8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
1/57
E N G R . P R O F E S S O R I . N . I T O D O
D E A N , C O L L E G E O F E N G I N E E R I N G
U N I V E R S I T Y O F A G R I C U L T U R E
M A K U R D I , N I G E R I A
E - M A I L : D R I T O D O @ Y A H O O . C O M
Biogas Production in Rural
Communities
Sensitization and Awareness Forum (SAF) on Renewable EnergyInitiatives in Edo State, Barden-Barden Hotel,
Benin, 25thAugust, 2009
mailto:[email protected]:[email protected]8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
2/57
Outline2
Introduction Feedstocks Production
Factors affecting production Methods of improving production
Economics Technologies
Types of plants Construction of plant
Preconstruction considerations Construction
Operation Output and pressure
Maintenance Safety issues
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
3/57
Introduction3
Biogas is produced when biomass is subjected tobiological gasification.
Nigerias animal waste resource base is estimated to
be 61 million tonnes/year Nigerias crop residue resource base is estimated to
be 83 million tonnes/year
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
4/57
Prof. I. N. Itodo 4
Energy source CapacityHydropower, large scale 10,000
Hydropower, small scale 734 MW
Fuelwood 13,071,464 ha (forest land1981)
Animal waste 61 million tonnes/year
Crop residue 83 million tonnes/year
Solar radiation 3.5-7.0 kWh/m2-day
Wind 2.4 m/s (annual average)
Nigerias Renewable Resources
ECN (2005). Renewable Energy Resources, Technology and Markets. Renewable EnergyMaster Plan. Energy Commission of Nigeria, Abuja. Pp.3-4
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
5/57
Introduction
Prof. I. N. Itodo
5
Biogas is a methane-rich gas produced from theanaerobic digestion of organic materials.
It is a high-grade fuel of 22 MJ/m3 (15.6MJ/kg).
The density of biogas is 1.2 kg/l at atmosphericpressure, which makes it denser than air.
The biomass materials are held in a digester orreactor.
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
6/57
Introduction6
The gas is produced from a three-phase process namely,hydrolysis, acid-forming and methane-forming phases.
It is a biological-engineering process in which a complex set ofenvironmentally sensitive micro-organisms are involved.
The gas is typically composed of 70% methane, 30% carbondioxide, 1-10% hydrogen, 1-3% nitrogen, 0.1% oxygen andcarbon monoxide and traces of hydrogen sulphide.
Factors affecting the production of this gas includetemperature, pH, total solids concentration of the slurry,
digester type and design, presence of toxic ingredients in thewaste stream and the carbon to nitrogen ratio of the slurry.
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
7/57
Introduction7
Biogas is used for cooking and heating and as such can beused in unit operations like frying and cold storage ofagricultural produces such as the refrigeration of fruitand vegetables.
Worldwide installed power capacity of biomass for grid-connected power generation and estimated annualenergy generation in 2008 is 4 GW and 227-357 TWh
Bubbling the gas through lime solution purifies it byremoving the carbon dioxide thereby improving itsheating value to about 56 MJ/m3.
The hydrogen sulphide is removed by bubbling the gasthrough sawdust impregnated with iron filling in amixture of 1:1.
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
8/57
Introduction8
The advantages of this technology are:
It is also a waste management technique because theanaerobic treatment process eliminates the harmfulmicro-organisms. About 85% of the pathogens contained
in the waste are killed by the anaerobic digestion process. The digested slurry is relatively odourless and attracts
much fewer flies than the fresh slurry.
Anaerobic digestion has also been used for sewage
treatment. It is a cheap source of energy because the feedstock is
usually waste materials.
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
9/57
Introduction9
The technology ensures energy independence as aunit can meet the needs of a family or community.
The digested slurry is a good fertilizer. It is claimed
that its value as fertilizer could double crop yield. The treated effluent from the anaerobic digestion
process is a good animal feed when treated andmixed with molasses and grains.
