What Is In Biomass Fuel?

Biomass fuels are renewable energy sources made from organic plant and animal waste materials. As renewable fuels made from natural waste products, they offer an alternative to traditional fossil fuels and provide an environmentally sustainable way to meet energy needs.

The term biomass refers to any organic material that comes from plants or animals. Biomass contains stored energy from the sun. Plants absorb the sun’s energy through photosynthesis. When biomass is burned, the chemical energy in plants is released as heat. Biomass burning is carbon neutral because the plants consumed the same amount of carbon in photosynthesis as is released into the atmosphere when burned. Common sources of biomass include forest residues, agricultural crops and crop waste products, wood chips, animal waste, human waste, and municipal solid waste.

Biomass fuels play an important role as renewable energy sources that can supplement or replace fossil fuels in the production of heat, electricity, transportation fuels, and products we use every day. Since biomass fuels come from plant and animal waste, they provide a clean way to use this waste instead of taking up space in landfills. As renewable fuels, biomass can go a long way in reducing dependence on fossil fuels and mitigating climate change.

Table of Contents

Plant Materials

One of the main sources of biomass fuel is plant materials. Plant materials that are commonly used include:

Wood: Wood and wood processing waste are a major source of biomass fuel. This can include wood scraps, sawdust, timber slash, and mill scraps from lumber mills, furniture factories, wood product manufacturers, and other wood users.
Agricultural crops and waste: The inedible parts of crops, such as corn husks and corn cobs, as well as agricultural crop residue are a significant source of biomass fuel. This includes corn stover, sugar cane bagasse, straw, seed fluff, nut shells, rice husks, and more.

Grasses: Grasses like switchgrass and miscanthus can be grown to produce high biomass for energy uses. These grasses require low fertilizer and chemical inputs and have good energy conversion efficiencies.
Algae: Algae and microalgae are emerging sources of biomass fuel. Microalgae can be grown in open ponds or bioreactors and converted to liquid biofuels or biogas.

Animal Materials

Animal manures and rendered fats from animal processing facilities are a significant source of biomass material. Cow, pig, and chicken manure contains organic matter like lignin that can be converted into useful biofuels and biogases.

Other animal byproducts like meat scraps, bones, fat, grease, feathers and blood discharged from slaughterhouses and processors are also collected and rendered into materials that can fuel boilers and digesters. Restaurants and institutions generate food waste containing animal fats and proteins that can provide feedstock.

The high energy density and availability of animal manures, rendered fats, and disposed food waste make them attractive biomass sources. Processing methods like anaerobic digestion and thermal conversion align with sustainability goals by extracting value from waste streams instead of costly disposal.

Municipal Waste

Municipal solid waste (MSW) refers to everyday items, packaging, food scraps, grass clippings, discarded furniture, clothing, paper, and cardboard that comes from homes, schools, hospitals, and commercial establishments. Municipal waste can be utilized as biomass fuel to provide energy for electricity or heating:

Food Waste: Food scraps, waste oils, grease waste, and expired or contaminated food items can be converted into biogas for energy through anaerobic digestion, a process that breaks down organic matter without oxygen.

Paper and Cardboard: Paper products like newspaper, office paper, magazines, and cardboard can be burned directly or converted into pellets for combustion to heat water or spaces.

Plastics: Plastic bags, packaging, bottles, wraps, among other items, when segregated, can be utilized as fuel for waste-to-energy plants.

Textiles: Fabric items from used clothing to furniture upholstery can be utilized as fuel in anaerobic digestion or combustion processes to generate energy.

Wood and Herbaceous Fuel

Some of the most common types of biomass fuel are wood and herbaceous materials like grasses and straw. These fuel sources come from plants and trees and are considered renewable energy because we can regrow trees and grasses fairly quickly compared to fossil fuels that take millions of years to form.

Specific examples of wood and herbaceous biomass fuels include:

Logs – Entire tree trunks or large branches can be burned directly for energy production at facilities equipped to handle large, solid fuels.
Wood chips – Chopping up wood waste into small chips provides more surface area for burning and allows them to be fed automatically into boilers and furnaces.

Wood pellets – Compressing wood chips into high-density pellets allows more energy to be produced per volume and makes them easier to store and transport.
Grasses – Tall grasses like switchgrass and miscanthus can be pelletized or burned directly as a biomass fuel source.
Straw – The stalks and stems left over after harvesting grain crops like wheat, rice, barley and oats can be burned as fuel either directly or made into pellets.

These solid woody and herbaceous biomass fuels release energy as they burn, which can generate electricity, provide heat, or power vehicles and machinery. As plants regrow, they recapture carbon dioxide from the atmosphere, achieving net zero or even negative carbon emissions when used for energy.

