Comparison of Long-Term Bioenergy with Carbon Capture and Storage to Reference Power Generation Technologies Using CO 2 Avoidance Cost in the U.S.

: Bioenergy with carbon capture and storage (BECCS) can sequester atmospheric CO 2 , while producing electricity. The CO 2 avoidance cost (CAC) is used to calculate the marginal cost of avoided CO 2 emissions for BECCS as compared to other established energy technologies. A comparative analysis using four different reference-case power plants for CAC calculations is performed here to evaluate the CO 2 avoidance cost of BECCS implementation. Results from this work demonstrate that BECCS can generate electricity at costs competitive with other neutral emissions technologies, while simultaneously removing CO 2 from the atmosphere. Approximately 73% of current coal power plants are approaching retirement by the year 2035 in the U.S. After considering CO 2 sequestered from the atmosphere and coal power plant CO 2 emissions displaced by BECCS, CO 2 emissions can be reduced by 1.4 billion tonnes per year in the U.S. alone at a cost of $88 to $116 per tonne of CO 2 removed from the atmosphere, for 10% to 90% of available biomass used, respectively. CAC calculations in this paper indicate that BECCS can help the U.S. and other countries transition to a decarbonized electricity grid, as simulations presented in this paper predict that BECCS power plants operate at lower CACs than coal plants with CCS. comparisons 1000-MW PCC, co-ﬁred with corn stover power plant with CCS. A PCC power plant without carbon capture and storage is used as the reference-case plant for CAC calculations.


Introduction
Currently, almost all forms of anthropogenic activity contribute to greenhouse gas (GHG) emissions [1,2]. According to the U.S. Environmental Protection Agency (EPA), the largest source of GHG emissions from human activities in the U.S. is the burning of fossil fuels for energy including electricity, heat, and transportation [3,4]. The U.S. Energy Information Agency (EIA) estimates that the U.S. emitted roughly 5.1 billion tonnes of energy-related CO 2 in 2017, while the global energy-related CO 2 emissions totaled roughly 32.5 billion tonnes [4]. Transportation was estimated to be the largest share of CO 2 emissions in the U.S., with a share of roughly 28.2% in 2018 [4]. These emissions emerge from the burning of fossil fuels to power transportation vehicles, such as automobiles, airplanes, and ships. Additionally, most of the fuel used for transport is petroleum based. Electricity production for homes is the second largest contributor to CO 2 emissions, where around 63% of electricity production comes from coal and natural gas combustion [4]. Industry in the U.S. accounts for 22% of CO 2 emissions, primarily from energy consumption and emissions from chemical reactions. The cement and steel industries for example generated approximately 41 and 62 million tonnes of CO 2 in 2019, respectively [5,6]. Agriculture accounts for roughly 10% of annual CO 2 emissions, namely from livestock, agricultural soils, and rice production [4]. from 2060 onwards. For the 1.5 • C target without BECCS, they approximated the cost to around $3220/tCO 2 by 2100. They suggest that the negative emissions produced by BECCS relieves pressure from the emissions cap set by climate policies [19].
This paper seeks to build on the knowledge produced by the researchers by trying to address some of the potential problems they have identified with BECCS in their work, namely, using the CO 2 avoidance cost to determine the cost of BECCS while considering various factors for land and biomass availability. Protected and sensitive lands are excluded from potential BECCS sites, and biomass is used only after sustainability goals and food, animal feed, fiber, and export markets are met without supply disruption.
The paper builds on previous work published by Langholtz et al. (2020) and seeks to further evaluate the costs of BECCS through CO 2 accounting equations, CO 2 avoidance costs, and comparisons with the electricity generation costs of neutral emissions technologies and co-fired biomass power plants [11]. We seek to evaluate the cost of BECCS implementation by using different reference cases for CO 2 avoidance cost (CAC) calculations. The flow of information used in this paper can be found in Figure 1.
$160/tCO2 in 2040. Without BECCS, however, Fajardy et al. estimate this price to be approximately $2340 by the year 2100. For the 1.5 °C target with BECCS, they estimate the cost of CO2 removal to be approximately $400/tCO2 in 2040, but project a decreased cost of $250-$260/tCO2 from 2060 onwards. For the 1.5 °C target without BECCS, they approximated the cost to around $3220/tCO2 by 2100. They suggest that the negative emissions produced by BECCS relieves pressure from the emissions cap set by climate policies [19].
This paper seeks to build on the knowledge produced by the researchers by trying to address some of the potential problems they have identified with BECCS in their work, namely, using the CO2 avoidance cost to determine the cost of BECCS while considering various factors for land and biomass availability. Protected and sensitive lands are excluded from potential BECCS sites, and biomass is used only after sustainability goals and food, animal feed, fiber, and export markets are met without supply disruption.
The paper builds on previous work published by Langholtz et al. (2020) and seeks to further evaluate the costs of BECCS through CO2 accounting equations, CO2 avoidance costs, and comparisons with the electricity generation costs of neutral emissions technologies and co-fired biomass power plants [11]. We seek to evaluate the cost of BECCS implementation by using different reference cases for CO₂ avoidance cost (CAC) calculations. The flow of information used in this paper can be found in Figure 1.

