CN106636508B - A kind of efficient circulation utilizes the iron-smelting process of top gas - Google Patents

Abstract

An ironmaking process for efficiently recycling blast furnace top gas. Make full use of the reduction potential of the blast furnace top gas to pre-reduce the sinter with high temperature at the tail of the sintering machine, eliminate the phenomenon of reduction and pulverization of the sinter in the blast furnace, and improve the metallurgical properties of the furnace charge. The use of sinter pre-reduction and cooling shaft furnace eliminates the sintering ring cooler, realizes efficient recovery of sinter waste heat, and reduces sintering energy consumption. Gas circulation process: blast furnace→dust collector→pressurizing device→sinter pre-reduction and cooling shaft furnace→waste heat recovery device→pressurizing device→gas reformer→pressurizing device→blast furnace. Sinter reduction and cooling process: Finished sinter → hot crusher → sinter pre-reduction and cooling shaft furnace → sinter whole grain screening device → transport to blast furnace top charging equipment.

Description

An Ironmaking Process for Efficiently Recycling Blast Furnace Top Gas

technical field

The invention relates to the technical field of ferrous metallurgy, in particular to a new energy-saving and emission-reducing technology for efficiently recycling blast furnace top gas to reduce sinter, recover waste heat from sinter and reform gas. It is suitable for blast furnace ironmaking process.

Background technique

1. Waste heat recovery in sintering process

In 2015, China's pig iron production was 691.4 million tons, accounting for 58.89% of the world's pig iron production; steel energy consumption was 380 million tce, accounting for about 13% of the country's total energy consumption. The energy consumption and _CO2 emissions of the blast furnace process accounted for 49.0% and 53.0% of the iron and steel industry, respectively. It can be seen that energy saving and emission reduction in the blast furnace process is very important to the economic and social development of our country;

In the sinter production process, the crushed sinter tail temperature is about 900°C, and it needs to be cooled to below 150°C to carry out a series of subsequent processing procedures such as granulation, transportation, and charging. The recovery and utilization of waste heat from tail sinter is one of the important ways to reduce the sintering energy consumption of blast furnace process. At present, the sinter cooling uses a blast type annular cooler, and the waste heat recovery of the tail sinter mainly has the following problems:

1) The air leakage rate of the cooling system is high. Generally speaking, the upper air leakage rate of large and medium-sized sinter coolers is 15% to 20%, and the lower air leakage rate is 20% to 30%. It is estimated that the loss of power generation due to air leakage in the upper part accounts for 27.3% of the existing power generation, which increases the energy consumption of the sintering process by 1.25~1.56kgce, and the air leakage in the lower part increases the energy consumption of the sintering process by 0.25~0.27kgce;

2) The recovery rate of sinter waste heat is low. Taking a typical 360m ² sintering machine in China as an example, the cooling section can be divided into 5 sections, from the beginning of cooling to the unloading, the first cooling section, the second section, and the fifth section. Based on the current technical level, waste heat is only recovered from the first and second ring cooling stages, and the waste heat from the third to fifth cooling stages is directly dissipated. The heat carried by the sinter in the third to fifth stages accounts for about 35% of the total waste heat resources of the sinter. In other words, currently 35% of sinter waste heat is dissipated in vain;

3) The quality of cooling exhaust gas is low, and secondary pollutants appear. In the cooling machine, the gas-solid cross-flow heat exchange is performed between the sinter and the cooling air, and because the height of the sinter material layer is limited (generally no more than 1.3m in China), the heat transfer time is short, so that the cooling can be completed Functional hot air, that is, the temperature of cooling exhaust gas cannot be too high from the source. As far as the current domestic level is concerned, the average temperature of the first-stage cooling exhaust gas is 350-380 °C, and the temperature of the second-stage cooling exhaust gas is 300-330 °C, resulting in low quality cooling exhaust gas and low heat recovery efficiency. In addition, the current structure of the cooling machine inevitably causes a large amount of particulate matter in the exhaust gas, which has become a key source of air pollution in the sintering operation area.

