Biomass Notes – S1/2014

Lecture 2 – Biomass Resources

Proximate Analysis:- The sample is heated and volatile material is driven off in an inert

atmosphere at high temperature (950°) using a slow heating rateo Representative of slow pyrolysis

- Classifies a fuel in terms of o Moisture contento Volatile mattero Ash contento Difference, fixed carbon

- These parameters are relevant to combustion, gasification and pyrolysis

- Low MC = good- Large VM = good- Low ash content = good

Ultimate Analysis:- Attempts to determine elemental composition- Used to determine combustion and gasification air requirements, flue

losses and likely emission levels- Usually reports C, H, N, S and difference by O

Lecture 3 – Biomass Resources & Supply Chain

Types of Biomass

Woody BiomassForest arising’s:

- What remains after logs extracted- Either on the ground of the “cutover” or at the “landing”- Low-cost biomass resource

o Operational costs covered by main timber operation- Collection costs can be significant

Thinning’s:- Thinning = removal of weaker and dominated trees so that remaining

trees can grow better- The thinned timber trees have energy value

Wood-Process Residues:- Produced at saw-mills, pulp-mills, fiberboard plants or furniture

manufacturers as a result of processing the logs or timber- Include bark, sawdust, shavings, wood chip rejects and offcuts- Very low cost but competition for uses such as fiber-board

Energy Crops:

- Purpose grown, fast-growing species- Short rotation forestry (SRF)

o High density plantingo Harvested at much younger ageo High energy yields per unit areao Require low nutrient input

Municipal Green Waste (MGW)- Used construction timber- Shipping pallets- Woody biomass from gardens

Environmental Issues:- Utilization of wood process residues for energy reduces:

o The amount of material going into landfill or uncontrolled burningo GHG emissions from transport

- Utilization of forest arising’s or energy crops have more complex issues:o Soil erosion, water quality, nutrient removal, biodiversity, use of

chemicals, addition of wastes to the soilo Site damage from vehicle accesso Nutrient depletiono Continuing to cut down forests is not sustainable

Non-Woody Biomass (ACR’s, animal & human residues, municipal wastes, energy crops)

Agricultural Crop Residues (ACR’s)- Tend to be low in moisture content (~30% wet basis)

o Suited to direct combustion and gasification- Wet wastes tend to be better suited to anaerobic digestion

Bagasse:- Fibrous residue left after sugar extraction- Most sure factories use bagasse as a source of heat for making steam

Energy Crops for Fuel ProductionEthanol:

- First generation ethanol requires starches and sugarso E.g. sugar-cane, corn, sweet sorghum, sugar beet

Biodiesel:- Production requires plant oils

o E.g. soy, rapeseed, canola, palm oil, jatropha

Designer Biomass- Genetically modified crops

Wet Organic Wastes:

- Converted via anaerobic digestion- Product is “biogas” that can be:

o Fuel for internal combustion engineso Burnt directly for heating

Lecture 4 – Chemical Thermodynamics

Stoichiometry:- Stoichiometric quantity of oxidizer is just the amount required to

completely burn a quantity of fuel

Lean Mixture (fuel lean):- Not enough fuel - Oxidizer > Fuel

Rich Mixture (fuel rich):- Too much fuel- Oxidizer < Fuel

Adiabatic Flame Temperature:- Temperature attained after combustion

Dissociation:- In combustion, if temperature is too high

Stable molecules break up = Dissociation

Lecture 5 – Combustion

Combustion and Steam SystemsSteam PlantsConsist of:

- Fuel delivery and storage systems- Fuel feeding systems- Combustors- Steam equipment

CombustionBiomass Combustion Equipment is most often based on coal combustion equipment. Issues running biomass fuels include:

- Higher moisture content lower efficiencies and sometimes higher emissions

- Different S, N and C content different emissions- Different ash content possible issues of slagging and fouling- Lower energy density by volume

