Biogas technology notes

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BIOGAS TECHNOLOGY

BASICS - RURAL DIGESTERS -

HIGH RATE DIGESTERS

Text Book: K.M. Mital, Biogas Systems,

Principles & Applications, 1996, New Age

Intrnl.. N.Delhi.

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National Project on Biogas Development

To promote and disseminate information

about biogas technology specifically, the

government organised the National Project

on Biogas Development nation-wide, and

several NGO's have been active in

implementing the programme on the ground.

Active dissemination was also undertaken by

the Khadi and Village Industries Commission

(KVIC), in the context of rural development

from small-scale income generating

opportunities.

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Applications of Biogas:

1. Cooking fuel- Design of Burner.

2. Lighting Fuel- Mantle lamp.

3. After removal of traces of H2S, NH3 and water vapour, fuel gas can be used for running stationary I. C. Engines.

I. C. Engines are used with pump for water supply or with generator for power.

4. Purified & filled in CNG cylinders, biogas is a useful automobile fuel for short journeys.

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Purpose of RURAL BIOGAS PLANTS

ENERGY RECOVERY:

FOR COOKING, LIGHTING, PUMPING, OR POWER- - WITH BURNER, MANTLE LAMP, ENGINE-PUMP AND GENERATOR

HYGIENIC DISPOSAL OF ANIMAL WASTE AS MANURE

SUBSTITUTES FOR FUELWOOD & KEROSENE

________________________________________

Another text book: Nijaguna, B.T., Biogas

Technology, New Age International publishers

(P) Ltd., 2002.

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Eliminating firewood burning in kitchen

by use of clean burning gas fuel.

A clean and particulate-free source of energy

also reduces the likelihood of chronic

diseases that are associated with the indoor

combustion of biomass-based fuels, such as

respiratory infections, ailments of the lungs;

bronchitis, asthma, lung cancer, and

increased severity of coronary artery disease.

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FEED FOR BIOGAS PLANT: WET

BIODEGRADABLE WASTE

Biogas systems offer an integrated system that

lends itself to a rural setting; the plants can be

maintained with a variety of organic residues, from

humans, animals, crops and domestic food waste.

It is a viable option for solid waste disposal in areas

of rapid urbanisation also.

It may be possible to manage BGS and modify by

individuals within the community, preferably the

plant owner, and reliance on 'outside' assistance

kept to a minimum.

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FEED FOR BIOGAS PLANT: WET

BIODEGRADABLE WASTE

DOMESTIC ANIMAL WASTES: Excreta of

cow, pig, chicken etc

MANURE, SLUDGE: Canteen and food

processing waste, sewage

MUNICIPAL SOLID WASTE: After separation

of non-degradable

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FEED FOR BIOGAS PLANT: WET BIODEGRADABLE WASTE (continued)

WASTE STARCH & SUGAR SOLUTIONS:

• Fruit processing, brewery, press_mud-from

sugar factory etc

• Sludge from activated sludge aerobic wwt

OTHER INDUSTRIAL EFFLUENTS:

• Pulp factory waste liquor,

• Leather industry waste.

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WET FERMENTATION:

FEED HAS SUBSTRATE TOTAL SOLID

CONCENTRATION, ( TSC) = 8 TO 9 %

FOR COW DUNG, RATIO OF DUNG TO WATER

= 1:1

FOR SUCH A SLURRY, BIOGAS PRODUCED

IS:

IN SUMMER AT 47 C, 0.06 M3 PER KG DUNG

ADDED PER DAY

IN WINTER AT 8 C, 0.03 M3 PER KG DUNG

ADDED PER DAY

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DRY FERMENTATION OR SOLID STATE

FERMENTATION :

FEED SUBSTRATE TOTAL SOLID CONCENTRATION, ( TSC) OF 20 TO 30 %, A MIX OF COW DUNG AND A WIDE VARIETY OF AGRO-RESIDUES.

FOR CATTLE DUNG AND MANY AGRO-RESIDUES AT INITIAL CONCENTRATIONS OF TSC BETWEEN 16 TO 25 % BIOGAS PRODUCTION HAS BEEN DEMONSTRATED SATISFACTORILY IN SMALL BATCH TYPE AND PLUG FLOW TYPE DIGESTERS.

