Pre-desulfurization based cold-bonded pellets and method for producing the same

Abstract

The application discloses a kind of cold consolidation pellets based on pre-desulfurization and preparation method thereof, belong to pellet preparation technical field.The method of the application comprises:1) steel slag is ground and is treated, and porous steel slag is obtained;2) the steel slag after pretreatment is mixed with metallurgical sludge, ammonia type absorbent according to proportion, first, metallurgical sludge and ammonia type absorbent are mixed evenly, then steel slag is added and continues to mix evenly, and balling raw material is obtained;3) water is added to balling raw material and is mixed evenly, and green ball is pressed;4) industrial waste gas is introduced, and the green ball after pressing is carbonated, and cold consolidation pellet is obtained.The application can effectively solve the problem of competition between SO2 and CO2 in industrial waste gas when using industrial waste gas to carbonize cold consolidation pellet, and the problem of affecting carbonation reaction, so as to further improve the strength of the obtained pellet.

Description

Technical Field

[0001] This invention belongs to the field of pellet preparation technology, and more specifically, relates to cold-consolidated pellets based on pre-desulfurization and their preparation method. Background Technology

[0002] Cold-bonded pelletizing is a process that utilizes a binder to undergo a physical-chemical reaction to solidify iron ore particles. The resulting cold-bonded pellets can be processed in a rotary hearth furnace to produce metallized products, which can then be further incorporated into blast furnaces, converters, and other processes. Cement and water glass are common binders used in cold-bonded pelletizing. They utilize calcium silicate, sodium silicate, and other silica-containing calcium-magnesium minerals to absorb CO2 from the air, undergoing a carbonation reaction with CO2 in the process, thereby increasing the solidification strength of the pellets.

[0003] It is worth noting that the steel industry accounts for approximately 8% of global carbon dioxide emissions annually, and this figure is expected to rise rapidly with increasing crude steel production. Statistics show that on average, producing one ton of crude steel generates about two tons of CO2 emissions and 600 kg of slag. In the long term, CO2 emission reduction and comprehensive utilization of solid waste in the steel industry have received widespread attention.

[0004] The applicant's research found that during the preparation of cold-solidified pellets, industrial flue gas containing a certain concentration of CO2 can be introduced into the green pellets. Compared to the existing method of using air to carbonate the pellets, the industrial flue gas contains a relatively higher concentration of CO2, which can increase the carbonation rate of the pellets. However, further research by the applicant revealed that a certain amount of SO2 is present in the introduced industrial flue gas. Although the concentration of SO2 in the flue gas is lower than that of CO2, the solubility of SO2 in solution is much higher than that of CO2. This is because SO2 is absorbed by the solution to form sulfurous acid, while CO2 forms carbonic acid upon dissolution. Sulfurous acid has a higher degree of dissociation than carbonic acid, thus leading to the generally higher solubility of SO2 compared to CO2. Furthermore, the Ca2+ formed from dicalcium silicate and tricalcium silicate in steel slag... 2+ Besides CO2 2- The reaction also involves SO3. 2- The reaction forms CaSO3, which is then oxidized to CaSO4. Therefore, SO2 and CO2 compete for energy during the carbonation process of the pellets, thus affecting the carbonation process of the steel slag and consequently the strength of the cold-bonded pellets. Summary of the Invention

[0005] 1. The problem to be solved

[0006] The purpose of this invention is to provide a pre-desulfurized cold-consolidated pellet and its preparation method. By adding an ammonia absorbent to its components, the competition between SO2 and CO2 in the industrial waste gas during the carbonation of cold-consolidated pellets can be effectively solved, which affects the carbonation reaction, thereby further improving the strength of the obtained pellets.

[0007] 2. Technical Solution

[0008] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0009] This invention provides a method for preparing pre-desulfurized cold-consolidated pellets, comprising the following steps:

[0010] (1) Steel slag pretreatment;

[0011] Steel slag is ground and subjected to pore-forming treatment to obtain porous steel slag;

[0012] (2) Mix the raw materials to obtain the briquetting raw materials;

[0013] The pretreated steel slag is mixed with metallurgical dust and ammonia absorbent in a certain proportion. First, the metallurgical dust and ammonia absorbent are mixed evenly, and then the steel slag is added and mixed evenly to obtain the briquetting raw material.

