Method for utilizing converter side blowing CO2 to cooperate with converter dephosphorization and desulfurization

Abstract

The invention discloses a method for utilizing converter side blowing CO2 to cooperate with converter dephosphorization and desulfurization, and belongs to the technical field of converter steelmaking. According to the method, side-blowing spray guns are arranged below a converter molten pool line and below a molten steel level, and in the converter blowing process, the flow and the mixing proportion of side-blowing CO2 and O2 are dynamically adjusted according to the smelting process: in the early stage of blowing, the heat absorption characteristic of side-blowing CO2 is utilized to stabilize the volume expansion effect generated by contact carbon reaction, and the stirring kinetic energy in a molten pool is greatly improved; slag-metal interface mass transfer is enhanced; in blowing upgrading, the weak oxidizability of side-blown CO2 is utilized to assist in removal of inclusions and harmful gas, a stirring dead zone of a traditional top-bottom combined blowing process is eliminated through lateral jet flow, the thermodynamic contradiction that low temperature is needed for dephosphorization and high temperature is needed for desulfurization is solved by utilizing the physicochemical characteristics of CO2, the dephosphorization and desulfurization efficiency is remarkably improved, and the method is suitable for industrial production. And the steel material consumption and the gas cost are reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of converter steelmaking, and particularly relates to a method for dephosphorization and desulfurization by utilizing converter side blowing CO2. BACKGROUND

[0002] As a core process of modern steel production, converter steelmaking has been constantly evolving around the goal of high efficiency, low cost and green. Converter steelmaking is the mainstream process of current steel production, and dephosphorization and desulfurization are the core tasks of converter smelting. With the urgent and strict requirements of high-end steel on phosphorus and sulfur content, the traditional converter smelting process gradually shows the following deficiencies in kinetics and thermodynamics:

[0003] (1) Insufficient stirring dead zone and kinetics: Although the top blowing oxygen stream has strong impact, it has limited effect on the deep pool bottom, and is easy to form a flow dead zone at the bottom of the furnace. The bottom blowing gas can assist stirring, but in the later stage of the service furnace, the stirring intensity is greatly attenuated due to element blockage or failure. This leads to slow updating speed of slag-gold interface, deteriorated reaction kinetics conditions, and difficult dephosphorization and desulfurization reaction.

[0004] (2) Contradiction between temperature and reaction thermodynamics: The dephosphorization exothermic reaction of the converter requires a relatively "low temperature" environment. However, the traditional top blowing oxygen gas process belongs to an oxidation reaction, and the molten pool temperature rises rapidly, which easily exceeds the best temperature range of dephosphorization, leading to deterioration of dephosphorization thermodynamic conditions and even "phosphorus return". The existing bottom blowing oxygen gas can only rely on physical sensible heat cooling, and cannot effectively and quickly reduce the molten pool temperature to start the dephosphorization reaction.

[0005] (3) Insufficient gas source and weakened stirring in the later stage: The carbon content in the molten steel decreases in the later stage of smelting, and the CO bubbles generated by oxygen reaction are greatly reduced. At this time, the self-stirring capacity of the molten pool begins to weaken. If only relying on the bottom gas blowing with limited flow, it cannot provide enough stirring power to complete the deep dephosphorization and desulfurization task.

[0006] These problems are not isolated, but are interrelated and mutually restrictive, and the root cause lies in the significant deviation between the reaction environment provided by the traditional process and the ideal metallurgical path. Therefore, the application proposes a method of utilizing converter side blowing CO2, which directly acts on the deep part of the molten pool through side blowing jet, breaks the bottom flow dead zone, and significantly improves the reaction kinetics conditions. In addition, the characteristics of the endothermic reaction between CO2 and carbon in the molten steel (CO2+C→2CO) are fully utilized, the "cold zone effect" caused by the reaction heat absorption reduces the nozzle temperature, effectively avoids the side blowing gun from being burned out, and at the same time, the "expansion effect" brought by the double volume CO bubbles generated by the reaction greatly improves the stirring power. Through strengthening the intensity of the unstable flow of the molten pool and controlling the local reaction steel temperature, the dephosphorization and desulfurization during the whole service period of the converter are realized. SUMMARY

[0007] The application realizes accurate "chemical regulation" of temperature and "three-dimensional stirring" of flow field in the molten pool by introducing CO2 at a specific sidewall height of the converter, and solves multiple problems such as desulfurization and dephosphorization by using the heat absorption characteristics and volume expansion characteristics of CO2 in the reaction.

[0008] Specifically, the application discloses a method for dephosphorization and desulfurization by blowing CO2 on the side of a converter, and the method comprises the following steps: arranging one or more layers of lances in the molten pool area of the sidewall of the converter; and dynamically adjusting the blowing mode and flow ratio of top blowing oxygen and side blowing CO2 according to different stages of the smelting process, and adjusting the molten pool temperature by the heat absorption reaction of CO2 and carbon in the molten pool to strengthen dephosphorization, and assisting desulfurization by the dynamic conditions of bottom and side blowing stirring.

