3.1. Assessment of the Carbon Footprint of Gas Turbine Installation
In accordance with the methodology described above, an assessment of the carbon footprint of the GTI during its production and use in Russia has been made. The boundaries of the system are defined by the production of structural materials, including material processing, production of the gas turbine unit, production and installation of the foundations for the gas turbine unit, waste management at the end of the life of the gas turbine unit). The stages of GTI operation and transportation of materials, raw materials and other resources were not considered as these stages were not included in the objectives of this study.
The life cycle inventory of the GTA included the collection of data on the main flows of structural materials, both qualitatively and quantitatively. In determining the material consumption for the GTU-16P based on the PS-90GP-2 aircraft engine, the material content of the CF6 aircraft engine (General Electric, USA) was used as an analogue [
49]. The sub-engine frame and other elements of the gas turbine unit were assumed to be made of structural steel. The materials used in the manufacture of the GTU-16P and their manufacturing processes are shown in
Table 2. The main materials used in the production of the GTU are steel (51%) - structural and stainless (chromium), and nickel alloys, which make up a fairly high percentage (about 30%) and are used in the combustor and turbines (
Figure 5).
At the stage of production and installation of the foundation for the gas turbine unit, the costs of materials for the foundation, land acquisition works (including transfer of land to another category) and site preparation were considered, taking into account the energy resources for their implementation (electricity, heat supply, fuel for construction equipment) (
Table 3). The data for the inventory analysis during the production and installation of the foundation for a gas turbine unit were taken from the Ecoinvent 3.8 database for a similar installation (10 MW gas turbine unit) [
13].
The waste management phase at the end of the life of the gas turbine plant involves dismantling, sorting and recycling of the construction materials (
Table 4). Approximately 80% of the materials used in the manufacture of gas turbine units should be recycled according to the manufacturers’ recommendations. The calculations are based on data confirming that the materials generated at the end of the gas turbine unit’s service life are waste.
Figure 6 shows the carbon footprint of the life cycle stages of the gas turbine installation.
On the basis of the data obtained on the carbon footprint of the stages of the GTI life cycle per MWh of electricity produced, it was determined that the main contribution comes from the manufacturing and installation of the foundation for the gas turbine unit (62% of total emissions), consisting of the carbon footprint of the production of materials (0.11 kg CO2-eq./MWh) and the consumption of energy resources (0.08 kg CO2-eq./MWh). The carbon footprint of the production of the GTI was 0.108 kg CO2-eq/MWh (35.2% of the total emissions), with the majority of the carbon footprint coming from material processing (0.066 kg CO2-eq/MWh). The recycling of the gas turbine unit and the foundation for the GTI had the smallest carbon footprint - 0.008 kg CO2-eq/MWh (2.7% of total emissions). The largest carbon footprint among the considered processes, resources and works was the production of materials - 0.153 kg CO2-eq/MWh, which represents half of the total emissions from the life cycle stages of the gas turbine unit.
For comparison, the carbon footprint of the 10 MW GTI [
13] is 0.374 kg CO
2-eq/MWh and includes the production of the gas turbine unit (only steel was considered) and the production of the foundation for the GTI, but excludes the processing of materials during the production and disposal of the gas turbine unit.
The carbon footprint of a gas turbine unit is highly dependent on the carbon footprint of the individual materials. The carbon footprint of the production of basic metals depends on the technology and production method (e.g. blast furnace or electric arc furnace for steel), the raw materials used (virgin or recycled), the electricity source used (thermal, nuclear, renewable, etc.), the alloy brand, etc.
Table 5 shows the carbon footprint of the main metals used in the production of technically complex equipment. The carbon footprint values of the metals used for the calculations (from the Ecoinvent 3.8 database) are between the minimum and maximum values shown in the
Table 5.
The global contribution of the metallurgical sector to total greenhouse gas emissions is about 9% [
73].
