1. A method for producing granular direct reduced iron is characterized by comprising the following steps:

the preheated granular iron ore and the preheated feed gas are in countercurrent contact to carry out reduction reaction to obtain granular direct reduced iron;

wherein the average particle size of the granular iron ore is 0.015-4.00mm, the temperature of the preheated granular iron ore is 500-750 ℃, the feed gas contains a reducing gas and an optional diluent gas, the temperature of the preheated feed gas is 450-650 ℃, and the average flow velocity of the feed gas is less than the minimum fluidization velocity of the granular iron ore.

2. The method for producing granular dri according to claim 1, wherein the reduction reaction pressure is 0.05 to 3.00 MPa;

preferably, the flow ratio of the reducing gas to the particulate iron ore in the feed gas is 500-2000Nm³Reducing gas/t iron ore.

3. The method for producing granular direct reduced iron according to claim 1, wherein the reduction reaction time of the granular iron ore is 1 to 15 hours, preferably 2 to 10 hours.

4. The method for producing granular dri according to any one of claims 1 to 3, wherein the reducing gas contains hydrogen, and the volume fraction of hydrogen in the reducing gas is not less than 99%;

or, the reducing gas comprises hydrogen and carbon monoxide, the volume fraction of the hydrogen in the reducing gas is not less than 90%, and the volume fraction of the carbon monoxide in the reducing gas is not more than 10%;

preferably, the volume fraction of the reducing gas in the raw material gas is not less than 70%;

preferably, the diluent gas comprises nitrogen and/or argon.

5. The method for producing granular dri according to claim 4, further comprising the steps of subjecting the reduction off-gas generated during the reduction reaction to an optional decarburization treatment and a dehydration treatment to obtain a purified off-gas;

preferably, the purified tail gas can be used as raw material gas for recycling;

preferably, a decarbonizing agent and the reduction tail gas are mixed, and decarbonization treatment is carried out to remove carbon dioxide in the reduction tail gas, wherein the decarbonizing agent comprises calcium oxide;

preferably, the calcium carbonate obtained after the decarburization treatment is regenerated at 650-950 ℃, and the regenerated calcium oxide can be reused as a decarburization agent.

6. A system for producing granular direct reduced iron, characterized in that the production of granular direct reduced iron is performed by the method for producing granular direct reduced iron according to any one of claims 1 to 5;

the production system of the granular direct reduced iron comprises a reduction reactor, wherein an air inlet, an air outlet, a feed inlet and a discharge outlet are formed in the reduction reactor;

the feed inlet pipeline is used for conveying feed gas and communicated with a gas inlet of the reduction reactor, the feed inlet pipeline is provided with a first preheater, the feed inlet pipeline is used for conveying granular iron ore and communicated with a feed inlet of the reduction reactor, and the feed inlet pipeline is provided with a second preheater.

7. The system for producing granular dri according to claim 6, wherein a rotating member is provided in the reduction reactor.

8. The granular dri production system according to claim 6, wherein the reduction reactor comprises any one of a flow-through multi-stage furnace reactor, an air-suspension rotary kiln reactor or a flood dragon reactor.

9. The system for producing granular direct reduced iron according to any one of claims 6 to 8, further comprising a condensing means connected to an exhaust port of the reduction reactor, the condensing means being connected to the gas inlet duct;

or, the production system of the granular direct reduced iron further comprises a decarburization device and a condensation device, an exhaust port of the reduction reactor is connected with the decarburization device, the decarburization device is connected with the condensation device, and the condensation device is connected with the air inlet pipeline;

preferably, the system for producing granular direct reduced iron further comprises a regeneration device, and the regeneration device is connected with the decarburization device.

10. Use of the method for producing granular dri according to any one of claims 1 to 5 or the system for producing granular dri according to any one of claims 6 to 9 in the field of dri production.

Background

In the global iron and steel smelting industry, various iron making technologies comprise blast furnace iron making technology and non-blast furnace iron making technology, wherein the non-blast furnace iron making technology comprises direct reduction and smelting reduction, and the direct reduction comprises gas-based reduction and coal-based reduction. The blast furnace ironmaking technology has the largest production scale and usage amount, and a large amount of dust, carbon dioxide and other gases are discharged in the coking and sintering processes in the blast furnace ironmaking process, thereby bringing great pressure to the environment. In the non-blast furnace ironmaking technology, the gas-based reduction process reduces iron oxide in iron ore into metallic iron simple substance by using reducing gas, has higher ironmaking efficiency than the traditional carbon reduction method, does not need coking and sintering, and has cleaner production process.

At present, the gas-based reduction technology mainly adopts a Midrex gas-based shaft furnace technology and a HYL gas-based shaft furnace technology, and the gas-based shaft furnace is used for mixing iron ore and a binder, roasting at high temperature to obtain oxidized pellets, and then reducing at high temperature by using reducing gas. The reducing gas mainly comes from synthetic gas obtained by steam conversion or reforming of natural gas, synthetic gas obtained by coal gasification, coke oven tail gas in coke industry and the like. Reducing gas in the Midrex gas-based shaft furnace enters the shaft furnace at 850-950 ℃, the reaction pressure is about 0.5MPa, and metallized pellets with the metallization rate of 92-93% can be obtained; the reducing gas of the HYL gas-based shaft furnace needs to be preheated to 900-₂the/CO is 5.6-5.9, and the metallized pellet with the average metallization rate of 91-95 percent can be obtained.

Besides shaft furnace technology, gas-based reduction technology is also fluidized bed technology, the most representative of which are the FINMET technology and the H-IRON technology. FinFET is a representative technology of fluidized bed direct reduction, is also the only fluidized bed direct reduction process in production at present, is developed by the union of Otto and Venezuela FIORe company, adopts four-stage series fluidized beds to finally obtain a product with the metallization rate of about 93 percent, and thermally presses the product to obtain the final product. The H-IRON technology is a high-pressure low-temperature fluidized reduction technology, which is jointly developed by Hydro carbon Research Inc and Bethlehom Steel Conp, wherein the reducing gas contains 96 percent of hydrogen, a fluidized bed comprising three beds is adopted, mineral powder stays in the reducing bed for 45 hours, the bed is operated within the range of a bubbling bed at an operating gas speed, the reducing degrees of 47 percent (first section), 87 percent (second section) and 98 percent (third section) are respectively obtained in each section, and H are respectively obtained₂The conversion per pass is about 5 percent, the operation is interrupted, and no commercial device runs due to the economic benefit problem of the technology.

