2.1 Quantification of GHG emissions with the GHG Protocol method

Among the different methodologies for quantifying, analyzing and managing corporate GHG emissions, the GHG Protocol Corporate Accounting and Reporting Standard is the most used tool worldwide by companies and governments (^{WBCSD, 2014}).

The GHG Protocol is a management method, compatible with the International Organization for Standardization (ISO) and the Intergovernmental Panel on Climate Change (IPCC) quantification methodologies. Its application in Brazil is adapted to the national context. It was developed by the World Resources Institute in association with the World Business Council for Sustainable Development in 1998, and it is periodically updated (^{FGV/WRI, 2009}). In addition to its wide use, this tool stands because it offers a structure to account GHG with a modular and flexible way. Its policy neutrality and the fact that it is based on a wide public consultation process were also decisive factors for choosing this methodology and using it in this work.

According to this method, companies need to assess their responsibility for GHG emissions from (a) their internal operations, (b) the purchase of energy from sources outside the corporation and internal use, and (c) emissions from products upstream and downstream of the value chain. These responsibilities are referred as Scope 1, Scope 2, and Scope 3, respectively (^{Patchell, 2018}).

All the potential sources of GHG emissions into the atmosphere from the industrial establishment were identified. All activities and operational routines were verified. The studied plant is integrated with the transformation cycle starting at iron ore. The pig iron is manufactured in a blast furnace, with charcoal as its main reducing agent.

The identified emission sources were based on the amount of fuel used by the fleet, internal industrial processes, total consumed energy and generated effluents. These sources were classified as direct (Scope 1) or indirect (Scope 2), as established in the GHG Protocol methodology. Due to insufficient data to report Scope 3 emissions, only the mandatory reports (Scopes 1 and 2) were chosen.

Quantification of emissions was performed using the methodology of the Brazilian GHG Protocol Program v. 2018.1.4 (^{EAESP/FGV, 2021}). The methodology of this research followed the guidelines and information contained in this method.

Three limits were defined: the temporal range (reference period), the organizational limits, and the operational limits. The reference period was the time frame for quantification of emissions (from January until December 2018) and served as the basis for the analysis of emissions data. The organizational limits physically delimit where the work will be performed. The Brazilian GHG Protocol Program considers two approaches to consolidate emissions: operational control (when the company has the authority to define and implement operating policies, including 100% of its emissions in the inventory) and equity participation (inclusion of emissions according to equity interests, reflecting its participation percentage in the operation). The operational limit refers to all activities within the organizational limits that emit GHG. Identification of emission sources is required, as well as distinguishing between direct and indirect emissions in order to associate them with the corresponding scopes.

The GHG Protocol includes calculations based on specific emission factors for the analyzed components. The approach used to calculate GHG emissions is the application of documented emission factors. The emission factor is a mathematical indicator of the amount of GHG emitted to the atmosphere in relation to a given emission source.

Each spreadsheet of the tool was programmed using the formula and the emission factor to quantify the emission, presenting, in the end, the scope emission and its condensation. The tool has a model of source transformation into CO₂ equivalent (CO₂eq), considering the global warming potential (GWP) of each GHG.

Emission factors determine how much of a GHG was emitted by the activity. It corresponds to a representative value reporting the amount of GHG emissions or removals to an associated activity. A practical example is how much CO₂ is emitted when one liter of fuel is consumed (^{SEBRAE, 2015}).

The agents that publish factors used as reference by the Brazilian GHG Protocol calculation tool are (a) the IPCC (scientific basis that presents standard values), (b) the National Energy Balance (BEN), (c) the Brazilian Ministry of Science, Technology, Innovations and Communications (MCTIC), (d) the Brazilian Ministry of Environment (MMA), and (e) the Department for Environment Food and Rural Affairs (DEFRA).

The Brazilian GHG Protocol tool uses the emission estimation method (estimation approach), which consists of emission data (such as data on electricity consumption and gasoline burning in vehicles) multiplied by appropriate emission factors (used to determine the quantity emitted by a given source, depending on some parameters). Thus, to calculate emissions or removals of different GHG, in general, the tool performs the calculation according to Eq. (1) below:

where E _GHG GHG emissions or removals, C is the combination of activity information (activity data), and EF is the emission factor.

