CN118813885A - A method and system for ironmaking by upgrading and circulating coal gas - Google Patents

Abstract

The invention discloses an iron-making method and system for upgrading and recycling coal gas. According to the invention, through a multi-stage gas reforming system, CO ₂、CH₄ and the like are converted into CO and H ₂ by efficiently utilizing waste heat, so that the quality of gas is improved and the waste heat resources are efficiently recovered. On one hand, the obtained upgraded gas is introduced into a newly added pre-reduction furnace in front of a feeding belt to pre-reduce blast furnace iron-containing furnace materials; on the other hand, the solid fuel can be sprayed into the blast furnace through the blast furnace body and the spray gun of the tuyere so as to reduce the solid fuel demand. In addition, the sintering ore and pellet ore roasting system can be introduced to replace solid fuel or utilize the characteristic of hydrogen reduction heat absorption to cool and prereduce the high-temperature finished ore. The invention realizes the high-efficiency recovery of waste heat resources and the cyclic utilization of carbon in the smelting process, reduces the emission of CO ₂ and pollutants in the smelting process, and reduces the production cost.

Description

A method and system for ironmaking by upgrading and circulating coal gas

Technical Field

The present invention relates to the field of steel smelting, and in particular to an ironmaking method and system for upgrading and circulating coal gas, and more particularly to a low-carbon ironmaking method and system for upgrading and circulating coal gas based on blast furnace ironmaking tail gas and waste heat.

Background Art

A large amount of process tail gas and waste heat will be generated during the smelting process of the steel industry. Efficient use of tail gas and waste heat in the production process is an important measure to achieve energy conservation and emission reduction. Process tail gas mainly includes blast furnace gas, converter gas, coke oven gas, etc. At present, with the development of hydrogen metallurgical technology, it has become a hot topic to purify the above tail gas and inject it into the blast furnace to replace part of the solid fuel. Blast furnace gas is mainly removed from _CO2 by chemical adsorption, and then sprayed into the blast furnace from the tuyere after heating, thereby realizing the recycling of blast furnace gas. Converter gas and coke oven gas are mainly purified to remove harmful impurities, and then directly injected into the blast furnace through the tuyere. At present, the blast furnace injection of converter gas and coke oven gas and coupled blast furnace gas circulation have been demonstrated industrially, but the test results show that there are problems such as low gas utilization, complex gas treatment process and high cost. In addition, blast furnace slag, as a by-product of ironmaking, has a slag discharge temperature of about 1400-1550°C, and the sensible heat of each ton of slag is equivalent to 50-60kg of standard coal. However, the currently commonly used water slag flushing process has the problem of low heat utilization rate.

CN 116287504 A discloses a method for utilizing carbon dioxide by high oxygen enrichment and full oxygen blast furnace injection. In this method, the _CO2 component is removed from the top gas discharged from the full oxygen blast furnace through a _CO2 removal device, and the top gas after _CO2 removal is heated and then sprayed into the furnace from the lower tuyere of the furnace body; and the top gas after _CO2 removal is heated and then blown into the blast furnace from the tuyere of the blast furnace together with pure oxygen and coal powder. However, this technology requires the addition of a _CO2 removal device to remove _CO2 from the top gas. At present, the _CO2 removal means are mainly adsorption separation, which has a high cost and a low separation efficiency. The quality-improved gas after _CO2 removal needs to be heated and sprayed by a heating furnace, and sprayed from the furnace body and tuyere, and the heating device increases fuel consumption.

CN 115198043 A discloses a low-carbon smelting system and method based on a blast furnace-steelmaking furnace process coupled with a carbon cycle. The scheme is that the steelmaking furnace is connected to the blast furnace, and is used to receive the carbon-containing molten iron discharged from the blast furnace for steelmaking to obtain steelmaking gas. A CO concentration monitoring device is connected to the steelmaking furnace, and is used to detect the CO concentration in the steelmaking gas in real time. A gas collection and processing device is connected to the steelmaking furnace and the blast furnace, and is used to collect and process high CO concentration steelmaking gas to obtain CO-rich gas and _CO2 -rich gas. A heating device is connected to the steelmaking furnace, and is used to collect low CO concentration steelmaking gas and burn it to obtain heat, and the heat is used to heat the CO-rich gas sprayed back to the blast furnace; a storage and pressurization device is connected to the gas collection and processing device and the steelmaking furnace, and is used to collect and spray the _CO2- rich gas to the steelmaking furnace. This technical solution recycles converter gas in stages. The CO concentration of converter gas in the middle stage of blowing is high, while the CO concentration of steelmaking gas in the early and late stages of blowing is low. Only the gas with high CO concentration in the middle stage of steelmaking is directly injected into the blast furnace, and the gas in the early and late stages of blowing is used for heating. Therefore, the utilization efficiency of converter gas is low. In addition, the gas in the middle stage of converter still contains 15% to 20% CO ₂ . Direct injection into the blast furnace will affect the combustion state of the blast furnace tuyere, the temperature of the cyclotron zone, the combustion state of pulverized coal, and increase carbon consumption.

