Abstract

Goal and scope definition

This study had two main objectives. The first objective was to develop updated cradle-to-gate LVL manufacturing LCI data. The second was to assess environmental impacts associated with LVL production in the United States by performing a cradle-to-gate LCA, focusing on two regions: the SE and the PNW. The results of this study provided information on current environmental performance of the regional LVL production in the United States. The outcomes of this life-cycle impact assessment (LCIA) study can be used by LVL plant managers and wood associations to identify potential process improvements and to enhance environmental performance of LVL production in the two regions.

In accordance with international standards (ISO 2006b, 2006c; International Reference Life Cycle Data System 2010), the scope of the present LCA study covered the life-cycle stages of LVL from forest resource activities through veneer production to the final LVL product leaving the plant. The present LCA provided a cradle-to-gate analysis of environmental impacts and cumulative energy of manufacturing and transportation of raw materials to the veneer and LVL production facilities.

Allocation procedure

Selecting an allocation approach is an important part of an LCA study. In the present study, all primary energy and environmental outputs were assigned to various coproducts by mass allocation. The decision was based on the fact that LVL as the final product contained more than 90 percent of the mass leaving the system and because the specific gravities of both LVL and associated coproducts were similar. The earlier CORRIM study applied mass allocation, whereas in this study, economic allocation was performed in addition to mass allocation because the wood product PCR suggests using economic allocation for a multioutput process when the difference in revenues is more than 10 percent (FPInnovations 2015). The results of the analysis using economic allocation are provided.

Functional unit

In accordance with the PCR (FPInnovations 2015), the declared unit for LVL was 1 cubic meter (1 m³). A declared unit was used in instances where the function and the reference scenario for the whole life cycle of a wood building product cannot be stated (ISO 2007, FPInnovations 2015). For conversion of units from the US LVL industry measure, 1 ft³ of LVL equals 0.02832 m³ with a final product ovendried moisture content of 6 percent. All input and output data were allocated to the declared unit of product based on the mass of products and coproducts in accordance with ISO 14044 (ISO 2006b). As the analysis does not take the declared unit to the stage of being an installed building product, no service life was assigned.

System boundaries

The system boundary begins with regeneration in the forest and ends with LVL at the mill gate (Fig. 1). The system boundary included forest resources, transportation of roundwood to the primary breakdown facility, dry veneer production, dry veneer transportation to the LVL facility if needed, phenol-formaldehyde (PF) resin production, and LVL production. Three unit processes in LVL manufacturing included lay-up, hot pressing, and sawing and trimming. Packaging of LVL was also considered in the system boundary. Resources used for the cradle-to-gate production of energy and electricity consumed on-site were included within the cumulative system boundary. In addition, ancillary material consumption data, such as motor oil, paint, and hydraulic fluid, were included in the analysis. Off-site emissions that were accounted for include those from grid electricity production, transportation of feedstock and the resin, and off-site fuel production.

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System investigated

The cradle-to-gate LCA of LVL manufacturing included three major life stages: forestry operations, dry veneer production, and LVL production. The PF resin used in LVL production as part of the resin system was included in the analyses and considered as an upstream process in LVL production.

Inventory approach

The relevant primary quantitative data to develop gate-to-gate inventory, including input and output flows associated with the unit processes included in the system boundaries of LVL production, were collected through surveys. The surveyed plants provided detailed annual production data on their facilities for the year 2012. This survey tracked raw material and energy inputs, product and by-product outputs, and pertinent emissions to water and air as well as solid waste generation. Secondary data, such as pre–mill gate processes (e.g., forestry operations, dry veneer production, and electricity production), were retrieved from peer-reviewed literature and public databases.

There were two major energy sources used at the LVL plants: electricity and natural gas. The electrical grid composition for the PNW and SE regions of the United States was adopted from the US LCI database (NREL 2012). Natural gas (31.8%) and coal (30.2%) power made up most of the PNW (WECC) grid, while coal (56.4%) and nuclear (25.2%) made up most of the SE (SERC) grid. Another major on-site energy source used was natural gas. Burning natural gas generated steam that was then used in the hot-pressing unit process.

