Bioenergy Basics

Bio Energy
(Introduction)
Dr. Sourav Poddar
Department of Chemical Engineering
National Institute of Technology, Tiruchirappalli
Tamil Nadu

World's Population
10
6.7
0
2
4
6
8
10
12
2008 2050
Year
Population
(billion)
60%
63-
160%
Increase in
Population Energy demand
World populations is currently 6.7 b but it is predicted to
reach 10 b by year 2050. So the question is, how can a
world of 10 billion people be provided with adequate
supplies of energy. During the same period of time our
energy demand will increase by 63 to 160 %.
World Energy Prospects

Other concerns
Pollution
Climate change
Resource depletion
But in regards to energy the gap between demand and
supply of energy is not the only concern that that we
have. Concerns over : resource depletion, pollution
and climate change.

Renewable energy sources
Summary of energy
resources
consumption in
United States, 2004
Alternate sources of feedstock are needed to supplement the looming imbalance between supply and demand of fossil-based
feedstocks.
Renewable energy source could provide adequate supplies of clean, safe and sustainable energy. At 47% of renewable
energy consumption, biomass is the single largest renewable energy resource. Therefore there is a strict need for
development of new technologies that can make biomass resources accessible to supply this increasing demand.

Some bioenergy history Bioenergy is not new!
1850s: Ethanol used for lighting (http://www.eia.doe.gov/
kids/energyfacts/sources/renewable/ethanol.html#motorfuel)
1860s-1906: Ethanol tax enacted (making it no longer competitive
with kerosene for lights)
1896: 1st ethanol-fueled automobile, the Ford Quadricycle
(http://www.nesea.org/greencarclub/factsheets_ethanol.pdf)
1908: 1st flex-fuel car, the Ford Model T
1919-1933: Prohibition banned ethanol unless mixed with petroleum
WWI and WWII: Ethanol used due to high oil costs
Early 1960s: Acetone-Butanol-Ethanol industrial fermentation discontinued in US
Today, about 110 new U.S. ethanol refineries in operation and 75 more planned

The difference between biomass and fossil fuels

Waste Biomass
Crop and forestry residues, animal manure, food
processing waste, yard waste, municipal and C&D solid
wastes, sewage, industrial waste
New Biomass: (Terrestrial & Aquatic)
Solar energy and CO2 converted via photosynthesis to
organic compounds
Conventionally harvested for food, feed, fiber, &
construction materials

Crop residues
Animal manures
Food / feed processing residues
Logging residues (harvesting and
clearing)
Wood processing mill residues
Paper & pulping waste slurries

Municipal Solid Waste
Landfill gas-to-energy
Pre- and post-consumer residues
Urban wood residues
Construction & Demolition wastes
Tree trimmings
Yard waste
Packaging
Discarded furniture

Category Billions of
BTUs
Ohio (%)
Crop residues 53,717 18
Animal
manures
2,393 1
Forest residues 33,988 12
Landfill wastes 199,707 69
crop residue
animal manure
forest residue
MSW, C&D
Ohio data
(modified from Jeanty et
al., 2004)

crop residue
animal manure
forest residue
MSW, C&D
(modified from Perlack et
al., 2005)
Category Millions of
dry tons/yr
U.S. (%)
Crop
residues
218.9 43
Animal
manures
35.1 7
Forest
residues
178.8 35
Landfill
wastes
78 15
U.S. Data

Biomass to Bioenergy
Biomass: renewable energy sources coming from
biological material such as plants, animals,
microorganisms and municipal wastes

Bioenergy Types
Biofuels
Liquids
Methanol, Ethanol, Butanol, Biodiesel
Gases
Methane, Hydrogen
Bioheat
Wood burning
Bioelectricity
Combustion in Boiler to Turbine
Microbial Fuel Cells (MFCs)

Advantages of Biomass
Widespread availability in many parts of the world
Contribution to the security of energy supplies
Generally low fuel cost compared with fossil fuels
Biomass as a resource can be stored in large amounts, and
bioenergy produced on demand
Creation of stable jobs, especially in rural areas
Developing technologies and knowledge base offers
opportunities for technology exports
Carbon dioxide mitigation and other emission reductions
(SOx, etc.)

Drawbacks of Biomass
Generally low energy content
Competition for the resource with food, feed, and
material applications like particle board or paper
Generally higher investment costs for conversion
into final energy in comparison with fossil
alternatives

Biofuel Applications: Liquids
Ethanol and Butanol: can be used
in gasoline engines either at low
blends (up to 10%), in high blends in
Flexible Fuel Vehicles or in pure form
in adapted engines
Biodiesel: can be used, both
blended with fossil diesel and in pure
form. Its acceptance by car
manufacturers is growing

Process for cellulosic bioethanol
 http://www1.eere.energy.gov/biomass/abcs_biofuels.html

Why Butanol?
More similar to gasoline than ethanol
Butanol can:
 Be transported via existing pipelines (ethanol
cannot)
Fuel engines designed for use with gasoline without
modification (ethanol cannot)
Produced from biomass (biobutanol) as well
as petroleum (petrobutanol)
Toxicity issues (no worse than gasoline)

Biodiesel from triglyceride oils
Triglyceride consists of glycerol backbone + 3 fatty acid tails
The OH- from the NaOH (or KOH) catalyst facilitates the breaking of the
bonds between fatty acids and glycerol
Methanol then binds to the free end of the fatty acid to produce a methyl
ester (aka biodiesel)
Multi-step reaction mechanism: Triglyceride→Diglyceride
→Monoglyceride →Methyl esters+ glycerine

Biodiesel, glycerin
Fuel Grade
Biodiesel
Fertilizer K3PO3
water
Catalyst Mixing
Methanol
Neutralization
Acid (phosphoric)
Biodiesel,
impurities
Methanol Recovery
Crude Glycerine
Recovered
methanol
Wash water
Phase Separation
gravity or centrifuge
Purification
(washing)
Catalyst NaOH
Crude Biodiesel (methyl ester)
Crude glycerin
Excess methanol
Catalyst KOH
Raw Oil
Transesterification Reaction
Biodiesel Production

Biofuel Applications: Gases
Hydrogen: can be used in fuel
cells for generating electricity
Methane: can be combusted
directly or converted to ethanol

Bioheat Applications
Small-scale heating systems for
households typically use firewood
or pellets
Medium-scale users typically
burn wood chips in grate boilers
Large-scale boilers are able to
burn a larger variety of fuels,
including wood waste and refuse-
derived fuel
Biomass Boiler
(for more info: Dr. Harold M. Keener, OSU Wooster, E-mail keener.3@osu.edu)
Heat can also be produced on a medium or large scale through cogeneration which provides heat for
industrial processes in the form of steam and can supply district heat networks.

Bioelectricity Applications
Co-generation: Combustion
followed by a water vapor
cycle driven turbine engine is
the main technology at
present
Microbial Fuel Cells (MFCs):
Direct conversion of biomass
to electricity
Heat can also be produced on a medium or large scale through cogeneration which provides heat for industrial
processes in the form of steam and can supply district heat networks.

