PEER-REVIEW ARTICLE PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 7806 Carbon Footprint and Techno-economic Analysis to Decarbonize the Production of Linerboard via Fuel Switching in the Lime Kiln and Boiler: Development of a Marginal Abatement Cost Curve Rodrigo Buitrago-Tello,a Richard A. Venditti,a,* Hasan Jameel,a Peter W. Hart,b and Ashok Ghosh b The US Pulp and Paper (P&P) industry heavily relies on fossil sources, with lime kiln operations posing a significant challenge for achieving zero on-site fossil emissions. This study assesses the greenhouse gas (GHG) reduction potential and costs associated with alternative fuels in lime kiln operations for linerboard production. Various options, including bio-based fuels including pulverized biomass, gasification of biomass, crude tall oil, bio-methanol, and traditional fuels such as fuel oil and petcoke, were analyzed through detailed process simulations and Life Cycle Assessment. Results indicate that per ton of product, 2,789 kg of CO2-eq is emitted, with 69% being biogenic CO2 and 31% fossil CO2-eq. Notably, replacing the natural gas boiler with a biomass boiler reduces Global Warming Potential (GWP) by 41%, while switching lime kiln fuel to biofuels achieves a 5.5% reduction. Combining a biomass boiler with pulverized biomass fuel use in the lime kiln yields a substantial 93.1% reduction in Scope 1 and 2 emissions, at a cost of $76/ton of CO2-eq avoided. DOI: 10.15376/biores.19.4.7806-7823 Keywords: Alternative lime kiln fuel; Biomass boiler; Life cycle assessment; Marginal abatement cost curve Contact information: a: Department of Forest Biomaterials, North Carolina State University, Raleigh, NC 27607, USA; b: Research and Development, WestRock, Richmond, VA 23219, USA; * Corresponding author: richard_venditti@ncsu.edu, Telephone: 919-515-6185 Synopsis The effect of switching fossil fuels with bioenergy to decarbonize the production of linerboard is revealed by an integrated environmental and economic evaluation and the construction of the Marginal Abatement Cost Curve INTRODUCTION The US Pulp and Paper (P&P) Industry has the third highest energy demand of all industrial sectors behind chemical manufacturing and petroleum/coal industries, with 8.7 trillion BTU per year (IEA 2022). Although most of the energy comes from renewables, the industry still has a high dependency on fossil fuels, which represent significant contributions to GHG emissions. The lime kiln is one of the larger users of fossil fuels. In the kiln, calcium carbonate is calcinated to regenerate calcium oxide, which is used to causticize sodium carbonate in the green liquor to form sodium hydroxide, reducing the demand for pulping chemicals in the system (Tran 2007). PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 7807 The variation in the prices of fossil fuels and the commitment to reduce GHG emissions have driven the adaptation of renewable sources in the operation of lime kilns. For example, 90% of the energy demand in Swedish lime kilns is supplied by biofuels, including tall oil pitch (63%), wood and bark dust (24%), and methanol combined with non-condensable gases (NCGs) (3%). In Finland, 42% of the energy is supplied with biofuels, the most common being biomass gasification (18%), followed by tall oil pitch (13%), wood dust and lignin (8%), and methanol/NCGs (6%) (Berglin and Von 2022). Biofuels have shown little operational difference compared to fuel oil or natural gas (Berglin and Von 2022) and it is estimated the replacement of natural gas or fuel oil with bio-based fuels in lime kilns represents a 10% reduction in the GHG emitted by the European P&P industry (Taillon et al. 2018). The US pulp and paper (P&P) industry needs to adopt more efficient technologies to match the energy performance of European mills. Compared to their European counterparts, US mills are generally less energy-efficient, consuming more energy per ton of product. European mills have achieved higher energy efficiency, allowing them to utilize biomass excesses and coproducts as energy sources in lime kiln operations. On the contrary, natural gas is the main fuel in lime kiln operations in the US. Before fracking for natural gas in the early 2000s, natural gas was so expensive that several mills burned bio- based coproducts available in the mill rather than using natural gas (Francey et al. 2009; Manning and Tran 2015; Hart 2020a,b) After widespread implementation of fracking, the price of natural gas decreased and pulp and paper mills began to implement more cheap natural gas fuels in their processes. Recently, the US government has set the goal of 50 to 52% GHG reductions below 2005 levels by 2030, covering all sectors, followed by a net-zero emissions no later than 2050 (Kerry and McCarthy 2021). These ambitious goals and the unpredictable fluctuation in fossil fuel prices are leading the US P&P to incorporate technologies to reduce the GHG emissions. The use of bio-based fuels may represent a reduction in on-site fossil emissions. Still, the transformation of raw materials into suitable lime kiln fuel (pulverized or gasified biomass) or the extraction and adaptation of secondary streams from the process (lignin, methanol, crude tall oil (CTO), or tall oil pitch (TOP)) implies indirect emissions that might diminish the benefit achieved. Moreover, the alternatives may represent an additional cost for the mill, making them less attractive or nonviable depending on operating conditions. While the use of bio-based fuels may represent a reduction in on-site fossil emissions, there are practical considerations such as the generation of ash, which can affect costs and efficiency by the buildup of insulating layers from deposits. Previous studies have shown the economic and environmental benefits of incorporating alternative fuels in lime kiln operations when surplus biomass and surplus electricity are available in the mill, it is possible to reduce GHG emissions and assure the economic viability of the alternatives (Kuparinen et al. 2016, 2017; Kuparinen and Vakkilainen 2017). However, these conditions are contrary to those faced by the US P&P industry. The present study evaluated various renewable fuels for lime kiln operations in the production of linerboard, one of the largest and growing sectors in US P&P industry (Elhardt 2017). The alternatives include pulverized or gasified biomass, CTO, TOP, bio- methanol, turpentine, and lignin. Additionally, other traditional lime kiln fuels were evaluated (fuel oil, petcoke, and tire-derived fuel (TDF)), as well as the replacement of the natural gas boiler by a biomass boiler. The net fossil CO2 reductions of the alternatives were determined through a detailed process mass and energy balance simulation using PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 7808 WinGEMS. The alternatives are categorized by constructing a marginal carbon abatement cost curve (MACC), this MACC categorizes the alternatives by the cost of reducing 1 ton of CO2-eq (carbon abatement cost) and shows the CO2-eq reductions offered by each alternative. This study highlights operational conditions applicable to the US P&P sector, demonstrating the potential for significant carbon savings if these alternative fuels are adopted in US linerboard production. Implementing these best practices could result in substantial environmental and economic benefits, aligning the US industry with global sustainability standards. MATERIALS AND METHODS Definition of the Baseline The mill in this work is a continuous linerboard unbleached mill, which is a virgin grade (new, unused wood fibers), with a production of 100 short ton per hour or 90.72 tons/h. The configuration and operating conditions were defined based on information reported in the literature and databases and industry experts’ recommendations (Rydholm 1967; Grace et al. 1983; ResourceWise 2023; Fastmarkets 2023). Detailed information is included in the supporting information section (Appendix). Figure 1 shows the system boundary for the Cradle-to-Gate Life Cycle Assessment (LCA) developed and the main areas that compose the mill. Fig. 1. System boundary for the Linerboard mill (base case) The life cycle inventory is based on the mass and energy balance for a mill configuration modeled in WinGEMS (Metso, version 5.3, Espoo, Finland), a specialized process simulation software for the P&P industry. The Ecoinvent database was used to determine the contribution of the upstream processes. The GWP was determined using the IPCC 2013 GWP 100a method, available in OpenLCA. The method expresses GHG emissions, in kilograms CO2 equivalent, over a time horizon of 100 years. A mass allocation factor is used to allocate the GWP among the different coproducts in the system. PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 7809 Evaluation of Alternatives to Reduce the GWP The combustion of alternative lime kiln fuels, and the biomass boiler were incorporated into the base simulation model. The scenarios evaluated are in Table 1. For each scenario, the linerboard production remained the same; some of the fuels can substitute for 100% natural gas in the lime kiln (fuel oil, pulverized biomass, biomass gasification, CTO, and TOP), whereas others have limited substitution (methanol, turpentine, petcoke, and TDF) (Francey et al. 2009; Taillon et al. 2018; Hart 2020a,b). The GWP of the scenarios was estimated based on a Cradle-to-Gate LCA by implementing the IPCC 2013 GWP 100a method. The alternatives were classified into four groups; the first was the replacement of the natural gas boiler with a biomass boiler to produce steam and electricity for the mill. The second group corresponds to external bio-based fuels that can displace 100% of the natural gas demand in the lime kiln. The third group corresponds to fuels that are available in the mill, such as CTO, methanol, and turpentine, or it can be extracted from the streams available in the mill, which is the case of lignin. The last group corresponds to other fossil fuels that can be burned in the lime kiln. The conditions for integrating each alternative are included in the supporting information section. Table 1. Alternative Technologies to Reduce the GWP in the Production of Linerboard Scenarios Fuel Use Min (%) Medium (%) Max (%) Base case: Natural gas - - 100 1. Replacement of natural gas boiler with a biomass boiler 2. External bio-based fuels 2.1 Pulverized biomass 25 50 100 2.2 Biomass gasification - - 100 2.3 Tall oil pitch (TOP) 25 50 100 3. Bio-based products or bio-based streams available in the mill 3.1 Crude tall oil (CTO) 25 50 100 3.2 Lignin 25 - 50 3.3 Methanol - - 10 3.4 Turpentine - - 10 4. Other fossil-based fuels 4.1 Fuel oil - - 100 4.2 Petcoke 25 50 85 4.3 Tire-derived fuels (TDF) - - 15 RESULTS AND DISCUSSION Carbon Footprint To develop a representative picture of carbon footprint for linerboard production and to evaluate improvements in such, a detailed process simulation was developed in PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 7810 WinGEMS. The operating conditions were based on both literature values and information from industrial experts. Baseline and various scenario mass and energy balance simulations were determined. The results for each case are listed in the supporting information section. These data, along with the LCI from the Ecoinvent database (Wernet et al. 2016), were entered into OpenLCA to estimate the GWP. Figure 2 shows the total CO2-eq emissions in the production of linerboard for the baseline case. A total of 69% of the total emissions correspond to biogenic CO2; of these emissions, 82.3% came from black liquor combustion, the primary energy source in the process; 12.3% came from the biomass boiler that burns residual biomass from the woodyard and external hog fuel, and 5.4% came from the lime kiln. The lime kiln has both anthropogenic CO2 from burning natural gas and biogenic CO2 from the CaCO3 conversion to CaO and CO2. The biogenic CO2 from CaCO3 originates from Na2CO3 from the black liquor burnt in the recovery boiler. In this case, the ratio between the fossil and the biogenic CO2 in the lime kiln is 66% biogenic to 34% fossil CO2. Fig. 2. CO2-eq emissions in the production of one machine dry (10% moisture) kg of linerboard product Regarding the GWP, the linerboard production has a total emission of 0.865 kg CO2-eq / kg machine dry (MD) product (10% moisture content). Of these emissions, 48.1% are on-site emissions (Scope 1), 48.6% are indirect emissions from upstream processes and the disposal of waste (Scope 3), and 3.3% are from the purchase of electricity (Scope 2). Note the purchase of electricity is low because there is significant on-site production of electricity. The total emissions are similar to those reported in the literature for unbleached paperboard (0.714 kg CO2-eq/kg product as an industry wide average) (Hart 2020b), and the process reported in Ecoinvent 3.8 as “containerboard production, linerboard, kraftliner- Rest of the world” (0.735 kg CO2-eq/kg product) (Francey