阅读说明：本技术 一种球团焙烧还原一体化生产金属化球团的系统及方法 (System and method for integrally producing metallized pellets through pellet roasting and reduction ) 是由 左海滨 韦润培 陈衍彪 于 2021-08-27 设计创作，主要内容包括：本发明涉及球团矿处理技术领域,提供了一种球团焙烧还原一体化生产金属化球团的系统及方法,该系统包括链篦机、回转窑、还原区和成品输送机；回转窑和还原区连接处设置挡板；回转窑内设置第一煤气喷枪；挡板下方设置第二煤气喷枪、第一氮气喷枪及第一氢气喷枪；还原区底部设置台车,还原区沿台车方向设置有若干第二氢气喷枪；还原区后段的台车下方设置有第一抽风机；第一抽风机后设置第二氮气喷枪。本发明在球团焙烧完成后直接利用其热量进行还原,实现一体化生产；本发明方法可生产出满足电炉入炉要求的高金属化率球团；富氢还原不仅获得了金属化球团,还原过程只排放水蒸气,降低成本；利用工艺过程产生的烟气合成氨,实现了烟气的高值化利用。(The invention relates to the technical field of pellet ore treatment, and provides a system and a method for integrally producing metallized pellets by roasting and reducing pellets, wherein the system comprises a chain grate, a rotary kiln, a reduction area and a finished product conveyor; a baffle is arranged at the joint of the rotary kiln and the reduction zone; a first gas spray gun is arranged in the rotary kiln; a second gas spray gun, a first nitrogen spray gun and a first hydrogen spray gun are arranged below the baffle; the bottom of the reduction area is provided with a trolley, and the reduction area is provided with a plurality of second hydrogen spray guns along the direction of the trolley; a first exhaust fan is arranged below the trolley at the rear section of the reduction zone; and a second nitrogen spray gun is arranged behind the first exhaust fan. The invention directly utilizes the heat of the pellet to reduce after the pellet is roasted, thereby realizing integrated production; the method can produce the high metallization rate pellets meeting the requirement of charging the electric furnace; the hydrogen-rich reduction not only obtains the metallized pellets, but also only discharges water vapor in the reduction process, thereby reducing the cost; the flue gas generated in the process is utilized to synthesize ammonia, so that high-value utilization of the flue gas is realized.)

1. A system for integrally producing metallized pellets by roasting and reducing pellets is characterized by comprising a chain grate, a rotary kiln, a reduction area and a finished product conveyor;

a baffle is arranged at the joint of the rotary kiln and the reduction zone and used for ensuring that pellets smoothly fall to the reduction zone and controlling the inflow of the gas of the rotary kiln into the reduction zone; a first gas spray gun is arranged in the rotary kiln; a second gas spray gun, a first nitrogen spray gun and a first hydrogen spray gun are arranged below the baffle;

the bottom of the reduction area is provided with a trolley, and the reduction area is provided with a plurality of second hydrogen spray guns for providing reduction hydrogen along the direction of the trolley; a first exhaust fan is arranged below the trolley at the rear section of the reduction zone; a second nitrogen spray gun is arranged behind the first exhaust fan;

and drying and preheating the pellets on the grate, oxidizing, desulfurizing and decomposing the pellets in the rotary kiln, then carrying out hydrogen reduction on the trolleys in the reduction zone, and outputting the pellets subjected to the hydrogen reduction treatment through a finished product conveyor.

2. The system for integrally producing metallized pellets through pellet roasting and reduction as claimed in claim 1, wherein the system further comprises a second exhaust fan arranged at the outlet of the reduction zone, and the second exhaust fan is connected with the rotary kiln through a flue.

3. The system for integrated production of metallized pellets by pellet roasting and reduction as claimed in claim 1, further comprising an ammonia synthesis unit: the ammonia synthesis unit comprises a lime bed layer, a compressor, a synthesis tower, a pre-heater in front of the tower, a cooling device, an ammonia separator and a liquid ammonia storage tank;

the hydrogen-nitrogen mixed gas pumped out by the first exhaust fan passes through the lime bed layer and enters the synthesis tower through the compressor, the heater in front of the synthesis tower heats the synthesis tower, the hydrogen-nitrogen mixed gas produces ammonia-hydrogen-nitrogen mixed gas in the synthesis tower, the temperature is reduced through the cooling device, the ammonia is separated through the ammonia separator, and the separated ammonia enters the liquid ammonia storage tank through the pipeline after being pressurized and liquefied.