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
10/57
Introduction10
The disadvantages of the technology are:
Gas yield from the digester may not be steady whichtherefore makes it unreliable thereby necessitating
storage. It is a low-pressure gas production system and as
such cannot be bottled for use outside the site of production thereby restricting the technology only to
the site of production.
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
11/57
Introduction11
To date the main interest in the third world in biogastechnology has come from countries of Asia and thePacific region.
Despite the numerous advantages of using biogas
technology as a source of energy and a source of nitrogen-rich fertilizer, it has made only little impact in
Africa and Latin America.
Attitude to biogas technology varies from region toregion. While the west often sees new and renewableenergy sources as morally superior, green or soft orappropriate, the third world suspects that they aresecond-class technology.
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
12/57
Introduction12
The Sokoto Energy Research Centre has constructed andoperated more than twenty one (21) biogas plants of 10 20 m3 capacity across the country using differentfeedstocks such as cow dung, human excreta, piggery andpoultry wastes.
The Raw Materials Research and Development Councilfunded the construction of a float-drum type of biogasplant at the University of Agriculture, Makurdi in 1999.
The United Nations Development Programme (UNDP)has successfully introduced the floating drum, plastic
balloon and other types of biogas plants to Yobe, Kanoand Jigawa states under the African 2000 Low Technology Biogas System.
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
13/57
Introduction13
The success story of the use of biogas in Nigeria isillustrated by its use in Kwachiri community where afamily of forty (40) have been using it for their dailycooking needs since 2003.
The United Nations Development Programme hasalso introduced this technology to some abattoirs insome Northern states of Nigeria.
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
14/57
14
Fig. 1: Biogas plant at the University of Agriculture, Makurdiand the burning flame from the plant
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
15/57
Feedstocks15
Animal wastes and plant residues are excellentfeedstock for biogas production because they areorganic compounds that contain carbon andnitrogen in the required proportion.
Animal waste such as poultry waste, cattle waste,piggery waste and human excreta are used in biogasproduction.
Crop residues and crops such as water hyacinth havealso successfully been used as feedstock in biogasproduction.
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
16/57
Prof. I. N. Itodo 16
Livestock Manureproduced(milliontonnes)
Populationbased onFMA, 1997(million)
Manureproduced2001calculated(milliontonnes)
Cattle 170.4 21 197.6
Sheep 13 38.5 15.1
Goat 21.1 62.4 24.5
Pig 13.2 9.6 15.3
Poultry 28.1 42.9 32.6Total 245.9 285.1
Calculated manure production of Nigerias livestock
ECN (2005). Renewable Energy Resources, Technology and Markets. Renewable EnergyMaster Plan. Energy Commission of Nigeria, Abuja. Pp.3-4
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
17/57
Production17
Biogas is produced from a three-phase processnamely the hydrolysis, acid-forming and methane-forming phases.
In the hydrolysis phase, extra cellular enzymessecreted by acidogens break down the complexorganic material into simple, soluble molecules.
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
18/57
Production
Prof. I. N. Itodo
18
These molecules are broken down into volatile fattyacids (e.g. propionic and butyric acids), carbondioxide, ammonia and hydrogen by acidogens in theacid-forming phase.
In the methane-forming phase, methanogens ormethane-formers convert the VFA into methane,carbon dioxide, carbon monoxide, nitrogen and
hydrogen sulphide. In this phase too, a synthesis ofcarbon dioxide and hydrogen takes place to alsoform methane and water.
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
19/57
19
Hydrolysis phase
Acid-forming phase
Methane-formingphase
Simple soluble molecules
CH4,
CO2, N, H
2, H
2S
VFA,NH
3,CO
2,H
2,etc
CO2+4H
2= CH
4+2H
2O
Feedstock (e.g. poultry waste) + water
Fig.2: Flow diagram of biogas production process
Prof. I. N. Itodo
F ff i bi d i
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
20/57
Factors affecting biogas production
20
Temperature
Total solids concentration (TS)
Retention time
pH Loading rate
Carbon-to-nitrogen ratio of slurry
Toxicity
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
21/57
Temperature21
Temperature is an important parameter that affectsbiogas production.
