Method for inhibiting nitrogen increase and regulating and controlling oxygen increase of tapping molten steel

Abstract

The invention discloses a method for inhibiting nitrogen increase and regulating and controlling oxygen increase of tapping molten steel, and belongs to the technical field of metallurgy. Aiming at intense nitrogen absorption and oxygen absorption tendency during tapping of low-carbon oxygen deposition molten steel, water or mixed water slurry added with carbon substances and organic matters is continuously injected into a steel ladle and a tapping stream before tapping and in the tapping process; in a physical space and an action system between a steel ladle and a steelmaking furnace, a large amount of water vapor is evaporated to drive and dilute air, a closed tapping system environment for isolating the air is formed, and effective isolation of tapping molten steel and the air is achieved; and (2) the heat energy of the molten steel is used for promoting pyrolysis of the added carbon / organic matter and reducing the water vapor, the oxidation capacity of the water vapor on the molten steel is adjusted by changing the adding amount of the carbon / organic matter to generate the change of the corresponding reducing gas product amount, and nitrogen increase inhibition and oxygen increase regulation and control on the molten steel in the tapping process are achieved. The method is simple and easy to implement, low in cost, capable of saving resources and particularly suitable for low-carbon / ultra-low-carbon low-nitrogen steel needing vacuum treatment.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metallurgy, more particularly, to a method for inhibiting nitrogen increase and controlling oxygen increase of molten steel during tapping process of a steelmaking furnace, which is low in oxygen or carbon-oxygen product after the end of smelting and is not suitable for further carbon increase. BACKGROUND