4. The system for integrally producing metallized pellets through pellet roasting and reduction as claimed in claim 1, wherein the trolleys of the reduction zone are inclined upward at a certain angle along the running direction.

5. The system for integrally producing metallized pellets through pellet roasting and reduction as claimed in claim 1, wherein a gas leakage early warning device is provided under the baffle plate to detect the amount of gas leaked from the rotary kiln into the reduction zone, and when the leaked gas is greater than a set threshold value, an early warning message is given.

6. The system for integrally producing metallized pellets through pellet roasting and reduction as claimed in claim 1, wherein the inner wall of the reduction zone is provided with a heat insulating material, and the trolley is provided with a sealing cover; the spray head of the first hydrogen spray gun faces the lower right side of the trolley in operation.

7. The system for integrally producing metallized pellets through pellet roasting and reduction as claimed in claim 2, wherein the negative pressure of the first exhaust fan and the negative pressure of the second exhaust fan are both controlled to be 18-20 kPa.

8. A method for integrated production of metallized pellets by pellet firing reduction, using the system according to any one of claims 1 to 7, characterized in that the method comprises:

s1, drying and preheating pellets on a grate, providing heat required by oxidizing roasting in a rotary kiln by a first gas spray gun, and oxidizing, desulfurizing and decomposing to obtain high-temperature pellets with the temperature of 1200 +/-100 ℃;

s2, the high-temperature pellets obtained in the step S1 fall onto a trolley of a reduction zone through a baffle, and a second gas spray gun arranged below the baffle consumes excessive oxygen to prevent the oxygen from leaking to the reduction zone; the first hydrogen spray gun below the baffle plate provides hydrogen for reduction for the pellets entering the reduction zone trolley and prevents the hydrogen from flowing back to the rotary kiln; the first nitrogen spray gun balances the negative pressure environment generated by the first hydrogen spray gun, and the air pressure in the reduction area is ensured to be stable; continuously carrying out reduction reaction on the pellets in the reducing atmosphere of the second hydrogen spray gun in the process of running the pellets on the trolley;

s3, when the temperature of the reduction zone is reduced to below 600 ℃, the mixed gas of hydrogen and nitrogen is extracted by the first exhaust fan, the pellet is cooled by the nitrogen of the second nitrogen spray gun and then is output by the finished product conveyor, and the flue gas is extracted from the outlet of the reduction zone by the second exhaust fan and then is returned to the rotary kiln by the flue.

9. The method for integrally producing metallized pellets through pellet roasting and reduction as claimed in claim 8, further comprising:

s4, pumping the hydrogen-nitrogen mixed gas by a first exhaust fan, passing through a lime bed layer, passing through a compressor, entering a synthesis tower, heating the synthesis tower by a heater in front of the tower, generating ammonia-hydrogen-nitrogen mixed gas in the synthesis tower, reducing the temperature by a cooling device, separating the ammonia gas by an ammonia separator, and leading the separated ammonia gas to enter a liquid ammonia storage tank through a pipeline after being pressurized and liquefied.

10. The method for integrally producing metallized pellets through pellet roasting and reduction as claimed in claim 8, wherein in step S2, the pellets are kept for not less than 25min at 1200 ℃ to 600 ℃ on the reduction zone trolley.

Technical Field

The invention relates to the technical field of pellet processing, in particular to a system and a method for integrally producing metallized pellets by roasting and reducing pellets.

Background

Under the background of 'carbon neutralization and carbon peak reaching', more strict emission reduction requirements are put forward for various industrial departments,especially in the steel industry where emissions are high. The production by utilizing clean energy becomes an important way for energy conservation and emission reduction in the steel industry. Under the practical exploration of a plurality of metallurgists all over the world, hydrogen metallurgy becomes a solution for reducing CO in the steel smelting process₂The important mode of discharge. The search for the combination of hydrometallurgy and the pelletizing process is an important direction for the development of the pelletizing process.

Since the pellet process was proposed in the 20 th of the 19 th century, three main ways of production using shaft furnaces, grate-rotary kilns and belt-type calciners have been developed over a hundred years of practical exploration. Although the grate-rotary kiln method appears late, the produced pellet ore has the advantages of uniform quality, high strength and the like, has good development prospect, further optimizes the production process to improve the quality of the pellet ore, and simultaneously realizes energy conservation, emission reduction and energy efficient utilization, thereby being a field of the grate-rotary kiln system which needs to be focused on in future development.