Power Plant Siting (OR-SAGE)
The Oak Ridge Sitting Analysis for power Generation Expansion (OR-SAGE) was used to determine potential power plant sites based on proximity to saline aquifers for CO 2 storage [20]. This model, developed by Oak Ridge National Laboratory, divides the continental U.S. into 700 million cells (with an area of 2.5 acres each) and determines the proximity of each cell to critical parameters. Cells that are too far away from saline aquifers or that are within hazardous or protected areas are excluded. The OR-SAGE model considers factors such as population growth, energy demand, water availability, and geological formations and hazards when suggesting potential sites for BECCS powerplants. Figure A1 in Appendix D illustrates the gridded map of potential BECCS sites in the U.S. when exclusionary radii of 80 km and 121 km are used. This grid of the U.S. is then superimposed with potential feedstock harvesting locations provided by the Billion-Ton Report and the Biomass Logistics Information and Transport (BILT) model. A more detailed table listing the parameters considered by the OR-SAGE model can be found in Table A9 in Appendix D.

Feedstock Composition
The proximate and ultimate analyses of potential feedstock predicted by the Billion-Ton Report were determined using Phyllis2, a biomass composition database maintained by the Energy Research Center of the Netherlands (ECN) [21]. In the case of blended fuels, which account for a majority of cost estimates, a weighted average of the proximate analysis and ash composition is used. The composition of the feedstocks used in this study can be found below, in Table A1 in Appendix A. The composition of the syngas used can be found in Tables A2 and A3 in Appendix A.

Feedstock Costs and Supply Chain
According to analysis presented in the Billion-Ton Report, the U.S. has the potential to produce approximately 1 billion tonnes of biomass capable of being used towards BECCS by the year 2040. However, not all of these resources can be used towards BECCS, since there are considerations needed regarding economic, environmental, and social factors. To account for these, biomass resources in this analysis will exclude biomass required for food, fiber, and feed. Furthermore, land allocation, risk of rain and erosion, sustainability, and conservation are considered in determining potential crops for BECCS plants. Resources that are protected or environmentally sensitive are not included, and this study ensures that demand for food, feed, fiber, and export are all met without supply disruption before being used towards BECCS. Feedstocks in this analysis include switchgrass, miscanthus, corn stover, wheat stover, pine, poplar, willow, and hardwood and softwood logging residues. The costs and emissions reported in the Billion-Ton Report for the feedstocks are inclusive of harvesting, growing, and pretreatment. Tables A7 and A8 found in Appendix C list the costs and CO 2 emissions assumed for all feedstocks used in this analysis. Information from the Billion-Ton Report is then used in the BILT model to approximate supply chain costs and emissions [22].

Power Plant Modeling
Power plant economics and performance simulations were performed using the Integrated Environmental Control Model [23]. The IECM was used to simulate the electricity generation costs and emissions of pulverized combustion and integrated combined cycle power plants running on biomass feed. PC powerplants are divided into four subsections in the IECM: Base plant, NOx control, SO 2 Control, and CO 2 Capture, Transport and Storage. Critical parameters used in the modeling of PC powerplants can be found in Appendix E in Table A10. IGCC powerplants are divided into seven subsections in the IECM: Overall Plant, Air Separation Unit, Gasifier Area, Sulfur Removal, CO 2 Capture, Transport and Storage, and Power Block. Critical parameters used in the modeling of IGCC powerplants can be found in Appendix E in Table A11.

