The document discusses biogas purification techniques. It begins by defining biogas and describing its production through anaerobic digestion of organic waste. The main processes that occur in digestion tanks are then explained. It also details the typical composition of impure biogas and desired composition after purification. The two main steps of purification treatment, cleaning and upgrading, are introduced. Several key techniques for biogas cleaning and purification are then outlined, including water scrubbing, membrane processes, adsorption methods, and biological techniques. Cryogenic separation is also briefly discussed.

1. Biogas Purification
S K SINGH
CENTRE FOR ENERGY STUDIES
IIT DELHI

2. 2
Contents
Content Page no.
What is Biogas? 3
Biogas production 4-5
Processes in plant tanks 6-9
Composition of impure Biogas produced 10-11
Target contents 12
Why more methane 13
Why less contaminated contents 14
Two steps of biogas purification
treatment
15
Cleaning techniques 16-21
Water scrubbing 17
Membrane process 18
Adsorption by gas-liquid film 19
Adsorption by Iron oxide 20
Biological techniques 21
References 22

3.  Biogas is a naturally occurring
mixture of gases , produced by
Breakdown of organic matter by
bacteria in anaerobic conditions.
 Biogas is a renewable energy source.
 In India , Biogas is also known as
“Gober Gas”.
What is Biogas?
3

4. 4
Biogas Production

5.  Biowaste is crushed into smaller
pieces and Slurrification processed.
 We Use this slurrified waste for the
anaerobic digestion process.
 Biowaste is heated around 37°C
 Leave that tank unused for 3 weeks,
so anaerobic digestion.
 Finally ,we do purification of the gas
to remove Impurities and carbon
dioxide.
How is biogas produced?
5

6. plant tanks
6

7. plant tanks
7

8.  Hydrolysis
 Acidogenesis
 Acetogenesis
 Methanogenesis
Processes occurred in
digestion tanks are
8

9. Processes occurred in plant tanks are
Hydrolysis
 Several microbes secrete Enzymes ,
which cleave the different the
complex macromolecules into simpler
one.
 Organisms Responsible are-
Bacteroides , clostridium and
Acetivibro.
9
Acidogenesis
 Fermentation products from hydrolysis are
converted into various organic acids ,
alcohols ,ammonia ,carbon dioxide , and
hydrogen.
 Organisms Responsible are-
Enterobacterium , Acetobacter,
Eubacterium.

10. Processes occurred in plant tanks are
Acetogenesis
 Fermented products are oxidized
 In addition to hydrogen gas we also
get acetate and carbon dioxide
formed.
 Organisms Responsible are-
Syntrophomonas , syntrophus,
Clostridium and Syntobactor
10
Methanogenesis
 Fermentation of Organic compounds to
produce methane at the end

11. Composition of Biogas
11
Component Agricultural
Waste
Landfills Industrial waste
Methane 50-80 50-80 50-70
Carbon dioxide 30-50 20-50 30-50
Hydrogen Sulphide 0.7 0.1 0.8
Hydrogen 0-2 0-5 0-2
Nitrogen 0-1 0-1 0-1
Oxygen 0-1 0-1 0-1
Carbon monoxide 0-1 0-1 0-1
Ammonia Traces Traces Traces
Water Saturation Saturation Saturation
Siloxanes Traces Traces Traces

12. Before Purification
Contents in Raw material
gas
12
[CELLRANGE]
, 60
[CELLRANGE]
, 37.5
[CELLRANGE]
, 7.5
[CELLRANGE]
, 2.5
[CELLRANGE]
, 5
[CELLRANGE]
, 1.5
In Anaerobic degraded products
Methane carbon dioxide
Nitrogen Water
Hyrocarbons ,H2S,NH3 Oxygen
[CELLRANGE]
, 50
[CELLRANGE]
, 27.5
[CELLRANGE]
, 22.5
[CELLRANGE]
, 2.5
[CELLRANGE]
, 5
[CELLRANGE]
, 2.5
In Landfills
Methane carbon dioxide
Nitrogen Water
Hyrocarbons ,H2S,NH3 Oxygen

13. Target contents after
purification
Methane 95-99%
Carbon-dioxide 1-5%
Little or No hydrogen Sulphide
13

14. High calorific Values 15-
30MJ/Nm3
More light energy than other
Hydrocarbons, Fossil fuel and gasoline
Producing significantly less CO2
and pollutants
Less smog
Less Unhealthy Air
Why more methane?
14

15. Why Less Hydrogen
Sulphide?
Highly Corrosive
Highly Toxic
Highly Harmful to environment
Corrosive to the Metallic parts of
Engine , pipes ,valves etc
Reduce the life span of process
15

16. Two steps of biogas purification treatment
16
eave and return on the
sheet posted on the
classroom door.
 Cleaning
(Removal of toxic compounds
H2S,N2,O2,Si,H2,VOCs,CO,NH3)
 Upgrading
(Adjustment of CO2 to increase calorific
values)

17. Main Techniques For
Cleaning and purification
Water Scrubbing Adsorption
Cryogenic Separation
Basically deep freezing
In situ upgrading
17
Membrane technologies Bio-technologies

18. Water scrubbing
18
1. Water scrubbing desolves CO2
and H2S
2. Thus we get less amount of CO2
And H2S .
3. This increase the amount of CH4
by 58% to 82%

19. High pressure
membrane Process
High pressure feed from
compressor
01
At high pressure
Membrane separates
according to size of
molecules and solubility.
02
After three stages we get
90% CH4 mixture
03
19

20. Uses micro porous hydrophobic film as
interface between gas and liquid
CO2 and H2S will dissolve in liquid in
liquid as they are more polar
We can collect CH4 from gas
easily,
In Membrane gas flows in one
direction
Adsorption by Gas –
Liquid film
20

21. Adsorption by Iron Oxide
for H2S
21
1) This reaction will reduce H2S and Form Iron Sulphide
2) Occurs in at least 120C
Optimal tempurature is 25-500C.
3) Reaction is Endothermic.
4) Iron oxide regenerated by oxidation after the above
process is highly exothermic and may lead to self ignition
if not properly controlled.

22. Biological techniques
22
• Injection of Oxygen directly into the
digester tank.
• Thiobacillus bacteria growing on the
filter bed. Before entering filter bed 4-6%
of air is added to the biogas.
• H2S is oxidized by bacteria growing the
filter bed. 350°C is the temperature at
which H2S is converted to biologically
converted to sulfur.
• Sulfur is retained as yellow clusters from
the biological filter bed.

23. Cryogenic Techniques
 Different gases condense at different
temperature.
 Boiling point of carbon dioxide is greater
than of methane
 Gradual decrease of temperature
 Cooler reduces the temperature to -55 °C
23

24. References
• Book for: Biogas ,Sources,Purification and Uses
https://www.researchgate.net/publication/312899782_Biogas_sources_p
urification_and_uses
• Technologies for biogas upgrading in biomethane by Amir Izzuddin Adnan 1 , Mei Yin Ong 1 ,
Saifuddin Nomanbhay 1,*, Kit Wayne Chew 2 and Pau Loke Show 2