At present, the direct reduction technology adopts a shaft furnace technology for the most part, and adopts a coal-based direct reduction technology for a small amount so as to produce metal pellets with high metallization rate or hot-press the pellets into blocks as products. In the fluidized bed technology using iron powder as a product, only a few factories run due to the reasons of long retention time of iron ore powder, low utilization efficiency of reducing gas, low metallization rate of the product, fluidization caused by mutual adhesion of iron particles at high temperature, unstable running of the device, poor economic benefit and the like.

Therefore, it is necessary and urgent to develop a gas-based reduction method of iron ore with low reaction temperature, high utilization rate of reducing gas, and no need of introducing binder and sintering process, so as to alleviate the problems of long process flow, high energy consumption and large pollution of raw material treatment of iron ore in the existing reduction technology of the gas-based shaft furnace of iron ore, and the problems of low utilization rate of reducing gas, low product metallization rate, long reaction time, high energy consumption, and influence on fluidization due to mutual adhesion among iron particles at high temperature in the reduction technology of gas-based fluidized bed.

In view of the above, the present invention is particularly proposed.

Disclosure of Invention

The first purpose of the invention is to provide a production method of granular direct reduced iron, which does not need to introduce other binders for balling and high-temperature roasting processes, greatly reduces pollution and energy consumption, and simultaneously adopts a low-temperature reduction method, thereby not only needing no special high-temperature resistant materials, but also reducing the bonding probability in the reduction process and reducing the energy consumption.

A second object of the present invention is to provide a production system using the above production method of granular direct reduced iron.

A third object of the present invention is to provide a use of the production method or the production system for direct reduced iron using the above-mentioned pellets.

The invention provides a production method of granular direct reduced iron, which comprises the following steps:

the preheated granular iron ore and the preheated feed gas are in countercurrent contact to carry out reduction reaction to obtain granular direct reduced iron;

wherein the average particle size of the granular iron ore is 0.015-4.00mm, the temperature of the preheated granular iron ore is 500-750 ℃, the feed gas contains a reducing gas and an optional diluent gas, the temperature of the preheated feed gas is 450-650 ℃, and the average flow velocity of the feed gas is less than the minimum fluidization velocity of the granular iron ore.

Further, the reduction reaction pressure is 0.05-3.00 MPa;

preferably, the flow ratio of the reducing gas to the particulate iron ore in the feed gas is 500-2000Nm³Reducing gas/t particulate iron ore.

Further, the reduction reaction time of the particulate iron ore is 1 to 15 hours, more preferably 2 to 10 hours.

Further, the reducing gas comprises hydrogen, and the volume fraction of the hydrogen in the reducing gas is not less than 99%;

or, the reducing gas comprises hydrogen and carbon monoxide, the volume fraction of the hydrogen reducing gas is not less than 70%, and the volume fraction of the carbon monoxide in the reducing gas is not more than 10%;

preferably, the volume fraction of the reducing gas in the raw material gas is not less than 70%;

preferably, the diluent gas comprises nitrogen and/or helium.

Further, the method also comprises the step of carrying out optional decarburization treatment and dehydration treatment on the reduction tail gas generated in the reduction reaction process to obtain purified tail gas;

preferably, a decarbonizing agent and the reduction tail gas are mixed, and decarbonization treatment is carried out to remove carbon dioxide in the reduction tail gas, wherein the decarbonizing agent comprises calcium oxide;

preferably, the purified tail gas can be used as raw material gas for recycling;

preferably, the calcium carbonate obtained after the decarburization treatment is regenerated at 650-950 ℃, and the regenerated calcium oxide can be reused as a decarburization agent.

The invention also provides a production system of the granular direct reduced iron, which adopts the production method of the granular direct reduced iron to produce the direct reduced iron;

the production system of the granular direct reduced iron comprises a reduction reactor, wherein an air inlet, an air outlet, a feed inlet and a discharge outlet are formed in the reduction reactor;

the feed inlet pipeline is used for conveying feed gas and communicated with a gas inlet of the reduction reactor, the feed inlet pipeline is provided with a first preheater, the feed inlet pipeline is used for conveying granular iron ore and communicated with a feed inlet of the reduction reactor, and the feed inlet pipeline is provided with a second preheater.

Further, a rotating member is provided in the reduction reactor, and the rotating member rotates or moves the particles along a plane perpendicular to the flow direction of the reducing gas.

Further, the reduction reactor comprises one of a flow-through multi-stage furnace reactor, an air-suspension rotary kiln reactor or a flood dragon type reactor.

Further, the device also comprises a condensing device, wherein an exhaust port of the reduction reactor is connected with the condensing device, and the condensing device is connected with the gas inlet pipeline;

or, the production system of the granular direct reduced iron further comprises a decarburization device and a condensation device, an exhaust port of the reduction reactor is connected with the decarburization device, the decarburization device is connected with the condensation device, and the condensation device is connected with the air inlet pipeline;

preferably, the system for producing granular direct reduced iron further comprises a regeneration device, and the regeneration device is connected with the decarburization device.

The invention also provides an application of the production method of the granular directly reduced iron or the production system of the granular directly reduced iron in the field of directly reduced iron production.

Compared with the prior art, the invention has the beneficial effects that:

(1) the invention provides a production method of granular direct reduced iron, which comprises the steps of carrying out countercurrent contact on granular iron ore with a specific particle size and a specific preheating temperature and feed gas at the specific preheating temperature to carry out reduction reaction to obtain granular direct reduced iron; wherein the content of the first and second substances,because the particle size of the granular iron ore is smaller, the reduction reaction speed at the same temperature is higher than that of the traditional pellet ore, other binders and sintering processes are not required to be introduced, the energy consumption and pollution are greatly reduced, meanwhile, the granular iron ore and the feed gas at the specific preheating temperature are directly subjected to the reduction reaction, the reduction reaction is carried out at a low temperature by utilizing the heat of the materials, the low-temperature reduction reaction does not need special high-temperature-resistant materials, and the bonding probability among solid particles in the reduction process is further reduced; the average flow velocity of the raw material gas is lower than the minimum fluidization velocity of the granular iron ore, so that the gas cannot pass through a bed layer (the granular iron ore) in a bubble form to cause insufficient conversion rate of gas reaction; in addition, compared with the prior iron ore reduction technology, the production method of the granular direct reduced iron provided by the invention has the advantages that CO is generated by the method₂Low dust discharge, cleanness and high efficiency.