BECCS Scenarios
To calculate the cost of BECCS in 2040, three scenarios were developed to account for the effects of differences in feedstock preparation and power generation technologies. The three scenarios can be found in Table 1.

CO 2 Avoidance Cost
The CO 2 avoidance cost is the CO 2 cost at which the energy product cost is the same for either a fossil fuel plant without CCS or the same fossil fuel plant that includes the capital and efficiency losses of adding CCS [24,25].
The CO 2 Avoidance Cost (CAC) can be described by the following equation [9,26]: where LCOE is the levelized cost of electricity, i.e., the revenue required to break even (in $ per MWh), and E is the emissions intensity of the power plant in (tonnes CO 2 per MWh). BECCS refers to the power plant scenario with carbon capture and storage (BECCS), and the ref notation refers to the reference-case energy technology. IECM calculates the 'revenue required to break even ($ per MWh)', which summarizes the total annual cost of running a power plant with respect to its total MWh output. A weighted LCOE was calculated using the reported revenues required to break even, number of power plants, and capacity per power plant for each BECCS scenario. Emissions intensities are also an output of the IECM program, and similar weighted averages were calculated for both BECCS and reference cases.

Cost of BECCS Equations
The cost of BECCS can be described by the following equations: Here, the cost of electricity refers to the IECM output "revenue required to break even". The difference between Equations (2) and (3) is that Equation (3) accounts for revenue generated by BECCS through production of electricity. Based on a 90% capacity factor, which is the fraction of operating hours per year, and the MW net output from the IECM, annual MWh production can be calculated. The wholesale rate was determined by taking the average wholesale rate in the specified region.

Comparative Analysis Using CAC
One benefit of using CAC to describe the cost of BECCS implementation is that the equation can be used to compare two sets of power generation technologies to determine which one is most cost-effective in removing CO 2 from the air. Depending on the referencecase power plant used in CAC calculations, the CAC will have a different meaning [27]. Thus, it is imperative to clearly describe the bounds for CAC in order to not misrepresent costs. Table 2 presents the different reference cases used in this study and their implications.  Figure 2 illustrates the cost of BECCS for the three BECCS scenarios considered in this study, i.e., (i) integrated biomass gasification combined cycle (IBGCC-BECCS) with non-pelletized biofuel, (ii) pulverized biomass combustion (PBC-BECCS) with pelletized biofuel, and (iii) IBGCC-BECCS with pelletized biofuel using Equations (2) and (3). In all power-generation scenarios, the cost of BECCS increases with increasing levels of CO 2 sequestration and biomass utilization, because the most cost-efficient fuels (in MJ/$) are utilized initially, thus requiring the usage of the more expensive, less energy-dense feedstocks at higher levels of biomass utilization. The average fuel-intensity values (in MJ/$) for the three BECCS scenarios can be found in Figure 3, where each point represents a mixture of biomass fuels. As shown in Figure 3, the energy intensity of the 30% PBC pelletized scenario is at a maximum, and this corresponds to the minimum cost of BECCS for this scenario found in Figure 2. The cost of BECCS is the lowest in the pelletized IBGCC-BECCS scenario, and both IBGCC-BECCS scenarios (pelletized and non-pelletized) sequester CO 2 at lower costs than pelletized PBC-BECCS plants. Pelletization of the feedstock before gasification in IBGCC plants decreases the cost of BECCS, due to the decrease in moisture content and the increase in the energy density of the feedstock after pelletization. Pelletization helps bring down the costs of transporting and storing the feedstock. Furthermore, pelletized feedstock can be transported longer distances without decomposing. The cost of BECCS is analogous to the LCOE, except it represents the cost per tonne of CO 2 that is captured, transported, and stored by a BECCS power plant. For BECCS 1 (Equation (2)), the cost of BECCS for IBGCC-BECCS pelletized plants ranges between $88 and $116 per tonne of CO 2 removed from the atmosphere. BECCS 2 (Equation (3)) considers the revenue generated from wholesale of electricity, and for IBGCC-BECCS pelletized plants, the cost of BECCS ranges between $62 and $83 per tonne of CO 2 removed from the atmosphere.  (2)) represents the cost of BECCS alone while BECCS 2 (Equation (3)) represents the cost of BECCS with the wholesale of electricity [11].

