The theory, operation and current status of
biogas and biomass air gasification
technologies: A case study of the University of
Fort Hare Projects
Sampson Mamphweli
University of Fort Hare
Institute of Technology
Tel: 0406022311
E-mail: smamphweli@ufh.ac.za
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
1. STEP
Hydrolysis macromolecule
(Hydrolytic phase)
2. STEP
3. STEP
Acetic acid formed
(Acetogene phase)
Acidification
(Acidogene phase)
pH: 5.5-6.7
pH: 5-6
4. STEP
Methane formation
(Methanogene phase)
pH: 6.6-8.0
Hydrogen
Carbon dioxide
Biomass
Carbohydrates
Proteins
Fats
Biogas
Methane
Carbon
dioxide
Sugars
Amino acids
Fatty acids
Fatty acids
(Propionic acid)
Alcohols
Acetic acid
Hydrogen
Carbon
dioxide
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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
Data logger
Sensor output
COMPUTER
Temperature probes 1 and 2
Gas sensors
Gas to house
Flow meter
Inlet pipe
Reinforced
Concrete
dome
Temperature
probe 2
BIOGAS
Inner
Brick wall
Brick wall
SLURRY
Sawdust
Stirrer
30 cm blade
Temperature
probe1
Slurry outlet
Digester floor
106 cm
20 cm
20
cm
Concrete slab
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Biogas digesters research activities
• Design, installation and performance monitoring
H2S sensor
Flow meter
Biogas
hose
Laptop
Hydrophobic
filter
Gas pump
12V battery
CO2 sensor
H2 sensor
Data logger
CH4 sensor
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Biogas digesters research activities
• Biogas yield from cowdung before digester insulation
0.35
0.3
Gas yield / m3
0.25
y = 0.002x2 - 0.0199x + 0.0356
R² = 0.9489
0.2
0.15
0.1
0.05
0
2
4
6
8
10
12
Time / days
14
16
18
20
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Biogas digesters research activities
• Biogas yield from cow dung vs COD concentration
0.6
45000
40000
0.5
Gas yield
35000
0.4
30000
25000
pH
Biogas yield / m3
COD
0.3
20000
0.2
15000
10000
0.1
5000
0
0
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
Retention time / days
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Biogas digesters research activities
• Biogas yield from cow dung and donkey dung
0.6
Biogas yield / m3
0.5
0.4
Cow
Donkey
0.3
0.2
0.1
0
4
6
8
10
12
14
16
18
Retention time / days
20
22
24
26
28
30
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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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(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.
4.5
6
6
measured data
regression line
4
measured data
regression line
measured data
regression line
5
5
3
2.5
2
1.5
log bacteria counts(cfu/g)
log bacteria counts (cfu/g)
log bacteria counts (cfu/g)
3.5
4
3
2
4
3
2
1
1
1
0.5
0
0
5
10
15
Time/Days
(a)
20
0
0
20
40
60
Time/Days
(b)
80
0
0 25 50 75 100 125 150
Time/Days
(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
H2O
Pyrolysis
N2,Tar,CH4
Oxidation
CO,H2O
Reduction
CO2,H2
Producer gas
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THE PROCESS
The Gas Producer
The pollution-free answer to
providing inexpensive energy
through consumption of Bio-mass
material!
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!
Prototype for R&D
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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
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