Method for producing a reducing gas

Abstract

The invention relates to a method for producing a reducing gas wherein said method comprises the following steps: - heating a reaction gas that contains at least: • 30% in volume (vol%) of H2, • 3vol% of CH4, • 5vol% of CO2, • 5vol% of CO, the remainder being up to 15vol% H2O, up to 5vol% N2, and impurities, to a temperature from 400°C to 1100°C, by means of electrical energy, - releasing said heated reaction gas into a reformer containing catalysts so that said heated reaction gas is transformed into a reducing gas containing at least CO and H2, the cumulated vol% of CO and H2 in the reducing gas being higher than the cumulated vol% of CO and H2 in the reaction gas.

Description

[0001] Method for producing a reducing gas

[0002]

[0001] The present invention relates to a method for producing a reducing gas. More precisely, the present invention relates to a method for producing a reducing gas using electric energy to heat the reaction gas.

[0003]

[0002] In the process of direct reduction of iron, a reducing gas is injected inside the shaft to react with the iron ore. This reducing gas is produced beforehand using a reformer that performs the processes of dry reforming or steam reforming where a gas mainly composed of methane is transformed into a reducing gas using a chemical reaction.

[0004]

[0003] The reformer is formed of a reacting part, where the reforming chemical reaction takes place, that contains catalysts to activate the reaction and a heating part that contains burners to heat the gas and maintain it at the needed temperature for the reaction to take place.

[0005]

[0004] However, this process causes CO2 emissions and CO2 emissions need to be reduced in the steel industry. There is also a problem in that the amount of reduced iron produced is limited by the production of reducing gas inside the reformer. There is thus a need for an alternative method that solve these problems.

[0006]

[0005] The aim of the present invention is therefore to remedy to the aforementioned drawbacks by providing a method to produce a reducing gas that allows to produce more reducing gas while reducing CO2 emissions produced by a reformer that comprises burners.

[0007]

[0006] For this purpose, a first object of the present invention consists in a method for producing a reducing gas wherein said method comprises the following steps:

[0008] - heating a reaction gas 11 that contains at least:

[0009] o 30% in volume (vol%) of H2,

[0010] o 3vol% of CH4,

[0011] o 5vol% of CO2,o 5vol% of CO,

[0012] the remainder being up to 15vol% H2O, up to 5vol% N2, and impurities, to a temperature from 400°C to 1100°C, by means of electrical energy, - releasing said heated reaction gas 11 into a reformer 5 containing catalysts 6 and comprising burners 9 so that said heated reaction gas 11 is transformed into a reducing gas 14 containing at least CO and H2, the cumulated vol% of CO and H2 in the reducing gas 14 being higher than the cumulated vol% of CO and H2 in the reaction gas 11.

[0013]

[0007] The method for producing a reducing gas according to the invention may also have the optional features listed below, considered individually or in combination:

[0014] - the reaction gas 11 is heated to a temperature from 600°C to 1100°C, - the reaction gas 11 is heated to a temperature from 600°C to 800°C, - the reaction gas 11 contains up to 20vol% of CH4, up to 70vol% of H2, up 20vol% of CO2, and up to 20vol% of CO,

[0015] - the cumulated vol% of CO and H2 in the reducing gas 14 is at least 80vol%,

[0016] - before the heating step, the reaction gas 11 is preheated to a temperature from 350°C to 600°C,

[0017] - the preheating is done using a heat exchanger,

[0018] - the temperature inside of the reformer 5 is increased to a temperature from 900°C to 1100°C by burning a combustion gas 12a and circulating it,

[0019] - before being burnt, the combustion gas 12a is preheated to a temperature from 200°C to 450°C, using a heat exchanger,

[0020] - before being burnt and after the optional preheating step, the combustion gas 12a is heated to a temperature from 200°C to 1000°C, by means of electrical energy,

[0021] - the reducing gas 14 is further used in a direct reduction of iron process, - a top gas 16 coming from a direct reduction shaft 15 undergoes a treatment step to form a dry top gas 17 and wherein said dry top gas 17 is mixed with natural gas to form the reaction gas 11.

[0008] Other characteristics and advantages of the invention will be described in greater detail in the following description.

[0022]

[0009] The invention will be better understood by reading the following description, which is provided purely for purposes of explanation and is in no way intended to be restrictive, with reference to:

[0023]

[0010] Figure 1, which is a representation of a reformer using the method according to the invention,

[0024]

[0011] Figure 2, which is a representation of a reformer using the method according to the invention in a direct reduction of iron process configuration,

[0025]

[0012] With reference to Figure 1, the method for producing a reducing gas according to the invention will be described in detail.

