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EP-3980566-B1 - METHOD AND SYSTEM FOR PRODUCING STEEL OR MOLTEN-IRON-CONTAINING MATERIALS WITH REDUCED EMISSIONS

EP3980566B1EP 3980566 B1EP3980566 B1EP 3980566B1EP-3980566-B1

Inventors

  • DUARTE ESCAREÑO, Pablo, Enrique

Dates

Publication Date
20260506
Application Date
20200601

Claims (13)

  1. A method to produce steel or molten iron containing materials (22) with reduced emissions of carbon dioxide comprising producing DRI (18) in a direct reduction furnace (12, 50) with a reducing gas (6) comprising hydrogen (16); melting at least a portion of said DRI in a melting furnace (20) and generating hot gases (24); producing steam and/or hot water (28, 40) using the heat contained in said hot gases (24); characterized by producing hydrogen (16) from said steam and/or hot water (28, 40) by electrolysis and feeding at least a portion of said hydrogen (16) to said direct reduction furnace (12, 50) as a component of said reducing gas (6) to produce said DRI (18).
  2. A method to produce steel or molten iron containing materials (22) according to claim 1, further characterized by generating electric energy (42) utilizing said steam (40); and using said electric energy (42) to produce said hydrogen (16) by electrolysis.
  3. A method for producing steel or molten iron containing materials (22) according to claim 1, wherein said melting furnace (20) is an electric arc furnace (EAF).
  4. A method for producing steel or molten iron containing materials (22) according to claim 1, further characterized by producing oxygen (36,124) by electrolysis and using at least a portion of said oxygen (36,124) to raise the temperature of reducing gas (6) prior to its feeding to the reduction reactor (12, 50).
  5. A method for producing steel or molten iron containing materials (22) according to claim 1, further characterized by producing oxygen (36,124) by electrolysis and using at least a portion of said oxygen (36, 124) in the electric-arc furnace (20) wherein said steel or molten iron containing materials (22) are produced.
  6. A method for producing steel or molten iron containing materials (22) according to claim 1, further characterized by obtaining at least a portion of the water used for producing hydrogen by electrolysis from condensed water vapour contained in an exhausted reducing gas stream extracted from said direct reduction furnace as top gas (58).
  7. A system (10) to produce steel or molten iron containing materials (22) with reduced emissions of carbon dioxide, comprising a direct reduction furnace (12, 50) to produce DRI (18) with a reducing gas (6) comprising hydrogen (16); a DRI melting furnace (20) to melt said DRI (18) generating hot gases (24); a heat recovery unit (26) to produce steam and/or hot water (28, 40) using the heat contained in said hot gases (24); and an electrolysis unit (34) to produce hydrogen (16) from said steam and/or hot water (28), which hydrogen (16) is fed to said direct reduction furnace (12, 50) as a component of said reducing gas (6) to produce DRI (18).
  8. A system (10) to produce steel or molten iron containing materials (22) according to claim 7, further comprising an electric power generator (44) to produce electric energy (42) utilizing steam (40) from the heat recovery unit (26), which electricity is used in said electrolysis unit (34) to produce hydrogen (16).
  9. A system (10) for producing steel or molten iron containing materials (22) according to claim 7, wherein said DRI (18) is melted in an electric-arc furnace (20) and high-temperature gases (24) are generated, and also comprising a first heat exchange unit (26) to produce steam or hot water (28, 40) using heat from said high-temperature gases (24) effluent from said electric-arc furnace (20); further characterized by also comprising an electrolysis unit (34) to produce hydrogen (16) from said steam or hot water (28); a first conduit (116) connecting said electrolysis unit (34) and said direct reduction furnace (12, 50) to feed at least a portion of said hydrogen (16) to produce said DRI (18); and an electric-arc furnace (20, 90) to melt said DRI (18) to produce said steel or molten iron containing materials (22).
  10. A system (10) for producing steel or molten iron containing materials (22) according to claim 7, further characterized by comprising an electric generator (44) to produce electric energy (42) using said steam (40) and electric conducting means connecting said electric generator (44) and said electrolysis unit (34) to produce said hydrogen (16) by electrolysis.
  11. A system (10) for producing steel or molten iron containing materials (22) according to claim 9, further characterized by comprising a second conduit (126) connecting said electrolysis (34) unit and said first conduit means (116) to feed at least a portion of oxygen (36,124) produced by electrolysis in said electrolysis unit (34) to raise the temperature of reducing gas (6) prior to being fed to said direct reduction furnace (12, 50).
  12. A system (10) for producing steel or molten iron containing materials (22) according to claim 9, further characterized by comprising a gas cooler (66) connected to said direct reduction furnace (12, 50) to cool at least a portion of exhausted reducing gas extracted from said direct reduction furnace (12, 50) as top gas (58) containing water formed by the reduction of iron oxides to metallic iron; a fourth conduit (158) connecting said direct reduction furnace and said gas cooler; and a fifth conduit (168) connecting said gas cooler and said electrolysis unit (34).
  13. A system (10) for producing steel or molten iron containing materials (22) according to claim 12, further characterized by comprising a water treatment unit to clean and condition said condensed water (68) prior to being used in said electrolysis unit (34).