Microbial fuel cells (MFCs)
Electrons flow from an anode through a resistor to a cathode
where electron acceptors are reduced. Protons flow across a
proton exchange membrane (PEM) to complete the circuit.
In this regard, microbial fuel cells, in which biomass fuels are directly converted to electrical
energy by undergoing oxidation-reduction (redox) reactions at an anode and a cathode is a
promising technology.

Bio-electro-chemical devices
Bacteria as biocatalysts convert the biomass “fuel” directly to
electricity
Oxidation-Reduction reaction switches from normal electron
acceptor (e.g., O2, nitrate, sulfate) to a solid electron acceptor:
Graphite anode
It’s all about REDOX CHEMISTRY!

Microbial fuel cells in the lab
•Two-compartment MFC
• Proton exchange membrane:
Nafion 117 or Ultrex
• Electrodes: Graphite plate
84 cm2
• Working volume: 400 ml
ANODE CATHODE
Membrane
Anode
Cathode

Anode
Proton Exchange
Membrane
Cathode
Anode
compartment
Cathode
compartment
Cellulose
β-Glucan
(n≤7)
β-Glucan (n ≤7)
Glucose
Cellodextrin
β- Glucan (n-1)
n≥2
n=1
6CO2 + 24e- + 24H+
Butyrate
4CO2 + 18e- + 18H+
Propionate
Acetate
3CO2 + 28e- + 28H+
2CO2 + 8e- + 8H+
O2
H2O
e-
e-
Not to Scale
Bacteria Cell
Bacteria
Cell Wall
H+
e-
H+
e-
H+
e-
e-
H+

Name of State/UT
Biomass IPP
Bagasse
Cogeneration
Non-Bagasse
Cumulative
Installed Capacity
(as on 31.12.2019)
(In MW) (In MW) Cogeneration
(In MW)
Andhra Pradesh 171.2 206.9 105.57 483.67
Bihar 12 100.5 12.2 124.7
Chhattisgarh 222.4 20 2.5 244.9
Gujarat 44.5 20.8 12 77.3
Haryana 19.4 102 89.26 210.66
Karnataka 137.3 1729.8 20.2 1887.3
Madhya Pradesh 92.5 0 14.847 107.347
Maharashtra 217 2351 16.4 2584.4
Punjab 138.5 161 173.95 473.45
Rajasthan 114.3 4.95 2 121.25
Tamilnadu 218.7 750.4 43.55 1012.65
Telangana 60.1 98 2 160.1
Uttrakhand 0.12 72.6 57.5 130.22
Uttar Pradesh 28 1929.5 159.76 2117.26
West Bengal 300 - 19.92 319.92
Odisha 50.4 - 8.82 59.22
Himachal Pradesh - - 9.2 9.2
Kerala - - 2.27 2.27
Meghalaya - - 13.8 13.8
Jharkhand - - 4.3 4.3
Assam - - 2 2
Manipur - - - 0
Nagaland - - - 0
Arunachal - - - 0
Tripura - - - 0
Sikkim - - - 0
Mizoram - - - 0
Goa - - - 0
J & K - - - 0
Total 1826.42 7547.45 772.047 10145.917
State-wise Installed Capacity of Biomass IPP/Bagasse
Cogeneration/Non-Bagasse Cogeneration in India as
on 31.10.2020 (information as received from SNAs)

Combustion of biomass material

Oxidation of other elements into gasses, ash or slag

Applications
Lower vs. higher temperature pyrolysis

Sources of agricultural residues

Using the outputs from the anaerobic digestion of biomass material

Using composting for heat and power
Transesterification

Problems with using vegetable oils as fuel

Converting vegetable oils into biodiesel

Gasification
What is Biomass Gasification?

Gasification reactions and changes in enthalpy

Bubbling fluidized bed gasification

Indicative Schematic – Power Gen

Schematic of the Transesterification process

Biogas
Biogas and biogas technology

Factor affecting biogas production

Calorific values of commonly used fuels

Biogas Production Potential from different Wastes

Raw Materials for Gasification

Average maximum biogas production from different feeds
* Average gas production from dung may be taken as 40 lit/kg. of fresh dung when no temperature control is
provided in the plant. One Cu. m gas is equivalent to 1000 liters.

Components of the bio-gas production plant

Points to be considered for construction of a biogas plant

Schematic of a typical Biogas Plant

Floating dome type Bio-gas Plant

Biogas Plants – Reduction in Global Warming

Simple sketch of household biogas plant

Biogas Bottling Plant
BGFP Project at Village – Talwade, Taluka- Trimbakeshwar, District- Nashik (Maharashtra)

Industrial waste and co-products

Forms of biomass and wood fuel

Chemical Composition of biomass
Switchgrass chemical composition (%)
Cellulose
32.0-36.8
Ash
2.1-3.7
Hemicellulose
21.1-22.6
Lignin
18.0-20.7
Extractives
8.3-15.7
Cellulose (%) Hemicellulose (%) Lignin (%) Extractives (%) Ash (%)
Hybrid
Poplar
29.2-37.0 15.5-18.4 24.2-26.1 6.9-18.2 0.5-1.0
Pine 42.2-42.7 19.3-19.9 32.0-32.9 2.9-3.7 0.4-0.5

O
O
CHO
OH
OCH3
OH
OCH3
CH2
b-methyl-g-octalactone
(whisky-lactone) Vanillin Eugenol
clove
odor
vanilla
odor
α-Tocopherol (Vitamin E)
Flavonoids (Antioxidant activities)
Policosanols (long-chain primary alcohols)- improve blood lipid levels, reduce platelet
aggregation
Docosanol (C22), Tetracosanol (C24), Hexacosanol (C26),
Octacosanol (C28), Triacontanol (C30), and Dotriacontanol (C32).
coconut
odor
Non Structural: Extractives
a-pinene

Non Structural: Ash
Al
0.1-0.3
Ca
13.5-18.7
Fe
0.3-2.4
K
15.0-29.7
Mg
9.7-12.8
Mn
0.4-0.7
Na
0.3-1.3
P
4.3-14.6
S
3.2-6.0
Si
22.3-45.5
Inorganic composition of switchgrass ash (%)
• Corrosion
• Slagging and fouling
• Catalyst impairment
• Catalytic properties
http://biomassproject.blogspot.com/2014/01/chlorine-
corrosion-ghost-feared.html

Structural: Cellulose
 Paper products: paper, paperboard,
 Fibers: rayon, cellophane,
 Biofuels: ethanol, butanol, ...,
 Consumables: powder cellulose used an inactive fillers in drug tablets, thickeners and
stabilizers in processed foods,
 Bioplastics: microbeads used inside a host of liquids that require abrasives such as
toothpaste or cosmetics, Bottles,…
 Chemicals, …
Glucose: C6 sugar

