The document discusses various topics related to biomass energy including: - Types of biomass gasification such as pyrolysis, hydrolysis, hydrogenation, and gasification. Pyrolysis involves thermal decomposition of biomass in an inert atmosphere. Hydrolysis uses water to break chemical bonds. Hydrogenation treats substances with hydrogen gas. - Gasification is a process that converts biomass into syngas (carbon monoxide and hydrogen) using heat in the absence of oxygen. - Biodiesel production involves transesterification of vegetable oils or animal fats with methanol in the presence of a catalyst to produce biodiesel and glycerin. - Biomass can be used to generate

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