Sampson Mamphweli University of Fort Hare

Institute of Technology

Tel: 0406022311

E-mail: smamphweli@ufh.ac.za

The theory, operation and current status of biogas and biomass air gasification

technologies: A case study of the University of Fort Hare Projects

OVERVIEW OF RESEARCH AT FHIT

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Biogas digester types

• Biogas produced in anaerobic digesters consists of methane (50-80%), carbon dioxide (20-50%) and trace levels of other gases such as hydrogen, carbon monoxide, nitrogen, oxygen and hydrogen sulphide.

• Anaerobic digesters are made out of concrete, steel, bricks or plastic. They are shaped such as troughs, basins or ponds, and may be placed underground or on the surface depending on the design and climatic conditions of an area.

• There are two basic types of digesters, which are batch type and continuous type.

• There are three types of continuous digesters, these are: Vertical tank systems, horizontal tank or plug-flow systems and multi tank systems.

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The digestion process

• Anaerobic decomposition occurs in three basic stages as a result of the activity of a variety of microorganisms. Initially, a group of microorganisms converts organic material into a form that a second group of organisms utilizes to form organic acids and complete the decomposition process.

• A number of factors affect the rate of digestion and biogas production. The most important is temperature.

• Anaerobic bacteria communities can endure temperatures ranging from below freezing to above 57 oC, but they thrive best at temperatures of about 37oC (mesophillic bacteria) and 55oC (thermophillic bacteria).

• Bacteria activity, and thus biogas production, falls off significantly between 39oC and 51oC and gradually from 35oC to 0oC.

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The digestion process

• Hydrolysis is an enzyme mediated stage where insoluble organic compounds such as proteins, fats, lipids and carbohydrates are converted into soluble organic components such as amino acids, fatty acids, monosaccharides, and other simple organic compounds.

• Acidogenesis or fermentation is the next step where soluble compounds produced in the first stage are further degraded resulting in the production of carbon dioxide (CO2), hydrogen (H2), organic acids, alcohols and some organic sulphur compounds.

• Acetogenesis is the third stage of acetic acid formation (acetogenesis) combines the prior acidification with methane formation. The starting substrates are a number of final products from the acidification phase. Examples include, chain fatty acids, propionic acid, polymer substrates (carbohydrates, fats, proteins) and butyric acid. Together with lactic acid, alcohols and glycerol, these substrates are converted by the acetogenic micro-organisms into acetic acid, hydrogen and carbon dioxide

• Methanogenesis: Methanogens convert the acetate and hydrogen to methane and carbon dioxide. Methanogenic bacteria are divided into three categories. Hydrogenotrophic methanogens use hydrogen to convert carbon dioxide to methane. Acetotrophic methanogens split acetate into methane and carbon dioxide. Finally, methylotrophic methanogens produce methane directly from methyl groups, such as methanol, and mono-, di-, and trimethylamines.

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The digestion process

Biomass Carbohydrates

Proteins

Fats

Sugars

Amino acids

Fatty acids

Fatty acids

(Propionic acid)

Alcohols

Hydrogen

Carbon dioxide

Acetic acid

Hydrogen

Carbon

dioxide

Biogas

Methane

Carbon

dioxide

1. STEP

Hydrolysis macromolecule

(Hydrolytic phase)

2. STEP

Acidification

(Acidogene phase)

3. STEP

Acetic acid formed

(Acetogene phase)

4. STEP

Methane formation

(Methanogene phase)

pH: 5-6 pH: 5.5-6.7 pH: 6.6-8.0

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Energy from biogas

• Approximately 1.15 kg of organic waste provides 1 m3 of biogas, equivalent of 1.7 kWh of energy.

• The energy can be used for direct heating or power generation purposes.

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Biogas digesters installations at UFH

The research is focused on:

– Design, installation and performance monitoring

of biogas digesters.

– 5 biogas digesters installed at Fort Cox college, Melani village and UFH.

– 110 digesters planned for Nkonkobe municipality-implementation imminent.

– At least 4 digesters planned for schools in Chris Hani District Municipality

– Demonstrate the use of biogas technology as a cheap and sustainable option.

