Biomass as an Energy Resource

• Biomass is a key focus in the module due to its potential as an energy resource
• The module explores how to tap and utilize biomass for usable energy production

Importance of Non-Conventional Energy Resources

• Growing concerns about fossil fuel depletion and environmental impact necessitate exploring non-conventional energy resources
• Development of non-conventional energy resources is ongoing and will likely supplement, rather than replace, conventional resources
• Biomass is one example of a non-conventional energy resource to be discussed
• Biomass will be discussed in terms of its broad classification and composition

Definition of Biomass

• Biomass is organic material usable as an energy resource
• Examples of biomass include wood, crops, seaweed, and animal waste
• Biomass encompasses materials from plants and animals, including their waste and residues
• The United Nations Framework Convention on Climate Change defines biomass as:
  • Non-fossilized and biodegradable organic material from plants, animals, and microorganisms
  • Products, byproducts, residues, and waste from agriculture, forestry, and related industries
  • Non-fossilized and biodegradable organic fractions of industrial and municipal wastes
  • Gases and liquids recovered from the decomposition of non-fossilized and biodegradable organic materials
• Biomass is considered a sustainable energy resource due to its replenishment rate

Sustainability and Carbon Neutrality

• Biomass is constantly formed through the interaction of CO2, air, water, soil, and sunlight with plants and animals.
• Carbon in biomass comes from atmospheric CO2 via photosynthesis, not from fossil resources
• Emitted CO2 from burning or digesting biomass is recycled
• Energy from biomass is considered carbon neutral

Photosynthesis and Biomass Growth

• Biomass grows via photosynthesis, absorbing solar energy, carbon dioxide, and water
• Photosynthesis produces carbohydrates (plant cell walls) and releases oxygen
• Biomass includes living and recently dead biological species suitable for fuel or chemical production

Exclusions from Biomass Definition

• Biomass excludes organic material transformed into coal and petroleum over millions of years by geological processes.
• Coal and petroleum are conventional, non-renewable energy resources.
• Biomass mainly comes from botanical and biological resources, or a combination of both

Formation of Biomass

• Solar radiation incident on green plants and photosynthetic organisms facilitates chemical reactions and photosynthesis
• In green plants, photosynthesis converts atmospheric CO2 into carbohydrates like sugars, starches, celluloses, and hemicelluloses, using sunlight, chlorophyll, and water.
• X molecules of CO2 react with Y molecules of water in presence of sunlight, which is the photosynthesis process, and convert into carbohydrate plus oxygen
• 6 CO2 molecules react with 6 H2O molecules in the presence of radiant energy of the sun, and produce glucose + oxygen
• Chains of simple structures result in formation of complex hydrocarbons like sucrose, starch, and cellulose
• Respiration, the reverse of photosynthesis, produces CO2, water, and energy

Energy Absorption and Biomass Content

• The net rate of energy loss in respiration is less than the rate of energy gain during photosynthesis
• Net energy absorbed from solar radiation during photosynthesis can be calculated from its combustion process
• Delta Q is the enthalpy change of the combustion process
• Delta Q = (energy absorbed from photons of solar radiation) - (energy of respiration)
• Net value of delta Q is 4.8 electron volts per carbon atom
• 4. 8 electron volts converts to 470 kilojoules per mole of carbon or 16 megajoules per kilogram of carbohydrate
• This value represents the energy content of biomass measured using a calorimeter (calorific value)

Types of Biomass

• Biomass types include maiden biomass and waste biomass
• Maiden biomass is also known as virgin or primary biomass
  • Terrestrial: forest biomass, grasses, energy crops, cultivated crops
  • Aquatic: seaweed, water hyacinth, algae
• Waste Biomass
  • Agricultural Solid: livestock manures, agricultural crop residue
  • Industrial: demolition of wood, sawdust, waste oil/fat
  • Forest Residue: bark, leaves, floor residues
  • Municipal Waste: municipal solid waste, bio solids, sewage

Classification Descriptions

• Agriculture crops: gasified for producer gas, or converted into solid fuel
• Forests: fuel wood, charcoal, producer gas
• Forest waste and residues utilized at the mill
• Fast growing trees such as poplar, pine, eucalyptus, switch grass, miscanthus are cultivated for energy
• Urban Waste:
  • Municipal Solid Waste (MSW): combustion/incineration or landfill gas
  • Sewage Sludge: converted into biogas

Energy Crops

• Sugar plants (sugar cane, sweet sorghum, sugar beet) are raw material for ethanol production
• Sugarcane processing yields molasses and bagasse, which can be used to form ethanol
• Sweet sorghum is sometimes supplied as a raw material when supply is not required in the sugar mill
• Starch plants such as cassava contain high amounts of starch
• Oil plants such as palm, soybean, rapeseed and groundnut produce waste oils which are used for energy

