WHAT IS BIOMASS ENERGY?
As we’ve moved into the 21st century, the use of renewable energies as a solution to stifle the effects of climate change is becoming an increasingly necessary endeavor. In the past few decades, more attention has been focused on how we can apply more environmentally-friendly energy solutions to mass-produce enough electricity to keep up with the international demand for it. With several different types of renewable energy options, the knowledge about the methodology and application of each one can seem, at times, endless.
In the past few decades, more attention has been focused on one particular type of renewable energy – known as “biomass”. Biomass energy has been a common source used in still-developing countries. While not as widely applied in the west anymore, new technologies have evolved to capture, store, and use energy extracted from biomass material through a diverse set of processes.
Knowing how energy can be harvested from biomass requires understanding the fundamentals of the different types of conversion processes. Energy harvesting and its many forms can be overwhelming, and this guide to understanding biomass serves to break down the basics of what biomass energy actually is, how it’s extracted, and how it can be executed sustainably and utilized in day-to-day life.
Humans and Energy – A brief overview
Long before the industrial revolution, biomass was the primary source of energy for the world. Technically, mankind’s first intentional interactions with fire can be thought of as the first conversion of organic material into energy to produce heat or cook raw foods. For thousands of years, humans have utilized biomass energy in the form of wood-burning fires and other organic material longer than any other heat source. As humankind progressed from nomadic hunters into hunter-gathering societies, the use of fire as an energy source was pivotal to our development and survival. As centuries progressed, wood-burning stoves and fireplaces provided energy for heating homes and cooking needs long before the advent of in-home electricity.
By the middle of the 19th century, the coal-powered steam engine quickly ushered society into the new age of manufacturing. Coal and steam engines allowed for the mass production of goods and textiles, and as people began to change the way they traveled and worked, the demand for carbon-rich coal to fuel this new way of life became a political and economic driver. Coal began to take the place of wood as a heating and energy source because it was easy to transport, and because it held more energy than its predecessor.
As technology advanced, the potential of oil began to be better understood as well, and by the end of the 19th century, coal mines and crude oil wells were the driving source of energy for a booming new world. Today, traditional methods of burning wood for power to turn turbines and heat homes have been replaced by other energy sources – namely coal, petroleum, and natural gas from fracking.
As we have come into the 20th and 21st century, however, scientists have noted how the prolonged and excess use of burning fossil fuels has impacted our atmosphere, and what those global impacts are. First known colloquially as “global warming”, and now more appropriately referred to as climate change, the atmospheric shift in conditions that we are experiencing is a result of unchecked greenhouse gases being released into our atmosphere and they have a laundry list of adverse effects on oceanic, atmospheric, and terrestrial processes. These greenhouse gases, like carbon dioxide and methane, are the products of burning what are known as fossil fuels (or non-renewable resources). These are finite resources, and can not replace themselves fast enough to keep up with the rate at which they are being consumed. That’s why renewable energy sources, like biomass, are being studied and utilized more and more.
To fully grasp the complexities and extraordinary capabilities that biomass energy has, understanding its role as an integral part of our planet’s carbon cycle and why that’s important as it relates to energy is key.
What is the carbon cycle, and what does it have to do with biomass?
Carbon is the foundation for all living organisms on Earth. In short, the carbon cycle is essentially Earth’s way of recycling all of its carbon atoms. It is a circular process where carbon is exchanged between the atmosphere and biosphere, with all carbon being in a constant cycle of transformation . Carbon is found in all living things, and just as it is exchanged in photosynthesis, it is also processed in decomposition where it has the potential to be stored (or sequestered) into the Earth. After millions of years stored inside the ground, and after prolonged heating and pressure from the overlying rock above it, the decomposed matter turns to oil or coal (“fossil” fuels). The problem with using fossil fuels for energy purposes is that they do not re-absorb carbon, and rather release carbon dioxide into the atmosphere, disrupting the Earth’s natural balance. This is where turning to renewable energy, like biomass, to solve our dependency on coal and oil becomes effective.
So if organic matter is biomass, and we can extract energy from biomass – then we know a pile of wood may store energy, but it will not emit energy unless something is done to it.