Structural: Hemicellulose
 Biofuels: ethanol, butanol, butanediol,...,
 Chemicals: furfural, lactic acid used in food, pharmaceutical and textile industries,
 Xylitol: used for food applications (sweetener, chewing gums), pharmaceutical and
cosmetics (mouthwashes and toothpastes)
 Bioplastics: Polylactic acid is the raw material
Xylose: C5 sugar
Mannose: C6 sugar
Galactose: C6 sugar
Arabinose: C5 sugar

CARBON FIBER (cars,
wind turbine, aircraft)
Structural: Lignin
 Energy: power for biorefinery
 Chemicals: vanillin used a fragrance for food preparations, intermediate in herbicides,
antifoaming agents, ingredient in household products,…
 Resins, concrete mixtures
 Fibers: carbon fibers, carbon foams
 Bioplastic: garbage bags,…

Advantages and disadvantages of energy farming

Introduction
 Challenges of waste agricultural biomass (WAB) to energy
conversion technologies
• Inherent uneven and troublesome characteristics of the materials.
• Technology should address the followings:
 Low bulk density,
 Variable and often high moisture content,
 Combustibility,
 Affinity to spoilage and infestation
 Geographically dispersed and varied material,
 Seasonal variations in yield and maturity,
 A short window of opportunity for harvest and demands on labor and machines
that often conflict with main crop (grain),
 Local regulations that put limits on utilization, storage, transportation and
emissions.

Introduction
 Technological options for improvements
• Before end-use energy applications, WAB materials have to convert
into some improved secondary forms.
• This basic process of upgrading into a variety of convenient secondary
fuels is known as beneficiation.
BENEFICIATION
Drying Dewatering Sizing Densification Separation Torrefaction
Baling Pelletization Briquetting

 Densification
• WAB materials usually take many shapes and sizes, while a particular
biomass energy conversion technology (feeding system, conversion reactor
and the conversion process itself) usually could accept a specific range of
physical forms.
• Deviations from the design features could lead to not only fuel handling
and maintenance issues but also considerable reduction in energy
conversion efficiencies.
• One of the major limitations of biomass for energy purposes is its low bulk
density.
• Densification is one promising option for overcoming these limitations.
• Densification of biomass is a process of reducing the bulk volume of the
material by mechanical means for easy handling, transportation and
storage.
• Biomass densification represents technologies for converting plant residues
into fuel.

 Densification
• Because of their uniform shape and size, densified products may be
easily handled using standard handling and storage equipment, and
they can be easily adopted in direct-combustion, gasification,
pyrolysis, and utilized in biochemical conversions.
Introduction

 Densification
• The process for biomass densification can be classified into baling,
pelletization, extrusion, and briquetting.
• Bales are a traditional method of densification commonly used to
harvest crops. A bale is formed using farm machinery (called a baler)
that compresses the chop.
• Briquetting and pelletization are the most common processes used for
biomass densification for solid fuel applications.
• These high-pressure compaction technologies, also called “binderless”
technologies.
• These processes can increase the bulk density of WAB material from an
initial bulk density of 40-200 kg/m3 to a final compact density of 600-
1200 kg/m3.
Introduction

 Densification
Bales
Briquettes
Pellets
Introduction

 Densification
• The most common raw materials used in densification of WAB in
include
 Wood processing residues, mainly sawdust,
 Loose crop residues such as rice husk, coffee husk, tamarind seeds,
tobacco stems, coir pith and spice waste, and
 Charcoal fines.
• The material is compacted and agglomerated under pressure.
• Depending on the material, the pressure, and the speed of
densification, additional binders may be needed to bind the material.
Introduction

 Densification
• Why Biomass Densification?
 Improved transportation
 More efficient storage
 Bales vs. loaves
 Reduced biomass losses
 Moisture reduction
 Improvements in processing equipment
• Goal: To increase mass per unit of volume
Introduction

 Densification
• Advantages:
 Reduces transportation and storage costs,
 Improves the handling characteristics,
 Enhances net heating value of the material per unit volume,
 Produces a fuel having more uniform size and properties,
 Reduces biodegradation of residues,
 Produces clean and durable fuel,
 Increases efficiency and reduces emissions during final energy conversion
process
• Further, the combustion of uniformly sized, densified WAB can be
controlled more precisely than loose, low bulk density biomass and
thus increase energy conversion efficiency and reduce emissions.
• It also reduces or eliminates the possibility of spontaneous
combustion seen with loose materials.
Introduction

 Densification
• Despite of the significant benefits of densification of WAB,
widespread dissemination and usage of the technology is hindered by
number of issues:
 High investment cost and process energy requirements,
 Undesirable combustion characteristics such as poor ignitability and smoking
due to use of improper process parameters and lack of process quality control,
and
 Tendency of the densified products to loosen when exposed to water or even
high humidity weather.
Introduction

Preprocessing
Biomass harvested
 low energy density;
 high moisture content;
 size, shape, density variables
Preprocessing treatments
 size reduction,
 cleaning,
 separating and sorting,
 mixing/blending,
 controlling moisture,
 densifying
 chemically or biochemically treating
Biofuels
Chips
Pellets
Briquettes
improved fuel quality

Preprocessing
 Main processes
• Main preprocessing operations of WAB materials include sizing (or
size reduction), separation (or sieving) and moisture removal.
• Size reduction and separation processes are aimed at obtaining more
uniform and pre-determined particle size distribution required for
optimum operational performance of the subsequent stage of the
densification process.
• Biomass size reduction is performed to increase the specific surface
area available in the biomass in order to ease the handling and
improve the heat and mass transfer characteristics of feedstock, e.g.
to improve the drying or combustion properties.
• Moisture removal is an essential unit operation in WAB to energy
conversion processes, as most of the raw forms of materials contain
excessively high moisture content, resulting many undesirable
characteristics.

 Size reduction
• Size reduction consists of breaking or cutting a solid biomass to
smaller pieces.
 Cutting mostly involves shearing action, whereas breaking involves some degree
of impact and attrition (friction).
 Depending on the material type and application, size reduction is achieved by
one or more steps; eg. chopping (coarse materials) followed by grinding (fine
materials).
Preprocessing techniques
Straw in raw form Chopped straw Straw in graunded form

 Size reduction
• As size reduction is an energy intensive unit operation, it is important
to have information on specific energy consumption a given
technology.
• In general, energy consumption of sizing of biomass materials
depends on initial particle size, moisture content, material properties,
feed rate of the material and machine variables.
• In particular, the energy required to grind or chop biomass increases
exponentially as desired particle size decreases.
• Since some conversion processes require small biomass particles, size
reduction technology must reduce energy requirements and
subsequent cost.

 Size reduction
• Size reduction equipment can also be further categorized as primary
and secondary types.
 Typically, primary reduction equipment is selected to maximize the amount of
processed materials in the desired size range, while minimizing fines.
 Secondary type provides a ground product of greater uniformity in sizing.
• Another method of classification is on the basis of applying
fundamental stress on the biomass material in size reduction as:
 Impact,
 Attrition,
 Shear, and
 Compression.

