to
the thermal decomposition of hemicellulose, cellulose, and lignin.
• Fixed Carbon:
• The weight remaining after the release of volatiles, excluding ash.
• Ash Content:
• Residual weight at the end of the analysis, typically at 600–900°C (under an oxidative
atmosphere).Indicates inorganic mineral content.
Thermogravimetric analysis
Biomass Component Degradation
• Hemicellulose:
• Decomposes in the temperature range of 200–320°C.Rapid release of volatiles.
• Cellulose:
• Decomposes in the range of 320–400°C.
• Sharp weight loss due to pyrolysis.
• Lignin:
• Decomposes slowly over a broad range of 200–900°C.
• Contributes to char formation.
Thermogravimetric analysis
• Typical TGA and DTG diagram of biomass in nitrogen atmosphere
Thermogravimetric characterization of wood stalks as gasification and pyrolysis feedstock. Recent Advances in Bioenergy Research Volume III
Thermogravimetric analysis
• Typical TGA and DTG diagram of biomass in air atmosphere
Thermogravimetric characterization of wood stalks as gasification and pyrolysis feedstock. Recent Advances in Bioenergy Research Volume III
Applications of TGA Analysis in
Biomass Research
• Characterizing Thermal Behavior:
• Understanding the decomposition profile of biomass for pyrolysis, gasification, or combustion
applications.
• Optimization of Biomass Conversion:
• Determining suitable temperature ranges for processes like liquefaction, torrefaction, and biochar
production.
• Feedstock Comparison:
• Evaluating the thermal stability and compositional differences between various types of biomass.
• Kinetic Analysis:
• Estimating activation energy and reaction kinetics for the thermal degradation of biomass.
• Ash Analysis:
Van Krevelen plot
• The derivative of Van Krevelen Plot was drawn against the atomic ratio
of Hydrogen (H): Carbon(C) to Oxygen (O): Carbon (C).
Fourier Transform Infrared (FTIR)
Spectroscopy
• Utilized in identifying functional groups present in the samples.
• Based on the interaction of infrared radiation with a sample, measuring
the frequencies at which the sample absorbs IR light.
• The spectra are collected within the range of 400–4000 cm−1 wave
numbers.
Fourier Transform Infrared (FTIR)
Spectroscopy
Key regions:
• Functional Group Region (4000–1500 cm⁻¹):
• Contains sharp peaks indicating specific functional groups. Example: O-H (3200–3600
cm⁻¹), C-H (2800–3000 cm⁻¹), C≡C or C≡N (2100–2300 cm⁻¹).
• Fingerprint Region (1500–400 cm⁻¹):
• Complex pattern unique to each molecule, used for identification.
Fourier Transform Infrared (FTIR)
Spectroscopy
• X-axis: Wavenumber (cm⁻¹), inversely proportional to wavelength.
• Y-axis: Transmittance (%) or Absorbance.
• https://chem.libretexts.org/Ancillary_Materials/R
eference/Reference_Tables/Spectroscopic_Refe
rence_Tables/Infrared_Spectroscopy_Absorption
_Table
XRD
• Used to determine crystalline and amorphour nature of sample
• The scan speed of angle 2θ ranges from 10°–40° at a speed of 1°/min.
• The crystalline indices (CrI) of the biomass sample can be calculated as
follows
where I002 is the intensity of at 2θ = 20 for crystalline portion (cellulose)
and Iamorphous is the peak at 2θ = 16.6 for the amorphous portion (cellulose,
hemicellulose, and lignin).