[0026]

[0013] The method for producing a reducing gas according to the invention consists first in heating a reaction gas 11 by means of electrical energy. The reaction gas 11 contains at least 30% in volume (vol%) of H2, 3vol% of CH4, 5vol% of CO2, 5vol% of CO and the remainder is H2O up to 15vol%, N2 up to 5vol%, and impurities. The heated reaction gas 11 is then released into a reformer 5 that contains catalysts 6 and comprises burners. The reaction gas 11 is then transformed into a reducing gas 14 inside the reformer 5. The cumulated vol% of CO and H2 in the reducing gas 14 is higher than the cumulated vol% of CO and H2 in the reaction gas 11. This is due to the reactions that take place inside the reformer 5. The burners 9 allow to heat the reformer 5 so that the temperature needed for the reaction gas 11 to be transformed into a reducing gas 14 can be maintained inside the reformer 5.

[0027]

[0014] Heating the reaction gas 11 using electrical energy before it is released into the reformer 5 allows to reduce the energy that needs to be produced by the burners 9 of the reformer 5 to heat the reaction gas 11 , thus reducing the CO2 emissions of the reforming process when using a reformer 5 that comprises burners 9.

[0028]

[0015] Preferably, the reaction gas 11 is heated to a temperature from 400°C to 1100°C. More preferably, the reaction gas 11 is heated to a temperaturefrom 600°C to 1100°C. Even more preferably, the reaction gas 11 is heated to a temperature from 600°C to 800°C.

[0029]

[0016] The reaction that takes place using the method according to the invention is the reaction of methane reforming. It consists in transforming methane into a reducing gas 14. The preferred reaction that takes place in the invention is the reaction of dry reforming: CH4 + CO2 — 2CO + 2H2. A secondary reaction, the reaction of steam reforming, can also take place inside the reformer: CH4 + H2O — CO + 3H2. It uses the water present in the reaction gas 11 to transform the methane.

[0030]

[0017] The preferred compositions for the reaction gas 11 are listed in Table 1. The composition of the reaction gas is not limited to the gases and their respective proportions listed in Table 1. The proportions of gases are expressed in vol%.

[0031]

[0032] Table 1

[0033]

[0018] Preferably, the cumulated vol% of CO and H2 in the reducing gas 14 produced is at least 80vol%.

[0034]

[0019] A reformer 5 is represented in Fig 1. Usually, the reformer 5 comprises tall tubes 7 of around 7 to 9m of height that serve as reactors. The reaction gas 11 enters at the bottom of the tubes 7 and exit at the top of the tubes 7 after being transformed into a reducing gas 14. The tubes 7 contain catalysts 6 from the bottom to the top. The catalysts 6 allow to activate the chemical reaction between methane, CO2 and / or H2O. The reformer 5 also comprises a heating part 8 that contains burners 9 that burn a combustion gas 12a and circulate it to heat the tubes 7, and thus the reaction gas 11, to the temperature that is needed for the reaction that is from 700°C to 1100°C. The heating part 8 also allows to maintain the temperature inside the reformer 5 as the reaction is endothermic and thus cools down the gas. The combustion gas 12a is burnt using an oxygen source 12b that is also supplied to the burners 9 and is mixed with the combustion gas 12a at the tip of the burners9. The oxygen source 12b is preferably air or a synthetic comburant. The oxygen source 12b preferably contains O2 from 10vol% to 99.5vol%.

[0035]

[0020] Usually, the reaction gas 11 enters the reformer at a temperature from 450°C to 600°C. Due to this, the gas needs to be heated inside the reformer 5 to the needed temperature for the reaction that is from 700°C to 1100°C. However, undesired carbon deposition happens under 860°C damaging the catalyst performance. To avoid this, the gas is heated to a temperature that is superior to 860°C and catalysts 6 are not present at the bottom of the tubes 7 and are replaced by a material, alumina for example, that only serves to enhance the heating of the reaction gas 11. As only the catalysts 6 can activate the reforming reaction, the amount of reducing gas 14 produced in the reformer 5 is directly linked to the number, the size and the activity of the catalysts 6 inside the reformer 5. By not having catalysts 6 at the bottom of the tubes 7, the quantity of reducing gas 14 produced is thus limited.