(2) The invention also provides a production system of the granular direct reduced iron, the production system adopts the production method of the granular direct reduced iron to produce the direct reduced iron, and the production system has simple process flow and convenient operation. In view of the advantages of the above-described method for producing granular direct reduced iron, the same advantages are also provided by the production system.

(3) The invention also provides an application of the production method of the granular directly reduced iron or the production system of the granular directly reduced iron, and the production method of the granular directly reduced iron or the production system of the granular directly reduced iron has good application in the field of production of the directly reduced iron in view of the advantages of the production method of the granular directly reduced iron or the production system of the granular directly reduced iron.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is a schematic flow diagram of a granular direct reduced iron production system according to an embodiment of the present invention;

FIG. 2 is a schematic flow diagram of a granular direct reduced iron production system according to still another embodiment of the present invention;

FIG. 3 is a schematic flow diagram of a granular direct reduced iron production system according to still another embodiment of the present invention;

FIG. 4 is a schematic structural view of a flow-through multi-stage furnace reactor according to the present invention;

FIG. 5 is a schematic structural view of an air-suspension rotary kiln reactor provided by the present invention;

FIG. 6 is a schematic structural diagram of a shoveling and lifting component in the air-suspension rotary kiln reactor provided in FIG. 5;

FIG. 7 is a schematic structural diagram of a flood dragon type reactor provided by the invention;

FIG. 8 is a schematic structural view of a helical blade in the flood dragon type reactor provided in FIG. 7.

Icon: r1-reduction reactor; e1-first preheater; e2-second preheater; r2-decarbonization device; r3-regeneration unit; e3-condensation device;

10-a housing; 11-a stirring shaft; 12-material tray; 13-a blanking pipe; 14-a stirring arm; 15-a scraper; 16-air holes;

20-a main cylinder; 21-reducing; 22-a slewing cylinder section; 23-a closure mechanism; 24-a lifting component;

30-a rotating shaft; 31-a helical blade; 32-gas path channel; 33-sealing member.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments, and it should be understood that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

According to a first aspect of the present invention, there is provided a method for producing granular direct reduced iron, comprising the steps of:

the preheated granular iron ore and the preheated feed gas are in countercurrent contact to carry out reduction reaction to obtain granular direct reduced iron;

wherein the average particle size of the granular iron ore is 0.015-4.00mm, the temperature of the preheated granular iron ore is 500-750 ℃, the feed gas contains reducing gas and optional diluent gas, the temperature of the preheated feed gas is 450-650 ℃, and the average flow velocity of the feed gas is less than the minimum fluidization velocity of the granular iron ore.

Specifically, in the prior art, oxidized pellets or lump ores are generally used as production raw materials of granular direct reduced iron, when the oxidized pellets are used as raw materials, iron ore and a binder are mixed and sintered to obtain oxidized pellets, and then the oxidized pellets are reduced at a high temperature by reducing gas, so that time and labor are consumed in the process, a large amount of energy consumption and pollutants are generated, more than 80% of iron ore is fine ore, the lump ore is few, and the loss of the crushed iron ore to a proper grain size is large, and the use has restrictions. The invention adopts the granular iron ore with the average grain diameter within the specific range of 0.015-4.00mm as the raw material, and because the granular iron ore has smaller grain size, the reduction reaction speed at the same temperature is higher than that of the traditional oxidized pellet or lump ore, and other binders and sintering processes are not required to be introduced, the energy consumption and pollution can be greatly reduced. And granular iron ores are common in the market, and the raw materials are easy to obtain. For example, the particulate iron ore may be derived from any one or a combination of at least two of particulate magnetite, particulate hematite, particulate specularite, iron scale produced during iron and steel making, or smelted iron slag.

The size of the average particle diameter of the particulate iron ore is directly related to the size of the reduction reaction rate. The average particle size of the granular iron ore is too low (less than 0.015mm), so that the dust is easily too large, the void ratio is too low, the gas passing is influenced, the pressure drop and the energy consumption are increased, the average particle size of the granular iron ore is too high (more than 4.00mm), the reduction rate is easily slow, the product metallization rate is not high, a reaction pipeline is blocked, and the like, so that the average particle size of the granular iron ore is limited within a specific numerical range. Typical but non-limiting particulate iron ores have an average particle size of 0.015mm, 0.02mm, 0.04mm, 0.05mm, 0.08mm, 0.1mm, 0.2mm, 0.4mm, 0.5mm, 0.8mm, 1.0mm, 1.2mm, 1.4mm, 1.5mm, 1.8mm, 2.0mm, 2.2mm, 2.4mm, 2.5mm, 2.8mm, 3.0mm, 3.2mm, 3.4mm, 3.5mm, 3.8mm or 4.0 mm.

The feed gas comprises a reducing gas and optionally a diluent gas. The reducing gas is mainly used for reducing the granular iron ore, and common reducing gases include, but are not limited to, hydrogen, carbon monoxide, and the like. By "optional" herein is meant that the feed gas may comprise only reducing gas or both reducing gas and diluent gas, i.e., diluent gas may be optionally added. Common diluent gases can be inert gases such as nitrogen, argon, and the like.

The granular iron ore and the feed gas are preheated before the reduction reaction, the reduction reaction can be carried out at low temperature by utilizing the heat of the materials, the temperature of the reduction reaction can reach 450-. The temperature of the preheated particulate iron ore is 500 ℃ and 750 ℃, and typical but not limiting temperatures are 500 ℃, 550 ℃, 600 ℃, 650 ℃, 700 ℃ or 750 ℃. The temperature of the preheated feed gas is 450 ℃ to 650 ℃, and typical but not limiting temperatures are 450 ℃, 480 ℃, 500 ℃, 520 ℃, 550 ℃, 580 ℃, 600 ℃, 620 ℃ or 650 ℃. In addition, the granular iron ore and the feed gas are preheated and then subjected to reduction reaction, so that the defect that all heat is brought into the shaft furnace by the preheated gas is overcome, the reaction temperature is more uniform, and the problems of uneven material temperature and particle accumulation and adhesion are solved.

