22MEX01 Renewable Energy Sources

Unit III Bioenergy

Biomass Resources - Biomass Conversion Technologies - Factors Affecting Biogas Production -Biogas Plant Types KVIC Model - Deenbandhu Model - Cogeneration Plant in Rice Mill- Ethanol Production - Energy Recovery from Urban Waste. Transportation Challenges - Economics.

What is bio mass?�

• Biomass is organic material derived from plants, animals, and microorganisms that can be used as a renewable energy source. It stores energy from the sun in the form of chemical energy through photosynthesis.

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Solar energy

Photosynthesis

Bio mass

Energy generation

Organic Matter present in Biomass

• Carbohydrates
• Cellulose – main structural component of plant cell walls.
• Hemicellulose – complex carbohydrates associated with cellulose.
• Starch – energy storage in plants.
• Lignin - Found in plant and animal biomass, made of amino acids.
• Proteins - Found in seeds, fruits, algae, and animal tissues.
• Lipids (Fats and Oils) - Found in seeds, fruits, algae, and animal tissues.
• Simple Sugars - Glucose, fructose, sucrose — easily digestible energy sources.

Sources of Biomass

• Agricultural residues – straw, husk, stalks.
• Forestry residues – wood chips, sawdust, bark.
• Animal waste – manure, dung.
• Municipal solid waste – biodegradable fraction.
• Energy crops – sugarcane, switchgrass, jatropha.
• Aquatic biomass – algae, water hyacinth.

• Bio mass
• solid
• 1. Wood
• 2.Municipal Refuse
• 3.Char
• 4. straw

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• Liquid
• 1.Methanol
• 2. Ethanol

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• Bio gas
• 1.Hydrogen
• 2. Bio gas
• 3. Methane

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Organic wastes & their estimated availability in India

BIO MASS CONVERSION

• Direct combustion
• Thermo chemical conversion

- Pyrolysis

- Gasification and liquefaction.

• Bio chemical conversion

-Anaerobic digestion

- Fermentation

Direct Combustion

Direct combustion is the simplest and most common method of converting biomass into usable energy. In this process, biomass is burned in air to produce heat energy, which can be used directly or converted into electricity.

Thermochemical conversion is the process of converting solid biomass into useful energy (heat, gas, liquid fuels, or char) using heat and chemical reactions under controlled conditions

Gasification

• Gasification is a thermochemical conversion process in which biomass is converted into a combustible gas mixture (called producer gas or syngas) by partial oxidation at high temperature (≈ 800–1000 °C) with a limited supply of oxygen, air, or steam.

Pyrolsis

• Pyrolysis is a thermochemical conversion process in which biomass is decomposed by heat in the absence of oxygen (typically 400–600 °C), producing solid (biochar), liquid (bio-oil), and gaseous (syngas) products.

Bio chemical conversion

• Anaerobic digestion is a biochemical process in which microorganisms break down organic matter (biomass, animal waste, sewage, food waste) in the absence of oxygen to produce biogas (CH₄ + CO₂) and digestate (organic fertilizer).

Stages of Anaerobic Digestion

Hydrolysis

Complex organic matter (carbohydrates, proteins, fats) → simple sugars, amino acids, fatty acids.

Acidogenesis

Simple molecules → volatile fatty acids, alcohols, H₂, CO₂.

Acetogenesis

Volatile fatty acids → acetic acid, H₂, CO₂.

Methanogenesis

Methanogenic bacteria convert acetic acid + H₂ + CO₂ → Methane (CH₄) + CO₂ (biogas).

• Fermentation is a biochemical conversion process in which microorganisms (mainly yeast and bacteria) break down sugars and starches from biomass into ethanol (alcohol) and carbon dioxide under anaerobic conditions

• Preparation – Biomass is crushed/hydrolyzed to release fermentable sugars.
• Fermentation – Microorganisms (e.g., Saccharomyces cerevisiae) convert sugars into ethanol + CO₂.
• Distillation – Ethanol is separated and purified to required concentration.
• Utilization – Ethanol used as biofuel (blended with petrol), solvents, or chemicals.

Products

• Bioethanol fuel – blended with gasoline (E10, E20, etc.).
• Alcohol production – beverages, industrial alcohol.
• CO₂ production – used in soft drink industry, refrigeration.