Understanding how biomass can “store” energy inside of it (like how wood, crops, and gas do) requires comprehending the carbon cycle and how it applies to energy extraction.
As we know, organic matter like plants and crops perform photosynthesis. This process takes energy from the sun in the form of light, along with water and carbon dioxide, and turns it into oxygen and glucose. The product of this reaction is it contains stored energy from the sun. For example, as a tree grows, it absorbs carbon dioxide from the air. The tree uses photosynthesis to isolate the carbon, and it uses that carbon to build itself. Bark, wood, leaves – all the organic components of the tree are made from carbon. When the tree dies, it rots away – and if left uninterrupted, the carbon would be released back into the atmosphere as carbon dioxide. The methodology behind biomass energy is that by using organic matter as an energy supply, we intercept the carbon cycle and use the released carbon productively for energy. Rather than contribute to the excess of carbon dioxide being released into the atmosphere from mankind’s previous blunders in energy harvesting, this carbon – whether it be from trees, plants, crops, or waste – would be recycled into usable energy.
What exactly is biomass energy?
Does a natural resource need to power it in the same way the sun powers solar?
In simplest terms, biomass is any type of organic material (plant or animal byproduct) that can be used to produce energy. Energy is stored inside the biomass, and it has to undergo some sort of process for that energy to be used. A common way you have already used biomass as energy is anytime you’ve sat around a wood-burning fireplace and warmed up; or used a campfire to cook food. By burning the biomass (wood), you are putting it through a type of conversion – and using the energy (in this case, heat) it produces.
Renewable’s unsung hero
Windmill farms and solar panels have become the face of the shift to renewable energy. Most people associate renewable energy systems with solar panels on roofs of houses, or windmills in the distance of a freeway. While these are both great options as sources of renewable energy in their own right – it is also true that their productivity is dependent on the resources that drive them. We know that solar panels’ ability to produce energy is dependent on the strength and presence of sun rays, wave turbines are dependent on the right ocean conditions, and wind farms need consistent airflow to function at their highest efficiency.
One of the most, if not the most appealing aspect of biomass energy, is that the product needed in order to produce the energy is the biomass itself – and it can be supplied at a near-constant rate. Biomass is considered renewable energy because the products used for it (trees, crops, etc.) can always be grown – and waste, unfortunately, will always exist.
Different types of biomass energy
The most common types of biomass material used for energy are wood and wood byproduct, animal and human waste, crops and plants, and gas stored in landfills.
Wood and wood byproduct like chips, bark, sawdust, and scraps make up a large fraction of biomass energy. Industrial users account for the majority of wood/wood byproduct use, and places like paper and sawmills are even able to use their scrap or waste products in steam generators to produce electricity in sort of a closed-loop cycle.
One man’s trash is another man’s energy source. Burning municipal solid waste can turn into heat energy – one ton of garbage can hold nearly as much energy as 500 pounds of coal. When considering coal is a finite resource and waste is constantly being produced by humans, this seems like a reasonable solution tradeoff. Animal waste like livestock manure can also be used as prolific substrates to generate biogas.
Along with animal waste, crops and certain plants can be converted into synthetic fuels and be used to create gasoline substitutes and blends, and biofuels. Different types of starch heavy crops like sugarcane, corn, and wheat can be used as what is known as a “biomass feedstock”. Energy crops like switchgrass and algae are also viable candidates.
Gas can also be derived from organic waste decomposing in landfills. In regards to harvesting biomass, landfills hold vast amounts of untapped potential as organic matter decomposes and produces natural gas stores.
What can we use biomass energy for?
The energy that is derived from biomass can be used for the same services we use other types of energy for. Biomass is unique in that it can undergo different conversions and processes that produce different mediums like fuels, materials, and chemicals that can be used for energy and electricity in different ways. Biomass products can be converted to biofuels to power vehicles, heat homes, power generators and machinery, and other processes that would otherwise be powered from fossil fuels.
Making biomass (organic material) into energy
So energy is stored inside of biomass naturally. How do we get it out?
Biomass can either be combusted for heat or converted through other processes to be liquid and gas fuels. There are a few main ways that energy is extracted from biomass.
