Bio-energy with carbon capture and storage
The carbon in the trees or crops used for the biomass comes from the greenhouse gas carbon dioxide (CO2), which they extract from the atmosphere whilst growing. As of 2019 most BECCS stores some of the carbon and leaves the rest with the bioenergy in the form of a biofuel, such as ethanol. By providing aviation biofuel and reducing the environmental impact of aviation BECCS may help with climate change mitigation. Alternatively the bioenergy could be used in the form of electricity and a larger proportion of the CO2 stored permanently by injection into geological formations.
As of 2019 five facilities around the world are actively using BECCS technologies and are capturing approximately 1.5 million tonnes per year (Mtpa) of CO2 The IPCC Fifth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC), implies a range of negative emissions from BECCS of 0 to 22 gigatonnes.
There are other non-BECCS forms of carbon dioxide removal and storage including afforestation, biochar, carbon dioxide air capture and biomass burial and enhanced weathering. Pyrogenic carbon capture and storage (PyCCS) or biochar is superior in fixing carbon for a longer time. Afforestation is still multiple times cheaper than BECCS.
Bio-energy is derived from biomass which is a renewable energy source and serves as a carbon sink during its growth. During industrial processes, the biomass combusted or processed re-releases the CO2 into the atmosphere. The process thus results in a net zero emission of CO2, though this may be positively or negatively altered depending on the carbon emissions associated with biomass growth, transport and processing, see below under environmental considerations. Carbon capture and storage (CCS) technology serves to intercept the release of CO2 into the atmosphere and redirect it into geological storage locations. CO2 with a biomass origin is not only released from biomass fuelled power plants, but also during the production of pulp used to make paper and in the production of biofuels such as biogas and bioethanol. The BECCS technology can also be employed on such industrial processes.
It is argued that through the BECCS technology, carbon dioxide is trapped in geologic formations for very long periods of time, whereas for example a tree only stores its carbon during its lifetime. In its report on the CCS technology, IPCC projects that more than 99% of carbon dioxide which is stored through geologic sequestration is likely to stay in place for more than 1000 years. While other types of carbon sinks such as the ocean, trees and soil may involve the risk of adverse feedback loops at increased temperatures, BECCS technology is likely to provide a better permanence by storing CO2 in geological formations.
The amount of CO2 that has been released to date is believed to be too much to be able to be absorbed by conventional sinks such as trees and soil in order to reach low emission targets. In addition to the presently accumulated emissions, there will be significant additional emissions during this century, even in the most ambitious low-emission scenarios. BECCS has therefore been suggested as a technology to reverse the emission trend and create a global system of net negative emissions. This implies that the emissions would not only be zero, but negative, so that not only the emissions, but the absolute amount of CO2 in the atmosphere would be reduced.
|Ethanol production||Fermentation of biomass such as sugarcane, wheat or corn releases CO2 as a by-product||Industry|
|Pulp and paper mills||
|Biogas production||In the biogas upgrading process, CO2 is separated from the methane to produce a higher quality gas||Industry|
|Electrical power plants||Combustion of biomass or biofuel in steam or gas powered generators releases CO2 as a by-product||Energy|
|Heat power plants||Combustion of biofuel for heat generation releases CO2 as a by-product. Usually used for district heating||Energy|
Research by Rau et al. (2018) estimates that electrogeochemical methods of combining saline water electrolysis with mineral weathering powered by non-fossil fuel-derived electricity could, on average, increase both energy generation and CO2 removal by more than 50 times relative to BECCS, at equivalent or even lower cost, but further research is needed to develop such methods.
The main technology for CO2 capture from biotic sources generally employs the same technology as carbon dioxide capture from conventional fossil fuel sources. Broadly, three different types of technologies exist: post-combustion, pre-combustion, and oxy-fuel combustion.
Oxy‐fuel combustion has been a common process in the glass, cement and steel industries. It is also a promising technological approach for CCS. In oxy‐fuel combustion, the main difference from conventional air firing is that the fuel is burned in a mixture of O2 and recycled flue gas. The O2 is produced by an air separation unit (ASU), which removes the atmospheric N2 from the oxidizer stream. By removing the N2 upstream of the process, a flue gas with a high concentration of CO2 and water vapor is produced, which eliminates the need for a post‐combustion capture plant. The water vapor can be removed by condensation, leaving a product stream of relatively high‐purity CO2 which, after subsequent purification and dehydration, can be pumped to a geological storage site.
The key challenges of BECCS implementation using oxy-combustion method is associated with combustion process. For the high volatile content biomass, the mill temperature has to be maintain at low temperature to prevent the risk of fire and explosion. In addition, the flame temperature is lower. Therefore, the concentration of oxygen needs to be increased up to 27-30%.