[0002] Nitrogen is harmful to most steel grades, and the precipitation of nitrides will have varying degrees of negative impact on certain properties of steel. Pure oxygen steelmaking greatly reduces the nitrogen content of molten steel at the end of smelting by producing carbon oxide bubbles through strong carbon-oxygen reaction (mostly controlled below 20 ppm), but due to the high solubility of nitrogen in molten steel (the quasi-saturation nitrogen content of the nitrogen absorption test of molten steel can reach more than 400 ppm), the control of nitrogen increase of molten steel after the end of smelting of low-nitrogen steel is very important. The tapping process of molten steel from the steelmaking furnace to the ladle is carried out in an open space, and it is difficult to isolate air, so the tapping stream will inevitably suck in the surrounding air, and the exposed surface of the molten steel already poured into the ladle will also come into contact with the air above, and the air containing 78% nitrogen will inevitably cause a certain increase in nitrogen of the molten steel; generally, according to the oxygen content of the molten steel and the tapping process, the nitrogen increase of the tapping molten steel is 3-10 ppm. In order to reduce or inhibit the nitrogen increase of the molten steel during tapping, steelmakers have made great efforts and adopted many measures, such as Chinese patent application 2010105887600 "A method for preventing nitrogen increase of molten steel during tapping of a converter" discloses a method of "blowing argon into the ladle to expel the air in the ladle" using the argon blowing stirring brick originally intended for molten steel stirring before and during tapping; the flow rate of the bottom argon blowing before tapping is 2-6 Nm 3 / min, and the maximum during the tapping process is 0.3-1 Nm 3 / min; Chinese patent 2012104875361 "A control method for nitrogen content during tapping of a converter" and Chinese patent application 2022105729277 "A process for reducing nitrogen increase of low-carbon cold-rolled steel during tapping" both disclose a method of "blowing argon originally intended for molten steel stirring into the bottom of the ladle using the argon blowing stirring brick to drive away the air above the molten steel in the ladle" before and during tapping; Chinese patent 2016101057294 "A method for reducing nitrogen content of semi-steel smelting in a converter" adds dolomite and white ash at 2 / 3 of the tapping to form a molten steel surface cover layer in the later tapping stage, which has some dilution and air isolation effect on the molten steel in the ladle, which is beneficial to reducing the nitrogen absorption of the molten steel during tapping. However, the above and other related existing technologies all have the following defects and problems: 1) the argon flow rate for molten steel stirring is too small relative to the demand for driving, isolating and diluting air in the system consisting of the tapping port of the steelmaking furnace, the tapping stream and the ladle (especially the maximum flow rate during tapping is only 1 Nm3 / minute, and after expansion by heating to 1055°C, less than 6m 3 / min ((273+1500) / 298=5.95), it is difficult to isolate air by argon, not to mention the effect of denitrogenation; 2) the number of argon molecules is close to 40 and the number of air molecules is about 29, the low-temperature argon blown into the bottom will sink in the lower part of the ladle and gradually push the air from bottom to top, but when the argon layer reaches the ladle port, the argon flow no longer rises but sinks to the periphery of the ladle due to the increase in density caused by the decrease in temperature, and it cannot expel the air in the large gap between the steel tapping port of the steelmaking furnace and the upper edge of the ladle; 3) the argon gas stirring element (gas permeable brick) of the molten steel is mostly arranged eccentrically at two points (two gas permeable elements with an angle of about 90° and a distance of 0.3-0.5r from the center of the bottom surface of the ladle), due to the fact that the density of argon is much higher than that of air (the number of argon and air molecules is about 39 and 29 respectively), the actual air isolation and dilution effect caused by concentrated bottom blowing argon is not significant: (1) before tapping, (i) if a large amount of argon is used to drive air, the entering argon will gradually push the air from bottom to top, that is, argon can only protect the range of its filling height, but when the argon layer reaches the ladle port, the argon flow no longer rises but sinks to the periphery of the ladle due to the increase in density caused by the decrease in temperature, and it cannot expel the air in the large gap between the steel tapping port of the steelmaking furnace and the upper edge of the ladle, (ii) due to the relatively small amount of gas blowing, a very long time is needed to fill the argon in the ladle, which increases the ladle turnover cycle time and causes some problems and losses, (iii) the filling of argon in the ladle before tapping is completely destroyed by the high-temperature gas flow rising in the lower part of the ladle at the moment of tapping, and it no longer has a protective effect, (iv) a very important problem is that if a large amount of argon is blown into the empty ladle for a long time, the gas permeable element will be rapidly cooled and then instantaneously and sharply heated during tapping, which will seriously affect the service life of the gas permeable element, and it is not allowed in actual production (for example, the argon blowing time of at least 3.2 minutes and up to 9.5 minutes in the patent application 2010105887600 "A method for preventing nitrogen increase of molten steel during tapping of converter" is not conceivable in actual production); (2) during tapping, (i) the argon blown in will appear high-speed upward floating under the driving force of the large buoyancy above the gas permeable element, and will escape the molten steel surface in a small area on the side of the gas permeable element installation to become an upward flow due to the effect of the tapping molten steel flow, but the non-gas permeable element installation side cannot protect the tapping flow and the molten steel surface at all, (ii) the argon / air mixed gas above the gas permeable element during tapping still has a relatively high density, and after passing through the ladle port, it will sink to the periphery of the ladle due to the increase in relative density caused by heat dissipation, and it also cannot drive / expel the air in the large gap between the steel tapping port of the steelmaking furnace and the upper edge of the ladle above the gas permeable element.4) Based on the design principle that the steelmaking furnace should not interfere with the ladle at any position, a large height gap of several meters (larger for converters than for electric furnaces) must be maintained between the tapping spout and the upper edge of the ladle. This opens a door for the continuous supply of air to the ladle due to airflow in the tapping environment (such as crosswinds in the workshop during windy conditions, airflow related to the plant ventilation design, and the intake of air from the surrounding area during tapping). This also creates a hidden danger of the steel stream drawing in a large amount of air from the tapping spout, and current technology cannot offer any improvement. 5) The tapping of steel from the steelmaking furnace involves the initial velocity of liquid falling under the static pressure of the molten steel inside the furnace. According to Bernoulli's equation, a negative pressure is formed around the high-speed steel stream from the tapping spout. This means that the continuous stream of molten steel, composed of droplets, draws in and carries surrounding gas as it falls, penetrating deep into the bottom of the molten pool already formed in the ladle. Simultaneously, an upward flow forms above the center of the ladle, starting from the tapping spout area and moving downwards around the molten steel stream, and upwards above the molten steel surface within the ladle. The large, open circulation around the ladle opening clearly indicates that this circulation begins with the large intake of a mixture of air and other gases in the ladle opening area; 6) As the tapping process progresses, the liquid level inside the ladle continuously rises, and the distance between the liquid surface above the venting element and the top of the ladle continuously decreases. The distance from when the blown argon gas escapes from the liquid surface to when it begins to sink towards the outside of the ladle opening also continuously decreases. In other words, the effect of blowing argon gas within the very small space above the venting element is constantly decreasing; 7) Due to the enormous kinetic energy of the tapping stream and the gas produced by the reaction within the molten steel... The discharge of entrained gases and other factors cause deoxidation products, steelmaking slag carried by the steel flow, and materials added during the tapping process to mix thoroughly with the molten steel. This results in the molten steel and slag mixture inside the ladle remaining in a highly turbulent, exposed state with a high ferrite content until tapping is complete. It is impossible to form a stable covering layer above the molten steel, and the interaction between the molten steel and the mixed gas in the upper space of the ladle cannot be reduced. Moreover, the source of nitrogen increase during the tapping process is the intake of air scattered inside and outside the steel flow, especially for molten steel undergoing precipitation deoxidation. Furthermore, and importantly, all existing technologies are applied to molten steel with high oxygen levels and actual carbon-oxygen products far exceeding the equilibrium carbon-oxygen product at the tapping temperature. During tapping, the decrease in temperature and environmental pressure (including the static pressure of the molten steel itself within the furnace and the negative pressure generated by the high-speed falling tapping stream) intensifies the carbon-oxygen reaction within the molten steel. The additional reaction product, carbon monoxide, effectively repels and prevents the intake of external gases (at least before the addition of deoxidizing alloying materials at one-third of the conventional tapping time), reducing the likelihood of nitrogen intake into the molten steel stream and ladle pool. 8) Adding materials to isolate the molten steel surface absorbs a significant amount of heat, increasing the tapping temperature loss. In summary, existing technologies only provide extremely limited air isolation and dilution within the ladle, which is negligible compared to the need to create air repellency, isolation, and dilution within the system consisting of the furnace tapping outlet, the tapping stream, and the ladle.