Biogas production process

Biogas production process (Anaerobic digestion) is a multiple stage process in which some main stages are

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Chemical reactions involved in biogas production:

C₆H₁₂O₆ → 3CO₂ + 3CH₄

CO₂ + 4H₂ > CH₄ + 2H₂O  

CH₃COOH  > CH₄ + CO₂

• Digester is fed a mixture of water and waste called a slurry.
• Daily, fresh slurry is added, displacing previous days load that bacteria have started to digest.
• First, digestible organic matter is broken down by acid-producing bacteria.
• By-products are then broken down by methane-producing bacteria.

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BIOGAS PRODUCTION PROCESS

�Biogas Feedstock�

• Any organic material can be used
• Production rate depend on type of feed stock used.
• Woody materials such as straw are very difficult to digest
• Animal dung digests readily
• Pretreatment may be needed for some materials ( Chopping etc.)

The Quantity, Rate And Composition Of Biogas Generated Depends On �

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• The nature and concentration of the substrate,
• Feed rate,
• pH value,
• Bacterial population,
• Temperature, and
• Chemical inducers.

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CLASSIFICATION OF BIO GAS PLANT

• Continuous and batch types.

Continuous Type

• Single stage
• Double stage
• The dome and drum types.
• Different variation in drum type.

TYPES OF BIO GAS PLANT�

• Family size biogas plants (1 to 10 m³ ) – KVIC, Deenbandhu, Janta, Pragati, Flexi etc.
• Large scale biogas plants (10 to 140 m³) – KVIC
• Large scale plants above 1000 m³ – UASB, Modified UASB, BIMA Digester (suitable for industrial effluents, MSW, fruit and vegetable waste etc.)

Out let Pipe

In let Pipe

Digester

Drum

FLOATING DRUM TYPE BIOGAS PLANT (KVIC Digester)

Gas outlet

Inlet

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Outlet

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Janta fixed dome biogas plant

Fixed Dome type family size Biogas plant��[1] Deenbandhu��[2] Modified for solid state�

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SELECTION OF SITE FOR A BIOGAS PLANT

• Distance – plant and site of gas consumption
• Open space- for sunlight to fall on the plant to maintain optimum temperature
• Water table- preventing seepage of water
• Seasonal run off – prevent the interference of run off water
• Distance from wells
• Space requirement
• Availability of water
• Source of cow dung /material for biogas generation

DIGESTER DESIGN CONSIDERATION

• Volume of waste to be digested
• Type and amount of waste available
• Period of digestion
• Method of stirring
• Method of adding slurry and removing digested slurry
• Climate condition of region
• Information about sub soil condition and water table
• Type of cover

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FACTORS AFFECTING OPTIMUM BIOGAS PRODUCTION

• Temperature ( 35-37^oC Mesophilic condition )
• C/N ratio ( optimum between 25:1 to 30:1)
• pH ( optimally pH between 6.8-7.2)
• Solid content ( feed material should have approx. 10:1 )
• Should not have toxic material/ harmful material to bacteria in digester
• HRT ( Hydraulic Retention Time – 30, 40, 55 days)
• Loading rate

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Cont.,

• Pressure
• Toxicity due and product
• Mixing or stirring or agitation of the content of digester
• Types of feed stock
• Acid accumulation inside the digester
• Nutrients

Cogeneration power plant

• Cogeneration is the simultaneous production of electricity and useful thermal energy (heat/steam) from the same energy source (coal, gas, biomass, diesel, etc.).
• Fuel Input – Primary fuel (natural gas, coal, biomass, bagasse, etc.) is supplied to the prime mover.
• Power Generation – Fuel is burnt in a prime mover (steam turbine, gas turbine, or reciprocating engine) to generate mechanical power which drives a generator → produces electricity.
• Heat Recovery – Instead of wasting the exhaust heat to the atmosphere (like in conventional plants), the exhaust gases/steam are captured in a Heat Recovery Boiler/Heat Exchanger.
• Useful Heat Output – The recovered heat is utilized in the form of process steam, hot water, or heating for industrial processes, space heating, or drying.
• Overall Efficiency – Achieves 65–85% efficiency, compared to 30–40% of conventional power plants.