 Size reduction
• Types of equipment:

(a) Disc type chipper (b) Drum type chipper (c) Straw shredder
(d) Hammer mill (e) Knife mill (f) Disc mills

 Size reduction
• Shredders
• The shredders or choppers are mainly used with stalk forage, such as rice straw,
wheat straw and maize stover.
• Biomass needs to be chopped with a chopper (rotary shear shredder)/ knife
mill/ tub grinder to accommodate bulk flow and uniformity of feed rate.
(a) Straws, stalks and grasses (b) Straw bales

 Size reduction
• Shredders
• A chopper, knife cutter, or knife mill is often used for coarse size reduction (>50
mm) of stalk, straw, and grass feed stocks.
• According to the mode of cutting, choppers can be divided into cylinder or
flywheel types. Large and medium size choppers are generally flywheel types,
but the majority of small choppers are cylinder type.
Moving
blades
Upper feed
roller
Lower
feed roller
Stationary bottom
blades
Biomass
material in

 Size reduction
• Hammer Mill
• Hammer mills consist of rotating shafts with fixed or swing hammers are
attached to them.
• The material is fed into a hammer mill from the top and by gravity falls into the
grinding chamber.
• The material is contacted by a series of swinging hammers.
Swinging
hammer
Peripheral
screen
Biomass
material in
Ground
particles out

 Size reduction
Specific Energy Consumption
• For a given equipment, SEC is determined critically by the factors such as
properties of the biomass material, feeding or operating speed, moisture
content, initial particle size and final particle size.
Biomass Material
Moisture content
(% on wet basis)
Screen size (mm)
0.8 1.6 3.2
Wheat straw
8 51.0 37.5 10.7
12 45.3 43.5 24.2
Maize stover
8 21.1 16.2 6.3
12 34.2 19.7 11.1
Switchgrass
8 63.4 50.2 23.9
12 56.6 58.4 26.9
Specific energy consumption of WAB in hammer milling (in kWh/t)

 Separation
• The raw forms of WAB materials are often contaminated with items
such as sand particles, soil, stones, metal particles and other foreign
materials.
 Presence of such contaminants could damage or increase the wear of
machinery. An increased wear of machinery, in turn, creates a growth of
contaminants, thereby intensifying the effects.
• In WAB densification, separation or screening is used at different
stages, both before and after the compaction process
 former for the purpose of removing the contaminants and segregate into
required particle size range, and
 latter for removal of dust and fines from the densified products (especially in
the case of pellets)

 Separation
• Sieves or screens are used for the separation of particles according to
their sizes (segregation or classification) or for the production of
closely graded materials.

 Separation
• The screens are vibrated by means of a mechanical system. The
screen is usually inclined at an angle to the horizontal; multiple
screens are also used.

 Drying and Dewatering
• Moisture content of WAB is one of the main factors affecting the
performance of densification processes.
• The quality of densified products and successful operation of the
machines is highly sensitive to the moisture content, which preferably
should be <15%.
• Typically, moisture content has to be reduced up to this level following
the size reduction, for which a dryer is normally used.
• Drying equipment may possibly be eliminated due to the lower
moisture content of many WAB materials, such as rice husk, coffee
husk and groundnut shells.
• In contrast, drying is essential for sawdust, wet coir pith, bagasse,
bagasse pith, mustard stalk, etc.

• Removal of moisture in the WAB materials needs energy and
therefore increases the pre-processing energy requirement.
• If heat for the dryer is recovered from a waste heat source, energy
efficiency could be improved.
• Wet biomass materials containing considerably high moisture content
can be dewatered prior to drying.
• This process refers to the removal of portion of the moisture in the
feedstock in liquid phase.
• Whereas in drying process, the moisture is removed as vapor.
• Overall energy efficiency can often be improved by dewatering wet
feed stocks prior to thermal drying.

• Basic dewatering technologies include:
 Open air storage,
 Filters,
 Presses,
 Screening devices,
 Centrifuges,
 Hydro cyclones extrusion and expression process
Feed
Belt
alignment
Belt
Belt
drive
Residues
Belt
tensioning
Linear / peripheral
pressure
Belt
washing
Belt alignment Belt
washing

• Drying is another essential pre-treatment process required in biomass
energy conversion systems.
• There are many types of dryers that could be used to dry biomass
materials, which could be classified as
Classification Alternatives
Drying media (i.e. the stream passing
through the material to be dried)
Flue gas, hot air or superheated steam
Method of heat transfer Direct- or indirect-fired
Heat transfer media Flue gas, hot air, steam, or hot water
Pressure Atmospheric, vacuum or high pressure
Nature of heat source Passive: Open sun, solar dryer,
natural ventilation
Active: Dryer burners, boiler (flue gas or steam),
recovered waste heat from facility processes

• Eg: Pneumatic dryer

 Main processes
• Pretreatment of biomass improves the binding characteristics of
biomass that is low in lignin content.
• Pretreatment of herbaceous and woody biomass increases both its
physical and chemical properties, thereby making the material easy to
densify and helping minimize the costs of transport, handling, and
storage.
• Some of the commonly used pretreatment processes are pre-heating,
steam explosion, steam conditioning, torrefaction and ammonia
fiber explosion (AFEX)
• Several other pretreatment processes such as chemical, physico-
chemical (microwave, and radio frequency heating) and biological
pretreatment have been developed, which are mainly tested and used
for bio-fuel applications than densification.

 Main processes
• Pre-treating biomass prior to densification improves properties like
durability, bulk and energy density, and calorific value and reduces the
specific energy consumption.
• Other promising methods of improving the binding characteristics
include addition of natural or synthetic binders.
• Lignocellulosic biomass, which does not bind easily, can be improved
by adding either natural or commercial binders like protein or
lignosulfonates.

 Preheating and Steam Conditioning
• Pre-heating biomass before densification is widely used as it results in
a higher quality product.
• Most commercial pellet or briquette producers use pre-heating to
form more stable and dense product pellets or briquettes.
• Pre-heating could increase the throughput of densification and
reduce the specific energy requirement for the densification process.
• Steam conditioning is a process where steam is added to the biomass
to make the natural binder, lignin, more available during densification.
• By disrupting lignocellulosic biomass materials via steam conditioning
will improve the compression characteristics of the biomass.

 Steam Explosion
• During this process high pressure saturated steam (~ 200 C) is supplied
to biomass materials in a reactor for a short period of time (2 – 10
minutes).
• The substrate is quickly flashed to atmospheric pressure, and the water
inside the substrate vaporizes and expands rapidly, disintegrating the
biomass.
• This process produces significant physical, chemical, and structural
changes in the biomass and makes more lignin sites available for
binding during pelletization
• It causes hemicelluloses to become more water soluble and makes
cellulose and lignin more accessible through depolymerization, and
makes lignin more available for binding during densification.