Combustor de-rating (can’t burn as much fuel in same place) Need larger combustors

- More difficult fuel handling operations

Combustion of solid biomass fuels occurs in four key stages:

1. Heating & Drying2. De-volatilization

(Distillation of volatile gases)3. Combustion of Volatiles

(Visible flame when burning wood)4. Char Oxidation

(Combustion of fixed residual carbons – glowing embers)

Phase 1: Heating & Drying.- Moisture in biomass is bound in two forms:

1. Bound or hygroscopic water2. Free or capillary water

- Fiber saturation point = when only bound moisture remains- Biomass is heated and the surplus moisture evaporates

o Occurs at low temperatures, starting around 100°Co Surface moisture drops to saturation point and evaporation front

moves into biomass leaving behind only water vaporo Evaporation requires energy and hence lowers the temperature of

the combustion chambero Moisture varies between 10-50% (coal ~ 3-20%)

Phase 2: De-volatilization.- At higher temperatures, the biomass starts to degrade thermally and a

range of gases are produced- Biomass produces much more volatiles than coal- Occurs during pyrolysis and gasification

Phase 3: Combustion of Volatiles.- Ignition takes place between 630-730°C- Volatiles act exothermally with oxygen to produce mainly CO2 and water

vapor- Has important effect on emissions

o Biggest determinant is the flame temperature- Air-staging is an important way to control volatiles

o Desire excess air to promote burnout of gases and any particulates (soot) that may have formed

o Desire low air to avoid NOX formation NB - conflicting requirements!

Phase 4: Combustion of Fixed Carbons.- Once moisture and volatiles are driven off, fixed carbon component

remains as “char”, which begins to burn as oxygen becomes available- Small particles controlled by chemical reaction- Large particles controlled by diffusion

Issues to Consider in Biomass Combustion:- Emissions are better than coal but still need to be controlled- Emissions from incomplete combustion

o Key is to provide enough air by good combustion design

o BUT too much air leads to inefficient combustion and NOX

o Good mixing and homogeneity promotes complete combustion

AshFuel quality and combustor design & operation are critical to control ash. Ash can be characterized as:

- Extraneous inorganic material (entrained ash)o Has been added during harvesting, handling and processing of the

fuel- Inherent inorganic material (inherent ash)

o Exists as part of the organic structure of the fuelo More mobile than entrained ash

Fly Ash:- Small ash particles present in the flue gas- Formed from vaporization and subsequent nucleation of very small

particles, then grow by coagulation, agglomeration and condensation- Responsible for slagging and fowling

Bottom Ash:- Ash that remains on the bottom of the grate after combustion- Non-volatile components may melt and coalesce inside and on the surface

of the fuel- Build up on grate can lead to problems

Slagging:- Associated principally with sintering and fusion of ash particles that

deposit on surfaces within the furnace, at T>1000°C- Can cause poor combustion conditions, blockages of ash can lead to

outages, can reduce heat exchange to boilers reducing efficiency

Fouling:- Lower temperature process, driven by deposition of volatile inorganic

species in the ash- Causes problems with blockages, corrosion and metal wastage

Potential uses of Ash:- Construction and landscaping materials- Cement or mortar- Aggregates- Fertilizer

CombustorsFixed Bed Combustors:

- Include grate furnace and underfeed stokers- Primary air passed through a fixed bed, in which drying, de-volatilization

and char-burnout takes place- Secondary air introduced to burn volatiles

- Grate furnaces – appropriate for biomass fuels with high moisture and ash contents