The traditional chain grate-rotary kiln system comprises three main bodies, namely a chain grate, a rotary kiln and a circular cooler. The screened green pellets are sent to a chain grate machine through a material distribution system, and are sent to a rotary kiln after being dried and preheated in the chain grate machine. The roasting process of the pellets is completed in a rotary kiln, the roasting temperature is controlled between 1250 ℃ and 1300 ℃, and hot pellets with the temperature of about 1200 ℃ are obtained. And then, discharging the glowing pellets into a receiving hopper of the circular cooler through a chute, and distributing the glowing pellets on a trolley through a distributing device. As the trolley is operated, heat in the pellets exchanges heat with air, and the air is gradually heated while the pellets are gradually cooled. At the tail of the circular cooler, the pellets are cooled to below 150 ℃, discharged to a finished product adhesive tape machine through a discharge hopper and finally conveyed to a finished product bin. The hot flue gas is returned to the grate and the rotary kiln through the flue and is used for drying and preheating pellets and improving the temperature in the rotary kiln. In addition, the flue gas with lower temperature is directly discharged after being treated. The pellets are heated, reflowed and reduced in a blast furnace to finally produce molten iron. In the above process, the pellets are cooled and heated again, and if changes can be made in the process, the energy consumption in the smelting process may be reduced.

Disclosure of Invention

The invention aims to overcome at least one of the defects of the prior art, provides a system and a method for integrally producing metallized pellets by roasting and reducing pellets, can overcome the defects of higher energy consumption, longer production line and the like in the prior art, and is used for solving the problems of low energy utilization rate in the pellet cooling process and higher energy consumption in the prior blast furnace smelting process so as to realize low-carbon iron making. Meanwhile, the flue gas generated in the process is efficiently utilized, and further energy conservation and emission reduction are realized.

The invention adopts the following technical scheme:

on one hand, the system for integrally producing the metallized pellets by roasting and reducing the pellets comprises a chain grate, a rotary kiln, a reduction area and a finished product conveyor;

a baffle is arranged at the joint of the rotary kiln and the reduction zone and used for ensuring that pellets smoothly fall to the reduction zone and controlling the inflow of the gas of the rotary kiln into the reduction zone; a first gas spray gun is arranged in the rotary kiln and used for providing heat required by oxidizing roasting; a second gas spray gun (consuming excessive oxygen and preventing oxygen from leaking to a reduction zone from the rotary kiln), a first nitrogen spray gun (balancing air pressure) and a first hydrogen spray gun are arranged below the baffle;

the bottom of the reduction area is provided with a trolley, and the reduction area is provided with a plurality of second hydrogen spray guns for providing reduction hydrogen along the direction of the trolley; a first exhaust fan is arranged below the trolley at the rear section of the reduction zone; a second nitrogen spray gun (used for cooling pellets and preventing the pellets from being reoxidized) is arranged behind the first exhaust fan;

and drying and preheating the pellets on the grate, oxidizing, desulfurizing and decomposing the pellets in the rotary kiln, then carrying out hydrogen reduction on the trolleys in the reduction zone, and outputting the pellets subjected to the hydrogen reduction treatment through a finished product conveyor.

In any of the above possible implementations, there is further provided an implementation, wherein the system further includes a second exhaust fan disposed at an outlet of the reduction zone, and the second exhaust fan is connected to the rotary kiln through a flue.

Any of the possible implementations described above, further providing an implementation, the system further comprising an ammonia synthesis unit: the ammonia synthesis unit comprises a lime bed layer, a compressor, a synthesis tower, a pre-heater in front of the tower, a cooling device, an ammonia separator and a liquid ammonia storage tank;

the hydrogen-nitrogen mixed gas pumped out by the first exhaust fan passes through the lime bed layer and enters the synthesis tower through the compressor, the heater in front of the synthesis tower heats the synthesis tower, the hydrogen-nitrogen mixed gas produces ammonia-hydrogen-nitrogen mixed gas in the synthesis tower, the temperature is reduced through the cooling device, the ammonia is separated through the ammonia separator, and the separated ammonia enters the liquid ammonia storage tank through the pipeline after being pressurized and liquefied.

In any of the above possible implementations, there is further provided an implementation in which the trolley of the reduction zone is inclined upward at an angle in the direction of travel.

In any of the foregoing possible implementation manners, there is further provided an implementation manner that a gas leakage early warning device is disposed below the baffle plate, and is configured to detect an amount of gas leaked from the rotary kiln into the reduction area, and send early warning information when the leaked gas is greater than a set threshold.