 Steam Explosion
• The extent of chemical and structural modifications from steam-
explosion pretreatment depends on residence time, temperature,
particle size and moisture content.
Un-treated
Steam-
Exploded
Barley Straw Canola Straw Oat Straw Wheat Straw

 Ammonia Fiber Explosion (AFEX)
• AFEX is a pretreatment method that uses aqueous ammonia at
elevated temperatures and pressures to produce higher hydrolysis
yields for many herbaceous feedstocks.
• This process reduces lignin and removes some hemicellulose while
decrystallizing cellulose in the biomass.
• The major advantage of this process is little biomass degradation.

 Ammonia Fiber Explosion (AFEX)
• AFEX pretreatment of biomass offers significant advantages for
densification, storage, transportation and integrated with subsequent
processing steps.
• AFEX-treated biomass is relatively dry and inert, it is more easily
stored, transported, and densified to further improve bulk handling
properties.
• AFEX treatment transfers some lignin and hemicellulose oligomers to
the surface of biomass fibers where it can act as a binding agent
• Several other chemical pretreatment techniques for lignocellulosic
materials have been developed by using different chemicals such as
acids, alkalis, oxidizing agents and ozone.

 Torrefaction
• Torrefaction is a method of changing the properties of biomass
materials by slowly heating it in an inter-environment to a maximum
temperature of 300°C.
• The process is also called a mild pyrolysis as most of the smoke-
producing compounds and other volatiles are removed resulting in a
final product that has approximately 70% of the initial weight and 80–
90% of the original energy content.
• Thus, treatment yields a solid uniform product with lower moisture
content and higher energy content compared to the initial biomass.
• Temperatures over 300°C are not recommended as these initiate the
pyrolysis process.
• Torrefaction reduces variability in the feedstock caused by differences
in types and species of raw materials, climatic and seasonal variations,
storage conditions, and time.

 Torrefaction
Biomass residues
before and after
torrefaction
Biomass pellets
and torrefied
biomass pellets

 Torrefaction
• Torrefaction affects biomass physical characteristics like grindability,
hydrophobicity, pelletability, and calorific value.
• Biomass loses the tenacious nature that is coupled to the breakdown of the
hemicellulose matrix and depolymerization of the cellulose, resulting in a
decrease in fiber length.
• Torrefaction also results in the shrinking of the biomass structure, making it
light-weight, flaky, and fragile, improving the grinding and pulverizing
process
• It improves binding during pelletization by increasing the number of
available lignin sites.
• Torrefaction not only improves the physical properties of biomass, but also
significantly changes its proximate and ultimate composition, making it more
suitable for fuel applications

 Overview
• The fuel quality of WAB could be improved by means of compaction
into high density and regular shape.
Densification – the process

 Overview
• Low bulk density, loose forms and wide variations of particle sizes are
common drawbacks of WAB
Figure 3.1: Loose waste agricultural biomass

 Overview
 Loose material
 high moisture biomass,
 non-uniform particle sizes,
 susceptible to spoilage,
 low energy content
High energy density
No off gas emissions during storage
Hydrophobic in nature, low grinding energy
No fines in the final product
 High density pellets
 Low moisture content, uniform size
 Easy to store and
 transport to long distances

 Physical attributes of densified biomass
• The quality of densified biomass products such as briquettes and
pellets depends on strength and durability of the particle bonds.
• The quality is influenced by a number of process variables, like die
dimensions, length to diameter ratios, die temperature, speed,
pressure, binders, and pre-heating of the biomass materials.
• The two important aspects of densification are:
 The ability of the particles to form densified products with
considerable mechanical strength, and
 The ability of the process to increase density.

 Quality parameters of densified biomass
• Moisture Content
 Moisture is a vital constituent in densified biomass products; its presence in too
much or too low quantities would affect the quality attributes.
 High moisture content could lead to spoilage due to microbial decomposition,
resulting in significant dry matter loss.
 This reduces the energy content and could also have negative effect on the final
quality where cracks occur.
 Densified products with lower moisture content tend to break up, creating more
fines during storage and transportation.
 The optimum moisture content is primarily dependent on process conditions
like initial moisture content of the feedstock, temperature, and pressure.
 Higher moisture in the final product results when the initial moisture content is
greater than 15% on wet basis.

• Bulk and Unit Density
 Bulk density and unit density are important parameters for handling, storage
and transportation.
 The two parameters are greatly influenced by not only the material properties
such as moisture content and particle size distribution, but also the process
parameters such as pressure and temperature.
 In general, materials with higher moisture and larger particle sizes reduce the
unit and bulk density, while higher process temperatures and pressures increase
the unit and bulk density of the final product.
 The maximum apparent density of a densified product from nearly all materials
is to a rough approximation constant; it will normally vary between 1200-1400
kg/m³ for high pressure processes. The ultimate limit is for most materials
between 1450 to 1500 kg/m³.

• Durability Index
 The durability index is a quality parameter defined as the ability of densified
materials to remain intact when handled during storage and transportation.
 Thus, durability of a densified product is its physical strength and resistance to
being broken up.
 The bonding performance of the particle during densification process critically
determines the durability of the products.
 Moisture increase durability when water soluble compounds, such as water
soluble carbohydrates, lignin, protein, starch and fat are present in the feed
material.
 High starch content acts as a binder and increases durability.
 Protein will plasticize with heat and moisture and act as a binder to increase the
durability of the products.
 Lignin too, at elevated temperatures (>140 °C), acts as a binder and increases
durability.

• Fines Content
 The presence of dust particles or fines in the densified product is an undesirable
attribute, which could affect adversely the end-use energy conversion process,
especially when co-firing with other fossils fuels.
 Fines are generated during transportation and storage by the breakdown of the
densified products.
 Densified products processed under suboptimal conditions, such as low
moisture, low temperature, and with less desirable chemical compositions or
with insufficient die size and roller speeds, are less durable and can result in
more fines in the final product.
 Presence of fines in higher quantities can lead to spontaneous combustion and
dust explosion problems during final energy conversion processes.

• Heating Value
 The heating (or calorific) value of densified products depends on
process conditions like temperature, particle size, and feed
pretreatment.
 In general, products with higher densities and lower moisture
contents have greater heating values.
 The typical higher heating values (HHVs) of briquettes and pellets
range from 17–18 MJ/kg, which could be enhanced further up to
20–22 MJ/kg through pretreatment processes like steam explosion
or torrefaction prior to densification.