et al. 2009). The differences in the results arise from assumptions made in the simulation model and in the LCA model used herein. In the present study, the demand for raw materials and emissions are based on mass and energy balances from the process simulation, assuming standard operating PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 7811 parameters in the industry for this type of pulp grade; in contrast, the referenced cases were based on a top-down approach, integrating average values of the industry to a production line level. To have a detailed view of the sub-process contributions, a hotspot analysis was performed to identify critical sub-processes. Table 2 shows the detailed contribution of each process to the GWP. Table 2. GWP Contribution of the Different Areas Involved in the Production of 1 kg of Linerboard SCOPE Process Subprocess GWP (kg CO2-eq/kg product) Contribution (%) Scope 1 On-site emissions Fossil CO2 Lime kiln 5.34*10-02 6.17% Fossil CO2 Natural gas boiler 3.63*10-01 41.92% Scope 2 Electricity from the grid Electricity demand 2.85*10-02 3.30% Scope 3 Production of external fuels External hog (Power plant) 3.48*10-03 0.40% Natural gas - Boiler 4.75*10-02 5.48% Natural Gas - Lime kiln 6.99*10-03 0.81% Pulp biomass Forestry activities (Logs) 7.28*10-02 8.41% Wood chips 8.29*10-02 9.58% Makeup chemicals NaOH makeup 9.73*10-03 1.12% Na2SO4 makeup 9.39*10-04 0.11% CaO 2.33*10-02 2.69% Tall oil production H2SO4 3.76*10-04 0.04% Transport Transport biomass 1.53*10-01 17.66% Transport materials 6.16*10-04 0.07% Waste disposal Dregs 3.39*10-03 0.39% Grits 4.46*10-03 0.51% Ashes 2.00*10-05 0.002% Sludge 1.14*10-02 1.3% TOTAL 8.65*10-01 100% The red color indicates a high contribution, while green indicates low contribution. The on-site emissions are the primary source of GHG emissions in the system; 41.9% of the GWP is attributed to the fossil CO2 from natural gas combustion for steam and electricity generation in the mill; whereas 6.2% comes from fossil CO2 from natural gas combusted in the lime kiln. These emissions may be avoided by introducing renewable alternatives, such as a biomass boiler, or renewable fuels in the lime kiln. Likewise, pulpwood production corresponds to 18% of the GWP; these emissions come mainly from the combustion of fossil fuels in forestry operations such as harvesting, forwarding, and wood chipping. Pulpwood transport is an important contributor to the GWP, given the PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 7812 transport distance from the field to mill (200 km) and the high biomass demand in the process (4.4 wet tons of wood total/1 MDT of linerboard). In the present study, the emissions related to chemical manufacture are 0.034 kg of CO2-eq/ kg of product or 4% of the total GWP. This is much lower than bleached grades of paper and board, as linerboard does not require bleaching chemicals. The GWP contribution from purchased chemicals has been reported as 0.101 kg CO2-eq/kg of product for bleached market pulp (Tomberlin et al. 2020), 0.297 kg CO2eq/kg of product for bleached softwood fluff pulp (Buitrago-Tello et al. 2022), and 0.552 kg CO2-eq/kg pulp for softwood acetate dissolving pulp (Echeverria et al. 2021). This difference is particularly due to the demand for sodium chlorate for the on-site production of chlorine dioxide (Tomberlin et al. 2020; Echeverria et al. 2021; Buitrago-Tello et al. 2022). Given that on-site emissions are the main contributor to the GWP, the present study focused on alternatives to reduce Scope 1 emissions by introducing alternative fuels for energy production and lime kiln operations. It is worth mentioning that reducing emissions by the transport of pulp wood also requires attention, considering that variables, such as the location and aerial density of the biomass, and the transport media available in the supply chain can greatly affect the GWP contribution; however, this aspect is out of the scope of the present study. The alternatives evaluated are listed in Table 1; the detailed GWP results for the scenarios are reported in the supporting information section. The GWP is reported in two ways. The first is aligned with the Greenhouse Gas Reporting Program (GHGRP) established by the EPA (EPA 2021), where only Scope 1 and Scope 2 emissions are considered. The second is a cradle-to-gate approach, where emissions Scopes 1, 2, and 3 are included in the GWP. Table 3 shows the change in the on-site emissions (Scope 1), the indirect emissions by the electricity demand (Scope 2), and the indirect emissions from other upstream processes (Scope 3) by implementing the alternative technologies. It also shows the net change by only considering emissions Scope 1 and 2 (GHGRP approach) and the total change by considering emissions Scope 1, 2, and 3 (cradle to gate approach). Overall, the alternatives based on biofuels showed a reduction in the on-site emissions, particularly with the integration of the biomass boiler. However, the benefit achieved with these alternatives is reduced when the indirect emissions are considered (cradle-to-gate approach), especially for biomass gasification and lignin extraction. Regarding switching natural gas for other fossil-based fuels, most alternatives represent an increase in the GWP; this increase is greatest by implementing petcoke with 85% replacement. These fossil-based scenarios are considered because these are possible fuels that can be used in the lime kiln and may have economic advantage. The use of petcoke and fuel oil has been shown to increase the fossil emissions in producing other paper grades, given the high carbon and low energy content compared to natural gas (Buitrago-Tello et al. 2022). The use of TDF does not represent a meaningful difference as, from a CO2 perspective, it can be considered as substitute when the price is competitive compared with natural gas. Metals emissions from the wire reinforcements in tires may limit the total amount of TDF, which can be permitted for use in a kiln. There are clear differences in the GWP when Scope 3 indirect emissions are considered. For the biomass boiler scenario, there is an 81.5% reduction for Scope 1+2 and only a 41.3% reduction when considering Scope 1+2+3 (Table 3). This difference arises mainly from the GWP associated with the production and transport of the biomass to the mill. PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 7813 Table 3. Detailed Changes in the Emissions Scope 1, 2, and 3 by Implementing Alternative Fuels in Lime Kiln Operations and by Replacing the Natural Gas Boiler with Biomass Boiler Energy Likewise, the reduction achieved in emissions Scope 1 and 2 by implementing bio- based fuels in the lime kiln is around 11% for some alternatives, including pulverized biomass-100%, biomass gasification, CTO-100%, and TOP-100%. This value corresponds to the potential reductions reported for the P&P in Europe by switching to alternative lime kiln fuels (Berglin and Von 2022). Nonetheless, the maximum reduction for these alternatives is 5.6% when the Scope 3 indirect emissions are considered (Pulverized biomass and CTO-100%). The use of turpentine and methanol offers a marginal reduction of total GWP (lower that 1%) despite these materials being available in the mill. For lignin, the potential reduction is 7.3% considering only emissions Scope 1 and 2, but the indirect emissions reduce the benefit to a marginal value (0.7%). In addition, emissions Scope 2 are reduced from the scenario lignin-25% to lignin-50% due to a combined increase in the steam and electricity demand. Because the demand for electricity by the Lignoboost process is higher than the surplus electricity from the increment in the Emission Scope 1 Scope 2 Scope 1+2 Scope 3 Total Total Biogenic Base case (kg CO2/kg machine dry linerboard) 0.416 0.029 0.445 0.421 0.865 1.924 Change in the Emissions (%) Biomass Boiler -87.2% 1.2% -81.5% 1.2% 41.3% 34.4% Pulverized biomass (25%) -3.1% -0.2% -3.0% 0.1% -1.4% 1.3% Pulverized biomass (50%) -6.2% 0.0% -5.8% 0.3% -2.9% 2.5% Pulverized biomass (100%) -12.5% 1.4% -11.6% 0.7% -5.6% 5.0% Biomass Gasification -12.6% 9.7% -11.2% 6.4% -2.6% 6.3% Tall oil pitch (25%) -3.0% -0.1% -2.8% 0.5% -1.2% 1.0% Tall oil pitch (50%) -6.0% -0.7% -5.6% 0.8% -2.5% 1.9% Tall oil pitch (100%) -12.5% -0.6% -11.7% 1.5% -5.3% 3.9% Crude tall oil (25%) -2.2% 0.6% -2.0% 0.5% -0.8% 1.9% Crude tall oil (50%) -5.0% 1.0% -4.6% 0.5% -2.1% 3.3% Crude tall oil (100%) -11.5% -0.5% -10.8% -0.3% -5.7% 7.1% Lignin (25%) -3.3% -30.8% -5.0% 4.8% -0.2% 3.7% Lignin (50%) -6.5% -19.4% -7.3% 6.4% -0.7% 4.2% Methanol (10%) -1.0% 0.6% -0.9% 0.1% -0.4% 0.7% Turpentine (10%) -0.9% 0.3% -0.8% 0.1% -0.4% 0.6% Fuel Oil 5.2% -5.1% 4.5% 0.3% 2.5% 0.0% Petcoke (25%) 4.3% 0.7% 4.1% 0.2% 2.2% 0.0% Petcoke (50%) 6.5% 0.2% 6.1% 0.2% 3.2% 0.0% Petcoke (85%) 12.3% 0.1% 11.5% 0.5% 6.2% 0.0% TDR (15%) 0.2% 0.8% 0.3% -0.3% 0.0% 0.0% PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 7814 steam demand, the Scope 2 emissions are reduced from a 25% substitution to a 50% substitution of natural gas by lignin. Hotspot Analysis of the Alternatives Understanding that reduction methods for Scopes 1 and 2 may have tradeoffs in increases in Scope 3, and to provide a more detailed view of the associated tradeoffs, a hotspot analysis was performed for sub-areas in the alternative scenarios that showed a reduction in the overall net GWP, considering the cradle-to-gate approach emissions Scope 1, 2, and 3. In this hotspot analysis, the relative contribution per area was defined based on the total GWP (Scope 1 2, and 3) in the base case as Eq. 1, (1) where i corresponds to the area, j to the scenario, and bc to base case. Table 4 shows the highest reduction achieved for each alternative, the hotspot results are included in Table S17. The maximum GWP reduction is achieved by the replacement of the natural gas boiler with a biomass boiler (41.3% reduction in the GWP). In this case, the fossil CO2 emissions avoided from the natural gas combustion represent a 41.9% reduction, additionally the avoided demand of natural gas represents a Scope 3 reduction of 5.5%. Still, there are some areas that increase the GWP decreasing the net GWP savings somewhat. Pulverized biomass is the alternative that offers the maximum reduction among the lime kiln fuels evaluated. In this case, the avoided emissions from the production and combustion of natural gas are realized but tempered by the indirect emissions associated with the procurement, transport, drying and pulverization of biomass. In this case, the reduction in the GWP increases with the amount of energy supplied by the pulverized biomass system, achieving a maximum reduction of 5.9% at 100% displacement of natural gas. For biomass gasification, the avoided emissions by displacing natural gas are the same as for pulverized biomass. However, the lower HHV of the syngas (6.5 MJ/kg) (Rofouieeraghi 2012) compared to pulverized biomass (20.5 MJ/kg) (Valmet 2015), and a modest production ratio (0.9 kg syngas/ kg dry biomass) (Rofouieeraghi 2012) increases the demand of biomass, and therefore the indirect emissions. Regarding TOP, this is a co-product of the distillation of CTO, with a HHV comparable to fuel oil (40.3 MJ /kg vs. 44.6 MJ /kg) (Francey 2009; Valmet 2015). Given this energy content and its bio-based origin, it might be expected to offer a better reduction in the GWP. Nevertheless, the indirect emission associated with the CTO distillation reduces the net benefit to a net 5.3% GWP reduction. Likewise, CTO has a lower energy content of 38.4 MJ/ kg (Lundqvist 2009), but it has the advantage of being available in the mill. Generally, it is more economically favorable to sell the CTO to the distilleries and buy back the tall oil pitch (Berglin and Von 2022); however, some mills still use this co- product as lime kiln fuel (Bajpai 2018). According to the results, the maximum reduction in the GWP by implementing CTO combustion in the lime kiln is 5.8%. The extraction of lignin has various effects on the mass and energy balance. The lignin extraction implies a reduction in the black liquor solids to the recovery boiler. In the present model, the energy content of the extracted solids is countered by increasing the fuel demand in the biomass boiler. Additionally, the recirculation of liquor from the Lignoboost (CO 2 eq ij - CO2eq i,bc ) Total CO2eq bc × 100% PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 7815 process to the evaporator increases the steam demand, and consequently, the production of on-site electricity rises along with the increased steam production. This additional steam demand also contributes to the biomass demanded in the boiler. These changes in the energy balance are reflected in a reduction in the emissions Scope 2, and an increase in the biomass for energy production (Table 4). Table 4. Hotspot Analysis for Alternatives that Represent a Reduction in the GWP for Linerboard Production. PV= Pulverized Biomass, BG= Biomass Gasification, TOP=Tall Oil Pitch, Crude