[0014] (3) Pressing the raw ball;

[0015] Add water to the briquetting material obtained in step (2), mix well, and press into raw briquetting material;

[0016] (4) Carbonation treatment;

[0017] Industrial waste gas is introduced to carbonate the pressed green pellets, resulting in cold-bonded pellets.

[0018] It should be noted that using industrial waste gas for carbonation treatment of pellets, compared to room temperature air, can utilize the high CO2 content and certain temperature and humidity of industrial waste gas to increase the carbonation reaction rate of pellets, thus significantly shortening the time for natural carbonation. However, this also brings new problems. In addition to a high concentration of CO2 (compared to air), industrial waste gas also contains a certain amount of SO2. The presence of SO2 will compete with CO2. During carbonation, steel slag will also react with SO2, eventually generating CaSO4, which will cause a decrease in the compressive strength of the pellets. This is because the structure of CaSO4 is relatively loose and fragile, while the crystal structure of CaCO3 is dense and has excellent mechanical strength compared to CaSO4. Therefore, the presence of SO2 will affect the carbonation reaction between CO2 and steel slag, resulting in a decrease in the strength of the resulting pellets. To solve the above problem, this invention proposes to add an ammonia absorbent to the pelletizing material. During the carbonation of the pellets, the ammonia absorbent will react with SO2 first, consuming the SO2 in the industrial flue gas, without affecting the carbonation reaction of the steel slag, thereby effectively improving the strength of the resulting carbonized and cold-solidified pellets.

[0019] As a further improvement of the present invention, ammonium bicarbonate with a purity of >99.5% is selected as the ammonia absorbent. When ammonium bicarbonate is used as the ammonia absorbent, the NH3 decomposed by heat during pellet carbonation forms an alkaline environment, which can consume SO2 in the waste gas without affecting the carbonation reaction of steel slag. At the same time, the decomposition will also generate additional CO2, which acts as an internal carbon source, further increasing the CO2 partial pressure and further accelerating the carbonation reaction process.

[0020] Furthermore, in this invention, the mass ratio of steel slag, metallurgical dust, and ammonia absorbent is 1:(10-20):(0.05-0.1). Controlling this ratio utilizes the difference in solubility between CO2 and SO2, absorbing as much SO2 as possible without affecting CO2 entry, and preventing the small amount of SO2 in the flue gas from reacting with Ca. 2+ The contact reaction forms a weak sulfuric acid slag, which affects the reaction of CO2 and Ca. 2+ The carbonation reaction enhances the strength of the pellets. However, if the proportion of ammonia absorbent is too low, the generated NH4... + The effective absorption components are too low, thus failing to achieve complete SO2 absorption; while when too much ammonia absorbent is added, the generated NH4+... + If there are too many effective absorbent components, CO2, which is also a weakly acidic gas, will begin to absorb CO2 while absorbing SO2, thus reducing the CO2 concentration.

[0021] Furthermore, it is worth noting that the timing of adding the ammonia absorbent is crucial. By first mixing the ammonia absorbent with metallurgical dust and sludge for 5-8 minutes, and then adding it to the treated steel slag and mixing for 10-15 minutes, the mixing method of the pelletizing material can be optimized. This avoids the ammonia absorbent directly adsorbing or coating the steel slag surface, thus significantly reducing the contact area between the ammonia absorbent and the steel slag. Using the mixing method of this invention, the ammonia absorbent is first mixed with the metallurgical dust and sludge. The ammonia absorbent coats the metallurgical dust and sludge, allowing it to absorb SO2 passing through the flue gas outside the steel slag solution system, selectively allowing CO2 to pass through. This reduces both the SO2 in the flue gas and its impact on the steel slag itself. When the three pelletizing materials are mixed together, the ammonia absorbent comes into direct contact with the steel slag, and the NH4 formed by the decomposition of ammonium bicarbonate... + It reacts with SO2 to form ammonium sulfate, which crystallizes and coats the steel slag or fills the pores of the steel slag during water evaporation, affecting the calcium content. 2+ and CO3 2- The transfer of plasma in the solution affects the carbonation effect, which in turn reduces the formation of pellet strength in the later stage.

