Determination of life cycle GHG emission factor for paper products of Vietnam

2.1 Methods

The research method diagram and system boundary for determining LCA GHG emission factor of writing paper, tissue paper, and carton box are presented in Figures 1 and 2, respectively.

Figure 1

Method diagram and system boundary.

Figure 2

Types and locations of pulp and paper mills in Vietnam.

Virgin pulp and used paper are inputted into the paper production processes as materials. Materials are transported from the pulp mills and/or recycled villages to the paper mills. Both virgin pulp and used paper are either domestic and/or imported sources. In the virgin pulp processing process, under a certain temperature and pressure, cellulose is extracted from the wood by chemicals. In the paper production process, hydraulic crushing, paper machining, paper pressing, and paper drying are four main stages, except for the extra stage of carton box machining which is only for the carton box. Electricity from the national grid and heat produced from coal-fired boilers are energy sources for the production processes, diesel is an energy source for transportation. In pulp and paper mills, the black liquor is used as biomass-derived energy. In this analysis, the GHG emission of woods is considered as neutral because trees grow by absorbing CO₂ through photosynthesis.

LCA GHG emissions are principally calculated as the following:

where direct emissions occur during the use of materials or fuels (e.g. Combustion of fossil fuel) and indirect emissions occur during the production of materials or fuels (e.g. Production of a virgin pulp)

The following formulas are developed based on ISO 14067 guidelines and considered the environmental burdens of the paper mill’s processes and domestic transportation:

where

where E_W, E_T, E_C, E_K, E_CB are LCA GHG emission factor of writing paper, tissue paper, corrugated paper, kraft-liner paper, and carton box, respectively; r_1W, r_1T, r_1C, r_1K are proportion of recycled material inputs for producing writing paper, tissue, corrugated paper, and kraft-liner paper, respectively; r_2W, r_2T, r_2C, r_2K are proportion of material recovery after use of writing paper, tissue, corrugated paper, and kraft-liner paper, respectively; E_VT, E_VW are GHG emission factors of virgin pulp used to produce tissue and writing paper, respectively; E_RT, E_RW are GHG emission factors of used paper used to produce tissue and writing paper, respectively; E_PT, E_PW are GHG emissions from the production process of a ton of tissue and writing papers respectively; E_VK is the GHG emission factor of virgin pulp used to produce kraft-liner paper; E_RC, E_RK are GHG emission factors of used paper used to produce corrugated and kraft-liner, respectively; E_PC, E_PK, E_CBM are GHG emissions from the production process of a ton of corrugated paper, kraft-liner paper, and carton box machining, respectively; T_TR–W, T_TR–T, T_TR–C, T_TR–K, T_TR–CB are GHG emissions from domestic transports in a life cycle of a ton of writing paper, tissue paper, corrugated paper, kraft-liner paper, and carton box, respectively. The GHG emission from materials’ transport is estimated based on the distance between paper mills. It is the sum of the emission from virgin pulp transport (from pulp mills to paper mills) and the emission of paper and/or used paper transport (between paper mills, from paper recycling village to paper mills).

It is noted that the paper mills recover fibers from wastewater. The average recovery ratio of corrugated paper and other papers is 3% and 5%, respectively. These amounts are subtracted from the domestic recycled pulp flows.

For open-loop recycling analysis, allocation factor determination is very important, it will help LCA results are not subjective by implementers. Allocation factor, a, can be determined based on the mean number of uses and mean fiber age [10,11]. However, the calculation process is relatively complicated and requires comprehensive data. This study uses a simple, but standardized one: an allocation factor is identified based on the recovering ratio and the number of times the fiber is recycled [12].

where a is the allocation factor; z is the recovering ratio of used paper (z = 45% [13]); and u is the number of recycling times in Vietnam (u = 5 times [13]).

2.2 Data

There are three types of paper mills in Vietnam include (I) pulp and paper; (II) paper products (writing paper, tissue, kraft, corrugate paper); and (III) carton box and other packaging papers. The paper mills are divided into three scales: (i) large scale (capacity > 1,00,000 tons of product/year); (ii) medium scale (capacity of 1,000–10,000 tons of product/year); and (iii) small scale (capacity <300 tons of product/year), accounts for about 4%, 50%, and 46% of the total number of paper mills, respectively [14].

Domestic used paper is classified at source and collected by retail collectors, transported to collection agents in the papercraft villages, and then transported to the pulp and paper mills. Greenhouse gas emissions from delivery to consumers and collection from small collectors are not included in this study. Most paper mills are located in central areas of the North and the South (Figure 2), and the transportation of materials and paper products is relatively independent between the regions.

