A method for direct reduction of iron in a gas-based shaft furnace

Abstract

The present invention relates to the field of metallurgical technology, and specifically to a method for direct reduction of iron in a gas-based vertical furnace, comprising a reducing gas preparation unit, a reducing gas temperature control and tempering unit, a vertical furnace reduction unit, a waste heat recovery unit, a gas purification unit, a reducing gas purification unit, and a circulating gas heating unit, wherein the reducing gas preparation unit produces a high-temperature reducing gas with carbon monoxide and hydrogen as main components through non-catalytic partial oxidation of raw gas and a recarburizing agent, and can effectively control water vapor in the reaction system. The reducing gas purification unit realizes the effective separation of inert components in the reducing gas recycling process through the setting of the process flow and the improvement of the gas separation method. Through the above-mentioned improvements, the technical problems existing in the existing gas-based vertical furnace process, such as the high water vapor content in the high-temperature reducing gas produced by the non-catalytic reforming conversion reaction, and the accumulation of inert components during the reducing gas recycling process, which affects the quality of the reducing gas and the full utilization of chemical energy, are overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgy, and in particular to a method for direct reduction of iron in a gas-based shaft furnace. Background Art

[0002] Gas-based vertical furnace direct reduction technology is a metallurgical method that uses reducing gas with a temperature lower than the melting temperature of the charge to reduce iron oxide charge and obtain metallic iron. It has the advantages of short process, low pollution, low energy consumption and low greenhouse gas emissions.

[0003] The existing mature gas-based shaft furnace direct reduction technologies mainly include Midrex and HYL-III processes, as well as some improved processes based on these two processes through the adjustment and improvement of process routes. The existing mainstream process routes basically adopt the catalytic reforming of methane-containing raw gas into a reducing gas mainly composed of hydrogen and carbon monoxide, and then pass the reducing gas into the shaft furnace device under certain temperature and pressure conditions, so that the iron oxide is reduced to a solid direct reduced iron (DRI) product mainly composed of metallic iron under the reducing atmosphere conditions in the shaft furnace. In this technical route, a methane reforming conversion catalyst with a noble metal as the active component is required. The problems are: (1) The active component in the catalyst is relatively sensitive to the sulfur content in the raw gas, and the raw gas needs to be finely desulfurized; (2) The catalyst is made of noble metals, resulting in high investment and operating costs; (3) Since the methane catalytic reaction usually proceeds at a high temperature, the problem of catalyst deactivation caused by carbon deposition is a huge challenge; (4) The high-temperature catalytic performance of noble metal oxides as catalysts is unstable, and their active components are easily sintered at high temperatures, resulting in phase change, which causes their catalytic activity to decrease.

[0004] Another technical route is to prepare reducing gas by non-catalytic partial oxidation of methane. Compared with the catalytic conversion reducing gas technical route, the non-catalytic partial oxidation conversion process does not use a catalyst, so its advantages are: (1) the raw gas does not need to be set up with a fine desulfurization process; (2) the expensive cost of precious metal catalysts and fine desulfurizers is eliminated, and the problems such as equipment shutdown caused by catalyst deactivation and replacement are avoided; (3) the non-catalytic partial oxidation of methane is a mild exothermic reaction that can be carried out at high temperature. It can completely crack and convert large molecular hydrocarbons and other organic matter in the methane-containing raw gas, and is conducive to the positive chemical equilibrium of the methane conversion reaction. However, the hydrogen content in the commonly used methane-containing raw gas such as natural gas and coke oven gas is much higher than the carbon content. During the conversion process of preparing high-temperature reducing gas under partial oxidation and high temperature conditions, due to the high activity of hydrogen, hydrogen is more likely to combine with oxygen to form water, resulting in a high water content in the high-temperature reducing gas. At the same time, this process technical route also has the technical problem of excessively high water vapor content in the high-temperature reducing gas during actual production operation. For example, Shi Xuejun et al. published "Simulation of the Purification System for Reducing Gas Production by Non-catalytic Partial Oxidation of Natural Gas" (Modern Chemical Industry, 2018, 38(6): 206-210.), Chen Dong'er published "Calculation and Simulation Research on Acetylene and Reducing Gas Production by Partial Oxidation of Natural Gas" (Master's Thesis, Southwest University, 2022, pp. 56-57), and other related literature all pointed out that the reducing gas produced by non-catalytic partial oxidation of methane contains more than 15% water vapor. However, the gas-based shaft furnace direct reduction process requires that the content of reducing components such as CO and H2 in the reducing gas should be increased as much as possible, and the content of non-reducing components such as water, nitrogen, and carbon dioxide should be reduced. It is usually hoped that the CO+H2 content in the reducing gas should be greater than 86%. Obviously, if the water vapor content in the high-temperature reducing gas prepared by the non-catalytic partial oxidation conversion of methane is too high, it will inevitably affect the CO and H2 content in the reducing gas. At the same time, the water vapor in the high-temperature reducing gas not only has no reducing effect on the iron ore, but also absorbs and carries a large amount of system heat, and releases a large amount of phase change sensible heat during the cooling process after reduction in the reducing gas vertical furnace, resulting in technical problems such as low system energy utilization and high energy consumption.