Figure 2.
Scenario-average cost of BECCS (in $ per tonne of CO2 captured) for the three BECCS scenarios. BECCS1 (Equation (2)) represents the cost of BECCS alone while BECCS2 (Equation (3)) represents the cost of BECCS with the wholesale of electricity [11].

CAC Calculations Using PC Powerplants with Coal
Pulverized coal combustion (PCC) power plants were considered as a reference case for the CAC calculations, as they are the most common type of coal power plant currently found in the U.S., as well as the third-largest producer of electricity in the U.S. [28]. A PCC plant powered by bituminous Appalachian coal was used as a reference case in CAC calculations. Reference-case power plants of varying capacities were simulated in the IECM to accurately reflect the range of power plant sizes present in potential BECCS scenarios. The CAC for PBC-BECCS plants ranges between $45 and $59 per tonne of CO 2 avoided when using a PCC power plant reference case without CCS. The CAC increases with increasing levels of biomass utilization due to the scarcity of inexpensive, high-energydensity feedstocks. The avoided emissions costs of other technologies reported in the literature can be found in Table 3 [29]. This cost is competitive with the CAC of neutral emissions technologies. The CAC for PBC BECCS plants ranges between $45 and $58 per tonne of CO 2 avoided when using PC powerplants without CCS as the reference case. Figure 4 illustrates the range of CACs for this calculation.

CAC Calculations Using PC Powerplants with Coal
Pulverized coal combustion (PCC) power plants were considered as a reference for the CAC calculations, as they are the most common type of coal power plant curre found in the U.S., as well as the third-largest producer of electricity in the U.S. [28]. A plant powered by bituminous Appalachian coal was used as a reference case in CAC culations. Reference-case power plants of varying capacities were simulated in the IE to accurately reflect the range of power plant sizes present in potential BECCS scena The CAC for PBC-BECCS plants ranges between $45 and $59 per tonne of CO2 avo when using a PCC power plant reference case without CCS. The CAC increases with creasing levels of biomass utilization due to the scarcity of inexpensive, high-energysity feedstocks. The avoided emissions costs of other technologies reported in the li ture can be found in Table 3 [29]. This cost is competitive with the CAC of neutral e sions technologies. The CAC for PBC BECCS plants ranges between $45 and $58 per to of CO₂ avoided when using PC powerplants without CCS as the reference case. Figu illustrates the range of CACs for this calculation.  The high CAC for solar and offshore wind can be explained by the low-capacity tors of these technologies, mainly due to their intermittent nature. Thus, it would three to four times the capacity (in MW) to generate the same amount of MWh that a f fuel power plant would produce [18].   The high CAC for solar and offshore wind can be explained by the low-capacity factors of these technologies, mainly due to their intermittent nature. Thus, it would take three to four times the capacity (in MW) to generate the same amount of MWh that a fossil fuel power plant would produce [18].

CAC Calculations Using NGCC Power Plants for Reference
Similarly to the analysis presented in the previous section, CAC calculations were conducted using an NGCC power plant as the reference case. NGCC power plants currently generate the greatest amount of electricity in the U.S. [28]. The CAC for PBC-BECCS power plants ranges between $47 and $64 per tonne of CO 2 avoided when using an NGCC power plant without CCS as the reference for CAC calculations. Figure 5 illustrates the range of CACs for the three BECCS scenarios.

CAC Calculations Using NGCC Power Plants for Reference
Similarly to the analysis presented in the previous section, CAC calculations were conducted using an NGCC power plant as the reference case. NGCC power plants currently generate the greatest amount of electricity in the U.S. [28]. The CAC for PBC-BECCS power plants ranges between $47 and $64 per tonne of CO2 avoided when using an NGCC power plant without CCS as the reference for CAC calculations. Figure 5 illustrates the range of CACs for the three BECCS scenarios.

