Method for improving burst temperature and reduction degree of superfine iron ore concentrate pellets

Abstract

The invention relates to the technical field of iron ore concentrate pellet manufacturing methods, and discloses a method for improving the burst temperature and reduction degree of superfine iron ore concentrate pellets, which comprises the following steps: collecting straws, crushing and screening to obtain straw powder; the method comprises the following steps: weighing straw powder, fine iron powder and bentonite according to the mass percentage, uniformly mixing, and adding water to prepare green pellets; after the green pellets obtained in the step 2 are screened, drying and roasting are sequentially conducted, then cooling is conducted to the normal temperature, and the superfine iron ore concentrate pellets with the burst temperature and the reduction degree improved are obtained. Agricultural waste straw is adopted as an additive instead of an expensive organic binder, the burst temperature and the reduction degree of the superfine iron ore concentrate pellets are remarkably improved, and the cost is reduced. The method is realized under the condition that the utilization rate of the superfine iron ore concentrate is not reduced by adjusting ore blending. Specifically, the burst temperature of the pellets is remarkably increased to 540 DEG C from 380 DEG C, and the reduction degree of the pellets is increased to 48.55% from 25.65%.

Description

Technical Field

[0001] The invention relates to the technical field of iron ore concentrate pellet production methods, and in particular to a method for improving the bursting temperature and reduction degree of ultrafine iron ore concentrate pellets. Background Art

[0002] Ultrafine iron ore pellets are widely used in the metallurgical industry for steel production, but there are two main problems in the production process: low burst temperature and low reduction degree. These problems lead to a low proportion of ultrafine iron ore in pellets and high application costs. Current technology usually relies on expensive organic binders to increase the burst temperature and reduction degree of pellets, but this method not only increases production costs, but also limits the utilization rate of ultrafine iron ore.

[0003] In traditional production methods, ultrafine iron ore concentrate pellets are prone to bursting at higher temperatures, affecting the strength and use of the pellets. Low reduction also means that the pellets are inefficient in blast furnace smelting, resulting in more energy consumption and higher coke demand. In order to solve this problem, the development of new additives has become a research focus.

[0004] In addition, agricultural waste straw is a renewable resource, but about 300 million tons of straw are not used reasonably every year, and most of them are burned or discarded, causing environmental pollution and waste of resources. Although straw has some applications in the fields of energy and agriculture, its applicability and effect in pellet production have not been fully studied. Therefore, how to use straw as an additive to increase the burst temperature and reduction degree of pellets while achieving sustainable utilization of resources has become a technical problem that needs to be solved urgently. Summary of the invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a method for improving the detonation temperature and reduction degree of ultrafine iron ore concentrate pellets.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for increasing the detonation temperature and reduction degree of ultrafine iron ore concentrate pellets comprises the following steps:

[0008] Step 1: Collect straw, crush and sieve to obtain straw powder;

[0009] Step 2: Weigh straw powder, iron ore powder and bentonite according to mass percentage, mix well and add water to prepare green balls;

[0010] Step 3: After screening the green balls obtained in step 2, they are dried and roasted in sequence, and then cooled to room temperature to obtain ultrafine iron ore concentrate pellets with improved bursting temperature and reduction degree.

[0011] Preferably, in step 1, the crushed straw is sieved through a 100-mesh sieve.

[0012] Preferably, in step 1, the straw powder obtained includes corn straw powder, rice straw powder, etc.

[0013] Preferably, in step 1, the ignition point of the straw powder obtained is 235°C-275°C to ensure that the straw powder can be effectively burned under a drying temperature condition of 200-500°C.

[0014] Preferably, in step 2, the weight percentages of the straw powder, iron ore concentrate and bentonite weighed are: 0-2.0% straw powder, 98% iron ore concentrate and 1.6% bentonite.

[0015] Preferably, in step 3, the green ball roasting temperature is 1000°C-1250°C.

[0016] Preferably, in step 3, the specific method of drying the green balls is: placing the green balls in a drying furnace at a drying temperature of 175° C. for 3 hours.

[0017] The beneficial effects of the present invention are:

[0018] (1) Using agricultural waste straw as an additive instead of expensive organic binders significantly improves the burst temperature and reduction degree of ultrafine iron ore pellets without reducing the utilization rate of ultrafine iron ore by adjusting the ore blending. Specifically, the burst temperature of the pellets was significantly increased from 380°C to 540°C, and the reduction degree of the pellets increased from 25.65% to 48.55%.

[0019] (2) The production and use costs of ultrafine iron ore concentrate pellets are reduced.

[0020] The cost of iron ore concentrate is 1,050 yuan / ton, the use ratio of bentonite is 1.0%, and the use cost is 5.5 yuan / ton. The cost of straw powder is 980 yuan / ton, and the use ratio is 1.5%, and the use cost is 14.7 yuan / ton. Straw powder has dual uses in the pellet production process:

[0021] (a) Provide calorific value. The calorific value of straw powder combustion is 13388kJ / kg. When converted into standard coal, 1.5% straw powder generates 6.7kg / t of heat in the pellet production process. At present, the energy consumption generated by pellet production is 25.1kg / t. The price of standard coal is 1200 yuan / ton. Adding 1.5% straw powder will reduce the energy cost by 8.1 yuan / ton.

