Carbon Negative Energy from Biomass Energy Facilities
In 2014, over 180 nations set a goal to limit the increase of global temperatures to 1.5 °C, compared to pre-industrial levels. To achieve this goal, the Intergovernmental Panel on Climate Change called for the widespread deployment of large-scale “carbon-negative” solutions by 2040. One carbon-negative technology that has recently gained significant attention is biomass energy production.
What is Carbon Negative Energy?
When a person or organization produces a carbon footprint that is less than zero, they are said to be carbon negative. Essentially, this means that their actions and functions have the net effect of removing carbon dioxide from the atmosphere instead of adding more.
Biomass energy facilities use the combustion of biomass wastes to generate heat and high-pressure steam to drive turbines and produce electricity. Most biomass power plants can use wood waste biomass from a variety of sources, providing power and a vital regional waste disposal resource.
Carbon Negative Energy from Biomass Energy Facilities
While greenhouse gas reductions vary among plants and locations, biomass energy facilities are generally considered carbon-neutral according to the Office of Energy Efficiency & Renewable Energy. Some biomass power is very carbon-negative due to reductions in landfill waste and reduced methane gas emissions. Even with landfill gas recovery, the diversion of biomass waste from a landfill can significantly reduce the emission of greenhouse gases. A facility’s carbon footprint can be further reduced by using biodiesel in trucks and equipment.
Dry wood is a mixture of cellulose, hemicellulose, and lignin. The ash-free chemical composition of dry wood is usually represented chemically as CH2O. Therefore, CH2O measurements can be used to approximate the amount of methane and carbon dioxide released from a landfill as woody material undergoes anaerobic decomposition. Anaerobic decomposition results from moisture, lack of air, and anaerobic and methane-forming bacteria. These are the same conditions found in swamps and marshes where methane, or marsh gas, is generated.
The decomposition process varies, but usually, wood waste deposited in a construction and demolition landfill will generate landfill gas slower than in a municipal solid waste landfill. But usually, there is no landfill gas recovery system at a construction and demolition landfill. Once water accumulates and oxygen is depleted, anaerobic decomposition will produce six to seven tons of carbon dioxide emissions per biomass MW/hour. Waste paper is lignin-free wood and decomposes similarly but more rapidly than woody material.
On average, one ton of dry, ash-free wood left to decompose in a landfill will produce 0.27 tons of methane and 0.73 tons of carbon dioxide. However, the average 25 MW biomass power plant uses just over one dry ton of wood per net MW/hour. Therefore, a biomass energy facility diverts biomass waste from a landfill, where it would produce over a quarter ton of methane and nearly three-quarters of a ton of carbon dioxide.
Methane is nearly 21 times as strong a greenhouse gas as carbon dioxide. So diverting one MW/hour of biomass power avoids releasing about 6 tons of CO2 equivalent. Using only landfill diverted biomass, the average 25 MW biomass power plant reduces carbon dioxide emissions by about 1.2 MM tons per year.
However, most landfills practice landfill gas recovery, and when calculating emissions, the EPA model uses a default value of 50% landfill gas recovery. Still, industry experts in southern California, the birthplace of landfill gas recovery technology, estimate that landfill gas recovery is approximately 65%. Therefore, the net methane emissions into the atmosphere are about 0.1 tons of methane emissions avoided per biomass MW/hour or 2.1 tons of carbon dioxide equivalent.
The Role of Biomass Energy Facilities in the Future
Energy from biomass is a significant portion of the global energy mix. The industry’s rapidly advancing technology is causing it to play an ever-increasing role in global energy production. In addition, bioenergy already makes a substantial contribution to reducing carbon emissions, and based on current trends and policies, the industry is likely to continue growing.
In 2020, California biomass energy facilities produced 5,628 gigawatt-hours of electricity, or about 2.95% of the state’s generation portfolio. Currently, the state has 87 biomass plants operating with an installed capacity of approximately 1,259 megawatts. With the increasing interest in and need for renewable and sustainable energy solutions, biomass energy facilities offer an ideal solution that combines recycling with power generation.
Carbon negative energy from biomass power plants can be obtained from a wide range of waste biomass fuel sources. Along with wood waste diverted from municipal landfills to avoid methane generation, biomass energy plants can also use:
- Forestry and sawmill industry byproducts
- Wood product manufacturing waste
- Non-recyclable waste paper
- Recycled paper mill wastes and sludges
- Clean wood from construction and demolition sites
- Tree trimmings from utility right-of-way clearance
- Urban tree removals
- Process waste from biodiesel, cellulosic fuels, and chemical production
- Straw, husks, and other agricultural waste from grain crops or grain processing
Biomass can be a complicated subject, but biomass energy production offers many benefits that make it suitable as a sustainable alternative to fossil fuels. Unlike fossil fuels which can be depleted, biomass is abundantly available around the globe. Considering that biomass can be sustainably managed and is deemed carbon-neutral, it is a viable option as a primary source of renewable energy that can help lessen our dependence on fossil fuels.
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