Pre-combustion carbon capture refers to the process of capturing CO2 before the energy generations. It is often composed of five operating stations: oxygen generation, syngas generation, CO2 separation, CO2 compression, and power generation. Basically, the fuel will first go through a gasification process by reacting with oxygen to form a stream of CO and H2, which is syngas. The products will then go through a water-gas shift reactor to form CO2 and H2. The CO2 that is produced will then be captured, and the H2, which is a clean source, will be used for combustion to generate energy. The process of gasification combined with syngas production is called Integrated Gasification Combined Cycle (IGCC). Normally, it would require an Air Separation Unit (ASU) to serve as the oxygen source. However, research proves that with the same flue gas, oxygen gasification has little advantage over air gasification, and they both have a similar thermal efficiency of roughly 70% using coal as the fuel source. Thus, the use of ASU is not really necessary in pre-combustion.
Biomass is considered "sulfur-free" as a fuel for the pre-combustion capture. However, there are other trace elements in biomass combustion such as K and Na that could accumulate in the system and finally cause the degradation of the mechanical parts. Thus, further developments of the separation techniques for those trace elements are needed. And also, after the gasification process, CO2 takes up to 13% - 15.3% by mass in the syngas stream for biomass sources, while it is only 1.7% - 4.4% for coal. This limit the conversion of CO to CO2 in the water gas shift, and the production rate for H2 will decrease accordingly. However, the thermal efficiency of the pre-combustion capture using biomass resembles that of coal which is around 62% - 100%. Besides, some researches also proved that instead of using a biomass/water slurry fuel feed, using a dry system is more thermally efficient and also more practical for biomass.
In addition to pre-combustion and oxy-fuel combustion technologies, post-combustion is a promising technology which can be used to extract CO2 emission from biomass fuel resources. During the process, CO2 is separated from the other gases in the flue gas stream after the biomass fuel is burnt and undergo separation process. Because it has the ability to be retrofitted to some existing power plants such as steam boilers or other newly built power stations, post-combustion technology is considered as a better option than pre-combustion technology. According to the fact sheets U.S. CONSUMPTION OF BIO-ENERGY WITH CARBON CAPTURE AND STORAGE released in March 2018, the efficiency of post-combustion technology is expected to be 95% while pre-combustion and oxy-combustion capture CO2 at an efficient rate of 85% and 87.5% respectively.
Development for current post-combustion technologies has not been entirely done due to several problems. One of the major concerns using this technology to capture carbon dioxide is the parasitic energy consumption. If the capacity of the unit is designed to be small, the heat loss to the surrounding is great enough to cause to many negative consequences. Another challenge of post-combustion carbon capture is how to deal with the mixture's components in the flue gases from initial biomass materials after combustion. The mixture consists of a high amount of alkali metals, halogens, acidic elements, and transition metals which might have negative impacts on the efficiency of the process. Thus, the choice of specific solvents and how to manage the solvent process should be carefully designed and operated.
Biomass sources used in BECCS include agricultural residues & waste, forestry residue & waste, industrial & municipal wastes, and energy crops specifically grown for use as fuel. Current BECCS projects capture CO2 from ethanol bio-refinery plants and municipal solid waste (MSW) recycling center.
Up to date, there have been 23 BECCS projects around the world, with the majority in North America and Europe. Today, there are only 6 projects in operation, capturing CO2 from ethanol bio-refinery plants and MSW recycling centers.
5 BECSS projects have been canceled due to the difficulty of obtaining the permission as well as their economic viability. The canceled projects include: the White Rose CCS Project at Selby, UK can capture about 2 MtCO2/year from Drax power station and store CO2 at the Bunter Sandstone. The Rufiji Cluster project at Tanzania plan to capture around 5.0-7.0 MtCO2/year and store CO2 at the Saline Aquifer. The Greenville project at Ohio, USA has capacity of capturing 1 MtCO2/year. The Wallula project was planned to capture 0.75 MtCO2/year at Washington, USA. Finally, the CO2 Sink project at Ketzin, Germany.