Subsequently, emissions or removals are converted to identify the amount of CO₂eq in tons (tCO₂eq). This calculation is made considering the global warming potential of each GHG (Eq. [2]):

where E are GHG emissions or removals in CO_2eq, E _GHG are emissions or removals from GHG, and GWP is the global warming potential of GHG.

GWP values used as a reference and emission factors used in the inventory were provided by the GHG Protocol estimation tool. The simplified method presented above represents the quantification of emissions by the Brazilian GHG Protocol tool for the following categories: stationary combustion, mobile combustion, fugitive emissions (Scope 1) and energy (Scope 2). The calculation of industrial processes and effluents categories (Scope 1) was performed with alternative data that will be discussed below.

2.2 Industrial processes category

The Industrial Processes category requires the value already calculated by Eq. (1). It is a more complex and particular category to be calculated (it will depend on the operation of each organization). There is a reporting space in the tool to enter these values.

According to Eq. (1), the data of each activity are multiplied by their respective emission factors to obtain the corresponding value for GHG emissions or removals. Thus, when the equivalent emission factors are not found in the literature, it is possible to calculate them by mass balance, since the amount of carbon present in a ton of precursor (supervised item) is known (^{IPCC, 2006}).

This work adopted the methodology used by the Guidelines for national greenhouse gas inventories (^{IPCC, 2006}). The calculation was made using the carbon content and the mass balance. The emission factor is the carbon content in tons multiplied by the CO₂ molecular weight: 44 t of CO₂ correspond to 12 t of C (3.6667 t of C).

The equivalent emission is obtained with Eq. (3):

where EF is the emission factor, CC is the carbon content in tons, and 44/12 is the molecular mass to carbon atomic mass ratio.

The values equivalent to carbon content of each item were obtained through laboratory analyzes of the carbon amount of each element, performed by the company itself. The values obtained after these calculations (emissions in tons of CO₂) were introduced in the Brazilian GHG Protocol tool to follow the calculation of CO₂eq emissions.

2.3 Effluent category

For the calculation of this category, the type of treatment performed and the amount of waste or effluent produced based on the number of active persons in the plant were recorded. There are two different ways to account these emissions: (a) as Scope 1 direct emissions if the company performs any treatment of effluents or solid waste generated within the established organizational limit; (b) as Scope 3 indirect emissions when the company collects all wastes and effluents and gives them a different destination, where another company is responsible for their treatment (^{SEBRAE, 2015}).

The studied company has a sewage treatment station equipped with an anaerobic filter, which receives effluents only from the bathrooms located in the upper part of the plant (treatment of sanitary effluents). This area is located in the sector of the company that covers foundry/valves and the parts yard, which is composed of 69 employees.

The GHG Protocol tool follows five steps for this quantification:

Step 1. Sequential treatments applied to effluents. It is necessary to identify if two types of anaerobic treatment are applied sequentially to the generated effluent; in the case of the company under study they were not applied.

Step 2. Estimation of wastewater generation data (amount of wastewater generated in the inventory year in m³ yr^-1). This calculation is performed by multiplying the per capita contribution of sewage (data available in the guideline DZ-215 [Table I]) by the number of employees (^{INEA, 2007}). Thus, the calculation was:

70 × 69 = 4830 L day^-1 4830/1000 = 4.830 m³ day^-1 4.830 × 365 = 1,762.95 m³ yr^-1

Step 3. Effluent organic composition data: the effluent degradable organic load data must be filled, choosing whether the data unit corresponds to biological oxygen demand (BOD) or chemical oxygen demand (COD). The following calculation was made based on the DZ-215 guideline (Table I):

25 × 69 = 1725 g BOD day^-1 1725/1000 = 1.725 kg BOD day^-1 1.725 × 365 = 629.625 kg BOD yr^-1

The value inserted in the Brazilian GHG Protocol tool was the degradable organic component of the effluent, which was obtained by dividing the value found in the amount of liquid effluent generated by the value of the unit of organic load contribution:

629.625/1,762.95 = 0.357 kg BOD m^-3

Then, data regarding the amount of nitrogen present in the effluent and the N₂O emission factor of the effluent needed to be filled. If there is no specific N₂O emission factor, this data may not be filled and remain as a blank field. In this case, the tool will use the default suggested by the ^{IPCC (2006)}. Nitrogen data entered in the quantification tool were obtained through monthly reports issued by the National Service for Industrial Learning (SENAI). This institution estimated the average value to calculate GHG emissions, which was 45 kg N m_-3.

