Barrios et al. Biotechnology for Biofuels and Bioproducts
(2025) 18:48
Page 8 of 23
• In the enhanced dewatering scenario, the only vari- able is the change in solids content after pressing due to enzyme treatment and starch addition. • The dryer consumes medium pressure (MP) steam, which was adjusted to control the natural gas consumed in the NG. • Steam savings were reflected as a reduction in fuel usage. The steam energy produced by the RB and BB is assumed to remain constant. • The electricity demand is assumed to remain constant. Techno-economic analysis (TEA) The economic analysis evaluates the financial implica- tions of implementing enzymatic treatment and starch addition to enhance dewatering and increase solids con- tent after pressing in bleached hardwood kraft pulp and board production. Figure 2 illustrates the process flow used to estimate costs for both the baseline and enhanced dewatering scenarios. A reduction in natural gas con- sumption, resulting from energy savings, can significantly reduce costs for a pulp and paper mill. The potential eco- nomic benefits are estimated by integrating the cell-free enzyme technology to increase solids content after press- ing. Changes in natural gas costs due to change in con- sumption, along with procurement costs for enzymes and starch in the enhanced dewatering scenario, were con- sidered, as shown in Fig. 2. Key inputs for the analysis, including costs for natural gas, enzymes, and starch, were sourced to assess the savings from reduced natural gas consumption against the added expenses of enzyme and starch procurement, providing a comprehensive assess- ment of the economic feasibility of the enhanced dewa- tering strategy [55, 56]. The primary parameters influencing cost savings are enzyme usage, natural gas fuel, and starch costs. A sensitivity analysis was conducted to evaluate the impact of cost variability on overall savings. For this analysis, a ± 25% variation was applied to each parameter. Natural gas prices, which are the most significant contributor to cost savings, were varied between 4.35 to 7.25 USD/GJ, with results ranging from − 7.27 to − 15.30 USD/ADt. Enzyme and starch costs were also varied by ± 25%; enzyme cost savings remained largely stable, while changes in starch costs had a smaller impact on total savings. More details on the variation in savings due to changes in these primary cost parameters are provided in Figure S2 and Table S3.”
Table 2 Specifications of the simulated mill, including baseline and enhanced dewatering scenarios, used to evaluate the impact of the cell-free enzyme treatments on solids content increase after press
Parameter
Baseline
Enhanced dewatering
Fiber type
Bleached hardwood Bleached hardwood
Paper grade
Cartonboard
Cartonboard
Production (ADt/day)
1356
1356
Powerhouse configuration
RB, NB, BB
RB, NB, BB
Electricity demand (kWh/ ADt)
980
980
Power self-sufficiency % 93 Solids before dryer % 39 Solids after dryer % 95
93 50 95 0.5 0.5
Enzyme (wt.% OD) Starch (wt.% OD)
– –
ADt: air-dried ton, RB: recovery boiler, NB: natural gas boiler, BB: biomass boiler
the highest share of bleached hardwood fiber in its fur- nish, was used as a reference for comparison. The speci- fications of the simulated mill, baseline scenario, and enhanced dewatering scenarios are shown in Table 2. The uncertainty in the reported reduction in GWP was estimated using a sensitivity analysis (SA) approach [54]. The primary variable influencing fossil fuel consumption and direct emissions in the LCA was the solids content after pressing, which directly affects the final GWP. Therefore, the SA was based on the experimental variation of solids, with a standard deviation of ± 1%. However, to account for expected variability at a larger scale, a range of ± 2% was applied to capture potential process fluctuations. The simulation was run with solids after pressing varying between 48% (minimum) and 52% (maximum). The uncertainty in the GWP reduction was expressed as the mean ± half the range. The method, which uses a range based on standard deviation and scales it for larger-scale variability, provides a straightforward estimate of uncertainty, with clear results for GWP reduction. More details on the uncertainty calculations can be found in Table S2.
Considerations of the simulation process
• The powerhouse consists of the recovery boiler (RB), biomass boiler (BB), and natural gas boiler (NB). • CO 2 emissions from the RB, BB, and part of the limekiln (due to the calcination process) are considered biogenic and thus carbon neutral. • Fossil CO 2 emissions are released by gas combustion at the limekiln and NB.
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