[0005] Furthermore, existing gas-based shaft furnace direct reduction processes utilize raw gases such as natural gas and coke oven gas, which contain a certain amount of inert gases such as N2 and Ar. These inert components remain in the reducing gas during the raw gas conversion process, shaft furnace reduction, and post-reduction tail gas cooling and decarbonization and desulfurization purification processes. Furthermore, due to chemical equilibrium constraints, the primary utilization rate of chemical energy in gas reduction processes typically does not exceed 40%. To fully utilize the chemical energy of CO and H2 in the reducing gas to reduce iron ore during the gas-based shaft furnace reduction process, the CO and H2 in the reducing gas must be recycled. As the reducing gas circulates, inert components such as N2 accumulate. When these inert components reach a certain concentration, they severely impact the shaft furnace reduction efficiency, rendering the reduction reaction inefficient. The existing solution involves recycling a portion of the reducing gas (shaft furnace top gas) and burning the remaining top gas to provide heat for heating the reducing gas and catalytic conversion of the raw gas. Although this method avoids the accumulation of inert gases in the reducing gas to a certain extent, it creates a new problem: part of the top gas is burned to provide heat, and the chemical energy of a large amount of CO and H2 in the reducing gas to reduce iron ore is not fully utilized, resulting in low utilization of the reducing gas and high energy consumption of the system. Summary of the Invention

[0006] To address the aforementioned technical problems existing in the prior art, the present invention provides an improved process for a gas-based shaft furnace direct iron reduction method, based on the existing technology for producing reducing gas through non-catalytic partial oxidation of methane. This method not only addresses the technical issue of high water content in high-temperature reducing gas, a problem inherent in the existing technology for producing reducing gas through non-catalytic partial oxidation of methane, but also, by modifying the location and extraction method of the reducing gas purification unit, effectively overcomes the prior art issue of enriching inert gases such as nitrogen during the recycling of reducing gas, which impacts reducing gas quality and shaft furnace reduction efficiency.

[0007] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions.

[0008] A gas-based shaft furnace direct iron reduction method comprising a reducing gas preparation unit, a reducing gas temperature adjustment and tempering unit, a shaft furnace reduction unit, a waste heat recovery unit, a gas purification unit, a reducing gas purification unit, and a circulating gas heating unit, characterized in that:

[0009] The reducing gas preparation unit converts the raw gas, an appropriate amount of carbon supplement and an appropriate amount of oxygen into a high-temperature reducing gas under the conditions of normal pressure to 8 MPa and 800 to 2000°C, wherein the reducing gas component in the high-temperature reducing gas is ≥86% (V / V) and the H2O content is ≤8% (V / V);

[0010] The reducing gas purification unit is used to separate the components of the purified furnace top gas to obtain reducing gas with H2 or CO or H2+CO as the main components. The reducing gas is recycled.

[0011] Furthermore, the raw gas is one or more of natural gas, shale gas, coalbed methane, oilfield gas, refinery gas, coke oven gas, and pyrolysis gas. Further preferably, when the hydrogen content in the raw gas is ≥25% (V / V), the raw gas is pre-treated for hydrogen extraction and then fed into the reducing gas preparation unit with an appropriate amount of carbon supplement and an appropriate amount of oxygen to prepare high-temperature reducing gas. The extracted hydrogen is fed to the circulating gas heating unit and recycled after being heated. By adopting this preferred technical solution, on the one hand, the concentration of methane in the raw gas can be increased, promoting the forward movement of the subsequent reducing gas preparation unit to produce high-temperature reducing gas, and reducing the size and investment of related equipment; on the other hand, the ratio of hydrogen to carbon in the raw gas can be reduced, reducing the amount of water generated by hydrogen during the partial oxidation process, thereby achieving a certain control over the water content in the high-temperature reducing gas generated by the reducing gas preparation unit.

[0012] Furthermore, the carbon replenishing agent is one or more of coal, coal coke, petroleum coke, biomass carbon, activated carbon, and carbon dioxide;

[0013] Furthermore, the raw gas and oxygen are preheated to ≯700°C. In this technical solution, the raw gas and oxygen are preheated before conversion, so that the raw gas and oxygen have higher initial energy when they enter the reducing gas preparation unit. Once the reaction system begins to react, more raw gas and recarburizing agent can be quickly converted, shortening the reaction time of the materials in the reducing gas preparation unit, greatly improving the reaction rate and conversion efficiency.

[0014] Furthermore, the reducing gas purification unit utilizes one or more of adsorption, absorption, membrane separation, and cryogenic separation methods to effectively separate the reducing and inert gas components in the top gas, with the separated reducing gas components being recycled. This preferred technical solution also controls the water vapor content in the circulating gas, thereby increasing the H2+CO concentration in the inlet gas and the reduction efficiency of the shaft furnace.

[0015] Furthermore, the circulating gas heating unit adopts an external heat source heating method, and supplementary gas is selectively added as reducing gas during the heating process.

[0016] Furthermore, the supplementary gas is one or more of purified coal gas, blast furnace gas, converter gas, hydrogen, and carbon monoxide.

[0017] Furthermore, the reducing gas temperature adjustment and tempering unit adjusts the high-temperature reducing gas from the reducing gas preparation unit and the medium-high-temperature circulating gas from the circulating gas heating unit to high-temperature reducing gas that meets the requirements of the shaft furnace in the shaft furnace reduction unit through temperature adjustment and component adjustment; the temperature adjustment process selects the amount of oxygen added according to the temperature adjustment and tempering of the reducing gas; after the reducing gas temperature adjustment and tempering unit, a high-temperature reducing gas with a temperature of ≥900°C, a reducing gas component of ≥90% (V / V) and a H2O content of ≤8% (V / V) is obtained.

[0018] Furthermore, the waste heat recovery unit recovers heat from the crude top gas exhausted from the shaft furnace. This recovered heat is used to provide heat and / or steam for the circulating gas heating unit, feed gas preheating, and oxygen preheating. Furthermore, the steam is fed into the circulating gas heating unit to remove carbon deposits, and the generated gas is used as reducing gas or fuel.