In any of the above possible implementation manners, there is further provided an implementation manner, wherein the inner wall of the reduction zone is provided with a heat insulation material, and the trolley is provided with a sealing cover; the spray head of the first hydrogen spray gun faces the lower right side of the trolley in operation.

Any one of the above possible implementation manners further provides an implementation manner, and the negative pressure of the first exhaust fan and the negative pressure of the second exhaust fan are controlled to be 18-20 kPa.

There is further provided in any of the possible implementations described above an implementation in which the gas for each of the nitrogen gas injection lance, the hydrogen gas injection lance, and the gas injection lance is provided from a nitrogen gas cabinet, a hydrogen gas cabinet, and a gas cabinet, respectively.

There is further provided in any of the above possible implementations an implementation in which the product conveyor is a product tape machine.

In another aspect, the present invention also provides a method for integrally producing metallized pellets by pellet roasting and reduction, wherein the method comprises the following steps:

s1, drying and preheating pellets on a grate, providing heat required by oxidizing roasting in a rotary kiln by a first gas spray gun, and oxidizing, desulfurizing and decomposing to obtain high-temperature pellets with the temperature of 1200 +/-100 ℃;

s2, the high-temperature pellets obtained in the step S1 fall onto a trolley of a reduction zone through a baffle, and a second gas spray gun arranged below the baffle consumes excessive oxygen to prevent the oxygen from leaking to the reduction zone; the first hydrogen spray gun below the baffle plate provides hydrogen for reduction for the pellets entering the reduction zone trolley and prevents the hydrogen from flowing back to the rotary kiln; the nitrogen spray gun balances the negative pressure environment generated by the first hydrogen spray gun, and the stable air pressure of the reduction area is ensured; continuously carrying out reduction reaction on the pellets in the reducing atmosphere of the second hydrogen spray gun in the process of running the pellets on the trolley;

s3, when the temperature of the reduction zone is reduced to below 600 ℃, the mixed gas of hydrogen and nitrogen is extracted by a first exhaust fan, the pellet is cooled and then output by a finished product conveyor, and the flue gas is extracted from the outlet of the reduction zone by a second exhaust fan and then is returned to the rotary kiln through a flue.

In any of the above possible implementations, there is further provided an implementation, where the method further includes:

s4, pumping the hydrogen-nitrogen mixed gas by a first exhaust fan, passing through a lime bed layer, passing through a compressor, entering a synthesis tower, heating the synthesis tower by a heater in front of the tower, generating ammonia-hydrogen-nitrogen mixed gas in the synthesis tower, reducing the temperature by a cooling device, separating the ammonia gas by an ammonia separator, and leading the separated ammonia gas to enter a liquid ammonia storage tank through a pipeline after being pressurized and liquefied.

In any of the above possible implementations, there is further provided an implementation that, in step S2, the pellets are maintained for not less than 25min at the interval of 1200 ℃ to 600 ℃ on the reduction zone trolley.

In any of the above possible implementations, there is further provided an implementation manner that, in step S2, the hydrogen flow rate is 5L/min.

In any of the above possible implementations, there is further provided an implementation that, in step S3, the nitrogen flow rate is 15L/min.

In any of the above possible implementation manners, there is further provided an implementation manner that, in step S3, the metallization ratio can reach 90% when the pellet finished product is output.

The invention has the beneficial effects that: the invention takes pure hydrogen as a reducing agent, and directly utilizes the heat of the pellet to reduce after the pellet is roasted, thereby realizing integrated production. The method provided by the invention can produce the high-metallization-rate pellets meeting the charging requirement of the electric furnace and relieve the problem of shortage of the amount of scrap steel. The hydrogen-rich reduction not only obtains the metallized pellets, but also only discharges water vapor in the reduction process, thereby reducing the pollution to the environment and the cost of flue gas treatment. In addition, the flue gas generated in the process is utilized to produce synthetic ammonia, so that high-value utilization of the flue gas is realized.

Drawings

Fig. 1 is a schematic structural diagram of a system for integrally producing metallized pellets through pellet roasting and reduction according to an embodiment of the present invention.

In the figure: 1-a chain grate; 2-a rotary kiln; 3-a first gas spray gun; 4-a second gas spray gun; 5-a baffle plate; 6-a first hydrogen spray gun; 7-trolley; 8-a first exhaust fan; 9-a second nitrogen lance 1; 10-a reduction zone; 11-first nitrogen lance 2; 12-nitrogen monitoring device; 13-flue; 14-nitrogen gas baffle; 15-gas leakage early warning device; 16-a second hydrogen spray gun; 17-a second hydrogen spray gun; 18-finished product tape machine; 19-nitrogen gas holder; 20-hydrogen gas holder; 21-a second exhaust fan 2; 22-gas chamber; 23-quicklime bed layer; 24-a compressor; 25-a synthesis column; 26-pre-column preheater; 27-a waste heat boiler; 28-a cooling device; 29-an ammonia separator; 30-liquid ammonia storage tank.