For the cradle-to-gate LCA analysis, the gate-to-gate LVL LCI data developed using the survey data were linked to available forest resources (Johnson et al. 2005; Puettmann et al. 2013a, 2013b), dry veneer production LCI data (Kaestner 2015; M. Puettmann, personal communication, April 24, 2015), and finished LVL packaging (Puettmann et al. 2013a, 2013b) along with any required transportation to construct the cradle-to-gate LCI. Complete details of this study for LCI development for LVL production and the CORRIM project can be found in Bergman and Alanya-Rosenbaum (2017a, 2017b).

Cutoff rules

According to the PCR (FPInnovations 2015), if the mass–energy of a flow is less than 1 percent of the cumulative mass–energy of the model flow, it may be excluded, provided that its environmental relevance is minor. This analysis included all energy and mass flows for primary data.

In the primary surveys, manufacturers were asked to report total HAPs specific to their wood products manufacturing process regardless of whether they were less than the 1 percent cutoff. These are methanol, acetaldehyde, formaldehyde, propionaldehyde (propanal), acrolein, and phenol. If applicable to the wood product, HAPs are reported in the LCI Data section of Bergman and Alanya-Rosenbaum (2017a, 2017b). Under Title III of the Clean Air Act Amendments of 1990, the US EPA has designated HAPs that wood products facilities are required to report as surrogates for all HAPs. All HAPs are included in the LCI; no cutoff rules apply.

Data quality requirements

The present study collected data from representative LVL manufacturers in the PNW and the SE that use average technology for their regions. The dry veneer produced at the product manufacturing facilities mills in the two regions of the United States is the raw wood input to LVL production.

Total US LVL production for 2012 was 1.31 million m³. The United States has eight companies with 15 operating production facilities, with seven in the PNW region and eight in the SE region. Of the 15 plants, six facilities participated in the study. Two US LVL plants representing 8.5 percent of 2012 US production (0.111 million m³) for the PNW region and four US LVL plants representing 26.4 percent of 2012 US production (0.344 million m³) for the SE region participated in the study by providing primary data for each region (APA—The Engineered Wood Association 2014). Although the number of plants surveyed may be small compared with a “typical” mail survey, the level of detail and amount of primary mill data were very high. Each facility contributed a substantial amount of time completing the questionnaire, ranging from 20 to 28 hours, with an average of 24 hours, including follow-up questions. In addition, to aid in data quality, the authors conducted a site visit after all the survey data were collected and analyzed. The PNW and the SE are the primary regions for producing structural wood products such as LVL. The surveyed plants provided detailed annual production data on their facilities, including on-site energy consumption, electrical usage, veneer volumes, and LVL production for 2012. Wilson and Dancer (2005) performed a 2000 US LVL LCI study that covered 34 percent (0.187 million m³) and 52 percent (0.221 million m³) of production for the PNW and the SE, respectively. The production of surveyed facilities for 2012 showed a decrease of 40 percent from 2000 for the PNW and an increase of 56 percent for the SE. In addition, unlike the earlier 2000 study, 2012 LVL production data were not available by region. Therefore, total LVL production data by region could not be quantified for 2012.

To ensure data of the highest quality, data control measures were taken. Quantitative mass balances were performed to verify data quality. First, mass balances at individual facilities were conducted where the data were found to be consistent for the surveyed mills. Second, overall wood mass in and total wood mass out for both regions were calculated, and the difference was less than 2 percent. A difference less than 10 percent is considered good for wood product production. In addition, the primary data obtained from the surveys were weight averaged. The weighted coefficient of variation representing the variability in the collected process data was calculated and presented. Additionally, a sensitivity analysis investigating the energy inputs into LVL production was performed to investigate the robustness of the impact assessment results.

Assumptions and limitations

The data collection, analysis, and assumptions followed the protocol defined by CORRIM in “Research Guidelines for Life-Cycle Inventories” (2014). To conform to ISO 14040 (ISO 2006c), additional considerations are listed below:

• Although small in quantity relative to the wood mass, impacts from production of the resin system were included in the analysis.

• The authors did not collect 2012 primary forest resource data but used secondary data from earlier LCA studies to develop the cradle-to-gate analysis. It is expected that forest resource data will be updated in the near future. As mentioned previously, to develop new EPDs, new underlying LCA data must be continually generated per the North American wood product PCR (FPInnovations 2015).