Tall Oil=CTO, TP= Turpentine The chemical balance is also affected by the Lignoboost process, a fraction of sodium is lost in the production of the lignin press cake (2.7 kg NaOH/ton). Additionally, there is sulfur added by the black liquor acidification with sulfuric acid; this acidulation reduces the demand of sodium sulfate (3.9 kg Na2SO4/ton reduction) makeup. However, the indirect emissions associated with sodium hydroxide are higher compared to sodium sulfate (1.4 kg CO2-eq/kg NaOH vs 0.17 kg CO2-eq/ kg Na2SO4). This results in increased indirect emissions from the pulping chemicals. Moreover, the Lignoboost process requires CO2 (purchased from external sources in this simulation) and sulfuric acid for the precipitation of lignin, increasing the indirect emissions associated with chemicals. The extraction also implies other indirect emissions as electricity demanded in the lignin dryer and transport of additional materials. Marginal Abatement Cost Curves The alternatives were categorized by developing a Marginal Abatement Cost Curve (MACC). This curve shows the Cost of Avoided Carbon (CAC) in US $/ton of CO2-eq, Scope Alternative Process Biomass Boiler PV (100%) BG TOP (100%) CTO (100%) Lignin (50%) Methanol (10%) TP (10%) Scope 1 Fossil CO₂ (Lime kiln) - -6.2% -6.2% -6.2% -6.2% -3.1% -0.6% -0.6% Fossil CO₂ (Boiler) -41.9% 0.1% 0.1% 0.2% 0.6% - 0.1% 0.2% Scope 2 Electricity (mill) - - - - - -1.5% - - Scope 3 Chemicals - - - - 0.1% 1.3% - - Biomass (Energy) 3.3% 0.5% 1.9% - - 0.9% - - Natural gas production (Boiler) -5.5% - - - 0.1% - - - Natural gas production (Lime Kiln) - -0.8% -0.8% -0.8% -0.8% -0.4% -0.1% -0.1% Alternative Fuel Production - - 0.7% 1.4% - 0.9% - - Transport 2.8% 0.4% 1.7% 0.1% 0.3% 1.4% 0.1% - Net Reduction -41.3% -5.9% -2.6% -5.3% -5.8% -0.7% -0.4% -0.4% PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 7816 and the potential CO2-eq reduction by implementing each technology for the established mill´s production. CAC= Net Present Value CO2eq avoided in 10 years of operation (2) The MACC was built considering emissions Scope 1 and 2 (GHGRP approach), and the total emissions associated with the entire system (cradle-to-gate approach). Table 5 shows the total cost of implementing each technology, the changes in the annual operating and maintenance costs, and the NPV in an 11-year lifetime (the first year is for construction), with a 15% rate of return. In addition, the NPV and the CAC of each alternative was estimated considering two carbon-offset prices, $11/ton and $47/ton. These values are prices projected for 2030 and 2050, respectively (Bloomberg Finance 2022), and correspond to a market scenario where all types of carbon saving suppliers are allowed, including the offsets having avoided emissions (which is the case of the present study) rather than removing the carbon from the atmosphere (Bloomberg Finance 2022). MACC-Emissions Scope 1 and 2 The MACC shown in Fig. 3a categorizes the alternatives according to the CAC, considering the onsite emissions (Scope 1 emissions) and the emissions derived from the production of the energy inputs (Scope 2 emissions). The width of each bar corresponds to the amount of CO2eq avoided per year achieved by implementing the alternative. In addition, the total CO2eq avoided per air-dry ton for each alternative is included in the green labels. The utilization of pulverized biomass and the combustion of TOP were found to be the most cost-effective method to reduce the GWP in the lime kiln at $54 and $78 per ton CO2-eq avoided, respectively. This can be contrasted to another quote for carbon savings in a lime kiln used for cement production in Taiwan, of about $26/per ton CO2-eq (Huang and Wu 2021). The largest annual amount of carbon savings is through the implementation of the biomass boiler at a price of $79/per ton CO2-eq. Some of the other technologies have a high CAC, including gasification, methanol, turpentine, and lignin. Coproducts CTO and TOP do not show the same high CAC as the other coproducts such methanol, turpentine, and lignin. PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 7817 Table 5. Capital Cost, Net Present Value, and Carbon Avoided Carbon for Alternatives to Reduce GWP in the Production of Linerboard Scenario ton CO2-eq avoided /year (Scope 1+2) Investment Capital (Millions) Operating cost (millions/year) NPV (Millions) CAC (dollars / t CO2-eq avoided) Minimum offset price for a NPV = 0 ($/ ton CO2- eq avoided) $0/ t CO2-eq avoided $11/ t CO2-eq avoided $47/ t CO2-eq avoided Offset price = $0/ ton CO2-eq avoided Offset price = $11/ ton CO2-eq avoided Offset price = $47/ ton CO2-eq avoided Pulverized biomass 100% 40,253 $17.11 ($0.08) ($21.66) ($19.00) ($10.27) $54 $47 $26 $89 TOP 40,428 $1.30 $4.96 ($31.52) ($28.84) ($20.08) $78 $71 $50 $130 Biomass Boiler 281,753 $178.85 ($1.37) ($223.04) ($204.38) ($143.33) $79 $73 $51 $132 CTO 37,416 $1.30 $5.25 ($33.30) ($30.82) ($22.71) $89 $82 $61 $148 Turpentine 10% 2,935 $1.30 $0.95 ($7.38) ($7.18) ($6.55) $251 $245 $223 $418 Methanol 10% 2,961 $0.52 $1.22 ($8.01) ($7.81) ($7.17) $270 $264 $242 $449 Lignin 50% 25,250 $17.43 $7.90 ($70.06) ($68.39) ($62.91) $277 $271 $249 $461 Biomass gasification 38,727 $61.86 $10.88 ($145.49) ($142.92) ($134.53) $376 $369 $347 $624 Pulverized biomass +biomass boiler 322,005 $195.96 ($1.44) ($244.70) ($223.38) ($153.61) $76 $69 $48 $116 Note: The NPV and the CAC were estimated assuming three prices for the carbon offsets: $0, $11, and $47 dollars for ton of CO2-eq (Bloomberg Finance 2022) PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 7818 Under this approach considering only scope 1 and 2, some lime kiln fuels have a CO2-eq reduction ranging between 10.6 to 11.6%, including pulverized biomass, biomass gasification, CTO, and TOP (Table 3). However, pulverized biomass represents a low capital investment compared to biomass gasification and a low operating and maintenance cost compared with CTO and TOP; leading to a low NPV among these alternatives and consequently a low CAC (Table 5). A B Fig. 3. Marginal abatement cost curve for alternatives to reduce the GHG emissions in the production of linerboard: a) CO2 avoided based on scope 1 and 2, b) CO2 avoided based on scope 1, 2, and 3. The production rate for the mill is 2,177 tons per day. PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 7819 For CTO, the onsite CTO production is used to cover the energy demand in the lime kiln. The revenue lost by burning this biofuel instead of selling it as a coproduct is considered an operating cost in the analysis, which increases the NPV and consequently the CAC of this alternative. In contrast, for the TOP scenario, the CTO is sold to the market while the TOP demanded in the lime kiln is purchased at the same CTO price. The CTO lime kiln demand is 22,733 tons CTO/ year, while the TOP demand is 21,993 tons TOP/per year, which represents a higher operating cost for CTO and therefore a higher CAC than TOP. This result is reasonable given the price tendencies that CTO and TOP have shown in recent years (Niemeläinen 2018). Regarding lignin combustion, the negative NPV is three times the value of the pulverized biomass negative NPV (Table 5); with lignin combustion having only a 7.3% reduction in emissions Scope 1 and 2 relative to the base case (Table 3), making this biofuel the less cost effective among the co-products. In contrast, the combustion of turpentine and methanol represents a low capital investment, given the few adaptations required in the lime kiln. Nonetheless, the high price in the market for these alternative fuels ($750/ton and $350/ton, respectively), and the low reduction in the GHG emissions makes the CAC higher compared to other alternatives with a high capital investment. For alternative lime kiln fuels, the MACC shows that pulverized biomass is the most cost-effective alternative fuel, followed by TOP, CTO, turpentine 10%, methanol 10%, lignin 50%, and biomass gasification. This last alternative has a high demand for biomass, increasing the capacity required for biomass processing and drying, plus the gasifier. These components increase the capital investment resulting in a CAC superior among all the lime kiln alternatives. Regarding the installation of the biomass boiler (working with an existing turbine), this alternative implies a high capital investment ($179 million) and operating and maintenance costs; however, it offers the maximum reductions (81.5%) with a relatively low CAC of $79/ ton of CO2 avoided. Considering implementing both the pulverized biomass system in the lime kiln plus the installation of the biomass boiler, the total GHG emissions avoided per year are 322,006 tons of CO2-eq per year, with a cost of US $76 per ton. MACC-Emissions Scope 1, 2, and 3 The total avoided emissions are reduced when Scope 3 emissions are considered along with Scope 1 and 2 for each alternative, increasing the CAC (Fig. 3b). This change is largest for biomass gasification and lignin. For biomass gasification, the CAC is more than doubled by the indirect emission from the biomass demand and other raw materials required in the gasification system. For lignin extraction, the CAC is 5.7 times higher by the indirect emissions associated with chemicals, including sodium hydroxide, sulfuric acid, and carbon dioxide. In addition, under this approach the CAC ranking changes, being more favorable for CTO than for TOP; this change is derived from the indirect emissions from CTO distillation into derived products, including TOP. The MACC in this approach shows that the most cost-effective alternative lime kiln fuel is still pulverized biomass, followed by CTO, TOP, turpentine 10%, methanol 10%, biomass gasification, and lignin 50%. It is worth noting that the total GHG emissions avoided per year by implementing both the pulverized biomass plus implementing the biomass boiler at the same time are 315,863 tons of CO2 per year, given a CAC of US $77/ton, which is only one dollar above the CAC when Scope 1 and 2 emissions are considered. PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 7820 Given that none of the alternatives offer a cost saving, the CAC analysis was performed assuming a revenue from the avoided CO2-eq emissions. In this analysis only emissions in Scope 1 and 2 are considered, also two prices are assumed for the avoided emissions: a carbon offset price of $11 per ton of CO2-eq avoided, a price expected by 2030 under the current conditions of the market, and a price of $47 per ton of CO2-eq avoided, the expected value by 2050. These prices are values for alternatives that avoid emissions rather than removing them (Bloomberg Finance 2022). The NPV and the CAC for each offset price is shown in Table 5. For the $11 and $47 offset prices, none of the alternatives showed a negative CAC; indicating that the alternatives represent a cost for the mill for the projected offset prices. Therefore, the minimum offset price in the market was calculated to obtain a NPV equal to zero (last column in Table 5). This minimum offset price was compared with the off-set prices assumed ($11 and $47/ton CO2-eq), and also with the offset prices of alternatives that store or sequester carbon, in this case $224/ton by 2029 and $120/ton by 2050 (Bloomberg Finance 2022). As shown in Table 5, the minimum offset prices are above $11 and $47/ton of CO2- eq, the expected prices for alternatives that avoid carbon. Compared to the alternatives that store or sequester carbon, all the alternatives have a price above $224/ ton, except for pulverized biomass, TOP, and biomass boiler. However, by 2050, technologies such as direct air capture will become more widely adopted, reducing the price to $120/ton, a price lower than the minimum offset value of most of the alternatives considered in this study. The only alternative that may compete with direct air carbon capture technology is pulverized biomass, with an offset price of $89/ton of CO2-eq avoided (Table 5). CONCLUSIONS The U.S. pulp and paper industry is largely dependent on fossil fuels, with lime kiln operations representing a key challenge in achieving zero on-site fossil emissions. This study evaluates the GHG reduction potential and associated costs of alternative fuels for lime kiln operations in linerboard production, and the replacement of natural gas to cover the electricity and steam demand in the process. The alternative fuels for the lime kiln include external biomass and coproducts generated from mill operations. For this pulp grade, 2,789 kg of CO2-eq are emitted per ton of product, from which 1,924 kg corresponds to biogenic CO2 (69%), and 854 kg (31%) corresponds to fossil CO2- eq. Two major contributions to GWP are the natural gas boiler and the lime kiln. In this study, the replacement of the natural gas boiler by a biomass boiler represents a 41% reduction in the GWP, and fuel switching natural gas in the limekiln by biofuels achieves a 5.5% reduction. The cost of the avoided carbon (CAC) was determined as 54 to 1600 $/ton CO2-eq