Detailed Description

Specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that technical features or combinations of technical features described in the following embodiments should not be considered as being isolated, and they may be combined with each other to achieve better technical effects. In the drawings of the embodiments described below, the same reference numerals appearing in the respective drawings denote the same features or components, and may be applied to different embodiments.

As shown in fig. 1, a system for integrally producing metallized pellets by pellet roasting and reduction according to an embodiment of the present invention includes a grate 1, a rotary kiln 2, a reduction zone 10, and a finished product conveyor (finished product belt conveyor 18); a baffle 5 is arranged at the joint of the rotary kiln 2 and the reduction zone 10 and used for ensuring that pellets smoothly fall into the reduction zone 10 and controlling the inflow of gas of the rotary kiln 2 into the reduction zone 10; a first gas spray gun 3 is arranged in the rotary kiln 2; a second gas spray gun 4, a first nitrogen spray gun 11 and a first hydrogen spray gun 6 are arranged below the baffle 5; the bottom of the reduction area 10 is provided with a trolley 7, and the reduction area 10 is provided with a plurality of second hydrogen spray guns 17 for providing reduced hydrogen along the direction of the trolley 7; a first exhaust fan 8 is arranged below the trolley 7 at the rear section of the reduction zone 10; a second nitrogen spray gun 9 is arranged behind the first exhaust fan 8; the pellets are dried and preheated on the grate 1, oxidized, desulfurized and decomposed in the rotary kiln 2, then subjected to hydrogen reduction on the trolleys 7 of the reduction zone 10, and the pellets subjected to hydrogen reduction are discharged through a finished product conveyor 18.

The drying and preheating of green pellets are completed in the grate 1, and the pellets begin to be oxidized when the preheating temperature is higher than 200 ℃. The pellets are oxidized to produce Fe₂O₃From Fe₂O₃The strength of the pellets is greatly improved by the crystallization and recrystallization effects of (A). In the grate 1-rotary kiln 2, pellets with higher strength can be largely prevented from falling and breaking while rolling in the kiln. The preheated pellet ore with certain strength immediately enters the rotary kiln 2, and further undergoes unfinished chemical reactions in the grate 1, such as oxidation, desulfurization, decomposition and the like. The first gas spray gun 3 which is ignited in the rotary kiln 2 provides heat required by oxidizing roasting, pellet ore with the temperature of about 1200 ℃ is obtained through high-temperature roasting, and high-temperature flue gas generated by roasting is used for drying and preheating pellets in the chain grate 1.

Then, the pellets roll down on the trolley 7 of the reduction zone 10, and a baffle 5 and a second gas spray gun 4 arranged below the baffle 5 are arranged at the joint of the reduction zone 10 and the rotary kiln 2. The second gas lance 4, which is ignited, consumes the excess oxygen to prevent the oxygen from leaking into the reduction zone 10 and combining with the hydrogen to cause explosion, and also has the function of secondary heating of the pellets. The baffle 5 arranged above the second gas spray gun 4 can ensure that the pellets fall down smoothly, and simultaneously reduce the entering amount of gas in the rotary kiln 2 from the joint of the rotary kiln 2 and the reduction zone 10, so that the oxygen removal effect is ensured. In addition, preferably, a gas leakage early warning device 15 is further arranged, and the potential safety hazard in the production process is further reduced. After falling into the reduction zone 10, the pellets are transported forward by the trolley 7, and metallic iron is formed under the action of hydrogen in the transportation process. While the hydrogen and the pellet ore react with each other to produce the metallic iron, water vapor is also generated on a reaction interface. Subsequently, the water vapor leaves the reaction interface through the pores, diffuses out of the pellets step by step, and finally enters the gas phase. Hydrogen is lighter than water vapour, so, preferably, the trolley 7 needs to be raised at an angle during movement to make it an inclined straight line when viewed in cross section, thereby ensuring contact between hydrogen and pellets and reducing the possibility of secondary wetting of the pellets by water vapour. To ensure that hydrogen does not escape from the junction of the rotary kiln 2 and the reduction zone 10, the nozzle of the first hydrogen lance 6 is kept at a distance from the junction of the rotary kiln and the reduction zone. Because the first hydrogen spray gun 6 is arranged at a far position, negative pressure is generated between the connection part and the nozzle of the first hydrogen spray gun 6, and therefore, a first nitrogen spray gun 11 is arranged near the inlet of the reduction zone 10, and the stable air pressure in the reduction zone 10 is ensured. The first nitrogen spray gun 11 uses pure nitrogen, the flow rate of the nitrogen is controllable, and the nitrogen is adjusted according to the data of the nitrogen detection device (concentration monitoring) 12; preferably, a nitrogen partition plate 14 is arranged in front of the first nitrogen spray gun 11 (the spray head of the first hydrogen spray gun 6 is arranged outside the nitrogen partition plate 14, namely the spray head of the first hydrogen spray gun 6 is not influenced to spray hydrogen to the reduction zone 10), so that the space between the nitrogen partition plate 14 and the baffle plate 5 is mainly filled with nitrogen, and the contact between oxygen and hydrogen can be further prevented while the air pressure is balanced; on the other hand, the amount of nitrogen after the nitrogen partition 14 and before the first exhaust fan 8 can be reduced, and the concentration of hydrogen in the reduction zone 10 is prevented from being diluted by nitrogen, thereby ensuring the reduction efficiency.