[0019] The advantages and positive effects of the gas-based shaft furnace direct iron reduction method of the present invention over the existing technical solutions are:

[0020] (1) In the gas-based shaft furnace direct reduction method of the present invention, based on the full utilization of the existing non-catalytic partial oxidation of methane gas to produce high-temperature reducing gas to obtain a large amount of sensible heat energy, in order to address the problem of high water content in the products generated by the non-catalytic partial oxidation of methane gas due to its high hydrogen-carbon ratio (the ratio of hydrogen to carbon elements), a recarburizer is introduced into the reducing gas preparation process. By utilizing the characteristics that the carbon-rich recarburizer in the reaction system with water vapor has lower heat absorption and activation energy than the hydrogen-rich methane gas reaction system, the hydrogen-rich methane gas and the carbon-rich recarburizer are converted into a high-temperature reducing gas mainly composed of carbon monoxide and hydrogen. Through the synergistic effect of the recarburizer and methane, not only the problem of high water content in the high-temperature reducing gas produced by the non-catalytic partial oxidation of methane gas is solved, but also the content of effective gas in the reducing gas is increased, thereby improving the energy efficiency of the system.

[0021] (2) In the gas-based vertical furnace direct reduction iron method of the present invention, since the reducing gas preparation unit is a synergistic reaction system of methane gas and a recarburizing agent, it has a certain dilution effect on methane gas compared with the existing non-catalytic partial oxidation process of methane gas, and can achieve controllable adjustment of the reaction rate of selective oxidation of methane gas and a recarburizing agent under oxidizing atmosphere conditions, thereby increasing the carbon monoxide and hydrogen content in the reducing gas. Therefore, the reducing gas preparation unit in the method of the present invention has the function of controlling and adjusting the distribution of the reaction system products.

[0022] (3) In order to reduce the loss of CO and H2 during the recycling of reducing gas, the existing gas-based shaft furnace reduction technology increases the concentration of inert components in the furnace top gas by increasing the number of reducing gas cycles, thereby reducing the loss of CO+H2 caused by removing the inert components. However, this will reduce the concentration of CO+H2 in the circulating gas due to the increase in the concentration of inert components, thereby reducing the content of CO+H2 in the reducing gas of the entire reduction system and reducing the efficiency of the direct iron reduction system. The present invention purifies the H2 and / or CO components in the shaft furnace top gas, thereby separating and removing the inert components in the reducing gas during the recycling process, thereby reducing or avoiding the problem of the chemical energy of H2 and CO in the top gas of the existing gas-based shaft furnace process being not fully utilized for the reduction of iron ore, thereby improving the utilization rate of the furnace top gas and reducing the energy consumption of the system. At the same time, since the actual technical effect of purifying the H2 and / or CO components in the shaft furnace top gas is to remove the inert components in the circulating gas, the reducing gas is not affected by the inert components during the recycling process, the concentration of CO+H2 in the reducing gas is maximized, the loss of CO and H2 in the reducing gas is reduced, and the efficiency of the direct reduced iron system is improved.

[0023] (4) The existing non-catalytic partial oxidation technology is used to process the high-temperature reducing gas produced, through complex treatment processes such as waste heat recovery and desulfurization, to obtain room-temperature reducing gas that meets the stringent requirements of the hydrogen-carbon ratio, and to be used for downstream chemical synthesis. The method of the present invention utilizes the high-temperature reducing gas obtained by the non-catalytic partial oxidation of methane gas, and then subjecting it to temperature adjustment and tempering treatment to obtain the high-temperature reducing gas that meets the requirements of the vertical furnace. Compared with the existing utilization method, in the method of the present invention, the gas-based vertical furnace direct reduction system operates under high-temperature conditions, and the requirements for the hydrogen-carbon ratio and sulfur in the reducing gas are much more relaxed. Therefore, there is no need to cool down and desulfurize the high-temperature reducing gas. This not only solves the problem of low energy utilization caused by the inability to directly utilize the sensible heat of the high-temperature reducing gas, but also has the technical effect of complementing the advantages of the methane non-catalytic partial oxidation technology and the gas-based vertical furnace direct reduction technology process, thereby making more full use of the sensible heat energy of the high-temperature reducing gas and improving the comprehensive energy utilization efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention is a schematic flow diagram of a method for direct reduction of iron using a gas-based shaft furnace;

[0025] Figure 2 It is a schematic flow chart of implementation example 1;

[0026] Figure 3 It is a schematic flow chart of implementation example 2;

[0027] Figure 4 It is a schematic flow chart of implementation example 3;

[0028] Figure 51 is a schematic flow chart of implementation example 4. DETAILED DESCRIPTION

[0029] To fully illustrate the purpose, concept, technical features, and efficacy of the present invention, the technical solution of the present invention is further described in detail below in conjunction with specific embodiments of the present invention so that those skilled in the art can better understand the essence of the present invention. It should be noted that the following specific embodiments are only intended to illustrate the concept and specific implementation of the present invention, and the content of the present invention is not limited thereto.

[0030] The main purpose of the present invention is to provide a method for direct reduction of iron in a gas-based shaft furnace. The greatest technical improvements of this method over the prior art are: first, minimizing the water vapor content in the high-temperature reducing gas obtained by non-catalytic partial oxidation in the reducing gas preparation unit; and second, solving the problem of enrichment of inert components such as N2 during the recycling of the reducing gas. In all the following embodiments of the present invention, reducing gas / reducing gas component refers to H2, CO, or H2+CO; reducing gas, high-temperature reducing gas, medium-high temperature circulating gas, medium-temperature circulating gas, high-temperature circulating gas, high-temperature inlet reducing gas, crude top gas, clean top gas, and coal gas refer to gases whose main components are H2+CO, which may contain one or more other gases such as H2O, CO2, N2, or rare gas components; and circulating gas refers to gases whose main components are H2, CO, or H2+CO, which may contain small amounts of one or more other gases such as H2O, CO2, N2, or rare gas components.

