Biofuels Lec 3-Biogas: part 1

Chemical Engineering Department | University of Jordan | Amman 11942, Jordan

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Dr.-Eng. Zayed Al-Hamamre

Biofuels

Lec 3-Biogas: part 1


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Content

History of Biogas

Biogas: Green Energy

Biogas utilization

Biogas Plants


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What’s Biogas?

What Biogas is NOT …

Biogas is NOT pure methane (natural gas).

Biogas is NOT biodiesel.

Biogas is NOT bioethanol.

It’s a gaseous Biofuel made up of a mixture of methane (60%) and carbon dioxide (40%) – with trace amounts of hydrogen sulfide and water vapor (contaminants).


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• One of the oldest forms of renewable energy

• Marco Polo mentioned the use of the technology. Probably goes back 2000-3000 years ago in ancient Chinese literature

• The earliest evidence of use in Assyria (10th

century BC)

History of Biogas


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• Jan Baptita Van Helmont determined in 1630 that flammable gases could evolve from decaying organic matter.

• Anaerobic digestion first described by Benjamin Franklin 1764.

• Count Alessandro Volta in 1776 found a correlation between amount of decaying organic matter and amount of flammable gas produced.

• In 1808, Sir Humphrey Davy determined that methane was present in the decay process.

History of Biogas


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• First digestion plant was built in 1859 in Bombay, India for a leper colony

• Exeter, England, in 1895: biogas used to power street lamps

• 1920’s and 30’s interest in anaerobic digestion increased

• Interest in Biogas has been cyclical

History of Biogas


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1808 – Sir Humphrey Davy found

that methane was present in the gases that is formed by

the Anaerobic Digestion of

manure

1884 – Louis Pasteur student,

Ulysse Gayon, performed the

anaerobic fermentation of

manure and water at 35ºC and obtained 100 liters of Biogas per

cubic meter of Manure.

1895 – Biogas is used to light up the streets

in Exeter, England

1957 – A British

Inventor, Bates,

modifies his car to run on

Biogas produced from

pig manure.

2005 – The Biogas Support

program in Nepal wins the

AshdenReward for

installing over 150,000

Biogas Plants in rural areas. And a Biogas powered train

starts it's service in Sweden

History of Biogas


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Composition of biogas


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• Insignificant amounts of oxygen and hydrogen sulfide (H2S).

• Biogas burns without soot or ash being produced

• Methane is a combustible gas

• Biogas will be used to generate energy for the cooking needs here at Rosalie Forest Eco Lodge

Biogas: Green Energy

Visible improvement in rural hygiene.

Environmental benefits on a global scale.

Protects the earth's natural resources.

Eco friendly energy production.

Boon for the rural economy

Advantages of biogas


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GASES

Biogas : Impure; expensive to compress and very expensive to liquefy; 600 BTU/ft3

or 80.2 BTU/gal. (vol.) @ atmospheric pressure

Methane: Higher energy content than biogas (no CO2); expensive to compress and

very expensive to liquefy; 1031 BTU/ ft3 or 137.8 BTU/gal. (vol.) @ atmospheric

pressure

Gaseous Propane (LP Gas) : 2570 BTU/ft3 or 343.6 BTU/gal. (vol.) @ atmospheric

pressure

LIQUIDS

Liquefied Propane (LP Gas) : Concentrated, high energy liquid fuel 91,600 BTU/gal.

Petroleum Gasoline : High energy, compact liquid fuel 124,000 BTU/gal.

#1 Diesel Fuel : High energy, compact liquid fuel 136,000 BTU/gal.

Compare Fuel BTU Values…


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Biogas is low in BTUs/gal. (vol.), so it isn’t feasible to useas a motor fuel. It needs to be used as a stationary fuel,such as in an electrical power-generating plant or boiler.

1 Gal.

Liquid

Petroleum

= 1700 Gal.

of Biogas

Compare Fuel BTU Values…


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Emissions vs. other Fuels

• Every emission lowered (except methane)

• Much cleaner, More efficient


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Keep in Mind…

Biogas can be burned and used as a heat source (produce hot air, hot water or steam).