[0022] (b) Improve the reducibility of pellets. At a pelletizing ratio of 30%, the coke ratio will decrease by 0.26kg / t for every 1% increase in pellet reducibility. For ultrafine iron ore concentrate pellets, adding 1.5% straw powder can increase the pellet reducibility by 17%. Based on the metallurgical coke price of 2,200 yuan / ton, 1.5% straw powder reduces the coke cost by 9.5 yuan / ton.

[0023] In summary, the net cost of 1.5% straw powder is calculated as: 14.7-8.1-9.5=-2.9 yuan / ton.

[0024] (3) The use of straw powder as an additive provides a new way to rationally utilize straw, an agricultural waste, reduces straw accumulation and pressure on the environment, and provides a sustainable way of resource utilization.

[0025] That is, by adopting the method of the present invention, the bursting temperature and reduction degree of ultrafine iron ore concentrate pellets can be effectively increased, the physical properties of the pellets can be improved, and the utilization rate and benefit of the ultrafine iron ore concentrate pellets in the ironmaking process can be increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the production process of using straw powder as an additive to produce ultrafine iron ore concentrate pellets in the present invention;

[0027] Figure 2 The microscopic morphology of the ultrafine iron ore concentrate powder used in the present invention;

[0028] Figure 3 The microscopic morphology of the straw powder used in the present invention;

[0029] Figure 4 is the thermogravimetric curve of the straw powder used in the present invention;

[0030] Figure 5 The explosion temperature curves of the ultrafine iron ore concentrate pellets under different straw powder ratios in the present invention;

[0031] Figure 6 The reduction degree curve of the ultrafine iron ore concentrate pellets under different straw powder ratios in the present invention;

[0032] Figure 7 The macroscopic morphology of the pellets after the reduction degree detection of the ultrafine iron ore concentrate pellets with different straw powder ratios in the present invention. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0034] Embodiment: corn stalks or rice straws are collected, crushed and sieved through 100 meshes to obtain stalk powder; 0-2.0% of stalk powder, 98% of ultrafine iron concentrate and 1.6% of bentonite are weighed according to mass percentage, mixed and then water is added to obtain green balls; after screening the green balls obtained above, the screened green balls are placed in a drying furnace at a drying temperature of 175°C and a drying time of 3 hours, and then the dried green balls are placed in a pellet roasting cup, roasted at a temperature of 1000°C-1250°C, and then cooled to room temperature to obtain ultrafine iron concentrate pellets with improved burst temperature and reduction degree.

[0035] In the embodiment, the pelletizing ore green balls are prepared by using a disc ball making machine with a diameter of 1000mm, a disc height of 200mm, a rotation speed of 24r / min, and a disc inclination of 47°. The ball making time is controlled to be 18-20min and the green ball moisture is 9.0-9.6%. The prepared green balls with a diameter of 12-12.5mm are taken for bursting temperature detection.

[0036] The pellet bursting temperature measuring instrument is produced by Suzhou Jiangdong Precision Instrument Co., Ltd. The size of the heating chamber of the measuring instrument is Φ80×1000 or Φ70×180mm. The temperature at which one ball out of 25 balls breaks is the bursting temperature of the pellet, and the unit is ℃.

[0037] The subsequent drying, roasting and cooling of the pelletized ore raw balls are carried out using a pelletized ore roasting cup equipment, which is produced by Anshan Kexiang Instrument Co., Ltd., model KXQT-2022A, roasting capacity: 5-15kg, the diameter of the pelletized ore roasting cup is Φ160mm, and the temperature adjustment range is: 25-1350℃.

[0038] The reduction degree (RI / %) of the finished pellets is determined according to the method of GB / T 13241-2017.

[0039] The ultrafine iron concentrate used in the embodiment of the present invention is magnetite, and its raw material chemical composition is shown in Table 1, and its particle size distribution is shown in Table 2. The ultrafine iron concentrate used has a high iron grade (>65%), low phosphorus and low sulfur, but a high silicon content. From the perspective of raw material particle size distribution, the proportion of particles with a diameter of -0.028mm in the ultrafine iron concentrate used exceeds 80%, which is far lower than the current standard that the proportion of particles with a diameter of -0.075mm is greater than 80%. The microscopic morphology is as follows Figure 2 As shown, from the microscopic morphology, the particle size distribution of ultrafine iron ore concentrate is mainly concentrated between 0.005-0.02mm.