This is because it affects the enzymatic activities of
the micro-organism responsible for thebioconversion of substrates into gas.
Biogas can be produced at the psychophilic (below20c), mesophilic (20c-40c) and thermophilic
(40c-65c) temperatures. Table 1 is the advantages and disadvantages of
producing gas at each of these temperatures.
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
22/57
22
Temperature
range
Advantage(s) Disadvantage(s)
Psychophilic None 1. Bioconversion is
slow and incomplete
2. Longer detention
time is required
3. Heating of the
digester is required
Mesophilic This temperature
corresponds to the
ambient temperature of
the Tropics and as such
no heating is required
thus reducing cost of
production
Longer detention time
may be required to
enable complete
conversion of the
available carbon
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
23/57
23
Thermophilic 1. Higher rate of gas
production
2. Allows heavier organic
loading
3. Lower detention time4. Enables the use of
comparatively smaller
size digesters
5. Digestion is much
more sanitary than
digestion at the other
temperatures because
of the few pathogens
that can survive at this
temperature
6. Mechanical transport
and handling of the
digester is easier
because the slurry is
less viscous
Digestion is easily
upset at this
temperature
Prof. I. N. Itodo
T t l lid t ti f l (TS)
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
24/57
Total solids concentration of slurry (TS)
24
Slurry is diluted by the addition of liquid and concentrated by theaddition of slurry solids.
Slurries of feedstock used in the anaerobic digestion process toproduce biogas are usually classified as low (less than 10% TS) andhigh (TS greater than 20%).
Low TS Slurries of low TS are easier to handle by pumps and pipe works
compared to those of high TS. If the slurry is too thin, the solid matter separates and falls to the
bottom instead of remaining in suspension resulting in reduced gasyield.
High TS If the slurry is too thick, the biogas produced is trapped within the
slurry and rises to the surface with great difficulty resulting inreduced gas yield.
Prof. I. N. Itodo
R t ti ti
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
25/57
Retention time
25
Generally, 30 days is considered as a minimum timeframe for optimum bacterial decomposition to takeplace to produce biogas and destroy the toxicpathogens found in waste.
Prof. I. N. Itodo
H
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
26/57
pH
26
The pH value of the slurry in the digester is animportant indicator of methanogenic performance.In the absence of any other indicator, pH value alonehas been used to check the digester environment.
Gas will be produced if the pH is between 6.6 and7.6. Gas production is highest when the pH is
between 7.0 and 7.2.
Beyond this pH limits, digestion can proceed butwith less efficiency.
Prof. I. N. Itodo
Loading rate
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
27/57
Loading rate
27
The quantity of waste that is fed into a digester dependson the capacity of the digester, the temperature at whichdigestion is taking place, the retention time and theefficiency of bioconversion of the waste into biogas.
Increasing the loading rate after the optimum valueincreases the TS concentration of the slurry, whichresults in an accumulation of some inhibitory compounds that reduce the rate of gas yield.
In a simple biogas plant, 1.5 kg/m3/day is already quite ahigh loading rate. Temperature controlled andmechanically stirred large scale plants can be loaded atabout 5 kg/m3/day.
Prof. I. N. Itodo
Carbon to Nitrogen ratio of slurry
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
28/57
Carbon- to-Nitrogen ratio of slurry
28
The microbial population involved in anaerobic digestionrequires sufficient nutrient to grow and multiply. Each speciesrequire both a source of carbon and nitrogen.
If there is an insufficient quantity of nitrogen present, thebacteria will be unable to produce the enzymes which are
needed to utilize the carbon. If there is too much nitrogen, particularly in the form of
ammonia, it can inhibit the growth of bacteria. An optimum ratio of Carbon to Nitrogen (C: N) of
between 20:1 and 30:1 is recommended for optimummethanogenic performance.