[0031] The basic process flow diagram of the method of the present invention is shown in Figure 1 .like Figure 1As shown, a gas-based shaft furnace direct reduction iron method of the present invention includes operating units such as a reducing gas preparation unit, a reducing gas temperature adjustment and tempering unit, a shaft furnace reduction unit, a waste heat recovery unit, a gas purification unit, a reducing gas purification unit, and a circulating gas heating unit. The high-temperature reducing gas obtained by the reducing gas preparation unit is temperature-adjusted and tempered in the reducing gas temperature adjustment and tempering unit to obtain high-temperature inlet reducing gas that meets the requirements for entering the furnace. The high-temperature inlet reducing gas is fed into the shaft furnace reduction unit, where iron-containing charge is reduced to produce direct reduced iron products. The generated crude top gas is processed by the waste heat recovery unit, the gas purification unit, the reducing gas purification unit, and the circulating gas heating unit. The resulting gas is returned to the reducing gas temperature adjustment and tempering unit as circulating gas to be adjusted to a high-temperature inlet reducing gas that meets the requirements for entering the furnace. The biggest technical improvement of the present invention over the prior art is that, on the one hand, a recarburizing agent is introduced into the reducing gas preparation unit, thereby converting methane raw gas, an appropriate amount of recarburizing agent and an appropriate amount of oxygen into high-temperature reducing gas under normal pressure ~ 8MPa and 800 ~ 2000°C. The reducing gas component (H2 + CO) in the obtained high-temperature reducing gas is ≥86% (V / V), and the H2O content is ≤8% (V / V); on the other hand, the present invention sets a reducing gas purification unit to separate the components of the purified top gas to obtain a reducing gas with H2 or CO or H2 + CO as the main components, so that the inert components in the circulating gas can be effectively separated during the recycling of the reducing gas, thereby solving the technical problem of continuous accumulation of inert gas during the recycling of the reducing gas in the prior art, improving the utilization efficiency of the top gas in the existing vertical furnace process and reducing the energy consumption of the system.

[0032] In the aforementioned reducing gas preparation unit, the main chemical reactions occurring among the raw gas, an appropriate amount of carbon supplement and an appropriate amount of pure oxygen are as follows:

[0033] CH4+0.5O2→CO+2H2 ΔH=-27.32KL / mol

[0034] CH4+2O2→CO2+2H2O ΔH=-802.6KJ / mol

[0035] C+0.5O2→CO ΔH=-110.6KL / mol

[0036] C+O2→CO2 ΔH=-393.8KJ / mol

[0037] H2+0.5O2→H2O ΔH=-241.84KJ / mol

[0038] CO+0.5O2→CO2 ΔH=-282.96 KJ / mol

[0039] C+H2O→CO+H2 ΔH=+131.4KJ / mol

[0040] CH4+H2O→CO+3H2 ΔH=+206.15KJ / mol

[0041] C+CO2→2CO ΔH=+172.6KL / mol

[0042] CH4+CO2→2CO+2H2 ΔH=+247.27KJ / mol

[0043] CO+H2O→CO2+H2 ΔH=-41.2KJ / mol

[0044] From the above reaction, it can be seen that in a relatively simple partial oxidation reaction system of methane-containing raw gas (the hydrogen element is much greater than the carbon element), due to the addition of a carbon-rich recarburizing agent, on the one hand, the partial oxidation of equal moles of carbon provides greater reaction heat, providing energy conditions for subsequent endothermic reactions; on the other hand, due to the competitive relationship between the hydrogen element in the reaction system to generate hydrogen and water, with the addition of the recarburizing agent, compared with methane, the heat absorbed by the reaction of equal moles of carbon with water vapor is less, and the reaction activation energy is low, the reaction is easier to proceed, and the hydrogen element that generates water in the original system can be converted into hydrogen, thereby reducing the water content in the high-temperature reducing gas obtained by conversion while increasing the output of reducing gas.

[0045] In the technical solution of the present invention, the reducing gas temperature adjustment and conditioning unit can select the amount of oxygen to be added according to the reducing gas temperature adjustment and conditioning conditions. For example, when the temperature of the high-temperature reducing gas is relatively low, the circulating gas is mainly hydrogen (because the reduction of iron ore by hydrogen is an endothermic reaction, in order to keep the shaft furnace running at a high temperature, reducing gas with a higher temperature condition is required), or the temperature of the medium-high temperature circulating gas is relatively low, by adding oxygen, on the one hand, the temperature of the reducing gas is increased by the heat release of partial oxidation controlled by oxygen; on the other hand, by controlling the temperature increase by oxygen, the equilibrium of the water-gas reaction in the reducing gas is controlled to shift, thereby achieving the purpose of adjusting the hydrogen-carbon ratio in the reducing gas. When the temperature of the high-temperature reducing gas is relatively high and the temperature of the medium-high temperature circulating gas is relatively high, the reducing gas temperature adjustment and conditioning unit may not add oxygen. The reducing gas temperature adjustment and conditioning unit can be used to adjust the high-temperature reducing gas and medium-high temperature circulating gas with different components, temperatures, pressures and hydrogen-carbon ratios, thereby obtaining a high-temperature reducing gas that meets the requirements for entering the furnace.