for different alternative lime kiln fuels and the biomass boiler. Replacement of natural gas by biomass either in the lime kiln or the boiler has similar and very low CAC, 54 and 79 $ /ton CO2 avoided, respectively. The use of mill coproducts (turpentine/CTO// methanol/lignin) represent a higher CAC because of the high price of these coproducts in the market. In constructing the marginal abatement cost curve to categorize the alternatives, Scopes 1, 2, and 3 emissions were considered, rather than only direct Scope 1 and 2 emissions. Some indirect emissions (Scope 3) can significantly increase the cost of PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 7821 abatement. For example, in the case of biomass gasification and lignin as alternative fuels for lime kiln operations, the abatement cost is 2 and 5.5 times higher, respectively, compared to considering only Scope 1 and 2 emissions. Finally, implementing the biomass boiler along with the pulverized biomass in the lime kiln represents a reduction of 93.1% in emissions Scope 1 and 2 (81.5% and 11.6%, respectively). These two technologies represent a total CAC of $76/ ton of CO2-eq avoided. The CAC can be further reduced if the mill gets a revenue from the CO2 avoided. For instance, assuming a selling price of $11 and $47 per ton of CO2-eq avoided, the total CAC is $69 and $48/ton of CO2-eq avoided, respectively. ACKNOWLEDGMENTS The authors thank the Fulbright Program and the Colombian Institute of Educational Credit and Technical Studies Abroad (ICETEX) for providing the funding for Buitrago-Tello’s doctoral studies under the “Fulbright-Pasaporte a la Ciencia” fellowship program. Support by the Forest Biomaterials of NCSU is also appreciated. REFERENCES CITED Bajpai, P. (2018). “Forest biorefinery,” in: Biermann’s Handbook of Pulp and Paper, Elsevier, Amsterdam, Netherlands, pp. 603-617. DOI: 10.1016/b978-0-12-814240- 0.00025-2 Berglin, N., and Von, A. S. (2022). Biofuels in Lime Kilns. Operating Experience in the Nordic Pulp and Paper Industry (Report No. 2022:847), Energiforsk, Stokolm, Sweden. Buitrago-Tello, R., Venditti, R. A., Jameel, H., Yao, Y., and Echeverria, D. (2022). “Carbon footprint of bleached softwood fluff pulp: Detailed process simulation and environmental life cycle assessment to understand carbon emissions,” ACS Sustainable Chemistry & Engineering 10(28), 9029-9040. DOI: 10.1021/acssuschemeng.2c00840 Echeverria, D., Venditti, R. A., Jameel, H., and Yao, Y. (2021). “Process simulation- based life cycle assessment of dissolving pulps,” Environmental Science & Technology 56(7), 4578-4586. DOI: 10.1021/acs.est.1c06523 Elhardt, M. (2017). “Analyzing the North American corrugated market with Fisher SolveTM,” (https://www.fisheri.com/whitepapers/analyzing-the-north-american- corrugated-market), Accessed 14 Aug 2023. EPA (2021). “Greenhouse gas reporting program (GHGRP) - Pulp and paper,” (https://www.epa.gov/ghgreporting/ghgrp-pulp-and-paper), Accessed 25 July 2023. Fastmarkets (2023). “RISI Mill asset database,” (https://www.risiinfo.com/), Accessed 02 Feb 2023. Francey, S. (2009). Impacts of Burning Alternative Fuels in Lime Kilns at Kraft Pulp Mills, Master’s Thesis, University of Toronto, Toronto, Canada. Francey, S., Tran H., and Jones A. (2009). “Current status of alternative fuel use in lime kilns,” Tappi Journal 8(10), 33-39. DOI: 10.32964/TJ8.10.33 PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 7822 Grace, T. M., Malcolm, E. W., and Kocurek, M. J. (1983). “Pulp and paper manufacture: Alkaline pulping,” in: Technical Section Canadian Pulp and Paper Association, Atlanta, GA, USA. Hart, P. W. (2020a). “Alternative ‘green’ lime kiln fuels: Part II—Woody biomass, bio- oils, gasification, and hydrogen,” TAPPI Journal 19(5), 271-279. DOI: 10.32964/TJ19.5.271 Hart, P. W. (2020b). “Alternative ‘green’ lime kiln fuels: Part I—pulping/recovery byproducts,” TAPPI Journal 19(5), 263–69. DOI: 10.32964/TJ19.5.263 Henze, V. (2022). “Carbon offset prices could increase fifty-fold by 2050,” (https://about.bnef.com/blog/carbon-offset-prices-could-increase-fifty-fold-by-2050/), Accessed 12 Dec 2023. Huang, Y. H., and Jung, H. W. (2021). “Bottom-up analysis of energy efficiency improvement and co2 emission reduction potentials in the cement industry for energy transition: An application of extended marginal abatement cost curves,” Journal of Cleaner Production 296, article ID 126619. DOI: 10.1016/j.jclepro.2021.126619 IEA (2022). “Tracking industry,” (https://www.iea.org/energy-system/industry), Accessed 24 Sept 2022. Kerry, J., and McCarthy, G. (2021). The Long-Term Strategy of the United States: Pathways to Net-Zero Greenhouse Gas Emissions by 2050, The United States Department of State and the United States Executive Office of the President: Washington, D.C., USA. Kuparinen, K., and Vakkilainen, E. (2017). "Green pulp mill: Renewable alternatives to fossil fuels in lime kiln operations," BioResources 12(2), 4031-4048. DOI: 10.15376/biores.12.2.4031-4048 Kuparinen, K., Vakkilainen, E., and Hamaguchi, M. (2017). “Analysis on fossil fuel-free operation in a northern pulp and paper mill,” in: Proceedings International Chemical Recovery Conference, Halifax, Nova Scotia, Canada. Kuparinen, K., Vakkilainen, E., and Kärki, J. (2016). “Electrolysis and biomass conversion as options to produce renewable alternatives for fossil lime kiln fuels,” in: Pulping, Engineering, Environmental, Recycling, Sustainability Conference 2016, PEERS 2016, 1(1), TAPPI Press, Atlanta, GA, USA, pp. 502–509. Lundqvist, P. (2009). Mass and Energy Balances over the Lime Kiln in a Kraft Pulp Mill, Master’s Thesis, Uppsala University, Stockholm, Sweden. Manning, R., and Tran, H. (2015). “Impact of cofiring biofuels and fossil fuels on lime kiln operation,” Tappi Journal 14(7), 474-480. DOI: 10.32964/TJ14.7.474 Niemeläinen, M. (2018). Tall Oil Depitching In Kraft Pulp Mill, Master’s Thesis, Aalto University, Espoo, Finland. ResourceWise (2023). “FisherSolve Database,” (https://www.resourcewise.com/platforms/fishersolve#), Accessed 14 Feb 2023. Rofouieeraghi, P. (2012). Biomass Gasification Integrated into a Reference Canadian Kraft Mill, Master’s Thesis, Université de Montréal, Montreal, Canada. Rydholm, S. A. (1967). Pulping Processes, Interscience Publishers, New York, NY, USA. Taillon, J., Horvath, A., and Oksman, A. (2018). “Replacement of fossil fuel with biomass in pulp mill lime kilns,” O Papel 79(3), 85-89. Tomberlin, K. E., Venditti, R., and Yao, Y. (2020). “Life cycle carbon footprint analysis of pulp and paper grades in the united states using production-line-based data and integration,” BioResources 15(2), 3899–3914. DOI: 10.15376/biores.15.2.3899-3914 PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 7823 Tran, H. (2007). “Lime kiln chemistry and effects on kiln operations,” TAPPI Kraft Recovery Course, Atlanta, GA, USA. Valmet (2015). “WinGEMS® – General energy and material balance system for Windows, Version 5.4,” (https://www.valmet.com/automation/applications/process- optimization/pulp/wingems/), Accessed 02 Feb 2023. Wernet, G., Bauer, C., Steubing, B., Reinhard, J., Moreno-Ruiz, E., and Weidema, B. (2016). “The Ecoinvent Database version 3 (part I): Overview and methodology,” International Journal of Life Cycle Assessment 21(9), 1218–30. DOI: 10.1007/s11367-016-1087-8 Article submitted: November 29, 2023; Peer review completed: July 10, 2024; Revised version received and accepted: August 20, 2024; Published: August 30, 2024. DOI: 10.15376/biores.19.4.7806-7823 https://www.valmet.com/automation/applications/process-optimization/pulp/wingems/ https://www.valmet.com/automation/applications/process-optimization/pulp/wingems/ PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 1 SUPPLEMENTARY INFORMATION Buitrago-Tello, R., Venditti, R. A., Jameel, H., Hart, P. W., and Ghosh, A. (2024). "Carbon footprint and techno-economic analysis to decarbonize the production of linerboard via fuel switching in the lime kiln and boiler: Development of a marginal abatement cost curve," BioResources 19(4), 7806–7823. TABLE OF CONTENTS INTRODUCTION 2 LINEBOARD PRODUCTION PARAMETERS 2 Woodyard 2 Digester 2 Multiple effect evaporator 4 Condensate stripper 4 Recovery, biomass, and natural gas boiler 5 Back-pressure and condensing turbine 6 Causticizing plant 7 Lime kiln model 8 Paper machine 10 ELECTRICITY DEMAND 11 LIFE CYCLE INVENTORY AND GWP 11 MARGINAL ABATEMENT COST CURVE 23 Capital Investment 23 Direct cost structure 25 Sensitivity Analysis 26 PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 2 INTRODUCTION The present document compiles the assumptions included in the process simulation for producing linerboard using a continuous kraft pulping process, and the information used to estimate the GWP and the Marginal Abatement Cost Curve LINEBOARD PRODUCTION PARAMETERS Woodyard The model includes the mass balance for the woodyard, including a debarker, chipper, and a chip screen (Fig. S1). The assumptions are included in Table S1: Table S1. Main Assumptions for the Woodyard (Hart 2022; Fisher International Inc, n.d.) Chips demand Chips from roundwood - purchased wood chips ratio = 1:1 Biomass moisture content: 50% Temperature: 20 °C Debarker yield Softwood roundwood yield: 90% Bark free roundwood + 10% Bark Chipper and screen yield Chips yield: 95.5% Chips to pulping + 4.5 % Hog fuel Fig. S1. Woodyard operations Digester Table S2 includes the assumptions for the continuous digester. The flashed steam from the weak black liquor is used to pre-steam the chips; the excess steam is sent to a condenser to extract turpentine (Fig. S2). After cooking, the pulp is washed using the stripped condensate from the weak black liquor evaporator and fresh water. PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 3 Table S2. Assumptions for the Pulping Area (Grace, Malcolm, and Kocurek 1983; Hart 2022) Presteaming Turpentine Formed = 0.9 gal / Ton pulp = 3.7 kg/ton pulp White Liquor charge Active alkaline on wood: 0.15 as NaOH Active alkaline concentration: 105 g/l as NaOH Sulfidity, on AA basis: 25% Reduction efficiency: 95% Causticizing efficiency: 82% Digester conditions Liquor to wood ratio = 3:1 Temperature: 160°C Yield: 56% Pulp Kappa: 110 (%lignin = 0.15 * kappa) Pulp composition: Cellulose: 68.5%, Lignin: 16.5%, Hemicellulose: 15% Fibrilizer & Refining Input pulp consistency: 6% Screener Input pulp consistency: 1%, Rejects are returned to fibrilizer (2% rejection , 35% consistency) 3 washing stages Washing using stripped condensate Pulp consistency: 10% Efficiency Factor: 2 Outlet pulp consistency: 14% Fig. S2. Continuous digester and washers PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 4 Multiple effect evaporator A counter-current six-effect evaporator concentrates the weak black liquor to 55% solids; the heat transfer area and the outlet vapor temperature are assumed on each body. After the evaporator, the black liquor is sent to a concentrator to increase the solids content to 69%; the concentrator assumptions are shown in Table 3. The black liquor is concentrated in a six-effect evaporator. The first body uses low- pressure steam to concentrate the liquor, and the clean condensate from this body is returned to the power plant. The rest of the bodies use the steam from the black liquor evaporation; the foul condensate from the bodies is sent to a stripping column. This column reduces the COD and separates methanol; the stripped condensate is used to wash the pulp in the washers (Fig. S2). Additionally, soap is extracted after the third body and is treated with sulfuric acid to produce crude tall oil; the yield of this reaction is 85% (Evdokimov et al. 2017). Table S3. Concentrator Assumptions (Hart 2022) Concentrator 69% solids content Condensate temperature: 85 °C Liquor temperature: 115 °C Steam economy: 1.8 Fig. 3. Multiple-effect evaporator configuration Condensate stripper The fouling condensate from the evaporator and concentrator are steam stripped to extract the methanol and recirculate the condensate to wash the pulp. Table S4. Condensate Stripper Assumptions (Valmet 2015) Outlet stripped condensate 125 °C Overhead vapor temperature 112 °C Feed-to-steam ratio 5 %Methanol stripping 5 lb /Ton of pulp = 2.5 kg / ton of pulp PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 5 Recovery, biomass, and natural gas boiler The heat and power demand are covered by burning the concentrated black liquor in the recovery boiler, burning the hog fuel from the woodyard and external hog fuel in a biomass boiler, and external natural gas in a natural gas boiler. The external hog fuel demand is controlled by setting the steam production at the hog fuel boiler at 10,000 lb of steam /hour.1 Tables S4 to S6 show the main assumptions included in these boilers (Hart 2022; Fisher International Inc, n.d.; Valmet 2015; Grace, Malcolm, and Kocurek 1983). Table S5. Recovery Boiler Assumptions Excess air (%) 0.15 Fraction of the total chloride entering in the liquor which leaves in stack gas as NaCl 0.06 Loading factor 1* Dregs