CN 116836736 A discloses a stable coke oven gas injection process and injection system for a blast furnace, wherein the coke oven gas is sequentially passed through a crude de-oiling and de-naphthalene device, a gas compressor, a gas deep purification device, a buffer tank, a preheating device, a flame arrester, and a spraying device connected to a gas pipeline, and then sprayed into the blast furnace through the blast furnace tuyere. After the coke oven gas is de-oiled and de-naphthalene purified, the gas composition contains about 20% to 25% CH _{4 ,} which first decomposes and absorbs heat during the combustion process at the tuyere, causing the temperature of the tuyere and the whirlpool to change, resulting in increased energy consumption. The process is equipped with a preheating device to preheat the coke oven gas before entering the furnace, and the preheating device consumes energy medium, resulting in increased energy consumption.

In view of the problems of complex process, high cost, low utilization rate and waste of resources existing in the above-mentioned existing processes, the present invention proposes a low-carbon ironmaking method based on the exhaust gas and waste heat of blast furnace ironmaking process to upgrade and recycle coal gas. The process characteristics are to utilize the process exhaust gas and slag waste heat of the process itself, to carry out self-reforming and upgrading of coal gas through multi-stage reforming reaction, and to circulate pre-reduction of iron-containing furnace charge and injection, thereby achieving energy saving and emission reduction.

Summary of the invention

The purpose of the present invention is to provide an ironmaking method and system for upgrading and recycling coal gas. The ironmaking method is specifically a low-carbon ironmaking process that efficiently utilizes the tail gas and waste heat in the blast furnace ironmaking process to self-reform and upgrade the coal gas, and recycles the upgraded coal gas with a higher temperature, pre-reduced iron-containing furnace charge, and injected.

In order to achieve the above purpose, the present invention adopts the following technical solutions:

In one aspect, the present invention provides an ironmaking method for upgrading and circulating coal gas, wherein the ironmaking method comprises:

The converter gas (high-temperature gas produced during converter steelmaking, with a high temperature of 1400-1600°C) and the coke oven gas are introduced into the furnace from the lower gas inlet of the gas primary furnace;

The gas primary furnace comprises a reforming chamber located at the upper part and a dust collecting chamber located at the lower part. The reforming chamber is filled with reforming catalytic balls with a porous structure. The mixed gas rises in the reforming chamber, and _CH4 therein reacts with _CO2 and _H2O ( _CH4 + _CO2 ＝2CO+ _2H2 , _CH4 + _H2O ＝CO+ _3H2 ) to generate _H2 and CO. The reaction absorbs heat to reduce the converter gas temperature while improving the quality of the mixed gas. The dust in the converter gas contains substances such as CaO and metal Fe, which have a catalytic effect on the reforming reaction, and gradually falls downward into the dust collecting chamber under the action of gravity.

The mixed coal gas initially reformed by the coal gas primary reforming furnace is pressurized by the first compressor, purified by the dust removal system, mixed with the blast furnace gas, and then sprayed into the waste heat coal gas reforming furnace through the mixed gas spray gun;

The waste heat gas reforming furnace is divided into two parts, the upper part is a high temperature zone (≥800-850°C), and the lower part is a low temperature zone (<800°C); liquid high temperature blast furnace slag (1450-1550°C) is introduced into the waste heat gas reforming furnace through a blast furnace slag inlet, and the slag outlet is located above the mixed gas spray gun. Under the impact of the high-speed mixed coal gas flow, the liquid high temperature blast furnace slag completes heat exchange by convection and radiation. The blast furnace slag condenses from liquid to solid during the falling process, and is broken into fine particles under gas purge; while the mixed coal gas is heated, _CH4 in the gas reacts with _CO2 and _H2O again to generate H ₂ and CO, and at the same time react to absorb heat and reduce the temperature of blast furnace slag; the blast furnace slag after cooling and crushing enters the lower low-temperature zone, and the high-quality and high-temperature coal gas after quality improvement and temperature increase is discharged from the top coal gas outlet of the waste heat gas reforming furnace, and part of it is blown into the blast furnace through the blast furnace body spray gun and the blast furnace tuyere spray gun; the existing blast furnace coal gas circulation process is to remove _CO2 through adsorption, and then it is heated by a hot blast furnace or a plasma heating furnace and then sprayed into the tuyere or the furnace body. The method of the present invention omits the adsorption and heating process. Compared with the traditional blast furnace ironmaking process, the _CO2 emission per ton of iron is reduced by ≥25%.

