Skoglund et al.
10.3389/fther.2023.1282028
lignocellulosic ethanol fermentation for alcohol-to-jet fuel production in a pulp mill. Ong et al. (2020) proposed a kraft mill-integrated design for a hydrothermal liquefaction process. Mongkhonsiri et al. (2020) designed a biomass gasi fi cation process for integration in a pulp mill, aiming to produce of succinic acid and DME. Ribeiro Domingos et al. (2021) compared different black liquor gasi fi cation routes for production of methanol and dimethyl ether (DME). Alternatively, or additionally, to recover the biogenic carbon by extracting side streams from the pulping process, the biogenic carbon could be recovered through “ end-of-pipe ” capture from mill fl ue gas streams. The captured CO 2 could then be utilized for production of bio-based chemicals in Carbon Capture and Utilization (CCU) concepts. For example, the CO 2 could be reacted with hydrogen produced via electrolysis to form methanol (Marlin et al., 2018). On-site opportunities for CO 2 utilization in Kraft pulp mills include, e.g., tall oil manufacturing, lignin extraction and production of precipitated calcium carbonate (Kuparinen et al., 2019). New process concepts are also being developed, which could replace core process units in the mills with new technologies that could reduce the use of fuel and combustion-related emissions and/ or provide opportunities for more ef fi cient capture of CO 2 . Some of these opportunities involve replacing the lime kiln, which is the conventional calcination process, either by an oxyfuel combustion or an electri fi ed plasma calcination process (Lefvert and Grönkvist, 2023). Amongst other potential bene fi ts, the CO 2 from the calcination reaction would then be obtained as a pure stream that could be captured directly without the need for separation froma fl ue gas (Svensson et al., 2021). Another novel concept, that was recently evaluated, could be to replace the conventional power boiler ( fl uidized bed) with a chemical looping combustion system with oxygen uncoupling (Saari et al., 2023). However, while small- scale capture from the calcination process can be very ef fi cient, larger-scale capture is typically required to reach acceptable economies of scale for BECCS applications. And with regards to the scale of capture from the power boiler, this will only be signi fi cant in larger integrated pulp and paper mills, while the power boiler is used to a much lesser extent in ef fi cient pulp- only mills. To manage the energy balances of the mill when a larger share of the biomass is valorized as by-products and no longer is available for combustion on-site, or when new heat demands are introduced, such process changes must typically also be combined with energy ef fi ciency improvements and/or electri fi cation of heat production (Lipiäinen et al., 2023). When investigating a potential future integration of carbon capture in a pulp or paper mill, it is thus also necessary to consider the expected strategic development in the mill and investigate how new process concepts may affect the potential for carbon capture and the site-wide energy balances. Several studies have investigated the integration of post- combustion amine-based carbon capture in the chemical pulping industry. More recent examples include the work by Onarheim et al. (2017a), Onarheim et al. (2017b), Kuparinen et al. (2023) and Nwaoha and Tontiwachwithikul (2019). These studies have investigated heat integration opportunities, effects on mill energy balances, as well as capture and emission avoidance costs for different capture con fi gurations applied to different fl ue gas
limitation for BECCS, however, is the access to sustainable sources of biomass and biogenic carbon that can be captured. A number of studies have raised concerns that large-scale implementation of purpose-grown biomass for BECCS could have many negative effects including, but not limited to, loss of biodiversity, increased competition for agricultural land, and increased emissions due to land use change (Smith et al., 2016; Hanssen et al., 2022). Kraft pulp mills have been shown to be promising candidates for BECCS, since they have large existing point sources of biogenic CO 2 emissions, originating from biomass that is used primarily for production of useful materials. More speci fi cally, pulp mills use biomass as feedstock to produce pulp and by-products, such as turpentine and tall oil. The kraft-pulping process is energy-intensive and has large emissions of biogenic CO 2 mainly due to the combustion of black liquor. Black liquor is a slurry of spent processing chemicals and biogenic compounds, and the combustion of the liquor is an important part of the regeneration of the processing chemicals that also supply energy to the process. Kuparinen et al. (2019) estimated the global technical potential for capture of (mainly biogenic) CO 2 from kraft pulp mills to 135 Mt/yr. Recently, Rosa et al. (2021) estimated the technical potential for biogenic CDR from existing point sources in 30 European countries, and found the potential for CDR from pulp and paper plants to be 62 (+/-5) Mt/yr. This is similar to previously reported potentials for BECCS in the pulp and paper industry, with estimates of 60 Mt/yr in Europe (Jönsson and Berntsson, 2012). A large share of this BECCS potential is found in Sweden (Hansson et al., 2017; Rootzén et al., 2018) and in Finland (Kuparinen et al., 2019), each with annual emissions from chemical pulp mills of around 20 Mt/yr. With increasing demands for renewable carbon resources from other sectors, the pulp and paper industry is under pressure to strive towards better utilization of the biomass resource, and to convert a larger share of the biomass feedstock into valuable products. This can be enabled by integration of new technologies and processes for extraction and valorization of side streams from the pulp by- products. For example, there are opportunities for extracting renewable and valuable chemicals from the kraft black liquor (Akbari et al., 2018; Pola et al., 2022). One such possibility is the extraction of lignin (Hubbe et al., 2019), which can be further processed into biochemicals, biomaterials or biofuels (Téguia et al., 2017). By extracting the lignin from the black liquor, the amount of biomass that is combusted is reduced, but another valuable by-product is produced. Another advantage of lignin extraction is that the heat transfer area of recovery boilers is often the main bottleneck for mill throughput, and by removing some of the lignin from the black liquor, this bottleneck can be removed, and production increased (Vakkilainen and Välimäki, 2009). Other opportunities for biomass valorization in pulp mills, which have attracted attention in recent literature include the integration of various biore fi nery processes with the mill. Results by Granacher et al. (2022) show that pulp-mill integrated biore fi neries is an economically viable way to achieve better resource utilization [see also Granacher et al. (2023) for a general overview of pulp mill biore fi nery options]. More speci fi cally, Geleynse et al. (2020) investigated the integration of
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