[002] Steel industry, like many other human activities, is a source of C02 emission in the atmosphere. Many technologies are implemented or under development to decrease those C02 emissions at different levels of the production, through for example recycling of blast furnace, coke oven or converter top gas. This recycling may be performed, after appropriate treatments, by injection into another steelmaking device or use as syngas for other productions.

[003] These technologies aim to decrease direct C02 emissions of the manufacturing of steel products.

[004] However, customer of such steel products, such as car makers, also have to reduce the carbon footprint of their products and to do so request steel products fulfilling all their usual standards in terms of physical properties and quality, but also in terms of carbon footprint. This C02 carbon footprint is not limited to the direct emissions of the manufacturing process itself.

[005] There is so a need for a method allowing to determine and reduce the C02 footprint of steel products.

[006] This problem is solved by a method according to the invention, wherein a given tonnage of steel products is to be manufactured in at least two steelmaking units, the method including a target definition step wherein an overall expected level of C02 emissions from all steelmaking units to manufacture such tonnage of steel products is defined, a maximum level of C02 emissions is predefined for each steelmaking unit, a calculation step wherein an expected level of C02 emissions is calculated for each steelmaking unit, such calculation being done considering all C02 contributions linked to raw materials, energy sources and processes initially selected for manufacturing the steel products following an initial manufacturing route, a comparison step between respective calculated expected levels and predefined targets, wherein if any or all expected emissions is above its respective maximum level, modifying the final selection of any or all the raw materials, energy sources and processes to define an optimized manufacturing route with optimized levels of C02 emissions, optimized level being lower than or equal to maximum level, and a production step wherein the tonnage of steel products is manufactured in the steelmaking units according either the original manufacturing or the optimized manufacturing route when defined.

[007] The method of the invention may also comprise the following optional characteristics considered separately or according to all possible technical combinations:

- a first steel product is manufactured in the first steelmaking unit and then send to the second steelmaking unit to be transformed into a second steel product,

- finally selected raw material are chosen among coal, coke, iron ore, biomass, sintered ore, agglomerates, pellets, direct- reduced iron (DRI), scrap, mineral additions, alloying elements, oxygen or hydrogen,

- finally selected raw material are chosen among biomass, scrap, cold-bonded pellets, direct- reduced iron (DRI), mineral additions, alloying elements, oxygen or hydrogen,

- scrap is of different type and is chosen among old scrap, new scrap, prime scrap, home scrap, pit scrap, shredded, plates and structure scrap, heavy melting scrap, cast scrap, coil scrap or busheling scrap,

- finally selected energy sources are chosen among renewable electricity, electricity produced by internal recycling of exhaust gas from the steel manufacturing process or by capture of heat released by products from the steel manufacturing process,

- finally selected processes are chosen among direct reduction processes, hydrogen- based ironmaking, steel electrolysis, blast furnace with top-gas recycling, blast furnace with top-gas conversion, electric-arc-furnace steelmaking, converter steelmaking, scrap melting,

- the method further includes a step, after the production step, of establishing a certificate indicating the optimized level of C02 emissions associated to part or all of the tonnage of manufactured steel products,

- the method further includes a step, after the production step, of first calculating the cumulated value of C02 emitted in manufacturing step of all steelmaking units for manufacturing the tonnage of steel products, then calculating the difference between such cumulated value and the overall expected amount of C02 emissions for said tonnage of steel products as defined in first target definition step to determine the amount of C02 that was not emitted, allocating all or part of this not-emitted amount of C02 to a green tonnage of steel products, said green tonnage being lower than the global tonnage, to calculate a reduced level of C02 emissions for such green tonnage of steel products by reducing the expected level of C02 emissions triggered by its manufacturing by such not-emitted amount of C02, and establishing a certificate indicating said reduced level of C02 emissions associated to such green tonnage of steel products, - the reduced level of C02 emissions associated to the green tonnage of steel products is equal to zero.

[008] Other characteristics and advantages of the invention will emerge clearly from the description of it that is given below by way of an indication and which is in no way restrictive, with reference to the appended figures in which:

Figure 1 is a flowchart of a method, according to the invention, for manufacturing steel

[009] Figure 1 represents a flowchart of a method to manufacture steel products according to the invention. The manufacturing of a given tonnage T _gi0 b of steel products is performed in at least two steelmaking units S,. The steel product may be chosen among liquid steel, steel semi-product, steel flat product, steel long product. Among steel flat product, it may be a slab, a hot-rolled coil, a cold-rolled coil, a sheet, a plate. Among long products, it may be a hot rolled, cold rolled or drawn bar, rebar, railway rails, wire, rope, sections such as U, I, or FI section beam, a sheet pile, a bloom, a billet. [0010] In a first step 100, two targets are defined: an overall expected level E _gi0 b of C02 emissions from all steelmaking units S, to manufacture the tonnage T _giob of steel products and a maximum level of CO2 emissions Emax, for each steelmaking unit Si.