CAC Calculations Using Biomass References
CAC calculations were also performed using power plants powered by biomass as reference plants. In this set of simulations, the PC and IGCC reference power plants were modeled to generate electricity using pelletized switchgrass feed without CCS. The CO₂ avoidance cost using these reference cases helps describe the cost of carbon capture and storage in PC and IGCC technologies. The CAC for PBC-BECCS plants using PBC power plants without CCS as the reference case ranges between $39 and $61 per tonne of CO2 avoided. Figures 6 and 7 illustrate the range of CACs for the three BECCS scenarios using biomass-powered reference cases. The lower CAC calculated when using IBGCC plants as the reference case reflects the higher cost of electricity generation in IBGCC systems.

CAC Calculations Using Biomass References
CAC calculations were also performed using power plants powered by biomass as reference plants. In this set of simulations, the PC and IGCC reference power plants were modeled to generate electricity using pelletized switchgrass feed without CCS. The CO 2 avoidance cost using these reference cases helps describe the cost of carbon capture and storage in PC and IGCC technologies. The CAC for PBC-BECCS plants using PBC power plants without CCS as the reference case ranges between $39 and $61 per tonne of CO 2 avoided. Figures 6 and 7 illustrate the range of CACs for the three BECCS scenarios using biomass-powered reference cases. The lower CAC calculated when using IBGCC plants as the reference case reflects the higher cost of electricity generation in IBGCC systems.  Figure 6. CO 2 avoidance cost (in $ per tonne of CO 2 avoided) of BECCS using a PBC power plant reference case without CCS fueled by pelletized corn stover. Figure 6. CO2 avoidance cost (in $ per tonne of CO2 avoided) of BECCS using a PBC power plant reference case without CCS fueled by pelletized corn stover.

Corn Stover Co-Firing
Literature research indicates that a corn stover feedstock can be co-fired up to 30 weight percent in coal power plants with little technical modification [30]. The avoidance costs of co-fired power plants are explored to understand the effect of the CO2 credit experienced by a biomass co-fired feedstock. Biomass feedstock, for the purposes of CO₂ accounting, can be considered to have negative emissions, because unlike coal, plants sequester atmospheric CO₂ at much faster rates. Figures 8 and 9 present the CAC of co-fired corn stover power plants. The CAC for a 30% corn stover co-fired plant is found to range

Corn Stover Co-Firing
Literature research indicates that a corn stover feedstock can be co-fired up to 30 weight percent in coal power plants with little technical modification [30]. The avoidance costs of co-fired power plants are explored to understand the effect of the CO 2 credit experienced by a biomass co-fired feedstock. Biomass feedstock, for the purposes of CO 2 accounting, can be considered to have negative emissions, because unlike coal, plants sequester atmospheric CO 2 at much faster rates. Figures 8 and 9 present the CAC of co-fired corn stover power plants. The CAC for a 30% corn stover co-fired plant is found to range between $70 to $104 per tonne of CO 2 avoided with a PCC plant without CCS as reference. CAC values were found to decrease with increasing power plant size and co-firing percentage of biomass. Due to the benefits of economy of scale experienced by larger power plants, regardless of cofiring percent, larger power plants were found to have lower CAC. This effect of economy of scale is seen in all PC power plants simulated in this study. Increasing the percentage of co-firing decreases the CAC linearly, due to the linear decrease in the emissions intensity of co-fired power plants (based on linear increases in the CO 2 credit gained by using biomass feedstocks).