 Overall mechanism
• Densification of WAB materials through briquetting and pelletizing
basically represents compaction of grinds in a form of systematic
agglomeration involving pressure.
• Densification essentially involves two parts:
 The compaction under pressure of loose WAB material to reduce
its volume and
 The agglomeration of the WAB material so that the product
remains in the compressed state.
Densification mechanisms

 Overall Mechanism
• Further, three basic processing stages could be recognized during
densification of biomass.
 Firstly, the compaction of the materials with low to moderate pressure (0.2–
5.0MN/m2) will reduce the space between particles and form a closely packed
mass where the energy is dissipated due to inter-particle and particle-to-wall
friction.
 Secondly, the particles are forced against each other and undergo plastic and
elastic deformation, which significantly increases the inter-particle contact;
particles become bonded through the intermolecular attractive forces.
 Thirdly, increase of the pressure further will result collapsing of the cell walls of
the cellulose constituent of the material, a significant reduction in volume
results in the density of the material reaching the true density of the
component ingredients.

 Overall Mechanism
• The stages of deformation mechanism of powder particles under
compression

 Bonding Mechanism
• The quality of densified products of WAB is critically determined by
the intensity of bonding or interlocking between individual particles of
the material.
• The densification of biomass under high pressure results in
mechanical interlocking and increased adhesion/cohesion (adhesive
forces at the solid/liquid interface and cohesion forces within the solid
are used for binding) of the solid particles, which form intermolecular
bonds in the contact area.
• Though several fundamental processes and mechanisms of attaining
and maintaining the self-bonding have been proposed, universally
accepted model is yet to be established.

• Bonding Agents.
 In case that the inborn binders do not provide the required quality levels (such
as strength, durability, heating values, dust and fines level), as demanded by the
end-user, additives (i.e. added binders) have to be blended with the raw
material.
 Selection of such binders (the type and amount) mainly depends on the
strength of the bonding, the cost and the environmental friendliness of the
material of the binder.
 When strength, durability or heating values of the densified products do not
match with the quality standards or marketing requirements, additives are
added to the feed to enhance the quality or to minimize the quality variations.
 Bonding agents can also be used in order to reduce wear in production
equipment and increase abrasion-resistance of the densified biomass fuel.

• Bonding Agents.
 Many bonding agents have been explored and used in improving the quality of
densified products of WAB materials.
 Some of these bonding agents include starches (e.g. maize, rice, potato), stalks
(e.g. corn), bran (e.g. wheat, rice), molasses, natural paraffin, plant oil, lignin
sulphate and synthetic agents.
 The binders used in biomass densification could be categorized as the matrix
type and the film type.

 Factors Affecting Densification
• Moisture Content.
 Moisture content should be as low as possible, generally in the range of 10-15 %
on wet basis.
 High moisture content will pose problems in grinding and excessive energy is
required for drying.
 Nevertheless, moisture content has an important role to play as it facilitates
heat transfer.
 Too high moisture causes steam formation and could result an explosion. Most
suitable moisture content could be of 8-12% on wet basis.
 Usually, briquetting process could accommodate relatively high moisture
content (preferably up to 15% on wet basis), whereas pelletization demands
much lower moisture contents (< 10% on wet basis).

• Material Properties
 Although biomass densification technology is well developed, WAB
material preparation and densification equipment are very
sensitive to the specific characteristics of raw materials.
 In terms of the WAB material, following properties play important
role in the densification process:
 Particle size and shape distribution
 Flow ability and cohesiveness
 Surface forces
 Adhesiveness
 Hardness

 In particular, particle shape and size distribution play a vital role in
the compaction and agglomeration stages of the densification
process.

 In the case of briquetting, relatively larger particles sizes (> 6 mm) are desirable,
leading to better interlocking of the particles and increasing the durability,
whereas in pelletization, relatively smaller particle sizes are required.
 Optimum particle size distribution for quality pellets
Sieve size (mm) Material retained on sieve (% mass)
3.0  1
2.0  5
1.0  20
0.5  30
0.25  24
<0.25  20

• Temperature and Pressure
 The compression strength of densified biomass depended on the temperature
at which densification was carried out.
 Maximum strength was achieved at a temperature around 220 C. At a given
applied pressure, higher density of the product was obtained at higher
temperature. Both strength and moisture stability increased with increasing
temperature.
 High pressures and temperatures during densification may develop solid bridges
by a diffusion of molecules from one particle to another at the points of contact.

 Main Classifications of Technologies
• The densification technologies use any one of the following methods
in producing densified products:
 Binder-less densification,
 Direct densification of biomass using binders and
 Pyrolyzed densification using a binder.
• Different densification processes and technologies could be classified
based on number of factors such as
 Type of equipment,
 Operating condition,
 Mode of operation,
 Applied pressure, etc.
Densification technologies

• Classification based on type of equipment
 Three main types: Piston press, Screw press, Pelletizing
 Other: Roller press, Low pressure or manual press.
 Densified biomass can be categorized into two main types: briquettes and
pellets.
 The products formed in the piston and screw presses are larger in size and
known as briquettes.
 Briquettes can have different shapes and are greater in size, with 50 - 60 mm in
diameter and 300 - 400 mm in length.
 The briquettes produced by a piston press are completely solid, while screw
press briquettes usually have a concentric hole, which give better combustion
characteristics
 Pellets have cylindrical shape and are small in size, about 6 to 25 mm in
d.iameter and 30 to 50 mm in length.

• Classification based on the operating condition
 Depending on the operating conditions, the WAB densification technologies
could be categorized into two groups: Hot and high pressure densification; Cold
and low pressure densification
 Hot and high pressure densification:
 Is the most common type of densification, and it is essentially a process of
compaction of biomass under heated condition.
 The heating of the biomass is mostly or totally generated by friction during
compaction.
 Usually no binding agent is required for this type of densification for producing
briquettes, but required to set the process parameters appropriately to realize the
necessary quality levels.
 The piston presses and screw extrusion machines are the two main high pressure
technologies are used at present.

• Classification based on the operating condition
 Cold and low pressure densification:
 Cold and low pressure densification processes employ relatively low
pressure and temperature.
 In this process, the densification could be carried out with or without
addition of bonding agents.
 In the case of densification using binder, a binding agent is added to glue
together the biomass particles.
 Since there is no need to soften lignin, the temperature and pressure
required are low.
 Low pressure compaction includes manually operated briquetting presses
of different types.

• Classification based on the mode of operation
 Based on mode of operation it falls into two categories: Batch densification and
Continuous densification
 The piston presses usually represent batch type densification technology, while
screw extrusion machines and pelletizing machines represent continuous
densification.
• Classification based on the applied pressure
 On the basis of compaction pressure, the densification technologies can be
divided into the following types: High pressure compaction, and Low or
Medium pressure compaction with a heating device.
 High pressure densification technologies employ processing pressures above
100 MN/m2, while medium pressure technologies between 5 – 100 MN/m2 and
low pressure technologies less than 5 MN/m2.