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STAGES OF MICROBIAL DECOMPOSITION: 1. HYDROLYSIS OF BIOPOLYMERS [CARBOHYDRATES, PROTEINS] TO MONOMERS 2. CONVERSION OF SUGARS, AMINO ACIDS, FATTY ACIDS TO HYDROGEN, CO2, AMMONIA AND ACETIC, PROPIONIC AND BUTIRIC ACIDS 3. CONVERSION OF H2, CO2, ACETIC ACID TO CH4 AND CO2 MIXTURE

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Lab experiment to show biogas evolution

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Questions on BGT

What properties of biogas have to be improved before it is used as an engine fuel?

Write short notes on (i) Feedstock for biogas, (ii) Dry and wet fermentation, (iii) Microbial and biochemical aspects.

Discuss the operating parameters for biogas production by anaerobic digestion.

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TYPES OF RURAL BIOGAS PLANTS

FIXED DOME: JANATHA, DINABANDHU

FLOATING DRUM: K.V.I.C

COMBINED FEATURES: PRAGATI

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The Planning Research and Action Division (PRAD)

based in Uttar Pradesh, developed the 'Janata' fixed-

dome plant, based on a modified design widely used in

China.

Key features of the Janata model, is the fixed-dome. With

this design, the inlet and outlet tank volumes are

calculated for minimum and maximum gas pressures

based on the volumes displaced by the variation of gas

and slurry within the system.

The Janata system is about 30% cheaper to construct

than a KVIC model of the same capacity with added

advantages that there are no moving parts, making local

construction possible and maintenance easy. Janata

plant is more appropriate for small-scale users.

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Janatha Digester:Fixed Dome

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Floating drum biogas plant

(rural)

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The basic plant, which came to be known as the

KVIC model, consists of a deep well, and a floating

drum, usually made of mild steel. The system

collects the gas, which is kept at a relatively

constant pressure. As more gas is produced, the

drum gas holder consequently rises. As the gas is

consumed, the drum then falls. The biomass slurry

moves through the system, as the inlet is higher

than the outlet tank, creating hydrostatic pressure.

Only completely digested material can flow up a

partition wall, which prevents fresh material from

'short-circuiting' the system, before flowing into the

outlet tank.

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K.V.I.C floating drum plant

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Dinabandhu biogas plant

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Pragati rural biogas plant

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• COMBINES FEATURES OF KVIC &

DEENABANDU,DEVELOPED IN

MAHARASHSTRA

• LOWER PART: SEMI-SPHERICAL IN

SHAPE WITH A CONICAL BOTTOM

• UPPER PART: FLOATING GAS HOLDER

• POPULARIZED IN MAHARASHTRA,

UNDARP, PUNE

Pragati rural biogas plant

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DRY FERMENTATION OR SOLID

STATE FERMENTATION :

FOR CATTLE DUNG AND MANY

AGRO-RESIDUES AT INITIAL

CONCENTRATIONS OF Total Solid

Content BETWEEN 16 TO 25 %

BIOGAS PRODUCTION HAS BEEN

DEMONSTRATED SATISFACTORILY

IN SMALL BATCH TYPE AND PLUG

FLOW TYPE DIGESTERS.

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Fresh biomass added to

The top of decomposing

Biomass bed becomes

acidogenic zone. Effluent

taken from bottom.

Methanogenic zone is in

the middle having high

SRT. Compaction of fresh

biomass gives high wet

density within a short

period.

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Table: Different types of biogas plant recognized by MNES

(Ministry of Non-Conventional Energy Sources). After Gate,

1999.

1. Floating-drum plant with a cylinder digester (KVIC model).

2.Fixed-dome plant with a brick reinforced, moulded dome

(Janata model).

3. Floating-drum plant with a hemisphere digester (Pragati

model).

4. Fixed-dome plant with a hemisphere digester (Deenbandhu

model).

5. Floating-drum plant made of angular steel and plastic foil

(Ganesh model).

7.Floating-drum plant made of pre-fabricated reinforced

concrete compound units.

8. Floating-drum plant made of fibreglass reinforced polyester.

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Subsidies were granted on plants upto 10 Cu.m (a large

family-sized system), and usually for the models recognized

by the government, as listed in table, though there may be

regional differences. Allowances were paid towards

investment costs, to every user and for every biogas plant

that was installed, in what may be interpreted as a measure

of intent to promote biogas technology, and perhaps the most

critical instrument in determining initial uptake. The extent of

the allowance was dependent on the size of plant, socio-

economic status of the user, and geographical region,

according to rules worked out by central government.

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Limitations for Use of rural BGT

The family size biogas program cannot cater to the

needs of the poor, as these groups fail the technical

requirements to maintain a viable plant. For even

the smallest-sized plant, three to four cattle are

needed to provide the necessary quantity of dung.