Poplar-Derived Bio-SNG Co-Firing
Similarly to the work presented above in the corn stover co-firing section, the cost using BECCS feedstocks in NGCC systems was explored. Research conducted by Carb et al. (2011) suggests that bio-SNG has the potential to sequester CO₂ at low CO₂ avoidan 0 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Poplar-Derived Bio-SNG Co-Firing
Similarly to the work presented above in the corn stover co-firing section, the cost of using BECCS feedstocks in NGCC systems was explored. Research conducted by Carbo et al. (2011) suggests that bio-SNG has the potential to sequester CO 2 at low CO 2 avoidance costs [31]. Literature review indicates that bio-SNG, i.e., upgraded bio-syngas, can be co-fired with fossil natural gas if the following conditions are met: a minimum CH 4 percentage of 90%, and removal of sulfurous, nitrous, and chlorine-based contaminants [32]. The economics of NGCC power plants co-fired with upgraded syngas from poplar was studied, and the LCOE economics of these plants are presented in Figures 10 and 11. The CAC for a 10% bio-SNG power plant using an NGCC reference case without CCS is presented in Figure 12. The LCOE for 10% co-fired NGCC plants was found to range between $119 and $127 per MWh, with larger power plants producing electricity at lower cost. The CAC for 10% co-fired NGCC plants was found to range between $145 and $162 per MWh when using an NGCC power plant without CCS as the reference case. Differences in costs can be attributed to power plant size. IBGCC-BECCS power-generating systems do not experience this economy of scale as discussed in previous sections. costs [31]. Literature review indicates that bio-SNG, i.e., upgraded bio-syngas, can be cofired with fossil natural gas if the following conditions are met: a minimum CH4 percentage of 90%, and removal of sulfurous, nitrous, and chlorine-based contaminants [32]. The economics of NGCC power plants co-fired with upgraded syngas from poplar was studied, and the LCOE economics of these plants are presented in Figures 10 and 11. The CAC for a 10% bio-SNG power plant using an NGCC reference case without CCS is presented in Figure 12. The LCOE for 10% co-fired NGCC plants was found to range between $119 and $127 per MWh, with larger power plants producing electricity at lower cost. The CAC for 10% co-fired NGCC plants was found to range between $145 and $162 per MWh when using an NGCC power plant without CCS as the reference case. Differences in costs can be attributed to power plant size. IBGCC-BECCS power-generating systems do not experience this economy of scale as discussed in previous sections.

Comparing BECCS Power Plants to PCC Power Plants with CCS
Research conducted by Grubert et al. (2020) indicates that by the year 2035, power plants generating approximately 630 GW of power in the U.S. will face retire [33]. Thus, there will be a need to construct facilities to replace the retired coal plan meet the demand for electricity. Before moving forward and constructing facilities to erate electricity, it is important to understand the relative performances of BECCS p plants and PCC plants with CCS. In order to do this, the CAC for both BECCS p plants and PCC power plants with CCS will be calculated using a PCC power plant out CCS as the reference case. Results comparing the CAC for BECCS and PCC p with CCS can be found in Figure 13, where it is shown that BECCS power plants op at CO₂ avoidance costs lower than those of PCC with CCS plants, with PBC plants ating at the lowest CAC cost.

Comparing BECCS Power Plants to PCC Power Plants with CCS
Research conducted by Grubert et al. (2020) indicates that by the year 2035, coal power plants generating approximately 630 GW of power in the U.S. will face retirement [33]. Thus, there will be a need to construct facilities to replace the retired coal plants to meet the demand for electricity. Before moving forward and constructing facilities to generate electricity, it is important to understand the relative performances of BECCS power plants and PCC plants with CCS. In order to do this, the CAC for both BECCS power plants and PCC power plants with CCS will be calculated using a PCC power plant without CCS as the reference case. Results comparing the CAC for BECCS and PCC plants with CCS can be found in Figure 13, where it is shown that BECCS power plants operate at CO 2 avoidance costs lower than those of PCC with CCS plants, with PBC plants operating at the lowest CAC cost.

Summarized Results
A summary of the calculated ranges of CAC values for the three BECCS cases c sidered in this study can be found in Table 4. Results from reference cases 5 and 6 indi that the IBGCC plants generate electricity at higher costs than PBC plants. Lastly, sim values for calculated CACs in reference cases 2 and 4 indicate that the cost of carbon c ture and storage in PC and NGCC plants is similar. This similarity can be attribute both plants based on post-combustion CO₂ capture using monoethanolamine (MEA).

Future Work
To further build on our understanding of BECCS, the three following areas have b identified as potential research. The first area is with regards to quantifying the reven gained from the wholesale of electricity. These revenues will consider the state in wh

Summarized Results
A summary of the calculated ranges of CAC values for the three BECCS cases considered in this study can be found in Table 4. Results from reference cases 5 and 6 indicate that the IBGCC plants generate electricity at higher costs than PBC plants. Lastly, similar values for calculated CACs in reference cases 2 and 4 indicate that the cost of carbon capture and storage in PC and NGCC plants is similar. This similarity can be attributed to both plants based on post-combustion CO 2 capture using monoethanolamine (MEA).