The iron-containing charge for the blast furnace is introduced into the furnace from the top of the pre-reduction furnace after screening and weighing in the ore trough, and part of the high-quality and high-temperature coal gas is introduced into the furnace through the reduction furnace air inlet at the bottom of the pre-reduction furnace to pre-reduce the iron-containing charge for the blast furnace to obtain a pre-reduction charge with a metallization rate of ≥40%; the pre-reduction charge is sent into the blast furnace through a feeding belt after passing through the cooling section of the reduction furnace; the coal gas in the pre-reduction furnace is discharged from the coal gas outlet on the top of the reduction furnace and circulated again into the waste heat gas reforming furnace, finally forming a carbon cycle for the entire system.

In the traditional blast furnace ironmaking process, the iron-containing charge for the blast furnace enters the ore trough after cooling, and then is introduced into the blast furnace through the feeding belt. In the method of the present invention, a pre-reduction furnace is added after the ore trough; the charge is pre-reduced by high-quality and high-temperature coal gas in the pre-reduction furnace, which improves the metallization rate of the iron-containing charge for the blast furnace, can reduce the coke ratio and coal ratio of the blast furnace, reduce production costs and carbon emissions, and reduce _CO2 emissions per ton of iron smelted in the blast furnace by 20% to 30%.

According to the ironmaking method of the present invention, preferably, a baffle with a large-pore structure is embedded in the reforming chamber of the gas primary furnace, and its main function is to delay the rising speed of the mixed coal gas and improve the mixing degree between the gases, thereby increasing the reforming efficiency.

According to the ironmaking method of the present invention, preferably, the mixing ratio of coke oven gas and converter gas entering the primary gas treatment furnace is controlled to be (0.4-0.5):1, and the outlet gas temperature of the primary gas treatment furnace is controlled to be ≥850°C.

The converter gas temperature is relatively high (1400-1600°C). Under high temperature conditions, _CH4 in the mixed gas reacts with _CO2 and _H2O ( _CH4 + _CO2 ＝2CO+ _2H2 , _CH4 + _H2O ＝CO+ _3H2 ) to generate _H2 and CO. Since the reaction is endothermic, the quality of the mixed gas is improved while the converter gas temperature is reduced. Specifically, the mixing ratio of coke oven gas and converter gas is controlled to be (0.4-0.5):1 by a flow control device. The outlet gas temperature is controlled to be ≥850°C by adjusting the height and volume of the gas primary furnace, the gas flow rate, and increasing the outlet gas temperature monitoring of the gas primary furnace. At this temperature and mixing ratio, the highest reforming efficiency in the furnace is about 50%-60%. The reforming efficiency is low below this temperature, and if the low-temperature mixed gas continues to remain in the furnace, heat loss will occur due to the reduced reforming efficiency. Therefore, a waste heat power generation device is connected to the top gas outlet of the gas primary furnace to recover the remaining sensible heat. While recovering the heat, the gas temperature is lowered to a range that the first compressor can withstand (≤200°C).

According to the ironmaking method of the present invention, preferably, in the waste heat gas reforming furnace, in order to further reduce the content of CO ₂ in the mixed coal gas and improve the coal gas quality, a coal injection system is added to spray coal injection fuel above the mixed gas injection gun in the waste heat gas reforming furnace. More preferably, the coal injection fuel is selected from biomass fuel, sieved difficult-to-use coal powder or coke powder, etc., and the fixed C in the coal injection fuel reacts with CO ₂ and H ₂ O in the mixed coal gas to generate CO and H ₂ (H ₂ O+C＝CO+H ₂ , CO ₂ +C＝2CO), and the reaction is an endothermic reaction, which can further improve the sensible heat utilization rate of blast furnace slag and improve the quality of the mixed coal gas.

According to the ironmaking method of the present invention, in the waste heat gas reforming furnace, the temperature of the upper blast furnace slag is reduced to 800-900°C, and the particle size of the blast furnace slag after the impact of the high-speed mixed coal gas flow and heat exchange is uneven. In order to meet the requirements of the subsequent blast furnace slag utilization process, it is preferred to add a crushing device in the waste heat gas reforming furnace to pulverize the blast furnace slag; the pulverized blast furnace slag enters the lower low temperature zone (<800°C). More preferably, a hot blast furnace heat exchanger is set in the lower low temperature zone, and the hot blast furnace heat exchanger adopts a pipeline heat exchange method, and preheats the cold air in the pipeline by heat exchange with the blast furnace slag. The cold air is heated and used for the hot blast furnace. The hot blast furnace is used to continuously provide high-temperature hot air to the blast furnace to promote the ironmaking reaction in the blast furnace. More specifically, the blast furnace slag is heat exchanged with the cold air, and the blast furnace slag is cooled to 100-150°C. The generated high-temperature air is introduced into the hot blast furnace after dust removal. The hot blast furnace continues to heat by burning blast furnace gas to increase the air supply temperature of the blast furnace. At present, the key to improving the air temperature of the hot blast stove of the blast furnace is that the high calorific value coal gas resources are scarce. The process of the present invention adopts high calorific value waste heat to preheat the air temperature of the hot blast stove, which can increase the air temperature at a low cost, thereby improving the efficiency of the blast furnace.

