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W. Ingwersen et al. / Journal of Cleaner Production 131 (2016) 509 e 522
Fig. 1. Generic processes are shown for pulp production, papermaking, and converting. Each box represents a separate unit process for the pulp LCIs used in this study.
uptake that was included, emissions of CO 2 from combustion and decay of biogenic sources were included across all phases of the life cycle. With this method for developing inventory, all inputs and outputs to processes are tracked to achieve a carbon balance. Wood residuals from debarking and chipping are assumed to be collected for use as fuel for pulp production, and allocation was performed on a mass-basis for these processes. For Albany, saw- mills provide some waste residues as fuels, but not at Box Elder. The pulp is made in mills via a thermo-chemical process from wood chips. Inputs to pulping include various fuel sources, pur- chased electricity, processing chemicals, and water. To represent the pulping process, data were solicited from 2010 to 2014 from seven pulp mills. Transportation distances from harvest location to pulp mill were estimated based on data from the Commodity Flow Survey (BTS, 2009), and mode was assumed to be heavy-duty tractor trailer. 2.1.2. Paper towel production Paper towel production includes both papermaking and paper converting, including embossing, rolling paper on cores and putting rolls in primary packaging. The papermaking and converting lines operate independently. Towels are tracked by a speci fi c pair of making and converting lines (a line pair). Two line pairs, each from a different North American facility, were thus chosen based on their operation for producing the same paper substrate, i.e. Bounty regular, over the same time period, differences in papermaking and converting technologies, and differences in facility characteristics. Table 1 summarizes some of the key differences between the selected lines. Conventional facility level product allocation by mass or value did not provide the needed accuracy to obtain accurate inventories representative of the line pairs. Totally avoiding allocation was impossible because of con fi dentiality, lack of line level monitoring of some inputs and outputs, and because of the need to attribute some of the processes serving multiple lines (e.g. utilities) to a roll from a speci fi c line pair. IPSA is a structured method for assessing the inputs and outputs related to a product of interest when the intention is to compare products from speci fi c production lines in one or more complex industrial facilities (Fig. 2). It uses sub-process modeling to avoid allocation when data are available at a sub- process level, and provide clear allocation when not available, within the context of a structured approach. In Step 1, a full list of fl ows into and out of the facility including material, energy, prod- ucts, and releases were obtained from the facilities. Information was obtained on equipment and throughput to model capacities. In Step 2, fl ows were assigned to direct process (papermaking and converting); ancillary (e.g., boilers) and non-process (e.g., storage space) based on equipment usage data. In Step 3, fl ows further split among the direct processes to papermaking and converting line pairs, and among the ancillary processes based on equipment type.
operations through pulp production. Not included in LCIs, but an important consideration for data reliability and appropriateness for environmental indices, is that independent third-party veri fi cation systems (e.g., auditing by Price Waterhouse Coopers for Forest Stewardship Council standards) are used to ensure sustainable forest management and wood traceability. P & G works with global multi-stakeholder organizations (e.g. World Wildlife Fund) on the development of tools and scienti fi c methods to protect both the commercial value and services that forests provide, such as biodi- versity, watershed protection, and climate moderation (Procter and Gamble, 2015a, 2015b). Pulp mills commonly acquire a large fraction of their non- electricity energy needs from combustion of biomass fuels like wood chips and recovered fuels like black liquor that are of biogenic origin. Emissions of carbon dioxide from biogenic sources are typically excluded from facility reporting in systems such as EPA's GHG eGRET tool (US EPA, 2015a, 2015b, 2015c). This study includes biogenic CO 2 emissions in the inventory, as recommended by a recently developed product category rule for market pulp (FP Innovation, 2015). Therefore, CO 2 emissions were determined by calculations based on standard methods using the carbon content of the reported fuels used (US EPA, 2015a, 2015b, 2015c). Forestry and sawmills are represented with data generated by the Consortium for Research on Renewable Industrial Materials (CORRIM) (Puettmann et al., 2010; Wagner et al., 2009), except for data on land occupation/conversion and carbon uptake. The COR- RIM data include processes to grow, fell, delimb, skid, load timber onto a truck, and replant following harvest. The wood chips and forest residues for pulp production for the paper towels come from multiple sources and co-product generation processes, such as lumber and mill scrap and on-site chipping. Data from CORRIM do not separately identify the different sources of wood chips that become the pulp. A very conservative approach is used for this model and the trees are assumed to be grown exclusively for pulp production with no allocation for other uses. Under con fi dentiality disclosure agreements, land occupation and conversion data were collected and averaged from multiple growers as primary sources used by the pulp mills. Carbon uptake was calculated using stan- dard IPCC methods based on forest species harvested, harvest density, wood density; assuming 0.5103 kg C/kg oven dry wood (IPCC, 2007). Age of trees at harvest ranged from 6 to 68 years and harvest volume 40 e 219 dry m 3 /hectare (Binkley, 2014; Cochran and Dahms, 2000; USFS, 1983). Wood densities ranged from 445 to 574 kg/m 3 at 12% moisture. The burning of plantation residue following harvest is assumed to not occur, as consistent with the third party veri fi cation standards. In accordance with product carbon foot printing standards (BSI, 2011; EC, 2013; GHG Protocol, 2011), only the carbon sequestered in the trees that were har- vested was accounted for in carbon uptake; other carbon uptake associated with forest land was excluded. For the portion of carbon
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