[0036]

[0021] In the method according to the invention, the reaction gas 11 is heated to a temperature from 400°C to 1100°C, preferably from 600°C to 1100°C, using electrical energy before entering the reformer 5. The more the reaction gas 11 is heated before the reformer 5, the less the reaction gas 11 needs to be heated inside the reformer 5 by the heating part 8. Catalysts 6 can thus be put on a higher extent at the bottom of the tubes 7 inside the reformer 5 as the temperature where carbon deposition does not occur will be exceeded faster. The hotter the reaction gas 11 at the entrance of the reformer 5, the more catalysts 6 can be put at the bottom of the tubes 7 and the earlier the reforming reaction can start inside the tubes 7. By having more catalysts 6 inside the reformer 5, the amount of reducing gas 14 produced is increased.

[0037]

[0022] Preferably, the catalysts 6 inside the reformer 5 are composed of inert oxide covered in nickel. Preferably, the inert oxide is alumina. The nickel cover acts as the active surface of the catalyst 6 to activate the reforming reaction. The inert oxide acts as the support for the nickel.

[0038]

[0023] Preferably, before the heating step, the reaction gas 11 is preheated to a temperature from 350°C to 600°C. Said heating step is preferably doneusing a heat exchanger 10. Preferably, said heat exchanger 10 uses the fumes 13 of the combustion gas 12a exiting the heating part 8 of the reformer 5 that are still hot and can transfer their energy to the reaction gas 11. This step allows to save energy by reusing the energy coming from the heating part 8 of the reformer 5 and thus, less electric energy is needed to heat the reaction gas 11.

[0039]

[0024] Preferably, the temperature inside the reformer 5 is increased and maintained by burning a combustion gas in the burners 9. Preferably, before being burnt, the combustion gas 12a is preheated to a temperature from 200°C to 450°C, using a heat exchanger 10. This step allows to use less energy for the combustion of the gas and thus further reducing the CO2 emissions of the process. The heat exchanger used for preheating the combustion gas 12a can be the same as the heat exchanger used for preheating the reaction gas 11.

[0040]

[0025] Preferably, before being burnt and after the optional preheating step, the combustion gas 12a is heated to a temperature from 200°C to 1000°C, more preferably to a temperature from 600°C to 800°C using electrical energy. This allows to reduce even more the CO2 emissions of the process.

[0041]

[0026] Preferably, the oxygen source 12b is preheated in a heat exchanger 10 and / or using electrical energy before being mixed with the combustion gas 12a. The heat exchanger 10 can be the same as the one used to preheat the reaction gas 11 and / or the combustion gas 12a.

[0042]

[0027] Preferably, the reducing gas 14 that is produced using the method according to the invention is further used in a direct reduction of iron process. As the method according to the invention allows to produce more reducing gas, it can also increase the production of steel through the direct reduction of iron (DRI) process.

[0043]

[0028] In the DRI process, a top gas 16 exits the direct reduction shaft 15.

[0044] The top gas 16 undergoes a treatment step where a part of it is extracted, the purged gas 19. The purged gas 19, optionally, undergoes a step of water vapor removal in a scrubber and is also optionally mixed with natural gas to form the combustion gas 12a used to feed the burners 9. After this step, whatremains from the top gas 16, after removing water vapors in a scrubber, is a dry top gas 17. This dry top gas 17 can be mixed with an entry gas 18 to form the reaction gas 11. Preferably, the entry gas 18 is natural gas. This mixing allows to recycle the top gas 16 and save natural gas.

[0045]

[0029] The preferred compositions for the dry top gas 17 are listed in Table 2. The composition of the dry top gas 17 is not limited to the gases and their respective proportions listed in Table 2.

[0046]

[0047] Table 2

[0048]

[0030] Heating the reaction gas 11 with electric energy before it is introduced into the reformer allows to use less energy from the burners 9 and thus reduces the CO2 emission coming from the combustion. Also, using electric energy coming from renewable sources allows to reduce even more the CO2 emissions of the process.

[0049]

[0031] For heating the reaction gas 11 and optionally the combustion gas 12a, any electric device 1 using electric energy can be used. For example, an electric resistance heater, an electric rotating heater, an electric arc heater, a plasma heater or an electric induction heater can be used.

[0050]

[0032] An embodiment of the invention in a direct reduction of iron process is represented in Fig 2. In this embodiment, the reaction gas 11 is heated using electric energy with an electric device 1 then introduced into the reformer 5 where it is transformed into a reducing gas 14 then injected into a direct reduction shaft 15 to be used in a direct reduction of iron process.