A deficiency in the carbon content of animal manure used foranaerobic digestion can be corrected by the addition of plant
wastes, which are high in carbon content.
Prof. I. N. Itodo
Toxicity
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
29/57
Toxicity
29
Many compounds can be toxic to methanogens if presentin sufficient concentration in digesters although some areneeded, they quickly become inhibitory. Sources of toxicity in biogas plants are:
The various salts, heavy metals such as Copper, Zinc and
Nikel present in the waste, antibiotics in the feed foranimals that produce the waste and ammoniaconcentrations of the slurry in excess of 3000 mg/l.
Formation of aromatics such as phenol, P-cresol, ethylphenol, indole and skatole during the microbial
degradation of proteins contained in the waste being fedinto the digester.
High concentrations of volatile fatty acids in the digester.
Prof. I. N. Itodo
M th d f i i bi d ti
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
30/57
Methods of improving biogas production
30
The anaerobic digestion process can be improved bythe pre-treatment of organic wastes, the mixing ofdifferent waste types, the addition of chemicals anduse of media materials among others.
The addition of certain chemicals such as nickelaccelerates and increases gas yield.
The use of mixed substrate. E.g. 25% poultry manureand 75% brewery waste water.
Pre-treatment of the feedstock such as milling todiminish the particle size, swelling in an alkalinesolution and heating of the feedstock.
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
31/57
Methods of improving biogas production
31
Re-concentrating flushed waste (waste to whichfresh waste has been added to increase its TSconcentration).
Stirring or mixing of the digester content. Two-phase anaerobic digestion of waste. The two-
phase concept consists of first digesting the waste inan acid phase. The gaseous and liquid products of
this phase are separately conveyed into separatemethane fermenters to enable biogas production.
Prof. I. N. Itodo
Economics of Biogas Production
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
32/57
Economics of Biogas Production
32
A biogas plant is economically viable if:
1 m3 of biogas is produced from 1m3 of digestervolume
18-20 m3
of biogas is produced from 1m3
of feedstock
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
33/57
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
34/57
34
Fig. 3: Floating-drum Plant
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
35/57
35
Fig. 4: Fixed dome plant
Prof. I. N. Itodo
Construction of Biogas Plants
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
36/57
Construction of Biogas Plants
36
Preconstruction consideration
Availability of feedstock to meet the daily need ofmanure to be fed into the digester
Location Sizing of plant
Material of construction
Tools
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
37/57
Availability of feedstock37
The amount of manure fed daily into a digester isdetermined by the volume of the digester itself,divided over a period of 30-40 days.
Thirty days is chosen as a minimum time frame foroptimum bacterial decomposition to take place toproduce biogas and destroy many of the toxic
pathogens found in wastes.
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
38/57
Location38
The digester pit should not be dug within 13 meters of a drinkingwater well or spring.
If the water table is reached during digging, it will be necessary tocement the inside of the digester pit although this increases the cost.
The digester should be located near the source of the feedstock sothat excessive time is not spent transporting the manure.
Be sure that there is enough space to construct the digester. Be sure that water is readily available for mixing with the manure. Provision should be made for slurry storage. Select a site that is open and exposed to the sun. Locate the gas plant near the point of gas consumption this tends to
reduce cost and pressure losses in piping the gas.
Prof. I. N. Itodo
Sizing of Biogas Plant
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
39/57
Sizing of Biogas Plant
39
How much gas can be expected per day from theavailable feedstock?o The available feedstock is from six (6) cattle
o Each cattle produces an average of 10 kg of waste per day
o 1 kg of fresh manure yields 0.05 m3 of biogas
o The animals will, therefore, produce about 3.0 m3 of gas
o Therefore, the size of the plant will be 3 m3.