• For the secondary data for forest resource incorporated into the analysis, data included growing seedlings, planting, thinning, fertilization (where applicable), and final harvest.

• For regional forest harvesting, a single estimate of the average volume harvested per unit area was developed by weighting three combinations of management intensity (low, medium, and high intensity) and site productivity based on the relative percentage of the land base they occupy. Puettmann et al. (2013a, 2013b) list specific inputs, input assumptions, variations in harvest equipment, and fuel consumptions for the three management intensities for the two regions.

• Harvesting cycles averaged 27 and 45 years for the SE and PNW regions, respectively.

• Land use impacts, including biodiversity, were not incorporated into the present study. The forests were considered to be replanted as forests and eventually returned to their previous state.

• Forest carbon increases and decreases were not tracked but considered that the harvested trees were being sustainably managed through the ASTM standards D7612-10 and D7480-08 (ASTM International 2010, 2014b).

• Temporal dimensions of greenhouse gas (GHG) emissions were not included because the study focused on the cradle-to-gate production, which occurs within a relatively short time frame, versus cradle-to-grave production, where long-term GHG emissions and carbon sinks have a greater influence on the global warming (GW) impact category (Bergman 2012).

• All flow analyses of wood and bark in the process were determined on an ovendry weight basis using a weighted production density of 543 and 563 kg/m³ for the PNW and the SE, respectively.

• The water consumption for two SE plants were combined with dry veneer production. Veneer production consumed 285 liters/m³ LVL, with the rest, 2 liters/m³, allocated to SE LVL production (Kaestner 2015, Puettmann et al. 2016a).

• Biogenic CO₂ emissions were tracked and reported, but the TRACI 2.1 impact method (Bare 2011) does not count the contribution of wood-derived CO₂ emissions from burning wood fuel in the boiler toward the GW impact estimate.

• Carbon content for wood products is assumed to be 50 percent by mass of ovendried wood.

• As mentioned previously, the regional LVL production for year 2012 was not available; therefore, quantitative regional representativeness was not provided.

Impact category method

The LCIA was performed using the TRACI 2.1 method (Bare 2011). TRACI is a midpoint impact assessment method developed by the US EPA specifically for the United States. Five impact categories were examined, including GW (kg CO₂ eq), acidification (kg SO₂ eq), eutrophication (kg N eq), ozone depletion (kg chlorofluorocarbons-11 eq), and photochemical smog (kg O₃ eq). These five impact categories are reported consistent with the requirement of the wood products PCR (FPInnovations 2015). In this study, environmental burdens were assigned to the LVL and the coproducts (i.e., sawdust) both by mass and economic value in order to investigate the effect of allocation method on the results.

Sensitivity analysis

A sensitivity analysis was performed to determine how sensitive the results are to certain changes in parameters (i.e., on-site natural gas and electricity consumption) at the LVL plant. Analysis was completed in line with ISO 14040 standards (ISO 2006c). The effect of variation in the consumption of natural gas and electricity on cumulative primary energy consumption (CPEC) and GHG emissions was investigated.

Critical review

An internal review of this cradle-to-gate LVL LCA study, including the associated SimaPro model, was conducted by Dr. Maureen Puettmann, WoodLife Environmental Consultants. The purpose of the internal review was to check for errors and for conformance with the PCR prior to external review.

LCI analysis

Material inputs to develop gate-to-gate LVL LCIs for the SE and PNW regions are provided in Table 1. To evaluate data quality, a weighted-average mass balance of the LVL plants was performed. The data consistency was high based on the weighted production coefficient of variation (CoVw) values calculated for system inputs and outputs. For the final product, LVL, the data showed good consistency between facilities, with a CoVw of 4.0 and 2.9 percent for the SE and the PNW, respectively. In addition, the CoVw for total feedstock was 6.5 percent (SE) and 4.1 percent (PNW).

Table 1 Gate-to-gate material flow analysis of 1 m³ of laminated veneer lumber (LVL) manufacturing in the Southeast (SE) and Pacific Northwest (PNW) regions.