- Fuel direction vs. air flow:o Counter-current

Flame and flow in opposite direction Good for fuels with low heating value

o Co-current Same direction Good for dry fuels

o Cross-current Flue gas removed in the middle of the furnace

Fluidized Bed Systems:- Contains a vessel with a perforated bottom plate, and is filled with a

suspension bed of hot, inert granular material- Primary air enters from below through an air-distribution plate at a high

enough velocity to “fluidize” the bed

- Fluidization: consider a particle subject to aerodynamic drag forceso Particle is “fluidized” at the point where aerodynamic drag just

balances garavity

Advantages DisadvantagesCan flexibly deal with different fuel types

Long start-up time

Low NOX can be achieved Need small particlesHigh combustion efficiency High dust loads entrained with flue gasPossibility to add S absorbing materials in the bed

Bed material must be periodically replaced

Can be fired successfully down to low loads of 35% capacity

High capital cost and operating costs

No moving parts in the hot combustion chamber

Bubbling Fluidized Bed (BFB):- Bed material is located in the bottom part of the furnace- Fluidization velocity = 1-3 m/s- Biomass fuels fed into the bed

(As opposed to coal fed onto the bed)- 20 MWTh scale and above

Circulating Fluidized Bed (CFB):- Fluidization velocity = 4-10 m/s- Sand particles are smaller- Bed material fills reactor and circulates around- Higher turbulence

Better mixing and more homogeneous temperature distribution- Compared to BFB’s:

o Larger capital costo Higher dust loado Smaller particle size required

- 30 MWTh scale and above

Pulverized Fuel Combustion:- Fuels with small particle size - Fuel injected tangentially into a cylindrical furnace to establish a

rotational flow- De-volatilization and char burnout occur simultaneously due to small

particle size Allows for rapid changes in load

- Fuel feeding must be controlled carefully

Lecture 8 – Gasification and PyrolysisPyrolysis and gasification can be thought of as truncated versions of the combustion process.

Pyrolysis- “Thermal degradation of biomass in the absence of an oxidizing agent”

Biomass + Heat Oils, char, gases

- Goal is usually to maximize the product of the liquid fuel producto Referred to as bio-oil, bio-crude, pyrolytic-oil, pyrolysis-oil, taro Dark brown mobile liquid

- Process is endothermic - requires a continuous source of heat to the pyrolyzing particles

- Various methods:o Direct heat transfer with hot gases

o Indirect heat transfer through heat exchange surfaceso Circulating solids

- Products are quite variable and depend on:o Temperatureo Heating rateo Fuel characteristicso Pressureo Oxygen

Effect of Temperature- As temperature increases (>280°C), there is enough energy to eventually

break bonds in molecular structure and the biomass is sequentially broken down

o Hemicellulose breaks down first, then cellulose, then lignin- Initial product is tars- At even higher temperatures (>500°C) these tars crack, generating CH4,

H2, CO, CO2, and H2O

- At higher temperatures, gas products are favored- At lower temperatures, tar of char products are favored

Effect of Heating Rate- Different kinds of pyrolysis distinguished by heating rate

- Faster heating reduces char yield- Higher temperature increases gas yield

Slow Pyrolysis:- Charcoal production- HR = 1-100 K/s- Long residence time- Low temperature =~300°C- Yield: 30% oils, 35% char, 35% gas

Fast Pyrolysis:- Designed to increase oil yields- Rapid heating rates =~1000 K/s- Short residence time- Moderate temperature =~450-600°C- Yield: 75% oils, 12% char, 13% gas- Requires smaller particles- Insulating char layers must be removed

Flash Pyrolysis:- Even higher HR =~10,000 K/s- Even higher liquid yields- Smaller particle size needed

Pyrolysis Reactors

Fixed Bed:- Batch process- Biomass set on a grate, walls heated- Slow heat transfer and long residence time

Low liquid yieldAblative Process:

- Biomass impacts a hot metal surface that is externally heated Removes insulating char layer

Increases heat transfer rates- Quite large particles can be used- Mechanically involved and difficult to scale up

Twin-Screw Process:- Biomass mixed with high-temperature sand (~500°C)- Screw conveys and mixes sand- High HR’s can be achieved with good control of residence time- Sand must be reheated in separate vessel- Risk of ash/sand conglomeration- Risk of mechanical failure