At Ethanol plants
Illinois Industrial Carbon Capture and Storage (IL-CCS) is one of the milestones, being the first industrial-scaled BECCS project, in the early 21st century. Located in Decatur, Illinois, USA, IL-CCS captures CO2 from Archer Daniels Midland (ADM) ethanol plant. The captured CO2 is then injected under the deep saline formation at Mount Simon Sandstone. IL-CCS consists of 2 phases. The first being a pilot project which was implemented from 11/2011 to 11/2014. Phase 1 has a capital cost of around 84 million US dollars. Over the 3-year period, the technology successfully captured and sequestered 1million tonne of CO2 from the ADM plant to the aquifer. No leaking of CO2 from the injection zone was found during this period. The project is still being monitored for future reference. The success of phase 1 motivated the deployment of phase 2, bringing IL-CCS (and BECCS) to industrial scale. Phase 2 has been in operation since 11/2017 and also use the same injection zone at Mount Simon Sandstone as phase 1. The capital cost for second phase is about 208 million US dollars including 141 million US dollar fund from the Department of Energy. Phase 2 has capturing capacity about 3 time larger than the pilot project (phase 1). Annually, IL-CCS can capture mourned 1 million tonne of CO2. With the largest of capturing capacity, IL-CCS is currently the largest BECCS project in the world.
In addition to the IL-CCS project, there are about three more projects that capture CO2 from the ethanol plant at smaller scales. For example, Arkalon at Kansas, USA can capture 0.18-0.29 MtCO2/yr, OCAP at Netherlands can capture about 0.1-0.3 MtCO2/yr, and Husky Energy at Canada can capture 0.09-0.1 MtCO2/yr.
At MSW recycling centers
Beside capturing CO2 from the ethanol plants, currently, there are 2 models in Europe are designed to capture CO2 from the processing of Municipal Solid Waste. The Klemetsrud Plant at Oslo, Norway use biogenic municipal solid waste to generate 175 GWh and capture 315 Ktonne of CO2 each year. It uses absorption technology with Aker Solution Advanced Amine solvent as a CO2 capture unit. Similarly, the ARV Duiven at Netherlands uses the same technology, but it captures less CO2 than the previous model. ARV Duiven generates around 126 GWh and only capture 50 Ktonne of CO2 each year.
Techno-economics of BECCS and the TESBiC Project
The largest and most detailed techno-economic assessment of BECCS was carried out by cmcl innovations and the TESBiC group (Techno-Economic Study of Biomass to CCS) in 2012. This project recommended the most promising set of biomass fueled power generation technologies coupled with carbon capture and storage (CCS). The project outcomes lead to a detailed “biomass CCS roadmap” for the U.K..
Some of the environmental considerations and other concerns about the widespread implementation of BECCS are similar to those of CCS. However, much of the critique towards CCS is that it may strengthen the dependency on depletable fossil fuels and environmentally invasive coal mining. This is not the case with BECCS, as it relies on renewable biomass. There are however other considerations which involve BECCS and these concerns are related to the possible increased use of biofuels. Biomass production is subject to a range of sustainability constraints, such as: scarcity of arable land and fresh water, loss of biodiversity, competition with food production, deforestation and scarcity of phosphorus. It is important to make sure that biomass is used in a way that maximizes both energy and climate benefits. There has been criticism to some suggested BECCS deployment scenarios, where there would be a very heavy reliance on increased biomass input.
Large areas of land would be required to operate BECCS on an industrial scale. To remove 10 billion tons of CO2, upwards of 300 million hectares of land area (larger than India) would be required. As a result, BECCS risks using land that could be better suited to agriculture and food production, especially in developing countries.
These systems may have other negative side effects. There is however presently no need to expand the use of biofuels in energy or industry applications to allow for BECCS deployment. There is already today considerable emissions from point sources of biomass derived CO2, which could be utilized for BECCS. Though, in possible future bio-energy system upscaling scenarios, this may be an important consideration.
Upscaling BECCS would require a sustainable supply of biomass - one that does not challenge our land, water, and food security. Using bio-energy crops as feedstock will not only cause sustainability concerns but also require the use of more fertilizer leading to soil contamination and water pollution. Moreover, crop yield is generally subjected to climate condition, i.e. the supply of this bio-feedstock can be hard to control. Bioenergy sector must also expand to meet the supply level of biomass. Expanding bioenergy would require technical and economic development accordingly.
Just as other carbon capture and storage technologies, one of the challenges of applying BECCS technology is to find suitable geographic locations to build combustion plant and to sequester captured CO2. If biomass sources are not close by the combustion unit, transporting biomass emits CO2 offsetting the amount of CO2 captured by BECCS. BECCS also face technical concerns about efficiency of burning biomass. While each type of biomass has a different heating value, biomass in general is a low-quality fuel. Thermal conversion of biomass has a typical efficiency of 20-27%. Coal-fired plant has an efficiency of about 37% for comparison.
BECCS also faces a question whether the process is actually energy positive. Low energy conversion efficiency, energy-intensive biomass supply, combined with the energy required to power the CO2 capture and storage unit impose energy penalty on the system. This might lead to a low power generation efficiency.