per solids entering furnace 5 High heating value (HHV) 5200 Btu /lb Reduction fraction 0.9 Smelt temperature 750 °C Gas temperature 250 °C (Efficiency = 67%) Pressure 850 psi Temperature 850 F Blowdown 5% * The nominal loading is 500 kg of dry solids / m2 / hr. The loading factor is the fraction of the nominal loading Table S6. Hog Fuel Boiler Assumptions Moisture in fuel 50% Excess air 10% Hog fuel composition (default value) Carbon: 51.5 %, Hydrogen: 6.1%, Oxygen: 41.1%, Nitrogen:0.1%, Sulfur:0.1%, Inerts: 1.1% High heating value (HHV) 4900 Mcal /mt Outlet gas temperature 176.7°C (efficiency 72.6%) External hog fuel demand Controlled by setting the steam flow at 150,000 lb/h Temperature 825 F Pressure 850 psi Blowdown 2% Table S7. Natural Gas Boiler Assumptions Excess air 10% Natural Gas composition Carbon: 74.8%, Hydrogen: 25.2% High heating value (HHV) 13283.6 Mcal /mt Combustion efficiency 85% PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 6 Natural gas demand Controlled by setting the condensing turbine condensate at 10,000 lb/h Temperature 825 F Pressure 850 psi Blowdown 2% Back-pressure and condensing turbine The model includes a back-pressure and a condensing turbine to generate electricity; the assumptions are included in Tables S8 and S9. The system has a sootblow of 1.5% of the total high-pressure steam. The rest of the high-pressure steam is distributed equally between the two turbines and is expanded to 160 psi. 50% of the mill’s medium- pressure steam demand is extracted from the back-pressure turbine and 50% from the condensing turbine. After the first extraction, the remaining steam is expanded to 60 psi; the low- pressure steam demand is controlled by the second extraction in the condensing turbine. In addition, the natural gas demand is controlled by setting the condensate flow in the condensing turbine as 10,000 lb/h. Table S8. Back-Pressure Turbine Assumptions First stage 160 psi, adiabatic efficiency 70% Extraction 50% of the medium-pressure steam demand Second stage 60 psi, adiabatic efficiency 70% Table S9. Condensing Turbine Assumptions First stage 160 psi, adiabatic efficiency 70% First extraction 50% of the medium-pressure steam demand Second stage 60 psi, adiabatic efficiency 70% Second extraction Controlled by the low-pressure steam demand Third stage 20 psi, adiabatic efficiency 70% Steam to condenser 10,000 lb/h PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 7 Fig. S3. Back-pressure and condensing turbine Causticizing plant The causticizing plant includes a smelt dissolving tank, a green liquor clarifier, the wash and extraction of dregs, the slaking and causticizing units, a white liquor clarifier, a mud washer and filter, a lime kiln, a lime kiln scrubber. The causticizing plant has a controller for the make-up sodium hydroxide and sodium sulfate demand, depending on the active alkaline and sulfidity set in the digester. Table S10 shows the assumptions for the different unit operations that compose the causticizing plant. Table S10. Causticizing Plant Assumptions Smelt dissolving tank Intermediate smelt temperature = 250 °C T = 12*(TGL) - 11*(TWL) where: TGL = temperature of green liquor (measured in the mill) TWL = temperature of weak liquor (measured in the mill) Green Liquor Clarifier Suspended solids in clarified liquor: 20ppm Underflow: 25% consistency Dreg washer Efficiency Factor (E) = 3, Consistency of outlet solids = 50% Slaking and causticizing ▪ Make-up with CaO ▪ Lime charge = 0.82, mole [CaO + Ca(OH)2]/mole CO3 in green liquor ▪ Fraction of CaSO4 dissolved, Default = 1 ▪ "A" in the formula, Density = 1 + (TDS as a fraction)*A (Default = 0.712) ▪ Pressure in slaker and causticizer(s) (Default = 760 mm Hg) ▪ Volume of vessel 1,2, and 3 (or residence time) = 50 min ▪ Rate constant for slaking at 95°C (suggested value: 0.18 minute-1) (Activation energy of 11.2 kcal/mole assumed) ▪ Rate constant for causticizing at 95°C (suggested value: 1.9 liters/mole minute) (Activation energy of 11.2 kcal/mole assumed) Grits loss 0.1% liquor loss, 0.5% solids loss White Liquor Clarifier Suspended solids in clarified liquor: 100ppm, Underflow: 25% consistency Mud Washer Mud loss: 10%, Suspended solids in clarified liquor: 15ppm, Underflow: 40% consistency (mud) PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 8 Mud Filter Input consistency: 25%, Efficiency Factor (E): 2, Consistency of outlet solids: 80% Kiln Scrubber ▪ Na2SO4 dust removal efficiency: 99% ▪ Na2CO3 dust removal efficiency: 99% ▪ NaCl dust removal efficiency: 99% ▪ Water demand: Controlled to adjust TTA white liquor to 113 Fig. S4. Causticizing plant Lime kiln model The causticizing plant includes a lime kiln simulation model that determines the mass and energy balance of drying and calcinating the lime mud. This balance is used to estimate the natural gas demand and the alternative fuels demand for the scenarios proposed in the present study. The model includes different reactions to estimate the mass balance: a) The carbonation of the Ca(OH)2 remaining in the lime mud, which is a small fraction of the suspended solids (~0.03) 𝐶𝑎(𝑂𝐻)2(𝑎𝑞) + 𝐶𝑂2(𝑔) → CaCO3(𝑠) + H2O(𝑙) PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 9 b) The reaction of water-soluble sodium from the white liquor with CO2 to form Na2CO3 2𝑁𝑎(𝑂𝐻)(𝑠, 𝑙) + 𝐶𝑂2(𝑔) → Na2CO3(𝑠) + H2O(𝑔) c) The formation of CaSO4 by the presence of sulfur in the system 𝐶𝑎𝐶𝑂3 + 𝑁𝑎2𝑆𝑂4 → CaSO4 + Na2CO3 2𝐶𝑎𝑂 + 2𝑆𝑂2 + 𝑂2 → 2 CaSO4 d) And the calcination of CaCO3 𝐶𝑎𝐶𝑂3 → 𝐶𝑎𝑂 + CO2 The energy balance is determined based on the sensible heat from the mud’s initial temperature to 100°C, the energy required to dry the mud, the sensible heat from 100°C to 800°C, and the energy demand from the calcination. The sensible heat corresponds to the change in the enthalpy of the primary mud components (CaCO3, water, and CaO) using equation S1.(Lundqvist 2009) The mud’s drying energy demand is determined assuming a heat of evaporation of 2257 kJ/kg of water evaporated.(Lundqvist 2009) The energy required for calcination is based on the heat of reaction (42657.9 kcal/kmol).(Lundqvist 2009) ∆𝐻 = (𝑎0(𝑇2 − 𝑇1) + 𝑎1 2 (𝑇2 2 − 𝑇1 2) + 𝑎2 3 (𝑇2 3 − 𝑇1 3) + 𝑎3(ln(𝑇2) − ln(𝑇1)) − 𝑎4(𝑇2 −1 − 𝑇1 −1)) 𝐸𝑞. 𝑆1 The values for the coefficient of the equation are in Table S11 (Lundqvist 2009). Table S11. Heat Capacity Coefficients for Different Compounds Component a0 a1 a2 a3 a4 CaO 0.949 3.71 1.01 -27 -10574 CaCO3 1.009 25.36 0.64 -4.7 -20965 H2O(l) 4.03 487 0 0 0 The fuel demand is determined based on the energy required for heating, drying, and calcinating the mud. The model includes three combustion blocks (Fig. S5), one for the natural gas feed, a second block for the alternative fuel (pulverized biomass, syngas, crude tall oil, etc.), and a third block in case the user wants to include an additional fuel for instance non-condensable gases (NCG). On each block, the user defines the moisture content, the high heating value, the composition (carbon, hydrogen, oxygen, nitrogen, sulfur, and inerts fraction), the exit gas temperature, and the heat loss. The fuel demand is determined based on the energy required to heat, dry, and calcinate the lime mud. The evaporated water and the biogenic CO2 from the CaCO3 are mixed with the flue gases. Whereas the oxygen and SO2 to form CaSO4 are extracted. Table 10 summarizes the restrictions assumed in the lime kiln model. PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 10 Table S12. Lime kiln Model Assumptions Limekiln ▪ Fraction excess air, typically 0.10 ▪ Exit lime temperature, 800 °C ▪ Exit gas temperature, 150 °C ▪ Heat loss due to convection, 0.10 fraction ▪ Percent availability of output lime, 85% ▪ Weight fraction of total input Ca (mud and makeup) converted to CaSO4, if sufficient sulfur is available. 0.06 ▪ Fraction of incoming suspended solids in dust leaving the kiln, by weight. 0.1 ▪ Fraction of incoming Na vaporized, by weight, 0.5 Fig. S5. Lime kiln model Paper machine In the paper machine, the pulp is diluted to a 3% consistency before going to a tickler refiner/beater where 0.15% of the incoming fiber is lost; then, the pulp is sent to a primary and secondary cleaner to eliminate any undesirable material in the headbox. Next, the fibers are suspended in water to a 0.5% consistency and then sprayed in the headbox over the wire to orientate the fibers. Then the water is drained by gravity in the table rolls and by vacuum in suction boxes, couch, and trim to a 16% consistency. Finally, the sheet is pressed and dried to a final consistency of 90%. The pulp drier consumes low and medium-pressure steam in two sections: the seal pit that keeps water at 50°C using low- pressure steam, and the drying section that uses medium-pressure steam to evaporate the water in the pulp to the desired moisture content; a steam economy factor of 1.4 is assumed for this section. PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 11 ELECTRICITY DEMAND The electricity demand was determined based on factors reported in the literature (Nilsson et al. 1995; Martin et al. 2000). Table 12. Electricity Demand Per Area Area or Unit Operation (kWh/ADt) Raw Materials Preparation Debarking 20 Chipping and conveyors 63 Pulping Digester 43 Washing and Screening 103 Screening and storage 74 Chemical recovery Black liquor concentration 66 Causticizing & lime kiln 42 Powerhouse 125 Wastewater treatment 35 Other 15 Papermaking Forming and pressing 238 Drying section 21 TOTAL 845 LIFE CYCLE INVENTORY AND GWP The net GWP for the scenarios under study were determined based on the inputs and outputs from the mass and energy balance (Table S13) the mass allocation factors for each scenario (Table S14) and the GWP of the upstream processes and waste treatment (Table S15). The GWP for each scenario was determined according to the following equation: GWP𝑠𝑐𝑒𝑛𝑎𝑟𝑖𝑜 = 𝐿𝐵𝑀𝐴𝐹𝑠𝑐𝑒𝑛𝑎𝑟𝑖𝑜 ∗ (𝑂𝑛𝑠𝑖𝑡𝑒 𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛𝑠𝑠𝑐𝑒𝑛𝑎𝑟𝑖𝑜 + ∑ 𝐹𝑙𝑜𝑤𝑖,𝑠𝑐𝑒𝑛𝑎𝑟𝑖𝑜 ∗ 𝐺𝑊𝑃𝑖) LBMAF = Linerboard mass allocation factor i = upstream process or waste generated in the system The GWP for each upstream process and waste treatment was determined by transforming the Ecoinvent database life cycle inventory an data reported in the literature into CO2-eq emissions through the method IPCC 2013 GWP 100-years included in OpenLCA 1.10.2.(“OpenLCA,” n.d.) The GWP for the scenarios considered are shown in Table S16. PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 12 ALTERNATIVE SCENARIOS Biomass Boiler In this scenario, it is assumed that the natural gas boiler is replaced by a biomass boiler that burns the internal hog fuel from the wood yard and external biomass to cover the steam demand in the mill, and the production level remains the same. It is also assumed that the back-pressure and the condensing turbine do not require any modification. External bio-based fuels This group includes external bio-based fuels that can cover the total energy demand in the lime kiln. In the case of pulverized biomass, the system includes a biomass dryer and a hammer mill with an electricity demand of 4.4 kWh/ton of water evaporated (Rofouieeraghi 2012) and 48.5 kWh/t of wood processed, respectively.(Wind et al. 2018) The external biomass is dried from 50% to 5% moisture content using the flue gasses from the recovery boiler as the heat source.(Hart 2020) The high heating value assumed for the pulverized biomass is 20.5 MJ/kg.(Valmet 2015) The lime kiln can be operated at different feed levels (Manning and Tran 2015), the present study assumes a 25, 50, and 100% displacement of natural gas. Regarding the gasification system, this scenario includes a biomass dryer and a circulating fluidized bed (CFB) gasifier; the biomass is first dried to a 10% moisture content using the flue gasses from the recovery boiler as a heat source; the electricity demand factor is the same as for the previous scenario. The CFB gasifier's production ratio is 0.9 kg syngas/ kg dry biomass. (Rofouieeraghi 2012) The rest of the life cycle inventory as the electricity demand and other raw materials were adapted from the process available in the Ecoinvent database defined as "synthetic gas production, from wood, at fluidized bed gasifier-Rest of the world."(Wernet et al. 2016) For the TOP scenario, the on-site CTO is sold and upgraded by distillation into different fractions, including tall oil fatty acids (38%), tall oil rosins (34%), distilled tall oil and heads (12%) and tall oil pitch (16%).(Aryan and Kraft 2021) The production of 1 ton of all these co-products is equivalent to 402 kg CO2;(Cashman, Moran, and Gaglione 2016) therefore, it is assumed TOP on-site emissions are equivalent 64.1kg CO2/ton, whereas the indirect emissions from CTO are based on the base case. The TOP is bought and transported to the mill to cover 25, 50, and 100% of the lime kiln energy demand. Bio-based Products or Bio-based Streams Available in the Mill This group includes the streams that are available in the mill (methanol, turpentine, CTO) and the extraction of lignin, which is a potential co-product in the production of kraft pulp.