[0051]

[0033] To form the reaction gas 11 , an entry gas 18 is first mixed with the dry top gas 17 that results from the treatment of the top gas 16 that comes from the direct reduction shaft 15. The reaction gas 11 is then preheated to a temperature from 350°C to 600°C using a heat exchanger 10. After the preheating step, the gas is heated to a temperature from 400°C to 1100°C with electric energy using an electric device 1. After the heating step, the gasis introduced into the tubes 7 of the reformer 5 that contains catalysts 6 composed of alumina covered in nickel. The reaction gas 11 is heated to a temperature from 900°C to 1100°C inside the reformer 5 and upon reaching the catalysts 6, the reforming reaction is activated and the reaction gas 11 is transformed into a reducing gas 14 that is then injected into the direct reduction shaft 15.

[0052]

[0034] The temperature inside the tubes 7 of the reformer 5 is increased and maintained thanks to the heating part 8 that contains burners 9 that use a combustion gas 12a that is composed of the purged gas 19 that is retrieved from the top gas 16 mixed with natural gas from the natural gas entry 12c. Before being burned, the combustion gas 12a is first preheated to a temperature between 200°C and 450°C using the same heat exchanger 10 as the one used to preheat the reaction gas 11. It is then further heated to a temperature from 200°C to 1000°C with electric energy using another electric device 1. It is then distributed to the burners 9 and mixed with an oxygen source 12b that was also preheated in the heat exchanger 10. It is finally burned inside the heating part 8. The fumes 13 that result from the combustion gas 12a exits the heating part 8 and go to the heat exchanger 10 to be used as a heating medium to preheat the reaction gas 11, the combustion gas 12a and the oxygen source 12b.

[0053]

[0035] The invention is not limited to the embodiment represented in Fig 2 and other configurations can be considered.

[0054]

[0036] The method according to the invention allows to successfully produce more reducing gas while reducing CO2 emissions.

Claims

CLAIMS1) A method for producing a reducing gas wherein said method comprises the following steps:- heating a reaction gas (11 ) that contains at least:• 30% in volume (vol%) of H2,• 3vol% of CH4,• 5vol% of CO2,• 5vol% of CO,the remainder being up to 15vol% H2O, up to 5vol% N2, and impurities, to a temperature from 400°C to 1100°C, by means of electrical energy,- releasing said heated reaction gas (11) into a reformer (5) containing catalysts (6) and comprising burners (9), so that said heated reaction gas (11) is transformed into a reducing gas (14) containing at least CO and H2, the cumulated vol% of CO and H2 in the reducing gas (14) being higher than the cumulated vol% of CO and H2 in the reaction gas (11 ).2) A method for producing a reducing gas according to claim 1 , wherein said reaction gas (11 ) is heated to a temperature from 600°C to 1100°C.3) A method for producing a reducing gas according to claim 2, wherein said reaction gas (11 ) is heated to a temperature from 600°C to 800°C.4) A method for producing a reducing gas according to any of the preceding claims, wherein said reaction gas (11) contains up to 20vol% of CH4, up to 70vol% of H2, up 20vol% of CO2, and up to 20vol% of CO.5) A method for producing a reducing gas according to any of the preceding claims, wherein the cumulated vol% of CO and H2 in the reducing gas (14) is at least 80vol%.6) A method for producing a reducing gas according to any of the preceding claims, wherein, before the heating step, said reaction gas (11) is preheated to a temperature from 350°C to 600°C.7) A method for producing a reducing gas according to claim 6, wherein said preheating is done using a heat exchanger.8) A method for producing a reducing gas according to any of the preceding claims, wherein the temperature inside of the reformer (5) is increased to a temperature from 900°C to 1100°C by burning a combustion gas (12a) and circulating it.9) A method for producing a reducing gas according to claim 8, wherein, before being burnt, said combustion gas (12a) is preheated to a temperature from 200°C to 450°C, using a heat exchanger.10)A method for producing a reducing gas according to claim 8 or 9, wherein, before being burnt and after the optional preheating step, said combustion gas (12a) is heated to a temperature from 200°C to 1000°C, by means of electrical energy.11)A method for producing a reducing gas according to any of the preceding claims, wherein said reducing gas (14) is further used in a direct reduction of iron process.12)A method for producing a reducing gas according to claim 11 , wherein a top gas (16) coming from a direct reduction shaft (15) undergoes a treatment step to form a dry top gas (17) and wherein said dry top gas (17) is mixed with natural gas to form the reaction gas (11).

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