Alternative biomass sources
Globally, 14 Gt of forestry residue and 4.4 Gt residues from crop production (mainly barley, wheat, corn, sugarcane and rice) are generated every year. This is a significant amount of biomass which can be combusted to generate 26 EJ/year and achieve a 2.8 Gt of negative CO2emission through BECCS. Utilizing residues for carbon capture will provide social and economic benefits to rural communities. Using waste from crops and forestry is a way to avoid the ecological and social challenges of BECCS.
Municipal solid waste(MSW) is one of the newly developed sources of biomass. Two current BECCS plants are using MSW as feedstocks. Waste collected from daily life is recycled via incineration waste treatment process. Waste goes through high temperature thermal treatment and the heat generated from combusting organic part of waste is used to generate electricity. CO2emitted from this process is captured through absorption using MEA. For every 1 kg of waste combusted, 0.7 kg of negative CO2emission is achieved. Utilizing solid waste also have other environmental benefits.
Co-firing coal with biomass
There are currently 200 cofiring plants in the world, including 40 in the US. Studies showed that by mixing coal with biomass, we could reduce the amount of CO2 emitted. The concentration of CO2 in the flue gas is an important key to determine the efficiency of CO2 capture technology. The concentration of CO2 in the flue gas from the co-firing power plant is roughly the same as coal plant, about 15% . This means that we can reduce our reliance on fossil fuel.
Even though co-firing will have some energy penalty, it still offers higher net efficiency than the biomass combustion plants. Co-firing biomass with coal will result more energy production with less input material. Currently, the modern 500 MW coal power plant can take up to 15% biomass without changing the component of the steam boiler. This promising potential allows co-firing power plant become more favorable than dedicated bio-electricity.
It is estimated that by replacing 25% of coal with biomass at existing power plant in China and the U.S, we can reduce emission by 1Gt per year. The amount of negative CO2 emitted depends on the composition of coal and biomass. 10% biomass can reduce 0.5 Gt CO2 per year and with 16% biomass can achieve zero emission. Direct-cofiring (20% biomass) give us negative emission of -26 kg CO2/MWh (from 93 kg CO2/MWh).
Biomass cofiring with coal has efficiency near those of coal combustion. Cofiring can be easily applied to existing coal-fired power plant at low cost. The implementation of co-firing power plant on the global scale is still a challenge. The biomass resources have to meet strictly the sustainability criteria and the co-firing project would need the support in term of economic and policy from the governments.
Even though co-firing plant may be an immediate contribution to solving the global warming and climate change issues, co-firing still has some challenges that need to consider. Due to the moisture content of biomass, it will affect the calorific value of the combustor. In addition, high volatile biomass would highly influence the reaction rate and the temperature of the reactor; especially, it may lead to the explosion of furnace.
Based on the current Kyoto Protocol agreement, carbon capture and storage projects are not applicable as an emission reduction tool to be used for the Clean Development Mechanism (CDM) or for Joint Implementation (JI) projects. Recognising CCS technologies as an emission reduction tool is vital for the implementation of such plants as there is no other financial motivation for the implementation of such systems. There has been growing support to have fossil CCS and BECCS included in the protocol. Accounting studies on how this can be implemented, including BECCS, have also been done.
There are some future policies that give incentives to use bioenergy such as Renewable Energy Directive (RED) and Fuel Quality Directive (FQD), which require 20% of total energy consumption to be based on biomass, bioliquids and biogas by 2020.
In 2018 the Committee on Climate Change recommended that aviation biofuels should provide up to 10% of total aviation fuel demand by 2050, and that all aviation biofuels should be produced with CCS as soon as the technology is available.
In February, 2018, US congress significantly increased and extended the section 45Q tax credit for sequestration of carbon oxides. This has been a top priority of carbon capture and sequestration (CCS) supporters for several years. It increased $25.70 to $50 tax credit per tonnes of CO2 for secure geological storage and $15.30 to $35 tax credit per tonne of CO2 used in enhanced oil recovery.
In the 2014 AMPERE modeling project, based on 8 different integrated assessment models, the future deployment of BECCS is predicted to help meet the US emissions budget for the future 2 °C scenario in the Paris Agreement. In the middle of the 21st century, the scale of the BECCS deployment ranges from 0 Mt to 1100 Mt CO2per year. And by the end of the century, the deployment ranges from 720 Mt to 7500 Mt CO2per year, while most of the models predict the scale to be within 1000 Mt to 3000 Mt by 2100. A research group from Stanford University has modeled the technical potential of BECCS in the US in the year 2020. According to their calculations, about one-third of the potential biomass production in total is located close enough to the geological storage site, which results in a CO2capturing capability of 110 Mt - 120 Mt.
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