[0009] Preferably, the blowing mode is divided into three stages.

[0010] In the early blowing stage, i.e. the stage of 30% of the total oxygen supply time, the side blowing lance is blown by pure CO2 or gas with a CO2 volume concentration of 80% or more, the heat absorption effect of CO2 is used to control the molten pool temperature rising speed to facilitate dephosphorization, and the top blowing oxygen lance is operated at a high lance position to perform slagging, and the top blowing oxygen flow is controlled at 90%-100% of the rated flow.

[0011] In the middle blowing stage, i.e. the stage of 30%-70% of the total oxygen supply time, the side blowing is switched to mixed gas of oxygen and CO2, the oxygen volume ratio is 40%-80%, the top blowing oxygen lance is operated at a standard lance position to perform decarburization, and the top blowing oxygen flow is kept at 100% of the rated flow.

[0012] In the late blowing stage, i.e. the stage of 70%-end of the total oxygen supply time, the side blowing is performed by pure CO2 gas, the flow is 0.05-0.25 Nm 3 / min / t, the top blowing oxygen lance is kept at a standard lance position or a low lance position, and the top blowing oxygen flow is gradually reduced to 50%-80% of the rated flow or stopped before the end point.

[0013] Preferably, the high lance position is 20%-40% higher than the standard lance position, the low lance position is 0%-10% lower than the standard lance position, and the standard lance position is the reference working height set in the conventional smelting operation of the converter.

[0014] Preferably, the side blowing lance is arranged in two layers, the lower layer is located at a height of 1.2-1.5 meters from the inner bottom surface of the furnace shell, and the upper layer is located at a height of 0.8-1.0 meters from the lower layer, 4-6 lances are arranged in each layer, and the lances are distributed in a circularly symmetrical manner.

[0015] Preferably, the side blowing lance adopts a ring slit type or a capillary type structure, the material thereof is selected from high-temperature resistant alloy or composite ceramic material, and a magnesium carbon brick protection layer is built outside the lance.

[0016] Preferably, in the middle of the blowing, the proportion of oxygen in the mixed gas is gradually linearly or stepwise increased from 40% to 80% as the carbon content decreases.

[0017] Preferably, in the later stage of the blowing, pure CO2 gas is used to replace argon for soft stirring and end-point control of the molten steel.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] 1. Compared with the traditional bottom blowing of inert gas, the CO2 gas sprayed from the multiple layers of the sidewall can more effectively penetrate the entire depth and radius of the molten pool during the rising process, forming a three-dimensional and powerful stirring. In particular, when the O2 and CO2 mixed gas is blown from the side wall in the middle of the blowing, a "dot matrix" heat-exchange coupling is formed in the molten pool, generating a high-energy turbulent flow far superior to the bottom blowing of Ar or N2, greatly strengthening the mass transfer process and doubling the lime dissolution and slag-gold reaction rate.

[0020] 2. The sidewall lance used in the present application is protected by the static pressure of the upper molten steel and is wrapped with magnesite carbon bricks outside, so its working environment is much better than that of the bottom blowing element directly contacting the high-temperature furnace bottom, and therefore its service life is significantly prolonged. At the same time, the method can use CO2 to completely replace Ar for stirring in the later stage, fundamentally reducing the consumption of expensive inert gas and the cost of bottom blowing system maintenance.

[0021] 3. By blowing the mixed gas from the side wall, the best conditions for "low-temperature dephosphorization and high-temperature desulfurization" are created, and a local "reaction microzone" is formed in the molten pool. The heat-absorbing effect of CO2 avoids local hot spots and is beneficial to dephosphorization.

[0022] 4. By using the strong heat-absorbing effect of the side blown CO2, the excess heat generated by the carbon-oxygen reaction can be directly and quickly absorbed from the inside of the molten pool. This new cooling method is more rapid and effective than the traditional external regulation by controlling the height of the oxygen lance, so as to fundamentally suppress the temperature fluctuations of the molten pool and significantly inhibit the violent splashing caused by the reaction being too violent and the temperature rising too fast. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a schematic diagram of the overall structure of the present application;

[0024] Figure 2 is a layout diagram of the CO2 side blowing lance;

[0025] Figure 3 is a schematic diagram of the reaction path.

[0026] In the figure: 1, converter body; 2, top blowing oxygen lance; 3, lower layer side blowing lance; 4, upper layer side blowing lance; 5, gas source supply and control system. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work are within the protection scope of the present application.