Fluidized Beds:- Similar to fluidization process used for combustors- Biomass introduced into a bed of hot, solid particles fluidized by a gas- Provides a very good heat transfer- Two types:

1. Bubbling beds – lower velocity2. Circulating beds – higher velocity

Gasification- “A partial oxidation process that converts a solid fuel into a gaseous fuel”- Products are gas, char and oils- Optimized for high gas yields – ideally CO & H2

- Liquid product (tar) is undesirable- Oxidizing agent is typically:

o Air LCV gas is producedo Pure oxygen medium CV gas is produced

- Gas composition depends on the temperature usedo Higher temperatures break down hydrocarbons and tars to CO &

H2

Process of Gasification1. Heating & Drying

Temperature raised and water is driven off

2. Pyrolysis (de-volatilization)Biomass begins to degrade thermally (in the presence of oxygen) and volatile oils are driven off, leaving behind char.

3. Partial OxidationVolatiles and some char are partially burned in the oxidizer to generate heat and produce gas

4. ReductionReaction between heated CO2 or H2O and the remaining char (C), adding CO or H2 to the producer gas

The aim of the gasifier reactor is to:- Produce volatile gases and carbon char- Convert the volatiles to CO, H2 and CH4 gases- Convert the char to CO

Gasifier DesignsMoving Bed Gasifier:

- Oldest technology- Biomass bed sits on fixed grate and moves down as progressively gasified- Smaller scale – 0-15 tons dry biomass per hour- Hard to scale up

Updraft Gasifier (counter-Current Moving bed):- Fuel fed from top- Oxidizer fed from bottom- Fuel size, shape and moisture content are not critical to operation- Suitable for direct heating but not for use in engines

Downdraft Gasifier (co-current moving bed):- All introduced in the bed instead of under it- Syn-gas removed at the bottom- Pyrolysis tars must pass through the high-temperature oxidatuion zone

where they convert into simple hydrocarbons giving a gas with low tar content

- Better for internal combustion engines or gas turbines- Large portion of biomass is converted to heat leading to LCV gas

Crosscurrent Gasifier:- Simple design- The air and gas product move across the feedstock flow- Controlling the gas to pass evenly through the zones is difficult and poor

quality gas results

Fluidized Bed Designs:- Most common in larger sized reactors- Hot bed of sand or dolomite particles are kept in constant motion by the

airo Air is introduced through a nozzle at the base

- Feedstock of small particle size fed into the upper part of the reactor- Due to good mixing, temperature is more even (800-1000°C) but the

product gas contains tar and ash

o Gas cleanup must be a key part of the process- Bed materials may agglomerate and therefore need to be changed

BFB’s:- Fuel is fed into or on top of the sand bed- Gasification medium (air or CO2) is introduced from below at speeds of 2-

3 m/s- Syngas drawn off at top

Advantages DisadvantagesHigh rates of throughput compared with moving beds

High particulate content resulting in gas

Good mixing, heat transfer and control of temperature high conversion of carbon

Large bubbles may results in gas bypass through reactor

Tar content low (still requires cleanup)

CFB’s:- Similar to BFB’s- Fluidization velocity is higher ~5-10 m/s- Bed particles are suspended throughout the reactor and must be re-

circulated- Compared with BFB’s:

o Higher yieldso Lower tar contento Even higher particulate contento Possibility of erosion at high velicity

Lecture 9 – Biochemical Gasification

Anaerobic Digestion- The decomposition of organic wastes to gaseous fuel by bacteria in a low

oxygen environment. - Arises naturally in marshy grounds and landfills

o Can be captured from landfills (“landfill gas”) or deliberately harnessed in biogas plants.

- Products are primarily CH4 and CO2

- Four stages1. Hydrolysis2. Acidogenesis3. Acetogenesis4. Methanogenesis

Hydrolysis- Fermentative hydrolytic bacteria break down fats, proteins and

carbohydrates into smaller molecules. I.e. break down larger sugar based molecules into smaller ones.

