This PPT covers the contents of OCH 752 ENERGY TECHNOLOGY, as per Anna University curriculum.

1. OCH752 ENERGY TECHNOLOGY
UNIT IV BIOMASS ENERGY
Biomass origin - Resources – Biomass
estimation. Thermochemical conversion –
Biological conversion, Chemical conversion –
Hydrolysis & hydrogenation, solvolysis,
biocrude, biodiesel power generation gasifier,
biogas, integrated gasification.

2. Biomass

3. Carbon Cycle

4. Types of Biogas Digesters
• Fixed Dome Biogas Plants
• Floating Drum Plants
• Low-Cost Polyethylene Tube Digester
• Balloon Plants
• Horizontal Plants
• Earth-pit Plants
• Ferro-cement Plants

5. Fixed Dome Biogas Plants

6. Function of a Fixed-Dome Biogas Plant

7. Fixed Dome Biogas Plants
• Consists of a digester with a fixed, non-movable gas
holder, which sits on top of the digester.
• When gas production starts, the slurry is displaced into
the compensation tank.
• Gas pressure increases with the volume of gas stored
and the height difference between the slurry level in
the digester and the slurry level in the compensation
tank.
• The costs of a fixed-dome biogas plant are relatively
low.
• It is simple as no moving parts exist.

8. Fixed Dome Biogas Plants
• No rusting steel parts and hence a long life of the plant
(20 years or more) can be expected.
• The plant is constructed underground, protecting it
from physical damage and saving space.
• While the underground digester is protected from low
temperatures at night and during cold seasons,
sunshine and warm seasons take longer to heat up the
digester.
• No day/night fluctuations of temperature in the
digester positively influence the bacteriological
processes.

9. Fixed Dome Biogas Plants
• The construction of fixed dome plants is labor-
intensive, thus creating local employment.
• Fixed-dome plants are not easy to build.
• They should only be built where construction
can be supervised by experienced biogas
technicians.

10. Working of Fixed Dome Biogas Plant
• A fixed-dome plant comprises of a closed, dome-shaped digester
with an immovable, rigid gas-holder and a displacement pit, also
named 'compensation tank'.
• The gas is stored in the upper part of the digester.
• When gas production commences, the slurry is displaced into the
compensating tank.
• Gas pressure increases with the volume of gas stored
• i.e. with the height difference between the two slurry levels.
• If there is little gas in the gas-holder, the gas pressure is low
• Digesters of fixed-dome plants are usually masonry structures
• Structures of cement and ferro-cement exist.
• The top part of a fixed-dome plant (the gas space) must be gas-
tight.

11. Floating Drum Biogas Plant

12. Floating Drum Biogas Plant
• Om 1956, Jashu Bhai J Patel from India designed the
first floating drum biogas plant, popularly called Gobar
gas plant.
• Floating-drum plants consist of an underground
digester (cylindrical or dome-shaped) and a
moving gas-holder.
• The gas-holder floats either directly on the
fermentation slurry or in a water jacket of its own.
• The gas is collected in the gas drum, which rises or
moves down, according to the amount of gas stored.
• The gas drum is prevented from tilting by a guiding
frame.

13. Floating Drum Biogas Plant
• When biogas is produced, the drum moves up adn
when it is consumed, the drum goes down.
• If the drum floats in a water jacket, it cannot get stuck,
even in substrate with high solid content.
• After the introduction of cheap Fixed-dome Chinese
model, the floating drum plants became obsolete as
they have high investment and maintenance cost
along with other design weakness

14. Bio-gas for Cooking

15. Biogas for Cooking
• Biogas production for domestic cooking depends on an
affordable appropriate digester at a suitable scale for domestic
use.
• In any digester, the waste is mixed with water to create the
right environment for the bacteria to decompose the biomass.
• As this is an anaerobic process, this has to happen without the
presence of oxygen in an airtight tank.
• The biogas accumulates at the top of the tank where it is
collected and taken by pipe to the user.
• The slurry has to be removed regularly from the tank. It can be
used further, e.g. as agricultural fertilizer.

16. Component of Household Digester
• Collection space: raw, liquid, slurry, semi-solid
and solid animal, human or agricultural waste
• Anaerobic digester
• Slurry storage
• Gas handling: piping; gas pump or blower; gas
meter; pressure regulator; and condensate
drain(s).
• End-use device: cooker, boiler or lighting
equipment

17. Component of Household Digester
• For transporting biogas from the digester to the
cooking place a tube is needed.
• Stoves for this system contain a valve to premix the
biogas with the right amount of oxygen.
• Also a burner to combust the mixture and a
structure to hold a cook-pot.
• Stoves and ovens for biogas application are similar to
those of conventional appliances.
• Most of these conventional appliances can be
adapted for the use with biogas by modification of
the burners

18. Advantages of Using Bio-gas
• Biogas burns very cleanly, and produces fewer pollutants
during cooking than any other fuel except electricity.
• Biogas provides instant heat upon ignition, no pre-heating or
waiting time is required.
• Most biogas burners are able to regulate the flow-rate to turn
down fire-power from high heat to small low heat for
simmering.
• Biogas can be used for lighting as well.
• The by-product (slurry) from the digester can be used as
fertilizer.
• Biogas is a renewable fuel that is ‘carbon negative’: unless
there are leakages in the system.
• Burning biogas in a cook stove releases less greenhouse gases
than if the dung was left on the ground to decompose
naturally.