- Direct combustion: (Burning) → Produces heat, can be used to power turbines/generators.
- Biological conversion: (Fermentation & Bacterial Decay) → Produces liquid and gaseous fuels.
- Conversion: (Chemical & Thermochemical conversion) → Produces liquid, gaseous, and solid fuels.
Direct combustion: (Burning)
Direct combustion is the most used method for converting biomass to energy.
As mentioned previously, burning wood is historically the most popular method of producing energy. Wood burning was the biggest energy provider for large countries like the U.S until the mid 19th century, homes were heated by it and factories fueled by it. Today, however, chopping wood logs simply can’t supply large-scale energy needs, so other ways to process the material for combustion are used. Wood shavings can be manufactured in large quantities to be easily transported, as well as plants, manure, and feedstock crops.
Waste can also be successfully burned to produce energy and generate electricity. Waste-to-energy plants are waste management facilities that specialize in combusting waste to produce electricity. These sites mass-burn large quantities of waste stored in bunkers and move them into furnaces to be incinerated. The heat from this reaction heats up water stored inside a boiler, in turn making steam that powers a turbine to drive an electrical generator. The electricity produced from this process can then enter the electrical grid. According to data collected by the US Waste Industry, combusting 1 metric ton of municipal solid waste can generate up to 600 kWh (kWh = a unit of energy equivalent to 3,600 kilojoules, a common unit used by electric companies), which would avoid using a quarter ton of US coal. For comparison, a residential home in the US uses on average of 867 kWh per month.
While these plants work similarly in nature to coal-burning plants, instead of the coal being burned it is solid waste brought in from or diverted from landfills. Not only do landfills emit harmful greenhouse gases into the air like carbon dioxide and methane, but they can leach other hazardous pollutants underground and potentially be the cause of groundwater contamination. Combustion of human waste is beneficial as it both reduces the size of landfills and their harmful ecological effects and repurposes MSW into usable energy.
Biological conversion: (Fermentation & Bacterial Decay)
When animals and plants die and decompose, bacteria move in and feed on them as a natural part of the decomposition process. Have you ever forgotten a packed lunch in a bag, and opened it to find your apple slices slowly turning soft and spoiled?
This type of decomposition is the same that happens in places like landfills – and it is referred to as “anaerobic”, which means it happens without, or with very little oxygen. As organic matter decomposes, it produces methane – a natural gas. When organic matter decomposes in a semi-closed environment like a landfill (or like the apple slices in a plastic bag) the lack of access to oxygen means that organic material will break down slower, and therefore produce methane longer.
Methane (CH4) is rich in energy stores, and when people talk about “natural gas”, methane is generally what they’re describing as it can be produced by natural processes. Too much methane in the atmosphere, as we know, facilitates an increase in general atmospheric warming known as the greenhouse gas effect. Excess methane can also be the trigger for fires near landfills, as well as water and air pollution.
In a way to both utilize the energy benefits of methane and reduce the potential for it leaching into groundwater systems and the atmosphere, wells can be drilled into the ground to capture and store methane from the decomposing material. The gas can then be moved into a series of pipes and chambers where it is cleaned and filtered, then engines can burn the gas into usable electricity. Not only does this reduce the amount of harmful methane gas that would otherwise pollute the ground and atmosphere, but it again redirects it into energy.
Just like our ancestors have been using fire for centuries to produce heat and food, they’ve also long experimented with fermenting crops like wheat and grapes to produce things like alcoholic beverages. By adding a fungus (yeast) to biomass, a similar type of process can be made to produce a type of fuel that can be used for energy. A type of alcohol called “ethanol” is able to be produced from crops like corn, wheat grass, and sugar cane. Crops with a high sugar and starch content can be used to make ethanol, and are known as “feedstock”.
While ethanol doesn’t operate as efficiently as it would need to fully replace gasoline, it can be blended with gasoline to operate vehicles and machinery. There are common ethanol blends, “E10” and “E15” refer to the percentage (10% – 15%) of ethanol that is mixed in with our gasoline. This produces a more eco-friendly fuel, as ethanol is considered a renewable resource and it does not release the greenhouse gas emissions that fossil fuels do.