The preheated granular IRON ore and the preheated feed gas are in countercurrent contact, so that the gas-solid contact efficiency of the feed gas and the granular IRON ore can be enhanced, the reduction reaction is more sufficient, high conversion rate and metallization rate can be still obtained at low temperature, the average flow rate of the feed gas is limited within the minimum fluidization speed of the granular IRON ore, the sufficient contact efficiency of gas passing through the granular IRON ore is ensured, the condition that the gas needs to adopt higher gas speed (generally 0.8-1m/s at minimum) to ensure that the granules are in a fluidization state in a fluidized bed is avoided, the retention time is shorter, and the gas can pass through a bed layer in a bubble form, so that the conversion rate is lower, and the gas single-pass conversion rate in H-IRON is only about 5 percent.

Minimum fluidization velocity (U) of particulate iron ore_mf) Can be measured by experiments or calculated by empirical formula, and the empirical formula is usually adopted(principle of fluidization engineering, golden gush, etc., P19). In the reduction reaction process of the present invention, the average flow velocity of the raw material gas is less than the minimum fluidization velocity (U) of the particulate iron ore_mf) The contact between the raw material gas and the granular iron ore can be more sufficient, the utilization efficiency of the raw material gas is greatly improved compared with that of a fluidized bed, and the energy consumption in the process is reduced. Meanwhile, the production method greatly improves the operation flexibility and stability because the particles do not need to be kept in a fluidized state at any time.

The invention provides a production method of granular direct reduced iron, which comprises the steps of carrying out countercurrent contact on granular iron ore with a specific particle size and a specific preheating temperature and feed gas at the specific preheating temperature to carry out reduction reaction to obtain granular direct reduced iron; the granular iron ore has smaller particle size, the reduction reaction speed at the same temperature is higher than that of the traditional pellet ore, other binders and sintering processes are not required to be introduced, so that the energy consumption and pollution are greatly reduced, meanwhile, the granular iron ore and the feed gas at the specific preheating temperature are directly subjected to the reduction reaction, the reduction reaction at low temperature is realized by utilizing the heat of the materials, the low-temperature reduction reaction does not need special high-temperature-resistant materials, and the bonding probability among solid particles in the reduction process is further reduced; the average flow velocity of the raw material gas is lower than the minimum fluidization velocity of the granular iron ore, so that the gas can not pass through a bed layer (the granular iron ore) in a bubble form to cause insufficient conversion rate of gas reaction, and in addition, compared with the prior iron ore reduction technology, the production method of the granular directly reduced iron provided by the invention adopts CO₂Low dust discharge, cleanness,High efficiency.

In a preferred embodiment of the invention, the particulate iron ore has an average particle size of 0.05 to 2mm, preferably 0.1 to 1 mm.

As a preferred embodiment, the above-mentioned use of the small-particle-size granular iron ore does not require the introduction of other binders and sintering processes, greatly reduces pollution, and the reduction speed is faster than that of pellets due to the small particle size, and also greatly reduces the power consumption of gas because the small-particle-size granules do not require fluidization.

As an alternative embodiment of the invention, the reduction reaction pressure is from 0.05 to 3.00 MPa. Typical but non-limiting reduction reaction pressures are 0.05MPa, 0.06MPa, 0.08MPa, 0.10MPa, 0.2MPa, 0.4MPa, 0.5MPa, 0.8MPa, 1.00MPa, 1.20MPa, 1.40MPa, 1.50MPa, 1.80MPa, 2.00MPa, 2.20MPa, 2.40MPa, 2.50MPa, 2.80MPa or 3.00 MPa.

The further limitation on the pressure of the reduction reaction reduces the flow velocity of the reduction gas, reduces the pressure drop of the gas passing through the bed layer, and reduces the probability of particle back mixing caused by particle fluidization.

As an alternative embodiment of the present invention, the flow ratio of the reducing gas to the particulate iron ore in the raw material gas is 500-2000Nm³Reducing gas/t particulate iron ore. The flow ratio of the reducing gas to the particulate iron ore is 500Nm³Reducing gas/t particulate iron ore, 1000Nm³Reducing gas/t particulate iron ore, 1500Nm³Reducing gas/t particulate iron ore or 2000Nm³Reducing gas/t particulate iron ore.

As for the flow ratio of the reducing gas in the raw material gas to the granular iron ore, the gas amount of the required reducing gas is different due to different types and iron content distribution of the granular iron ore, and the interval given by the invention is the preferable range of common iron ore with the total iron content of 50-70 percent, such as the range used for smelting poor iron ore or other iron ores, and the range can be expanded again.

As an alternative embodiment of the present invention, the reduction reaction time of the particulate iron ore is 1 to 15 hours. Typical but non-limiting reduction reaction times are 1h, 2h, 4h, 5h, 6h, 8h, 10h, 12h, 14h or 15 h.

By further limiting the reduction reaction time, the granular iron ores have enough reduction reaction time to obtain high metallization rate, and the low efficiency caused by overlong reaction time can be avoided.

As an alternative embodiment of the invention, the reducing gas comprises hydrogen, and the volume fraction of hydrogen in the reducing gas is not less than 99%, and may be from 99 to 100%.

As yet another alternative embodiment of the invention, the reducing gas comprises hydrogen and carbon monoxide, the volume fraction of hydrogen in the reducing gas being not less than 90%, the volume fraction of carbon monoxide in the reducing gas being not more than 10%, i.e. the volume fraction of hydrogen is between 90 and 100%, and the volume fraction of carbon monoxide is between 0 and 10%.

It should be noted that the requirement of the carbon monoxide content in the reducing gas is mainly determined according to the source of the reducing gas and the requirement of the carbon content in the reduced iron, and in the temperature range of the reduction reaction proposed by the present invention, carbon monoxide can be decomposed into carbon and carbon dioxide in addition to reducing iron oxide, so that the disproportionation reaction of excessive carbon monoxide is easy to occur, excessive coke is generated, the carbon content in the granular directly reduced iron product is too high, and the metallization rate is also reduced. The carbon monoxide content requirement given by the invention is given according to the carbon content requirement of the steel smelting industry in general, and can be adjusted in a larger range according to the downstream smelting requirement without influencing the protection range of the invention.

As an alternative embodiment of the present invention, the volume fraction of the reducing gas in the raw material gas is not less than 90%, that is, the volume fraction of the reducing gas in the raw material gas is 90 to 100%.