[0011] In a second step 110, which can be either performed after or in parallel to the first step 100, a calculation step is performed wherein an expected level of CO2 emissions Eexp, is calculated for each steelmaking unit Si. This calculation 110 is done considering all C02 contributions linked to raw materials, energy sources and processes initially selected for manufacturing the steel products for manufacturing the steel products according to an initial manufacturing route Ri.

[0012] Raw materials may be of different types. They may include coal, coke, iron ore, biomass, sintered ore, agglomerates, pellets, direct-reduced iron (DRI), scrap, mineral additions, such as limestone or dolomite, alloying elements but also gases such as oxygen or hydrogen. Scrap maybe of different typologies among, notably, old scrap, new scrap, prime scrap, home scrap, pit scrap, shredded, plates and structure scrap, heavy melting scrap, cast scrap, coil scrap or busheling scrap. [0013] Plate and structural scrap, often referred to as P&S in the scrap industry, is a cut grade of ferrous scrap, presumed to be free of any contaminates. Plate and structural scrap comprise clean open-hearth steel plates, structural shapes, crop ends, shearing, or broken steel tires. Heavy melting steel (HMS) or heavy melting scrap is a designation for recyclable steel and wrought iron. It is broken up into two major categories: HMS 1 and HMS 2, where HMS 1 does not contain galvanized and blackened steel, whereas HMS 2 does. Both HMS 1 and 2 comprise iron and steel recovered from items demolished or dismantled at the end of their life. Pit scrap is a by-product of flat steel products manufacturing process containing merely scale. Coil scrap contains discarded coils, because of quality issues by example, or residues of coil cutting. Cast Iron Scrap is an alloy of iron that contains high amounts of carbon. The carbon content makes it susceptible to corrosion. As a result, Cast Iron scrap is often rusted and worn. Cast iron scrap can be obtained from heating systems, vehicle components etc. Another kind is busheling scrap constituted of clean steel scrap and include new factory busheling (for example, sheet clippings, stampings, etc.).

[0014] By considering all C02 contributions linked to raw materials, it is meant that all C02 emissions linked to the production of those raw materials before they are used into the steel manufacturing process is taken into account. For example, when considering iron ore, all C02 emissions related to the mining extractions and ore processing have to be included into the calculation. Same for the scrap, even it is the recycling of an existing product, it has a C02 footprint coming from its former life which has to be considered into the calculation. Depending on its typology, C02 footprint may differ from one scrap to another.

[0015] Energy sources may also be various. They include electricity coming from renewable energy, such as from solar panels or windmills, but also electricity produced by power plant, which may use gases resulting from the steelmaking process, such as blast furnace gases or converter gases. It also includes any fuel, either gaseous or solid, fossil or organic, which may be used into the steel manufacturing process.

[0016] In order the calculation to be the most accurate it is important to not count a C02 impact twice. For example, if coke is considered as a raw material to the converter process and its impact included into the raw materials impact, it must not be considered as a fossil fuel and included into the energy sources impact.

[0017] Processes include all different processes performed along the manufacturing route MR, and their associated CO2 emissions. It includes pig iron production, liquid steel production and finishing processes. Pig iron production includes coking, sintering, pelletizing, blast furnace process, but also direct reduction and shaft furnace processes. Liquid steel production covers decarburization, dephosphorization and all secondary metallurgy or ladle treatments allowing to turn pig iron into liquid steel and adjust the composition of the liquid steel for further steps, it also includes the electric-arc-furnace steelmaking process. Finishing processes include notably casting, heating, rolling, cooling, coiling, shaping, levelling, welding, coating. When considering CO2 impact of a process, all by-products recycling or emission reduction technologies applied to said process has to be taken into account for the calculation. For example, blast furnace process without top-gas recycling does not have the same CO2 impact as the same blast furnace process wherein top-gas is not released to the atmosphere but rather re-injected into.