In summary, the high-quality and high-temperature coal gas after quality improvement and temperature increase is discharged through the coal gas outlet at the top of the waste heat gas reforming furnace. At this time, the coal gas temperature is 750-850℃, and the coal gas is mainly _H2 and CO, among which _H2 +CO≥90%, _CO2≤2 %; the blast furnace slag waste heat recovery rate is ≥80%.

According to the ironmaking method of the present invention, the coal gas in the pre-reduction furnace is discharged from the coal gas outlet on the top of the reduction furnace after pre-reduction of the charge and circulates into the reforming system again, finally forming a carbon cycle of the entire system. In order to improve the heat utilization rate of the coal gas, preferably, the distance between the waste heat coal gas reforming furnace and the pre-reduction furnace should be shortened as much as possible, and the insulation setting should be increased to reduce heat loss.

According to the ironmaking method of the present invention, preferably, the coal gas in the pre-reduction furnace is discharged from the coal gas outlet on the top of the reduction furnace, dedusted by a dust removal system, and then combined with the blast furnace gas, and then enters the waste heat gas reforming furnace.

According to the ironmaking method of the present invention, preferably, part of the high-quality and high-temperature coal gas discharged from the waste heat gas reforming furnace is introduced into the coal gas circulation system of the raw material preparation process and used as the raw material and/or fuel in the process of preparing the iron-containing charge for the blast furnace; and/or

The cooling equipment used in the preparation process of the iron-containing charge for the blast furnace is sealed, and then the high-quality and high-temperature coal gas is introduced, and the hydrogen reduction endothermic effect is utilized to cool the charge and pre-reduce it, thereby efficiently utilizing heat while increasing the metallization rate of the charge, thereby reducing the production cost and carbon emissions of the blast furnace.

In a more specific preferred scheme, the high-quality and high-temperature coal gas can also be partially introduced into the coal gas circulation system of the raw material preparation process, that is, the preparation process of iron-containing charge for blast furnace; first, it can be used as a rotary kiln heating raw material and a sintering machine blowing fuel, replacing carbonaceous fuel for carbon reduction; in addition, the existing process sintering cooling adopts sintering ring cooler blast cooling, and the pellets adopt pellet cooler air cooling. Both cooling methods have the disadvantages of high air leakage rate and large heat loss; because the high-quality and high-temperature coal gas has a high hydrogen content, hydrogen has the characteristics of reduction and heat absorption. Based on this, the pellet cooler and the sintering ring cooler can be sealed, and then the high-quality and high-temperature coal gas can be introduced, and the hydrogen reduction and heat absorption effect can be used to cool the charge and pre-reduction, which can efficiently utilize heat while increasing the metallization rate of the charge, thereby reducing blast furnace production costs and carbon emissions.

Another aspect of the present invention provides an ironmaking system for upgrading and circulating coal gas to complete any one of the above ironmaking methods.

The present invention uses a multi-stage coal gas reforming system to efficiently utilize waste heat to convert _CO2 , _CH4, etc. into CO and _H2 , thereby achieving improved coal gas quality and efficient recovery of waste heat resources. On the one hand, the obtained quality-improved coal gas is introduced into a pre-reduction furnace newly added in front of the feeding belt to pre-reduce the iron-containing charge of the blast furnace; on the other hand, it can be sprayed into the blast furnace through the spray guns of the blast furnace body and the tuyere to reduce the demand for solid fuel. In addition, it can also be introduced into the sintered ore and pelletized ore roasting system instead of solid fuel, or introduced into the sintered ore and pelletized ore cooling system to utilize the heat absorption characteristics of hydrogen reduction to achieve cooling and pre-reduction. Based on the above-mentioned process flow, the present invention realizes efficient recovery of waste heat resources and recycling of carbon in the smelting process, reduces _CO2 and pollutant emissions in the smelting process, and reduces production costs.

The beneficial effects of the present invention include:

(1) Taking advantage of the composition characteristics and waste heat of the steel plant's own process tail gas, low-quality gas is reformed through a multi-stage gas reforming system to convert CO ₂ , CH _4, etc. into CO and H ₂ , with H ₂ +CO ≥ 90% and CO ₂ ≤ 2%, thereby improving gas quality and efficiently recovering waste heat resources.