It should be noted that, at present, synthesis gas, generally H, is commonly used as the reducing gas for gas-based iron reduction in industry₂The volume ratio of the gas to the CO is 2-6, and depending on the source proportion of the synthesis gas, the adoption of higher hydrogen ratio and even pure hydrogen has certain difficulty, mainly because the reduction of the iron oxide by the hydrogen is an endothermic reaction, and the hydrogen ratio is higher than that of the iron oxideFor example, too high a temperature tends to lower the reduction reaction temperature, resulting in insufficient conversion of the iron ore powder.

The production method of the granular direct reduced iron adopts the granular iron ore with specific grain diameter and enhances the gas-solid contact efficiency, so that high conversion rate and metallization rate can be obtained at low temperature, further high hydrogen content even pure hydrogen can be used as the reducing gas, and the application range of the reducing gas composition is enlarged. Pure hydrogen (the volume fraction of hydrogen in the reducing gas is not less than 99%) is used as the reducing gas to reduce the granular iron ore, a novel iron making route of solar energy → electricity → hydrogen → metallurgy is opened, carbon dioxide is not discharged in the process, the processes of manually adding a binder, sintering and the like, which are necessary to be used in the traditional iron making process but are useless to the reducing process and cause environmental pollution, coke is not used, the emission of gases such as carbon dioxide in the coking process is avoided, and the energy consumption is reduced due to the simple steps.

As an alternative embodiment of the invention, the dilution gas comprises nitrogen and/or argon.

When the used raw material gas contains hydrogen, possibly carbon monoxide and a small amount of carbon dioxide, the hydrogen is converted into water vapor and the carbon monoxide is converted into the carbon dioxide in the reduction process, and due to the existence of chemical equilibrium, the conversion rates of the hydrogen and the carbon monoxide are basically within 40 percent, and the unreacted raw material gas in the reduction tail gas needs to be recycled.

As an alternative embodiment of the present invention, the method for producing granular direct reduced iron further comprises the step of subjecting the reduction off-gas generated during the reduction reaction to an optional decarburization treatment and a dehydration treatment to obtain a purified off-gas.

Preferably, the purified tail gas can be used as raw material gas for recycling.

The decarbonization treatment is to remove carbon dioxide in the reduction tail gas. Here, the "optional decarburization treatment" means that the decarburization treatment can be selectively conducted. When the reduction off-gas contains no carbon dioxide, the decarburization treatment may not be performed, and when the reduction off-gas contains carbon dioxide, the decarburization treatment may be performed. The dehydration treatment is to remove water vapor in the reduction tail gas.

Because the reduction tail gas has certain heat, the reduction tail gas is cooled firstly, then carbon dioxide is removed and dehydration is generally adopted in industry, wherein the carbon dioxide removal adopts a pressure swing adsorption or solvent absorption mode. The invention adopts a different decarburization mode, namely the reduction tail gas can directly enter the decarburization process without cooling.

In an alternative embodiment of the present invention, the reduction tail gas is directly mixed with a decarbonizing agent without cooling, so that decarbonization treatment is performed to remove carbon dioxide from the reduction tail gas, wherein the decarbonizing agent comprises calcium oxide.

As the reduction tail gas carries certain heat, the temperature can reach 400-700 ℃ generally, and the solid calcium oxide has good absorption capacity for carbon dioxide at the temperature, the calcium oxide can be used as a decarbonizing agent. And the calcium carbonate obtained after the decarburization treatment is regenerated at the temperature of 650-950 ℃ and is changed into calcium oxide and carbon dioxide again, and the calcium oxide obtained by regeneration can be used as a decarburization agent for recycling. The decarburization mode does not need to cool the reduction tail gas, so that the heat utilization of the reduction tail gas is more reasonable, and the decarburization mode has more advantages particularly when the content of carbon dioxide in the reduction tail gas is lower.

In addition, the decarburization mode can also be used for processing raw material gas with higher carbon dioxide content, namely when the carbon dioxide exceeds 3 percent or the process requirement, the preheated raw material gas is firstly deprived of the carbon dioxide by calcium oxide and then is subjected to reduction reaction with granular iron ore.

It should be noted that the reduction reaction of the preheated particulate iron ore and the preheated raw material gas is carried out in a reduction reactor, which is required to achieve sufficient contact between the particulate iron ore and the raw material gas to completely avoid agglomeration or caking of the materials.

As an alternative embodiment of the invention, the reduction reactor is provided with a rotating member, wherein the rotating member is a spiral, or a rotating arm, or a rotating drum.

In order to further achieve sufficient contact between the granular iron ore and the feed gas so that the reduction reaction is sufficiently performed, as a preferred embodiment of the present invention, the reduction reactor includes any one of a cross-flow type multi-stage furnace reactor, an air-suspension type rotary kiln reactor or a flood dragon type reactor.

The cross-flow type multi-stage furnace reactor, the air-suspension type rotary kiln reactor and the flood dragon type reactor are designed by the inventor according to the actual reaction requirement.

Specifically, as shown in fig. 4, the flow-through multi-stage furnace reactor includes: the device comprises a shell 10, a stirring shaft 11 and a plurality of material discs 12 arranged at intervals along the axial direction of the shell 10, wherein blanking pipes 13 for blanking are connected to the material discs 12; the upper parts of the material trays 12 are provided with stirring arms 14, and the stirring arms 14 are connected with scrapers 15 for uniformly distributing granular iron ores on the material trays 12; a plurality of air holes 16 are uniformly distributed on each material tray 12 and are used for fully contacting the granular iron ores uniformly distributed on the material trays 12 with the reducing gas in the raw material gas. The uniform distribution of the feed gas is realized through the plurality of air holes 16 uniformly distributed on the material tray 12, the feed gas can flow out layer by layer from bottom to top and can be fully contacted with the granular iron ore uniformly distributed on the material tray 12, the contact area of the granular iron ore and the reducing gas is effectively increased, and the reaction can be fully and completely carried out.