2. Pre-reduction of sinter to reduce pulverization

The sintering process is completed in a weak oxidizing atmosphere. The iron oxides in the finished sintered ore are composed of Fe ₃ O ₄ , Fe ₂ O ₃ and part of FeO. After the sintered ore enters the blast furnace, the chemical energy and thermal energy of the gas are consumed to reduce the iron oxides step by step. Therefore, the reducing property of sinter is an important factor affecting the energy consumption of blast furnace. Improving the metallurgical performance of sinter, especially the reducing performance is the long-term goal of blast furnace technological progress. But at present, the main means to improve the reduction performance of sinter is to improve the performance of sinter, and reduce the FeO content in sinter through sintering technology and process control means to improve its reducibility. For high alkalinity (R=1.9~2.3) sinter, the conventional requirement is RI >85%, and the high requirement is RI >90%. Sintered ore with poor reducibility will lead to poor reflow performance of sintered ore, which will affect the gas permeability of the blast furnace reflow zone and the utilization rate of gas in the upper part of the blast furnace, reduce the indirect reduction in the blast furnace, and increase the ratio of direct reduction (r _d ) , affecting the fuel ratio and output of the blast furnace. According to statistics, a 10% reduction in the indirect reduction of ore into the furnace will increase the coke ratio of the blast furnace and reduce the output by 8% to 9%. Under the current level of blast furnace fuel ratio in my country, the blast furnace fuel ratio will increase by 40kg/t above. Therefore, iron workers should attach great importance to the reducibility index of sinter. Pre-reduction of sintered ore has not been reported at home and abroad;

The low-temperature reduction pulverization performance (RDI) of sinter refers to the degree of pulverization due to reduction after the sinter is loaded into the blast furnace at a low temperature of 400-600 °C. The main reason is that sintered skeletal hematite (also known as regenerated hematite) undergoes lattice transformation during reduction at low temperature (from hexagonal lattice to cubic lattice during the transformation of Fe ₂ O ₃ to Fe ₃ O ₄ Grid) to generate a great internal stress, resulting in the fragmentation of sinter. There are many reasons for low-temperature reduction pulverization in sintering, such as mineral type, carbon distribution, A1 ₂ O ₃ and TiO ₂ content and other factors. The anatomy of the blast furnace and the analysis of the sampling and measurement of the upper part of the blast furnace show that the low-temperature reduction pulverization of sinter is the limiting link of the air permeability of the upper part of the blast furnace. China's metallurgical industry standard (YB/T-2005) stipulates that RDI _+3.15 >72%, and those that are 10% lower than the standard should generally be sprayed with pulverization inhibitors. At present, China's sinter ore RDI _+3.15 is generally low, which has seriously affected the production of blast furnaces. The existing production practice data proves that a 10% increase in RDI _-3.15 of sinter will affect the blast furnace output by more than 3%, and the fuel ratio will increase by 1.5% (at the current level, the fuel ratio will increase by 7.8kg/t). Therefore, when the sinter RDI _+3.15 is lower than 62%, effective measures should be taken to improve the low-temperature reduction strength of the sinter to keep the upper part of the blast furnace stable. Studies have shown that after the sinter is sprayed with CaCl ₂ solution, its low-temperature reduction pulverization index can be increased by about 50%, which greatly improves the air permeability of the upper material column of the blast furnace. However, the CaCl ₂ brought into the blast furnace will also increase, and its chemical reaction will form gaseous chlorides, which will have a negative impact on the blast furnace smelting and equipment.

3. Recycling blast furnace top gas

The process, equipment and technology of modern blast furnaces are basically mature, and there is not much room for energy saving and emission reduction. Therefore, creating new energy saving and emission reduction technologies for blast furnace ironmaking will become the focus of future research. Domestic and foreign research institutions and iron and steel enterprises have done a lot of research on this, and achieved certain results. For example, technologies such as blast furnace hydrogen-rich smelting and furnace top gas recycling have become current research hotspots. Blast furnace top gas contains a certain amount of CO, and taking advantage of this advantage to recycle it can reduce energy consumption, increase production efficiency, and reduce CO ₂ emissions in blast furnaces. The process route is that the coal gas is firstly dehydrated and CO ₂ removed, then pressurized and heated, blown into the hearth of the blast furnace from the tuyere, and enriched with oxygen at the same time. Industrial tests have proved that after injecting blast furnace top gas, the ratio of coke into the furnace is 433kg/t, and the average daily output is 1358t/d. The blast furnace coke ratio can be reduced by about 28.5%, and the output can be increased by about 27.3%. Studies have shown that simply injecting blast furnace gas into the blast furnace tuyeres or injecting blast furnace gas into the tuyeres after enriching oxygen will result in lower productivity and higher fuel ratio. CO ₂ must be removed from the furnace top gas and made into hot reducing gas and oxygen which are injected into the blast furnace at the same time. Under the current technical conditions, the use of blast furnace top gas injection technology will increase the cost of ironmaking. However, under the pressure of _CO2 emission reduction, research and application are also the general trend;

In order to effectively solve the above problems, it is proposed to use the blast furnace top gas to pre-reduce the high-temperature sintered ore after sintering, improve the metallization rate of the sintered ore in the furnace, improve the pulverization and reflow performance of the charge, and at the same time carry out waste heat treatment on the sintered ore. Recycling, banning sintering ring cooling equipment, improving waste heat recovery rate, reducing tail gas as gas-generating agent into gas-generating and reforming furnaces, and generating high-temperature hydrogen-rich gas to circulate into blast furnaces.

