PAPERmaking! Vol11 Nr2 2025

R Buitrago-Tello et al.

Original Article: Linerboard production and decarbonization

were debarked and then chopped into wood chips, with additional external wood chips purchased for the pulping process. The wood chips were then cooked to remove lignin. The resulting pulp was washed and sent to the paper machine, where the fibers were suspended in water, and the excess water was drained, forming a continuous sheet that underwent further drying through suction, pressure, and heat. In a typical kraft mill, heat integration is implemented primarily through the multiple-effect evaporator system, where steam is cascaded from higher to lower pressure effects, and through the recovery of heat from condensates and flue gases. Our simulation models captured these standard heat integration practices. For example, the base case evaporator system included six effects with a steam economy of 5.2 kg water evaporated per kg of steam used. Similarly, heat recovery from the black liquor oxidation system and condensate return systems was included in all scenarios. The liquor from the pulp washing, known as weak black liquor, was concentrated in a multiple-effect evaporator and subsequently burned in the recovery boiler to generate steam. This process also converted the inorganic elements into a mixture of molten salts, primarily sodium carbonate and sulfide, referred to as smelt. The smelt was then sent to the causticizing plant to recover the pulping chemicals. Waste wood from the wood yard and external waste biomass was burned in a hog fuel boiler, with additional heat produced by a natural gas boiler to cover the global steam demand. The high-pressure steam from the boilers was expanded in both a back-pressure turbine and a condensing turbine to generate electricity for the mill. A portion of the medium- and low-pressure steam from the turbines was extracted to meet the process’s heat requirements. To cover the mill’s full electricity demand, additional electricity was purchased from the grid. The baseline simulation was modified to model the alternatives listed in Table 1. The supporting information section describes these alternatives’ assumptions in detail. The capital investment, the changes in the operating parameters resulting from the integration of the alternatives, and the changes in the operating cost were determined according to the mass and energy balances from the simulation of each scenario and data reported in the literature. This information is also included in the supporting information section. The scenarios and main assumptions are shown in Table 1. The linerboard production rate remained consistent across all scenarios. Following standard practice in forest product LCAs, this study reported but did not include biogenic CO2 emissions in the carbon footprint calculations. Biogenic CO2 emissions from biomass combustion (recovery boiler,

hog fuel) and lime kiln operations (CaCO3 decomposition) were considered carbon neutral under the assumption that forest carbon stocks were maintained through sustainable forest management practices. This approach aligns with Intergovernmental Panel on Climate Change (IPCC) guidelines and ISO 14067 standards for carbon footprinting of products. 26 Carbon emissions were determined using a cradle-to-gate life cycle assessment (LCA) by applying the IPCC 2013 global warming potential (GWP) 100a method, which expresses greenhouse gas emissions in kg of CO2 equivalent over a 100-year time horizon. This methodology was selected for three primary reasons: (1) it aligns with the study’s focus on climate change mitigation and carbon footprint reduction; (2) it is widely accepted in industrial decarbonization studies, enabling direct comparison with similar research; and (3) it provides specific characterization factors for all relevant greenhouse gases encountered in pulp and paper operations. Contributions from upstream processes to the scenarios are based on data reported in the Ecoinvent database. 27 The list of inlet flows and their corresponding LCI database sources from Ecoinvent are included in Supporting Information, Table S13, and the life cycle inventory of the scenarios is included in Supporting Information, Table S14. Technologies for steam production Two scenarios were evaluated for steam generation: (a) replacing the recovery boiler with a high-efficiency recovery boiler, 20 and (b) replacing the natural gas boiler with two high-efficiency electric boilers (99% efficiency). 12 High-efficiency recovery boiler Replacing an old, inefficient recovery boiler with a modern, high-efficiency model is one way that the pulp and paper industry can reduce carbon emissions. By upgrading to a high-efficiency recovery boiler, a pulp and paper mill can lower its carbon emissions significantly by reducing the demand for fossil fuels and electricity purchased from the grid. This reduction results from an increase in steam production and on-site power generation. 20 In this scenario, the multiple-effect evaporation system and the condensing turbine are refurbished to accommodate the higher black liquor solids content and increased steam generation associated with the high-efficiency recovery boiler. Electric boilers Electric boilers use electricity as energy source rather than direct fossil or biomass fuel combustion. In the pulp and paper industry, electric boilers offer several advantages,

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