(Tomani 2010) In the case of CTO, the on-site CTO production is enough to supply 40% of the lime kiln energy demand. Therefore, for the scenario where CTO covers 25% of the lime kiln demand, the fraction sold to the market is lower compared to the base case, changing the mass allocation factors (see table S14). For the 50% and 100% scenarios, the CTO demand in the lime kiln is covered by the on-site CTO and external CTO. In these two scenarios, the GWP is mass allocated between the remaining products (linerboard, PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 13 turpentine, and methanol), and the GWP for the external CTO is based on the results from the base case. Similarly, in the scenario Turpentine-10%, the on-site production is enough to cover 14% of the lime kiln energy demand, therefore the amount sold is lower compared to the base case, changing the mass allocation factors. In the case of methanol-10%, the onsite production covers 4.3% of the lime kiln energy demand, therefore, the remaining fraction is covered by external methanol, and the emissions are mass allocated between linerboard, turpentine, and crude tall oil. The GWP associated to the external methanol is based on the emissions allocated to the production of methanol in the base case. In the lignin scenario, a fraction of the black liquor with a 36% solid content is extracted from the evaporator system. Then, the liquor is sent to a Lignoboost plant, where lignin is precipitated by reducing the pH with CO2 and sulfuric acid.(Fredrik Öhman et al. 2013) The precipitated lignin is filtered, the filtrate is returned to the evaporator system, and the lignin with a 70% moisture content is dried to a 4% moisture content in a dryer that uses the flue gas from the recovery boiler.(Tomani 2010) Although the lime kiln can be operated with 100% lignin, the extraction of black liquor is limited to a level that lignin covers a maximum of 50% of the total lime kiln demand; this is to avoid an excess demand in the biomass boiler, which replaces the energy content of the extracted liquor. Other fossil-based fuels Natural gas is the predominant lime kiln fuel in the US and Canada, however there are other alternative fossil fuels in lime kiln operations. For instance one third of the kilns in the United States and Canada burns fuel oil.(Francey, Tran, and Jones 2009) Additionally, petcoke is an alternative fossil fuel used in 20 US lime kilns and replaces 25% to 85% of traditional fuel.(Francey, Tran, and Jones 2009) Tire-derived fuel has been also tested in lime kiln operation, replacing 15% of the natural gas demand (Hart, Hanson III Glenn M., and Manning 2021). PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 14 Table S13. Life Cycle Inventory for the Scenarios Analyzed in the Present Study Inputs mt/ adt linerboard Nat gas Biomass boiler Syngas Pulverized biomass Tall Oil Pitch 25% 50% 100% 25% 50% 100% Pulp Biomass Logs (50% moisture) 2.33 2.33 2.33 2.33 2.33 2.33 2.33 2.33 2.33 Chips 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 2.10 Chemicals NaOH makeup 6.86*10-03 6.86*10-03 6.85*10-03 6.88*10-03 6.92*10-03 6.97*10-03 6.89*10-03 6.92*10-03 6.99*10-03 Na2SO4 makeup 5.37*10-03 5.37*10-03 5.37*10-03 5.31*10-03 5.26*10-03 5.14*10-03 5.32*10-03 5.26*10-03 5.14*10-03 CaO makeup 2.03*10-02 2.03*10-02 2.03*10-02 2.02*10-02 2.01*10-02 2.03*10-02 2.03*10-02 2.03*10-02 2.03*10-02 H2SO4 3.90*10-03 3.90*10-03 3.90*10-03 3.90*10-03 3.90*10-03 3.90*10-03 3.90*10-03 3.90*10-03 3.90*10-03 Power plant fuels External hog (Power plant) 8.82*10-02 8.03*10-01 8.82*10-02 8.82*10-02 8.82*10-02 8.82*10-02 8.82*10-02 8.82*10-02 8.82*10-02 Natural gas Boiler 1.35*10-01 - 1.35*10-01 1.35*10-01 1.35*10-01 1.35*10-01 1.35*10-01 1.35*10-01 1.35*10-01 Lime kiln fuels Natural Gas Lime kiln 1.98*10-02 1.98*10-02 - 1.49*10-02 9.90*10-03 1.49*10-02 9.90*10-03 Tall Oil Pitch (external) - - - - - - 8.42*10-03 1.47*10-02 2.83*10-02 Methanol - - - - - - - - - Syngas (Internal) - - 1.88*10-01 - - - - - - Biomass (5% mc or 10% mc for syngas) - - 2.31*10-01 1.37*10-02 2.74*10-02 5.48*10-02 - - - Water demand Water-Paper machine 16.20 16.20 16.20 16.20 16.20 16.20 16.20 16.20 16.20 Water - Brownstock washing 5.46 5.46 5.47 5.47 5.47 5.47 5.46 5.47 5.47 Water -Causticizing plant 3.75 3.75 3.75 3.74 3.75 3.75 3.75 3.75 3.75 Water-Power plant 2.92 2.92 2.92 2.92 2.92 2.92 2.92 2.92 2.92 Total Water demand 28.34 28.33 28.34 28.34 28.34 28.34 28.33 28.34 28.34 Electricity from Grid Linerboard mill (MWh/mt pulp) 5.54*10-02 5.61*10-02 5.48*10-02 5.52*10-02 5.48*10-02 5.58*10-02 5.54*10-02 5.51*10-02 5.47*10-02 Alternative fuel (MWh/mt pulp) 6.08*10-03 1.20*10-04 2.40*10-04 4.49*10-04 Outputs Natural gas Biomass boiler Syngas Pulverized biomass Tall Oil Pitch 25% 50% 100% 25% 50% 100% Products Pulp 1 1 1 1 1 1 1 1 1 Turpentine 3.35*10-03 3.35*10-03 3.35*10-03 3.35*10-03 3.35*10-03 3.35*10-03 3.35*10-03 3.35*10-03 3.35*10-03 CTO 1.30*10-02 1.30*10-02 1.30*10-02 1.30*10-02 1.30*10-02 1.30*10-02 1.30*10-02 1.30*10-02 1.30*10-02 Methanol 2.54*10-03 2.54*10-03 2.54*10-03 2.54*10-03 2.54*10-03 2.54*10-03 2.54*10-03 2.54*10-03 2.54*10-03 Emissions Nat gas Biomass boiler Syngas Pulverized biomass Tall Oil Pitch 25% 50% 100% 25% 50% 100% Onsite emissions CO2 Limekiln Total 1.61*10-01 1.61*10-01 2.29*10-01 1.72*10-01 1.83*10-01 2.05*10-01 1.66*10-01 1.72*10-01 1.83*10-01 CO2 Fossil -Lime Kiln 5.44*10-02 5.44*10-02 - 4.08*10-02 2.7162*10-02 - 4.10*10-02 2.80*10-02 CO2 Biogenic -Lime Kiln fuel - - 1.23*10-01 2.46*10-02 4.91*10-02 9.83*10-02 1.90*10-02 3.73*10-02 7.70*10-02 CO2 Biogenic Lime Kiln CaCO3 1.06*10-01 1.06*10-01 1.06*10-01 1.06*10-01 1.06*10-01 1.06*10-01 1.06*10-01 1.06*10-01 1.06*10-01 CO2 Biogenic Recovery Boiler 1.61 1.61 1.61 1.61 1.61 1.61 1.61 1.61 1.61 PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 15 CO2 Biogenic Hogfuel 2.41*10-01 9.16*10-01 2.41*10-01 2.41*10-01 2.41*10-01 2.41*10-01 2.41*10-01 2.41*10-01 2.41*10-01 CO2 Fossil Natural gas 3.70*10-01 - 3.70*10-01 3.70*10-01 3.70*10-01 3.71*10-01 3.70*10-01 3.71*10-01 3.71*10-01 Waste Dregs 1.04*10-02 1.04*10-02 1.04*10-02 1.04*10-02 1.04*10-02 1.04*10-02 1.04*10-02 1.04*10-02 1.04*10-02 Grits 4.94*10-03 4.94*10-03 4.94*10-03 4.93*10-03 4.94*10-03 4.93*10-03 4.94*10-03 4.93*10-03 4.93*10-03 Ashes 1.40*10-03 5.34*10-03 1.40*10-03 1.40*10-03 1.40*10-03 1.40*10-03 1.40*10-03 1.40*10-03 1.40*10-03 Wastewater Wastewater Paper machine 20.22 20.22 20.22 20.22 20.22 20.22 20.22 20.22 20.22 Wastewater Causticizing 6.58*10-01 6.58*10-01 6.57*10-01 6.57*10-01 6.57*10-01 6.57*10-01 6.57*10-01 6.57*10-01 6.57*10-01 Total Wastewater 20.88 20.88 20.88 20.88 20.88 20.88 2.09*10+01 2.09*10+01 2.09*10+01 Sludge 1.01*10-02 1.01*10-02 1.01*10-02 1.01*10-02 1.01*10-02 1.01*10-02 1.01*10-02 1.01*10-02 1.01*10-02 Table S13. Life Cycle Inventory for the Scenarios Analyzed in the Present Study (continued) Input mt/ adt linerboard Turpentine (10%) Methanol (10%) Crude Tall Oil Lignin 25% 50% 100% 25% 50% Pulp Biomass Logs (50% moisture) 2.33 2.33 2.33 2.33 2.33 2.33 2.33 Chips 2.10 2.10 2.10 2.10 2.10 2.10 2.10 Chemicals NaOH makeup 6.86*10-03 6.86*10-03 6.86*10-03 6.86*10-03 6.86*10-03 8.00*10-03 9.13*10-03 Na2SO4 makeup 5.37*10-03 5.37*10-03 5.37*10-03 5.37*10-03 5.37*10-03 3.40*10-03 1.45*10-03 CaO makeup 2.03*10-02 2.03*10-02 2.03*10-02 2.03*10-02 2.03*10-02 2.02*10-02 2.01*10-02 H2SO4 3.90*10-03 3.90*10-03 3.90*10-03 3.90*10-03 3.90*10-03 3.90*10-03 3.90*10-03 Power plant fuels External hog (Power plant) 8.82*10-02 8.82*10-02 8.82*10-02 8.82*10-02 8.82*10-02 8.82*10-02 8.82*10-02 Natural gas Boiler 1.35*10-01 1.35*10-01 1.35*10-01 1.35*10-01 1.35*10-01 1.35*10-01 1.35*10-01 Lime kiln fuels Natural Gas Lime kiln 1.79*10-02 1.79*10-02 1.49*10-02 9.92*10-03 - 1.48*10-02 9.83*10-03 CTO - - - 2.59*10-03 1.63*10-02 - - Methanol - 3.35*10-03 - - - - - Biomass to replace lignin - - - - - 1.60*10-01 1.87*10-01 Lignin extraction CO2 Lignoboost - - - - - 4.93*10-03 9.71*10-03 H2SO4 Lignoboost - - - - - 1.03*10-03 2.06*10-03 Lignin (70%) - - - - - 1.40*10-02 2.79*10-02 Water demand Water-Paper machine 16.20 16.20 16.20 16.20 16.20 16.20 16.20 Water - Brownstock washing 5.46 5.46 5.46 5.46 5.46 5.43 5.40 Water -Causticizing plant 3.75 3.75 3.75 3.75 3.75 3.74 3.74 Water-Power plant 2.92 2.92 2.92 2.92 2.82 4.23 4.22 Water-Lignoboost - - - - - 2.85*10-02 5.67*10-02 Total Water demand 28.33 28.34 28.33 28.34 28.24 29.64 29.62 Electricity from Grid Linerboard mill (MWh/mt pulp) 5.55*10-02 5.56*10-02 5.53*10-02 5.50*10-02 5.44*10-02 3.07*10-02 2.94*10-02 Alternative fuel (MWh/mt pulp) - - - - - 7.69*10-02 1.53*10-02 Outputs Turpentine (10%) Methanol (10%) Crude Tall Oil Lignin PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 16 25% 50% 100% 25% 50% Products Pulp 1 1 1 1 1 1 1 Turpentine mt/mt pulp 9.63*10-04 3.35*10-03 3.35*10-03 3.35*10-03 3.35*10-03 3.35*10-03 3.35*10-03 CTO 1.30*10-02 1.30*10-02 4.24*10-03 - - 1.30*10-02 1.30*10-02 Methanol 2.54*10-03 - 2.54*10-03 2.54*10-03 2.54*10-03 2.54*10-03 2.54*10-03 Emissions Turpentine (10%) Methanol (10%) Crude Tall Oil Lignin 25% 50% 100% 25% 50% Onsite emissions CO2 Limekiln Total 1.63*10-01 1.63*10-01 1.67*10-01 1.73*10-01 1.86*10-01 1.70*10-01 1.79*10-01 CO2 Fossil -Lime Kiln 4.90*10-02 4.90*10-02 4.08*10-02 2.72*10-02 4.06*10-02 2.70*10-02 CO2 Biogenic -Lime Kiln fuel 7.74*10-03 8.10*10-03 1.99*10-02 3.98*10-02 7.96*10-02 2.35*10-02 4.67*10-02 CO2 Biogenic Lime Kiln CaCO3 1.06*10-01 1.06*10-01 1.06*10-01 1.06*10-01 1.38*10-01 1.06*10-01 1.06*10-01 CO2 Biogenic Recovery Boiler 1.61 1.61 1.61 1.61 1.61 1.59 1.56 CO2 Biogenic Hogfuel 2.41*10-01 2.41*10-01 2.41*10-01 2.41*10-01 2.41*10-01 3.17*10-01 3.29*10-01 CO2 Fossil Natural gas 3.70*10-01 3.70*10-01 3.70*10-01 3.70*10-01 3.70*10-01 3.70*10-01 3.70*10-01 Waste Dregs 1.04*10-02 1.04*10-02 1.04*10-02 1.04*10-02 1.04*10-02 1.03*10-02 1.02*10-02 Grits 4.94*10-03 4.94*10-03 4.94*10-03 4.94*10-03 4.94*10-03 4.92*10-03 4.91*10-03 Ashes 1.40*10-03 1.40*10-03 1.40*10-03 1.40*10-03 1.40*10-03 1.84*10-03 1.92*10-03 Wastewater Paper machine 20.22 20.22 20.22 20.22 20.22 20.22 20.22 Wastewater Causticizing 6.57*10-01 6.58*10-01 6.57*10-01 6.57*10-01 6.56*10-01 6.58*10-01 6.59*10-01 Total Wastewater 20.9 20.9 20.9 20.9 20.9 20.9 20.9 Sludge 1.01*10-02 1.01*10-02 1.01*10-02 1.01*10-02 1.01*10-02 1.01*10-02 1.01*10-02 Table S13. Life Cycle Inventory for the Scenarios Analyzed in the Present Study (continued) Input mt/ adt linerboard Fuel Oil Petcoke Tired-derived fuels (15%) 25% 50% 85% Pulp Biomass Logs (50% moisture) 2.33 2.33 2.33 2.33 2.33 Chips 2.10 2.10 2.10 2.10 2.10 Chemicals NaOH makeup 7.02*10-03 7.57*10-03 8.28*10-03 9.28*10-03 7.01*10-03 Na2SO4 makeup 5.06*10-03 4.09*10-03 2.82*10-03 1.04*10-03 5.11*10-03 CaO makeup 2.03*10-02 2.02*10-02 2.01*10-02 1.99*10-02 1.98*10-02 H2SO4 3.90*10-03 3.90*10-03 3.90*10-03 3.90*10-03 3.90*10-03 Power plant fuels External hog (Power plant) 8.82*10-02 8.82*10-02 8.82*10-02 8.82*10-02 8.82*10-02 Natural gas Boiler 1.35*10-01 1.35*10-01 1.35*10-01 1.36*10-01 1.35*10-01 Lime kiln fuels Natural Gas Lime kiln - 1.68*10-02 9.88*10-03 4.93*10-03 1.68*10-02 Fuel Oil 2.36*10-02 - - - - Tired-derived fuels - - - - 5.13*10-03 Petcoke - 8.20*10-03 1.64*10-02 2.78*10-02 - PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 17 Water demand Water-Paper machine 16.20 16.20 16.20 16.20 16.20 Water - Brownstock washing 5.47 5.47 5.48 5.49 5.47 Water -Causticizing plant 3.74 3.74 3.73 3.73 3.74 Water-Power plant 2.82 2.92 2.82 2.82 2.92 Total Water demand 28.24 28.34 28.24 28.24 28.33 Electricity from Grid Linerboard mill (MWh/mt pulp) 5.54*10-02 5.56*10-02 5.51*10-02 5.48*10-02 5.56*10-02 Alternative fuel (MWh/mt pulp) - 2.13*10-04 4.26*10-04 7.22*10-04 2.56*10-04 Outputs Fuel Oil Petcoke Tired-derived fuels (15%) 25% 50% 85% Products Pulp 1 1 1 1 1 Turpentine mt/mt pulp 3.35*10-03 3.35*10-03 3.35*10-03 3.35*10-03 3.35*10-03 CTO 1.30*10-02 1.30*10-02 1.30*10-02 1.30*10-02 1.30*10-02 Methanol 2.54*10-03 2.54*10-03 2.54*10-03 2.54*10-03 2.54*10-03 Emissions Fuel Oil Petcoke Tired-derived fuels (15%) 25% 50% 85% Onsite emissions CO2 Limekiln Total 1.81*10-01 2.25*10-01 1.87*10-01 2.11*10-01 1.62*10-01 CO2 Fossil -Lime Kiln 7.477*10-02 7.29*10-02 8.04*10-02 1.04*10-01 5.55*10-02 CO2 Biogenic Lime Kiln CaCO3 1.06*10-01 1.06*10-01 1.07*10-01 1.07*10-01 1.07*10-01 CO2 Biogenic Recovery Boiler 1.61 1.61 1.61 1.61 1.61 CO2 Biogenic Hogfuel 2.41*10-01 2.41*10-01 2.41*10-01 2.41*10-01 2.41*10-01 CO2 Fossil Natural gas 3.71*10-01 3.70*10-01 3.71*10-01 3.72*10-01 3.70*10-01 Waste Dregs 1.04*10-02 1.04*10-02 1.04*10-02 1.04*10-02 1.04*10-02 Grits 4.93*10-03 4.92*10-03 4.91*10-03 4.89*10-03 4.93*10-03 Ashes 1.40*10-03 1.40*10-03 1.40*10-03 1.40*10-03 1.40*10-03 Wastewater Paper machine 20.22 20.22 20.22 20.22 20.22 Wastewater Causticizing 6.57*10-01 6.57*10-01 6.57*10-01 6.56*10-01 6.58*10-01 Total Wastewater 20.88 20.88 20.88 20.88 20.88 Sludge 1.01*10-02 1.01*10-02 1.01*10-02 1.01*10-02 1.01*10-02 PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 18 Table S14. Mass Allocation Factors *Includes pulverized biomass, biomass Gasification and tall oil pitch Table S15. GWP for the Upstream Processes and Wastes in the Production of Linerboard Process Value Unit Loblolly pine logs (dry basis). (Lan et al. 2020; Wernet et al. 2016) 6.36*10-02 kgCO2-eq/kg product Softwood forestry, pine, sustainable forest management | wood chips, wet, measured as dry mass | Cutoff, U, RoW. (Wernet et al. 2016) 4.02*10-02 kgCO2-eq/kg product Chlor-alkali electrolysis, diaphragm cell | sodium hydroxide, without water, in 50% solution state | Cutoff, U, RoW. (Wernet et al. 2016) 1.45 kgCO2-eq/kg product Sodium sulfate production, from natural sources | sodium sulfate, anhydrite | Cutoff, U, RoW. (Wernet et al. 2016) 1.78*10-01 kgCO2-eq/kg product Quicklime production, milled, loose | quicklime, milled, loose | Cutoff, U, RoW.