As shown in fig. 5 and 6, the air-suspension type rotary kiln reactor includes: the rotary kiln comprises a rotary kiln barrel, wherein the rotary kiln barrel comprises a main barrel body 20 and reducing parts 21 which are connected to two ends of the main barrel body and respectively shrink outwards, the reducing ends of the reducing parts 21 are connected with rotary cylinder sections 22, the rotary cylinder sections 22 are connected with a sealing mechanism 23, and a sealing assembly is arranged at the joint of the sealing mechanism 23 and the rotary cylinder sections; the main cylinder 20 is internally provided with a plurality of lifting components 24, so that the granular iron ore can form a multi-layer material curtain when the rotary kiln cylinder rotates, and the feed gas can pass through the multi-layer material curtain to fully contact with the granular iron ore. Through connect closing mechanism 23 on gyration shell ring 22 after the necking down, reduced the installation degree of difficulty of seal assembly between gyration shell ring 22 and closing mechanism 23, the multilayer material curtain of constitution has effectively increased the area of contact of granular iron ore with the feed gas, can react more fully completely.

As shown in fig. 7 and 8, the flood dragon reactor comprises a shell, a rotating shaft 30 is installed at the axis of the shell, a helical blade 31 for conveying solid materials is connected to the rotating shaft 30, and a plurality of gas path channels 32 for raw material gas to pass through are arranged on the helical blade 31; the solid material is filled in the reaction cavity of the shell and contacts with the feed gas in the reverse direction to carry out reduction reaction. Through the pivot 30 at flood dragon reactor internally mounted and at sealing member 33 between pivot and casing, effectively improved flood dragon reactor's leakproofness to make flood dragon reactor can the pressure-bearing operation. Through the helical blade 31 of installation on pivot 30 to combine the airtight structure of flood dragon reactor, can make granular iron ore be full of the reaction chamber space of whole reactor, effectively improved the filling rate of granular iron ore.

According to the second aspect of the invention, the production system of the granular direct reduced iron is also provided, and the production method of the granular direct reduced iron is adopted to produce the granular direct reduced iron;

the production system of the particle direct reduced iron comprises a reduction reactor R1, wherein an air inlet, an air outlet, a feed inlet and a discharge outlet are arranged on the reduction reactor R1;

the gas inlet pipeline for conveying the feed gas is communicated with a gas inlet of the reduction reactor, the gas inlet pipeline is provided with a first preheater E1, the feeding pipeline for conveying the granular iron ore is communicated with a feed inlet of the reduction reactor R1, the feeding pipeline is provided with a second preheater E2, and the specific process flow is shown in figure 1.

Specifically, the first preheater E1 preheats the raw material gas, the second preheater E2 preheats the granular iron ore, the preheated raw material gas and the preheated granular iron ore respectively enter the reduction reactor R1 through the gas inlet and the feed inlet of the reduction reactor R1, and countercurrent contact is performed to perform a reduction reaction. After the reduction reaction is finished, the reduction tail gas is discharged from an exhaust port of the reduction reactor R1, and the granular direct reduced iron is discharged from a discharge port of the reduction reactor R1.

As an alternative embodiment of the present invention, the system for producing granular direct reduced iron further comprises a condensing unit, and the exhaust port of the reduction reactor is connected to the condensing unit.

As still another alternative embodiment of the present invention, the system for producing granular direct reduced iron further comprises a decarbonizing apparatus R2 and a condensing apparatus E3, the exhaust port of the reduction reactor R1 is connected to the decarbonizing apparatus R2, the decarbonizing apparatus R2 is connected to the condensing apparatus E3, and the condensing apparatus E3 is connected to the gas inlet duct, as shown in FIG. 3.

Specifically, after the reduction reaction is finished, the reduction tail gas discharged from the reduction reactor R1 is introduced into a decarbonization device R2 to remove carbon dioxide in the reduction tail gas, then the reduction tail gas enters a condensation device E3 to remove condensed water, the reduction tail gas is removed with carbon dioxide and water to obtain purified tail gas, and the purified tail gas can be returned to an air inlet pipeline to be recycled as raw material gas or used as purge gas to enter the next flow.

As another alternative embodiment of the invention, the production system of the granular direct reduced iron further comprises a regeneration device R3, a regeneration device R3 and a decarbonization device R2 which are connected, and the specific process flow is shown in figure 3.

The calcium oxide in the decarbonization device R2 absorbs carbon dioxide and turns into calcium carbonate, the calcium carbonate can be sent to the regeneration device R3, the calcium carbonate in the regeneration device R3 is decomposed into carbon dioxide to be discharged, and the regenerated calcium oxide enters the decarbonization device R2 again for use.

As another alternative embodiment of the present invention, the decarbonization device R2 can also be used to process a raw material gas with a high carbon dioxide content, that is, when the carbon dioxide content exceeds 3% or the process requirement, the preheated raw material gas is first decarbonized by the decarbonization device R2, and then enters the reduction reactor R1 to perform a reduction reaction with the granular iron ore. The calcium oxide in the decarbonization device R2 absorbs carbon dioxide and turns into calcium carbonate, the calcium carbonate can be sent to the regeneration device R3, the calcium carbonate in the regeneration device R3 is decomposed into carbon dioxide to be discharged, the regenerated calcium oxide enters the decarbonization device R2 again for use, and the specific process flow is shown in figure 2.

As an alternative embodiment of the invention, a rotating member is provided in the reduction reactor.

As an alternative embodiment of the present invention, the reduction reactor comprises one of a flow-through multi-stage furnace reactor, an air-suspension rotary kiln reactor or a dragon reactor.

The details of the rotating parts and the reduction reactor are not described here.

According to a third aspect of the present invention, there is also provided a use of the above-described method for producing granular direct reduced iron or the system for producing granular direct reduced iron in the field of direct reduced iron production.

In view of the advantages of the method for producing granular directly reduced iron or the system for producing granular directly reduced iron, the method has good application in the field of producing directly reduced iron.

The technical solution of the present invention will be further described with reference to examples and comparative examples.

Example 1

The embodiment provides a production method of granular direct reduced iron, which comprises the following steps:

the preheated granular iron ore and the preheated feed gas are in countercurrent contact to carry out reduction reaction, the reduction reaction pressure is 2.5MPa, and the reduction reaction time of the granular iron ore is 8 hours, so that granular direct reduced iron is obtained;

wherein the granular iron ore comprises the chemical compositions of total iron, FeO and SiO₂、CaO、MgO、Al₂O₃The content of MnO is respectively 62.7%, 27.3%, 1.32%, 1.53%, 3.45%, 0.82% and 0.28%, the particle size of the granular iron ore is 100-300 meshes (48-150 μm, the average particle size is 0.105mm), and the temperature of the preheated granular iron ore is 600 ℃;

the raw material gas composition is as follows: h₂The content is more than 99.5 percent, and the temperature of the preheated feed gas is 600 ℃.