[0018] Once this expected level of CO2 emissions Eexp, is calculated, it is used into a comparison step 120 where it is compared with its respective predefined target emissions level Emaxi. If any or all Emxp, is above its respective Emax,, then an optimized manufacturing route OMR, with optimized levels of CO2 emissions Eoptim,, is defined by modifying the final selection of any or all of the raw materials, energy sources and processes so that Eoptirrii is lower than or equal to Emax, _. As a matter of example, for a given steelmaking unit Si, if the original manufacturing route MRi uses coal as raw material in a blast furnace, the optimized manufacturing route OMR1, may replace this coal by torrefied biomass so as to reduce the C02 emissions.

[0019] In the final selection raw materials are preferentially chosen among biomass, scrap, cold-bonded pellets, direct-reduced iron (DRI), mineral additions, alloying elements, oxygen or hydrogen. Finally selected energy sources are preferentially chosen among renewable electricity, electricity produced by internal recycling of exhaust gas from the steel manufacturing process or by capture of heat released by products from the steel manufacturing process. Finally selected processes are preferentially chosen among direct reduction processes, hydrogen-based ironmaking, steel electrolysis, blast furnace with top- gas recycling, blast furnace with top-gas conversion, electric-arc-furnace steelmaking, converter steelmaking, scrap melting. By hydrogen-based ironmaking it is meant any ironmaking process, such as a direct-reduction process or a blast-furnace process wherein the reducing gas is mainly composed of hydrogen, it encompasses also blast furnace with coke-oven gas injection. Blast-furnace wit top-gas recycling means a blast furnace process wherein top-gas exhausting from the blast furnace is at least partly re-injected into the blast furnace after appropriate treatments. Blast furnace with top-gas conversion means a blast furnace process wherein top-gas exhausting from the blast furnace is at least partly used to produce a syngas which is then further used in chemical, biochemical or power plants. [0020] Then in a last step 140A, 140B, the tonnage T _gi0b of steel products is manufactured in each steelmaking plant S, either 140A according to the original manufacturing route MR, or 140B according to the optimized manufacturing route OMR,.

[0021] In a first embodiment, after the production step, an additional is performed wich consists in establishing a certificate indicating the optimized level Eoptimi of C02 emissions associated to part or all of the tonnage T _giob of manufactured steel products. [0022] In another embodiment, another step may be performed after the production step which consists in first, calculating the cumulated value å(Eoptirrii) of C02 emitted in the production step by all steelmaking units S, for manufacturing the tonnage T _gi0 b of steel products, then calculating the difference A _em between such cumulated value å(Eoptirrii) and the overall expected amount E _giob of C02 emissions for said tonnage T _gi0 b of steel products as defined in the targets definition step 100 to determine the amount E _not Of C02 that was not emitted, allocating all or part of this not-emitted amount E _not of C02 to a tonnage T _gree n of steel products, T _gree n being lower than T _gi0 b, to calculate a reduced level of C02 emissions for such tonnage T _gree n of steel products by reducing the expected level of C02 emissions triggered by its manufacturing by such not-emitted amount of C02, and finally establishing a certificate indicating said reduced level of C02 emissions associated to such tonnage Tgr _een of steel products.

[0023] In a preferred embodiment, the reduced level of C02 emissions associated to the tonnage T _gre en of steel products is equal to zero

[0024] With the method according to the invention it is possible to determine and reduce the C02 footprint of steel products through the control of their manufacturing in several plants.

[0025] As a matter of illustration, one steelmaking unit S1 may produce a slab according to an original manufacturing route MR1 , said slab being then sent to a second steel manufacturing unit S2 where it is turned into a coil of galvanised steel for automotive according to a second original manufacturing route MR2. A tonnage T _gi0 b of galvanized steel is defined. Maximum level of C02 emissions Emaxl and EMax2 are defined for each unit. Calculation step 110 is performed to calculate expected level Eexpl and Eexp2 which are then compared 120 to the respective targets. Eexpl is superior to Emaxl then an optimized manufacturing route OMRi is defined by adjusting, for example, the amount of scrap charged to the converter and increasing the amount of blast furnace gas sent to a fermentation process. This optimized manufacturing route OMR1 has an optimized level of emissions Eoptiml inferior or equal to Emaxl . Eexp2 is inferior to Emax2, no optimized route needs to be defined. Then the slab is produced in steelmaking S1 according to the optimized manufacturing route OMR1 and then sent to the steelmaking unit S2 where it is turned to a coil of galvanized steel according to the original manufacturing route MR2. When delivered to the customer, the tonnage T _gi0b of produced galvanized steel has then a reduced global footprint, thanks to the method according to the invention.

[0026] Steelmaking units S1 and S2 could also both produced coils of galvanised steel and their respective cumulated productions would provide the global tonnage. [0027] The method can be applied to several steelmaking units belonging to a same company in order to reduce the global footprint of said company.