[0003] With the development of steelmaking technology and process level, the smelting of various primary steelmaking furnaces tends to top and bottom combined blowing. In addition to the bottom blowing oxygen or inert gas stirring to promote the mass transfer of the molten pool in the steelmaking process to obtain good smelting kinetics, the most important beneficial effect of combined blowing is that it can reduce the iron oxide content of the slag at the end of blowing and the oxygen content of the molten steel in the furnace, improve the iron yield, dephosphorization rate and reduce the total amount of slag or slag material consumption. The oxygen content of the molten steel at the end of blowing is related to the carbon content in the steel. In steelmaking practice, the activity oxygen content in the molten steel (under the condition of carbon remaining and steel liquid carbon content greater than 0.06%) and the product of activity oxygen content and carbon content (i.e. so-called "carbon oxygen product") are used to evaluate the degree of excessive oxidation of molten steel at the end of high-speed and high-flow intensified oxygen blowing. Theoretically, the equilibrium carbon oxygen product value of molten steel at the end of blowing at 1640℃ under atmospheric environment is about 0.0022~0.0025 (ignoring %*%), and usually only top blowing oxygen without bottom blowing steelmaking process (such as LD and large arc furnace, etc.) has higher oxygen content in molten steel (molten steel activity oxygen content is more than 600ppm), which is more than the equilibrium carbon oxygen product value (the carbon oxygen product exceeds 0.0030 when the end of low carbon steel is produced), and the top and bottom combined blowing steelmaking furnace can control the activity oxygen content of molten steel below 500ppm and the carbon oxygen product to 0.0016~0.0020 by reducing the partial pressure of carbon oxygen reaction product through bottom blowing bubbles, especially the bottom blowing oxygen combined blowing converter and advanced bottom blowing inert gas combined blowing converter can control the activity oxygen content of molten steel below 400ppm and the carbon oxygen product below 0.0014, which is much lower than the equilibrium carbon oxygen product level under atmospheric environment. In the case of low carbon oxygen product, the iron oxide content of the slag is correspondingly reduced, the distribution ratio of phosphorus and sulfur between the slag and the molten steel is improved, and the appropriate stirring also improves the denitrification of the molten steel to a certain extent, which greatly improves the technical and economic indicators of the smelting process in the steelmaking furnace and the quality of the molten steel, but it produces the problem of a large amount of oxygen and nitrogen absorption in the molten steel during the tapping process, which contains about 78% nitrogen and 21% oxygen in the air, and the lower the carbon oxygen product of the molten steel in the furnace, the higher the degree of oxygen and nitrogen increase in the molten steel during tapping.The amount of oxygen and nitrogen absorbed or dissolved by molten steel in the open environment during tapping is related to the initial carbon-oxygen product of the molten steel, in addition to the oxygen content and nitrogen content of the molten steel at the time of tapping. The specific theory and mechanism are as follows: 1) Oxygen in the molten steel is a surface active element, and the oxygen at the air / molten steel interface occupies part of the interface position that can also adsorb nitrogen, hindering the adsorption of nitrogen at these positions and the possible dissolution of nitrogen into the molten steel. Obviously, the lower the oxygen content in the molten steel, the fewer the interface positions occupied by oxygen, the more the nitrogen in the air occupies, and the more the nitrogen absorbed by the molten steel from the air (vice versa). Production practice also shows that when the oxygen content is high, the increase in the amount of nitrogen in the molten steel is small; 2) The lower the oxygen content in the molten steel, the more oxygen the molten steel reacts and absorbs from the environment air based on oxygen balance at the time of tapping, the higher the nitrogen content (partial pressure) in the remaining air after the molten steel reacts with oxygen in the micro-environment, and the more the molten steel absorbs nitrogen; 3) The more the actual carbon-oxygen product of the molten steel in the furnace is lower than the environmental equilibrium carbon-oxygen product, the more the ability of the molten steel to absorb oxygen from the air is reduced after the molten steel absorbs oxygen from the air and produces carbon monoxide through the carbon-oxygen reaction, and the more the ability of the molten steel to absorb oxygen and nitrogen is reduced, even when the carbon-oxygen product of the molten steel is very low, the molten steel only absorbs oxygen from the air without any carbon-oxygen reaction, there is no dilution of the air, and there is no denitrogenation of the molten steel. When the carbon-oxygen product of the molten steel in the advanced bottom blowing inert gas combined blowing converter is 0.0014 at the end of the blowing, the molten steel in the ladle has an additional increase of about 2-4 ppm of nitrogen and more than 100 ppm of oxygen relative to the carbon-oxygen product of the molten steel under the carbon-oxygen reaction equilibrium of the atmospheric environment (carbon-oxygen product 0.0025), which causes a negative impact on the quality of low-nitrogen steel due to the reduction of the oxygen / carbon-oxygen product of the molten steel at the time of tapping, and also causes the oxygen in the molten steel, which has been reduced in the steelmaking furnace, to increase significantly during the tapping process, increasing the consumption of deoxidizing alloy and worsening the quality of the molten steel.