[0022] As a further improvement of the present invention, the steel slag used in the present invention needs to be pre-treated with acidic pore-forming. The pore-forming process is as follows: first, the steel slag is ground to a particle size of -0.149mm with a mass percentage content of ≥95%, and then the steel slag is immersed in an acidic solution for pickling, controlling the free CaO content to decrease to 0.1% to 0.3%. Specifically, in the process of pickling the steel slag, by reducing the free CaO content in the steel slag to 0.1% to 0.3%, the decrease in f-CaO content means that f-CaO is leached out, the pores become more numerous, which facilitates subsequent carbonation. However, the f-CaO content cannot be reduced too low, as an excessively low f-CaO content will lead to a decrease in the strength and brittleness of the steel slag itself. Therefore, in the present invention, controlling the f-CaO content in the range of 0.1% to 0.3% is superior.

[0023] When pickling and creating pores in steel slag, the acidic solution used is a mixture of formic acid and acetic acid, with a formic acid:acetic acid molar ratio of 1:(0.5~2)mol / L. This treatment method solves the shortcomings of poor stability and low activity of steel slag as a binder. The resulting porous steel slag can effectively increase the specific surface area of ​​the steel slag and the contact points between CO2 and effective components such as silicates, enhance carbonation efficiency, and thus improve the strength of cold-bonded pellets and CO2 emission reduction efficiency.

[0024] As a further improvement of the present invention, the metallurgical dust in the pelletizing material is blast furnace ash or OG mixed dust, and the metallurgical dust has a particle size of -0.074mm and a mass percentage content of ≥80%.

[0025] As a further improvement of the present invention, the metallurgical dust and sludge is a combination of blast furnace ash and OG mixed dust and sludge, with a mass ratio of blast furnace ash to OG mixed dust and sludge of 1:(3-4). The cold-bonded pellets produced by the present invention need to contain a certain amount of carbon for use in the reduction reaction of iron oxide and zinc oxide. A suitable ratio of blast furnace ash to OG mixed dust and sludge is beneficial to the final quality of the pellets.

[0026] As a further preferred embodiment of the present invention, in step (4), the green pellets are placed in a curing box, and industrial waste gas is introduced for carbonation and solidification. The industrial waste gas is sintering flue gas or rotary hearth furnace flue gas, and the flow rate of the introduced industrial waste gas is 30,000 to 80,000 m / s. 3 The treatment time is 4-12 hours, with a temperature of 150-220℃, a CO2 concentration of 4-8 wt%, a CO content of 0.3-2 wt%, a water content of 4-8 wt%, and a treatment duration of 4-12 hours.

[0027] The method of this invention can effectively solve the problem of carbonation by introducing industrial flue gas during its preparation process, and also increase the partial pressure of CO2 to a certain extent, accelerate the carbonation reaction process of the pellets, thereby improving the strength of the obtained cold-solidified pellets.

[0028] Furthermore, in a more optimized manner, the pre-desulfurized cold-consolidated pellets obtained in this invention are placed in a rotary hearth furnace for drying and calcination. The drying temperature is 150–250°C, and the drying time is 5–10 min. The calcination temperature is 1250–1350°C, and the calcination time is 15–25 min. This treatment can, on the one hand, remove zinc-containing dust from the rotary hearth furnace; and on the other hand, produce metallized finished pellets that can be used as a coolant in the converter.

[0029] 3. Beneficial effects

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) The present invention provides a pre-desulfurized cold-consolidated pellet. First, the steel slag is acid-treated to create pores and improve its activity to make porous steel slag. Then, it is pelletized with metallurgical dust and ammonia absorbent. By adding ammonia absorbent, SO2 in the flue gas can be absorbed during the carbonation of the pellets in the process of passing industrial flue gas through the gas. This solves the competition problem between SO2 and CO2 in industrial waste gas and accelerates the reaction process of pellet carbonation to a certain extent, which is beneficial to improving the strength of the obtained cold-consolidated pellets.

[0032] (2) The pre-desulfurized cold-consolidated pellets provided by this invention use ammonium bicarbonate as the ammonia absorbent. On the one hand, ammonium bicarbonate is easily decomposed by heat during the carbonation process of the pellets, and the NH3 that can be decomposed can consume SO2 in the industrial waste gas without affecting the reaction between steel slag and CO2, thereby improving the carbonation reaction rate and reaction effect. On the other hand, ammonium bicarbonate also generates CO2 during the thermal decomposition reaction, which acts as an internal carbon source, further increasing the partial pressure of CO2 and accelerating the carbonation reaction process.