[0028] The present application proposes a method for dephosphorization and desulfurization by using converter side blowing CO2, and a system thereof comprises: a converter body 1, a top blowing oxygen lance 2, a side blowing CO2 lance system, a gas source supply and control system 5, and a parameter detection and feedback system. The flow, proportion and blowing mode of the top blowing oxygen and the side blowing CO2 are dynamically adjusted according to different stages of the smelting process.

[0029] (1) Side blowing CO2 lance system arrangement:

[0030] Position and number: Preferably, two layers of lances are arranged. The lower layer of side blowing lances 3 are located at 1.2-1.5 meters from the inner bottom surface of the furnace shell, mainly responsible for the stirring of the molten steel in the deep molten pool; the upper layer of side blowing lances 4 are located at 0.8-1.0 meters from the lower layer of lances, mainly responsible for the disturbance and emulsification of the slag-metal interface. 4-6 lances are uniformly arranged in each layer, symmetrically distributed.

[0031] Structure material: The lances adopt ring seam type or top dispersion type structure, so that the gas enters the molten pool in the form of fine bubble groups, increasing the gas-liquid contact area. The lance material is selected from high-temperature resistant alloy or composite ceramic, and is protected by external magnesite carbon brick.

[0032] (2) Dynamic blowing control based on smelting process:

[0033] Early blowing stage (0-30% of total oxygen blowing time): pure CO2 or high proportion of CO2 gas (CO2 volume concentration ≥80%) is used for side blowing. The strong endothermic characteristics of CO2 reaction with carbon in the molten steel are mainly used to absorb excess heat, inhibit splashing, promote slagging and start dephosphorization. The top blowing oxygen lance 2 maintains a high lance position (20%-40% higher than the standard lance position) for "soft blowing", which, together with the stirring effect of side blowing, promotes the initial slagging and starts the low-temperature dephosphorization reaction.

[0034] Middle blowing stage (30%-70% of total oxygen blowing time): switch to mixed gas of oxygen and CO2 for side blowing, and the oxygen proportion is gradually linearly or stepwise increased from 40% to 80%. The oxidation exothermic of O2 and the endothermic expansion of CO2 form high-energy turbulent flow in the molten pool, which strengthens the stirring and mass transfer, accelerates the dissolution of lime and the formation of slag. The top blowing oxygen lance 2 is lowered to the standard low lance position for "hard blowing", and oxygen is supplied at full flow. At this time, the strong stirring of the side blowing mixed gas and the top blowing jet together strengthen the mass transfer, accelerate the dissolution of lime, realize efficient decarburization and deep desulfurization.

[0035] Late blowing stage (70%-100% of total oxygen blowing time): mild stirring with low flow rate (about 0.05-0.25 Nm 3 / min / t) of pure CO2 gas. Its cooling effect prevents overburning of the molten steel, and the continuous stirring promotes the steel-slag balance, achieving deep desulfurization and purification of the molten steel, completely replacing the expensive argon. The top oxygen lance 2 is lowered to the standard low lance position or below the standard lance position by 0%-10%, and the top oxygen flow rate is gradually reduced or the lance is pressed to prevent over-oxidation of the molten steel, and the continuous stirring by side blowing promotes the steel-slag balance, achieving deep desulfurization and purification of the molten steel, completely replacing argon.

[0036] This embodiment takes a 120-ton top, bottom and side combined blowing converter as an example, and the rated oxygen supply flow rate of the top oxygen lance is 25000 Nm³ / h. The specific smelting process steps are as follows:

[0037] Step 1: Early blowing stage (0-30% of total oxygen blowing time): pure CO2 gas is supplied to the lower layer side blowing lance 3 and the upper layer side blowing lance 4 through the gas source supply and control system 5, and the total flow rate is controlled at 800-1200 Nm³ / h. The endothermic reaction of CO2 with carbon in the molten steel absorbs the excess heat at the beginning of blowing, controls the molten pool temperature rise rate at 25-40 ℃ / min, effectively inhibits the initial spatter, and at the same time promotes the formation of initial slag and starts the dephosphorization reaction.

[0038] The top oxygen lance 2 is operated at a high lance position (lance position 1.8-2.2 meters), and the oxygen flow rate is controlled at 90%-100% of the rated flow rate, i.e. 22500-25000 Nm 3 / h. The high lance position "soft blowing" combined with the stirring effect of side blowing CO2 promotes the generation of initial FeO and the rapid melting of lime, starting the low-temperature dephosphorization reaction;

[0039] Step 2: Switch to supply O2-CO2 mixed gas to the side blowing lances 3 and 4. The oxygen proportion in the mixed gas is gradually increased from 40% to 80%, and the total side blowing gas flow rate is increased to 1500-2000 Nm 3 / h. The instantaneous oxidation exothermic of oxygen in the molten pool and the endothermic expansion and reaction of CO2 to produce CO together form intense micro-turbulence inside the molten pool.