(2) It realizes the carbon cycle within the raw material preparation-blast furnace-converter process, reduces _CO2 and pollutant emissions in the ironmaking process, and has the ability to reduce carbon emissions by ≥40% compared with traditional ironmaking processes.

(3) Based on the quality improvement of coal gas and waste heat, a pre-reduction furnace is added before the blast furnace to produce pre-reduced iron-containing charge, which has the ability to increase the metallization rate of the blast furnace by 40% or more, thereby reducing the carbon emissions of the blast furnace.

(4) Utilize the waste heat of blast furnace slag to reform coal gas and preheat the hot blast furnace air, so as to achieve efficient utilization of blast furnace slag waste heat resources, and the blast furnace slag waste heat recovery rate is ≥80%.

(5) High-temperature high-quality coal gas can be injected through the blast furnace body and tuyere to reduce the carbon emissions of the blast furnace.

(6) The upgraded coal gas can be used in the raw material preparation process. On the one hand, it can replace solid fuel to reduce pollutant emissions. On the other hand, it can take advantage of the heat absorption characteristics of hydrogen reduction to serve as a coolant for high-temperature iron-containing furnace charges and achieve pre-reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow diagram of an ironmaking system and method for upgrading and circulating coal gas in a preferred embodiment of the present invention.

Description of reference numerals:

1. Rotary kiln, 2. Pellet cooler, 3. Sintering machine, 4. Sintering ring cooler, 5. Ore trough, 6. Pre-reduction furnace, 7. Reduction furnace cooling section, 8. Reduction furnace top gas outlet, 9. Reduction furnace air inlet, 10. Blast furnace, 11. Blast furnace gas, 12. Blast furnace body spray gun, 13. Blast furnace tuyere spray gun, 14. Hot blast furnace, 15. Converter, 16. Gas primary finishing furnace, 17. Reforming catalytic ball, 18-1. First pressurizer, 18-2. Second pressurizer, 18-3. Third pressurizer, 19. Coke oven gas, 20. Waste heat gas reforming furnace, 21. Coal injection system, 22. Blast furnace slag inlet, 23. Dust removal system, 24. Mixed gas spray gun, 25. Crushing device, 26. Hot blast furnace heat exchanger, 27. Raw material preparation process gas circulation system, 28. Waste heat power generation device.

DETAILED DESCRIPTION

In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments. It should be understood by those skilled in the art that the following specific description is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

The coal gas upgrading and recycling ironmaking method provided by the present invention can efficiently utilize the tail gas and waste heat in the blast furnace ironmaking process to self-reform and upgrade the coal gas, and recycle the upgraded high-quality and high-temperature coal gas, including pre-reduction of furnace charge, and use in blast furnace injection and raw material preparation. It mainly includes a coal gas primary reforming furnace, a waste heat coal gas reforming furnace, and a pre-reduction furnace.

As shown in FIG1 , a gas upgrading and circulating ironmaking system and a corresponding method flow chart in a preferred embodiment of the present invention are shown. The ironmaking method includes the following processes:

The converter gas (high-temperature gas produced during converter steelmaking) from the converter 15 and the coke oven gas 19 (pressurized by the second compressor 18-2) are introduced into the furnace from the lower gas inlet of the gas primary furnace 16.

The gas primary furnace 16 includes a reforming chamber located at the upper part and a dust collecting chamber located at the lower part, and the lower gas inlet is located at the bottom of the reforming chamber; the reforming chamber is filled with reforming catalytic balls 17 with a porous structure. Preferably, a baffle with a macroporous structure is embedded inside the reforming chamber, and its main function is to delay the rising speed of the mixed coal gas and improve the mixing degree between the gases, thereby increasing the reforming efficiency. The mixed coal gas converter gas temperature is relatively high (1400-1600°C). Under high temperature conditions, the mixed coal gas rises in the reforming chamber, and the _CH4 therein reacts with _CO2 and _H2O ( _CH4 + _CO2 ＝2CO+ _2H2 , _CH4 + _H2O ＝CO+ _3H2 ) to generate _H2 and CO. Since the reaction is endothermic, the mixed coal gas quality is improved while reducing the converter gas temperature. The dust in the converter gas contains substances such as CaO and metal Fe, which have a catalytic effect on the reforming reaction, and gradually falls downward into the dust collecting chamber under the action of gravity.

