What Are The Technologies Used In Biomass Energy?

Biomass energy refers to energy derived from organic matter, usually plants or plant-derived materials. According to the U.S. Energy Information Administration, biomass is the oldest energy source used by humans, with the earliest use of biomass energy through burning wood for cooking or heating dating back over a million years. Today, biomass remains an important energy source, providing about 5% of total primary energy use in the United States.

Biomass resources include wood, crops, algae, agricultural residues, and organic municipal solid waste. These biomass feedstocks can be directly combusted to produce heat and electricity or can be converted into liquid biofuels, biogas, and other energy products through various processes.

Some key benefits of biomass energy include its renewability, carbon neutrality when done sustainably, and potential to support rural economies. Since biomass absorbs carbon dioxide while growing, the CO2 released when biomass is burned is balanced by what was absorbed during growth. This makes biomass a carbon-neutral energy option when production is properly managed. Additionally, reliance on domestic biomass resources reduces dependence on imported fossil fuels.

Sources:

https://www.eia.gov/energyexplained/biomass/

https://www.nationalgeographic.org/encyclopedia/biomass-energy/

Table of Contents

Types of Biomass Resources

Biomass resources can be categorized into three main types:^[1]

Plant-based biomass – This includes agricultural crop residues like corn stalks, wheat straw, and sugarcane bagasse. It also includes dedicated energy crops like switchgrass and woody biomass from forests and sawmills.

Animal-based biomass – This refers to manure from livestock operations, which can be converted into biogas through anaerobic digestion.
Municipal waste biomass – This includes biodegradable waste materials like food scraps, paper, cardboard, yard trimmings, sewage sludge, and wood waste. These can be digested or combusted for energy production.

The most abundant and widely used biomass resources are plant-based, particularly agricultural residues and waste materials from crops like corn, wheat, rice, and sugarcane. Animal manure and municipal waste biomass are less widely used but offer significant potential as energy feedstocks.^[2]

Direct Combustion

Direct combustion is the process of burning biomass fuel directly to produce heat energy. It involves combusting raw biomass or processed biomass fuels like wood chips, pellets, or biogas in a boiler or furnace to generate hot air, hot water, or steam.

The technology for direct combustion of biomass is relatively simple and has been used for centuries in applications like cooking, home heating, and industrial processing. Modern biomass boilers and furnaces are efficient and low-emission technologies designed to maximize combustion while minimizing air pollution.

The most common direct combustion applications are:

Heat production – Biomass boilers in schools, hospitals, factories, district heating plants etc. provide hot water and steam.
Power generation – Steam from biomass combustion can drive turbines to generate electricity.
Cogeneration – Combined heat and power (CHP) plants use biomass to produce both heat and electricity.

According to the Bioenergy Consult, over 90% of current bioenergy usage involves direct combustion of biomass to provide heat for industrial facilities, buildings, and cooking applications. Though simple, it remains an effective biomass conversion technology.

Co-firing

Co-firing is an effective technology for producing renewable energy from biomass. It involves burning biomass together with coal in existing coal power plants. Biomass is burned along with the main fuel (coal) to produce electricity.

Co-firing biomass with coal offers several advantages. Most notably, it reduces coal usage and emissions. When biomass is burned together with coal, less coal needs to be burned to produce the same amount of electricity. This directly decreases coal consumption and carbon dioxide emissions.

Co-firing takes advantage of existing infrastructure since it uses current coal power plants. This avoids the capital costs of building dedicated biomass power plants. Existing power plants can be retrofitted to allow co-firing of biomass relatively inexpensively. This makes co-firing an attractive near-term option for many utilities to increase their renewable energy generation.

Overall, co-firing biomass with coal in existing power plants reduces coal usage and emissions while taking advantage of available infrastructure. This makes it an effective renewable energy technology using biomass.

Gasification

Gasification is a process that heats biomass through a controlled process, without combustion, to generate synthetic gas (syngas). This is done by heating the biomass to high temperatures with some oxygen, but not enough oxygen for full combustion. The lack of oxygen allows the biomass to break down into hydrogen, carbon monoxide, and carbon dioxide gases through a series of chemical reactions.

The resulting syngas can then be used as a fuel for generating electricity, transportation fuels, and chemicals. Gasification systems consist of a gasifier unit, a gas cleaning system, and energy conversion equipment. Inside the gasifier, the biomass reacts at high temperatures ranging from 700°C to 1200°C with oxygen and steam. This produces the syngas which contains CO, H2, CH4, CO2, N2, higher hydrocarbons, tar, and char particles.

Gasification has high efficiency for electricity production compared to direct combustion. The synthesized gas can be used in gas turbines, internal combustion engines, and fuel cells to generate electricity with efficiencies around 40-50%. Overall, gasification is a versatile process that can utilize a wide range of biomass feedstocks to produce syngas for flexible end-use applications.

Source: https://www.energy.gov/eere/fuelcells/hydrogen-production-biomass-gasification

Pyrolysis

Pyrolysis is the process of heating biomass in the absence of oxygen which leads to the thermal decomposition of the material (1). It is usually conducted at temperatures between 350-550°C or higher (2). The main product of pyrolysis is a liquid called bio-oil which can be refined into transportation fuels, chemicals and other products. Pyrolysis also produces combustible gas and a solid char residue.

