BIOGAS PROCESS
What is biogas?
- It is a gaseous product of natural bacterial decomposition process of organic matter in the absence of oxygen (anaerobic).
- Biodegradable materials include:
- Manure, animal slurry, food waste, human excreta, wastewater and MSW.
Why biogas upgrading is necessary?
- To increase the calorific value so transporting cost is low, /li>
- To remove contaminants (H2S, seloxane).
Heating value of upgraded biogas (bio-methane) > kerosene and close to natural gas and liquefied petroleum gas (LPG). Therefore can replace them.
Bio-methane can be compressed, bottled like LPG and distributed to households and other end users.
Bio-methane can be compressed, bottled like LPG and distributed to households and other end users.
BIOGAS PRODUCTION
Most of the waste is ORGANIC and can be used to generate BIOGAS.
Fundamental Processes
- Anaerobic digestion is the breakdown of organic material by micro-organisms in the absence of oxygen
- This natural, biological process takes place in four stages:
- Hydrolysis
- Acidogenesis
- Acetogenesis
- Methanogenesis
Biogas Contents
| Component | Symbol | % of Gas Content |
|---|---|---|
| Methane | CH4 | 40-70 |
| Carbon Dioxide | CO2 | 30-60 |
| Nitrogen | N2 | 0.1-10 |
| Hydrogen | H2 | 0.1-1 |
| CarbonMonoxide | CO | 0.1 |
| Oxygen | O2 | 0.1 |
| Hydrogen Sulfied | H2S | 0.1 |
Anaerobic Benefits
No oxygen is required
- Anaerobic digesters do not require energy for mechanical mixing in order to maintain adequate aeration
- Biomass production is reduced in anaerobic digestion as compared to aerobic digestion
Factors Affecting Operation
- Temperature
- Anaerobic digestion has been classified into three temperature ranges: psychrophilic (0-20ºC), mesophilic (20-42ºC), and thermophilic (42-75ºC)
- Temperature can have an effect on the final two stages of digestion, and it has been found that anaerobic digestion is most feasible in the mesophilic and thermophilic temperature ranges
- For a given degree of digestion to be attained, a higher temperature corresponds to a shorter time of digestion, and the increased reaction rates at these higher temperature ranges lead to decreased reactor sizes
- Biomethane Process
on average, about 50-70% methane and 30-50% carbon
dioxide and has a heating value of about 40% of that of natural gas.
Removing the carbon dioxide and other contaminants (upgrading) is
required in order to increase the heating value of the gas to the level
of LPG or natural gas. Two main technologies available for this purpose
are water or chemical scrubbing and pressure swing adsorption.
PSA system
The gas purification process begins with measuring the incoming gas and then blowing the gas to desulphurization pressure swing adsorbers (PSAs) in order to remove contaminants such as hydrogen sulphide and seloxane. The gas is then compressed further, cooled and dehydrated to remove moisture. The cool dry gas then passes to de-carbonating PSAs to remove the carbon dioxide and attain clean biomethane, which has high heating value.
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