Bioenergy with Carbon Capture and Storage (BECCS) is a climate technology designed to actively remove carbon dioxide (CO2) from the atmosphere. This process integrates energy generation from biological sources with the capture and permanent storage of CO2 emissions. BECCS offers a pathway to produce energy while achieving a net reduction in atmospheric carbon.
The Bioenergy Component
Bioenergy in BECCS originates from biomass, encompassing organic materials like plants, agricultural residues, and forestry waste. These sources naturally absorb CO2 from the atmosphere during growth through photosynthesis.
Once harvested, biomass converts into energy through various methods. Combustion is a common approach, where biomass is burned to produce heat and steam, driving turbines to generate electricity. Other methods include fermentation for biofuels like ethanol or biogas, and pyrolysis, which transforms biomass into bio-oil and syngas.
During these conversion processes, carbon stored in the biomass releases as CO2. In a typical bioenergy system without carbon capture, this CO2 would re-enter the atmosphere. BECCS captures this released CO2 to prevent its return to the atmosphere.
The Carbon Capture and Storage Component
Carbon capture and storage (CCS) involves separating CO2 from emissions generated by industrial processes and power plants. This separation occurs through methods like post-combustion and pre-combustion capture. Post-combustion capture, often in power plants, removes CO2 from flue gases after fuel combustion, typically using chemical solvents.
Pre-combustion capture processes fuel before combustion, converting it into a mixture of hydrogen and CO2, from which the CO2 is then separated. Once captured, CO2 is compressed into a liquid-like state for transportation, often via pipelines, to geological storage sites.
Storage involves injecting captured CO2 deep underground into specific geological formations. These include porous rock layers like saline aquifers or depleted oil and gas reservoirs. CO2 is injected below 800 meters, where pressure and temperature ensure it remains in a dense, supercritical fluid state, preventing escape. Geological sequestration aims for permanent storage.
Achieving Negative Emissions with BECCS
BECCS achieves net negative emissions by first having plants absorb CO2 from the atmosphere as they grow. When this biomass generates energy, the released CO2 is captured and prevented from returning to the atmosphere. This process permanently stores the carbon initially removed from the atmosphere.
This mechanism distinguishes BECCS from conventional carbon capture technologies. Traditional carbon capture focuses on preventing new CO2 emissions from entering the atmosphere, such as from fossil fuel power plants. BECCS, in contrast, actively extracts atmospheric CO2, making it one of the few technologies capable of carbon dioxide removal.
BECCS has the potential to remove CO2 from the atmosphere, with estimates for negative emissions ranging from zero to 22 gigatonnes per year. This capacity makes BECCS a valuable tool in climate change mitigation strategies, offering a pathway to reduce future emissions and address historical CO2 accumulations. It also provides a low-carbon energy source.
Key Considerations for BECCS Deployment
Deploying BECCS on a larger scale requires careful consideration of several practical factors, particularly sustainable biomass sourcing. Biomass cultivation for energy must avoid competition with land needed for food crops to prevent impacts on global food security. This involves selecting land that does not displace agricultural production or lead to deforestation.
Land use impacts extend to biodiversity and local ecosystems. Large-scale biomass plantations could alter natural habitats, potentially leading to biodiversity loss if not managed responsibly. Water requirements for growing bioenergy crops also demand careful assessment to prevent undue stress on local water resources.
Geological suitability of storage sites for captured CO2 is another consideration. Effective storage relies on identifying formations with sufficient porosity and permeability to accept large CO2 volumes, along with impermeable caprock layers to prevent leakage. The long-term stability of these storage sites is important to ensure the CO2 remains sequestered.