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Biogas digesters research activities • Design, installation and performance monitoring

Reinforced

Concrete

dome

30 cm blade

COMPUTER

Data logger

Gas sensors

Brick wall

Inner

Brick wall

Sawdust

Slurry outlet

Stirrer

106 cm

20 cm Concrete slab

BIOGAS

SLURRY

Temperature

probe1

Temperature

probe 2

Sensor output

Temperature probes 1 and 2

Gas to house

Flow meter

Inlet pipe

Digester floor

20

cm

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Biogas digesters research activities • Design, installation and performance monitoring

CO2 sensor Gas pump

H2 sensor

Hydrophobic

filter

Flow meter

Laptop

Data logger

12V battery

H2S sensor

CH4 sensor

Biogas

hose

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Biogas digesters research activities

• Biogas yield from cowdung before digester insulation

y = 0.002x2 - 0.0199x + 0.0356

R² = 0.9489

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

2 4 6 8 10 12 14 16 18 20

Gas

yie

ld /

m3

Time / days

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Biogas digesters research activities

• Biogas yield from cow dung vs COD concentration

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

0

0.1

0.2

0.3

0.4

0.5

0.6

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29

pH

Bio

ga

s y

ield

/ m

3

Retention time / days

Gas yield

COD

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Biogas digesters research activities

• Biogas yield from cow dung and donkey dung

0

0.1

0.2

0.3

0.4

0.5

0.6

4 6 8 10 12 14 16 18 20 22 24 26 28 30

Bio

ga

s y

ield

/ m

3

Retention time / days

Cow Donkey

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Biogas digesters research activities

• Bacteria activity in cowdung

– Bacteria that has been well documented in cow manure include Salmonella Sp,

Escherichia coli and Camphilobacter species.

– These are associated with human gastrointestinal infection.

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0 5 10 15 200

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Time/Days

log

bacte

ria c

ou

nts

(cfu

/g)

0 20 40 60 800

1

2

3

4

5

6

Time/Days

log

bacte

ria c

ou

nts

(cfu

/g)

0 25 50 75 100 125 1500

1

2

3

4

5

6

Time/Dayslo

g b

acte

ria c

ou

nts

(cfu

/g)

measured data

regression line

measured data

regression line

measured data

regression line

(a) Reduction of Campylobacter sp counts with retention time. (b) Reduction of E.

coli counts with retention time. (c) Reduction of Salmonella sp counts with

retention time.

(a) (b) (c)

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Digesters at UFH

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BIOMASS GASIFICATION

• Biomass gasifier converts wood and wood waste into charcoal

giving gas as a by-product.

• The gas is a mixture of CO2, CH4, H2, CO, H2O and N2.

• It has a heating value of 3-6MJ/kg and is used for heating and

electricity generation.

• The University of Fort Hare installed a150kVA System Johanson

Biomass Gasifier at Melani village for powering a community

bakery and for research purposes.

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Gasification process

Drying

Biomass + H2O Pyrolysis Oxidation Reduction

Producer gas

H2O N2,Tar,CH4 CO,H2O CO2,H2

The Gas Producer The pollution-free answer to

providing inexpensive energy through consumption of Bio-mass

material!

THE PROCESS

Gasifier 1.Fuel Compartment with Condensate trap 2.Inverted Reduction Cone 3. Combustion Chamber 4.Hearth 5. Ash Grate Activator

The Cyclone The Raw Gas is passed through the Cyclone, which removes the course dust from the raw gas

The Gas Scrubber / Cooler. After the course dust has been removed from the cyclone, the fine dust(5ml/N³) is carried with the sprayed scrubbing water over a low resistance porous scrubbing media. The water is recycled through an ambient cooling pond. The gas is cooled to ambient temp.

The long life particle interference filter….

The Particle Interference Filter The cooled gas is passed through the filter filled with course sawdust

The safety filter….

The Safety Filter Before reaching the engine, the clean gas is finally passed through a standard 5 micron double cartridge Donaldson Filter.

The generator….

The Generator…….

The engine….

The Engine……

The engine….

(CO) Emissions from Engine

Carbon neutral

The cooling pond….

The Cooling Pond…… Water contains no toxic elements and can be used for irrigation purposes!

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Prototype for R&D

BIOMASS CHARACTERIZATION

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• 150 kVA Melani village gasifier

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The gasifier

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Presented by: Sampson Mamphweli

Thank you