The pellets are conveyed to the first hydrogen spray gun 6) nozzle by the trolley to react with hydrogen, and the reduction reaction is rapidly carried out under the action of high temperature. The reduction of iron oxide follows the principle of gradual transformation, 570 ℃ is taken as a demarcation point, and different temperatures correspond to different transformation sequences:

t > 570 ℃:

3Fe₂O₃(s)+H₂＝2Fe₃O₄(s)+H₂O(g) [1]

Fe₃O₄(s)+H₂＝3FeO(s)+H₂O(g) [2]

FeO(s)+H₂＝Fe(s)+H₂O(g) [3]

t < 570 ℃:

3Fe₂O₃(s)+H₂＝2Fe₃O₄(s)+H₂O(g)

Fe₃O₄(s)+4H₂＝3Fe(s)+4H₂O(g) [4]

preferably, an infrared temperature measuring device for detecting the real-time temperature of the pellets is arranged in the reduction zone 10. According to the data fed back by the infrared temperature measuring device, the speed of the trolley 7 is controlled, so that the pellet ore can be kept for about 25min in the interval of 1200 ℃ to 600 ℃, and the reduction reaction at the stage is carried out according to the sequence as follows: fe₂O₃→Fe₃O₄→ FeO → Fe, the finally obtained pellet reduction degree is more than 90%.

The heat of the pellets in the reduction zone 10 is consumed in three forms, namely, heat convection with the gas, heat required for hydrogen reduction, and heat transfer between the pellets and the inner wall of the reduction zone and equipment (the trolley 7). Heat exchange between the pellets and the gas occurs primarily near the point of contact with the hydrogen gas, which is then heated to a temperature consistent with the pellets. In the nitrogen section before the hydrogen nozzle, the nitrogen flow rate is basically kept unchanged due to the second baffle plate 14 during smooth production, so that the heat exchange is small. In order to prevent excessive heat loss, heat insulation materials are laid on the inner wall of the reduction area 10, and sealing measures (a sealing cover is arranged) are taken. In summary, in a large part of the reduction zone 10, the heat in the pellets is basically used for heat exchange with hydrogen and reduction reaction. If the hydrogen flow rate is too fast, a large amount of heat is taken away to affect the reduction efficiency, and therefore, it is preferable to set the hydrogen flow rate to 5L/min. At the same time, this flow setting can reduce the effect of out-diffusion on reduction. In order to further ensure that the reduction process is in a hydrogen atmosphere and the highest reduction efficiency is obtained, the hydrogen sprayed into the reduction zone is pure hydrogen; meanwhile, the second hydrogen spray guns 16 and 17 are provided to supplement hydrogen, and the hydrogen flow rate may preferably be set to 5L/min, and the nozzle directions of the second hydrogen spray guns 16 and 17 are set to be downward right. Under the combined action of the three hydrogen spray guns (the first hydrogen spray gun 6, the second hydrogen spray guns 16 and 17) and the first exhaust fan 8, the hydrogen flows at a nearly constant speed in the space between the first hydrogen spray gun 6 and the first exhaust fan 8, so as to ensure the kinetic conditions of reducing the pellets in the space.