Biogas can be used to operate an engine generator set that produces electricity and if the waste heat is captured and used, (Combined Heat & Power-CHP), plant efficiency improves.

The monetary benefit occurs when the electricity generated is used to replace electricity that’s normally bought at retail.

A Combined Heat & Power (CHP) unit increases the cost of an anaerobic digester system.

You can store gas – but can’t store electricity.

The heating value of biogas is about 60% of natural gas and about 25% of

propane.

Biogas has corrosive nature and storage of biogas is not practical


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The Green Gas Principle

Households

Industry

VehiclesNatural gas

Biomethane

The possibility to inject produced biogas into the natural gas grid, and then withdraw a similar volume at another point on the grid provides essential synergies and economic advantages.

e.g. Southern California Gas

Biogas = Natural Gas


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Biogas utilization


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Biogas utilization


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Biogas utilization


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Biogas utilization


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Anaerobic

fermentation

is a natural

and

unavoidable

process

Biogas – a way to solve sanitation problems


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Biogas Plants

A biogas plant is the name often given to an anaerobic digester that treats farm

wastes or energy crops.

These plants can be fed with energy crops such as maize silage or biodegradable

wastes including sewage sludge and food waste.

During the process, an air-tight tank transforms biomass waste into methane

producing renewable energy that can be used for heating, electricity, and many other

operations.

• A Biodigester is a device that mimics the natural decay process of organic

matter

• Biogas is produced from anaerobic decay (decay that occurs without

oxygen)


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Anaerobic Digestion

• Reduce - Smell- Greenhouse gas- Pathogen level

• Produce biogas

• Improve fertilizer value of manure

• Protect water resources


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Spying on Nature – What can we learn from cows?

Inlet OutletBiogas digester

Cows convert biodegradable plants and water to milk, cow dung and

urine – and gases


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A new look at the cow – and bull

Inlet

Outlet

Biogas digester

The Biogas Plant


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A biogas plant operates though anaerobic digestion oforganic material

The Biogas Plant

Inlet Outlet

Biogas digester

Biogas


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• Any organic waste can produce biogas

• Human, manure, fruit and vegetable waste

What Type of Waste Does NOT Produces Biogas?

• Fiber rich waste such as wood, leaves, etc. are difficult to digest

• Heavy metals

• Inorganic materials in high concentration (Nitrate, Sodium, Sulphate, Sodium, Potassium, Calcium, Magnesium, etc)

What Type of Waste Produces Biogas?


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Integrating biogas in agriculture


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Biogas Cycle


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Agroetanol, Norrköping

Agricultural Wastes

Industrial

Organic Wastes

Household

Organic Wastes

Methane

Solid Digestate

CO2

ElectricityHeat

Energy

Inputs

HeatEnergy

Outputs

Material

Inputs

Material

Outputs

Liquid Effluent

Other Gases

Integrating biogas in agriculture


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Biogas Production Potential from different Wastes


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• Digester is fed a mixture of water and waste called a slurry

• Daily, fresh slurry is added, displacing previous days load that bacteria have started to digest

• First, digestible organic matter is broken down by acid-producing bacteria

• By-products are then broken down by methane-producing bacteria

(journeytoforever.org/biofuel_library/)

How Do Anaerobic Digesters (AD) Work?


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The AD system is divided into three processes: hydrolysis, acidogenesis/ acetogenesis, and

methanogenesis.

Stage I: Hydrolysis

Hydrolytic bacteria convert (breaking) complex organic matter (proteins, fats, and

carbohydrates) present in the waste feedstock into soluble fatty acids and other organic

monomers.

This process is mediated by hydrolytic enzymes including proteases, which degrade proteins,

lipases, which degrade fats, and cellulases, which degrade cellulose.

Acetate and hydrogen produced in Stage I can be used directly by methanogens.

Biochemical process of anaerobic fermentation/digestion

- Protein → Polypeptide and Amino Acid

- Fat/Lipids → Glycerin and Fatty Acid

- Amylose → Monosacride and Polysacride

- Nucleic Acids → Purines & Pyrimidines


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Byproducts, including ammonia and hydrogen sulfide, are also produced (Strik et al., 2005).