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Weighted-average energy inputs consumed on-site at the LVL manufacturing sites in SE and PNW plants are presented in Table 2. Electricity and natural gas were the primary energy inputs, where natural gas was used to generate heat. The production-weighted CoVw showed large variation for both regions except for propane consumption for the SE and natural gas consumption for the PNW (10% and 11%, respectively). At SE plants, gasoline consumption showed the largest variation.

Table 2 Gate-to-gate weighted-average on-site energy inputs to produce 1 m³ of laminated veneer lumber.

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Air emissions from the LVL plant were derived from the surveyed mills along with pertinent emissions data categorized by the US EPA (2002). When available, surveyed air emission data as primary data were selected over secondary data (Table 3). Waste generated was incorporated in the analysis as well.

Table 3 Direct outputs resulting from production of 1 m³ of laminated veneer lumber, gate to gate.^a

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Transport of materials to the LVL plant was accounted for in the analysis. The weighted-average transport distance for feedstock along with the resin to the LVL plants based on the survey results is provided in Table 4.

Table 4 Weighted-average delivery distance (one way) by mode for materials to laminated veneer lumber plant.

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Cumulative energy consumption

Table 5 presents the cradle-to-gate CPEC per 1 m³ of LVL in the SE and PNW regions. The major energy source used was wood fuel, about 36 and 53 percent for the SE and the PNW, respectively, resulting primarily from veneer production, which was used to generate thermal energy for log conditioning and drying and pressing veneers. Thus, 99 percent of the biogenic CO₂ was released during veneer production (280 and 394 kg per 1 m³ of LVL were produced in the SE and the PNW, respectively). For LVL production, energy consumption was dominated by fossil fuels, that is, natural gas and coal. Natural gas was used primarily for thermal energy generation for hot pressing the LVL billets and some for fueling thermal oxidizers for emission controls. Coal consumption in the SE (18%) and PNW (12%) resulted from coal-based electricity generation. Other resources used for electricity generation included hydroelectric, wind, solar, and geothermal energy resources. Forestry operations consumed relatively low energy, which was exclusively fossil fuels: 2.6 and 1.8 percent of the CPEC for the SE and PNW, respectively.

Table 5 Cumulative primary energy consumption per 1 m³ of cradle-to-gate laminated veneer lumber (LVL) (mass allocation).

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Life-cycle impact assessment

In this study, five midpoint impact categories were investigated. Environmental performance results for five impact categories along with energy consumption from nonrenewables; renewables; wind, hydroelectric, solar, geothermal, and nuclear fuels; renewable and nonrenewable resource use; and solid waste generated are presented in Tables 6 and 7 for the SE and the PNW, respectively. The results showed that the total primary energy consumption in the SE region for all three life-cycle stages is 9.98 GJ/m³, where it was 8.97 GJ/m³ in the PNW region. In both the SE and the PNW, the veneer production life-cycle stage consumed the most primary energy at 6.83 GJ/m³ (68.5%) and 6.75 GJ/m³ (75.3%), respectively.

Table 6 Environmental performance of 1 m³ of laminated veneer lumber (LVL), cradle to gate, Southeast (mass allocation).

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Table 7 Environmental performance of 1 m³ laminated veneer lumber (LVL), cradle to gate, Pacific Northwest (mass allocation).

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The contribution of major substances to the overall impact for the five impact categories considered are provided in Figure 2. Considering the GW impact category in terms of the contribution of life-cycle stages, the greatest contributor at both regions was veneer production, above 52 percent, followed by LVL manufacturing. The veneer production stage process dominates the impact at both regions, with about more than 50 percent contribution, for all impact categories except for ozone depletion and eutrophication. Of the two, the ozone depletion category stands out because it was dominated by the LVL stage. This was due mainly to the resin consumption occurring at the lay-up process. Electricity consumption followed by natural gas use had notable contributions to GW at the LVL manufacturing stage, where electricity has contributions of 42 and 45 percent to overall GW for the PNW and SE, respectively. Overall, the contribution of forestry operations to the resulting impacts was minor.