Step 4. Type of treatment applied to the effluent. In this case, the anaerobic reactor option was selected.

Step 5. CH₄ recovery. If applicable, this line shows the amount of methane recovered from the effluent treatment in the inventoried year. No value was inserted.

3.1 Quantification of GHG emissions through the Brazilian GHG Protocol tool

A survey regarding GHG emission sources of the studied company was carried out, corresponding to their operational limits. The data from 2017 (time limit of this work) consisted of the company’s operational control approach. Seventeen sources were identified within the following categories: stationary combustion, mobile combustion, fugitive emissions, industrial processes, and effluents and energy.

The stationary combustion category is related to the burning of fuels by fixed equipment, which can be owned by the company or rented to operate under its management. Mobile combustion is related to the burning of fuels by mobile equipment. Emissions resulting from the intentional or accidental release of GHG (generated by air conditioning gas leaks or fire extinguishers, for example) are accounted in fugitive emissions. The industrial processes category includes all sources of industrial processes emissions that transform materials, either chemically or physically, and there may also be GHG sources through the use of products. The effluents category includes the waste produced during industrial processes that is no longer used by the company (^{SEBRAE, 2015}). All of these reported categories refer to Scope 1.

Scope 2 refers to the accounting of GHG emissions from the generation of purchased electricity, heat or steam. These emissions are generated where the energy is produced and subsequently consumed by the inventoried company. It is noteworthy that if the company carrying out the inventory produces any of these types of energy, the emissions generated by this process cannot be reported in Scope 2. In this case, they must be reported in Scope 1, since they will become direct emissions produced by the inventoried company itself (^{SEBRAE, 2015}).

The required data to quantify the emissions were based on documented real data. Requisitions were made to the company’s Warehouse and Controlling sectors, weighing reports and vouchers were redirected to the Health, Safety and Environment sector. Then, all information was provided to the authors for further analysis.

For all items, the required information for data entry was collected, as required by the Brazilian GHG Protocol spreadsheet. The quantification was made from the determination of the sources of GHG emission.

GHG emissions (t GHG) inventoried by the GHG Protocol tool, as prescribed by the Kyoto Protocol, are shown in Table II. According to this table, CO₂ is the most representative GHG of the steel factory emissions. The amount of 36 483.01 t CO₂eq corresponds to 99.27% of Scope 1 GHG emissions (36 750.47 CO₂eq) of the analyzed factory. This is mainly due to the transformation of pig iron into steel in converters and electric furnaces of the steel factory. This process always releases CO and CO₂ (^{Carvalho et al., 2016}).

GWP is the GHG contribution to global warming. The GWP of methane and nitrous oxide used by the GHG Protocol tool were 25 and 298, respectively (^{IPCC, 2007}). So, the representative values of these GHG increased and the Scope 1 total emissions reached 44 778.33 t CO₂eq. Scope 2 emissions (considering GWP of CO₂ equal to 1) remained at 5 460.95 t CO₂eq. Figure 1 illustrates the total CO₂eq emissions.

Fig. 1 Total emissions (Scope 1 and Scope 2) in tons of carbon dioxide equivalent (t CO_2eq). (Source: Prepared by authors [2019]). 

The total GHG emissions reached 50 239.27 t CO₂eq (Fig. 1). Scope 1 emissions (44 778.33 t CO₂eq) were responsible for 89.13% of the total CO₂eq emitted by all sources. The configuration of the Brazilian energy matrix contributed to the reduced Scope 2 emissions (5 460.95 t CO₂eq or 10.87% of the total CO₂eq emitted). According to data from the Energetic Research Company (^{EPE, 2016}), 43.5% of the Brazilian energy consumption comes from renewable sources while in the rest of the world this percentage is 14%. Renewable energy represents 82% of the sources of electric power generation in Brazil. This scenario is very positive for Brazil, because plants generating energy from renewable sources generally emit less GHG and have lower operating costs.

Technological innovation in the industrial sector has a major impact on energy consumption and varies according to the level of technological development of the machinery and equipment used in the production process. The most sophisticated technologies in the industrial sector have high costs. As many countries do not have the opportunity to develop new technologies, they import these products. Scope 2 CO₂ emissions are reduced as new energy-saving technologies are used, rather than machines and equipment with lower energy consumption (^{Erdoğan et al. 2020}).