So how exactly do plain agriculture crops like corn and sugarcane end up powering our cars?
Feedstocks turn into ethanol via fermentation, a metabolic process that creates biological and chemical changes through enzymes.
The fermentation process takes feedstocks and puts them through a series of steps that eventually creates ethanol, including the following:
- Milling – Feedstocks are ground down to tiny bits called “meal”. The meal is starchy and full of carbohydrates.
- Liquification – Water is added, and the product is cooked. The heat breaks up the molecules, and an enzyme is added to catalyze (speed up) the breakdown.
- Saccharification – The substance breaks down into sugar, glucose.
- Fermentation – Yeast is added to the mix, which are single-celled organisms that break down the glucose. Yeast gets energy from glucose and produces ethanol.
- Distillation & Dehydration – The process of fermentation only produces a low concentration of ethanol. In order to become pure ethanol, it must be concentrated. The ethanol is then evaporated and condensed selectively in a process known as distillation.
- Denaturation – Gasoline is added to the mixture.
This process produces ethanol and ethanol blends as more environmentally friendly alternatives than relying on pure gasoline, a product of petroleum.
The ethanol production process also creates two main byproducts: distillers grains and carbon dioxide (CO2). Distillers grains are any residue left from the fermentation tanks of substances that could not be broken down; like larger grain bits, leftover yeast, etc. These are useful as an ingredient in livestock feed as its high in protein. The CO2 that is produced is a product of the fermentation reaction when yeast interacts with glucose while making ethanol. When CO2 is produced in a controlled environment like this, there is the potential for it to be captured and stored for other uses.
Algae also has the potential to be used as a biomass resource, and is currently being studied to see how it could best reach its potential as a biomass feedstock. Algae grows in water, produces photosynthesis quicker than other dryland feedstocks, and is able to store a large amount of usable energy. Because algae grows in water, it completely eliminates the amount of dryland space required to grow it, in stark contrast to other biofuel feedstock like wheat, corn, and soy – and it does not reduce land that could be used to potentially grow food crops. Since it can be grown in ocean water, it also does not deplete freshwater resources.
Algal biomass has promising advantages, and it may be more favorable than other biofuel products because of its natural anaerobic digestion. As it is replenished, it releases oxygen and absorbs pollutants and carbon emissions. Algae also contain natural oils that can be converted into its own type of biofuel. When algae are processed with high temperatures and high pressure, it creates a type of natural fuel dubbed the “green crude” that has similar properties to oil and can successfully be used as a biofuel. However, the issue with using algae as biofuel is that processing it can be extremely costly. Despite algae having a higher yield than other types of fuel stock crops, the high prices make algae an obsolete resource for still developing countries.
Conversion is the act of changing one material into something else. In most cases of harvesting biomass energy, some type of conversion is done in one way or another. However, biomass conversion refers to converting the organic material itself into gas or liquid fuels (known as biofuels or biodiesel) and then burning them for either heat or electricity.
Thermochemical conversion is a process that uses a combination of super high temperatures, water, and controlled amounts of oxygen to convert organic matter into usable energy mediums.
Thermochemical conversion can use any biomass materials – paper scraps, municipal solid waste (garbage), crops, and plants – and convert them into a different form for energy use.
This process starts with something called torrefaction. During torrefaction, the biomass is heated up to temperatures nearing 200 to 300 degrees Celsius, and is completely dried out. This changes the properties to have a better quality for future combustion applications. It also allows the biomass to lose the ability to spoil or rot by absorbing any more moisture. While the matter may lose some of its original mass during this process, it still retains the majority of its stored energy.
The dried out pieces of biomass are then compressed into smaller pellets or briquettes. Briquettes are small, easily storable dried-out biomass blocks that can be used along with, or as a substitute for coal. Briquettes can either be burned directly to produce steam to power turbines, or they can be “co-fired”. Co-firing is when biomass products like briquettes are burned alongside coal in coal plants. This not only reduces the amount of greenhouse gases being released into the atmosphere by cutting down on the amount of coal being burned, but it also reduces the demand for new factories to be erected to process biomass products only.