Other molecules such as volatile fatty acids (VFAs) with a chain length that is longer than

acetate e.g. propionate and butyrate must first be catabolised into compounds that can be

directly utilized by methanogens.

Stage III: Acetogensis.

Acetogenesis further converts the acidogenesis products into acetic acid, carbon dioxide, and

hydrogen.


Stage 2: Acidogenesis

Converts the hydrolysis products (amino acids, fatty acids, and sugars) into VFAs, alcohols,

carbon dioxide, and hydrogen.


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Stage IV: Methanogenesis

Here methanogens utilize the intermediate products of the preceding stages and convert them

into methane, carbon dioxide and water.

Methanogenic Archaea produce methane from the products of acido/acetogenesis.

There are two main types of microorganisms responsible for methane formation: acetoclastic

methanogens and hydrogen-utilizing methanogens.

Acetoclastic methanogens split acetate (an electron donor) into carbon dioxide and methane

(Lachavanne et. al., 1997).

Hydrogen-utilizing methanogens use hydrogen and reduce carbon dioxide to form methane

(Mara et al., 2003).

The former pathway is the dominant mechanism and typically accounts for approximately

70% of methane production in AD reactors because hydrogen is limited in AD.



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Acetogenic

bacteria

Fermentative

bacteria

Methanogenic

bacteria

Organic waste

Carbohydrates

Fats

Protein

Water

Bacterial

mass

H2 , CO2

acetic acid

Bacterial

mass

Methan

+ CO2

Bacterial

mass

Propionic acid

Butyric acid

Alcohols,

Other components

H2 , CO2,

acetic acid

Step 1:

Hydrolysis + Acidogenesis Step 2:

AcetogenesisStep 3:


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Energy balance – for composting and digestion

Aerobic conversion (composting):

C6 H12 O6 + 6O2 6 CO2 +6 H2 O

E= -3,880 kJ/mol

Anaerobic conversion (digestion):

C6 H 12 O6 + 2H2 O 3 CO2 + 3CH4 + 2H 2O

E= - 405 kJ/mol

Burning of biogas:

2CH4+ 6O2 CO2 + 6 H2 O

E = -3,475 kJ/mol


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Biogas Plant design


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Biogas Plant design


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Principles for design and construction

Gas collector:

fixed dome, or

floating dome

Continuous feeding

or batch feeding

Further

treatment or

direct

use

Pedro Kraemer, BORDA, India


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Efficiency of a biogas unit

Input:

1 kg of dry (95%) cattle dung will produce 2.5 kWh (rule of thumb)

1 kg dry (100%) matter can generate 2.5/0.95 = 2.63 kWh

Slurry contains 10% dry matter, thus 1 litre can generate 0.263 kWh

1 litre slurry (27oC, 90 days retention) releases 27 litre biogas

1 m3 of biogas can generate 6 kWh (rule of thumb)

So, 1 lit of slurry generates 0.027*6 = 0.162 kWh

Actual kWh

Potential kWh

Efficiency =0.162

0.262

= = 0.62

62% efficiency and the other 38% energy remains in the slurry


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Pre-treatment separation of non-digestible materials and

shredding Mixing Macerating Hygienisation/ sterilisation +/- other pre-treatment: e.g. concentration

Digestion

Aftertreatmnet Store Separate Upgrade

End use Land application Move and apply Transport market / or disposal

Biogas Plant design


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Type of Digesters

KVIC Floating Drum Plant

disseminated since 1962

Initial cost of installation is more for the Khadi Village Industries Commission plant.

Cost or repair and maintenance during operation is relatively high.

Steel gas holder needs to be replaced due to corrosion effect.

Life of digester is expected to be 30 years and that of the gas holder is 5-7 years.

Drum, which is exposed over the ground, does not allow the use of space over the plant for

other purposes.

As the gas holder is metallic, the low temperature during winters effects the gas production.

Most suitable for dung and night soil, other organic materials may clog the inlet pipe.