Preferably, the mixing ratio of coke oven gas and converter gas entering the primary gas furnace 16 is controlled to be (0.4-0.5):1, and the outlet gas temperature of the primary gas furnace 16 is controlled to be ≥850°C. Specifically, the mixing ratio of coke oven gas and converter gas is controlled to be (0.4-0.5):1 by a flow control device, and the outlet gas temperature is controlled to be ≥850°C by adjusting the height and volume of the primary gas furnace 16, the gas flow rate, and increasing the monitoring of the outlet gas temperature of the primary gas furnace. The maximum reforming efficiency in the furnace is about 50% to 60% at this temperature and mixing ratio. The reforming efficiency is low below this temperature, and the low-temperature mixed gas continues to be in the furnace, which will cause heat loss due to the reduction of reforming efficiency. Therefore, the waste heat power generation device 28 is connected to the gas outlet at the top of the primary gas furnace 16 to recover the remaining sensible heat, and the gas temperature is reduced to the tolerable range of the first compressor 18-1 (≤200°C) while recovering the heat.

The mixed coal gas preliminarily reformed by the coal gas primary reforming furnace 16 is pressurized by the first compressor 18-1, purified by the dust removal system 23, mixed with the blast furnace gas 11 (and the coal gas after the pre-reduction furnace 6 which is preferably circulated here later) (pressurized by the third compressor 18-3), and then sprayed into the waste heat gas reforming furnace 20 through the mixed gas spray gun 24; the mixed gas spray gun 24 is arranged at the bottom of the waste heat gas reforming furnace 20, and the outlet position of the spray gun is located directly below the slag outlet (the outlet end of the blast furnace slag inlet 22).

The waste heat gas reforming furnace 20 is divided into two parts, the upper part is a high temperature zone (≥800-850°C), and the lower part is a low temperature zone (<800°C); the liquid high temperature blast furnace slag (1450-1550°C) from the blast furnace 10 is introduced into the waste heat gas reforming furnace 20 through the blast furnace slag inlet 22, and the slag outlet (the outlet end of the blast furnace slag inlet 22) is located above the mixed gas spray gun 24. The liquid high temperature blast furnace slag completes heat exchange by convection and radiation under the impact of the high-speed mixed coal gas flow. The blast furnace slag condenses from liquid to solid during the falling process, and is broken into fine particles under the gas purge; while the mixed coal gas is heated, _CH4 in the gas reacts with _CO2 and _H2O again to generate H ₂ and CO, and at the same time react to absorb heat and reduce the temperature of blast furnace slag; the blast furnace slag after cooling and crushing enters the lower low-temperature zone, and the high-quality and high-temperature coal gas after quality improvement and temperature increase is discharged from the top coal gas outlet of the waste heat gas reforming furnace 20, and is partially blown into the blast furnace 10 through the blast furnace body spray gun 12 and the blast furnace tuyere spray gun 13; the existing blast furnace coal gas circulation process is to remove _CO2 through adsorption, and then heat it with a hot blast furnace or a plasma heating furnace and then spray it into the tuyere or the furnace body. The method of the present invention omits the adsorption and heating process. Compared with the traditional blast furnace ironmaking process, the _CO2 emission per ton of iron is reduced by ≥25%.

Preferably, in the waste heat gas reforming furnace 20, in order to further reduce the content of CO ₂ in the mixed coal gas and improve the coal gas quality, a coal injection system 21 is additionally provided to spray coal injection fuel above the mixed gas injection gun 24 in the waste heat gas reforming furnace 20. More preferably, the coal injection fuel is selected from biomass fuel, sieved difficult-to-use coal powder or coke powder, etc., and the fixed C in the coal injection fuel reacts with CO ₂ and H ₂ O in the mixed coal gas to generate CO and H ₂ (H ₂ O+C＝CO+H ₂ , CO ₂ +C＝2CO), and the reaction is an endothermic reaction, which can further improve the sensible heat utilization rate of blast furnace slag and improve the mixed coal gas quality.

In the waste heat gas reforming furnace 20, the temperature of the upper blast furnace slag is reduced to 800-900°C. After the impact of the high-speed mixed coal gas flow and the heat exchange, the particle size of the blast furnace slag is uneven. In order to meet the needs of the subsequent blast furnace slag utilization process, it is preferred to add a crushing device 25 in the waste heat gas reforming furnace 20 to pulverize the blast furnace slag; the pulverized blast furnace slag enters the lower low temperature zone (<800°C). More preferably, a hot blast furnace heat exchanger 26 is set in the lower low temperature zone. The hot blast furnace heat exchanger 26 adopts a pipeline heat exchange method to preheat the cold air in the pipeline through heat exchange with the blast furnace slag. After the cold air is heated, it is used for the hot blast furnace 14. The hot blast furnace 14 is used to continuously provide high-temperature hot air to the blast furnace 10 to promote the ironmaking reaction in the blast furnace. More specifically, the blast furnace slag is heat exchanged with the cold air, and the blast furnace slag is cooled to 100-150°C. The generated high-temperature air is dust-removed and introduced into the hot blast furnace 14. The hot blast furnace 14 continues to heat by burning blast furnace gas to increase the air supply temperature of the blast furnace 10. At present, the key to increasing the air supply temperature of the blast furnace hot blast furnace is that the high calorific value gas resources are relatively small. The process of the present invention uses high calorific value waste heat to preheat the air temperature of the hot blast furnace, which can increase the air temperature at a low cost, thereby improving the efficiency of the blast furnace.