The mean gas flow velocity was 0.065m/s when the raw material gas was passed through the bed, and the minimum fluidization velocity was 0.086m/s under the conditions of the granular iron ore having the particle size, the raw material gas and the reaction pressure.

In the reduction reactor, the flow ratio of the reducing gas in the raw material gas to the particulate iron ore is 1400Nm³Reducing gas/t particulate iron ore.

The reduction reactor is a cross-flow multi-stage furnace reactor.

Example 2

The embodiment provides a production method of granular direct reduced iron, which comprises the following steps:

the preheated granular iron ore and the preheated feed gas are in countercurrent contact to carry out reduction reaction, the reduction reaction pressure is 1.2MPa, and the reduction reaction time of the granular iron ore is 3 hours, so that granular direct reduced iron is obtained;

wherein the granular iron ore comprises the chemical compositions of total iron, FeO and SiO₂、Al₂O₃The content of MnO is 66.2%, 1.4%, 5.2%, 0.43% and 0.06%, the particle size of the granular iron ore is 50-200 meshes (75-270 mu m, the average particle size is 0.15mm), and the temperature of the preheated granular iron ore is 650 ℃;

the raw material gas composition is as follows: h₂Content 90%, N₂The content is 10%, and the temperature of the preheated feed gas is 550 ℃.

The feed gas was passed through the bed at a gas average flow velocity of 0.09m/s, and the minimum fluidization velocity was 0.13m/s under the conditions of the granular iron ore having the particle size, the feed gas and the reaction pressure.

In the reduction reactor, the flow ratio of the reducing gas to the particulate iron ore in the raw material gas is 1500Nm³Reducing gas/t particulate iron ore.

The reduction reactor is a flood dragon reactor.

Example 3

The embodiment provides a production method of granular direct reduced iron, which comprises the following steps:

the preheated granular iron ore and the preheated feed gas are in countercurrent contact to carry out reduction reaction, the reduction reaction pressure is 1.0MPa, and the reduction reaction time of the granular iron ore is 4.5h, so that granular direct reduced iron is obtained;

wherein the granular iron ore comprises the chemical compositions of total iron, FeO and SiO₂、Al₂O₃MnO contents of 62.67%, 0.59%, 4.52%, 1.59% and 0.26%, respectively, and granular formThe particle size of the iron ore is 40-100 meshes (150-380 mu m, the average particle size is 0.28mm), and the temperature of the preheated granular iron ore is 650 ℃;

the raw material gas composition is as follows: h₂75% of CO, 8% of CO₂Content of 0.5%, N₂The content is 16.5 percent, and the temperature of the preheated feed gas is 600 ℃.

The feed gas was passed through the bed at an average gas flow velocity of 0.035m/s, and at the conditions of the granular iron ore having the above particle diameter, the feed gas and the reaction pressure, the minimum fluidization velocity was 0.27 m/s.

In the reduction reactor, the flow ratio of the reducing gas to the particulate iron ore in the raw material gas was 1200Nm³Reducing gas/t particulate iron ore.

The reduction reactor is a flood dragon reactor.

Example 4

The embodiment provides a production method of granular direct reduced iron, which comprises the following steps:

the preheated granular iron ore and the preheated feed gas are in countercurrent contact to carry out reduction reaction, the reduction reaction pressure is 0.8MPa, and the reduction reaction time of the granular iron ore is 4 hours, so that granular direct reduced iron is obtained;

wherein the granular iron ore comprises the chemical compositions of total iron, FeO and SiO₂、Al₂O₃The content of MnO is 57.76%, 0.71%, 6.82%, 6.26% and 1.2% respectively, the particle size of the granular iron ore is 10-40 meshes (380-1700 mu m, the average particle size is 0.78mm), and the temperature of the preheated granular iron ore is 700 ℃;

the raw material gas composition is as follows: h₂The content is more than 99 percent, and the temperature of the preheated feed gas is 570 ℃.

The mean gas flow velocity was 0.4m/s when the feed gas was passed through the bed, and the minimum fluidization velocity was 0.63m/s under the conditions of the iron ore of this particle size, the feed gas and the reaction pressure.

In the reduction reactor, the flow ratio of the reducing gas to the particulate iron ore in the raw material gas is 1100Nm³Reducing gas/t particulate iron ore.

The reduction reactor is an air-suspension rotary kiln reactor.

Example 5

The embodiment provides a production method of granular direct reduced iron, which comprises the following steps:

the preheated granular iron ore and the preheated feed gas are in countercurrent contact to carry out reduction reaction, the reduction reaction pressure is 0.6MPa, and the reduction reaction time of the granular iron ore is 5 hours, so that granular direct reduced iron is obtained;

wherein the granular iron ore comprises the chemical compositions of total iron, FeO and SiO₂、CaO、MgO、Al₂O₃The content of MnO is respectively 55.2%, 0.29%, 8.69%, 0.01%, 6.53% and 0.07%, the particle size of the granular iron ore is 5-40 meshes (380-4000 mu m, the average particle size is 1.05mm), and the temperature of the preheated granular iron ore is 750 ℃;

the raw material gas composition is as follows: h₂88% of CO, 0.5% of CO₂Content 0.3%, CH₄Content 2.5%, N₂The content is 8.7%, and the temperature of the preheated feed gas is 500 ℃.

The feed gas was passed through the bed at a gas average flow velocity of 0.5m/s, and at the conditions of the particulate iron ore of this particle size, the feed gas and the reaction pressure, the minimum fluidization velocity was 0.82 m/s.

In the reduction reactor, the flow ratio of the reducing gas to the particulate iron ore in the raw material gas was 950Nm³Reducing gas/t particulate iron ore.

The reduction reactor is an air-suspension rotary kiln reactor.

Example 6

This example provides a system for producing granular direct reduced iron, which can be applied to the production method of granular direct reduced iron of examples 1 to 5.

The production system of the granular direct reduced iron comprises a reduction reactor R1, wherein an air inlet, an air outlet, a feed inlet and a discharge outlet are arranged on the reduction reactor R1;

the gas inlet pipeline for conveying the raw gas is communicated with a gas inlet of the reduction reactor, the gas inlet pipeline is provided with a first preheater E1, the feed pipeline for conveying the granular iron ore is communicated with a feed inlet of the reduction reactor R1, the feed pipeline is provided with a second preheater E2, and the specific process flow diagram is shown in figure 1.