[0033] (3) The pre-desulfurized cold-solidified pellets of the present invention are made from steel slag, metallurgical dust and industrial waste gas. The cold-solidified pellets can treat zinc-containing dust in the rotary hearth furnace. In this process, metallized finished pellets that can be used as converter coolant can also be produced. Attached Figure Description

[0034] Figure 1 This is a schematic flowchart of the cold-consolidated pellet preparation method based on pre-desulfurization of the present invention. Detailed Implementation

[0035] For ease of description, the steel slag composition used in the following examples is as follows: CaO: 49.90%, Fe2O3: 24.52%, SiO2: 11.67%, MgO: 3.94%, MnO: 2.13%, P2O5: 2.54%, Al2O3: 2.90%, TiO2: 1.27%, with the remainder being unavoidable impurities.

[0036] The present invention will be further described below with reference to specific embodiments.

[0037] Example 1

[0038] like Figure 1 As shown, the method for preparing cold-consolidated pellets in this embodiment includes the following steps:

[0039] (1) Pretreatment for steel slag hole making;

[0040] In this embodiment, a certain amount of steel slag, metallurgical dust, and ammonia absorbent were weighed out in a mass ratio of 1:15:0.08. The steel slag was first ground in a ball mill to a fine particle size, controlling the mass percentage content of the -0.149mm particle size to be ≥95%. Then, a mixed solution of formic acid and acetic acid (molar concentration ratio of formic acid to acetic acid was 1:1.2 mol / L) was added for acid washing, controlling the free CaO content to decrease to 0.2%.

[0041] (2) Mix the raw materials to obtain the briquetting raw materials;

[0042] First, metallurgical dust (i.e., a mixture of blast furnace ash and OG mixed dust at a mass ratio of 1:3.5) and ammonia absorbent are mixed evenly for 5-8 minutes, and then the treated steel slag is added and mixed evenly for 10-15 minutes to obtain briquetting raw material.

[0043] (3) Pressing the raw ball;

[0044] The raw material for briquetting is mixed with water and then pressed into green briquettes. The roller pressure is controlled at 25 MPa and the moisture content of the briquettes is controlled at 14%.

[0045] (4) Carbonation and solidification treatment of green pellets;

[0046] Sintering flue gas is introduced into the green pellets for carbonation and solidification treatment. The velocity of the introduced industrial waste gas is 60,000 m / s. 3 The process was carried out at a temperature of 180℃, a CO2 concentration of 6%, a moisture content of 6%, and a treatment time of 8 hours to obtain cold-consolidated pellets.

[0047] Comparative Example 1

[0048] The preparation method of the cold-consolidated pellets in this comparative example differs from that in Example 1 in that: no ammonia absorbent is added, and the pretreated steel slag and metallurgical dust are directly mixed, water is added, and the pellets are formed. All other process operations and process parameters are the same as in Example 1.

[0049] The performance of the obtained cold-consolidated pellets was tested, and the test results are shown in Table 1.

[0050] Comparative Example 2

[0051] The method for preparing cold-bonded pellets in this comparative example differs from that in Example 1 in that: in step (2), the pretreated steel slag, metallurgical dust and ammonia absorbent are mixed together for 15 minutes to obtain pelletizing material, and the remaining process operations and process parameters are the same as in Example 1.

[0052] The performance of the obtained cold-consolidated pellets was tested, and the test results are shown in Table 1.

[0053] Comparative Example 3

[0054] The preparation method of the cold-bonded pellets in this comparative example differs from that in Example 1 in that: in step (2), the pretreated steel slag and ammonia absorbent are first mixed for 10 minutes, and then metallurgical dust is added and mixed for another 8 minutes. The remaining process operations and process parameters are the same as in Example 1.

[0055] The performance of the obtained cold-consolidated pellets was tested, and the test results are shown in Table 1.

[0056] Comparative Example 4

[0057] The preparation method of the cold-consolidated pellets in this comparative example differs from that in Example 1 in that the amount of ammonia absorbent added is less, and the mass ratio of steel slag, metallurgical dust and ammonia absorbent is 1:15:0.02. The remaining process operations and process parameters are the same as in Example 1.

[0058] The performance of the obtained cold-consolidated pellets was tested, and the test results are shown in Table 1.