Contents of the invention

The content of the present invention is to use blast furnace top gas to pre-reduce the sintered ore at the machine tail, and at the same time cool the sintered ore and recover the heat. Gas is again injected into the blast furnace. The purpose of the research is to recycle blast furnace top gas to achieve energy saving and emission reduction in blast furnace process and to improve the metallurgical performance of sinter.

1. Use blast furnace top gas to pre-reduce sinter. Blast furnace top gas contains a large amount of CO and H ₂ has a strong reduction potential, and the sinter has a high temperature of about 900 °C when it reaches the tail of the machine. The lower part of the sintering machine tail crusher is equipped with a sinter pre-reduction and cooling shaft furnace. The crushed high-temperature sinter is loaded from the upper part of the shaft furnace, and the blast furnace top gas is fed into the lower part. The downward-moving sinter and the upward-flowing gas move toward each other, and the sinter is reduced and cooled;

1) Iron oxides are converted from high-valent iron to low-valent iron under reducing atmosphere and certain temperature conditions, and the reaction occurs:

3Fe ₂ O ₃ (s)+CO(g)=2Fe ₃ O ₄ (s)+CO ₂ (g) (1)

2Fe ₃ O ₄ (s)+2CO(g)=6FeO(s)+2CO ₂ (g) (2)

FeO(s)+CO(g)=Fe(s)+CO ₂ (g) (3)

The hydrogen in the gas also undergoes the same iron oxide reduction reaction. Blast furnace top gas has a high reduction potential, and the formula (1) and formula (2) will be more intense under the high temperature condition of 900 ℃, and the formula (3) will also occur in a certain period of time. Therefore, after the pre-reduction treatment, the reduction rate and metallization rate of the sinter are increased, which can greatly reduce the coke ratio of the blast furnace, and at the same time improve the smelting conditions of the blast furnace to achieve the purpose of increasing production and reducing costs;

2) The existence of Fe ₂ O ₃ is the root cause of low-temperature reduction pulverization of sinter. Fe ₂ O ₃ is reduced to Fe ₃ O ₄ at around 500 °C in the blast furnace, resulting in volume expansion and producing a large amount of powder. After low-temperature reduction of vanadium-titanium magnetite sinter, the powder smaller than 3.15 mm even reaches 70%, which seriously affects the normal production of the blast furnace. Since the heat exchange and reaction characteristics of the blast furnace determine that the reduction of Fe ₂ O ₃ to Fe ₃ O ₄ will inevitably produce a large amount of powder, it can be said that the reduction of powder produced by sinter in the blast furnace is irreversible. Utilize CO and H ₂ in the top gas of the blast furnace, carry out sinter pre-reduction in the sinter pre-reduction and cooling shaft furnace equipment to reduce the content of Fe ₂ O ₃ in the sinter, and screen the powder produced by the reduction of the shaft furnace before entering the blast furnace In addition, the pre-reduced sinter entering the blast furnace reduces or even produces no powder during low-temperature reduction. The air permeability and gas distribution in the blast furnace are significantly improved, and the coke ratio and CO ₂ emissions are reduced.

2. Use the sinter pre-reduction and cooling shaft furnace to replace the sintering ring cooling equipment to cool the sintering ore, which effectively solves the problems of high air leakage rate, poor cooling effect and low heat recovery efficiency of the ring cooling equipment;

Due to the good airtight performance of the shaft furnace, large volume utilization, and countercurrent exchange of cold and heat media, the cooling efficiency of sinter is high, which realizes uniform cooling of sinter and improves the quality of sinter; Basically all of them are absorbed by the gas, and the waste heat recovery rate can reach more than 90% after calculation, which is about 50% higher than that of the ring cooler; in addition, compared with the ring cooler, the reduction and cooling of the sinter by the shaft furnace basically does not require power. Therefore, the recovery cost is reduced, and the purpose of recovering sinter waste heat with high efficiency and low consumption is realized.