The specific reaction flow is as follows: the first preheater preheats the feed gas, the second preheater preheats the granular iron ore, the preheated feed gas and the preheated granular iron ore respectively enter the reduction reactor through the air inlet and the feed inlet of the reduction reactor, and countercurrent contact is carried out for reduction reaction. And after the reduction reaction is finished, the reduction tail gas is discharged from an exhaust port of the reduction reactor, and the granular direct reduced iron is discharged from a discharge port of the reduction reactor.

Example 7

This example provides a system for producing granular direct reduced iron, which can produce granular direct reduced iron by using the production methods of example 3 and example 5.

The production system of the granular direct reduced iron comprises a reduction reactor R1, wherein an air inlet, an air outlet, a feed inlet and a discharge outlet are arranged on the reduction reactor R1;

the gas inlet pipeline for conveying the feed gas is communicated with a gas inlet of the reduction reactor R1, the gas inlet pipeline is provided with a first preheater E1, the feed pipeline for conveying the granular iron ore is communicated with a feed inlet of the reduction reactor R1, and the feed pipeline is provided with a second preheater E2;

the production system of the direct reduction iron particles further comprises a decarburization device R2, a condensation device E3 and a regeneration device R3, wherein an exhaust port of a reduction reactor R1 is connected with the decarburization device R2, the decarburization device R2 is connected with the condensation device E3, the condensation device E3 is connected with an air inlet pipeline, and the regeneration device R3 is connected with the decarburization device R2, as shown in FIG. 3.

The specific reaction flow is as follows: the first preheater preheats the feed gas, the second preheater preheats the granular iron ore, the preheated feed gas and the preheated granular iron ore respectively enter the reduction reactor through the air inlet and the feed inlet of the reduction reactor, and countercurrent contact is carried out for reduction reaction. After the reduction reaction is finished, the reduction tail gas is discharged from an exhaust port of the reduction reactor, and the granular direct reduced iron is discharged from a discharge port of the reduction reactor;

the reduction tail gas discharged from the reduction reactor R1 is introduced into a decarbonization device R2 to remove carbon dioxide in the reduction tail gas, then the reduction tail gas enters a condensation device E3 to remove condensed water, the reduction tail gas is removed with carbon dioxide and water to obtain purified tail gas, and part or all of the purified tail gas can return to an air inlet pipeline to be used as raw material gas for recycling, and can also be used as purge gas to enter the next flow. The calcium oxide in the decarbonization device R2 absorbs carbon dioxide and turns into calcium carbonate, the calcium carbonate can be sent to the regeneration device R3, the calcium carbonate in the regeneration device R3 is decomposed into carbon dioxide to be discharged, and the regenerated calcium oxide enters the decarbonization device R2 again for use.

Comparative example 1

This comparative example provides a method for producing granular direct reduced iron, except that the average particle size of the granular iron ore was 500-2000 mesh (corresponding to particle sizes of 6.5-25 μm, average particle size of 12 μm), the composition of the remaining raw materials, process parameters and production steps were the same as in example 1, and the minimum fluidization velocity was 0.026m/s under the conditions of the granular iron ore of this particle size, the raw material gas and the reaction pressure.

Comparative example 2

This comparative example provides a method for producing granular direct reduced iron, except that the grain size of the granular iron ore was 4 to 12mm (average grain size was 7.6mm), and the composition of the raw materials, process parameters and production steps were the same as those of example 3.

Comparative example 3

This comparative example provides a method for producing granular direct reduced iron, except that the preheating temperature of the granular iron ore was 480 ℃ and the preheating temperature of the raw material gas was 440 ℃, and the composition of the remaining raw materials, process parameters, and production steps were the same as those of example 4.

In order to compare the technical effects of the respective examples and comparative examples, the following experimental examples were specifically set.

Experimental example 1

The metallization rate, carbon content, reducing gas conversion rate and total iron content of the granular directly reduced iron in each example and comparative example were measured, and the specific results are shown in table 1.

TABLE 1

Experimental groups	Metallization rate	Carbon content	Conversion rate of reducing gas	Total iron content
					Example 1	98.8％	-	23.6％	89.0％
Example 2	98.7％	-	26.0％	93.4％
					Example 3	96.8％	2.6％	30.3％	86.4％
Example 4	97.8％	-	30.7％	79.6％
					Example 5	96.7％	0.2％	33.7％	77.2％
Comparative example 1	50.3％	-	12.0％	75.1％
					Comparative example 2	82.7％	0.7％	26.2％	84.2％
Comparative example 3	9.7％	-	3.0％	61.2％

Note that "-" indicates that the carbon content was 0.

As can be seen from the data in Table 1, by adopting the method for producing the granular direct reduced iron, the utilization efficiency of the reducing gas is greatly improved while the high metallization rate is obtained, the conversion rate reaches 23-34 percent and is greatly higher than the conversion rate of 5 percent of the fluidized bed, which means that the energy consumption is greatly reduced, and by adopting the iron ore powder with high iron content, the total iron content of the product reaches 93 percent, which is the highest grade variety in the reduced iron.

The comparative example 1 adopts the granular iron ore with undersize, so the minimum fluidization speed is smaller, the average flow velocity of the raw material gas is higher than the minimum fluidization speed, the bed layer (the granular iron ore) is in a fluidized state, gas short circuit is caused, the product can only obtain 50 percent of metallization rate, and the conversion rate of reducing gas is greatly reduced.

Comparative example 2, in which granular iron ore having an excessively large size is used, the conversion rate of the granular iron ore is decreased, the product metallization rate is decreased, and the reducing gas utilization rate is decreased under the same reaction conditions and time due to the increased size.

In the comparative example 3, the granular iron ore and the feed gas both adopt lower preheating temperatures, so that the reduction reaction temperature is lower, and as a result, the conversion rates of the granular iron ore and the reducing gas are reduced sharply, and from the aspects of mechanics and reaction rules, the conclusion that the reaction rate is improved along with the temperature rise can be easily obtained, but the higher reaction temperature can put higher requirements on materials, and the heat loss can increase the energy consumption, and at the preferable reaction temperature of the invention, the high conversion rate and the high metallization rate can be achieved below 750 ℃.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.