[0059] Comparative Example 5

[0060] The preparation method of the cold-consolidated pellets in this comparative example differs from that in Example 1 in that: the amount of ammonia absorbent added is excessive, and the mass ratio of steel slag, metallurgical dust and sludge to ammonia absorbent is 1:15:0.2. The remaining process operations and process parameters are the same as in Example 1.

[0061] The performance of the obtained cold-consolidated pellets was tested, and the test results are shown in Table 1.

[0062] Comparative Example 6

[0063] The preparation method of the cold-consolidated pellets in this comparative example differs from that in Example 1 in that ammonium chloride is used instead of ammonium bicarbonate as the ammonia absorbent, and the mass ratio of ammonium chloride to steel slag and metallurgical dust is 0.08:1:15. All other process operations and parameters are the same as in Example 1.

[0064] Example 2

[0065] The method for preparing cold-consolidated pellets in this embodiment includes the following steps:

[0066] (1) Pretreatment for steel slag hole making;

[0067] In this embodiment, a certain amount of steel slag, metallurgical dust, and ammonia absorbent were weighed out in a mass ratio of 1:12:0.08. The steel slag was first ground in a ball mill to a fine particle size, controlling the mass percentage content of the -0.149mm particle size to be ≥95%. Then, a mixed solution of formic acid and acetic acid (molar concentration ratio of formic acid to acetic acid was 1:2 mol / L) was added for acid washing, controlling the free CaO content to decrease to 0.25%.

[0068] (2) Mix the raw materials to obtain the briquetting raw materials;

[0069] First, metallurgical dust (i.e., a mixture of blast furnace ash and OG mixed dust in a mass ratio of 1:4) and ammonia absorbent are mixed evenly for 8 minutes, and then the treated steel slag is added and mixed evenly for another 13 minutes to obtain briquetting raw material.

[0070] (3) Pressing the raw ball;

[0071] The raw material for briquetting is mixed with water and then pressed into green briquettes. The roller pressure is controlled at 20 MPa and the moisture content of the briquettes is controlled at 14%.

[0072] (4) Carbonation and solidification treatment of green pellets;

[0073] Sintering flue gas or rotary hearth furnace flue gas is introduced into the green pellets for carbonation and solidification treatment. The introduced industrial waste gas flow rate is 30,000 m / s. 3 The process was carried out at a temperature of 220℃, a CO2 concentration of 8%, a water content of 9%, and a treatment time of 12 hours to obtain cold-consolidated pellets.

[0074] The obtained cold-consolidated pellets are dried and calcined to produce metallized finished pellets. The specific operation is as follows:

[0075] Dry at 150℃ for 10 minutes, then calcine at 1350℃ for 15 minutes to form pellets.

[0076] The performance of the obtained cold-consolidated pellets was tested, and the test results are shown in Table 1.

[0077] Example 3

[0078] The method for preparing cold-consolidated pellets in this embodiment includes the following steps:

[0079] (1) Pretreatment for steel slag hole making;

[0080] In this embodiment, a certain amount of steel slag, metallurgical dust, and ammonia absorbent were weighed out in a mass ratio of 1:10:0.05. The steel slag was first ground in a ball mill to a fine particle size, controlling the mass percentage content of steel slag particles with a size of -0.149 mm to be ≥95%. Then, a mixed solution of formic acid and acetic acid (molar concentration ratio of formic acid to acetic acid was 1:1.2 mol / L) was added for acid washing, controlling the free CaO content to decrease to 0.3%.

[0081] (2) Mix the raw materials to obtain the briquetting raw materials;

[0082] First, metallurgical dust (i.e., a mixture of blast furnace ash and OG mixed dust in a mass ratio of 1:3) is mixed with an ammonia absorbent for 5 minutes, and then the treated steel slag is added and mixed for another 10 minutes to obtain the briquetting raw material.

[0083] (3) Pressing the raw ball;

[0084] The raw material for briquetting is mixed with water and then pressed into green briquettes. The roller pressure is controlled at 28 MPa and the moisture content of the briquettes is controlled at 13%.

[0085] (4) Carbonation and solidification treatment of green pellets;

[0086] Rotary hearth furnace flue gas is introduced into the green pellets for carbonation and solidification treatment. The introduced industrial waste gas flow rate is 50,000 m / s. 3 The process involves a temperature of 150℃, a CO2 concentration of 7%, a moisture content of 6%, and a treatment time of 4 hours to obtain cold-consolidated pellets.