How much gas is required to meet the needs of the user?o Six (6) persons are required to use the plant to meet their cooking
and lighting needso Each person requires an average of 0.6 m3 of gas for lighting and
cooking per day
o Therefore, six (6) persons will require 3.6 m3 of gas per day
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
40/57
Sizing of biogas plant40
What will be the volume of the fermentation tank orpit needed to handle the required mixture of manureand water?o The ratio of manure to water is 1: 1
o 6 cattle will give 60 kg/manure + 60 kg/water = 120 kg
o The total input per day will be 120 kg
o The input for six weeks (42 days) will be 120 kg x 42 days =5040 kg
o The rule of the thumb is 1000 kg = 1 m3
o Therefore, 5040 kg is 5.4 m3
o The minimum capacity of the fermentation well is 5.4 m3
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
41/57
Sizing of biogas plant41
What size and shape of fermentation tank or pit isrequired?o The shape of the tank is determined by the soil, subsoil and
water table. The example illustrated assumes that the earth is
not too hard to dig out and that the water table is low even inthe rainy season.
o An approximate size for the 6 m3 tank would be a diameter of1.5 m. Therefore, the depth required is 2.3 m.
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
42/57
Sizing of biogas plant42
What is the volume of the gas storage cap?o The drum is made to hold between 60% to 70% of the total
daily gas production
o Therefore, the volume of the gas holder will be 70% x 4 m3 =
2.8 m3
o If the gas holder is of diameter 1.5 m, the height of the gasholder will be 1.1 m
Prof. I. N. Itodo
Materials of Construction
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
43/57
Materials of Construction
43
The materials required for construction of the 4 m3 plantare:
Baked bricks, approximately 4000
Cement, foundation and wall covering, 28 -40 bags of
(50 kg) cement Sand 12 m3
Copper wire screen (25 cm x 25 cm)
Rubber or plastic hose
Gas outlet pipe 3 cm in diameter Mild steel sheeting 0.32 mm (30 gauge) to 1.63 mm (16
gauge) -9 m
Prof. I. N. Itodo
Tools
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
44/57
Tools
44
Some of the tools required for construction are:
Welding equipment for gas cap construction, pipefittings, etc
Shovels for concrete and masonry works Metal saw and blades for cutting steel
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
45/57
Construction45
Foundation and Walls Dig a pit 1.5 m in diameter to a depth of 2.5 m Line the floor and walls of the pit with baked brick bound
with lime mortar or clay.
Make a ledge or cornice at two-thirds the height of the pitfrom the bottom. The ledge should be some 15 cm widefor the gas cap to rest on when empty.
Extend the brickworks 30-40 cm above the ground, tobring the total depth of the pit to approximately 3 m.
Build the ledge up to the height of the brickwork extension above the ground. This forms the space to befilled with water in which the gas holder with sit in andfloat.
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
46/57
46
Fig. 5: Construction of biogas plant at the University of Agriculture, Makurdi
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
47/57
Foundation and walls47
Put in place the input and output piping for theslurry from 20 cm clay pipe. Place the input pipe 70cm above the bottom of the pit.
Place the output pipe 40 cm above the bottom of thepit opposite the input pipe and end at ground level.
Put copper screening of 0.5 cm holes at the mouth ofthe input and output pipes to exclude foreign matter
from the pit
Prof. I. N. Itodo
Gas Cap Drum
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
48/57
Gas Cap Drum
48
Fabricate the gas cap from mild steel sheeting of 1.63 mm (16gauge)
Make the height of the drum 1/3 the depth of the pit
Make the diameter of the drum 10 cm less than that of the pit
Cut a 3 cm hole on the cap Fix a rubber hose on the 3 cm hole.
Paint the inside and outside of the drum with a coat of paintor tar
Ensure that the drum is air tight by filling with water to check
for leakage Attach handles to either side of the drum for lifting the drum
during maintenance.
Prof. I. N. Itodo
Mixing and Effluent Tanks
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
49/57
g a d ue a s
49
Build a mixing pit to be placed near the outsideopening of the inlet pipe
Also, provide a pit at the outlet to catch the effluent.