Table III shows the detailed Scope 1 direct emissions: inputs used for combustion (stationary or mobile) in machinery and processes; fugitive emissions from reloading fire extinguishers; physical and chemical reactions of industrial processes, and treatment of sanitary effluents. It also exhibits the large representation of the stationary combustion category (24 407.88 t, 54.51% of the total GHG emissions of the analyzed factory), followed by the industrial processes category (19 762.50 t, 44.13% of the total GHG emissions of the analyzed factory). Figure 2 shows the percentage of participation of each category.

Fig. 2 Scope 1 greenhouse gases emissions by category. (Source: Prepared by authors [2019]). 

The stationary combustion category involves the burning of fuels through stationary equipment such as blast furnace, greenhouses and centrifugal machines (Table IV). A representative reduction in GHG emissions from a steel factory necessarily involves blast furnace as an important source of gas greenhouse gases. In a low carbon scenario, oxygen blast furnace with top gas recycling blast furnace (turbine for recovering top gases) is a technological possibility for reducing emissions. In a simplified way, the impact achieved with the mentioned technology is the capture of CO₂ through chemical absorption and reuse of gases (CO) in the blast furnace (^{CETESB, 2018}).

According to Table IV, the most used fuel was natural gas, which contributes to 66.88% of the GHG emissions (16 324.72 t) within the stationary combustion category. Charcoal is the second, with 33.10% of the GHG emissions (8 078.99 t).

Biogenic CO₂ emissions must be reported but not accounted, since they are considered neutral (CO₂ emission equals CO₂ removal). These emissions corresponded to 139 248.92 t (Fig. 3).

Fig. 3 Emissions in biogenic CO₂ (in metric tons). (Source: Prepared by authors [2019]). 

Analyzing data in Figure 3, the stationary combustion category has the largest contribution of this type of emission, since 139 216.23 t of biogenic CO₂ (99.98%) are equivalent to the charcoal consumed in the blast furnace of the steel factory (neutral emission). Mobile combustion emitted 32.69 t of biogenic CO₂ (0.023%), due to the fraction of biodiesel and ethanol present in diesel and domestic gasoline.

Scope 1 had the highest emissions from the industry, representing more than 89% of the CO₂eq total emissions. The stationary combustion category was highly representative, mainly due to the use of natural gas and, secondly, charcoal. Emissions accounted as CO₂eq corresponded only to emissions of CH₄ and N₂O, since CO₂ emissions (larger representation of emissions: 139 216.23 t) are not accounted because they are considered neutral.

Biogenic CO₂ emissions represented 7.91% (32.69 t CO₂) of the mobile combustion category (413.37 t CO_2eq). This amount is equivalent to the mandatory addition of ethanol in gasoline or biodiesel in diesel, regulated by specific resolutions in Brazil.

The configuration of the Brazilian energy matrix contributes to the reduced Scope 2 emissions, representing 10.87% (5 460.95 t CO_2eq) of the total inventoried GHG emissions (50 239.27 t CO_2eq).

The replacement of coal by charcoal is an important example of a GHG mitigation step in production processes. The use of renewable charcoal is an alternative way to mitigate GHG emissions, acting directly to improve resource efficiency during the carbonization process for pig iron production, ferroalloys and steel. Renewable biomass resources can be obtained from sustainably planted forests. Charcoal pig iron can be considered a green pig iron (^{Ministério do Meio Ambiente, 2016}).

For the metal production, the studied company melts the iron in blast furnaces using charcoal produced in its own unit. The use of biomass (such as charcoal instead of coal) is a very positive point that can be highlighted. If the company did not use renewable biomass, there would be no neutral emissions and its GHG emissions would be higher, since coal is a fossil and non-renewable source of GHG emissions.

When charcoal is used in the blast furnace, 139 216.23 t of biogenic CO₂ (considered neutral, CO₂ emission being equal to CO₂ removal) are emitted during the stationary combustion category. Total CO₂eq emissions from other fuels used in this category were 24 407.88 t CO₂eq. However, if the company had used national metallurgical coal, instead of charcoal, emissions related to the stationary combustion category would have risen to 139 897.206 t CO₂eq.

A survey was carried out using the public emissions registry on the website of the Brazilian GHG Protocol Program in order to compare GHG emissions from the steel factory under study with other inventoried steelworks during the same period (2017). The public emissions registry is a platform for the disclosure of corporate inventories of GHG emissions from organizations participating in the Brazilian GHG Protocol Program.