Future Work
To further build on our understanding of BECCS, the three following areas have been identified as potential research. The first area is with regards to quantifying the revenues gained from the wholesale of electricity. These revenues will consider the state in which the powerplant is located and the associated demand and wholesale price for electricity. The second area of potential research is with the process economics and optimization of syngas production. Understanding optimal conditions for syngas production can help reduce the cost of BECCS. Currently, there are 13 different biomass feedstocks used in our simulations, each with potentially different optimal conditions for syngas production. Should BECCS be implemented, designing a system that maximizes the heating value of the syngas produced will be crucial. The last area of research is with renewable natural gas, i.e., syngas produced from biomass capable of being used in natural gas powerplants. If syngas can be upgraded economically, the scope of BECCS can be widened to include natural gas powerplants.

Conclusions
BECCS has the capability of reducing the atmospheric CO 2 concentration, both through sequestered atmospheric CO 2 and through avoided emissions by replacing conventional coal power plants. This paper explores the potential supply of fuel and cost of BECCS under a range of feedstock options, power plant configurations and locations, and logistics. Results of the simulations performed for this paper indicated that, at a 90% capacity, BECCS in the U.S. has the potential to remove and sequester up to 737 million tonnes of CO 2 per year long term from the atmosphere. According to climate goals outlined by the Paris Agreement, BECCS has the potential to sequester approximately 25% of the carbon needed to achieve carbon neutrality by 2050 in the U.S.
Scenario-specific average costs indicated that the price of capturing, transporting, and storing CO 2 ranges between $88 and $116 per tonne of CO 2 for pelletized IBGCC-BECCS plants, with costs increasing with increasing levels of biomass utilization. In 2020, roughly 5.4 billion metric tonnes of CO 2 were released into the atmosphere in the U.S., with 1.1 billion tonnes of CO 2 coming from coal power plants [4]. Converting some of these coal power plants to BECCS power plants by the year 2040 can help limit annual CO 2 emissions in the U.S. to approximately 4 billion tonnes.
Calculations suggest that the CAC for pelletized PBC-BECCS plants ranges between $45 to $59 per tonne of CO 2 avoided when comparing to a reference case PCC power plant without CCS. Implementation of BECCS through co-firing was also explored in the case of co-firing corn stover with coal and bio-SNG with fossil natural gas. For 30% corn stover co-firing, the CAC ranges between $70 and $104 per tonne of CO 2 avoided. The CAC for 1000-MW co-fired stover PCC plants with CCS ranges between $70 to $87 per MWh, with the CAC decreasing with increasing biomass co-firing percentages. In bio-SNG co-fired NGCC plants, the LCOE was seen to range between $119 and $127 per MWh, depending on the size of the plant. The CAC for a 10% co-fired bio-SNG plant ranges between $145 and $162 per MWh when using an NGCC plant without CCS as the reference case. For PBC reference-case plants without CCS, the CAC for BECCS was seen to range between $39 and $61 per tonne of CO 2 avoided for BECCS-PBC plants, and between $46 and $97 per tonne of CO 2 avoided for IBGCC-BECCS plants.
Results from this study indicate that PBC plants will be the most cost-effective powergeneration technology to implement BECCS in the U.S. A comparative analysis of the CAC of BECCS and other energy technologies suggests that BECCS can generate electricity competitively with neutral emissions technologies while having a net-negative CO 2 footprint. Furthermore, comparative results presented in this study indicate that BECCS can operate with CAC values below those of PCC plants with CCS. Results presented in this study indicate that the CAC of BECCS is lower than that of solar and offshore wind, but higher than onshore wind and nuclear. Finally, it should be noted that several assumptions are involved in the model development and predictions. Better understanding of biomass pretreatment, gasification and conversion to power through research and development would greatly improve predictions and reduce the risks.

Conflicts of Interest:
The authors declare no conflict of interest.      Table A8. Carbon emissions associated with production, harvesting, and transportation of the different feedstocks used in this study. These results serve as an input for the BILT model [11].