In the North, there is a full range of paper mills and a balanced ratio of paper products, while in the South, the number of tissue production mills accounts for only 7% of total tissue mills in Vietnam. Therefore, this study surveyed and collected primary data at paper mills in the North.

Primary data include the materials (pulp and used paper), energy (electricity, coal, and diesel), and chemicals are operational data. For each data item of each paper mill type, the input data are the average value of the primary data collected. Detail information regarding the inventory of the foreground system of paper production is presented in Table 1. Generally, the filler is used to increase product quality and reduce production costs. Paper mills in Vietnam often mix filler about 8–10% in the paper production process. Transport of pulp and/or paper from pulp mills (type I) to other paper mills (types II and III) using 2.5 tons-truck (full load) averagely consumes 0.1 L of diesel per kilometer [15].

Secondary data include emission factors of imported virgin pulp and used paper, which is inputted to produce paper products, and energy sources were referred from scientific publications and prestigious reports. In recent years, the industry imports from abroad about 50% and 55% of pulp and used paper, respectively. The biggest pulp suppliers are North America (accounting for 40.5%), Latin America (33%), and Europe (13.3%). The biggest used paper suppliers are the USA (accounting for 47%), Japan (29%), and Europe (17%) [2]. This study uses the average emission factors: 508 kgCO_2eq/ton of kraft and 513 kgCO_2eq/ton of chemical–mechanical [16]. The emission factors of carton box and writing paper imported from Europe, Japan, and US are 964 kgCO_2eq [17], 810 kgCO_2eq [18], 1,040 kgCO_2eq [19] (carton box) and 800 kgCO_2eq [20], 830 kgCO_2eq [18], 1,152 kgCO_2eq [21] (writing paper), respectively. Then, emission factors of the paper products are calculated according to the contribution rate of imported raw materials from the above countries, resulted in 954 kgCO_2eq/ton of carton box and 987 kgCO_2eq/ton of writing paper. It is noted that the use and end-of-life phases of the papers were excluded from the above values. The emission factor of the Vietnamese grid in 2018 is 0.854 kgCO₂/kW h [22]. The GHG emission factors of coal use for boilers and diesel use for transportation are referred to as IPCC 2006 guidelines [15].

3.1 Open-loop recycling and allocation

The system boundaries and material flows for writing paper, tissue, and carton box are determined based on the open-loop recycling approach, as seen in Figure 3a and b. Virgin pulp and used paper were used as material inputs in paper mills of the three paper products. Used paper is recycled and allocated to paper products in subsequent life cycles. Carton box paper has a higher demand for used paper than writing paper and tissue. The used papers that are disposed and/or allocated to other paper mill types (such as votive paper, printing paper, and other packaging paper) are not considered in the scope of the boundary.

Figure 3

(a) System boundary and material flow for LCA of writing paper and tissue and (b) system boundary and material flow for LCA of carton box.

3.2 LCA GHG emission factor of the paper products

The LCA GHG emission factor of each paper product is calculated by Eq. 2–4. Table 2 presents a summary of the calculations.

As the results, LCA GHG emission factor (EFCO2eq) of writing paper, tissue paper, and carton box is 1,224 kgCO_2eq, 751 kgCO_2eq, and 1,366 kgCO_2eq, respectively. The LCA GHG emission factor of carton box product is higher than other products because its production process has more stages and consumes more energy.

The LCA system boundary of pulp and papers normally includes four primary life-cycle stages: pulp processing, paper production (includes converting papers to final paper products), transportation (transport-in-use), and end-of-life (landfill and incineration). In this study, the LCA system boundaries include the first three stages. To ensure comparability between this study and the cases over the world in the same systematic boundaries, the end-of-life stage of the paper products were excluded from the scope because of high uncertainty in the paper-use phases and disposal methods after use. Comparing over the cases, LCA GHG emissions of Vietnamese pulp and papers belong to the medium-high emission group and strongly relate to the energy mix. The industry consumes coal and chemicals intensively [2]. In addition, technologies of recovery energy from black liquor are ineffective [13]. Energy mix in the pulp and paper industry varies markedly between the countries. In Vietnam, coal and electricity are the two main energy sources, just a small amount of renewable energy is used from the black liquor recovery process in Bai Bang and An Hoa pulp and paper mills (type I). This situation is similar to the Chinese pulp and paper industry that used 64.1% of coal [23], while Europe used only 3% of coal [24] and the US used 8.7% of coal [25]. In European countries, USA, and Brazil, renewables such as hydropower and biomass play a major role in the energy mix, the system of recovering energy from black liquor is modernized. The emission factor of Chinese writing papers belonged to high emission group with over 1,500 kgCO_2eq [16], while the values in the US and Brazil were 1,152 and 1,050 kgCO_2eq, respectively [26,27]. The emission factor of tissue paper in Europe was 692 kgCO_2eq [28]. The emission factors of the carton box in Europe and the US were 964 and 1,040 kg CO_2eq [17,19].

