Alternative Energy Methods

Renewable Energy Resources

BIOMASS

Introduction

• Definitions:• “Different materials of biological origin that can be used as a

primary source of energy”• “Plant materials and animal waste used especially as a

source of fuel”• Exploited by humans for a very long time• Used to provide warmth• Late 1700s – approximately 2/3 of the volume of wood

removed from the American forest for energy generation• 1800s – a single households consumes 70 to 145 m3 of

wood annually for heating and cooking• Still used by US and Finland to supplement their total

energy usage

Source: Lee, S., Speight, J. G., Loyalka, S. K., “ Handbook of Alternative Fuel Technologies”, CRC Press, 2007

Introduction

Biomass utilization for energy in various countries:


2.8U.S.1.6Switzerland13.0Sweden4.0Norway0.4New Zealand13.0Ireland1.0Denmark3.0Canada0.2Belgium4.0Austria

Energy from Biomass Utilization (%)Country

Biomass Composition

• Energy stored in the form of:• Carbohydrates• Hydrocarbons • Esters

• Carbohydrates:• Most common components of biomass• Sugars or condensation polymers of simple sugars• Can be stored in:

» Sap (sugar cane)» Tubers (sugar beets)» Fruits

Source: Rosa, A.V., “Fundamentals of Renewable Energy Processes”, Elsevier Inc., 2005

Biomass Composition

• Hydrocarbons:• Generally polyisoprenes (terpenes) – polymers of the

alkyne hydrocarbon, (isoprene, C5H8)• Found in some euphorbia such as the rubber tree

• Esters (oils):• Result of a reaction of an acid (frequently of carboxylic

acid) and an alcohol liberating a molecule of water• Oil from the pulp of the fruit of a different nature from that

obtained from the seed of kernel• Oil of interest:

» Oil from the castor bean; insoluble in gasoline and can be used to lubricate gasoline pumps

» Palm oil, originally used by Rudolf Diesel in his engine, is of major interest as fuel

Source: Rosa, A.V., “Fundamentals of Renewable Energy Processes”, Elsevier Inc., 2005

Biomass Feedstock

• Categories of biomass feedstock:• Vegetable oil• Pure carbohydrates (e.g. sugar and starch)• Heterogeneous “woody” materials – lignocelluloses

• Factors taken into consideration a large-scale biomass program:

• Short- and long-term land availability• Productivities, species involved, and mixtures• Environmental sustainability• Social and socioeconomic factors• Economic feasibility• Ancillary benefits• Disadvantages and perceived problems


Photosynthesis

• Utilizes CO2 and water to produce simple sugars in the presence of solar energy, chlorophyll and other plant ingredients

• Photosynthesis chemical reaction:

6CO2 + 6H2O → C6H12O6 + 6O2 – 480 kJ/mol

• Primary selling point of biomass – potential use of CO2 to produce fuel (energy) and O2 – a win-win situation

Source: Hodge, B. K., “ Alternative Energy Systems and Applications”, John Wiley & Sons, Inc., 2007

Biomass Resources

• Agricultural crops - corn, soybeans and wheat that yield sugar and oils

• Agricultural crop residues – residues, such as stalks and leaves, of agricultural crops that are not harvested for commercial use

• Herbaceous energy crops – perennials that are harvested annually after reaching maturity (grasses: switchgrass, miscanthus, bamboo, fescue)

• Woody energy crops – hardwood trees harvested within 5 to 7 years of planting (poplar, willow, maple, cottonwood, sweetgum)


Biomass Resources

• Forestry residues – biomass not harvested or removed during logging, and materials removed during forest management operations

• Aquatic crops – kelp, seaweed and algae• Industrial crops – developed to produce specific

chemicals or feedstocks (e.g. Kenaf)• Animal waste – result from farm and processing

operations• Municipal waste – result from residential,

commercial and industrial sectors; can contain significant biomass with energy content


Biomass Resources

Source: www.genomocs.energy.gov

Biomass Resources

Forest ResourcesCrop ResiduesCornOtherPerennial Crops

28 % 27 %

31 %6 %

8 %


Biomass Fundamentals

Primary products:• Liquid fuels:

• Ethanol – ethyl alcohol; used as a fuel• Methanol – methyl alcohol; produced as a by-

product of gaseous fuels• Biodiesel – chemically modified vegetable oils

suitable for diesel fuel• Vegetable oil – oils contained in grains and seeds• Pyrolysis oil – a liquid fuel with a heating value of

17-20 MJ/kg



Primary products:• Gaseous fuels:

• Biogas – a mixture of CH4 and CO2; 55-70 % methane by volume

• Producer gas – a flammable gas containing CO, H2, CH4, N2, CO2 and higher hydrates

• Synthesis gas (syngas) – mixture of CO and H2


Conversion Routes of Biomass

Biomass

Thermal Biological Extraction

Direct Combustion Gasification Liquefaction Pyrolysis

Biogas Liquid Fuel Producer Gas

Fermentation Anaerobic Digestion

Liquid fuel Biogas

Oils


Thermal ConversionDirect Combustion

• Types:• Complete combustion - the woody components of

biomass burn much more efficiently releasing less toxic gases

• Incomplete combustion - causes release of CO, CO2 and NOx

• When conducted in a well-vented area, burning biomass can be a good substitute for combustion of conventional fossil fuel

• Results in lower sulfur emissions (0.05 to 0.2 wt%)



• The formation of particulates controlled at the source

• Large scale processes:• Biomass reduced into fine pieces for combustion in

a close-coupled turbine• Turbine separated from the combustion chamber

by a filter• 87% efficiency using lignocellulose material• Process feasible for 25 to 400 MW plants



Source: www1.eere.energy.gov

Processed biomass is the boiler fuel that produces steam to operate a steam turbine and generator to make electricity

Thermal ConversionDirect Combustion - Example

How much wood is needed to bring 1 L of water to the boil?

Data:Cp water = 4200 J/kg Kmwater = 1 kgHeat value of wood, h = 15 MJ/kgρwood = 600 kg/m3

Solution: Heat energy needed to heat 1 L of water from 20 oC to 100 oC:Q = ∆h = (t2 – t1)Cp water = 80 · 4200 = 336 kJHeat energy released in burning of 1 cm3 of wood:Q = 15 ·600·10-6 = 9 kJVolume of wood required:V = 336/9 = 37 cm3

Source: Boyle, G., “Renewable Energy”, Oxford University Press Inc., 2004

Thermal ConversionGasification

• Used for the conversion of biomass only for the past 30 years

• Product – syngas• Categories:

• Noncatalytic process – requires a very high temperature of operation (1300 oC)

• Catalytic process – operated at lower temperatures (900 oC and lower)

• The first system investigated at the pilot scale was a fluidized bed that incorporated dry ash-free (DAF) corn stover as the feed

• Corn stover has been selected as the feed since 1977 and if treated properly, has the potential to be converted into an energy source that would supply up to 2% of the US energy needs



• Operating temperatures: 840-1020 K• Feed rate: 27 kg/h• 0.25 x 106 Btu/h gas producedSource: Lee, S., Speight, J. G., Loyalka, S. K., “ Handbook of Alternative Fuel Technologies”,

CRC Press, 2007

Pilot plant fluidized bed for the gasification of corn stove


Sweden’s VEGA gasification system:• June 1991 – cogeneration power plant built in order to

demonstrate integrated gasification combined cycle (IGCC) technology

• 1992 – formation of bioflow with development of pressurized air-blown circulating fluidized bed gasifier technology for biomass

• 1993 – commission of the biomass integrated gasification combined cycle (BIGCC)

• Specifications:» System combines heat and power (CHP) for a direct

heating system» It generates 6 MW and 9 MW for district heating of

the city of Varnamo, Sweden


Thermal ConversionGasification – Vega System



Air-blown circulating fluidized bed gasifier with acatalytic reformer:

• Most processes use closed-coupled combustion with very little or no intermediate gas cleaning

• Operating temperature – 900 oC• Products leaving the gasifier: H2, CO, CO2, H2O, CH4,

C2H4, benzene and tars• Uses O2 and steam to help the process conversion• The effluent gas from the fluidized bed gasifier

contains syngas, which can be used for further processing without major purification; the hydrocarbon content at this stage is reduced by 95% or better