[0046] In the technical solution of the present invention, the waste heat recovery unit removes dust and recovers heat from the crude top gas, thereby improving the system's energy efficiency. The recovered heat can be further used to provide heat for the circulating gas heating unit, feed gas preheating, oxygen preheating, and / or to generate steam. A preferred technical solution involves feeding the generated steam and oxygen into the circulating gas heating unit to remove carbon deposits, while the generated coal gas is used as a reducing gas or fuel.

[0047] The purpose of the reducing gas purification unit is to effectively separate the reducing components (CO, H2) and inert components (N2, Ar, etc.) in the clean top gas, thereby separating and removing the inert components in the circulating gas. The gas purification method can adopt one or more of the commonly used adsorption, absorption, membrane separation, and cryogenic separation methods. During the inventor's technical research, it was discovered that in existing gas-based shaft furnace direct reduction processes, the top gas contains saturated water vapor during the recycling process. The embodiment of the present invention, by adopting the technical means of providing a reducing gas purification unit, not only solves the problem of inert component enrichment in the top gas, but also has the additional function of reducing the water vapor content in the circulating gas, which is beneficial to improving the H2+CO concentration in the inlet gas and the shaft furnace reduction efficiency.

[0048] The circulating gas heating unit adopts external heat source heating mode. Supplementary gas can be selectively added as process gas during the heating process. The supplementary gas is one or more of purified coal gas, blast furnace gas, converter gas, hydrogen and carbon monoxide.

[0049] In the technical solution of the present invention, the raw gas refers to a methane-rich gas, for example, it can be one or more of natural gas, shale gas, coalbed methane, oilfield gas, refinery gas, coke oven gas, and pyrolysis gas; the carbon replenisher can be a solid carbon replenisher or a gaseous carbon replenisher, wherein the solid carbon replenisher can be one or more of coal, coal coke, petroleum coke, and biomass carbon. When the carbon replenisher is a solid carbon replenisher, it needs to be prepared into particles of a certain particle size and then pneumatically conveyed into the reaction equipment through a carrier gas. Preferably, the carrier gas is directly selected from the raw gas.

[0050] The specific implementation of the present invention is further described in detail below through preferred embodiments.

[0051] Example 1

[0052] like Figure 2 As shown, the process system of this embodiment is provided with a reducing gas preparation unit, a reducing gas temperature control and tempering unit, a vertical furnace reduction unit, a waste heat recovery unit, a gas purification unit, a PSA hydrogen extraction unit, a PSA CO extraction unit, a circulating gas heating unit and a raw material preheater, wherein: the circulating gas heating unit is composed of two identical units (i.e., circulating gas heating unit I and circulating gas heating unit II). Due to the presence of carbon monoxide in the heated circulating gas, carbon deposits are inevitably generated during the heating process of the gas. When the carbon deposits affect the heat exchange efficiency of one of the units, the other unit is used to heat the reducing gas.

[0053] The raw gas (containing 2% inert gases such as N2), an appropriate amount of oxygen, and an appropriate amount of pulverized coal are fed into the reducing gas preparation unit. Under a pressure of 2.0 MPa, the natural gas and coal undergo a non-catalytic partial oxidation conversion reaction. The main chemical reactions that occur are as follows:

[0054] CH4+2O2=CO2+2H2O ΔH=-802.6KJ / mol

[0055] CH4+0.5O2=CO+2H2 ΔH=-27.32KJ / mol

[0056] H2+0.5O2→H2O ΔH=-241.84KJ / mol

[0057] C+O2=CO2 ΔH=-393.8KJ / mol

[0058] C+0.5O2=CO ΔH=-110.6KJ / mol

[0059] CO+0.5O2=CO2 ΔH=-282.96KJ / mol

[0060] C+H2O=CO+H2 ΔH=+131.4KJ / mol

[0061] CH4+H2O=CO+3H2 ΔH=+206.15KJ / mol

[0062] C+CO2=2CO ΔH=+172.6KJ / mol

[0063] CH4+CO2=2CO+2H2 ΔH=+247.27KJ / mol

[0064] CO+H2O=CO2+H2 ΔH=-41.2KJ / mol

[0065] The resulting high-temperature reducing gas is ~1200°C, with CO+H≮90% and H≯5% CO≯. This high-temperature reducing gas is further fed into the reducing gas temperature conditioning unit along with the high-temperature circulating gas at ~850°C for temperature conditioning and tempering, ultimately yielding high-temperature feed reducing gas at ≮900°C, ~93% (CO+H≮), and H≯5%. This high-temperature feed reducing gas is then fed into the shaft furnace reduction unit for the iron ore reduction reaction.

[0066] The crude top gas, discharged from the shaft furnace top at a temperature of ~350°C, passes through a waste heat recovery unit (for dust removal and sensible heat recovery) and a gas purification unit to remove carbon dioxide and sulfur, resulting in clean top gas. The clean top gas then passes through a PSA hydrogen extraction unit and a PSA CO extraction unit, yielding H2 and CO purities of ~98% and ~98%, respectively. The inert gas enrichment after H2 and CO purification has an N2 content of ≤30%. The inert gas enrichment is then combusted in a recycle gas heating unit to provide heat before being discharged through the chimney.

[0067] The gas purity of ~98% H2 and ~98% CO obtained by the PSA hydrogen extraction unit and the PSA CO extraction unit together constitute the circulating gas and are sent to the circulating gas heating device. They are heated to a high-temperature circulating gas of ~850°C by burning fuels such as natural gas. The flue gas after combustion is preheated with natural gas and oxygen in the raw material preheater and then sent to the chimney for discharge.