[0004] As a special case, for ultra-low carbon steel requiring vacuum decarburization treatment, it is often desirable to increase the oxygen appropriately during the tapping process (although there is an undesirable increase in nitrogen in the air environment, the oxidation of the molten steel by air can supplement the required oxygen), and the decarburization of the molten steel under vacuum can be naturally achieved only with the oxygen in the molten steel, in order to reduce the amount of oxygen blown during the vacuum decarburization process. SUMMARY

[0005] 1. Problem to be solved The present application aims to solve the problem of the tendency of molten steel to absorb nitrogen and oxygen during the tapping of low-nitrogen steel, forming a closed tapping system environment that completely isolates air, focusing on solving the problem that the existing technology cannot isolate and close the air in the large height gap between the tapping hole of the steelmaking furnace and the upper edge of the ladle, especially to overcome the difficulty of more nitrogen increase and a large amount of oxygen increase during the tapping process of low-oxygen and low-carbon-oxygen product molten steel at the end of smelting, and to achieve less nitrogen increase and controlled oxygen increase according to the needs of the molten steel during the tapping process.

[0006] 2. Technical solution The technical solution adopted by the present application is that the device of the present application is used to spray water flow or mixed water slurry containing carbon substance / organic substance into the ladle and / or the outflow of molten steel during the air replacement period before the beginning of tapping and the tapping process, air in the whole tapping system is replaced by evaporated water vapor and external air is isolated, nitrogen increase of molten steel in the tapping process is inhibited, and the oxidizability of the evaporated water vapor is changed by changing the total mass ratio of carbon substance / organic substance in the mixed water slurry, so as to realize the regulation and control of oxygen increase of molten steel in the tapping process. Specifically: 1) For steel grades that want or do not care about oxygen increase, (1) water flow is sprayed into the ladle in advance during the air replacement period, the air in the empty ladle and the tapping channel above it is driven and replaced by the heat storage and evaporation of water vapor in the hot ladle lining, (2) water flow is sprayed into the outflow and / or the ladle during the tapping process, the water vapor is evaporated by the heat energy of the molten steel to cover the molten steel surface in the ladle, wrap the outflow of molten steel and fill the whole longitudinal columnar space from the molten steel surface of the ladle to the tapping hole of the steelmaking furnace, (3) while isolating air to inhibit nitrogen increase of molten steel, water vapor covering the molten steel surface and wrapping the outflow of molten steel is also used to oxidize and increase oxygen of molten steel; 2) For steel grades that do not want to increase oxygen, (1) water flow or mixed water slurry containing carbon substance and / or organic substance is sprayed into the ladle in advance during the air replacement period to drive and replace the air in the empty ladle and the tapping channel above it, (2) when only water is sprayed during the air replacement period, carbon substance and / or organic substance is added to the water to concentrate the slurry into a mixed water slurry or the pre-mixed mixed water slurry is switched to be sprayed before the molten steel flows out of the tapping hole at the beginning of tapping, (3) mixed water slurry is continuously sprayed during the whole tapping process, water vapor is used to cover the molten steel surface in the ladle, wrap the outflow of molten steel and fill the whole longitudinal columnar space from the molten steel surface of the ladle to the tapping hole of the steelmaking furnace to isolate air and inhibit nitrogen increase of molten steel, at the same time, the heat energy of the molten steel is used to promote pyrolysis and carbonization of the mixed carbon substance and / or organic substance, the products reduce water vapor, a small amount of carbon dioxide and even oxidized iron in the molten steel, and by changing the total mass ratio of the added carbon substance and / or organic substance in the mixed water slurry, the amount of reducing gas produced is adjusted to adjust the oxidizability of the water vapor mixed gas, so as to realize the regulation and control of oxygen increase of molten steel in the tapping process.