Less than this and the plant are not economically or

operationally viable. Constraints may also exist in

the provision of space and water that are likewise

necessary for a biogas plant. According to Moulik,

the smallest 3 cu.m family size plant requires about

27 sq.m of land.

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HIGH RATE BIOGAS PLANTS FOR INDUSTRIAL

WASTE WATER TREATMENT

As part of biological waste treatment, reduces high BOD content to

make it suitable for aerobic biological treatment.

Faster disposal / recycling of waste water with partial recovery of

energy as fuel [biogas]

_______________________________________________________

Reference: Effluent Treatment & Disposal: I Ch. E, U.K.,

Symposium Series No 96, 1986, P 137-147, ‘Application of

anaerobic biotechnology to waste treatment and energy production’,

Anderson & Saw.

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TYPES OF HIGH RATE BIOGAS PLANTS

ANAEROBIC CONTACT

ANAEROBIC FILTER:UPFLOW,

DOWNFLOW

UPFLOW ANAEROBIC SLUDGE BLANKET

ANAEROBIC FLUIDISED/ EXPANDED BED

ANAEROBIC ROTATING CONTACTOR

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Anaerobic contact digester

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Upflow Anaerobic Sludge Blanket Digester

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Anaerobic treatment systems in India

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Hybrid reactor

The hybrid reactor can be used for a wide variety of industrial effluents and it is possible to maintain the desired pH conditions for both the acidogens and the methanogens. The inert matrix material increases the retention of the granular sludge and prevents the washout of the microbial population. By choosing a suitable highly porous packing material with a large specific surface, the adhesion of microbes can be greatly improved and the concentration of activated sludge in the reactors can be considerably enhanced.

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Hybrid reactor The rate of mass transfer is

also higher owing to the increased contact time between the feed and the microbes.

As the material which

immobilizes the microbes can capture most of the sludge when the slurry passes through the reactor, the loss of sludge is minimized. Apart from the advantages of simplicity in operation and design, the hybrid reactor

also works out to be more economical than fixed bed

system at the industrial scale.

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What criteria is applied in selecting a rural

biogas plant of a small family size?

Why is biogas is not supplied in cylinders like

LPG? Can we use same stove for both?

Explain hydraulic and solid retention time for

a fixed film biogas digester.

In a flood prone area, what type of small

biogas plant would you use?

Questions on BGT

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ANAEROBIC ROTATING

BIOLOGICAL DISC CONTACTOR

IT CONSISTS OF A

SERIES OF DISCS OR

MEDIA BLOCKS MOUNTED

ON A SHAFT WHICH IS

DRIVEN SO THAT THE

MEDIA ROTATES AT RIGHT

ANGLES TO THE FLOW OF

SEWAGE.

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Features of biogas lamp:

Brightness depends on gas pressure, air to

gas ratio, extent of mixing etc. Proper

nozzle adjustment is necessary to achieve

required light intensity.

Lamps designed for 100 candle-power,

consume 0.11 to 0.15 m biogas per hour.

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Biogas for electricity Generation

One kwh can be generated from 0.7m3 of

biogas to light 15 bulbs [60watts] for one

hour.

For lighting, power route is better than

direct burning

Economical for large sized plants,

requires high initial capital investment.

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Purification of biogas for storing in CNG

cylinders.

Removal of CO2: Scrubbing with limewater

or ethanol amine solution.

Removal of H2S: Adsorption on a bed of iron

sponge and wood shavings.

Removal of H2O:-

For the removal of moisture, pass the gas,

through the crystals of white silica gel.

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Biogas as I.C. engine Fuel

• Traces of H2S, NH3, water vapor to be removed

by absorption/adsorption.

• With modified fuel injection system, in stationary

diesel or petrol engine biogas can be used.

• In Diesel engine, dual fuel mode is needed.

• After initial start up with petrol, engine can

run on biogas

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Operating parameters

Retention time: The ratio of volume of slurry in the digester to the volume fed into and removed from it per day is called retention time. Thus a 20 liter digester is fed at 4 litres per day so that the volume of digester is constant the retention time is 5 days. The required retention time is normally 30 days for mesophilic

(25-35oC) conditions.

Volumetric organic loading rate: This can be expressed as kg Vs per volume per day based on the % weight of organic matter added each day to the digester volume.

Digester loading rate %= (Per cent of organic matter in feed)/(Retention Time)

Loading rate range is 0.7 to25 kg VS/ m3 / Day

Biogas technology notes

Education

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