As the carriage 7 moves forward, heat is consumed to some extent, and the reduction rate decreases. Since the reduction efficiency becomes too low and energy is wasted when the reduction is continued, a gas such as hydrogen and steam is recovered by the first exhaust fan 8. The first exhaust fan 8 is arranged below the trolley 7 in the reduction zone 10, thereby avoiding the secondary wetting of the pellets by the water vapor and the final reduction. In order to ensure the air draft effect and completely recover the hydrogen, the air draft negative pressure is controlled within the range of 18-20 kPa. In order to prevent external air from entering the reduction zone 10 due to negative pressure formed by air draft, a second nitrogen spray gun 9 is arranged behind the first exhaust fan 8, and the air pressure balance behind the reduction zone is ensured by utilizing the sprayed pure nitrogen. A part of the nitrogen from the second nitrogen lance 9 is drawn off by the first exhaust blower 8, and the other part flows out to the outlet of the reduction zone 10. The nitrogen flowing out of the outlet also plays a role of cooling the pellets, and the cold nitrogen exchanges heat with the hot pellets to prevent the pellets from being oxidized again due to overhigh temperature after leaving the outlet. To ensure the above effect, the nitrogen flow rate was set to 15L/min.

When the nitrogen flowing to the outlet reaches the tail part of the reduction zone 10, the nitrogen is recovered by a second exhaust fan 21 and is conveyed to the rotary kiln 2 through a flue 13. The flue gas recovered here is used for balancing the air pressure in the kiln, and the negative pressure of the second exhaust fan 21 is controlled in the range of 18-20 kPa. In addition, because the flue gas has a certain temperature (about 200 ℃), the heat of roasting can be partially supplemented to reduce the energy consumption of the first gas spray gun 3.

The finished metallized pellets cooled to a temperature below 50 ℃ (metallization rate about 90%) fall onto a finished belt conveyor 18 after leaving the reduction zone 10 and are sent to a finished product bin.

The gases for each of the nitrogen gas injection lances 11, 9, hydrogen gas injection lances 6, 16, and gas injection lances 3, 4 of the above process are supplied from a nitrogen gas tank 19, a hydrogen gas tank 20, and a gas tank 22, respectively.

Hydrogen, water vapour and nitrogen etc. through the first suction fan 8 will flow through the pipes into the quicklime bed 23 to remove water vapour and possibly trace CO leaking through the junction of the rotary kiln 2 and the reduction zone 10₂. The quicklime bed layer is composed of a plurality of (for example, 10) quicklime layers, and each layer mainly comprises a porous steel plate (with the aperture of 100mm) and quicklime particles (with the particle size of 60 mm). The positions of the small holes on the steel plate of each quicklime layer are different, so that the mixed gas can completely react when passing through. The following reaction will occur within the quicklime bed 23:

CaO+H₂O＝Ca(OH)₂ [5]

Ca(OH)₂+CO₂＝CaCO₃+H₂O [6]

the above reactions are all exothermic reactions in which water vapor and CO are removed₂And at the same time of impurities, the heat is supplemented for the hydrogen-nitrogen mixed gas so as to reduce the energy consumption in the ammonia synthesis process. The treated mixed gas is conveyed to a compressor 24 through a pipeline, a gas detection device is arranged in the pipeline, and if the condition that water vapor in the mixed gas is not completely removed is detected, the mixed gas is returned to the lime hydrate bed layer 23 through the pipeline for treatment. In order to ensure the degassing effect, the steel plate in the quicklime bed layer 23 is arranged to be detachable and needs to be replaced periodically. Hydrated lime is an important industrial product and can be used for disinfection and sterilization, acid soil improvement, sewage treatment, roadbed construction and the like. The changed slaked lime and the like are conveyed to a material workshop and can be processed for reproductionThe born lime can also be used for other purposes.

The temperature of the mixed gas extracted from the first exhaust fan 8 is about 350 ℃, and the temperature of the hydrogen-nitrogen mixed gas is still kept above 300 ℃ after the mixed gas is treated by the quicklime bed layer 23. The hydrogen-nitrogen mixed gas was pressurized to 27MPa by a compressor 24 and then introduced into a synthesis column 25. A catalyst used for ammonia synthesis, namely iron catalyst, is placed in the synthesis tower 25, and the temperature in the synthesis tower 25 is heated to about 500 ℃ by a pre-heater 26 in front of the synthesis tower. Finally, the mixed gas of hydrogen and nitrogen is used for producing the mixed gas of ammonia, hydrogen and nitrogen under the action of high temperature, high pressure and catalyst.