- Some H2 and CO produced

Acidogenesis- Acidogenic bacteria metabolize the hydrolysis products- Products are CO2 and H2 and short chain organic acids

Acetogenesis- Simple molecules created in Acidogenesis are further broken down by

acetogenic bacteria- Oxygen in the feedstock is also consumed- Products include acetate, CO2 and H2

Methanogenesis- Methanogenic bacteria converts acetate, CO2 and H2 released from

previous steps into the end products- End products = CH4, CO2 and trace gases

Elements of a Biogas Plant - Procurement of the fuel

o Organic wastes used on site or green crops grown specifically to supply the plant

- Bio-gasification of the slurry feedstock into a digester, collection of the gas and storage

- Scrubbing o Remove of H2

o Possibly remove CO2 - Biogas utilization (after scrubbing)

o In gas reticulation systemso Generation of heat and electricity

- Sludge disposal

Digester Process:- Enclosing organic material in a large tank and restricting oxygen supply

encourages the process- Proportion of CH4, CO2 and impurities such as H2S in the gas, depends on:

o Feedstock materialo Scale of the planto Retention time (RT) in the digestero Process temperature

Feedstocks:- Moisture content =~10-15%

o Anaerobic digestion is suited to wet wastes- Total Solid (TS) = amount of solid in the feedstock per total mass of the

feedstocko Low TS convenient handling (i.e. liquid), BUT lower yield

Containments:- Physical such as plastic – can reduce blockages- Chemical – might inhibit digestion process

Heating:- Internal coils or heat exchangers, or external heating jackets- Burns some of the biogas or uses waste heat from an associated engine as

heat source- Mesophilic digesters need a relatively stable temperature of 35°C (+- 4-

7°C)

Mixing:- Maintains an even temperature gradient- Maintains a homogeneous and even supply of feedstock- Prevents settlement of solids- Avoids crust formation on surface- Achieved by recirculating gas back through the tank digester

o Typically 30 x digester Volume needs to be re-circulated per day

Operation:- Require gas yields of 70-80% of the maximum theoretical yields per kg of

feedstock to ensure positive economics

Gas Scrubbing:- Removes inert components (N2 & CO2)

o Increases energy densityo Necessary if it is to be compressed or liquefied for a vehicle fuel

- Reduces corrosion of process equipment by removing H2S and water vapor

- Reduces potential health hazards and environmental pollution- Expensive process

Benefits BarriersDigester sludge can be used as fertilizer or animal feed supplement

Poor comprehensionRisk of biological process failing

Reduces nitrate pollution levels from conventional disposal of wet wastes

High transport costs of feedstocksMultiple end use decision outputs needed for what is a finite resource

Landfill Gas:- A large portion of MSW is biological material that once disposed of in

landfills, experiences conditions suitable for anaerobic digestion- Process is similar to AD, except that:

o Slurry is replaced with solid wasteo Enclosure tank reactor vessel is replaced with a hole in the ground

- Produced biogas is a mixture of CH4, CO2, H2S, and other gases- Process is slower than biogas digester due to lower temperature and

drier conditions but the end product gas is similar- In theory, for 1 ton of MSW 150-200 m3 of biogas can be produced with

a heat value of 5-6 MJ/kg- Extraction of landfill gas uses a network of perforated pipes laid as the

site is filled

Landfill Gas Uses:- Direct combustion in kilns, boilers and furnaces, provided the supply is in

close proximity to the usero This is the most cost effective use

- Electricity generation- Gas can be cleaned and then supplied to the gas utility network

Integrated Treatment of Municipal Wastes:- Includes solid and liquid wastes

o Usually the treatment of both is total separate: Solid = local landfill Liquid = local sewage treatment plant