Aquatic Plants

• Some aquatic plants grow faster than land plants
• Examples include water hyacinth, seaweed and algae

Biological Material/Waste

• Animal waste, aquatic species and biological waste can be used for energy
• Biomass selection can be determined using a questionnaire to determine if it is appropriate for energy generation
• If other alternative viable options exist then the material is discarded
• Is the feedstock a byproduct of main crops or woody biomass? If not then it cannot be considered
• It is is a byproduct then the feedstock can be implemented for energy generation

Biomass Structure

• Biomass is a complex compound of carbohydrate, proteins, fats, and minerals (sodium, phosphorus, calcium, iron)
• Components of woody biomass are extractives, cell wall components (cellulose, hemicellulose, lignin), and ash
• Extractives are substances separable by solvent extraction
• Lipids and hydrocarbons which are soluble in ether, or various types of phenolic compounds, carbohydrates and protein collectively called extractives
• Leaves and bark contain more extractives and less cell wall material
• Cell walls provide structural strength to plants
• Cell walls are made of carbohydrate and lignin
• Carbohydrates are cellulose or hemicellulose and provides strength
• Lignin holds the fibers together
• Plant constituents vary from plant to plant

Biomass Composition and Structure

• Some plants, like corn, soybeans, and potatoes, store starch, a carbohydrate polymer that can be used as a raw material for ethanol production.
• Fats, found mainly in seeds and roots of seed-bearing plants, are a source of energy.
• Fatty acids in fats and oils are used to produce energy.
• Ash, the inorganic component of biomass, is usually present in minor amounts and comprises elements essential for plant growth.

Cell Wall Constituents

• Polymeric composition of cell walls varies widely but is primarily made up of cellulose, hemicellulose, and lignin.
• The cell walls are majorly made up of 3 polymers these are cellulose, hemicellulose and lignin.

Cellulose

• Cellulose is the world's most common organic biopolymer.
• Cellulose is a homo polysaccharide of glucose (C6 sugar units) and the main structural component of cell walls.
• Glucose can be obtained from cellulose biopolymer.
• Cellulose makes up 40-45% of wood by dry weight.
• Cellulose has a crystalline structure of thousands of glucose units, but this structure requires harsh pretreatment to break down for energy use.
• Cellulose is primarily composed of D glucose units.
• Cellulose is a major contributor of tar during the gasification of biomass; biomass with less cellulose and more hemicellulose is preferred for gasification.

Hemicellulose

• Hemicelluloses are hetero polysaccharides consisting of C5 and C6 sugars (Hexosans and Pentosans) found in plant cell walls.
• Cellulose and hemicellulose are fiber compounds in the cell wall, with lignin binding them together.
• Cellulose has a crystalline structure resistant to hydrolysis, while hemicellulose has a random, amorphous structure that is easily hydrolyzed.
• Hemicellulose serves as a cementing material in plant cell walls, holding together cellulose micelles and fibers.
• Composition and structure of hemicellulose varies from biomass to biomass.
• Hemicellulose contains simple sugar residues like D-xylose, D-glucose, D-galactose, L-arabinose, D-glucuronic acid, and D-mannose; it mainly contains D-xylose.
• Hemicelluloses are soluble in alkali and easily hydrolyzed by acids or alkali.
• Hemicellulose yields more gases and less tar than cellulose during gasification, making biomass with higher hemicellulose suitable for gasification.
• Softwood hemicellulose mainly contains galactoglucomannans and arabino glucoronoxylan (7-15%).
• Hardwood hemicellulose mostly contains xylan (10-35%).
• Hemicelluloses decompose more easily than cellulose, both thermo chemically and biochemically, due to less stable intra-molecular linkage.
• Hemicellulose accounts for about 20-35% of dry wood, 28% of softwood, and 35% of hardwood.

Lignin

• Lignin is one of the most abundant organic polymers on Earth and the third important constituent of woody biomass cell walls.
• Lignin is an amorphous, highly complex, mainly aromatic polymer of phenylpropane units.
• Unlike cellulose and hemicellulose, lignin does not contain any carbohydrate in its polymeric structure.
• Lignin does not have a single repeating unit like celluloses or hemicelluloses but consists of a complex arrangement of substituted phenolic units.
• The precursors of lignin biosynthesis are p coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol.
• Lignin from softwoods (25-35%) mainly consists of a polymerization product of coniferyl alcohol, while lignin content in hardwoods ranges from 18-25%.