[0087] The obtained cold-consolidated pellets are dried and calcined to produce metallized finished pellets. The specific operation is as follows:

[0088] Dry at 200℃ for 8 minutes, then calcine at 1300℃ for 20 minutes to form pellets.

[0089] The performance of the obtained cold-consolidated pellets was tested, and the test results are shown in Table 1.

[0090] Example 4

[0091] The method for preparing cold-consolidated pellets in this embodiment includes the following steps:

[0092] (1) Pretreatment for steel slag hole making;

[0093] In this embodiment, a certain amount of steel slag, metallurgical dust, and ammonia absorbent were weighed out in a mass ratio of 1:20:0.1. The steel slag was first ground in a ball mill to a fine particle size, controlling the mass percentage content of the -0.149mm particle size to be ≥95%. Then, a mixed solution of formic acid and acetic acid (molar concentration ratio of formic acid to acetic acid was 1:0.5mol / L) was added for acid washing, controlling the free CaO content to decrease to 0.1%.

[0094] (2) Mix the raw materials to obtain the briquetting raw materials;

[0095] First, metallurgical dust (i.e., a mixture of blast furnace ash and OG mixed dust at a mass ratio of 1:3.5) and ammonia absorbent are mixed evenly for 6 minutes, and then the treated steel slag is added and mixed evenly for another 15 minutes to obtain briquetting raw material.

[0096] (3) Pressing the raw ball;

[0097] The raw material for briquetting is mixed with water and then pressed into green briquettes. The roller pressure is controlled at 30 MPa and the moisture content of the briquettes is controlled at 15%.

[0098] (4) Carbonation and solidification treatment of green pellets;

[0099] Sintering flue gas is introduced into the green pellets for carbonation and solidification treatment. The introduced industrial waste gas flow rate is 80,000 m / s. 3 The process was carried out at a temperature of 190℃, a CO2 concentration of 4%, a water content of 4%, and a treatment time of 12 hours to obtain cold-consolidated pellets.

[0100] The obtained cold-consolidated pellets are dried and calcined to produce metallized finished pellets. The specific operation is as follows:

[0101] Dry at 200℃ for 5 minutes, then calcine at 1250℃ for 25 minutes to form pellets.

[0102] The performance of the obtained cold-consolidated pellets was tested, and the test results are shown in Table 1.

[0103] Table 1. Performance test results of the pellets obtained in each embodiment and comparative example.

[0104]

[0105]

[0106] Based on the data in Table 1, we can see that:

[0107] Compared with Comparative Example 1, the compressive strength of the prepared pellets was lower when no ammonia absorbent was added, while the strength of the pellets was effectively improved after adding ammonia absorbent.

[0108] Compared with Comparative Examples 2-3, the timing of adding ammonia absorbents is also particularly important in Example 1. Directly mixing the three raw materials of steel slag, metallurgical dust and ammonia absorbent, or contacting the steel slag with the ammonia absorbent first and then mixing it with the metallurgical dust and slag, will affect the carbonation process and effect during pellet carbonation, thereby reducing the strength of the pellets.

[0109] Compared with Comparative Examples 4-5, the amount of ammonia absorbent added in Example 1 is also crucial. If too little is added, the improvement in pellet performance is not significant, while if too much is added, after absorbing SO2, it will continue to absorb CO2, thereby causing a decrease in CO2 partial pressure, which is not conducive to improving pellet strength.

[0110] Furthermore, to further investigate the changes in the compressive strength of the pellets in Example 1 and Comparative Examples 1-3 after different carbonation treatment times, the compressive strength of the pellets after 0h, 2h, 4h, 6h, 8h, 10h and 12h of carbonation was detected and recorded, and the results are shown in Table 2.

[0111] Table 2 Compressive strength of cold-consolidated pellets treated with different carbonation times

[0112] Example 1 21.6 74.1 132.4 168.3 175.3 172.2 170.4 Comparative Example 1 20.4 62.1 101.4 125.7 134.8 141.0 140.4 Comparative Example 2 21.0 82.4 110.4 118.5 122.6 125.3 125.6 Comparative Example 3 20.3 88.5 92.3 98.6 100.5 102.6 100.3

[0113] As can be seen from the data in Table 2, compared with Comparative Example 1, the addition of ammonia absorbent resulted in a greater increase in pellet strength within the same time period, and the final strength was also improved.