There are two main types of pyrolysis processes (3). Fast pyrolysis rapidly heats the biomass and produces 60-75% liquid bio-oil as the main product. Slow pyrolysis involves slower heating over several hours and produces more char. Pyrolysis offers a flexible way to produce different energy products depending on operating conditions.

Sources:
(1) https://www.ars.usda.gov/northeast-area/wyndmoor-pa/eastern-regional-research-center/docs/biomass-pyrolysis-research-1/what-is-pyrolysis/
(2) https://www.mdpi.com/1996-1073/11/11/3115
(3) https://www.sciencedirect.com/science/article/pii/S1364032122006049

Anaerobic Digestion

Anaerobic digestion is a process that utilizes bacteria to break down biomass in the absence of oxygen, producing biogas as an end product. This biogas is comprised primarily of methane and carbon dioxide (EPA). Biomass feedstocks such as animal manure, food waste, sewage sludge, and crop residues are placed in an anaerobic digester, an airtight tank, where they are decomposed by microorganisms. The decomposition process occurs in three stages – hydrolysis, acidogenesis, and methanogenesis (Welsh Government). In the hydrolysis stage, complex organic polymers are broken down into simpler monomers. Acidogenesis converts these monomers into volatile fatty acids, alcohols, ammonia, carbon dioxide and hydrogen sulfide. Finally, in methanogenesis archaea convert the organic acids into biogas comprised of approximately 60% methane and 40% carbon dioxide.

The methane generated through anaerobic digestion can be captured and utilized as a renewable energy source. The biogas can be used directly for heating and cooking, converted into electricity via engines or turbines, upgraded into renewable natural gas, or injected into natural gas pipelines. Anaerobic digestion offers environmental benefits such as diverting organic waste from landfills, reducing greenhouse gas emissions, and producing a renewable fuel source.

Fermentation

Fermentation is a microbial conversion process that uses microorganisms such as yeast or bacteria to convert biomass into useful products like alcohols. During fermentation, microorganisms metabolize sugars and starches present in biomass feedstocks, resulting in the production of metabolites like ethanol, butanol, and organic acids.

One major application of biomass fermentation is for producing ethanol fuel. Ethanol is commonly produced from the fermentation of sugar and starch crops like corn, sugarcane, and sugar beets. The biomass feedstock is pretreated to release the sugars, which are then fermented by yeast into ethanol. Ethanol is a clean burning fuel that can replace gasoline, and it is the most widely used biofuel today (Bright Green Partners, 2023).

Butanol is another alcohol fuel that can be produced via fermentation of biomass. While less common than ethanol, butanol has some advantages as a fuel – it has higher energy content than ethanol and can directly replace gasoline in conventional engines. Biobutanol is produced through acetone-butanol-ethanol (ABE) fermentation using anaerobic bacteria like Clostridium acetobutylicum (GFI, 2023). Biomass containing cellulose and hemicellulose is pretreated and hydrolyzed to sugars before ABE fermentation.

Biomass fermentation offers a renewable way to produce sustainable fuels and reduce dependence on fossil fuels. Advances in biotechnology and fermentation techniques continue to improve alcohol yields and economic viability of the process.

Biodiesel Production

Biodiesel is produced from oils extracted from biomass feedstocks such as vegetable oils, animal fats, and greases. The most common feedstocks are soybean oil in the United States and rapeseed oil in Europe. Other feedstocks include palm oil, jatropha oil, and waste cooking oil.¹

There are several steps involved in producing biodiesel from biomass:²

Biomass feedstocks are crushed to extract the oils.

The oils go through a process called transesterification where methanol and a catalyst are added to convert the oils into biodiesel and glycerin.
The glycerin is removed as a byproduct and the biodiesel goes through washing and drying processes to purify it.
The purified biodiesel can then be blended with conventional diesel fuel and used in diesel engines.

Biodiesel production is a growing industry as it provides a renewable fuel alternative to petroleum-based diesel. Most light and heavy-duty diesel vehicles today can run on biodiesel blends of up to 20% biodiesel without any engine modifications.

Advantages and Challenges of Biomass Energy

Biomass energy offers several benefits as a renewable energy source. First, biomass is abundant and readily available in many forms, including wood, agricultural residues, and municipal solid waste (Source). Since biomass absorbs carbon dioxide while growing, it is considered carbon-neutral when burned for energy. Additionally, utilizing biomass decreases reliance on fossil fuels and imports (Source).

However, there are also some challenges with biomass energy. Direct combustion of biomass can release pollutants like nitrogen oxides and particulates. There are also concerns about the impact on land use, as growing biomass feedstocks may compete with food production. Transporting and storing bulky biomass material can be expensive. Lastly, not all applications of biomass energy are carbon-neutral, especially if forests are cleared to produce biomass (Source).

Going forward, advancements in conversion technologies like gasification, anaerobic digestion, and pyrolysis may help maximize energy output and efficiency from biomass sources. With sustainable practices and advances in carbon capture technology, biomass can serve as a key renewable energy solution.