- May be beneficial to consider treating both in an integrated fashion in order to minimize costs and maximize the benefits

- As part of the treatment system:o An energy crop could be grown to absorb the effluent and sludge

components of the waste by land application Avoid dumping in the sea or waterways Biomass would then be harvested as additional duel for an

energy conversion plant

Lecture 10 – BioenergyPermanent Plantings

- Not harvested other than foro Thinning or ecological purposeso To remove debris for fire management

- Carbon stock plateaus- No revenue once maximum carbon stock reached

Rotational Crops- Benefit from offset of fossil fuel use- Ongoing revenue to fund management

Wood Chips

Conventional Wood Pellets

Torrefied Wood Pellets

LHV [MJ/kg] 7.4-11.4 17-18 21-22MC [%wet basis] 30-50 <10 <1Bulk Density [kg/m3] 250-400 650 900Energy Density [GJ/m3] 3.1 11.4 19.4

Torrefied Wood Pellets:- Torrefication can be described as a mild form of pyrolysis at

temperatures between 200-320°C- The biomass properties are changes to obtain a much better fuel quality

for combustion and gasification applicationo Removes moisture and low energy volatiles from the roasted wood

- More energy dense than wood – almost as dense as coal- Easier to grind than wood

Advantages:- Energy content per kg (energy density) is similar to coal and

approximately 17-37% greater than conventional wood pelletso Lower shipping costs per tonneo Improves handling characteristics

- Bulk density is lower than coal but higher than wood pelletso Higher bulk density lower shipping costs per tonne

- Requires less energy to grind than both wood pellets and coal- Can be ground in existing coal equipment- Ash content is similar to wood pellets but much lower than coal- Sulfur content is similar to wood pellets but much less than coal

Barriers to Bioenergy Implementation:- Low cost of fossil fuels- Concerns about using native forest biomass for fuels- Now removed from the LRET- Economics of fuel procurement

Lecture 12 – Liquid Biofuels for TransportationThe Need for Alternative Liquid Fuels:

- Oil is a major source of world energy use and CO2 emissions- Australia is increasingly reliant on imported oil, which increasingly comes

from fewer countries- Oil prices are rising

Alternative and Advanced FuelsBiofuels:

- Bioethanol, biodiesel, biobutanol, biogas, hydrogenation derived renewable diesel, hydrogen, etc.

Non-Biofuels:- Electricity, propane, LNG, Methanol, synthetic fuels from coal and natural

gas

Advantages of Liquid Fuels for Transportation:- High energy density- Quick and easy- Easy to handle and transport- Existing infrastructure- NB Historical Advantages of Oil that are Decreasing:

o Cheap

o Easy to find, mine, upgradeAlternatives:Transport Systems:

- Reduce need for transporto Telecommuting

- Increase public transport- Increase efficiency

Efficient Engines:- Clean diesel- Improved spark ignition engines

Hybrid Vehicles:- Liquid fuel/electrical transmission

Alternatives for Fossil Fuel Resources:Enhanced Oil Recovery (EOR)

- CO2 injection to increase recovery rate

Tar-sands- Heavy oils mixed with sand- Hard to extract

Gas-to-liquid Synfuels- Convert natural gas to liquid by Fischer-Tropsch

Coal-to-liquid Synfuels- Convert coal to liquid by gasification then Fischer-Tropsch

Oil-shale- Rock containing organic materials- Very hard to extract

Electrical Car Alternatives:- CO2 emissions depend on original source of energy- Battery technology developments will enable rapid increase in market

penetration

Advantages DisadvantagesIncrease drive train efficiency Expensive, heavy and bulky batteriesZero local emission Limited range and battery life

Long charging times

Biofuels- Fuel derived from biomass using biological or thermochemical processes- Utilizing recently “captured” carbon rather than historically captured

carbon reserves- Engines must be modified in order to effectively utilize biofuel