[0007] The technical solution of the present application uses water vapor to isolate air to reduce nitrogen increase of molten steel, and the difference between the present application and the prior art is: 1) Water vapor sufficient to drive, expel and isolate air can be produced By shooting a large amount of water from the upper part to the tundish flow and the bottom of the ladle / center of the liquid surface, it can be sufficient to quickly generate a consistent upward piston steam flow that completely avoids the occurrence of internal up-and-down circulation in the ladle, which can achieve good air driving, expelling and isolating effect to suppress the nitrogen absorption of the liquid steel; The total amount of water vapor generated by the water jet can be much larger than the maximum total amount of argon blowing in the prior art.

[0008] 2) Eliminate the intrusion of ambient air into the space of the tundish system from the source Because the specific gravity of water vapor is much lower than that of air (the molar number of water and air is about 18 and 29 respectively), the hydrogen-rich residual water vapor brought in by the tundish flow and the high-temperature water vapor generated by the water flow injected into the tundish flow and the center of the liquid surface converge in the ladle and expand outward from the ladle port and directly rise to the steelmaking furnace and then rise into the plant. That is, all water vapor will jointly form a water vapor columnar physical space that completely fills and wraps the steelmaking furnace tundish, tundish flow and ladle, especially for the height gap between the tundish port and the upper edge of the ladle. The ambient air flow is continuously expelled, blocked and diluted. Compared with the argon blowing dilution in the ladle in the prior art, the high-specific-gravity mixed gas containing 39.5 moles of argon rises to the ladle port and then diffuses and sinks to the four sides of the ladle due to temperature loss, which cannot rise to the tundish port, resulting in a large amount of air being sucked into the tundish flow from the tundish port and being brought down. The invention makes the liquid steel flow out of the tundish port surrounded by steam generated by the water jet, and the tundish flow can only suck in steam during the whole process.

