2. Unit 1: Biomass overview
• Biomass characterization: Types and Resources
• Fuels from biomass
• Terms and units used in biomass production
• Biomass fuel characterization – physical, chemical and thermal –
energy release.
• Direct use of biomass as energy: Size reduction, baling, palletisation,
briquetting technologies.
3. Biomass:
• Biomass refers to the mass of living
organisms, including plants, animals,
and microorganisms, or, from a biochemical
perspective, cellulose, lignin, sugars, fats, and
proteins.
• Biomass includes both the above- and
belowground tissues of plants, for example,
leaves, twigs, branches, boles, as well as roots
of trees and rhizomes of grasses.
6. Characteristics of Biomass
1. Heating value (MJ/kg):
It indicates the total amount of energy that is available in the fuel.
Heating value is mostly a function of a fuel’s chemical composition
and can be expressed in two ways: the higher heating value (HHV)
or the lower heating value (LHV).
HHV is the total amount of heat energy that is available in the fuel,
including the energy contained in the water vapor in the exhaust
gases.
LHV does not include the energy embodied in the water vapor.
Fuel High Heating Value (MJ/kg)
Coal 20 – 30
Agricultural
residues
15 – 17
Woody materials 18 - 19
7. 2. Moisture content
High moisture fuels burn less readily and provide less useful heat per
unit mass.
On the other hand, extremely dry fuel can cause dust problems,
leading to equipment fouling and potential explosion hazards.
Moisture content can be calculated on two bases: Wet or Dry
Wet basis:
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑖𝑛 𝑡ℎ𝑒 𝑓𝑢𝑒𝑙
𝑇𝑜𝑡𝑎𝑙 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑓𝑢𝑒𝑙
Dry basis:
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑖𝑛 𝑡ℎ𝑒 𝑓𝑢𝑒𝑙
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑑𝑟𝑦 𝑝𝑜𝑟𝑡𝑖𝑜𝑛 𝑜𝑓 𝑡ℎ𝑒 𝑓𝑢𝑒𝑙
8. 3. Composition
Ash content
Susceptibility to slagging and fouling
Volatile contents
Ash content is the mass fraction of biomass composed of incombustible mineral
material.
Grasses, bark and field crops residues have much higher ash content than wood.
Slagging and fouling are problems that occur if ash begins to melt during combustion,
forming deposits on combustor surfaces (fouling) or leaving hard chunks of glassy
material in the bottom of the combustion chamber known as slag or clinkers.
Certain mineral components in biomass fuels, primarily silica, potassium, and
chlorine, can cause these problems to occur at lower temperatures than normal.
9. 4. Fuel size and Density:
The particle size and density affect the burning characteristics, namely the
rate of heating and drying during the combustion process.
Fuel particle size also dictates the type of handling equipment required.
The wrong size fuel will negatively impact combustion process efficiency
and may cause jamming or damage to the handling equipment.
Smaller-sized fuel is more common for commercial-scale systems because
smaller fuel is easier to use in automatic feed systems and allows for finer
control of the burn rate by controlling the rate at which fuel is added to the
combustion chamber.
10. Direct use of biomass as energy
1. Size Reduction:
The purpose of size reduction of biomass is to transform the material
into a form that optimizes handling, storage, transportation, and
conversion (or direct combustion).
In addition, the process produces small particles that are conducive to
pelletization, increases the bulk density of the material, and enhances
the conversion process.
Size reduction processes can be categorized as:
a) Single fracturing mechanisms such as cutting, shredding, and/or
shearing mechanisms as found in forage choppers, rotary veneer
choppers, shredders, roller grinders, and crushers.
b) multiple-fracturing milling mechanisms such as knife mills, hammer
mills, ball/rod mills, disk (attrition) mills, and ultrafine mills.
12. 2. Baling of biomass:
Baling is a process that compresses material into a block (bale) which is
secured by plastic or wire strapping. The process reduces the volume of
the material which:
a) Reduces loose waste on site
b) Reduces transportation/waste disposal costs
c) Turns waste into a revenue generating product
Benefits of baling
Space
i. Reduces space taken up by waste on site
ii. Easier to store due to regular shape
iii. Increases ease of transportation
Costs
I. Reduced storage costs
II. Lower transportation costs
III. Reduced waste disposal costs
IV. Increased revenue (some baled materials can be sold to recyclers
creating additional revenue)
13. 3. Biomass Pelletes
Biomass pellets are a popular type of biomass fuel, generally
made from wood wastes, agricultural biomass, commercial
grasses and forestry residues.
Dense cubes pellets have the flowability characteristics similar to
those of cereal grains. The regular geometry and small size of
biomass pellets allow automatic feeding with very fine
calibration.
High density of pellets also permits compact storage and rational
transport over long distance.
Pellets are extremely dense and can be produced with a low
moisture content that allows them to be burned with very high
combustion efficiency.
15. Biomass Briquetting
Briquetting is the mechanical treatment to upgrade the loose biomass
into a higher density and uniform solid fuel via compaction with resulting
product of higher density, energy content and less moisture compared to
its raw material.
16. Biomass briquetting techniques
1. Screw press
Screw extrusion briquetting machines are suitable for small-scale applications
The central hole incorporated into the briquettes produced by a screw extruder helps in better
combustion characteristics due to a larger specific area.
The briquettes produced are homogenous and do not disintegrate easily showing a higher quality
These briquettes can be produced with a density of 1200Kg/m3 from loose biomass of bulk density
100 to 200 Kg/m3 . A higher density gives the briquette of higher heat value (KJ/Kg), and makes the
briquettes burn more slowly as compared to the raw materials
17. 2. Piston Press
In this technique, the material is fed into a cylinder, compressed by a piston into a slightly tapering die.
Then the compressed material is heated by frictional forces as it is pushed through the die either
mechanically by a reciprocating ram powered by a massive flywheel, or by a hydraulically driven
piston.
The production rate of these machines is between 25-1800 kg/h, depending on the press canal
diameter, the kind of materials pressed, and their properties.
Piston presses are basically of two types: mechanical and hydraulic piston presses.
Hydraulically operated machines apply pressure not only in longitudinal but also in radial direction
where the energy to the piston is transmitted from an electric motor via a high pressure hydraulic oil
system unlike the mechanical piston press.
It is compact and light and results in lower outputs due to the slower press cylinder compared to that of
the mechanical machine