In summary, the high-quality and high-temperature coal gas after upgrading and temperature raising is discharged from the coal gas outlet at the top of the waste heat coal gas reforming furnace 20. At this time, the coal gas temperature is 750-850°C, and the coal gas is mainly _H2 and CO, among which _H2 +CO≥90%, _CO2≤2 %; the blast furnace slag waste heat recovery rate is ≥80%.

The iron-containing charge for blast furnace in the traditional blast furnace ironmaking process (pellets and sintered ore obtained by roasting in rotary kiln 1 and sintering machine 3) enters the ore trough 5 after cooling (pellet cooler 2, sintering ring cooler 4), and then is introduced into the blast furnace through the feeding belt. In the method of the present invention, a pre-reduction furnace 6 is added after the ore trough 5; the iron-containing charge for blast furnace is introduced into the furnace from the top of the pre-reduction furnace 6 after screening and weighing through the ore trough 5, and part of the high-quality and high-temperature coal gas is introduced into the furnace through the reduction furnace air inlet 9 at the bottom of the pre-reduction furnace 6 to pre-reduce the iron-containing charge for blast furnace to obtain a pre-reduction charge with a metallization rate of ≥40%; the pre-reduction charge is sent to the blast furnace 10 through the feeding belt after passing through the reduction furnace cooling section 7; the improvement of the metallization rate of blast furnace entry can reduce the coke ratio and coal ratio of blast furnace, reduce production costs and carbon emissions, and reduce _CO2 emissions per ton of iron smelted in blast furnace by 20% to 30%.

The coal gas in the pre-reduction furnace 6 is discharged from the coal gas outlet 8 on the top of the reduction furnace and circulated again into the waste heat coal gas reforming furnace 20, finally forming a carbon cycle of the entire system. Preferably, after the coal gas in the pre-reduction furnace 6 is discharged from the coal gas outlet 8 on the top of the reduction furnace, it is combined with the blast furnace gas after dust removal by the dust removal system 23, and then enters the waste heat coal gas reforming furnace 20. In order to improve the heat utilization rate of the coal gas, preferably, the distance between the waste heat coal gas reforming furnace 20 and the pre-reduction furnace 6 should be shortened as much as possible, and the insulation setting should be increased to reduce heat loss.

Preferably, part of the high-quality and high-temperature coal gas discharged from the waste heat coal gas reforming furnace 20 can also be introduced into the raw material preparation process coal gas circulation system 27. First, it can be used as a rotary kiln 1 to heat raw materials and a sintering machine 3 to spray fuel, replacing carbonaceous fuel for carbon reduction. In addition, the existing process sintering cooling adopts blast cooling of the sintering ring cooler 4, and the pellets adopt air cooling of the pellet cooler 2. Both cooling methods have the disadvantages of high air leakage rate and large heat loss; because the high-quality and high-temperature coal gas has a high hydrogen content, hydrogen has the characteristics of reduction and heat absorption. Based on this, the pellet cooler 2 and the sintering ring cooler 4 can be sealed, and then the high-quality and high-temperature coal gas can be introduced, and the hydrogen reduction and heat absorption effect can be used to cool the charge and pre-reduction, and the heat can be efficiently utilized while increasing the metallization rate of the charge, thereby reducing the production cost and carbon emissions of the blast furnace.

Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims (11)