[0009] 3) Driving / expelling of air in the ladle before tundishing Different from the prior art of driving and expelling all air in the ladle by bottom blowing argon layer by layer upward before tapping, the present application only needs to partially expel air in the bottom and central area of the ladle before tapping, and the principle is as follows: (1) water sprayed from the upper part to the central area of the hot ladle bottom before tapping will evaporate a lot near the ladle bottom, and a steam layer with a certain height and a rising steam column up to the body of the steelmaking furnace will appear in the bottom and central area of the ladle respectively, thereby rapidly forming steam protection for the tapping stream and the ladle bottom, (2) the rising steam column is blocked by the body of the steelmaking furnace, and the steam column will expand to all directions and continue to rise after being blocked, thereby blocking air in the area between the tapping hole and the ladle hole from entering, (3) in the process that the tapping stream begins to flow out of the tapping hole and into the ladle, water vapor in the tapping system will expand sharply, thereby driving and diluting air, (4) after the steam stream is submerged into the molten steel, the residual hydrogen-rich steam and newly evaporated water vapor sucked and expelled will further expel and isolate the remaining air in the peripheral and upper space of the ladle from the bottom to the top and from the center to the periphery.If considering the water vapor of the gas column in the bottom of the ladle and the central area of the total volume space of the molten steel before tapping (k = 25-40%), the pre-water spraying time before tapping is t = k * (W / ρ) * 1000 / ((Q / 18) * 22.4 * (T-50+273) / 298) * 60 (seconds), for example, in the case of a 300-ton converter, a molten steel density of 6.9 tons per cubic meter, a ladle temperature T = 700°C, k = 40%, and a total water flow Q of 19 liters per minute (ladle volume 300 tons, strong wind in the workshop, and very low nitrogen content steel), the pre-water spraying time t = k * (W / ρ) * 1000 / ((Q / 18) * 22.4 * (T-50+273) / 298) = 40% * (300 / 6.9) * 1000 / ((19*1000 / 18) * 22.4 * (700-50+273) / 298) * 60 = 0.4 * 43.5 / ((19 / 18) * 22.4 * 923 / 298) * 60 = 14.3 (seconds); relatively, under the same conditions, Chinese patent application 2010105887600 "A method for preventing nitrogen increase in molten steel during tapping of a converter", uses "blowing argon into the ladle to expel air in the ladle, and the argon flow is controlled at 2-6 Nm3 / min, and the argon blowing time is controlled"; if the flow is controlled at the maximum of 6 Nm3 / min (there is no such large flow of permeable bricks in actual working conditions), because the density of argon is much higher than that of air, it is necessary to fill the ladle to expel the outlet gas (only the high tapping stream in the ladle can be protected), and the corresponding pre-blowing time is t = 100% * (300 / 6.9) / (6 * (700+273) / 298) * 60 = 133 (seconds); if the protection effect is sacrificed to some extent, and the same amount of gas is blown into the volume of 40% of the molten steel, it still needs a pre-blowing time of 53 seconds, which is four times the pre-blowing time of the present method.

[0010] 4) Nitrogen absorption protection of the molten steel surface in the ladle during tapping Compared with the prior art of only argon blowing and dilution in the ladle, the water vapor evaporated by the continuous water flow of the present application can completely fill the ladle space and cover the molten steel surface in the ladle, and the molten steel surface has no air and only contacts water vapor, which effectively inhibits the dissolution and absorption of nitrogen by the molten steel on the surface, especially the reaction and dissolution of nitrogen promoted by the deoxidation and alloying elements in the molten steel after deoxidation and alloying.

[0011] 5) Nitrogen absorption protection of the falling molten steel stream between the tapping hole and the molten steel surface in the ladle during tapping The existing any related technology has almost no protection for the molten steel flow, but the continuous water vapor jetting water flow to the molten steel flow and the molten steel surface of the present application can completely fill the physical space in the ladle and between the ladle opening and the tapping opening of the steelmaking furnace, replacing the air sucked from the periphery of the tapping opening in the prior art, and can also block the air with a large transverse flow speed in the plant from contacting the molten steel flow, thereby effectively inhibiting the large nitrogen absorption caused by the suction of air into the molten steel flow.

[0012] 6) Water vapor oxidizes and increases oxygen in molten steel Although the principle and mechanism are quite different, water vapor in contact with molten steel, like air, will cause oxidation and increase oxygen in molten steel, and the reaction is xMe + yH2O = MexOy + yH2 (Me is iron and / or alloying elements). From the metallurgical thermodynamic data of the reaction between the related gas and the molten steel, the following reaction will occur between water vapor and liquid iron: H2O (g) + Fe (l) = H2 (g) + FeO (l); ΔGθ = 13733 - 100.220T kJ / mol (applicable temperature range is 1799~2003K); Through calculation, it can be concluded that the equilibrium temperature of the above reaction is only 137K, which indicates that the water vapor that replaces air after evaporation of the water sprayed at the tapping temperature will definitely oxidize the molten steel and increase oxygen in the molten steel, although the amount of oxygen increase in the molten steel is not large compared with air, but in most cases it is not desirable. It is particularly emphasized that, in order to reduce the oxygen increase in the molten steel caused by the oxidation of water vapor, the start time of precipitation deoxidization and alloying of the molten steel should be delayed as much as possible during the implementation of the method, in order to maintain a high oxygen state of the molten steel for a long time, and to maximize the protection of the molten steel and alloy on the surface of the molten steel at the liquid surface in the ladle.

