Biomass Overview

Biomass Overview

• Biomass is a broad spectrum of organic matter, both vegetable and animal origin
• It includes biodegradable parts of products and residues, from agriculture, forestry, related industries, livestock waste and biodegradable parts of industrial and urban areas.
• Biomasses from agricultural crops and forestry, agricultural processing residues, waste from food industry, algae, and organic products deriving from biological activity of animals and humans are all considered.
• Examples include: tree and herbaceous species, agricultural and forest residues (straw, pruning etc.), agro-industrial residues (pomace etc.), zootechnical residues (droppings), municipal solid waste.
• Biomass from energy crops include oleaginous crops (rapeseed, soy, sunflower etc.), alcohol-producing crops (sugarcane, sorghum etc.), and ligno-cellulosic crops (poplar, black locust, eucalyptus etc.)
• 2016 EU Renewables share: 17%
• 2016 EU Bioenergy contribution: 59.2%
• 2016 EU Biomass H&C (Heat & Cooling): 74.6%

Photosynthesis

• Plants and other organisms convert light energy to chemical energy through photosynthesis
• Carbon dioxide and water are used to synthesize sugars and starches
• Photosynthetic efficiency is the fraction of light energy converted to chemical energy in plants and algae
• Simplified chemical reaction: 6 H2O + 6 CO2 + energy → C6H12O6 + 6 O2

Photosynthesis Efficiency

• 50% of solar spectrum (0.4-0.7 μm) can be effective
• 40% loss after reflection; only 20% in fact reflected
• 30% suitable for conversion; 70% losses during photochemical conversion
• 60% accumulated by the plant for maintaining its own metabolism
• In ideal conditions, 7% theoretically remains; average efficiency is 0.15-0.30%, peaks 1%

Biomass Potential

• Global annual carbon equivalent from photosynthesis is 200 billion tons. In energy terms, this is 72 Gtoe (gigatons of oil equivalent) annually, which is 6 times the current global annual energy requirement.
• European estimate of technically usable biomass potential is 400 Mtoe/year, equivalent to 20-25% of current energy consumption.
• Italian estimate of technically exploitable residual biomass is 31 Mt/year of dry matter (25 Mt from agro-forestry, 6 Mt from industrial sector).

Biomass Characterization

• Properties important for analysis: moisture content, proximate analysis (ash, volatile matter, fixed carbon), ultimate analysis (elemental composition), heating value, bulk density, alkali metal content.
• Moisture content on a wet basis is commonly reported and is crucial as it affects heating value. A 40% moisture increase in biomass can decrease energy value by approximately 66% MJ/kg.

Proximate Analysis

• The yield of various products after heating under controlled conditions. Used to assess volatile matter, fixed carbon, and ash content.
• Heating biomass to 400-500° C in an inert atmosphere allows for decomposition into volatile matter and char.
• Volatile matter content influences gasification ease.
• Residual matter (fixed carbon and ash) is assessed by combustion in the presence of oxygen.
• Volatile matter in biomass ranges from 70% to 80%.
• Coal volatile matter content ranges from 20% to 35%.

Ultimate Analysis

• Determination of the elemental composition (C, H, O, N, S, Cl) of the ash-free organic fraction of biomass.
• Cellulose, hemicellulose, lignin, and extractives determine the elemental composition (typical formula CH1.40O0.66)
• Oxygen content of biomass varies from 30% to 40% and doesn't contribute to the fuel value.

Heating Value

• The net enthalpy released when a fuel reacts with oxygen under isothermal conditions.
• Expressed as kJ/kg.
• Measured by direct calorimeter to assess heat involved; products are cooled to initial temperature.
• Higher Heating Value (HHV) includes latent heat of condensation of water vapor formed during the reaction, whereas Lower Heating Value (LHV, or net calorific value) excludes this, as the water vapor remains gaseous.

Alkali Metal Content

• All biomass contains alkali metals such as Na, K, Mg, and Ca, with amounts varying based on the biomass and harvesting location.
• These metals can react with silica and chlorine within the biomass, resulting in fouling and corrosion of combustion/gasification equipment.
• Annual biomass crops generally have higher alkali metal content than older growth biomasses (trees).
• Silica content in agricultural residues can be high; silica contamination from soil can increase the overall residue silica content, leading to problems like slagging in grates and fouling of tubes.

Moisture Content (MC)

• The proportion of water in biomass expressed as a percentage of the material's weight.
• Moisture content basis: on wet, dry basis, or dry ash-free basis, and must be correctly mentioned
• MC affects overall conversion process.
• Increasing moisture from 0% to 40% can decrease heating value by about 66% MJ/kg.

Biomass Boilers

• Used for industrial combustion purposes with wood, agricultural residues, and municipal solid waste.
• Successful combustion requires high temperatures for ignition, sufficient turbulence(mixing the fuel with oxidants), and sufficient time to complete oxidation.
• Low moisture content (typically <50%) is preferred for combustion. High moisture requires pre-drying which is energy intensive.
• The amount of primary, secondary and tertiary air is important to control the process.

Biomass Conversion Technologies

• Combustion, gasification, and pyrolysis

Emissions

• Particulates, CO, NOx, SOx, volatile organic compounds
• Electrostatic precipitators, bag filters, or scrubbers used for particulate removal
• Combustion modifications and post-combustion for NOx control
• Combustion modifications (manage mixing) and Post-combustion processes (converting NOx to inert nitrogen (SCR uses base metals, zeolite, precious metals)

Biomass Combustion Devices

• Household biomass boilers typically come in these three main types: firewood in logs, shredded wood, and crushed/pressed wood pellets

Pellet

• Fuel created from dried and pressed virgin wood without additives.
• High bulk density (600-700 kg/m³) compared to other unpressed fuels (wood chips).
• High calorific value (4200 kcal/kg), with energy density (3000-4000 kWh/m³).

Types of Boilers

• Wood chip boilers
• Pellet boilers
• Different types of large capacity biomass boilers including grate technology, bubbling fluidized bed (BFB), circulating fluidized bed (CFB) technology)

Gasification

• Thermochemical process transforming biomass into fuel gas (mixture of combustible gases).
• Suitable for various biomass feedstocks (dry biomass).
• Wet biomass needs pretreatment for gasification.
• Gasification produces electricity and heat, particularly in small-scale plants (<5 MWe to 10 MWe) and in combined cycles with gas turbines (≥30 MWe)

Biogas

• Product of anaerobic (no oxygen) biological process in the biogas plant.
• Methane is formed (biomass decomposes in humid atmosphere in air absence).
• Various substrates (manure, food production waste, vegetables/fruit).
• Important to maintain consistent temperature and residence time.
• Typical biogas composition: Methane (50-80%), Carbon dioxide (50-20%), Nitrogen(<1%), Hydrogen (<1%), Ammonia (<1%), Hydrogen Sulfide (<1%)

This quiz provides an overview of biomass, including its sources and classifications. You will learn about various types of biomass from agricultural, forestry, and urban areas, as well as their contributions to renewable energy. Test your knowledge on the significance of biomass in the context of sustainability.