Table V shows a comparison between the values of GHG emissions released by three steel companies with the emissions of the steel factory under study.

A direct comparison between steel industries is not possible, since they have different sizes and manufacturing capacities. The largest emissions are related to Scope 1, from the stationary combustion and industrial processes categories. This does not mean that emissions related to energy consumption should be disregarded (Scope 2 emissions). According to ^{Siitonen et al. (2010)}, the steel industry is one of the industrial sectors with the highest energy consumption. A global reduction of CO₂ emissions requires more energy efficiency of industrial plants, therefore seeking to efficiently apply the use of equipment is an important criterion in the CO₂ emissions benchmarking. Other forms of energy efficiency can be considered, such as reducing losses and maximizing the reuse of gases to reduce the demand of fuels.

The cogeneration process aims to stimulate the structuring of the electric energy production with the reuse of heat in synergy with steelmakers, blast furnaces and coke ovens (^{Santos et al., 2010}). Energy consumption during this process, the composition of the fuel and the technologies used, and the efficiency of resources can influence the CO₂ emission in the steel industry (^{Zhang et al., 2009}; ^{Huang et al., 2010}; ^{Xu et al., 2016}).

Through a brief analysis of the fuel used by the company for its fleets (cars, ambulances, forklifts and locomotive) within the mobile combustion category, it was observed that if the company chooses to use biofuels (replacement of commercial diesel oil by biodiesel and gasoline for ethanol) its emissions would be biogenic, i.e., emissions related to the natural carbon cycle (neutral emissions).

The assessment and control of GHG emissions is a way to revert the scenario of large emissions that has been causing a rise in the planet’s average surface temperature. Similar works based their research on the quantification of GHG emissions. ^{Hwang et al. (2017)} estimated GHG emissions and emission factors in nine incineration plants in Korea, measuring GHG concentrations in flue gas samples. ^{Kyung et al. (2017)} estimated the total GHG emissions generated from all stages of the life cycle of a sewer pipe system. Other works with similar proposals are the following: ^{Carvalho et al. (2017)} performed the quantification and analysis of GHG emissions from the Pontifical Catholic University of Rio de Janeiro to contribute with the university’s environmental agenda. ^{Almeida et al. (2020)} measured the related to GHG emissions of an electricity generation industry and proposed strategies to reduce environmental impacts from the use of natural gas. Both used the GHG Protocol tool.

3.2. Adaptation of the Brazilian GHG Protocol Program Tool for its use in monthly reports

Emission data obtained in a shorter period of time would provide a more efficient control of GHG emissions. This could be accomplished through the development of a monthly indicator. Thus, the GHG Protocol v. 2018.1.4 was adapted for monthly reporting. The methodologies and emission factors proposed by the original tool were not modified. The spreadsheet columns were maintained in order to measure emissions month by month, reorganizing and structuring the tool.

The GHG Protocol tool is flexible, making possible its use for several segments that need to quantify their emissions. Therefore, in this work only the tables applicable to the factory under study have been adapted, while those that were not applicable were disregarded because they were not necessary for the quantification of GHG emissions from the studied steel factory.

The original tool uses, in some calculations, the ARRED function in Excel (which rounds a number to a specified number of digits). The adapted tool did not round the number and used all decimal places so that the value was as real as possible. So, there was a small difference between the values calculated by the original tool and the adapted one. Rounding is a recognized technique and is widely used in mathematics (especially when there is no device for performing numerical calculations), since it makes easier to work with numbers that have a large number of digits. This feature was dismissed because Excel is a spreadsheet editor that auto performs the proposed count.

Tables VI, VII, VIII and IX show the values found using the adapted tool for monthly reports and the original tool from the GHG Protocol Program, by category. The company measured nitrogen data by laboratory analysis. The input values for the amount of nitrogen from the generated effluent corresponded to the average provided by the company (45 kgN m^-3). This value was repeated for 12 months. Thus, the values of total emissions in CO₂eq were the same for all months.

The adaptation of the tool was simpler in the case of scope 2 (energy category). The tool itself contained the total CO₂ emissions calculated monthly because of the necessary parameters to calculate this category (emission factors). The National Interconnected System (SIN) makes the parameters available monthly.