(Wernet et al. 2016) 1.17 kgCO2-eq/kg product Sulfuric acid production | sulfuric acid | Cutoff, U, RoW(Wernet et al. 2016) 9.84*10-02 kgCO2-eq/kg product External hog (Power plant). softwood forestry, pine, sustainable forest management | wood chips, wet, measured as dry mass | Cutoff, U, RoW. (Wernet et al. 2016) 4.02*10-02 kgCO2-eq/kg product Market for natural gas, high pressure | natural gas, high pressure | Cutoff, U, US. (Wernet et al. 2016) 3.59*10-01 kgCO2-eq/kg product Heavy fuel oil production, petroleum refinery operation | heavy fuel oil | Cutoff, U, RoW.(Wernet et al. 2016) 3.23*10-01 kgCO2-eq/kg product Biomass gasification. (Wernet et al. 2016; Rofouieeraghi 2012) 2.70*10-02 kgCO2-eq/kg biomass processed -10% moisture content Product Base case Biomass boiler External bio-based fuels* Crude Tall Oil Lignin Methanol (10%) Turpentine (10%) Other fossil-based fuels 25% 50% 100% 25% 50% Pulp 98.15% 98.15% 98.15% 99.00% 99.41% 99.41% 98.15 % 98.15 % 98.39% 98.38% 98.15% Turpentine 0.33% 0.33% 0.33% 0.33% 0.33% 0.33% 0.33% 0.33% 0.33% 0.09% 0.33% CTO 1.27% 1.27% 1.27% 0.42% 0.00% 0.00% 1.28% 1.28% 1.28% 1.28% 1.27% Methanol 0.25% 0.25% 0.25% 0.25% 0.25% 0.25% 0.25% 0.25% 0.00% 0.25% 0.25% PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 19 Biomass drying (from 50 % to 5% moisture content). (Wernet et al. 2016; Rofouieeraghi 2012) 4.25*10-03 kgCO2-eq/ kg biomass processed -50% moisture content Biomass drying (from 50 % to 10% moisture content). (Wernet et al. 2016; Rofouieeraghi 2012) 3.90*10-03 kgCO2-eq/ kg biomass processed -50% moisture content Biomass pulverization. 11,(Wind et al. 2018) 3.50*10-04 kgCO2-eq/kg biomass processed -5% moisture content Transport, freight, lorry 16-32 metric ton, EURO5. 11 1.72*10-01 t*km Market for green liquor dregs | green liquor dregs | Cutoff, U, GLO. 11 3.32*10-01 kgCO2-eq/kg waste Grits. Market for municipal solid waste | municipal solid waste | Cutoff, U, RoW. 11 9.20*10-01 kgCO2-eq/kg waste Market for wood ash mixture, pure | wood ash mixture, pure | Cutoff, U, RoW. 11 1.45*10-02 kgCO2-eq/kg waste Market for sludge from pulp and paper production | sludge from pulp and paper production | Cutoff, U, RoW. 11 1.15 kgCO2-eq/kg waste Electricity, high voltage, production mix | electricity, high voltage | Cutoff, U - US-SERC. 11 5.24*10-01 kg CO2 eq/ kWh Tall oil Pitch. 11,(Cashman, Moran, and Gaglione 2016) 4.46*10-01 kgCO2-eq/kg product Lignin drier (70% moisture content). (Wernet et al. 2016; Rofouieeraghi 2012) 2.88*10-01 kgCO2-eq/kg lignin dried CO2 for Lignoboost. Carbon dioxide production, liquid | carbon dioxide, liquid | Cutoff, U, RoW. 11 8.78*10-01 kgCO2-eq/kg product Sulfuric acid production | sulfuric acid | Cutoff, U, RoW.11 9.84*10-02 kgCO2-eq/kg product Grinded petcoke. Petroleum coke production, petroleum refinery operation | petroleum coke | Cutoff, U, RoW 11,(Ernst and Galitsky 2004) 3.62*10-01 kgCO2-eq/kg product Tired-derived fuels. 11,(Feraldi et al. 2013) 5.24*10-02 kgCO2-eq/kg product Table S16. GWP for the Scenarios Analyzed in the Present Study (continued) Process kg CO2-eq/kg product Turpentine (10%) Methanol (10%) Crude Tall Oil Lignin 25% 50% 100% 25% 50% Pulp Biomass Logs (50% moisture) 7.30*10-02 7.30*10-02 7.34*10-02 7.37*10-02 7.37*10-02 7.28*10-02 7.28*10-02 Chips 8.31*10-02 8.31*10-02 8.36*10-02 8.39*10-02 8.39*10-02 8.29*10-02 8.29*10-02 Chemicals NaOH makeup 9.76*10-03 9.76*10-03 9.82*10-03 9.86*10-03 9.86*10-03 1.14*10-02 1.30*10-02 Na2SO4 makeup 9.42*10-04 9.42*10-04 9.48*10-04 9.51*10-04 9.52*10-04 5.94*10-04 2.53*10-04 CaO 2.33*10-02 2.34*10-02 2.35*10-02 2.36*10-02 2.36*10-02 2.32*10-02 2.30*10-02 H2SO4 3.77*10-04 3.77*10-04 3.80*10-04 3.81*10-04 3.81*10-04 3.76*10-04 3.76*10-04 PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 20 Power plant fuels External hog 3.49*10-03 3.49*10-03 3.51*10-03 3.52*10-03 3.52*10-03 3.48*10-03 3.48*10-03 Natural gas-boiler 4.76*10-02 4.76*10-02 4.80*10-02 4.82*10-02 4.82*10-02 4.75*10-02 4.75*10-02 Lime kiln fuels* Natural Gas-lime kiln 6.30*10-03 6.30*10-03 5.28*10-03 3.54*10-03 - 5.22*10-03 3.46*10-03 Crude tall oil - - - 2.90*10-05 1.82*10-04 - - Methanol - 7.25*10-06 - - - - - Lignin Drying - - - - - 3.95*10-03 7.87*10-03 CO2 Lignoboost - - - - - 4.25*10-03 8.37*10-03 H2SO4 Lignoboost - - - - - 9.98*10-05 1.99*10-04 Biomass to replace natural gas - - - - - 6.31*10-03 7.36*10-03 Electricity Linerboard mill 2.86*10-02 2.87*10-02 2.87*10-02 2.87*10-02 2.84*10-02 1.58*10-02 1.51*10-02 Transport Transport biomass 1.53*10-01 1.53*10-01 1.54*10-01 1.55*10-01 1.55*10-01 1.63*10-01 1.65*10-01 Transport materials 6.17*10-04 6.74*10-04 6.21*10-04 6.68*10-04 9.02*10-04 7.00*10-04 7.83*10-04 On-site emissions CO2 fossil from fuel-lime kiln 4.82*10-02 4.82*10-02 4.04*10-02 2.71*10-02 - 3.99*10-02 2.65*10-02 CO2 biogenic from fuel-lime kiln 7.61*10-03 7.97*10-03 1.97*10-02 3.95*10-02 7.91*10-02 2.30*10-02 4.59*10-02 CO2 biogenic from CaCO3-lime kiln 1.05*10-01 1.05*10-01 1.05*10-01 1.06*10-01 1.38*10-01 1.04*10-01 1.04*10-01 CO2 biogenic- recovery boiler 1.59 1.59 1.60 1.60 1.60 1.56 1.53 CO2 biogenic-biomass boiler 2.37*10-01 2.37*10-01 2.39*10-01 2.40*10-01 2.40*10-01 3.11*10-01 3.23*10-01 CO2 fossil - natural gas boiler 3.64*10-01 3.64*10-01 3.67*10-01 3.68*10-01 3.68*10-01 3.63*10-01 3.63*10-01 Waste Dregs 3.40*10-03 3.40*10-03 3.42*10-03 3.43*10-03 3.43*10-03 3.36*10-03 3.34*10-03 Grits 4.47*10-03 4.47*10-03 4.49*10-03 4.51*10-03 4.51*10-03 4.44*10-03 4.43*10-03 Ashes 2.00*10-05 2.00*10-05 2.02*10-05 2.02*10-05 2.02*10-05 2.62*10-05 2.73*10-05 Sludge 1.14*10-02 1.14*10-02 1.15*10-02 1.16*10-02 1.16*10-02 1.14*10-02 1.14*10-02 CO2 emissions Total CO2 emissions 2.80 2.80 2.82 2.83 2.88 2.86 2.86 GWP 8.62*10-01 8.62*10-01 8.58*10-01 8.47*10-01 8.16*10-01 8.63*10-01 8.60*10-01 CO2 biogenic 1.94 1.94 1.96 1.99 2.06 2.00 2.00 *Includes the contribution from the electricity demanded by the alternative lime kiln fuel production Table S16. GWP for the Scenarios Analyzed in the Present Study (continued) Process kg CO2-eq/kg product Fuel Oil Petcoke Tired-derived fuels (15%) 25% 50% 85% Pulp Biomass Logs (50% moisture) 7.28*10-02 7.28*10-02 7.28*10-02 7.28*10-02 7.28*10-02 Chips 8.29*10-02 8.29*10-02 8.29*10-02 8.29*10-02 8.29*10-02 Chemicals NaOH makeup 9.96*10-03 1.07*10-02 1.18*10-02 1.32*10-02 9.95*10-03 PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 21 Na2SO4 makeup 8.85*10-04 7.16*10-04 4.93*10-04 1.83*10-04 8.94*10-04 CaO 2.33*10-02 2.32*10-02 2.30*10-02 2.28*10-02 2.27*10-02 H2SO4 3.76*10-04 3.76*10-04 3.76*10-04 3.76*10-04 3.76*10-04 Power plant fuels External hog 3.48*10-03 3.48*10-03 3.48*10-03 3.48*10-03 3.48*10-03 Natural gas-boiler 4.77*10-02 4.74*10-02 4.76*10-02 4.78*10-02 4.74*10-02 Lime kiln fuels* Natural Gas-lime kiln - 5.93*10-03 3.48*10-03 1.74*10-03 5.91*10-03 Fuel Oil 7.48*10-03 - - - - Tired-derived fuels - - - - 1.32*10-04 Petcoke - 1.46*10-03 2.91*10-03 4.94*10-03 - Electricity Electricity 2.85*10-02 2.86*10-02 2.84*10-02 2.82*10-02 2.86*10-02 Transport Transport biomass 1.53*10-01 1.53*10-01 1.53*10-01 1.53*10-01 1.53*10-01 Transport materials 1.01*10-03 7.43*10-04 8.70*10-04 1.05*10-03 6.92*10-04 On-site emissions CO2 fossil from fuel-lime kiln 7.34*10-02 7.15*10-02 7.90*10-02 1.02*10-01 5.45*10-02 CO2 biogenic from fuel-lime kiln - - - - - CO2 biogenic from CaCO3-lime kiln 1.04*10-01 1.04*10-01 1.05*10-01 1.05*10-01 1.05*10-01 CO2 biogenic- recovery boiler 1.58 1.58 1.58 1.58 1.58 CO2 biogenic-biomass boiler 2.37*10-01 2.37*10-01 2.37*10-01 2.37*10-01 2.37*10-01 CO2 fossil - natural gas boiler 3.64*10-01 3.63*10-01 3.64*10-01 3.65*10-01 3.63*10-01 Waste Dregs 3.39*10-03 3.39*10-03 3.38*10-03 3.38*10-03 3.39*10-03 Grits 4.45*10-03 4.44*10-03 4.43*10-03 4.41*10-03 4.45*10-03 Ashes 2.00*10-05 2.00*10-05 2.00*10-05 2.00*10-05 2.00*10-05 Sludge 1.14*10-02 1.14*10-02 1.14*10-02 1.14*10-02 1.14*10-02 CO2 emissions Total CO2 emissions 2.81*10+00 2.81*10+00 2.82*10+00 2.84*10+00 2.79*10+00 GWP 8.88*10-01 8.85*10-01 8.93*10-01 9.19*10-01 8.65*10-01 CO2 Biogenic 1.92 1.92 1.92 1.92 1.92 *Includes the contribution from the electricity demanded by the alternative lime kiln fuel production PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 22 Table S17. Hotspot Analysis for Alternatives that Represent a Reduction in the GWP for Linerboard Production Scope Alternative Process Biomass Boiler Pulverized Biomass (25%) Pulverized Biomass (50%) Pulverized Biomass (100%) Biomass Gasification Tall Oil Pitch (25%) Tall Oil Pitch (50%) Tall Oil Pitch (100%) Crude Tall Oil (25%) Crude Tall Oil (50%) Crude Tall Oil (100%) Lignin (25%) Lignin (50%) Methanol (10%) Turpentine (10%) Scope 1 Fossil CO₂ (Lime kiln) 0.0% -1.5% -3.1% -6.2% -6.2% -1.5% -3.0% -6.2% -1.5% -3.0% -6.2% -1.6% -3.1% -0.6% -0.6% Fossil CO₂ (Boiler) -41.9% 0.0% 0.1% 0.1% 0.1% 0.1% 0.1% 0.2% 0.4% 0.6% 0.6% 0.0% 0.0% 0.1% 0.2% Scope 2 Electricity (mill) 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% -1.5% -1.5% 0.0% 0.0% Scope 3 Chemicals 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.1% 0.1% 0.6% 1.3% 0.0% 0.0% Biomass (Energy) 3.3% 0.1% 0.2% 0.5% 1.9% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.7% 0.9% 0.0% 0.0% Natural gas production (Boiler) -5.5% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.1% 0.1% 0.1% 0.0% 0.0% 0.0% 0.0% Natural gas production (Lime Kiln) 0.0% -0.2% -0.4% -0.8% -0.8% -0.2% -0.4% -0.8% -0.2% -0.4% -0.8% -0.2% -0.4% -0.1% -0.1% Alternative Fuel Production 0.0% 0.0% 0.0% 0.0% 0.7% 0.4% 0.7% 1.4% 0.0% 0.0% 0.0% 0.5% 0.9% 0.0% 0.0% Transport 2.8% 0.1% 0.2% 0.4% 1.7% 0.0% 0.0% 0.1% 0.2% 0.2% 0.3% 1.2% 1.4% 0.1% 0.0% Waste disposal 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% Net reduction -41.3% -1.5% -3.0% -5.9% -2.6% -1.2% -2.5% -5.3% -1.0% -2.3% -5.8% -0.2% -0.7% -0.4% -0.4% PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 23 MARGINAL ABATEMENT COST CURVE Capital Investment The Marginal Abatement Cost Curve was developed based on the CO2-eq reductions of each scenario and the Net Present Value (NPV). The NPV was determined assuming an implementation of 11 years, with the first year for construction, and a start of operation in the second year. 75% of the capital investment is made in the first year and 25% in the second year. The annual maintenance capital and the annual maintenance and repair cost is 1% and 2% of the cost of the equipment, respectively. The cash flow analysis considers a linear depreciation of 10% during the 10 years. For the scenarios where the coproduct is used as alternative fuel in the lime kiln (crude tall oil, methanol, turpentine), the revenue lost by burning the fuel is considered an operating cost in the analysis. The equipment cost is based on secondary sources (Laboratory and Laboratory 2013; Benali et al. 2016; Rofouieeraghi 2012) and recommendations of industry experts (Hart 2022). The cost for biomass gasification system, pulverized biomass and lignin extraction was adjusted to the capacity and year of investment assuming different scale exponents recommended by industry experts (0.6, 0.4, and 0.2, respectively) (Hart 2022). The equipment cost of the rest of the alternative fuels were provided for the year 2022, (Hart 2022) while the biomass boiler was adjusted from a total capital investment of $158 million dollars for 2022, with a capacity of 400,000 lb steam/h (Hart 2022). PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 24 Table S18. Capital Investment of the Alternatives to Reduce the GHG Emissions in Linerboard Production Direct Cost % Total capital investment Pulverized biomass 100% (Laboratory and Laboratory 2013; Rofouieeraghi 2012) Gasification 100% (Laboratory and Laboratory 2013; Rofouieeraghi 2012) Tall Oil Pitch 100% (Hart 2022) Crude tall oil 100% (Hart 2022) Methanol 10% (Hart 2022) Turpentine 10% (Hart 2022) Lignin 50% (Benali et al. 2016) Biomass Boiler (Hart 2022) - Purchased Equipment 100% $6.580 $23.792 $0.500 $0.500 $0.200 $0.500 $6.704 - - Purchased Equipment Installation 13.3% $0.877 $3.172 $0.067 $0.067 $0.027 $0.067 $0.894 - - Instrumentation and Controls 20.0% $1.316 $4.758 $0.100 $0.100 $0.040 $0.100 $1.341 - - Piping 13.3% $0.877 $3.172 $0.067 $0.067 $0.027 $0.067 $0.894 - - Electrical Systems 13.3% $0.877 $3.172 $0.067 $0.067 $0.027 $0.067 $0.894 - - Service Facilities 6.7% $0.439 $1.586 $0.033 $0.033 $0.013 $0.033 $0.447 - Sub-Total Direct Cost 166.7% $10.966 $39.654 $0.833 $0.833 $0.333 $0.833 $11.173 $- Indirect Cost Pulverized biomass 100% Gasification 100% Tall Oil Pitch 100% Crude tall oil 100% Methanol 10% Turpentine 10% Lignin 50% Biomass Boiler - Engineering 20.0% $1.316 $4.758 $0.100 $0.100 $0.040 $0.100 $1.341 - - Construction Expenses 20.0% $1.316 $4.758 $0.100 $0.100 $0.040 $0.100 $1.341 - - Contractor Fee 13.3% $0.877 $3.172 $0.067 $0.067 $0.027 $0.067 $0.894 - - Inflation 20.0% $1.316 $4.758 $0.100 $0.100 $0.040 $0.100 $1.341 - - Contingency 20.0% $1.316 $4.758 $0.100 $0.100 $0.040 $0.100 $1.341 - Sub-Total Indirect Cost 93% $6.141 $22.206 $0.467 $0.467 $0.187 $0.467 $6.257 - TOTAL CAPITAL INVESTMENT 260% $17.107 $61.860 $1.300 $1.300 $0.520 $1.300 $17.429 $178.852 PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 25 Direct cost structure The change in the operation cost was based on the mass and energy balance and the prices reported for the alternative fuels and chemicals. The prices are included in Table S19. Table S19. Electricity and Chemical Prices Variable Cost Electricity (Cents per Kilowatthour) (Administration, n.d.) 7.26 Natural gas ($/1000 ft3) (Administration, n.d.) 5.5* biomass (hog fuel) ($/ton) (Administration, n.d.) 34.4 biomass transport ($-t km) (Stolaroff et al. 2021) 0.101 Crude tall Oil (US $/mt) (Niemeläinen 2018; Stolaroff et al. 2021) 400 Tall Oil Pitch (US $/mt) (Niemeläinen 2018) 400 NaOH (US $/mt)2 728 Na2SO4 (US $/mt)2 88 H2SO4 (US $/mt)2 88 Methanol (US $/mt) (IHSMarkit, n.d.) 350 Turpentine (US $/mt) 2 716 CO2 (US $/mt) (Inc. 2022) 250 *Electric power price Figure S6 shows the direct cost structure for each alternative. In the case of pulverized biomass in the lime kiln and biomass boiler to replace the gas boiler, the displacement of natural gas represents a savings in the direct cost of $0.08 and $1.37 million dollars per year, respectively. This is reasonable given the prices reported by linerboard mills in the US; for natural gas, the average price in Q1 2022 is $ 6.1/mmBTU, whereas for residual biomass, the price is $ 2.8/mmBTU (Fisher International Inc, n.d.). In contrast, biomass gasification has a direct cost of $10.9 million dollars per year due to the low syngas-to-biomass ratio that increases biomass demand compared to pulverized biomass. In the case of lignin, the biomass demand to replace the extracted black liquor also increases the direct cost; the demand of chemicals to precipitate the lignin also is a variable that increases the direct cost to $7.9 million dollars per year. In the case of TOP, CTO, turpentine and methanol, the high cost of the external alternative fuel and the revenue lost by burning the on-site alternative fuel production countered the net savings, giving a net direct cost of $4.96, $5.25, $0.95 and $1.22 million dollars per year, respectively. PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 26 Fig. S6. Direct cost structure for alternatives to reduce the GHG emissions in the production of linerboard. External alternative fuel and onsite alternative fuel refer to crude tall oil, methanol, and turpentine Sensitivity Analysis To identify the economic variables that affect the CAC (or the NPV), a sensitivity analysis was performed varying ± 25% the raw materials costs and the capital investment without including a revenue from the carbon offset (Fig. 7). In the case of pulverized biomass, the main variable is the natural gas price, with a variation of ±26.7% for the CAC, followed by capital investment with ±25.5%, biomass cost with ± 19.3%, and biomass transport with ± 5.7%. Among the alternative fuels that imply mayor modifications in the mill (biomass gasification, lignin extraction and pulverized biomass) this is the one with the lowest capital investment, and mayor savings in the direct costs. In the case of biomass boiler and biomass gasification; the capital investment is the factor that most affects the CAC, with a variation of ±25.9% for the biomass boiler, and ±13.7% for biomass gasification. The natural gas savings are more relevant for the biomass boiler with a variation of ±17.6% vs. a ±4% for biomass gasification, this is due the higher natural gas volume displaced on the first technology. The biomass price is also a variable with an important effect on the CAC, resulting in a variation of ±12.9% in the biomass boiler and ±11.5% in biomass gasification. For lignin extraction, biomass is the most important factor rather than capital cost, with a variation of ±10.7% by the biomass cost and ±3.1% by its transport cost. The biomass relevance in the CAC is a consequence of two factors. First, the energy provided in the recovery boiler by the extracted lignin is covered by increasing the biomass demand in the boiler; however, lignin has a higher HHV (26.5 MJ/kg vs. 20.5 MJ/kg). In addition, the steam demand increases by the liquor PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 27 return from the Lignoboost process, increasing the biomass demand in the boiler. Therefore, the capital investment is slightly less relevant with a variation of ±8.0%. Regarding the rest of the raw materials, natural gas savings has a variation of ±4.2%, followed by CO2 with a variation of ±4.1%, NaOH with ±2.8%; Na2SO4 savings with ±0.5%, and H2SO4 with ±0.3%. Regarding the streams available in the mill as lime kiln fuel alternatives (CTO, TOP, turpentine, and methanol), these alternatives have low capital investment; however, the high price of these alternative fuels compared to natural gas affects the CAC considerably. For CTO and TOP, the CAC variation is around ± 42 % with the cost of the alternative fuel, whereas for the natural gas and the capital investment are around ±18 and ±1.3%, respectively. For turpentine and methanol, the variation in the CAC by the alternative fuel cost is ±27.1% and ±30.1%; ±7.8% and ±7.2% with the natural gas cost; and ±5.7% and ±2.1% with the capital investment, respectively. In summary, the utilization of the streams available in the mill has low capital investment but the high price of these alternative fuels impacts the CAC considerably. For technologies that rely on biomass, as pulverized biomass, biomass boiler, and biomass gasification, the CAC has an important variation with the capital investment, followed by biomass. In the case of lignin extraction, the biomass demand is the variable that most impacts the CAC, given that the demand of biomass is increased to compensate the energy content of the extracted liquor. The savings in natural gas for all the alternatives is also relevant; in the case of pulverized biomass, the natural gas cost is the variable that most impacts the CAC. PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 28 Fig. S7. Sensitivity analysis for the Cost of Carbon Avoided (Scope 1 &2). Change in the variables is +/- 25% of the value assumed for each scenario. a) Pulverized biomass, b) Biomass boiler, c) Crude tall oil, d) Tall oil pitch, e) Turpentine, f) Methanol, g) Lignin extraction, h) Biomass gasification PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 29 REFERENCES Administration, U S Enenrgy Information. n.d. Average Price of Electricity to Ultimate Customers. https://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=table_5_03. ———. n.d. “Monthly Densified Biomass Fuel Report.” https://www.eia.gov/biofuels/biomass/#table_data. ———. n.d. “Natural Gas Prices.” https://www.eia.gov/naturalgas/. Aryan, V., and Kraft, A. (2021). “The crude tall oil value chain: Global availability and the influence of regional energy policies,” Journal of Cleaner Production 280, article no. 124616. DOI: 10.1016/j.jclepro.2020.124616 Benali, M., Ajao, O., Jeaidi, J., Gilani, B., Mansoornejad, B. (2016). “Integrated lignin- kraft pulp biorefinery for the production of lignin and its derivatives: Economic assessment and LCA-based environmental footprint,” in: Production of Biofuels and Chemicals from Lignin, (Zhen Fang and Richard L Smith Jr., ed.), 379–418, Singapore: Springer Singapore. DOI: 10.1007/978-981-10-1965-4_13 Cashman, S. A., Moran, K. M., and Gaglione, A. G. (2016). “Greenhouse gas and energy life cycle assessment of pine chemicals derived from crude tall oil and their substitutes,” Journal of Industrial Ecology 20(5), 1108–21. DOI: 10.1111/jiec.12370 Ernst, W., and Galitsky, C. (2004). “Energy Efficiency Improvement Opportunities for Cement Making,” https://www.osti.gov/servlets/purl/927882. Evdokimov, A. N, Kurzin, A. V., Trifonova, A. D., Popova, L. M., and Buisman, G. J. H. (2017). “Desulfurization of black liquor soap for production of crude tall oil with lower sulfur content,” Wood Science and Technology 51(6), 1353–63. DOI: 10.1007/s00226-017-0912-y Feraldi, R., Cashman, S., Huff, M., and Raahauge, L. (2013). “Comparative LCA of treatment options for US scrap tires: Material recycling and tire-derived fuel combustion,” International Journal of Life Cycle Assessment 18(3), 613–25. DOI: 10.1007/s11367-012-0514-8 Fisher International Inc. n.d. “FisherSolve Database.” Francey, S., Tran, H., and Jones, A. (2009). “Current status of alternative fuel use in lime kilns,” Tappi Journal 8(10), 33–39. Grace, T. M., Malcolm, E. W., and Kocurek, M. J. (1983). Pulp and Paper Manufacture: Alkaline Pulping. Pulp and Paper Manufacture. TAPPI. Hart, P. W. (2020). “Alternative ‘green’ lime kiln fuels: Part II—Woody biomass, bio- oils, gasification, and hydrogen,” Tappi Journal 19(5), 271–79. DOI: 10.32964/TJ19.5.271 Hart, P. W. (2022). “WestRock. Personal Communication, February.” WestRock. Hart, P. W., Hanson III, G. M., and Manning, R. (2021). Lime Kilns and Recausticizing: The Forgotten Part of the Kraft Mill, Tappi Press. IHSMarkit. n.d. “Methanol Production Capacity May Quintuple on Decarbonized Industry Transformation,” https://cleanenergynews.ihsmarkit.com/research- analysis/methanol-production-capacity-may-quintuple-on-decarbonized-ind.html. Inc., CO2 Gro. 2022. “CO2 GRO Inc. Inaugural 2022 ESG Report.” https://co2gro.ca/index.php/esg-report/. Laboratory, Idaho National, and Pacific Northwest National Laboratory. (2013). “Logistics, Costs, and GHG Impacts of Utility-Scale Cofiring with 20 % Biomass.” Lan, K., Ou, L., Park, S., Kelley, S. S., and Yao, Y. (2020). “Life cycle analysis of PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Buitrago et al. (2024). “Linerboard decarbonization,” BioResources 19(4), 7806-7823. 30 decentralized preprocessing systems for fast pyrolysis biorefineries with blended feedstocks in the southeastern United States,” Energy Technology 8(11). DOI: 10.1002/ente.201900850 Lundqvist, Per. (2009). Mass and Energy Balances over the Lime Kiln in a Kraft Pulp Mill, Uppsala University. Manning, R., and Tran, H. (2015). “Impact of cofiring biofuels and fossil fuels on lime kiln operation,” Tappi Journal 14(7), 474–80. DOI: 10.32964/tj14.7.474 Martin, N., Anglani, N., Einstein, D., Khrushch, M., Worrell, E., and Price, L. K. (2000). “Opportunities to improve energy efficiency and reduce greenhouse gas emissions in the U.S. pulp and paper industry,” Lawrence Berkeley National Laboratory. Berkeley, CA. https://digital.library.unt.edu/ark:/67531/metadc718850/m2/1/high_res_d/776606.pdf. Niemeläinen, M. (2018). Tall Oil Depitching in Kraft Pulp Mill, Tesis Magister, Aalto University. Aalto University. Nilsson, J. L., .Larson, E. D., Gilbreath, K., and Gupta, A. (1995). “Background Paper on Energy Efficiency and the Pulp and Paper Industry.” Available at https://www.aceee.org/files/proceedings/1995/data/papers/SS95_Panel1_Paper01.pdf. Öhman, F., Theliander, H., Tomani, P., and Axegard, P. (2013). “Method for separating lignin from black liquor,” US Patent No. 8,486,224 B2. “OpenLCA.” n.d. https://www.openlca.org/. Rofouieeraghi, P. (2012). Biomass Gasification Integrated into a Reference Canadian Kraft Mill, UNIVERSITÉ DE MONTRÉAL. Stolaroff, J. K., Pang, S. H., Li, W., Kirkendall, W. G., Goldstein, H. M., Aines, R. D., and Baker, S. E. (2021). “Transport cost for carbon removal projects with biomass and CO2 storage,” Frontiers in Energy Research 9 (May), 1–13. DOI: 10.3389/fenrg.2021.639943 Tomani, Per. (2010). “The lignoboost process,” Cellulose Chemistry and Technology 44 (1–3), 3–58. Valmet.(2015). “WinGEMS, 5.4.” 2015. Wernet, G., Bauer, C., Steubing, B., Reinhard, J., Moreno-Ruiz, E., and Weidema, B. (2016). “The Ecoinvent Database Version 3 (Part I): Overview and Methodology,” International Journal of Life Cycle Assessment 21(9), 1218–30. DOI: 10.1007/s11367-016-1087-8 Wind, S., Hannibal, N., Havu, A., Carsten, J., Claus, J.-H., and Martinsson, A. (2018). “Using wood powder as fuel in lime kilns,” in: Pulping Engineering and Environmental Recycling Sustainability Conference, PEERS 2018: Technical Solutions for Today and Beyond, 459–472. BioRes_19_4_7806_BuitrangoTello_VJHG_Carbon_Footpr_Technoecon_Decarboniz_Lineboard_23158.pdf BioRes_19_4_7806_Appendix 23158