Direct combustion is the most common method for converting biomass to useful energy. All biomass can be burned directly for heating buildings and water, for industrial process heat, and for generating electricity in steam turbines. Thermochemical conversion of biomass includes pyrolysis and gasification. Both are thermal decomposition processes in which biomass feedstock materials are heated in closed, pressurized vessels called gassifiers at high temperatures. They mainly differ in the process temperatures and amount of oxygen present during the conversion process.
Pyrolysis entails heating organic materials to — o F — o C in the near complete absence of free oxygen. Biomass pyrolysis produces fuels such as charcoal, bio-oil, renewable diesel , methane, and hydrogen. Hydrotreating is used to process bio-oil produced by fast pyrolysis with hydrogen under elevated temperatures and pressures in the presence of a catalyst to produce renewable diesel, renewable gasoline, and renewable jet fuel. Syngas can be used as a fuel for diesel engines, for heating, and for generating electricity in gas turbines.
It can also be treated to separate the hydrogen from the gas, and the hydrogen can be burned or used in fuel cells. The syngas can be further processed to produce liquid fuels using the Fischer—Tropsch process.
A chemical conversion process known as transesterification is used for converting vegetable oils, animal fats, and greases into fatty acid methyl esters FAME , which are used to produce biodiesel. Biological conversion includes fermentation to convert biomass into ethanol and anaerobic digestion to produce renewable natural gas.
Ethanol is used as a vehicle fuel. Renewable natural gas—also called biogas or biomethane —is produced in anaerobic digesters at sewage treatment plants and at dairy and livestock operations. It also forms in and may be captured from solid waste landfills. Properly treated renewable natural gas has the same uses as fossil fuel natural gas.
Researchers are working on ways to improve these methods and to develop other ways to convert and use more biomass for energy. In , biomass provided about 4, trillion British thermal units TBtu , or about 4. Of that amount, about 2, TBtu were from wood and wood-derived biomass, 2, TBtu were from biofuels mainly ethanol , and TBtu were from the biomass in municipal wastes. The amounts—in TBtu—and percentage shares of total U. The industrial and transportation sectors account for the largest amounts, in terms of energy content, and largest percentage shares of total annual U.
The wood products and paper industries use biomass in combined heat and power plants for process heat and to generate electricity for their own use. Liquid biofuels ethanol and biomass-based diesel account for most of the transportation sector's biomass consumption. Stationary fuel cells are used to generate electricity in remote locations, such as spacecraft and wilderness areas. Yosemite National Park in the U.
Hydrogen fuel cells may hold even more potential as an alternative energy source for vehicles. The U. Department of Energy estimates that biomass has the potential to produce 40 million tons of hydrogen per year. This would be enough to fuel million vehicles. Currently, hydrogen fuel cells are used to power buses, forklifts, boats, and submarines, and are being tested on airplanes and other vehicles.
However, there is a debate as to whether this technology will become sustainable or economically possible. The energy that it takes to isolate, compress, package, and transport the hydrogen does not leave a high quantity of energy for practical use.
The carbon cycle is the process by which carbon is exchanged between all layers of the Earth: atmosphere , hydrosphere , biosphere , and lithosphere.
The carbon cycle takes many forms. It is exchanged through photosynthesis, decomposition, respiration, and human activity. Carbon that is absorbed by soil as an organism decomposes, for example, may be recycled as a plant releases carbon-based nutrients into the biosphere through photosynthesis. Under the right conditions, the decomposing organism may become peat , coal, or petroleum before being extract ed through natural or human activity.
Between periods of exchange, carbon is sequestered, or stored. The carbon in fossil fuels has been sequestered for millions of years. When fossil fuels are extracted and burned for energy, their sequestered carbon is released into the atmosphere. Fossil fuels do not re-absorb carbon. In contrast to fossil fuels, biomass comes from recently living organisms. The carbon in biomass can continue to be exchanged in the carbon cycle.
In order to effectively allow Earth to continue the carbon cycle process, however, biomass materials such as plants and forests have to be sustainably farmed. It takes decades for trees and plants such as switchgrass to re-absorb and sequester carbon. Uprooting or disturbing the soil can be extremely disruptive to the process. A steady and varied supply of trees, crops, and other plants is vital for maintaining a healthy environment.
Algal Fuel Algae is a unique organism that has enormous potential as a source of biomass energy. Algae, whose most familiar form is seaweed , produces energy through photosynthesis at a much quicker rate than any other biofuel feedstock—up to 30 times faster than food crops! Algae can be grown in ocean water, so it does not deplete freshwater resources. It also does not require soil, and therefore does not reduce arable land that could potentially grow food crops.
Although algae releases carbon dioxide when it is burned, it can be farmed and replenished as a living organism. As it is replenished, it releases oxygen, and absorbs pollutant s and carbon emissions. Algae takes up much less space than other biofuel crops.
Department of Energy estimates that it would only take approximately 38, square kilometers 15, square miles, an area less than half the size of the U.
Algae contains oils that can be converted to a biofuel. At the Aquaflow Bionomic Corporation in New Zealand, for example, algae is processed with heat and pressure. Algae is an excellent filter that absorbs carbon emissions. Bioenergy Ventures, a Scottish firm, has developed a system in which carbon emissions from a whiskey distillery are funneled to an algae pool. The algae flourishes with the additional carbon dioxide. When the algae die after about a week they are collected, and their lipid s oils are converted into biofuel or fish food.