[0114] Although the concentration of SO2 in the exhaust gas is not very high compared to CO2, the solubility of SO2 (40:1) at room temperature is significantly higher than that of CO2 (1:1), causing the concentrations of SO2 and CO2 in the solution to reach the same order of magnitude. After the industrial exhaust gas enters the pelletizing process, the Ca in the hydration layer of the steel slag... 2+ It first reacts with SO2 to form sulfate, rather than reacting with CO2. Meanwhile, because calcium sulfate crystallizes much slower than calcium carbonate, the amount of precipitate formed is reduced, affecting the strength of the pellet consolidation.

[0115] Ammonium bicarbonate undergoes double hydrolysis. The presence of ammonium bicarbonate solution is due to the fact that the NH3 produced in the reaction is highly soluble in water (700:1), forming an alkaline solution, while HCO3-... 3- The CO2 gas produced by hydrolysis is easily soluble in alkaline solutions, so neither NH3 nor CO2 escapes from the reaction system. As a result, the hydrolysis of ammonium bicarbonate is hindered, and its solution can exist relatively stably.

[0116] When SO2 and CO2 enter the flue gas, SO2 dissolves and oxidizes, dissociating into SO3. 2- SO4 2- H + At the same time, the oxygen in the flue gas can act as an oxidant, reducing SO3. 2- Oxidized into the more acidic SO4 2- Compared to CO3 formed by the dissolution of CO2 2- SO4 2- The acidity is stronger, SO2 forms SO4 2- In the alkaline environment formed by ammonium bicarbonate solution, it preferentially reacts with NH4. + They combine to form ammonium sulfate, thereby mitigating the reaction between SO2 and CO2 and Ca. 2+ The competitive relationship makes Ca 2+ More of it reacts with CO2 to form calcium carbonate, which precipitates rapidly, thereby increasing the consolidation strength of the pellets.

[0117] Meanwhile, after the ammonium bicarbonate solution stabilizes the system, SO2 can be used to release CO2, which can replenish the CO2 concentration inside the pellets and serve as an internal carbon source, further improving the problem of insufficient CO2 inside the pellets due to the reduced porosity caused by the consolidation of the outer pellets.

[0118] Compared to Example 1, Comparative Example 2 shows that adding ammonia absorbents can effectively improve pellet strength. However, compared to Example 1, Comparative Example 2, which directly mixes the three raw materials, shows a greater increase in pellet strength in the first 2 hours compared to Example 1, which first mixes the ammonia absorbent with metallurgical dust and sludge before mixing it with steel slag. This is because the direct mixing method allows ammonium bicarbonate to come into direct contact with the steel slag, and the decomposition of ammonium bicarbonate to form an alkaline environment is conducive to the formation of Ca2+.2+ The generation of NH4, which is formed by decomposition. + CO2 acts directly on the surface of steel slag, absorbing SO2 and promoting CO3. 2- Formation. However, when the time exceeded 2 hours, the pellet lift was less than in Example 1, which is due to NH4. + Ammonium sulfate, formed by reacting with SO2, crystallizes and coats the steel slag during water evaporation, affecting the calcium content. 2+ and CO3 2- The transfer of plasma in the solution and the precipitation of calcium carbonate affect the carbonation effect, thereby reducing the formation of pellet strength in the later stage. In Example 1, the method of first mixing the ammonia absorbent with metallurgical dust and sludge, and then mixing it with steel slag, utilizes the ammonia absorbent to coat the metallurgical dust and sludge, reducing contact with the steel slag. This allows for the absorption of as much SO2 as possible from the flue gas outside the steel slag solution, while selectively allowing CO2 to pass through, thus reducing both the SO2 in the flue gas and its impact on the steel slag itself.

[0119] Compared with Comparative Example 3, Example 1 shows that mixing steel slag with ammonia absorbent first and then mixing it with metallurgical dust and sludge results in direct contact between the ammonia absorbent and the steel slag, leading to the decomposition of ammonium bicarbonate into NH4. + It reacts with SO2 to form ammonium sulfate, which crystallizes and coats the steel slag or fills the pores of the steel slag during water evaporation, affecting the calcium content. 2+ and CO3 2- The transfer of plasma in the solution affects the carbonation effect, which in turn reduces the formation of pellet strength in the later stage.

