Production Of Biogas from Anerobic Digestion

Hameed Akhtar 2k10-CHE-155

Sohaib Sajjad 2k10-CHE-156

“What we are doing to the forests of the world is but a

mirror reflection of what we are doing to ourselves and to

one another.” Mahatma Gandhi

“A nation that destroys its soils destroys itself. Forests are the lungs of our land, purifying the air and giving fresh strength to

our people. ”  Franklin D. Roosevelt

What is Bio Gas• Biogas is an alternative and renewable energy that can

be produced by the anaerobic (absence of oxygen) decomposition of organic matter.

•  Biogas can be produced from regionally available raw materials such as recycled waste and is a renewable energy source

• Typically, using organic wastes as the major input, the systems produce biogas that contains 55% to 70% CH4 and 30% to 45% CO2.

What is Bio Gas• Biogas is produced by anaerobic digestion with

anaerobic bacteria orfermentation of biodegradable materials such as manure, sewage, municipal waste, green waste, plant material, and crops.

• The gases methane, hydrogen, and carbon monoxide (CO) can be combusted or oxidized with oxygen.

• Landfill gas is produced by wet organic waste decomposing under anaerobic conditions in a landfill

What is Bio Gas• This energy release allows biogas to be used as a

fuel; it can be used for any heating purpose, such as cooking.

• It can also be used in a gas engine to convert the energy in the gas into electricity and heat.

• Biogas can be compressed, the same way natural gas is compressed to CNG, and used to power motor vehicles

In the UK, for example, biogas is estimated to have

the potential to replace around

17% of vehicle fuel.

Biogas Upgrading

• Raw biogas produced from digestion is roughly 60% methane and 29% CO2 with trace elements of H2S So it is not high quality enough to be used as fuel gas for machinery.

• The corrosive nature of H2S alone is enough to destroy the internals of a plant.

• Methane in biogas can be concentrated via a biogas upgrader to the same standards as fossil natural gas, which itself has had to go through a cleaning process, and becomes biomethane

Biogas Upgrading

• There are four main methods of upgrading: water washing, pressure swing absorption, selexol absorption, and amine gas treating

• The most prevalent method is water washing where high pressure gas flows into a column where the carbon dioxide and other trace elements are scrubbed by cascading water running counter-flow to the gas

Reduced GHG emissions

Potential reduction of VOC emissions

Pathogen and weed seed control

Improved water quality

Benefits

Biogas In Pakistan

National Bio Gas Program offer fix dom (6 m3  to 18 m3 )

small and medium bio gas plants is generally used for

cooking and lighting purposes.

Large units (25 m3 ,35 m3 , 50 m3, 100m3,200m3  )or more

mega units produce this gas in large quantities and can be used,

peter engines (tube wells , and Power Generation)

What is Biogas Digestion?

• Biogas Digestion is the process of taking biogas to produce electricity, heat, or hot water

• Biogas means a gas formed by carbon dioxide and methane from breakdown of organic materials such as manure.

What is a Digester?

• Digester is a vessel or container where the biogas process takes place. Bacteria breaks down manure or other waste products to create biogas.

• Products may be fed into the chamber such as manure or the container could be used to cover a place that is already giving off biogas such as a swamp or a landfill.

Manure collection and handling.Pre- Treatment

Anaerobic digestion.

By-Product recovery and effluent use

Biogas Recovery

Elements of Anaerobic Digestion Systems

Biogas Handling and Use

How Anerobic Degestion Work

Design of a Digester

How Digester Works

• Temperature must be kept between 65 degrees and 150 degrees

• 4 Types of bacteria breakdown the waste– Hydrolytic breaks organic material to

simple sugar and amino acids– Fermentative then converts to organic

acids– Acidogenic convert to carbon dioxide,

acetate, and hydrogen– Methanogenic produces biogas

MethanogenesisCO2 + 4 H2 → CH4 + 2H2O

CH3COOH → CH4 + CO2

Chemistry Overall Reaction

C6H12O6 → 3CO2 + 3CH4

• Hydrolysis: This is the first step where particulate materials get

converted to soluble compounds suitable for further breakdown in the next step.

• Acidogenesis: The second step of degradation is known as

fermentation or acidogenesis where the products of hydrolysis such as simple sugars, amino acids, fatty acids etc. break down further and produce final products of fermentation such as H2, CO2 and acetate.

Combined Heat and Power

• Also known as cogeneration• Using the heated water for other purposes

such as heating buildings or creating additional energy

Biogas Digester System Concerns

• Releases Nitrogen and ammonia into the atmosphere both of which hazardous

• Can release Hydrogen Sulfide a very toxic gas• Methane released can create explosive

atmosphere• Should raw materials get into water supply can

contaminate the water • Transportation is of a concern because

methane is explosive although new technology may allow it to be stored in powder form