To produce the GTI of the unearthly type, steel is one of the main metals used. According to the International Energy Agency (IEA), the carbon footprint of steel is 1.4 tonnes of CO2-eq. /t of steel produced and 1.85 tonnes CO
2-eq. / t according to the World Steel Association (WSA) [
50,
51]. The intensity of CO
2 emissions from steel production is influenced by the country’s industrial structure, technology, fuel choice, emission factor, steel plant capacity utilisation and materials (e.g. availability of steel scrap) [
73]. Each tonne of scrap used to make steel avoids 1.5 tonnes of CO
2 emissions and the consumption of 1.4 tonnes of iron ore, 740 kg of coal and 120 kg of limestone [
74]. The CO
2 emissions in steel production from the recycled materials are 0.4 CO
2-eq./t of steel [
52].
Steel is produced through two main technological chains: blast furnace (BF) steelmaking, which is based on the process of reducing iron ore in a blast furnace (BF) followed by the combustion of carbon from the pig iron in a basic oxygen furnace (BOF), and electric arc furnace (EAF) steelmaking, which is remelted either with scrap or with direct reduced iron (DRI). According to the WSA, BF-BOF uses 13.8% of scrap with emissions of 2.32 t CO
2-eq./t of steel, while EAF uses 105% of steel scrap with emissions of 0.67 t CO
2-eq./t. [
52]. China is the largest steel producer and the amount of CO
2 per tonne of steel in China is higher than in other countries. This is because almost all steel in China is produced in blast furnaces. Steel production in Europe is less polluting because 40% of steel in Europe is produced in electric arc furnaces [
75].
CO2 emissions are influenced by the source of electricity, as in the case of steel produced using electricity. According to the International Energy Agency’s (IEA) “Net Zero Emissions by 2050 Scenario” roadmap, the share of energy from renewable sources will increase from the current level of 10% to 60%, provided by solar, wind and hydro power engineering. The share of fossil fuels is reduced from 80% to about 20% [
76]. Coal currently provides about 75% of the steel sector’s energy and raw material needs, which is comparable to its share in the last decade. According to Net Zero Emissions (NZE), the share of emission-intensive blast furnaces in steel production will be reduced by about 10% by 2030 as existing plants are phased out [
50].
The aluminium industry is responsible for more than 1% of global anthropogenic greenhouse gas emissions [
7]. Over the past decade, the average global direct emission intensity of aluminium production has declined moderately, by an average of 2% per year. However, according to the NZE scenario, this decline will accelerate significantly to 4% per year by 2030 (18%) as a result of reductions in alumina refining and primary and secondary aluminium production [
77]. According to the International Aluminium Institute (IAI), the global average carbon footprint of primary aluminium production is 12.5 t CO
2-eq./t, and 0.6 t CO
2-eq./t when using recycled materials. [
58]. The energy cost of aluminium remelting is only 5% of the energy cost of primary aluminium production [
78].
Currently, almost all primary aluminium smelting processes use carbon anodes, which release CO
2 during the electrolysis process. The use of inert anodes and increased scrap production could help replace existing emission-intensive industries. By 2030, inert anodes will be used in about 7% of primary production [
77]. The “TÜV AUSTRIA Standards & Compliance” division conducted an independent verification of greenhouse gas emissions in the aluminium production process at the Krasnoyarsk aluminium plant “RUSAL” (Russia) and confirmed that aluminium produced using inert anode technology and hydroelectric power has specific emissions at the level of 0.01 t CO
2-eq./t of metal [
79].
68% of the world’s primary aluminium is produced using non-renewable energy sources (coal, natural gas) [
80]. Since 2010, the share of coal has increased and the share of hydropower has decreased, mainly due to the growing share of aluminium production in China, where more than 80% of production is coal-fired. In Europe, North America and South America, more than 80% of production is hydroelectric. By 2030, the emissions intensity of the entire power generation structure will be reduced by around 60% compared to today’s levels due to renewable energy sources. China has announced that, as part of its “Pollution Reduction and Carbon Emission Reduction Synergy Plan”, the production of recycled aluminium will reach 11.5 million tonnes by 2025 and the share of renewable energy sources will increase by more than 30% by 2030 [
77].