[0068] Since CO gas undergoes cracking and carbon deposition during the heating process, severe carbon deposition can affect the efficiency of the heat exchanger. Therefore, in this embodiment, the circulating gas heating unit is configured as two identical units, I and II. When carbon deposition in unit II seriously affects the heat exchange efficiency, unit I is used to heat the reducing gas, while oxygen and steam generated by the waste heat recovery unit are simultaneously fed into unit II. In the presence of oxygen and steam, the carbon deposits undergo a non-catalytic partial oxidation reaction to produce a coal gas composed primarily of CO+H2 and containing a small amount of water vapor, which is then fed into the reducing gas preparation unit. Circulating gas heating units I and II are used in a cycle, and the presence of water vapor and H2 in the coal gas significantly reduces the formation of carbon deposits during the non-catalytic partial oxidation process, ensuring the long-term stable operation of the device.

[0069] In this embodiment, under the condition that the reducing gas completes a single reduction process, the N2 content in the high-temperature reducing gas fed into the shaft furnace reduction unit is ≤1%, the N2 content in the crude top gas is ≤1% (after treatment in the waste heat recovery unit, the N2 content is ≤2%), the N2 content in the clean top gas is ≤4%, and the N2 content in the inert gas enriched gas is ≤30%. Existing gas-based shaft furnace direct reduction technologies generally extract a portion of the top gas treated by the waste heat recovery unit as fuel for heating, thereby achieving system thermal balance and addressing the N2 enrichment issue. In this embodiment, the N2 content in the inert gas enriched gas is ≤30%, significantly greater than the ≤2% N2 content in the top gas treated by the waste heat recovery unit. Furthermore, the (CO+H2) concentration in the inert gas enriched gas is also lower than the (CO+H2) concentration in the top gas treated by the waste heat recovery unit. When removing the same amount of N2, the effective gas (CO+H2) loss in this embodiment is significantly less than that in existing gas-based shaft furnace technology solutions. Increasing the number of cycles, which increases the concentration of inert components and reduces CO+H2 losses, also reduces the CO+H2 concentration in the recycle gas, further reducing the CO+H2 content in the entire reduction system and lowering reduction efficiency. Furthermore, the recycle gas is composed of ~98% H2 and ~98% CO, and contains very little water. Therefore, this embodiment significantly improves the utilization of the chemical reduction potential of top gas compared to existing gas-based shaft furnace technology solutions. It also addresses the problem of existing systems that prevents the full recycling of reducing gas due to the enrichment of inert gases such as N2.

[0070] Example 2

[0071] like Figure 3 As shown, the process system of this embodiment comprises a reducing gas preparation unit, a reducing gas temperature and tempering unit, a shaft furnace reduction unit, a waste heat recovery unit, a gas purification unit, a reducing gas purification unit, and a circulating gas heating unit. Similar to Example 1, the circulating gas heating unit in this embodiment is configured as a parallel system consisting of two identical units (i.e., circulating gas heating unit I and circulating gas heating unit II). However, unlike the process route of Example 1, the reducing gas purification unit in this embodiment utilizes a membrane separation hydrogen extraction process for gas purification.

[0072] The raw gas coke oven gas (containing 5% inert gases such as N2), an appropriate amount of oxygen, and an appropriate amount of pulverized coal are fed into the reducing gas preparation unit. Under a pressure of 1.0 MPa, the non-catalytic partial oxidation process of the coke oven gas and the gasification process of the coal are carried out simultaneously. The main chemical reactions that occur are as follows:

[0073] H2+0.5O2=H2O ΔH=-241.84KJ / mol

[0074] CH4+0.5O2=CO+2H2 ΔH=-27.32KJ / mol

[0075] CH4+2O2=CO2+2H2O ΔH=-802.6KJ / mol

[0076] C+O2=CO2 ΔH=-393.8KJ / mol

[0077] C+0.5O2=CO ΔH=-110.6KJ / mol

[0078] CO+0.5O2=CO2 ΔH=-282.96KJ / mol

[0079] C+H2O=CO+H2 ΔH=+131.4KJ / mol

[0080] CH4+H2O=CO+3H2 ΔH=+206.15KJ / mol

[0081] C+CO2=2CO ΔH=+172.6KJ / mol

[0082] CH4+CO2=2CO+2H2 ΔH=+247.27KJ / mol

[0083] CO+H2O=CO2+H2 ΔH=-41.2KJ / mol

[0084] Finally, a high-temperature reducing gas with a temperature of 1100°C, (CO+H2)≮90%, and H2O≯8% is obtained. The gas is then sent to the reducing gas temperature adjustment and tempering unit together with the medium-temperature circulating gas with a temperature of 700°C and an appropriate amount of oxygen. After temperature adjustment and tempering, a high-temperature furnace-feed reducing gas with a temperature≮900°C, 92% (CO+H2), and H2O≯5% is obtained. The gas is finally sent to the vertical furnace reduction unit for reduction reaction.

[0085] The high-temperature reducing gas entering the furnace undergoes reduction reaction in the vertical furnace reduction unit and is discharged to obtain crude top gas with a temperature of ~350°C. It then passes through the waste heat recovery unit (for dust removal of crude top gas and recovery of gas sensible heat) and the gas purification unit to remove carbon dioxide and sulfur to obtain clean top gas.

[0086] The clean furnace top gas passes through the membrane separation hydrogen extraction unit to obtain H2 with a purity of ~98% and hydrogen extraction tail gas, of which about 35% of the hydrogen extraction tail gas is used to replace the coke oven gas, increasing the supply of coke oven gas for the coking unit, thereby increasing the direct reduced iron production capacity of the vertical furnace reduction unit, and the hydrogen and the remaining approximately 65% ​​of the hydrogen extraction tail gas are recycled.