[0013] It should also be noted that for the production of ultra-low carbon steel (including some low carbon steel) that requires vacuum decarburization of low oxygen and low carbon-oxygen product, the molten steel will be decarburized by carbon-oxygen reaction under vacuum after tapping. When the oxygen content of the molten steel is not sufficient to reduce the carbon content in the steel to the target value, and oxygen needs to be blown to the molten steel, the forced decarburization by oxygen blowing during the vacuum decarburization process is harmful to the service life of the refractory material in the vacuum chamber, and the amount of oxygen blowing process also causes loss of iron evaporation. If the strong oxygen absorption capacity of the low oxygen content and low carbon-oxygen product of the molten steel can be utilized under the premise of inhibiting the increase of nitrogen in the molten steel, the harmless and moderate increase of oxygen in the molten steel during the tapping process is very beneficial and advantageous for the vacuum decarburization of low nitrogen steel, and also simplifies the difficulty and cost of simultaneous control of nitrogen and oxygen increase. It should be noted that for ordinary low carbon steel grades that need to inhibit nitrogen increase and have little effect on the quality of the molten steel and alloy loss after oxygen increase, that is, the "steel grade that does not mind oxygen increase" in the claims, only water flow can be sprayed during the air replacement period and the entire tapping process, in order to simplify the operation.

[0014] 7) The effect of mixed steam containing gaseous oxides such as carbonaceous substances, organic matter from high-temperature pyrolysis, and high-temperature reducing water vapor on the oxidation capacity of molten steel. When carbonaceous materials and / or organic matter are added to the sprayed water, the water vapor that evaporates due to heat will mix with the subsequent reducing gases: (1) The carbonaceous materials and / or organic matter sprayed into the ladle and towards the steel flow stream will also rapidly heat up to above 600°C, which is the temperature of the gaseous products of their large proportion of pyrolysis, after the water evaporates rapidly, releasing reducing small molecule hydrocarbon gases, which will then mix with the water vapor; (2) The residual solid carbon after the pyrolysis of carbonaceous materials and / or organic matter will mix with the water vapor at above 699°C, which is close to the molten steel. In the temperature range, carbon will undergo a reduction reaction of water vapor, C(s) + H2O(g) = CO(g) + H2(g) and possibly C(s) + 2H2O(g) = 2H2(g) + CO2(g) and CO(g) + H2O(g) = CO2(g) + H2(g). The reducing product gases released will mix into the water vapor; (3) In the temperature range close to the molten steel, carbon dioxide mixed in the water vapor reacts with the residual solid carbon after the pyrolysis of carbonaceous materials and / or organic matter, C(s) + The product gases released from the reaction CO2(g) = 2CO(g) mix with water vapor (pure carbon can begin to reduce pure carbon dioxide at temperatures above 708℃). After the aforementioned reducing gases mix with water vapor, on the one hand, the partial pressure of the reactant water vapor and the oxygen potential of the mixed gas are reduced, and on the other hand, the hydrogen content of the product after the water vapor oxidizes the molten steel is increased. The generated hydrogen and carbon monoxide will also combine with the oxygen in the molten steel. The multiple combined effects produce a hindrance effect on the reaction of water vapor oxidizing the molten steel. As the proportion of added carbon and / or organic matter relative to water increases, this hindrance effect is correspondingly enhanced. It is possible to regulate the oxygenation of molten steel by adjusting the proportion of added carbon and / or organic matter.

[0015] 8) The effect of additional hydrogen addition to molten steel One of the products of the oxidation process of molten steel by water vapor in contact with molten steel is hydrogen. Some of the hydrogen released in the reaction will be dissolved and absorbed by the molten steel. Compared with air with low water vapor partial pressure, the molten steel will have an additional small amount of hydrogen added, which will have a certain negative impact on the surface / subsurface quality and some internal quality of the billet at low casting speeds. It will also change the critical specification range of dehydrogenation refining for heavier and thicker final steel products. This needs to be taken seriously and corresponding measures should be taken, such as not using it for low-hydrogen steel with strict hydrogen control or adding a vacuum dehydrogenation process when necessary. Of course, the hydrogen added during tapping has little impact on billets and products produced by high casting speeds for thin-gauge products, and has no adverse effects on products that originally required vacuum dehydrogenation or vacuum decarburization.

[0016] 9) Additional temperature drop due to the physical heat absorption of the injected water and the mixed water slurry, and the heat absorption from the chemical reaction with the molten steel. The temperature effect of the injected substance on the tapping system is mainly: (i) the liquid heating endothermic, evaporation and gaseous heating endothermic of the injected water, (2) the heating, pyrolysis endothermic of the added carbon substance and / or organic matter, (3) the exothermic of the residual carbon after pyrolysis of the carbon substance / organic matter reducing water vapor and a small amount of carbon dioxide, (4) the endothermic of the water vapor oxidizing the liquid steel or the water vapor being reduced by the liquid steel, (5) the exothermic of the reaction of various reducing reaction products with oxygen in the steel / mixed steam, etc. In addition to offsetting the various temperature losses related to air entering the system during the tapping process, the overall steel temperature loss will slightly increase, and the entire tapping process will have an additional temperature drop. However, this temperature drop can be completely ignored in the engineering practice of moderate water injection.