The carbon footprint of titanium production depends on many factors, such as primary raw materials, production technology, source of electricity, and ranges from 1.0 to 36.0 t CO
2-eq. [
53,
61]. Up to 2.8 t CO
2-eq. per tonne of natural rutile used can be saved compared to upgrading/beneficiation of ilmenite by smelting and chemical processes to produce high quality titanium raw materials, such as titanium dioxide slag and synthetic rutile [
65].
The LCA conducted by “EarthShift Global” found that the “IperionX” recycled titanium powders to be produced at the company’s planned demonstration plant in Virginia (USA) using its proprietary technology, could have the life cycle carbon footprint of only 7.8 t CO
2-eq. / t [
65]. That is more than 90% lower than with traditional titanium powders produced by plasma atomization, and 80% lower than with a titanium ingot obtained by the Kroll method (35.58 t CO
2-eq./t) [
63]. However, to use the recycled titanium alloys completely for the manufacture of new parts for the GTI is not possible, due to a decrease in strength properties and resistance to corresponding temperatures.
According to the Nickel Institute data, the global average carbon footprint of Class 1 nickel is 13.0 t CO
2-eq. / t of the finished products [
66,
67]. China accounts for about 31% of global nickel production [
66], using mainly coal as an energy source. According to research [
72], nickel produced using mixed energy sources (grid mix) is 14.0 t CO
2-eq. / t, hydropower – 7.0 t CO
2-eq. / t., natural gas energy – 6.0 t CO
2-eq. / t. The main producer of nickel in Russia is the Norilsk Nickel company, which has one of the highest shares of renewable energy use (HPS) - 47% (2021) [
68].
Nickel and its alloys, including corrosion-resistant and high-temperature alloys (used in the combustion chamber, high-pressure turbine and power turbine of the GTI), are almost 100% recyclable and can be recycled indefinitely without loss of their quality. Nickel retains most of its primary metal value, with high-grade scrap typically containing at least 95% of the primary metal value. Recycling nickel requires approximately 20% of the energy required to extract and process the primary metal [
78]. For example, the estimated carbon footprint of 1 tonne of the primary nickel alloy “Inconel 718” is 8.507 t CO
2-eq. / t. The greenhouse gas emission reduction of recycled Inconel 718 nickel alloy is 6,940 t CO
2-eq. / t [
62].
Thus, the carbon footprint of individual materials used in the production of a GTI can affect the final carbon footprint of the gas turbine installation. The carbon footprint of metal production is also influenced by the country-specific fuel conversion factors used, CO2 emission factors from the country’s electricity grid, and factors for auxiliary/intermediate materials. Depending on the source of electricity production, the carbon footprint of producing 1 kWh of electricity may differ: coal - 820 g CO
2-eq., natural gas - 490 g CO
2-eq., biomass - 230 g CO
2-eq., solar energy - 41-48 g CO
2-eq., hydropower – 24.0 g CO
2-eq., nuclear energy – 12.0 g CO
2-eq., wind energy (sea) – 12.0 g CO
2-eq., wind energy (unearthly) – 11.0 g CO
2-eq. [
81].
When assessing the life cycle of technically complex equipment, the amount and type of primary energy consumed in the production of electrical energy is of great importance. The structure of generation capacities in different countries, as well as in different regions within the same country, differs significantly and depends on climatic and geographical conditions, availability of hydrocarbon fuels, natural resources, level of technological development, etc. [
31].
Currently, there is a problem in assessing the carbon footprint of electricity generation in Russia due to the lack of uniform, generally accepted regional coefficients for electricity generation. When calculating emission factors for the energy system, emissions for all types of energy production (thermal, nuclear, hydroelectric, renewable, etc.) are averaged and “evenly distributed” among all consumers - no account is taken of the specifics of electricity production and no adjustment is made for the import/export of electricity within the boundaries of the respective territory (region).
The carbon footprint of the electricity used to produce materials clearly has a large impact, which in turn affects the carbon footprint of the GTI itself. The use of renewable electricity to produce metals (e.g. green steel) will have a much lower carbon footprint than the use of fossil fuel energy.