Thermochemical conversion can also produce types of oil and gas through a process called pyrolysis. Pyrolysis is another method of heating biomass, where it is heated to extreme temperatures without oxygen. This keeps matter from combusting and allows the biomass to become chemically altered. This process can produce what’s known as pyrolysis oil (a type of bio-oil similar to tar) and “syngas”, a synthetic gas. Syngas is composed of carbon monoxide and hydrogen, and it can be purified of any pollutant particulates and toxins like mercury or sulfur it may carry after it has been processed. Fully processed syngas can be burned for heat, made into biofuels, or used for electricity.
Pyrolysis oil can also be burned to generate electricity, and can be made to create plastics and other fuel. Another beneficial product created through biomass conversion is biochar, a carbon-rich charcoal made as a result of pyrolysis. Biochar can be reintroduced into soil to aid in carbon sequestration and boost overall soil health.
Another way biomass can be converted directly to energy is through gasification. This is typically done to solid waste (MSW) and is similar to pyrolysis, except in gasification the substrate is heated to high temperatures with a controlled level of oxygen. During this process, molecules in the biomass break down and create syngas and a product called “slag”. Slag as a product of biomass is a dark viscous liquid, and it can be used in asphalt and cement production, or it can be generated into bio-oil and combustible gas.
Disadvantages of biomass energy
While biomass can be considered a renewable resource at its core, if proper management methods are not adhered to, they risk being used faster than they can replenish themselves. While the replenishment cycle of organic matter like plants and trees may not take as long as fossil fuels do, it is not advised to overuse or over exploit plant products for the sole intended purpose to combust or convert for energy needs. Furthermore, land that is used solely for feedstock crops is land that can not be used to grow agricultural crops for consumption. New growth areas also take a longer time to establish their role in the carbon cycle, and if forested areas are not sustainably managed to sequester carbon, the advantages brought about by using wood products for biomass fuel are not counteracted by equal tree growth. Burning biomass can also release toxins such as carbon dioxide, carbon monoxide, and other air pollutants. If these emissions are not properly maintained, burning biomass can contribute to pollutants similar to the ones released by fossil fuels.
Advantages of biomass energy
Many of the disadvantages of biomass relate back to improper or inadequate management of biomass resources. If managed properly, biomass fuels have the potential to meet productivity and return favorable levels of energy production. The advantages of biomass are that it’s a clean energy source and it can be replenished both naturally, and under controlled circumstances. Because the organic matter used as biomass gets its energy from the sun, any biomass source that uses photosynthesis as its own main energy driver can always be regrown. Crops, algae, and trees (wood) can be grown under controlled circumstances, and under proper resource management can be harvested sustainably. Planting feedstock for biomass can be done on unused or marginal lands, and can provide both jobs as well as an extra carbon sink to absorb any emissions that would be released if any of the feedstock were to undergo processing for fuel. The leverage biomass has against energy systems like wind and solar is that biomass’s energy is stored inside the organism itself, and can be used on an as needed basis instead of depending upon atmospheric conditions. Biomass also boasts an impressive amount of byproducts. Through a few basic methods, there are a wide variety of ways to process organic matter into usable biofuels, ethanol, pellets, briquettes, syngas, and slag to make and produce energy and electricity.
Biomass – its forms, uses, and future
Biomass energy encompasses a lot of different systems and processes. In short, biomass is any organic matter of which energy can be extracted from, through burning, biological conversion, or thermochemical conversion. Biomass typically comes in the form of crops, waste, manure, and wood products and biomass energy can be extracted in the form of heat, fuel, gas, or substrate to be used as fuel to produce electricity. Currently, biomass supports nearly 10% of the globe’s energy demand. Moving forward, scientists are looking for more ways to modernize biomass energies to fit a more sustainable development path.
Like all other forms of energy, biomass has its disadvantages, although the ones associated with it (depleting resources, releasing excess carbon, etc.) mainly stem from mismanagement of the resources themselves. As of now, biomass continues to be a useful energy source and promising method of energy production. Room for improvement and further observation as to how we can more successfully and efficiently manage fuel stocks (like algae) is going to require consumer attention and a demand for the product. With proper execution and resource management, utilizing biomass as a beneficial form of renewable energy seems like a promising endeavor as we continue to face a changing climate.