Description

BACKGROUND OF THE INVENTION The present invention generally relates to methods and systems for producing steel or similar molten-iron-containing materials in melting or smelting furnaces utilizing pre-reduced iron ore, known also as direct reduced iron (DRI) or sponge iron, wherein the emission of CO2 and other greenhouse gases is significantly low. Production of steel contributes with an important proportion of the CO2 industrial emissions mainly due to the use of coal as energy source and raw material in integrated steelmaking plants comprising blast furnaces and blast oxygen converters. Steel is also produced through an alternate route comprising direct reduction of iron ores Although several proposals of methods and systems for recovery of heat from hot gases to produce steam and power may be found in the prior art, the present invention offers an integrated system for "green" steelmaking wherein the CO2 footprint is considerably decreased since the reducing agent is hydrogen being transformed to water in an iron reduction facility and said water used to produce hydrogen by electrolysis with great economic advantages. Such an integrated system is the gist of the present invention. Applicants have found US patent 8,587,138 to Statler et al. as an example of some proposals to utilize the heat generated in the melting process of metals and smelting of ores to generate electricity. Statler however does not disclose or suggest the integration of a direct reduction plant with the metal melting plant to minimize the CO2 emissions of the steelmaking process. Document DE202011105262 disclose a method of producing reduced iron, where steam produced using hot gases from the process is used for producing H2 in a electrolyzer, where H2 is further used in methanol production. Some proposed methods for decreasing the CO2 emissions in steelmaking refer to utilization of renewable energy sources, such as solar, wind and biomass energy to produce electricity which is in turn used to produce hydrogen by electrolysis, however these systems are still under development and the cost of such electricity is still high as compared to the grid power available from other sources. Almost 70% of the energy losses in EAF (Electric Arc Furnace) steelmaking are associated with the off gas, through which about 15% of the energy input is lost as sensible heat. Un-combusted CO evolved during the melting and refining process carried out in the EAF is burnt with air in a post-combustion chamber for the off gas. It is estimated that more than 25% of the total energy input of the EAF (Electric Arc Furnace) can be recovered and utilized. This heat recovery of the EAF off gas however is not widely practiced due to the harsh environment of the fume system of the EAF and the discontinuity of the gases generation as the EAF process is a batch-process. The heat of the EAF (Electric Arc Furnace) off gas can be recovered using high-pressure tubes designed to withstand the fume system conditions at pressures of 15 to 40 bar and produce high-pressure steam at 216°C. The temperature of the off gas after the heat recovery step is reduced to about 600°C. Using a steam accumulator, the high-pressure steam production can be utilized in a continuous manner irrespective of the EAF (Electric Arc Furnace) process cyclic nature. Steam production at an average rate of 20 t/h from 140t/h EAF (Electric Arc Furnace) has been demonstrated by Tenova S.p.A. A second heat recovery stage can be added to use the heat content of the fume gases after the steam production, wherein the temperature of the off gas is lowered from about 600°C to about 200°C using a standard waste heat boiler. Utilizing the two heat recovery stages, about 75% to 80% of the total energy content of the EAF off gas can be recovered. This recovered energy amounts to about 24,000 megawatt hour (MWh/year). The present invention utilizes heat energy produced in steelmaking processes that otherwise is wasted by an integration of a DRI melting furnace, a DRI production plant and an electrolysis unit to generate hydrogen thus decreasing the use of hydrocarbons to produce said DRI and consequently the CO2 emissions to the atmosphere. SUMMARY OF THE INVENTION The present invention provides a method for producing molten steel or molten-iron-containing materials with reduced emissions of carbon dioxide comprising producing DRI in a direct reduction furnace with a reducing gas comprising hydrogen; melting at least a portion of said DRI in a melting furnace and generating hot gases; producing steam and/or hot water using the heat contained in said hot gases. From said steam is produced hydrogen and/or hot water by electrolysis and at least a portion of said hydrogen may be fed to said direct reduction furnace as a component of said reducing gas to produce said DRI (Direct Reduced Iron). The invention also provides a system for producing molten steel or molten-iron-containing materials wherein the CO2 emissions a