Algae has enormous potential as an alternative energy source. However, processing it into usable forms is expensive. The cost will likely come down, but it is currently out of reach for most developing economies. People and Biomass Advantages Biomass is a clean, renewable energy source. Its initial energy comes from the sun, and plants or algae biomass can regrow in a relatively short amount of time. Trees, crops, and municipal solid waste are consistently available and can be managed sustainably.
If trees and crops are sustainably farmed, they can offset carbon emissions when they absorb carbon dioxide through respiration. In some bioenergy processes, the amount of carbon that is re-absorbed even exceeds the carbon emissions that are released during fuel processing or usage. Many biomass feedstocks, such as switchgrass, can be harvested on marginal land s or pastures, where they do not compete with food crops.
Unlike other renewable energy sources, such as wind or solar, biomass energy is stored within the organism, and can be harvested when it is needed. Disadvantages If biomass feedstocks are not replenished as quickly as they are used, they can become non-renewable. A forest, for instance, can take hundreds of years to re-establish itself. This is still a much, much shorter time period than a fossil fuel such as peat.
It can take years for just a meter 3 feet of peat to replenish itself. Most biomass requires arable land to develop. This means that land used for biofuel crops such as corn and soybeans are unavailable to grow food or provide natural habitats. Most biomass plants require fossil fuels to be economically efficient.
An enormous plant under construction near Port Talbot, Wales, for instance, will require fossil fuels imported from North America, offsetting some of the sustainability of the enterprise.
Scientists and engineers estimate that it is not economically efficient to transport biomass more than kilometers miles from where it is processed. Burning biomass releases carbon monoxide, carbon dioxide, nitrogen oxides, and other pollutants and particulates.
If these pollutants are not captured and recycled, burning biomass can create smog and even exceed the number of pollutants released by fossil fuels. Zutshi, S. Beaugez, M. Hendrikx, S. Heydt, M. Oeltjenbruns, A. Munoraharjo, F. Choudhury, G. Upton, O. Siudak, M. Gunther, R. Balancing Biomass The Union of Concerned Scientists helped develop A Balanced Definition of Renewable Biomass , which are practical and effective sustainability provisions that can provide a measure of assurance that woody biomass harvests will be sustainable.
The Joseph C. Sterman stresses that he is not advocating a return to burning coal. But Sterman argues that the opposite is actually true. The faster a forest is growing, the greater the future carbon storage is lost. It had been assumed that young trees mop up more carbon than old ones because they are fast-growing, but recent studies have revealed that ancient woodland growing in temperate regions takes up more CO 2 than young plantations.
This is because in some cases, growth accelerates with age and CO 2 absorption is approximately equivalent to biomass Nature But even if old trees are continuing to draw down CO 2 , what happens when a tree dies? Current carbon accounting assumes that all the carbon from dead wood is released back into the atmosphere again. Removing forest thinnings and burning them to produce energy is therefore viewed as better than leaving them on the forest floor to rot.
However, Sterman argues that this fails to take account of the entire system. In she used a model to calculate the net emissions impact — the difference between combustion emissions and decomposition emissions, divided by the combustion emissions — when forestry residues are burned for energy.
Booth was so concerned by what she found that she co-ordinated a lawsuit against the EU in March eubiomasscase. Currently she is waiting to hear if the court will accept the case. Currently around two-thirds of renewable energy in Denmark is provided by biomass, and it plays a vital role in keeping district heating systems running, particularly when the wind fails to blow.
In Scott Bentsen in Copenhagen calculated the carbon debt and payback time for a combined heat and power generation plant in Denmark. His results suggested that the carbon debt was paid back after just one year, and that after 12 years greenhouse-gas emissions were halved relative to continued coal combustion Energies 11 These numbers are vastly different to the plus years of payback time estimated by Sterman, so what makes Danish biomass energy different to the kind of process seen at Drax?
Calculating the carbon payback time for a specific supply chain can play a significant role in helping to fine-tune management practices and minimize emissions. Scott Bentsen explains that there are a number of key differences. In this Danish study, the plant burns wood chips rather than pellets, which reduces processing energy.
Furthermore, the wood is sourced locally from mixed forests in a cold temperate region, which have different growing characteristics from trees in a warm temperate region. And the energy it produces is maximized, producing both heat for local houses and electricity.
He believes that calculating the carbon payback time for a specific supply chain can play a significant role in helping to fine-tune the management practices and minimize emissions from individual biomass energy plants Renewable and Sustainable Energy Reviews 73 Sterman accepts that there are arguments for using timber industry waste as a biofuel.
Energy form: UK biomass plants use wood pellets of leftover material from managed forests. Instead, McQueen Mason is investigating ways of making gas and liquid fuel from biomass, by getting micro-organisms and bacteria to munch their way through woody material, and collecting the resulting gas and liquid produced as the bugs digest the biomass. Pilot plants using sugar cane residue are already proving promising and could provide a solution to the vexing problem of de-carbonizing the petrochemical industry.
But even if living trees can claw back these carbon-dioxide emissions relatively quickly, there is a danger in front-loading our emissions in this way. And even if it remains as forest, wild fire, insect damage, disease and other ecological stresses including climate change itself may limit or prevent regrowth, so that the carbon debt incurred by biomass energy is never repaid.
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