Thermal ConversionGasification – Chrisgas Plant, Varnamo,

Sweden

Source: www.btltec.com


Indirect gasification:• Another gasification process technology• Biomass used low in sulfur and ash, highly reactive

and volatile• Biomass heated indirectly using an external means

such as heated sands in Battelle’s process –known as FERCO SilvaGas process

• A typical gaseous product from a gasifier is close to medium Btu gas

• A commercial-scale demonstration plant constructed in 1997 at Burlington, VT


Thermal ConversionGasification – FERCO Gasifier,

Burlington, VT• Uses: stocker gate,

conventional steam power cycle and electrostatic precipitator (ESP)-based particulate matter removal system

• Capacity: 200 tons/d• Heating value of

product gas: 450-500 Btu/scf



Process requirements of entrained flow reactor:• Very high temperature (1300 oC)• No catalyst• Very short residence time• Very fine particle size of solid feed, required for

efficient entrainment as well as for better conversion without mass transfer limitations; two processes:

• Torrefaction – mild thermal treatment at temperature of 250 to 300 oC, which converts solid biomass into a more brittle and easily pulverizable material called biocoal

• Pyrolysis – takes place at 500 oC and produces liquid product called bio-oil


Thermal ConversionLiquefaction

• Mid-to-late 1980s – interest began• The preliminary studies utilized woody biomass,

or lignocellulose material as a feedstock• McGill University in Canada – the first

documented “successful” production of ethanol from the liquefaction of woody material:

• Used aqueous hydrogen iodine• Operating conditions: 125 oC• Minimal char production


Thermal ConversionLiquefaction – Combined Wood-to-

Ethanol Process


LiquefactionLiquid solid

separationFermentation

Neutralization

Cellulose production

Lignin removal Distillation

Wood chips Ethanol

Xylose

Cellulose/lignin

Thermal ConversionLiquefaction


Slurry Fermenter Distillation

Water Ethanol

Water

Production of ethanol from glucose:C6H12O6 → 2 C2H5OH + 2 CO2

Thermal ConversionLiquefaction - Example


How much ethanol can be produced from a ton of sucrose?

SOLUTION:

C12H22O11 + H2O → 4 C2H5OH + 4 CO2

MSucrose = 342.296 kg/kgmolMWater = 18.016 kg/kgmolMEthanol = 46.068 kg/kgmolMCO2 = 44.01 kg kgmol

Therefore for 1 ton of sucrose, the water required for the reaction, and theethanol and CO2 formed are:

Water = (MWater/MSucrose) · 1 t = 0.053 t = 105.3 lbEthanol = (4MEthanol/MSucrose) · 1 t = 0.538 t = 1077 lbCO2 = (4MCO2/MSucrose) · 1 t = 0.514 t = 1029 lb

Thermal ConversionLiquefaction – Ethanol Properties


• Also called ethyl alcohol or grain alcohol• The nominal heating value - 101,000 Btu/gal, about

¾ the value of gasoline (on volumetric basis)• Motor vehicle that has a gas millage of 24 miles/gal

of gasoline would likely have an ethanol mileage of 18 miles/gal

• Used to improve the octane rating and emission characteristics of gasoline and commonly used in the form of a 10% blend in “gasohol” called E10 (10% ethanol, 90% gasoline)

• The highest blend, E85, contains 85% ethanol; used in flex fuel vehicles

Thermal ConversionPyrolysis

• The exact proportion of the end products depends on the pyrolysis process used (i.e. pressure, temperature)

• Technology identical to that used in the petroleum industry

• The first biocrude produced:• At a 30 kg/h scale• At operating conditions of 500 oC • Residence time of 1 s• The biocrude had the same oxygen and energy content as its

“natural crude” counterpart• Canadian researchers converted woody biomass into

fuel via pyrolysis in a 200 kg/h pilot plant• The fuel oil substitute produced (on 1000 t/d dry basis) at

approximately $3.4/GJ (the cost for light fuel oil $4.0 –4.6/GJ)



• ERCO (Energy Resources Company) unit:• Accepts biomass with a 10% moisture content at a rate of 100

tons/d• Has a minimal net energy efficiency of 70% and produces

gaseous, liquid and char products• Implements cogeneration system to convert the pyrolysis gas

into the electricity• Small fraction of pyrolysis gas also used to dry the entering

feedstock to the required 10% moisture• The average heating values for the pyrolytic oil and char: 10,000