Figure 4 shows the LCA GHG emissions associated with the input materials and processes. The emissions from transportation take the smallest fraction, accounted for 0.69% to 1.06%. It is noted that the burden of importing materials (transportation) is not considered in this scope. The emissions from materials (pulp and used paper) accounted for about 12.74% to 23.66% of total emissions. The biggest burdens come from the paper production process (crushing, machining, pressing, etc.), accounted for 75.65% to 86.31% of total emissions. This distribution is similar to other countries in the world [23,29].

Figure 4

GHG emissions from different inputs in the life cycle of paper products. (a) Carton box, (b) writing paper, (c) tissue paper.

Figures located in the bottom left corners of Figure 4 to unveil the percentage of GHG emissions contributed from different inputs in the life cycle of Vietnamese paper products. As seen, the emission from electricity use accounted for 23.12% to 32.97% of total GHG emissions, which is similar to the other countries [16,29]. The emission from coal use accounted for 45.02% to 52.47% of total GHG emissions, higher than the other countries normally accounted for 20% to 25% of total GHG emissions [30]. Some countries use gas and other energy instead of coal, such as European countries: 43.9% biomass, 26.3% gas, 24% electricity, and 3.0% coal [24]; the US: 43% biomass, 38.5% gas, 9.2% electricity, and 8.7% coal [25]. The emissions from chemicals use in Vietnam were low and responsible for only 0.87% to 5.53% of total GHG emissions.

At 2015-Paris Agreement, Vietnam has set a goal to 2030 that “…by domestic resources, 8% of the total GHG emissions will be reduced in comparison with normal developmental trajectory and the target can rise up to 25% when receiving international support by means of bilateral, multilateral cooperation and performing new mechanisms.” To reach the goal, all economic sectors, in general, and the pulp and paper industry needs to find out the solutions to diminish the sector’s energy intensity and GHG emission factor as well.

To achieve long-term and sustainable energy-saving effects for the paper industry, paper mills need to reduce the use of fossil energy in the pulp processing and paper production processes and increase the use of renewable energy. The effectiveness of these solutions has been shown in some literature [16,23]. Besides, the paper mills should improve production machinery systems such as installing inverters to reduce energy consumption and increase the durability of machinery, improving the convection systems to increase the boiler’s efficiency. Moreover, the energy recovery systems should be modernized. All the type I paper mills in Northern Vietnam currently have a black liquor-based energy recovery system in the pulp processing but the efficiency of the system is not high enough.

Assessing the possibility of reducing emissions when replacing virgin materials with recycled materials, the study has progressed to LCA for two paper product types in the same paper mill: one made from virgin materials and the other made from recycled materials (Figure 5). As seen, the GHG emissions of virgin paper-based products are often higher than that of recycled paper-based products. This suggests that trying to increase the percentage of used paper for the production process would reduce the burden on the environment. Indeed, the numbers of studies have shown similar results [16]. As the case with Spain’s tissue production, LCA GHG emission of recycled paper-based products was about 30% lower than that of virgin pulp-based products [29].

Figure 5

GHG emission of virgin paper-based products and recycle paper-based products.

Global recycling rates of materials in the pulp and paper industry is now over 70%, namely: USA (70%), EU (73%), Japan (81.3%), Asia (51.5%), the average of the world (59%), and Vietnam (45%) [13]. To reduce GHG emissions as well as production costs for the Vietnamese paper mills, it is necessary to increase the domestic-used paper rate in the material flows. The cost-effectiveness of the paper collection and classification system in the country needs to be improved. The awareness of handling recycling products is not commensurate and needs to be enhanced.

The pulp and paper industry is an economic sector with a natural fit for the circular economic model. Therefore, making use of recycled paper sources and saving energy is very important. To use recycled papers as a main material source in the paper mills, it is necessary to encourage paper recovery and recycling by legislating laws on recycling and saving resources as some developed countries have done. The pulp mills need to improve machinery to save energy and improve production efficiency by applying cleaner production and energy efficiency measures as well as using renewable energy.