19. Disadvantages of Using Bio-gas
• High investment costs for the digester, tubes, gas stove, and
pots.
• Biogas can increase the workload of women as it is often
made their task to run the digester.
• It is quite a physical burden to move all the biomass feedstock
and water to feed the digester.
• Slurry must be removed and taken to the field.
• It is not viable for elderly or sick people to run a biogas plant
on their own, if they don’t have labor to assist them in the
maintenance of the digester.
• Installations (depending on material and location) must be
protected against theft and damages.

20. Disadvantages of Using Bio-gas
• Especially metal tubes are a valuable good and often
prone to theft.
• Cultural rules might limit the acceptance of handling
dung or feces and their use as fuel for cooking.
• Cooking with biogas requires the change of
cooking habits, which might prevent the
adoption.
• Biogas is difficult to store and to transport to
other consumers.

21. Biogas – Fuel for I.C. Engines
• Biogas contains 50% to 70% of CH₄, 5-10 % of H₂ and up to 30
-40 % of CO₂.
• After being cleaned of carbon dioxide, this gas becomes a
fairly homogeneous fuel.
• It contains up to 80 % of methane.
• The calorific capacity of over 25 MJ/m³.
• The most important component of biogas, from the calorific
point of view, is methane.
• The other components are not involved in combustion
process, and rather absorb energy from combustion of CH₄ .
• They leave the process at higher temperature than the one
they had before the process.

22. Limitations - Biogas in I.C. Engines
• High CO₂ content reduces the power output, making it
uneconomical as a transport fuel.
• It is possible to remove the CO₂ by washing the gas with
water.
• The solution produced from washing out the CO₂ is acidic and
needs careful disposal.
• H₂S is acidic and if not removed can cause corrosion
of engine parts within a matter of hours.
• High residual moisture which can cause starting
problems.
• The gas can vary in quality and pressure.

23. Purification of Biogas for I.C. Engines
• CO₂ is high corrosive when wet and it has no combustion
value so its removal is must to improve the biogas quality.
a) Caustic solution
NAOH- 40% NAOH + CO₂ = NAHCO₃
b) Refined process
K₂CO₃ - 30 % K₂CO₃ + CO₂ = 2KCO₃
• CO₂ removal from biogas can be done by using
chemical solvents like mono-ethanolamine (MEA),
diethanolamine and tri- ethanolamine or aqueous
solution of alkaline salts.

24. Purification of Biogas for I.C. Engines
• Biogas bubbled through 10% aqueous solution of
MEA can reduce the CO₂ content from 40 to 0.5-
1.0% by volume.
• Chemical agents like NaOH, Ca(OH)₂, and KOH can be
used for CO₂ scrubbing from biogas.
• In alkaline solution the CO₂ absorption is assisted by
agitation.
• NaOH solution having a rapid CO₂ absorption of 2.5-
3.0% and the rate of absorption is affected by the
concentration of solution

25. Biogas in I.C. Engine applications
• Biogas can be used in both heavy duty and light duty
vehicles.
• Light duty vehicles can normally run on biogas
without any modifications.
• Heavy duty vehicles without closed loop control may
have to be adjusted, if they run on biogas.
• Biogas provides a clean fuel for both SI (petrol) and
CI (diesel) engines.
• Diesel engines require combination of biogas and
diesel
• Petrol engines run fully on biogas.

26. Biogas in I.C. Engine applications
• Biogas cannot be directly used in automobiles as it contains
some other gases like CO₂, H₂S and water vapor.
• For use of biogas as a vehicle fuel, it is first upgraded by
removing impurities like CO₂, H₂S and water vapor.
• After removal of impurities it is compressed in a three or four
stage compressor up to a pressure of 20 MPa and stored in a
gas cascade.
• If the biogas is not compressed than the volume of gas
contained in the cylinder.

27. Gasification

28. Gasification
• Gasification is a process that converts biomass- or fossil fuel-
based carbonaceous materials into carbon monoxide,
hydrogen and carbon dioxide.
• Reacting the material at high temperatures (>700 °C), without
combustion, with a controlled amount of oxygen and/or
steam.
• Resulting gas mixture is called syngas(from synthesis gas) or
producer gas.
• Power derived from gasification and combustion of the
resultant gas is considered to be a source of renewable
energy(When the source used is biomass)

29. Gasification

30. Gasification
• Lignocellulosic feedstocks such as wood and forest products
are broken down to synthesis gas.
• Primarily carbon monoxide and hydrogen, using heat.
• The feedstock is then partially oxidized, or reformed with a
gasifying agent (air, oxygen, or steam).
• Synthesis gas (syngas) is produced.
• The makeup of syngas will vary due to the different types of
feedstocks, their moisture content, the type of gasifier used.
• The gasification agent, and the temperature and pressure in
the gasifier.