Make provision for drying the effluent when theinfluent goes into full operation
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
50/57
50
Plant
size
(m3)
No.
of
animals
Water: waste
Per
day (1:1)
(Kg)
Vol. of
well
for
40 days
digestion
(m3)
No.
of
bricks
No. of
cement
Bags
(50 kg)
Qty.
of
Sand
(m3)
Gas
Prod.
Per day
(m3)
Qty. of
fertilizer
per
day
(kg)
No. of
persons
served
(cooking
+
lighting)
2 4 80 3.5 2800 22 9 2 4-8 4-6
3 6 120 5 3200 25 12 3 6-12 6-8
4 8 160 7 4000 28 12 4 8-16 9-11
5 10 200 8.5 4000 30 14 5 10-20 12-15
7.5 15 300 13 5200 32 16 7.5 15-30 15-20
10 20 400 17 6400 35 18 10 20-40 20-30
Table 2: Measurement for a number of biogas plants
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
51/57
Operation51
4 m3 (4000 liters) of manure are necessary for the start-up of the newdigester. In addition, approximately 20 kg of seeder is required to get the
bacteriological process started. The seeder can come from severalsources.
Put the manure and seeder and an equal amount of water into the mixingpit. Stir it into thick liquid called slurry. A good slurry is one in which themanure is broken up thoroughly to make a smooth, even mixture havingthe consistency of a thin cream. 50 kg of fresh manure is mixed with 50 kgof water and the mixture added to the digester every day.
It can take 4 to 6 weeks from the time the digester is fully loaded beforeenough gas is produced and the gas plant becomes fully operational.
The first drum full of the gas will probably contain so much carbon dioxide
that it will not burn. On the other hand, it may contain methane and air inthe right proportion to explode if ignited.
Prof. I. N. Itodo
Output and Pressure
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
52/57
p
52
The pressure output from the floating drum plantcan be regulated by the addition and reduction of
weight on the gas holder to increase the pressure ofgas flow from the plant.
This also affects the volume delivered at theappliance.
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
53/57
Maintenance53
Common problems encountered when operatingbiogas plants and the attendant maintenancepractices are provided in table 3.
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
54/57
54
s/no. Problem Possible reason(s) Solution
1 Gas drum will not rise Scum formation No gas formed
Leakage in the system
Patience. Thesystem needs
about 4 to 6 weeks
to get properly
started
Stir the digester
Dilute the digester
by adding some
water
Ensure that there is
no leakage in the
system
2 No gas at the appliance No gas formed
Not enough pressure inthe system to force the gas
from the digester to the
appliance
Gas leakage
Consider solution
#1 Adjust the inlet jet
of the appliance
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
55/57
55
3 No gas formed Toxicity in digester
Inappropriate waste-
water mixture
Flush out the
content of the
digester with water
Add more waste to
the digester
4 Inadequate quantity of
gas being formed
Inappropriate waste-
water ratio
Slurry too thick or toothin
Few population of
required microorganisms
Add a seeder from
another plant or a
sewage to thedigester
Add more waste to
the digester
5 Flame dies off too quickly
at the appliance
Pressure from the
digester too high
Adjust the inlet jet
of the appliance
Reduce the weighton the gas holder
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
56/57
Safety56
Spontaneous ignition of methane occurs when 4 -15% of the gas mixes with air and it has an explosivepressure of between 90 and 104 psi.
Do not attempt to light the first drumful of gas.Empty the gas contained and let the drum fill again
because it may contain methane and air in the rightproportion to explode when ignited.
Prof. I. N. Itodo
8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo
57/57
By-products57
Fertilizer The sludge that is produced from the anaerobic
digestion process is a better fertilizer and soil conditionerthan either composted or fresh manure. This is because:
a. The liquid effluent contains many elements essential toplant life. It contains nitrogen, phosphorous, potassiumand small amounts of metallic salts that areindispensable for plant growth.
b. When the sludge is applied on the soil as fertilizer, itsnitrogen is converted to ammonium ions (NH4
+), which
fix themselves to the negative charged clay particles ofthe soil, thereby making nitrogen available to theplants.
Top Related