Ethanol:- Formed by fermentation of sugars or hydrolysis of ethane- Typically used as a blend (E5/E10)

o Mixing properties with gasoline are important

Advantages DisadvantagesNeat ethanol (pure) is an excellent fuel Potential corrosion problemsHigh octane (>100) high compression ration increased efficiency

Starting problems in cold weather because vapor pressure is too low at low temperatures

Lower flame temperature lower NOX emissions

Lower energy density than gasoline decreased fuel economy

Biodiesel (FAME):- Fatty Acid Methyl Ester (FAME)- Formed from transesterification of soybean or rape seed oil using a

catalyst and methanol – byproduct = glycerol- Mixed with normal diesel (B10/B20) or used pure- Decreased emissions of particulates and CO when combusted in a diesel

engine

Biomass:- Agricultural and forestry wastes can be converted into energy

o Full and partial pyrolysiso Syngas from steam reforming to generate hydrogen

Biobutanol:- Anaerobic process to generate acetone (& butanol) by fermentation of

molasses or starch.- Low vapor pressure- Energy content is similar to petroleum- Can blend with petroleum

First Generation BiofuelsProcess:

1. Pretreatment (milling)2. For starches: enzymatic/acid hydrolysis to release monosaccharide’s3. Fermentation4. Product extraction – distillation and dehydration

Diesel:- Can be obtained from natural plant oils and animal fats through

transesterification reaction - Straight vehicle oil (SVO) can be burned in modified engines, HOWEVER

problems exist witho High viscosity injector chokingo Poor low temperature properties

Transesterification:- Original oils composed primarily of molecules of triglycerides- Involves the reaction with an alcohol (methanol/ethanol) in the presence

of a catalyst(Triglyceride) + (Methanol) (Glycerol) + (FAME)

- High quality fuel can results, which can be burned in unmodified enginesAdvantages Disadvantages

Can be burned in unmodified engines Low yield of fuel/haCan be blended with fossil fuels Direct competition with other usesDecreased emissions Increased NOxWhen produced from wastes, avoids disposal costs and enviro impacts

Led to massive deforestation in South-East Asia

Ethanol:- Produced by fermentation of monosaccharide’s (simple sugars)- Yeasts metabolize glucose- Starches can be broken down into glucose by enzymes or acids through

hydrolysis (adding H2O), then fermented- Carbon cycle:

o Closed cycle associated with ethanol production, fermentation and combustion

6CO2 + 12H2O + light 6CO2 + 12H2O + heat

Second Generation BiofuelsCellulosic Ethanol:

- Uses not just sugars and starches like first generation ethanol, but also uses cellulose and hemicellulose =~70% of the plant and are also made of sugars

Pretreatment:- Cell wall structure must be opened up (without degrading basic sugars) to

allow enzymes access for hydrolysis- Me

Methods:Acid hydrolysis, steam explosion, ammonia fiber expansion

Overall Process:1. Input biomass + energy2. Pretreatment + energy3. Hydrolysis + enzymes4. Fermentation + yeast, bacteria5. Product separation Output = residue (process fuel) + energy + co-products

Advantages (relative to 1st gen.) DisadvantagesLower cost raw materials Largely unknown technology at scale

no commercial scale plantsIncreased availabilityNo direct competition with food crops Cannot use lignin fractionIncreased GHG reduction Sustainability issue remain

Significant R&D is still required!

Third Generation BiofuelsFuels from AlgaeAlgae:

- Diverse and large groups of organisms- Interest for fuels are mostly on micro-algae because:

o High productivity, oil contento Non-competitive with arable land or fresh water

- Potential for carbon capture and recycling into fuels

Closed Systems vs. Open Ponds:Closed Systems:

- Possible to avoid infection by unwanted strains- Possible to avoid infestation by bugs that eat algae- Good control of conditions growth rate and/or yield optimized- CO2 capture facility- Water conservation

Open Ponds:- Much lower capital costs