31. Advantages – Gasification
• Potentially more efficient than direct combustion of
the original fuel.
• Can be combusted at higher temperatures or even in
fuel cells.
• Can be burned directly in gas engines.

32. Pyrolysis
• Pyrolysis is the thermal decomposition of materials
at elevated temperatures in an inert atmosphere.
• It involves a change of chemical composition.
• The word is coined from the Greek-derived elements
pyro "fire" and lysis "separating“.
• Pyrolysis is most commonly used in the treatment of
organic materials.
• It is one of the processes involved in charring wood.
• Pyrolysis of organic substances produces volatile
products and leaves a solid residue enriched in
carbon, char.

33. Pyrolysis
• Extreme pyrolysis, which leaves mostly carbon as the residue,
is called carbonization.
• Pyrolysis is the first step in the processes of gasification or
combustion.
• The process is used heavily in the chemical industry.
• Used in the Methane Pyrolysis conversion of natural
gas(methane) into non-polluting hydrogen gas.

35. Summary
• Pyrolysis is the thermal decomposition of biomass
occurring in the absence of oxygen.
• Fundamental chemical reaction that is the precursor
of both the combustion and gasification processes.
• Occurs naturally in the first two seconds.
• The products of biomass pyrolysis include biochar,
bio-oil and gases including methane, hydrogen,
carbon monoxide, and carbon dioxide
• Depending on the thermal environment and the final
temperature, pyrolysis will yield mainly biochar at
low temperatures, less than 450o C

36. Types of Pyrolysis
• Methane pyrolysis – In the presence of catalytic molten
metals for the direct conversion of methane to non-polluting
hydrogen fuel.
• Hydrous pyrolysis - In the presence of superheated water or
steam, producing hydrogen and also substantial atmospheric
carbon dioxide.
• Dry distillation - In the original production of sulfuric acid
from sulfates
• Destructive distillation - In the manufacture of charcoal, coke
and activated carbon
• Charcoal burning - The production of charcoal

37. Hydrolysis
• Hydrolysis is a chemical process in which a molecule of water
is added to a substance.
• This addition causes both substance and water molecule to
split into two parts.
• One fragment of the target molecule (or parent molecule)
gains a hydrogen ion.
• It breaks a chemical bond in the compound.
• Common kind of hydrolysis occurs when a salt of a weak acid
or weak base (or both) is dissolved in water.
• Water spontaneously ionizes into hydroxide anions and
hydronium cations.
• The salt also dissociates into its constituent anions and
cations.

38. Hydrolysis

39. Hydrogenation
• Treatment of substances with molecular hydrogen (H2),
adding pairs of hydrogen atoms to compounds.
• Requires a catalyst for the reaction to occur under normal
conditions of temperature and pressure.
• Most hydrogenation reactions use gaseous hydrogen as the
hydrogen source.
• The reverse of hydrogenation, where hydrogen is removed
from the compounds, is known as dehydrogenation.
• Hydrogenation differs from protonation or hydride addition
because in hydrogenation the products have the same charge
as the reactants.

40. Hydrogenation

41. Hydrogenation
• Hydrogenation reactions generally require three components:
the substrate, the hydrogen source, and a catalyst.
• The reaction is carried out at varying temperatures and
pressures depending on the catalyst and substrate used.
• The hydrogenation of an alkene produces an alkane.
• Platinum, palladium, rhodium, and ruthenium are known to
be active catalysts which can operate at lower temperatures
and pressures.

42. Biomass Gasification

43. Biomass Gasification
• Biofuels are fuels produced directly or indirectly from organic
material or biomass.
• It includes plant materials and animal and human waste.
• Production of electrical energy using biomass as a fuel
involves accessing the hydrocarbon portion of the biomass
that can be converted into heat.
• Biofuels are considered renewable as they use energy from
sunlight to recycle the carbon in the atmosphere in the form
of carbon dioxide.

44. Gasification - Definition
A thermal process which converts organic
carbonaceous materials (such as wood waste,
shells, pellets, agricultural waste, energy crops)
into a combustible gas comprised of carbon
monoxide (CO), hydrogen (H) and carbon
dioxide (CO2)

46. Biodiesel Production
• Produced from vegetable oils, yellow grease, used cooking
oils, or animal fats
• Produced by transesterification—a process that converts fats
and oils into biodiesel and glycerin (a byproduct)
• Approximately 100 pounds of oil or fat are reacted with 10
pounds of a short-chain alcohol (usually methanol) in the
presence of a catalyst (usually sodium hydroxide [NaOH] or
potassium hydroxide [KOH])
• 100 pounds of biodiesel and 10 pounds of glycerin (or
glycerol) will be produced.
• Glycerin, a co-product, is a sugar commonly used in the
manufacture of pharmaceuticals and cosmetics.

47. Thank you
Dr A R Pradeep Kumar, B.E., M.E., Ph.D.
Prof. /Mech.,
Dhanalakshmi College of Engineering,
Chennai
Email : dearpradeepkumar@gmail.com
99 41 42 43 37