Requires less excavation work during installation

Location of defects in gas holder and its repair is easy and can be done in the workshop


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Type of Digesters

Release of gas is at constant pressure because of fixed weight of steel gas holder and hence

efficiency of plant is higher.

Construction of digester is simple and hence no skilled labor is required but fabrication of

gasholder requires workshop facility

KVIC Digester (used in India and China)


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Deenbandhu Fixed Dome Plant Developed in early 80s

Capital investment for corresponding size of the plant is less.

As there are no moving parts, the maintenance cost is high.

Steel gas holder is not required.

Life of the plant is expected to be comparatively more.

As the unit is underground, the space above the plant can be used for other purposes.

Effect of low temperature is less.

Type of Digesters

Construction of dome portion of unit is a skilled job and only trained mason can do it.

Requires more excavation work.

Location of defects in the dome and their repair is difficult.

Release of gas is at variable pressure and it may cause reduction in efficiency of gas

appliances.


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Type of Digesters

It could be easily modified and

adopted for use of other types of

organic wastes.

Design consists of segments of

two spheres of different diameters

joined at their base

Fluctuating gas pressure

Lower cost compared to KVIC

model


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Basic Designs of Digester

• Continuous-fed

• Batch-fed


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Continuous-fed System

• Suited for large-scale manure substrate bioreactor.

• Steady biogas production can be expected.

• May require auxiliary equipment.

• Requires high liquid content.

• Temperature, loading rate, and solid content need to be carefully monitored.


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Batch-fed System

• The simplest design.

• Low cost.

• The feedstock is loaded one batch at time.

• Irregular biogas production.

• Can operate on high solid content.

• Less susceptible to fluctuation of factors.

• Requires manual labor.


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Bag Biodigester

• The idea is to make a small-scale, low-cost biodigester plant so that anyone in the world can make it and produce biogas.


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Type of Digesters

Fixed dome Digester


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Fixed-dome biogas digester

21

4

slurry3

Bird´s

eye view

12

34


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Floating-drum unit with water-jacket


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Type of Digesters

Floating drum Digester


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Anaerobic filter (off-plot system)

gas manhole

inflow

scumoutflow

filter mass

grillsludge

sedimentation tank filter tanks


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Anaerobic baffled reactor Off-plot system

gasmanholes

w

um outflow

dge

sedimentation inoculation of fresh wastewater with active sludge final settler

Anaerobic Baffled Reactor


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toilet sectionshowersection

anaerobic baffledreactor

waste-water


Public toilet with hidden treatment unit


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A public toilet with a biogas digester

Jan-Olof Drangert, Linköping University, Sweden


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Examples of Digesters Around the World

Costa Rica


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Construction of a BGD for asubsistence farm with 6 cows inGeorgia



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India (ARTI)



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United States Princeton, Minnesota Princeton, Minnesota



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A KVIC Type Biogas Plant


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20 m3/day Capacity KVIC Biogas Plant installed at IIT Delhi


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Large Biogas plants

Horizontal digester, built in Denmark (Nordisk Folkecenter 2001)

Vertical digester in Germany

(KRIEG AND FISHER 2008)


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Picture of farm scale biogas plant in Denmark

co‐digesting animal slurries and energy crops

Large Biogas plants


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Very lager and Centralised co-digestion plants

Digesting animal manure and slurries, collected from several farms

Centrally located in the manure collection area. Co-digest animal manure with a variety of other suitable co-

substrates (e.g. food- and fish industries) Largely applied in Denmark

size from 550 m3 to 8500 m3 treat1.2 million tons of animal slurry every year with 325.000 tons of other kinds of organic waste (Vietnamese digester 10 m3)

HRT :12-25 days Controlled sanitation process


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Centralised co-digestion plants

Schematic representation of the closed cycle of centralized anaerobic digestion

(AL SEADI 2001)


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Centralised co-digestion plants

Centralised co-digestion plant in Denmark (LEMVIG BIOGAS)


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Traditional biogas process – waste to energy


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Biofuels Lec 3-Biogas: part 1

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Transcript of Biofuels Lec 3-Biogas: part 1