The subsequent operation is identical to the coal-based ammonia synthesis process, i.e. the ammonia-hydrogen-nitrogen mixture is cooled by the cooling device 28 and then separated by the ammonia separator 29. The separated ammonia gas is liquefied under pressure and enters the liquid ammonia storage tank 30 through a pipeline.

The ammonia synthesis process can only produce a small amount of ammonia gas, and after the ammonia gas is separated, the residual hydrogen gas and nitrogen gas are sent to the synthesis tower 25 through pipelines to be continuously used as raw materials for synthesizing ammonia. In addition, the mixed gas after completion of the reaction in the synthesis tower 25 flows through a waste heat boiler 27 and a pre-tower preheater 26, respectively, to collect heat.

Compared with the traditional coal-based ammonia synthesis process, the process for producing ammonia by using the flue gas generated by the method provided by the invention cancels the processes of gas making, desulfurization, transformation and refining, and the pollution of cyanogen-containing sewage, sulfur-containing sewage, hydrogen sulfide-containing gas, carbon monoxide gas, coal ash, coal slag, copper liquid slag and the like generated by the processes disappears. In addition, the production line is also greatly shortened. The hydrogen-nitrogen-steam mixed gas generated by the method provided by the invention has a high temperature of more than 300 ℃, and compared with the traditional ammonia synthesis process, the energy consumption is further reduced, so that the flue gas waste heat in a reduction zone is fully utilized.

The principle of the method provided by the invention is that the metallized pellet is generated by utilizing the direct interaction of hydrogen and pellet ore, and the method can be classified as a gas-based direct reduction method. In the gas-based direct reduction process, the direct reduced iron produced by the Midrex and HYL-III processes accounts for more than 95 percent of the whole gas-based direct reduced iron yield. The energy consumption of the typical Midrex process is about 10.20GJ/t, wherein the energy consumption for heating is about 2.83; the energy consumption of the HYL-III process is about 10.40GJ/t, wherein the energy consumption for heating is about 2.75. The method provided by the invention uses more than 90% of heat for reduction from the pellets and does not need a large amount of external heat sources. Therefore, compared with the typical Midrex and HYL-III processes, the method provided by the invention can respectively reduce the energy consumption by more than 24.9 percent and 23.8 percent.

The reducing gas used in the Midrex process contains about 55% H₂36% CO and 3.6% CO₂. Considering that the utilization rate of CO is about 40%, about 18% of tail gas of Midrex process is CO₂. Correspondingly, the HYL-III process uses a reducing gas containing about 73% H₂14% CO and 7% CO₂Thus, a product containing about 12.6% CO can be produced₂The tail gas of (2). The method provided by the invention adopts pure hydrogen as reducing gas, and CO is not generated in the reducing process₂It is possible to reduce the CO by 18% and 12.6% respectively compared to the Midrex and HYL-III processes₂And (5) discharging. However, Midrex and HYL-III processes have their respective tail gas treatment modes, and the final CO₂The discharge amount is relatively small. Therefore, the two direct reduction processes are important modes of low-carbon smelting. Taking the Midrex process as an example, the emission of carbon dioxide per ton of steel in the Midrex process used in combination with an electric furnace is about half of that in the blast furnace-converter process. The method provided by the invention is also matched with an electric furnace for production. In conclusion, compared with the blast furnace-converter process, the method provided by the invention can reduce the emission of carbon dioxide per ton steel by more than 50 percent when used for smelting.

The conventional grate-kiln system is finally used only for obtaining qualified cold pellets, which are heated again after being conveyed to the blast furnace, and this process consumes a large amount of coke for heating and reduction. In addition, the carbon dioxide discharged from the reduction process is not a little pressure for environmental protection. In the face of the ever-decreasing coke resources and the need to accomplish the "carbon integration, carbon peaking" goal, changes must be made to the traditional smelting process. The invention directly carries out the integrated production of reduction after the roasting of the pellets is finished, so that the heat of the pellets is efficiently utilized. In addition, the hydrogen reacts with the pellet to generate flue gas, and high-value utilization is achieved, namely ammonia synthesis operation. Compared with the traditional ammonia synthesis and iron making process, the method provided by the invention has the advantages of production, reduced cost and energy consumption, greatly reduced influence on the environment and strong competitive advantage.

While several embodiments of the present invention have been presented herein, it will be appreciated by those skilled in the art that changes may be made to the embodiments herein without departing from the spirit of the invention. The above examples are merely illustrative and should not be taken as limiting the scope of the invention.