3. The gas discharged from the sinter pre-reduction and cooling shaft furnace is recovered by heat and then enters the gas-making and reforming furnace through the pressurizing device as a gas-making agent. The CO concentration of the reduced gas is reduced, while the CO ₂ concentration is increased. The reduced gas is reformed by gas-making and reforming furnaces to convert CO ₂ into CO, with a conversion rate of over 95%, making full use of the CO ₂ resources in the gas. The reformed gas with a strong reducing potential is injected into the blast furnace again to replace coke or pulverized coal to participate in the heat exchange and chemical reaction in the blast furnace, reduce the energy consumption of the blast furnace, improve the smelting conditions of the blast furnace, and realize energy saving, emission reduction and cost reduction of the blast furnace Purpose. Part of the gas discharged from the top of the blast furnace enters the sinter pre-reduction and cooling shaft furnace again to achieve the purpose of efficient recycling of the top gas of the blast furnace.

Description of drawings

Fig. 1 is the flow chart of the ironmaking process of efficiently recycling blast furnace top gas;

The markings in the figure are as follows:

1. Blast furnace body, 2. Dust collector, 3. Pressurizing device, 4. Sinter pre-reduction and cooling shaft furnace, 5. Sinter whole grain screening device, 6. Waste heat recovery device, 7. Gas-making reformer, 8. Sintering machine, 9. Crusher.

Detailed ways

After the blast furnace top gas is dedusted, it is transported to the sintering workshop through the gas pipeline. After pressurization, the sinter is sprayed from the bottom for pre-reduction and cooling of the shaft furnace, forming a convective movement with the falling high-temperature sinter, reducing the sinter and cooling down at the same time. The pre-reduced and cooled sinter is discharged from the shaft furnace, sintered into granules, screened and classified by the screening device, and the qualified sinter is transported to the top charging equipment of the blast furnace by a belt conveyor. The gas discharged from the top of the sinter pre-reduction and cooling shaft furnace passes through the waste heat recovery device to recover and utilize its heat. After recovering heat, the gas is pressurized by the pressurizing device, and then injected into the gas-making and reforming furnace together with pure oxygen. After gas-making and reforming, high-temperature hydrogen-rich gas is produced, and then injected into the blast furnace. The recycling of blast furnace gas is realized through the above process.

Gas circulation process: blast furnace→dust collector→pressurizing device→sinter pre-reduction, cooling shaft furnace→waste heat recovery device→pressurizing device→gas making, reforming furnace→pressurizing device→blast furnace.

Sinter reduction and cooling process: Finished sinter → hot crusher → sinter pre-reduction, cooling shaft furnace → sinter granulation and screening device → transport to blast furnace top charging equipment.

Claims (2)

1. a kind of efficient circulation utilizes the iron-smelting process flow of top gas, right using top gas reduction potential The high temperature sinter that tail unloads carries out prereduction, while sinter is cooled down, and obtains prereduced sinter, and recycle high-temperature coal The heat that gas carries；Coal gas after cooling sprays into blast furnace again after gas making, reburner are reformed, and technological process is as follows：

Prereduction is carried out, while cool down sinter and heat is returned to sintering machine tail sinter using top gas It receives, the gas after reduction enters gas making, reburner, and reforming generation coal gas of high temperature through gas making, reburner is blown again into blast furnace, Top gas is recycled, reaches blast furnace process energy-saving and emission-reduction, improves the purpose of Metallurgical Properties of Sinter：

1) blast furnace roof is contained into CO and H₂Coal gas, by gas pipeline transportation service to sintering mill (plant) after dedusting；

2) a sinter prereduction, cooling shaft furnace are set under rear of sintering machine crusher, shaft furnace bottom sets an exhaust outlet, Thus stock gas can be located to spray into, reduction unloads sinter, while it is cooled down with 900 DEG C of tail, completion reduction, Coal gas of high temperature after cooling goes out through vertical furnace top row；

3) coal gas of high temperature that vertical furnace top row goes out enters waste-heat recovery device, recycles heat；

4) coal gas after heat recovery enters gas making by pressue device, reburner is used as gas-forming agent, makes CO₂CO is converted into, is reformed Coal gas blast furnace is sprayed by air port again.

2. efficient circulation as described in claim 1 utilizes the iron-smelting process flow of top gas, it is characterised in that fully Rear of sintering machine sinter is restored using top gas, the coal gas CO concentration after reduction reduces, CO₂Concentration increases, and utilizes The coal gas after reduction is reformed in gas making, reburner, makes CO₂It is converted into CO conversion ratios and reaches more than 95%, it is very strong having after reforming The coal gas of reduction potential sprays into blast furnace again, takes full advantage of CO in coal gas₂Resource.