Btu/lb and 12,000 Btu/lb• Pyrolysis gas (nominal heating value of 150 Btu/lb), not

considered an end product - directly used in the cogeneration system


Thermal ConversionPyrolysis – ERCO Unit


Air6758 lb/h

Air5204 lb/h

Biomass8334 lb/h

Oil, GasChar & Ash13,538 lb/h

1022 lb/h Char146 lb/h Ash

Oil & Gas 1212,370 lb/h

To Dryer

Oil to Storage1292 lb/h

CycloneOil

Scrubber

OilCooler

GasTurbine Generator

Pyr

olyz

er


• Hydrocarb process:• Converts a mixed biomass and natural gas feedstock

into methanol, gasoline and char• Basic steps:

• Hydropyrolyzer - the biomass is gasified with recycled hydrogen-rich gas to form a methane-rich gas at 800 oC

• Methane pyrolyzer – CH4 is decomposed to C and H2 at 260 oC

• Methanol synthesis reactor - CO is catalytically combined with H2 to form methanol at 1100 oC



• Hydrocarb process:• For every 100 kg of biomass and 18 kg of methane

fed to the gasifier, approximately 67 kg of methanol and 40 kg of char were produced

• Advantages: • Char produced in this process is pure carbon and it can

be used as a clean fuel• Conversion of CH4 to methanol in the presence of

biomass decreases the CO2 emissions• Potential to replace the feedstock with other materials,

such as MSW (municipal solid waste), CH4 can be replaced with coal


Thermal ConversionPyrolysis – Hydrocarb Process


Gasifier

PyrolysisReactor

MethanolConverter

Methanol

PurgeNatural

GasBiomass

Char

4.65% CO1.54% CO239.76% CH412.6% H2O41.43% H2

12.09% CO; 0.194% CO212.83% CH4; 2.17% H2O72.12% H2

3.89% CO; 0.27% CO218.76% CH4; 0.06% H2O76.11% H2; 0.91% CH3OH

Char

Thermal ConversionLiquefaction – Pyrolysis Liquids

Properties


• Have a low viscosity and are dark brown in appearance

• Highly oxygenated and contain significant amount of water

• Highly unstable and highly corrosive (low pH)• Difficult storage due to the corrosive nature of

pyrolysis• Oxygen and water content makes them

incompatible with conventional hydrocarbon fuels

Thermal ConversionLiquefaction – Methanol Properties


• Also called wood alcohol• Can be used as a fuel in modified internal

combustion engines• The heating value of methanol is nominally

76,000 Btu/gal, only about 58% of the value of gasoline (on volumetric basis)

• A motor vehicle that has a gas mileage of 24 mile/gal would likely have a methanol mileage of about 14 miles/gal

Thermal ConversionLiquefaction – Methanol Properties


• Advantages:• The methanol-air flame temperature is lower than that

for gasoline• Produces lower amount of NOx; no SOx• Has limited soot and CO2 emission

• Disadvantages:• Lower energy density• Presents severe health hazards if ingested or absorbed• Soluble in water• Accidental ignitions can be hard to see, since it burns

with a nearly colorless flame

Biological ConversionAnaerobic Digestion

• Well known for the past 100 years • Mineralizes organically bound materials to CH4 and CO2• Most of the biomass feedstock studied have produced a

biogas rich in CH4• Penn State University digester:

• The first anaerobic digester• Utilized cow manure for biogas production • Operated for a total of 450 days to treat 1200 t of

manure• Composition of the biogas produced: 60% CH4, 32-34%

CO2, 6-8% N2, and trace amounts of H2S• 44 kW - total energy generation




• Biogas - also called swamp gas, landfill gas, or digester gas

• Involves relatively simple systems• Biogas produced in stages by different types of bacteria• Anaerobic digestion stages:

1. Breaking down the waste into sugars and amino acids by hydrolytic bacteria

2. Conversion of the sugars and amino acids to organic acids by fermentative bacteria

3. Conversion of the organic acids to H2, CO2, and acetate by acidogenic bacteria

4. Production of biogas from the acetic acid, H2 and CO2 by methanogenic bacteria



• Takes place in an airtight chamber called a digester

• Digesters modes of operation:• Batch• Continuous - produces a steady stream of biogas and

typically associated with large-scale operation• Temperature sensitive process• Required temperature - at least 68 oF, but

temperatures as high as 150 oF are possible• The higher the temperature, the shorter the

process time and smaller digester volume



• Composition of anaerobic digester: • Pre-mixing tank• Digester vessel• System using biogas• Means of spreading or distributing the digested

effluent



System

Mixer

BiogasCollector

MixingTank

Biomassin

Digester

EffluentDischarger

LagoonStorage

Extraction


• Produces biodiesel from feedstock such as vegetable oils and animal fats

• Biodiesel - composed of fatty acid alkyl esters• Oils can be extracted from seeds, nuts, and other

parts• Direct use of plant oils in diesel engines shortens

operating life and leads to engine maintenance issues

• The expected 10,000 h between engine overhauls can be reduced to 600 h for sunflower oil operation or 100 h for operation on linseed oil

Extraction


• The generic reaction:

triglyceride + methanol → methyl ester + glycerol

• Example of generic reaction - the simplified composition for olive oil:

(C17H33CO2)3C3H5 + 3CH3OH → 3C17H33CO2CH3 + C3H5(OH)3

Where C17H33CO2 - the fatty acid component of olive oil

Extraction- Example


How much biodiesel can be produced from a 100 lb of oil?

MOlive Oil = 885.402 kg/kgmolMMethanol = 96.126 kg/kgmolMBiodiesel = 889.434 kg/kgmolMGlycerol = 92.094 kg/kgmol

Therefore for 100 lb of oil, the methanol required and the biodiesel, andglycerol formed are:

Methanol = (MMethanolr/MOlive Oil) · 100 lb = 10.85 lbBiodiesel = (MBiodiesel/MOlive Oil)· 100 lb = 100.45 lbGlycerol = (MGlycerol/MOlive Oil) · 100 lb = 10.40 lb

Extraction– Biodiesel Properties


• Has a viscosity comparable to conventional diesel fuel and a cetane number about of 50

• Providers for a much longer time between overhauls compared with the use of plant oils

• Burns cleaner than conventional diesel fuel and significantly reduces emissions of CO, unburned and aromatic hydrocarbons, sulfates and particulate matter

Extraction– Biodiesel Properties


• Blends of up to 20% biodiesel with conventional fuel can be used without any engine or infrastructure (storage and distribution) modification

• B5, B10 and B20 are the usual biodiesel blends• Sufficient biomass feedstock exists to supply

1.9 billion barrels of biodiesel, about 5% of the total use of conventional diesel fuel

Extraction


• Basic process for producing biodiesel:• Base-catalyzed transesterification• Direct acid-catalyzed transesterification• Conversion of the oil to its fatty acids and then to biodiesel

• Advantages of the base-catalyzed transesterification:

• Occurs at low temperature and pressure• High conversion efficiency (98%)• Involves minimal side reactions• Conversion to biodiesel is direct, with no intermediate

compounds• No special materials needed in the reactor

Cost of Bioenergy

• The main factors determining the cost of energy from biomass:

• Capital cost including the cost of borrowing money – the main component

• Fuel cost• Operating and maintenance costs - usually proportional to

the output of the plant, and will depend on the fuel type – in particular, the nature of the emissions and the residues it leaves

• Decommissioning costs - usually covered by the scrap value of equipment

• The cost per kWh of output depends on the annual output, so it is important to maximize the load factor


Future Prospects

• Two opposing factors determining future demand for biomass:

• The rise in overall energy demand due to increasing population• The reduction demand for bioenergy due to a shift from traditional to

“modern” forms of energy• Biomass consumption will continue to rise during the

next few decades, but at lower rate than renewables in general or total primary energy

• Traditional biomass will remain the sole domestic fuel for over a quarter of the world’s population in 2030

• Allowing for increased food production for a growing world population, as much as 400-700 million additional hectares could be available for energy crops world-wide in the year 2050, without the loss of biodiversity. If used, this could provide of the order of 100 EJ of bioenergy per year


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