[0120] More specifically, although exemplary embodiments of the invention have been described herein, the invention is not limited to these embodiments, but includes any and all embodiments modified, omitted, such as combinations between various embodiments, adaptive changes, and / or substitutions, as would be apparent to those skilled in the art from the foregoing detailed description. The limitations in the claims are to be interpreted broadly as used in the language of the claims and are not limited to the examples described in the foregoing detailed description or during the implementation of this application, which should be considered non-exclusive. Any step listed in any method or process claim may be performed in any order and is not limited to the order set forth in the claims. Therefore, the scope of the invention should be determined solely by the appended claims and their legal equivalents, and not by the description and examples given above.

[0121] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In case of conflict, the definitions in this specification shall prevail. When a rate, pressure, temperature, time, or other value or parameter is expressed as a range, preferred range, or a range defined by a series of upper and lower preferred values, this shall be understood to specifically disclose all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether such range is disclosed individually. For example, the range 1-50 should be understood to include any number, combination of numbers, or subrange selected from 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50, as well as all decimal values ​​between the integers mentioned above, such as 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, and 1.9. Regarding subranges, specifically consider "nested subranges" extending from any endpoint of the range. For example, nested sub-ranges of the exemplary range 1-50 may include 1-10, 1-20, 1-30 and 1-40 in one direction, or 50-40, 50-30, 50-20 and 50-10 in another direction.

Claims

1. A method for preparing cold-consolidated pellets based on pre-desulfurization, characterized in that: Includes the following steps: (1) Steel slag pretreatment; Steel slag is ground and subjected to pore-forming treatment to obtain porous steel slag; (2) The raw materials are mixed to obtain the briquetting raw material; The pretreated steel slag is mixed with metallurgical dust and ammonia absorbent in a certain proportion; first, the metallurgical dust and ammonia absorbent are mixed evenly, and then the steel slag is added and mixed evenly to obtain the briquetting raw material. (3) Pressing the raw ball; Add water to the briquetting material obtained in step (2), mix well, and press into raw briquetting material; (4) Carbonation treatment; Industrial waste gas is introduced to carbonate the pressed green pellets, resulting in cold-bonded pellets. In step (2), the mass ratio of steel slag, metallurgical dust and sludge and ammonia absorbent is 1:(10~20):(0.05~0.1), and the ammonia absorbent is ammonium bicarbonate with a purity >99.5%; In step (2), the mixing time of metallurgical dust and ammonia absorbent is 5-8 min. After adding the pretreated steel slag, they are mixed together for 10-15 min.

2. The method for preparing cold-consolidated pellets based on pre-desulfurization according to claim 1, characterized in that, In step (1), the steel slag is acid-based to create pores. The pore-creating method is as follows: the steel slag is ground to a particle size of -0.149mm with a mass percentage content of ≥95%, and then the steel slag is immersed in an acidic solution for pickling, and the free CaO content is controlled to be reduced to 0.1%~0.3%.

3. The method for preparing cold-consolidated pellets based on pre-desulfurization according to claim 2, characterized in that: The acidic solution is a mixture of formic acid and acetic acid, wherein the molar ratio of formic acid to acetic acid is 1:(0.5~2).

4. The method for preparing cold-consolidated pellets based on pre-desulfurization according to claim 2, characterized in that, The metallurgical dust is blast furnace ash or OG mixed dust, and the particle size of the metallurgical dust is -0.074mm particle size with a mass percentage content of ≥80%.

5. The method for preparing cold-consolidated pellets based on pre-desulfurization according to claim 4, characterized in that, The metallurgical dust and sludge is a combination of blast furnace ash and OG mixed dust and sludge, with a mass ratio of blast furnace ash to OG mixed dust and sludge of 1:(3~4).

6. The method for preparing cold-consolidated pellets based on pre-desulfurization according to claim 2, characterized in that, In step (4), the introduced industrial waste gas is sintering flue gas or rotary hearth furnace flue gas, and the introduced industrial waste gas flow rate is 30,000~80,000 m / s. 3 / h, temperature is 150~220℃, treatment time is 4~12h.

7. A cold-consolidated pellet based on pre-desulfurization, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 6.

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