 Working Principles - agglomeration
• Agglomeration is a method of increasing particle size by gluing powder
particles together.
• This technology is used for a variety of powders, such as hydrated lime,
pulverized coal, fly ash, cement, and many others.
• The application of agglomeration for biomass is limited.
• Generally, two distinct principles could be distinguished, which are most
widely used for size enlargement of particulate materials: tumble
agglomeration and pressure agglomeration.
• In tumble agglomeration, agglomerates are formed during suitable
movement of the particulate materials containing binder in the processing
equipment.
• In pressure agglomeration, high forces are applied to a mass of particulate
materials within a confined volume to increase the density.
• Pressure agglomeration is accomplished in piston, roller, and extrusion
presses as well as in pelletizing machines.

 Working Principles - agglomeration
• The most commonly used method is tumbling agglomeration.
• The equipment consists of a rotating volume that is filled with balls of
varying sizes and fed with powder and often a binder.
• The rotation of the agglomerator results in centrifugal, gravitational,
and frictional forces from the smooth rolling balls.
• These forces, together with inertial forces, press the balls against the
powder, helping them to stick together and grow.
• Segregation of the balls takes place as their diameter starts growing.
• Large balls tend to “float” on the surface, whereas small balls are
mainly located at the bottom of the vessel.
• With an increased number of balls during the process, larger balls are
pushed outside as the bulk volume size of the agglomerator is limited.

 Agglomeration
• An agglomerator using granulation involves the following steps:
Fine raw material is continually added to the pan and
wetted by a liquid binder spray.
 The disc’s rotation causes the wetted fines to form small,
seed-type particles (nucleation).
 The seed particles “snowball” by coalescing into larger
particles until they discharge from the pan.
While pellets can be formed in batches, almost all tonnage
pelletizing is accomplished through continuous processes
using a disc pelletizer with a comparatively simple design.
• The fundamental problem in an agglomerator is maintaining a uniform
ball-size distribution during the operation.

 Agglomeration
• Agglomeration is a function of material properties and process parameter

 Working Principles
• Pressure agglomeration
Briquettes
Die
Heaters
Screw
Barrel
Hopper
Briquettes
Die
Heaters
Screw
Barrel
Hopper
Briquettes
Die
Heaters
Screw
Barrel
Hopper
(a) Ram and punch press
Punch‐ and‐die press
(b) Ram extrusion press
(c) Screw extrusion press
Solid Melting and
Briquettes
Die
Heaters
Screw
Barrel
Hopper
Solid Melting and
Briquettes
Die
Heaters
Screw
Barrel
Hopper
Solid Melting and
Pumping
Briquettes
Die
Heaters
Screw
Barrel
Hopper
(d) Pellet mill with ring
Solid
Conveying
Melting and
Pumping
Pumping
Briquettes
Die
Heaters
Screw
Barrel
Hopper
Solid
Conveying
Melting and
Pumping
Pumping
Briquettes
Die
Heaters
Screw
Barrel
Hopper
Solid
Conveying
Melting and
Pumping
Pumping
Briquettes
Die
Heaters
Screw
Barrel
Hopper
(f) Roller press /
Double roller press
(e) Flat die pellet mill with press rollers
die and press rollers
Solid
Conveying
Melting and
Pumping
Pumping
Briquettes
Die
Heaters
Screw
Barrel
Hopper
Solid
Conveying
Melting and
Pumping
Pumping
Briquettes
Die
Heaters
Screw
Barrel
Hopper
Solid
Conveying
Melting and
Pumping
Pumping
Briquettes
Die
Heaters
Screw
Barrel
Hopper
(f) Roller press /
Double roller press
Solid
Conveying
Melting and
Pumping
Pumping
Briquettes
Die
Heaters
Screw
Barrel
Hopper
Solid
Conveying
Melting and
Pumping
Pumping
Briquettes
Die
Heaters
Screw
Barrel
Hopper
Solid
Conveying
Melting and
Pumping
Pumping
Briquettes
Die
Heaters
Screw
Barrel
Hopper
(f) Roller press /
Double roller press
Briquettes
Die
Heaters
Screw
Barrel
Hopper
Briquettes
Die
Heaters
Screw
Barrel
Hopper
Briquettes
Die
Heaters
Screw
Barrel
Hopper

 Briquetting
• Densification of loose and smaller biomass waste using a briquette
press is a attractive solution to utilize biomass for fuel applications.
• Briquetting is usually performed using hydraulic, mechanical, or roller
presses.
• The briquettes’ densities generally range from 900 to 1300 kg/m3.
• The biofuel briquette is a clean and green fuel that can ideally be used
in furnaces, boilers, or open fires.
• In the biomass briquetting process, the material is compressed under
high pressure and temperature.
• During briquetting the biomass particles self-bond to form a briquette
due to thermoplastic flow.
• Advantages of briquettes are the ease of charging the furnace,
increased calorific value, improved combustion characteristics, reduced
entrained particulate emissions, and uniform size and shape.
• Furnaces that use other solid fuels can use briquettes also.

 Pelletization
• Pelletization is similar to briquetting, except that it uses smaller
dies (approximately 30 mm) to produce smaller densified
products called pellets.
• Pellet presses consist of two types: the ring die and the flat die.
• In both the ring- and flat-die machines, the die remains stationary,
and the rollers rotate.
• Some rotating die pellet mills are available in which the rollers
remain stationary during the production process.
• In principle, the incoming feed is delivered uniformly into the
conditioner for the controlled addition of steam and/or molasses.
• This unit operation helps improve binding of the material during
pelletization.
• Most pellet mills now have, mounted above the main unit, one or
more conditioning units where liquids such as water and molasses
can be added to improve pelletability.

 Roller Press
• Densification of WAB using roller presses works on the principle of
pressure and agglomeration, where pressure is applied between two
counter-rotating rollers with identical diameters and parallel axes.
Other densification technologies
Rotation
Agglomerated
sheet
Agglomerates
of accepted
sizes to
packing
Crusher
Ground biomass
to the feeder
Fine
particles
recycled
Screener
Rollers

Other densification technologies
 Manual Presses and Low Pressure Briquetting
• There are different types of manual presses used for briquetting
biomass feed stocks.
• They are used both for raw biomass feedstock or charcoal.
• The use of a binder is imperative.