Bioalcohols

Bioalcohols are a renewable liquid biofuel obtained through the fermentation of biomass feedstocks that contain appreciable amounts of sugar or materials that can be converted into sugar such as starch or cellulose. The main bioalcohols used as transportation fuels include ethanol, methanol and butanol.

Ethanol is produced through the microbial fermentation of sugars. In the United States, most ethanol is made from corn starch. Sugarcane and sugar beets are also common feedstocks for ethanol production. Brazil relies heavily on sugarcane as an ethanol feedstock. The ethanol yield depends on the feedstock, with theoretical yields ranging from about 300 liters per metric ton of feedstock for sugarcane to about 400 liters per metric ton for corn.

Methanol is most commonly produced from natural gas, but can also be produced from biomass through gasification processes. The resulting “synthesis gas” containing carbon monoxide and hydrogen can then be catalytically converted into methanol. Methanol made from biomass is chemically identical to petroleum-based methanol, but has less environmental impact.

Butanol is considered an advanced biofuel and can be used in higher blends with gasoline compared to ethanol. It is produced through acetone-butanol-ethanol (ABE) fermentation using feedstocks like corn, wheat and sugarcane. Biobutanol production is currently limited, but research is ongoing to improve yields.

Biodiesels

Biodiesels are liquid fuels typically made from vegetable oils, animal fats, or recycled restaurant greases. Common feedstocks include:

Soybean oil
Canola oil
Palm oil

Corn oil
Used cooking oil
Animal fats

These oils or fats undergo a chemical process called transesterification to transform them into biodiesel. This involves removing the glycerin and turning the triglycerides in the oils/fats into fatty acid methyl esters (FAME), which have properties similar to petroleum-based diesel fuel.

Biodiesels burn cleaner than standard diesel with reduced emissions of carbon monoxide, particulates, and hydrocarbons. However, nitrogen oxide emissions may be slightly higher. Biodiesels also biodegrade faster than petroleum diesel.

Biogases

Biogases are gaseous fuels produced from the breakdown of organic mater. The main types of biogases are methane, landfill gas, and sewage gas.

Methane

Methane is produced from the decomposition of livestock manure and organic materials in landfills. It is a renewable fuel source that can be captured and used to generate electricity and heat. Methane is a cleaner burning fuel than gasoline or coal.

Landfill Gas

Landfill gas is composed mainly of methane and carbon dioxide. As organic waste in landfills breaks down, it produces these gases which can be collected using a series of pipes and wells embedded in the landfill. The collected landfill gas can then be processed and used as an energy source.

Sewage Gas

Sewage gas refers to the methane produced from the anaerobic digestion of sewage. Anaerobic digesters at wastewater treatment plants contain bacteria that breakdown biodegradable material in sewage to produce biogas. The methane content of sewage gas makes it a valuable source of renewable energy.

Processing Methods

There are several key processes used to convert raw biomass into usable biofuels:

Drying

Drying biomass through direct or indirect heating reduces moisture content, increasing combustion efficiency and reducing problems associated with biological degradation and rot. Byproducts including heat and biogas are also harvested during this process.

Pelletizing

Compressing biomass into dense pellets through mechanical force improves handling, transport, and combustion performance. Binders or steam may be introduced during pelletization to increase durability.

Pyrolysis

Heating biomass to high temperatures in the absence of oxygen produces bio-oil, syngas, and charcoal through thermochemical decomposition. Slow, fast, flash, microwave, and other pyrolysis variants optimize production of specific fuel outputs.

Gasification

Converting biomass into combustible syngas through partial oxidation enables flexible power generation in gas engines and turbines or synthesis into liquid fuels via the Fischer–Tropsch process.

Environmental Benefits of Biomass Fuels

Biomass fuels provide several key environmental benefits compared to fossil fuels like coal, oil and natural gas. The main benefits relate to carbon emissions, waste utilization and sustainability.

On carbon emissions, biomass fuels are considered carbon neutral. This means that the carbon dioxide released when biomass fuels are burned is balanced out by the carbon dioxide that was absorbed as the plants grew. So unlike fossil fuels, using biomass does not introduce new carbon into the atmosphere.

In terms of waste, biomass energy provides a productive use for various waste materials like municipal solid waste, agricultural residues, wood waste, animal manure, etc. Rather than taking up space in landfills or releasing methane as they decompose, these materials can displace fossil fuels in energy production.

When it comes to sustainability, biomass fuels are renewable as long as new plants are grown at the same rate as they are utilized. This makes them superior to finite fossil fuel reserves. With sustainable farming and forestry practices, a continual supply of biomass feedstocks can be maintained.