[0087] The circulating gas is composed of hydrogen extraction tail gas, hydrogen and clean coal gas (~95% (CO+H2)). The circulating gas is sent to the circulating gas heating unit and heated to a medium-temperature circulating gas of ~700°C using the waste heat from dry coke quenching or the waste heat from the coke oven riser.

[0088] The circulating gas heating unit in this embodiment is composed of the same unit I and unit II, but its function is different from that of Example 1 in that the coal gas generated during the carbon deposition elimination process is sent to the coke oven to replace the coke oven gas, thereby increasing the coke oven gas supply and thereby improving the direct reduced iron production capacity of the vertical furnace reduction unit.

[0089] In this embodiment, since the hydrogen content of coke oven gas is higher than that of natural gas, and the thermal effects of the redox reactions of hydrogen, carbon monoxide and iron ore are different, the reduction of iron ore by hydrogen is an endothermic reaction, while the reduction of iron ore by carbon monoxide is an exothermic reaction. In addition, the temperature of the reducing gas obtained by the waste heat heating method is lower than that obtained by the fuel combustion heating method. Therefore, it is necessary to spray some oxygen into the reducing gas temperature control and tempering unit according to the real-time temperature, and increase the temperature of the reducing gas by controlling the oxygen and increasing the temperature.

[0090] Similar to the purpose of Example 1, the N2 content of the hydrogen-extracted tail gas in this embodiment is ≤12%, more than double the N2 content of approximately 3% in crude top gas (~5% after treatment in the waste heat recovery unit) and ~6% in clean top gas. When removing the same amount of N2, the loss of effective gas in this embodiment is far less than that in existing gas-based shaft furnace technology solutions. Furthermore, the clean top gas undergoes H2O removal during hydrogen extraction in the membrane separation hydrogen extraction unit, resulting in minimal water content in the recycle gas. Therefore, compared with the existing gas-based vertical furnace technology solution, this embodiment significantly improves the ability to utilize the chemical reduction potential of the furnace top gas, and at the same time solves the problem of the existing system that the reducing gas cannot be fully recycled due to the enrichment of inert gases such as N2. Moreover, under the same coking device conditions, the production capacity of the coking and co-production direct reduced iron in this embodiment is significantly improved compared with the existing vertical furnace direct reduced iron technology solution. Even after deducting the production capacity increase brought by the clean coal gasification as the raw gas, due to the use of the coke oven gas replacement solution, in this embodiment, the production capacity of the coking and co-production vertical furnace direct reduced iron can still be increased by about 30% compared with the existing coking and co-production vertical furnace direct reduced iron solution.

[0091] Example 3

[0092] like Figure 4 As shown, the process system of this embodiment is equipped with a raw gas hydrogen stripping pretreatment unit, a reducing gas preparation unit, a reducing gas temperature control and tempering unit, a vertical furnace reduction unit, a waste heat recovery unit, a gas purification unit, a membrane separation hydrogen stripping unit, and a circulating gas heating unit.

[0093] The main chemical reactions and working strategies of the reducing gas preparation unit are the same as those in Example 1.

[0094] The operating strategies of the reducing gas temperature and conditioning unit, shaft furnace reduction unit, and membrane separation hydrogen extraction unit in this embodiment are essentially the same as those in Example 2, with only the process gas composition and temperature differing. Compared to Example 2, in this embodiment, the coke oven gas is subjected to a feed gas hydrogen extraction pretreatment unit before entering the reducing gas preparation unit, extracting a significant amount of hydrogen from the coke oven gas. This extracted high-purity hydrogen replaces the clean coal gasification in Example 2 and is then fed to the circulating gas heating unit for heating before use.

[0095] In addition, similar to Example 2, the gas purification method of the reducing gas purification unit in this embodiment also adopts a membrane separation hydrogen extraction process.

[0096] In this embodiment, the coke oven gas is first extracted with hydrogen, and then the high-temperature reducing gas is produced by the reducing gas preparation unit. On the one hand, this method can increase the concentration of methane, promote the forward movement of the subsequent high-temperature reducing gas production reaction in the reducing gas preparation unit, and reduce the size and investment of related equipment; on the other hand, it can reduce the ratio of hydrogen to carbon in the raw gas, reduce the amount of water generated by hydrogen during the partial oxidation process, and thus achieve a certain degree of control over the water content in the high-temperature reducing gas generated by the reducing gas preparation unit.

[0097] In this embodiment, hydrogen is extracted from the coke oven gas by a raw gas hydrogen extraction pretreatment unit, and the extracted hydrogen participates in the gas-based shaft furnace reduction as a reducing gas. Therefore, the inert components such as N2 brought into the system by the coke oven gas can achieve the technical effect of Example 2 by adopting the operating strategy of the furnace top gas treatment unit of Example 2.

[0098] Example 4

[0099] like Figure 5 As shown, the process system of this embodiment is equipped with a reducing gas preparation unit, a reducing gas temperature adjustment and tempering unit, a vertical furnace reduction unit, a waste heat recovery unit, a gas purification unit, a membrane separation hydrogen extraction unit, and a circulating gas heating unit.

[0100] The main chemical reactions occurring in the reducing gas preparation unit are the same as those in Example 2.

[0101] The operating strategies of the reducing gas preparation unit, reducing gas temperature and conditioning unit, shaft furnace reduction unit, and membrane separation hydrogen extraction unit in this embodiment are essentially the same as those in Example 2, with only the process gas composition and temperature differing. Compared to Example 2, the hydrogen extraction tail gas generated by the membrane separation hydrogen extraction unit in this embodiment is entirely used to replace the coke oven gas and is not recycled. All hydrogen is recycled, and since carbon deposition does not occur during hydrogen heating, only one circulating gas heating unit is required in this embodiment.