[0040] The top oxygen lance 2 is lowered to the standard lance position operation (lance position 1.4-1.6 meters), and the top oxygen lance 2 maintains full-flow oxygen supply of 25000 Nm 3 / h for "hard blowing". At this time, the high-energy turbulence of side blowing accelerates the dissolution of lime and the formation of high-basicity slag, and combined with the strong penetration of top blowing, it creates the dynamic conditions for simultaneous and efficient dephosphorization and desulfurization reactions;

[0041] Step 3: Later stage of blowing (70%-100% of total oxygen blowing time): Switch to supply low flow pure CO2 gas to the lower side-blown lances 3, flow rate reduced to 300-500 Nm 3 / h; upper side-blown lances 4 switched to pressure-maintaining mode (flow rate 100-200 Nm 3 / h, to prevent clogging). The mild cooling effect of CO2 prevents overburning of the end-point temperature of the molten steel, and the sustained stirring effect promotes the material balance between the steel and the slag.

[0042] Top-blowing oxygen lance 2 lowered to standard lance position and gradually reduced to 60% of the rated flow rate (about 15000 Nm 3 / h) or stopped supplying oxygen 2 minutes before the end point, and pure stirring was performed using side-blown CO2. The end-point stirring was performed using side-blown CO2 instead of argon, which effectively reduced the sulfur content of the molten steel to below 0.010%.

[0043] This embodiment realizes precise control of the reaction rate, temperature and stirring intensity of the molten pool by dynamically adjusting the mixed blowing of side-blown CO2 and oxygen in stages. This method can significantly inhibit smelting spatter, effectively promote the simultaneous and efficient progress of dephosphorization and desulfurization reactions, and replace the traditional inert gas with inexpensive CO2 gas to complete end-point control. On the basis of ensuring the purity of the molten steel, it exhibits excellent smelting stability and economy.

[0044] Although embodiments of the present application have been shown and described, it is to be understood that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for dephosphorization and desulfurization by converter side-blown CO2 in cooperation with converter, characterized in that: One or more layers of side blowing lances are arranged in the molten pool area of the converter side wall. During the converter smelting process, the blowing mode and flow ratio of top blowing oxygen and side blowing CO2 are dynamically adjusted according to different stages of the smelting process. The molten pool temperature is controlled by the endothermic reaction of CO2 and molten pool carbon to strengthen dephosphorization, and the desulfurization is assisted by the bottom side blowing stirring dynamic conditions.

2. The method of claim 1, characterized in that: The blowing mode is divided into three stages: In the early stage of blowing, the side blowing lances use pure CO2 or gas with a CO2 volume concentration of ≥80% for side blowing from the start of blowing to the total oxygen supply time of 30%. The endothermic effect of CO2 is used to control the molten pool temperature to facilitate dephosphorization. At the same time, the top blowing oxygen lance uses high lance position operation for slagging, and the top blowing oxygen flow is controlled at 90%-100% of the rated flow. In the middle stage of blowing, the side blowing is switched to mixed gas of oxygen and CO2, with an oxygen volume ratio of 40%-80%, and the top blowing oxygen lance uses standard lance position for decarburization, and the top blowing oxygen flow is kept at 100% of the rated flow. In the later stage of blowing, i.e. 70% of the total oxygen supply time to the end, the side blowing uses pure CO2 gas, the flow rate is 0.05-0.25 Nm 3 / min / t, the top blowing oxygen lance keeps the standard lance position or low lance position, while gradually reducing the top blowing oxygen flow rate to 50%-80% of the rated flow rate or stopping top blowing before the end point.

3. The method of claim 2, characterized in that: The high lance position is 20%-40% higher than the standard lance position, the low lance position is 0%-10% lower than the standard lance position, and the standard lance position is the reference working height set by the conventional smelting operation of the converter.

4. The method of claim 2, characterized in that: The side blowing lances are arranged in two layers, the lower layer is located at a height of 1.2-1.5 meters from the bottom surface of the furnace shell, and the upper layer is located at a height of 0.8-1.0 meters from the lower layer. Each layer is arranged with 4-6 lances, which are distributed in a circular symmetric manner.

5. The method of claim 4, characterized in that: The side blowing lances adopt ring slit or capillary tube structure, the material is selected from high temperature resistant alloy or composite ceramic material, and the outer part of the lance is built with a protective layer of magnesite carbon brick.

6. The method of claim 2, characterized in that: In the middle stage of blowing, the oxygen ratio in the mixed gas is dynamically adjusted, gradually linearly or stepwise increased from 40% to 80% as the carbon content decreases.

7. The method of claim 2, characterized in that: In the late stage of blowing, pure CO2 gas is used instead of argon for gentle stirring and end point control of the molten steel.

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