 Energy Required for Densification
• Energy input for densification process could constitute a significant
fraction of densified biomass production cost, and could have a
significant impact on the economic viability of the technology.
• Biomass densification systems require energy for the two main
processes normally involved:
 fuel preparation, both preprocessing (sieving, drying, size reduction) and
pretreatment
 the densification process itself.
 The specific energy requirements for biomass densification depend on
the system used and process variables (e.g., temperature and
pressure), feedstock variables (e.g., moisture content and particle
size/distribution), and biochemical composition variables (e.g.,
presence of starch, protein, fat, and lignocellulosic composition).
Densification–the technology

• Specific energy consumption (SEC) of different technologies
• SEC for different materials
Technology Common Throughput
Range (kg/h)
SPC
(kWh/t)
Product Density
(kg/m3)
Piston Press 100 - 1800 50 - 70 300 – 600
Roller Press with Circular Die 3000 - 8000 20 - 60 400 – 700
Cog-Wheel Pellet Principle 3000 - 7000 20 - 60 400 – 600
High Pressure Piston Press 40 - 200 500 - 650 650 – 750
Biomass Material Equipment SEC
(kWh/t)
Biomass Material Equipment SEC
(kWh/t)
Sawdust Pellet mill 36.8 Sawdust Piston press 37.4
Straws Pellet mill 22 - 55 Straws Screw press 150 - 220
Straws + Binders Pellet mill 37 - 64 Grass Piston press 77
Switchgrass Pellet mill 74.5 Straws + Binder Ram exruder 60 – 95

• It is important to recognize the fact that there could be a significant
difference of the SEC estimated through the laboratory results and
commercial systems.
Technology Operation
Condition
Raw Material Density
(kg/m3)
SEC (kWh/t)
Compression In laboratory Sawdust 1000 4.0
Sawdust 1200 6.6
Commercial Sawdust 1200 37.4
Extrusion In laboratory MSW 1000 7.7
Commercial MSW 1000 16.4
Sawdust 1000 36.8

• Parameters of the most common densification equipment
Screw Press Piston Press Roller press Pellet mill
Optimum moisture content
of the raw material [%]
8-9 10-15 10-15 10-15
Final density of raw material
[g/cm3]
1-1,4 1-1,2 0,6-0,7 0,4-0,5
Specific energy consumption
[kWh/t]
36,8-150 37,4-77 29,91-83,1 16,4-74,5
Through puts [t/h] 0,5 2,5 5-10 5

 Performance comparison of different densification technologies
Performance comparison
Parameter
Densification Technology
Screw press Piston Press Roller press Pellet mill Agglomerator
Optimum moisture
content of the raw
material (%)
4 - 8 10 – 15 10 – 15 10 – 15 -
Particle size (mm) 2 - 6 6 - 12 < 4 < 3 0.05 – 0.25
Wear of contact parts High Low High High Low
Output from machine Continuous In strokes Continuous Continuous Continuous
Specific energy
consumption (kWh/t)
37 – 150 37 – 77 30 – 83 16 – 75 -
Through puts (ton/hr) 0.5 2.5 5 – 10 5 -
Unit density (g/cm3) 1.0 – 1.4 2.5 0.4 – 0.6 1.1 – 1.2
Bulk density (g/cm3) 0.5 – 0.6 < 0.1 - 0.7 – 0.8 0.4 – 0.5
Maintenance Low High Low Low Low
Combustion
performance of
briquettes
Very good Moderate Moderate Very good -

 Performance comparison of different densification technologies
Parameter
Densification Technology
Screw press Piston Press Roller press Pellet mill Agglomerator
Carbonization of
charcoal
Good
charcoal
Not
possible
Not
possible
Not
possible
Not
possible
Homogeneity of
densified biomass
Homogenous
Not
homogenous
Not
homogenous
Homogenous Homogenous
Suitability in gasifiers Suitable Suitable Suitable Suitable Suitable
Suitability for cofiring Suitable Suitable Suitable Suitable Suitable
Suitability for
biochemical conversion
Not suitable Suitable Suitable Suitable -
Addition of binder Not required Not required Required Not required Required
Shape Cylindrical Cylindrical
Generally
elliptical
Cylindrical Spherical
Performance comparison

Typical / Mainstream Biomass Dryer Technologies

Rotary Dryers - Direct Fired Single Pass

Air Emissions Control - Particulate

Supplemental Heat Options (Direct Fire)

Furnace Capital & Operating Costs

Air Emissions Control Capital Costs

Air Emissions Control Operating Costs

Fire Detection and Suppression

Why is the Handling System so important?
• Metering the fuel feed system is an important aspect of the biomass
gasification plant because it is used to control the entire process.
• The handling system controls the flow rate of fuel into the gasifier. If the
flow is variable then the gasifier will not maintain the desired
temperatures and will not be as efficient.

The problem
•Unlike liquids, the biomass solids do not deform under shear
stresses (causes jamming) and this is why the storage and handling
of biomass is so important.
•Reasons for many shutdown incidents of biomass gasifier plants can
be traced to the failure of the biomass handling system.
•Some biomass contains rocks and other debris when it arrives at
the plant.

Biomass Handling System
The Biomass Handling System can be broken down into 5
stages:
–Biomass receiving
–First Stage Screening (Optional)
–Storage
–Feed preparation
–Conveying
–Feeding

Biomass Receiving
The Biomass is first transported via truck or rail-car and unloaded at
the receiving station.

First Stage Screening (optional)
Sometimes depending on the type of biomass there is a first stage screening to
remove foreign materials.

Storage
Once received (or screened) the biomass is transported by
conveyor belt to one of the 2 types of storage types:
–Above ground storage for large biomass
–Silo or bunker for enclosed storage of smaller biomass.

Retrieval from Storage
The following are some methods of biomass retrieval from storage
–Simple gravity feed or chute
–Screw type auger feed
–Conveyor belt
–Pneumatic blower
–Pumped flow
–Bucket conveyor
–Front loader
–Bucket grab

Feed Preparation
•Once retrieved the biomass is transported to the Feed Preparation System
because biomass can not be fed directly into the gasifier for the following
reasons
–Presence of foreign materials like rocks and metals
–Unacceptable level of moisture in biomass
–Too large (or uneven) in size
•The feed preparation process consists of
–Screening
–Drying
–Sizing

Screening
•The most common foreign materials that must be removed are:
–Stones
–Ferrous metals like iron
–Non-ferrous metals like aluminum
•This is why there is a screening (possibly second) process that consists of
–De-stoner
–Non-ferrous metal separators
–Magnetic metal separation

De-stoner
•The purpose of a de-stoner is to separate heavier-than-biomass
materials like glass, stones and metals.
•Typically use vibratory actions in series with airflow to separate
materials according to specific gravity.

Non-Ferrous Metal Separators
Uses an eddy current to separate according to specific mass and resistivity

Magnetic Metal Separation
Use powerful magnets for separation of iron and other magnetic materials.

Drying
•Freshly cut biomass can contain up to 40-60% surface moisture and a
gasification process typically requires moisture to be less than 10-15%.
•Use heat in the flue gas or external sources of heat to reduce moisture levels.
•If moisture is not removed then the gasifier can not reach high enough
temperatures and the efficiency of the plant is decreased.

Sizing
Typical equipment that are used for cutting biomass into
different sizes.
–Chunker: 250 to 50 mm
–Chipper: 50 to 5 mm
–Grinder: <80 mm
–Pulverizer: dust <100 micrometers

Conveying
Once the biomass prepared, it is then transported to the hopper which gravity feeds the
feeder.

Main Types of Feeders
•Gravity Chute conveyor
•Screw Conveyor
•Pneumatic Injection
•Rotary Spreader
•Moving Hole Feeder
•Belt Feeder

Mode of Fuel Injection in Fluidized Beds
•Over-Bed System–handles coarser particles
•Under-Bed System–handles fine particles

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