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The approach for biogenic carbon accounting was adopted from the Norwegian Solid Wood Product PCR (Aasestad 2008) and the North American PCR (FPInnovations 2015) to ensure comparability and consistency. The North American PCR approach was followed for GW impact reporting; therefore, the default TRACI impact assessment method was used. This default method does not count the CO₂ emissions released during the combustion of woody biomass during production. Other emissions associated with wood combustion, such as fossil CO₂, methane, or nitrogen oxides, do contribute to and are included in the GW impact category. Using this method, total (fossil and biogenic) GHG emissions released were calculated as 323 and 207 kg for the SE and PNW, respectively, in the production of 1 m³ of LVL (Table 8). That same 1 m³ of LVL stores 995 and 959 kg CO₂ eq for the SE and PNW, respectively.

Table 8 Carbon balance per 1 m³ of laminated veneer lumber.

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Scenario analysis

The influence of using the mass and value allocation on the final product, LVL, and its associated coproducts on the impact assessment results were analyzed (Tables 9 and 10). The cradle-to-gate impact assessment results for the categories taken into consideration showed only a slight difference (1% to 2%) except for the ozone depletion impact category (6% and 10% for the SE and PNW, respectively), which is because of the increased contribution of the LVL production stage. Value allocation resulted in a 12 to 13 percent increase in the impact resulting from the LVL stage in all impact categories. This was owing to the environmental burdens shifted toward the production of LVL, where the economic value of the coproducts was minor. The difference in impact resulting from the veneer production stage ranged between 6 and 9 percent in all impact categories except ozone depletion. The ozone depletion impact category of the veneer production stage was about four times lower for value allocation compared with mass allocation in both regions. However, because the impact from ozone depletion was far higher for the LVL production stage, the difference between value and mass allocation for the overall ozone depletion impact was not major. Regardless, most of the ozone depletion impact at the veneer production stage was assigned to the wood boiler used in veneer drying. The fuel used in the wood boiler was a mixture of the coproducts coming from a downstream process at plywood production. The lower ozone depletion for economic allocation was a result of lower emissions allocated to coproducts owing to their low economic value. In addition, the difference in CPEC between the mass and value allocation was not significant at below 3 percent.

Table 9 Environmental impact assessment results for mass and value allocation for the Southeast region.^a

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Table 10 Environmental impact assessment results for mass and value allocation for the Pacific Northwest region.^a

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Comparison

To validate LCA studies, comparisons were performed. This study compared the energy inputs from the current 2012 study with the earlier CORRIM Phase I study to show how the CPEC for LVL was affected. The on-site, industry-average energy inputs reported in 2012 were substantially higher than for Phase I (Wilson and Dancer 2005; Puettmann et al. 2010, 2013a, 2013b). In particular, for the SE, electricity and natural gas consumption drove the total impact from energy with changes of 41 and 76 percent, respectively (Table 11). As expected from the higher CPEC value found earlier, the on-site energy inputs were substantially higher than for Phase I for the PNW as well (Wilson and Dancer 2005; Puettmann et al. 2013a, 2013b). In particular, electricity and natural gas consumption drove the total impact from energy with changes of 30 and 234 percent, respectively (Table 12). Therefore, a sensitivity analysis that investigated the energy inputs into LVL production was completed to see their overall impact. However, the apparent statistical differences between the older and current studies could not be adequately addressed because no statistical description of the data from the earlier study was available. The earlier CORRIM study did not perform sensitivity analysis. However, there was sufficient reason to attempt to quantify the energy impacts associated with LVL production.

Table 11 Production weighted-average Southeast (SE) on-site energy inputs for manufacturing 1.0 m³ of laminated veneer lumber.

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Table 12 Production weighted-average Pacific Northwest (PNW) on-site energy inputs for manufacturing 1.0 m³ of laminated veneer lumber.

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Sensitivity analysis

A sensitivity analysis was performed in accordance with the ISO 14040 standard to model the cradle-to-gate effects of varying on-site natural gas consumption and electricity consumption for LVL production. The effect of a 20 percent variation in the consumption of natural gas and electricity at the LVL plant on the CPEC and GW impact was investigated. Sensitivity analysis revealed that neither natural gas nor electrical consumption on-site had a substantial effect on cradle-to-gate CPEC and GW impact. This is due to fact that the dry veneer production had a relatively large effect in comparison with the environmental indicators associated with energy consumption, as shown in Table 5.