Oct 22, 20214 min read

Bioenergy 2021

In today's issue we will be covering one of the oldest and more complicated forms of renewable energy; bioenergy! For those that don't know, bioenergy is a form of renewable energy that harnesses the stored energy in recently living organic matter, also known as biomass (“Bioenergy Basics”). Essentially, bioenergy is the burning of dead organic matter (think felled trees, human trash and other biomass in general). Humans have been utilizing bioenergy for thousands of years, since we began burning wood to cook food and stay warm. Before being eclipsed by coal at the beginning of the industrial revolution in the mid 1800s, bioenergy was the dominant form of energy consumption in the United States (Renewable Energy Explained - U.S. Energy Information Administration (EIA)). The most common form of biomass is still wood, but we can also utilize agricultural crops, biogenic materials in our trash, and animal or human sewage (Biomass Explained - U.S. Energy Information Administration (EIA)). There are three ways that biomass is used to produce energy and electricity; burning, converting it to fuel, and decomposition.

Burning:

Burning, also known as direct consumption, is the most common way to convert biomass into usable energy. The most common biomaterials burned in the United States are raw materials (like wood) and municipal waste/garbage (Society). These materials are first dried out and prepped for burning through a process called torrefication. Through this process, the biomaterial “... loses about 20% of its original mass, but retains 90% of its energy” (Society). Once dried, biomaterials are burned in a boiler to produce steam which powers a generator, creating electricity.

Converting to fuel:

Biomass is converted to fuels through two main types of thermochemical processes; pyrolysis and gasification. According to the U.S Energy Information Agency both processes are, “... thermal decomposition processes in which biomass feedstock materials are heated in closed, pressurized vessels called gassifiers at high temperatures.” (Biomass Explained - U.S. Energy Information Administration (EIA)) The key difference between the two processes is the role of oxygen. Pyrolysis heats the biomass material “in the near complete absence of free oxygen” which results in fuels like bio-oil and renewable diesel. Gasification heats materials with controlled amounts of free oxygen to “... produce a carbon monoxide and hydrogen rich gas called synthesis gas or syngas” (Biomass Explained - U.S. Energy Information Administration (EIA)). Both of these refined materials can be used to produce energy, but syngas can also be used to create biofuel (Society).

Anaerobic decomposition:

Anaerobic decomposition is the process in which bacteria breaks down biomass material in the absence of oxygen, which in turn produces biogas, a renewable form of natural gas (Biogas-Renewable Natural Gas - U.S. Energy Information Administration (EIA)). Anaerobic decomposition happens throughout the natural world (in soil, swamps and in the bodies of animals and humans) and in the material world (in landfills and sewage systems). In landfills, as the bacteria works its way through the biomass, the decay produces methane which can be captured by a landfill gas collection and control system and used as an alternative for natural gas (Biogas-Renewable Natural Gas - U.S. Energy Information Administration (EIA)).

In the world of renewable energy, bioenergy is one of the more complex forms of energy creation. While technically renewable, it is not necessarily carbon neutral. This is because by harnessing decaying or dead biomass, we are intercepting the natural carbon cycle and repurposing it to produce larger amounts of energy. In doing this, we are burning and releasing the stored carbon in the biomass into the atmosphere in the short term, rather than the carbon being released directly back into the environment under a natural timeline (“Biomass Energy”). Since biomass can be restored within the human lifetime through processes such as growing trees, it is considered a renewable source of energy. According to the EPA, “A determination of carbon neutrality requires an assessment of the particular conditions under which a type of biomass (e.g., feedstock) is grown and consumed.” (US EPA) In the past few years, researchers have raised concerns about the net emissions of the bioenergy sector, particularly as it relates to the strained timeline we have for global climate change mitigation. This is of particular concern because biomass is the source of about 40% of the renewable energy consumed in the United States (The United States Consumed a Record Amount of Renewable Energy in 2020 - Today in Energy - U.S. Energy Information Administration (EIA)). Bioenergy is a fascinating and valuable source of energy today as we transition away from fossil fuels, but it is still to be seen if it has its place in a long term sustainable future.