[0102] In addition, similar to Example 2, the gas purification method of the reducing gas purification unit in this embodiment also adopts a membrane separation hydrogen extraction process.

[0103] In this embodiment, the heat recovered by the waste heat recovery unit is used to preheat the raw gas (coke oven gas, oxygen).

[0104] In this embodiment, the hydrogen-extracted tail gas does not participate in the recycling, and the hydrogen-carbon content in the coke oven gas is higher than that in natural gas, and there is no additional carbon source to supplement. In view of the above factors, after the crude top gas passes through the waste heat recovery unit, even if the carbon dioxide in the gas is not removed, it will not affect the subsequent replacement of the coke oven gas with the hydrogen-extracted tail gas. Therefore, in this embodiment, the gas purification unit is only used for desulfurization of the top gas, and no decarbonization is performed, saving investment and operating costs.

[0105] In this embodiment, all the N2 is used to replace the coke oven gas along with the hydrogen-extracted tail gas, and the N2 content in the circulating gas is extremely small, which can completely solve the problem of accumulation of inert gases such as N2 in the existing technical solutions. At the same time, by replacing the coke oven gas and the coking waste heat (coke dry quenching waste heat, coke oven riser waste heat, etc.) with the hydrogen-extracted tail gas, it seems that all the hydrogen-extracted tail gas is used to replace the coke oven gas, resulting in insufficient utilization of carbon monoxide. However, the actual situation is that the total amount of effective reducing gas (CO+H2) in the hydrogen-extracted tail gas is lower than the total amount of effective reducing gas (CO+H2) consumed in the existing technology (burning a part of the furnace top gas treated by the waste heat recovery unit). Therefore, this embodiment can not only solve the problem of enrichment of inert gases such as N2, but also increase the direct reduced iron production capacity of the coking co-production vertical furnace.

[0106] In the description of this specification, although the above description has shown and described the embodiments of the present invention, it can be understood that the above embodiments are exemplary and are not intended to limit the present invention. Any changes, modifications, substitutions, deformations and improvements made in form and details by ordinary technicians in this field within the spirit and principles of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A gas-based shaft furnace direct iron reduction method comprising a reducing gas preparation unit, a reducing gas temperature control and tempering unit, a shaft furnace reduction unit, a waste heat recovery unit, a gas purification unit, a reducing gas purification unit, and a circulating gas heating unit, characterized in that: The reducing gas preparation unit converts the raw gas, an appropriate amount of carbon supplement and an appropriate amount of oxygen into high-temperature reducing gas under the conditions of normal pressure to 8 MPa and 800 to 2000°C. The reducing gas component in the high-temperature reducing gas is ≥86% (V / V) and the H2O content is ≤8% (V / V). The raw gas and oxygen are preheated to ≯700°C. The reducing gas purification unit is used to separate the components of the purified top gas to obtain reducing gas with H2 or CO or H2+CO as the main components, and the reducing gas is recycled; The reducing gas temperature adjustment and conditioning unit adjusts the temperature and composition of the high-temperature reducing gas from the reducing gas preparation unit and the medium-high-temperature circulating gas from the circulating gas heating unit to produce high-temperature reducing gas that meets the requirements for entering the shaft furnace in the shaft furnace reduction unit. The temperature adjustment process selects the amount of oxygen added based on the temperature adjustment and conditioning of the reducing gas. After the reducing gas temperature adjustment and conditioning unit, a high-temperature reducing gas having a temperature of ≥900°C, a reducing gas component of ≥90% (V / V), and an H2O content of ≤8% (V / V) is obtained. The raw gas is one or more of natural gas, shale gas, coalbed methane, oilfield gas, refinery gas, coke oven gas, and pyrolysis gas.

2. The method for direct reduction of iron in a gas-based shaft furnace according to claim 1, characterized in that: When the hydrogen content in the raw gas is ≥25% (V / V), it is pretreated with hydrogen extraction and then sent to the reducing gas preparation unit with an appropriate amount of carbon supplement and an appropriate amount of oxygen to prepare high-temperature reducing gas. The extracted hydrogen is sent to the circulating gas heating unit and recycled after being heated.

3. The method for direct reduction of iron in a gas-based shaft furnace according to claim 1, characterized in that: The carbon replenishing agent is one or more of coal, coal coke, petroleum coke, biomass carbon and activated carbon.

4. The method for direct reduction of iron in a gas-based shaft furnace according to claim 1, characterized in that: The reducing gas purification unit adopts one or more of adsorption, absorption, membrane separation and low temperature separation methods to effectively separate the reducing gas components and inert gas components in the furnace top gas, and the separated reducing gas components are recycled.

5. The method for direct reduction of iron in a gas-based shaft furnace according to claim 1, characterized in that: The circulating gas heating unit adopts an external heat source heating method for heating, and supplementary gas is selectively added as reducing gas during the heating process.

6. The method for direct reduction of iron in a gas-based shaft furnace according to claim 5, characterized in that: The supplementary gas is one or more of purified coal gas, blast furnace gas, converter gas, hydrogen and carbon monoxide.

7. The method for direct reduction of iron in a gas-based shaft furnace according to claim 1, characterized in that: The waste heat recovery unit recovers heat from the crude top gas discharged from the top of the vertical furnace. The recovered heat is used to provide heat and / or generate steam for the circulating gas heating unit, raw gas preheating, and oxygen preheating.

8. The method for direct reduction of iron in a gas-based shaft furnace according to claim 7, characterized in that: The steam is fed into the circulating gas heating unit and combined with oxygen to remove carbon deposits, and the generated coal gas is used as reducing gas or fuel.

Images