1. A method for ironmaking by upgrading and circulating coal gas, wherein the method comprises: The converter gas and the coke oven gas are introduced into the furnace from the lower gas inlet of the gas primary conditioning furnace (16); The coal gas primary furnace (16) comprises a reforming chamber located at the top and a dust collecting chamber located at the bottom. The reforming chamber is filled with reforming catalytic balls (17) having a porous structure. The mixed coal gas rises in the reforming chamber, and _CH4 therein reacts with _CO2 and _H2O to generate _H2 and CO. The reaction absorbs heat to reduce the converter gas temperature while improving the mixed coal gas quality. The dust in the converter gas falls downward and enters the dust collecting chamber. The mixed coal gas initially reformed by the coal gas primary reforming furnace (16) is pressurized by a first compressor (18-1), purified by a dust removal system (23), mixed with the blast furnace gas (11), and sprayed into the waste heat coal gas reforming furnace (20) through a mixed gas spray gun (24); The coal gas primary reforming furnace (16) is divided into two parts, the upper part is a high temperature zone, and the lower part is a low temperature zone, by a temperature range; liquid high temperature blast furnace slag is introduced into the waste heat coal gas reforming furnace (20) through a blast furnace slag inlet (22), and the blast furnace slag inlet (22) is located above the mixed gas spray gun (24); the liquid high temperature blast furnace slag is impacted by the high-speed mixed coal gas flow, and heat exchange is completed by convection and radiation; the blast furnace slag condenses from liquid to solid during the falling process, and is broken into fine particles under the gas purge; while the mixed coal gas is heated, _CH4 in the gas reacts with _CO2 and _H2O again to generate H ₂ and CO, and react to absorb heat and reduce the temperature of the blast furnace slag; the blast furnace slag after cooling and crushing enters the lower low-temperature zone, and the high-quality and high-temperature coal gas after quality improvement and temperature increase is discharged from the top coal gas outlet of the waste heat coal gas reforming furnace (20), and part of it is sprayed into the blast furnace (10) through the blast furnace body spray gun (12) and the blast furnace tuyere spray gun (13); The iron-containing charge for the blast furnace is screened and weighed in an ore trough (5) and then introduced into the furnace from the top of a pre-reduction furnace (6). Part of the high-quality and high-temperature coal gas is introduced into the furnace through a reduction furnace air inlet (9) at the bottom of the pre-reduction furnace (6) to pre-reduce the iron-containing charge for the blast furnace and obtain a pre-reduction charge with a metallization rate of ≥40%; the pre-reduction charge is sent into the blast furnace (10) through a feeding belt after passing through a reduction furnace cooling section (7); the coal gas in the pre-reduction furnace (6) is discharged from a coal gas outlet (8) at the top of the reduction furnace and circulated again into the waste heat gas reforming furnace (20). 2. The ironmaking method according to claim 1, wherein a baffle with a large-pore structure is embedded in the reforming chamber of the gas primary reforming furnace (16). 3. The ironmaking method according to claim 1, wherein the mixing ratio of coke oven gas and converter gas entering the gas primary furnace (16) is controlled to be (0.4-0.5):1, and the outlet gas temperature of the gas primary furnace (16) is controlled to be ≥850°C. 4. The ironmaking method according to claim 3, wherein a waste heat power generation device (28) is connected to the top gas outlet of the coal gas primary furnace (16) to recover the remaining sensible heat. 5. The ironmaking method according to claim 1, wherein a coal injection system (21) is provided in the waste heat gas reforming furnace (20) for injecting coal injection fuel above the mixed gas injection gun (24) in the waste heat gas reforming furnace (20); fixed C in the coal injection fuel reacts with _CO2 and _H2O in the mixed gas to generate CO and _H2 , and the reaction is an endothermic reaction, thereby further improving the sensible heat utilization rate of blast furnace slag and improving the quality of the mixed gas. 6. The ironmaking method according to claim 5, wherein the coal injection fuel is selected from biomass fuel, sieved difficult-to-utilize coal powder or coke powder. 7. The ironmaking method according to claim 1, wherein a crushing device (25) is provided in the waste heat gas reforming furnace (20) to pulverize the blast furnace slag, and the pulverized blast furnace slag enters the lower low-temperature zone. 8. The ironmaking method according to claim 1, wherein a hot blast furnace heat exchanger (26) is arranged in the lower low-temperature zone, and the hot blast furnace heat exchanger (26) adopts a pipeline heat exchange method, and preheats the cold air in the pipeline by heat exchange with blast furnace slag. After the cold air is heated, it is used in the hot blast furnace (14), and the hot blast furnace (14) is used to continuously provide high-temperature hot air to the blast furnace (10) to promote the ironmaking reaction in the blast furnace. 9. The ironmaking method according to claim 1, wherein the coal gas in the pre-reduction furnace (6) is discharged from the coal gas outlet on the top of the reduction furnace, is dedusted by a dust removal system (23), and then is combined with the blast furnace gas, and then enters the waste heat gas reforming furnace (20). 10. The ironmaking method according to claim 1, wherein part of the high-quality and high-temperature coal gas discharged from the waste heat coal gas reforming furnace (20) is introduced into a coal gas circulation system (27) in a raw material preparation process to be used as a raw material and/or fuel in a process of preparing iron-containing charge for a blast furnace; and/or The cooling equipment used in the preparation process of the iron-containing charge for the blast furnace is sealed, and then the high-quality and high-temperature coal gas is introduced, and the hydrogen reduction endothermic effect is utilized to cool the charge and pre-reduce it, thereby efficiently utilizing heat while increasing the metallization rate of the charge, thereby reducing the production cost and carbon emissions of the blast furnace. 11. An ironmaking system for upgrading and circulating coal gas to complete the ironmaking method according to any one of claims 1 to 10.