[0040] Table 1 Main chemical components of ultrafine iron ore concentrate

[0041] raw material TFe FeO CaO <![CDATA[SiO2]]> MgO <![CDATA[Al2O3]]> P S Ultrafine iron concentrate 66.49 25.53 0.27 6.40 0.41 0.82 0.034 0.014

[0042] Table 2 Particle size composition of ultrafine iron ore concentrate powder

[0043] raw material +0.075mm 0.048-0.075mm 0.038-0.048mm 0.028-0.038mm -0.028mm Ultrafine iron concentrate 0 1.46 3.65 10.33 84.56

[0044] In the embodiment of the present invention, the elemental composition of straw powder was determined by an element analyzer. Industrial analysis of straw powder in the air was carried out according to the method described in GB / T212-2008, and the results are shown in Table 3. As can be seen from Table 3, the content of C and O elements in straw powder is relatively high, accounting for about 91.4% of the total. Mad represents water content, Aad represents ash content, Vad represents volatile matter content, and FCad represents fixed carbon content. It can be seen that the Vad content in straw powder is relatively high (>60%). Vad refers to the sum of combustible gas and volatile matter released when solid fuel is heated, indicating that the combustion of straw powder in the drying stage will lead to the release of volatile matter, thereby promoting the formation of pores inside the pellet.

[0045] Table 3 Elemental analysis and industrial analysis of straw powder

[0046]

[0047] The microstructure of the straw powder in the embodiment of the present invention is as follows: Figure 3 As shown, it can be found that the straw powder still has a certain fiber structure after crushing and screening.

[0048] The thermogravimetric curve of the straw powder in the embodiment of the present invention is as follows Figure 4 As shown, the combustion ignition temperature Ti is 255°C, the combustion peak temperature Tp is 295°C, and the combustion end temperature Tq is 480°C. Figure 4 In the figure, point A represents the intersection of a straight line parallel to the y-axis from the peak combustion temperature and the TG curve. A tangent line is drawn through point A, and a tangent line is drawn through point B (indicating the starting point of weight loss). The two tangent lines intersect at point C, from which the temperature corresponding to point C can be obtained, which is the ignition temperature of the fuel. Point D is the end point of the weight loss curve. The results show that the mass loss of straw powder drops sharply from Ti to Tp, about 25%; and in the Tp to Tq stage, the mass loss is more significant, about 44%. From Ti to Tq stage, the total mass decreases by 69%. This shows that the straw powder used can be effectively burned under drying temperature conditions of 200-500°C.

[0049] The bursting temperature curves of ultrafine iron ore concentrate pellets under different straw powder ratios in the embodiment of the present invention are as follows: Figure 5 As shown in the figure, the bursting temperature of the pellets increases significantly with the increase of the straw powder ratio. When the straw powder ratio reaches 2.0%, the bursting temperature of the pellets can reach 540℃.

[0050] The reduction degree curves of ultrafine iron ore concentrate pellets under different straw powder ratios in the embodiment of the present invention are as follows: Figure 6 As shown in the figure, the macroscopic morphology of the ultrafine iron ore concentrate pellets after reduction degree detection under different straw powder ratios is as follows Figure 7 As shown in the figure, the reduction degree of pellets directly affects the efficiency and quality of the ironmaking process. A higher reduction degree can convert the pelletized ore into metallic iron more completely, thereby improving the utilization rate of the ironmaking process while reducing energy consumption and production costs. Without adding straw powder, the reduction degree of ultrafine iron ore concentrate pellets is only 25.65%. Increasing the proportion of straw powder can effectively improve the reduction degree of pellets. When the proportion of straw powder increases from 0.0% to 2.0%, the reduction degree of pellets increases from 25.65% to 48.55%, an increase of 22.90%. Figure 7 It is more intuitively demonstrated that the increase in the proportion of straw powder helps to improve the reduction degree of ultrafine iron ore concentrate pellets.

[0051] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for increasing the detonation temperature and reduction degree of ultrafine iron ore concentrate pellets, characterized in that: The following steps are involved: Step 1: Collect straw, crush and sieve to obtain straw powder; Step 2: Weigh straw powder, iron ore powder and bentonite according to mass percentage, mix well and add water to prepare green balls; Step 3: After screening the green balls obtained in step 2, they are dried and roasted in sequence, and then cooled to room temperature to obtain ultrafine iron ore concentrate pellets with improved bursting temperature and reduction degree.

2. A method for improving the detonation temperature and reduction degree of ultrafine iron ore concentrate pellets according to claim 1, characterized in that: In step 1, the crushed straw is sieved through a 100-mesh sieve.

3. The method for improving the detonation temperature and reduction degree of ultrafine iron ore concentrate pellets according to claim 1, characterized in that: In step 1, the ignition point of the obtained straw powder is 235°C-275°C.

4. The method for improving the detonation temperature and reduction degree of ultrafine iron ore concentrate pellets according to claim 1, characterized in that: In step 2, the weight percentages of the straw powder, iron ore concentrate and bentonite are as follows: 0-2.0% straw powder, 98% iron ore concentrate and 1.6% bentonite.

5. The method for improving the detonation temperature and reduction degree of ultrafine iron ore concentrate pellets according to claim 1, characterized in that: In step 3, the green ball roasting temperature is 1000℃-1250℃.

6. The method for increasing the detonation temperature and reduction degree of ultrafine iron ore concentrate pellets according to claim 1, characterized in that: In step 3, the specific method of drying the raw balls is: Put the green balls into the drying furnace at a drying temperature of 175°C for 3 hours.

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