[0017] 10) Water injection amount for the tapping process The water injection amount for the tapping process is relatively much lower than that for the air replacement period before tapping, which is because: (1) the temperature of the liquid steel in the ladle after tapping is about twice the temperature of the hot ladle lining, the volume of the injected steam increases accordingly, (2) the steam generated by water injection during the tapping process is only a supplement to the previously generated water vapor that has expanded under the condition that the upper space of the tapping ladle is continuously decreasing, (3) more importantly, it is to generate continuous water vapor to continuously seal the upper space of the ladle when there is wind.

[0018] 11) Injection device used in the method of the present application The technical solution of the present application is realized by the injection device of the present application Figure 1), the water / mixed water slurry used is metered and then sprayed into the stream and ladle through the spray head. The device includes the following structures: (1) a fixed / oscillating spray gun with a water spray head mounted on a fixed / telescopic base, used to spray water into the stream and ladle and to position and adjust the jet drop point; the telescopic function is used to avoid interference between the spray gun and surrounding objects at the spray position, and the oscillating function is used to track the drop point of the water jet sprayed into the stream and ladle, and also used to continuously change the jet drop point to reduce the adverse effects on the refractory material when a single single-channel spray head is used to complete the pre-filling spray of a large-capacity ladle; (2) a spray head mounted at the top of the spray gun, used to spray water into the stream and ladle and to control the flow, cross-sectional shape and expansion angle of the water jet, and a single-channel single-sided single spray head with a relatively simple and best-effect inverted T-shaped or water-drop-shaped / isosceles trapezoidal cross-sectional liquid column flow outlet is recommended; (3) a spray water flow detection and control system, used to meter and control the spray water flow, including flow conversion during the air replacement period and the transition from the tapping process; (4) a carbonaceous and / or organic matter concentrated slurry or premixed water slurry pressurized delivery, flow detection and regulation system, used to pressurize the concentrated slurry or mixed water slurry and to meter and control its flow, including mechanical pump pressurization or pneumatic pressurization; (5) a water and concentrated slurry mixing device, used to improve the uniformity of the mixed water slurry; (6) a carbonaceous and / or organic matter concentrated slurry or premixed mixed water slurry storage tank at the tapping site; (7) a carbonaceous and / or organic matter concentrated slurry or premixed water slurry ground production, storage tank and pneumatic pressurized delivery system.

[0019] 12) Selection and determination of spray head To avoid the sprayed water jet from being overheated and vaporized prematurely and thus unable to enter the lower area of the ladle, the spray head is at most two and preferably a liquid column flow spray head with a near 0° expansion angle to reduce the specific surface area of the water jet subjected to heat and evaporation; when two spray heads are used to complete the spray, a circular cross-sectional liquid column flow spray head is preferably used, and a larger flow is sprayed towards the center of the cross-sectional area of the bottom of the ladle and a smaller flow is sprayed towards the center of the cross-sectional area of the middle and upper section of the ladle, and the approximate ratio of the larger flow to the smaller flow is about 2:1; when a double-channel single spray head is used to complete the spray, a circular cross-sectional liquid column flow spray hole is preferably used, and the larger flow is sprayed towards the center of the cross-sectional area of the bottom of the ladle and the smaller flow is sprayed towards the center of the cross-sectional area of the middle and upper section of the ladle by designing the included angle between the axes of the two-channel spray holes, and the approximate ratio of the larger flow to the smaller flow is about 2:1; when a single single-channel spray head is used to complete the spray, to avoid the water jet drop point being too concentrated (especially during the low-temperature ladle air pre-replacement period before tapping), an inverted T-shaped cross-section or water-drop-shaped / isosceles trapezoidal cross-section outlet liquid column flow spray head is preferably used to spray towards the center of the cross-sectional area of the bottom surface or lower section 1 / 4-1 / 3 height of the ladle, and the outlet bottom edge of the spray head is downward to increase the water quantity in the lower part of the ladle; the specific shape of the cross-sectional liquid column flow outlet of the spray head outlet and the relationship between its dimensions are shown in the drawingsFigure 2 As shown in the figure, H / D≥3, D>d, G≥g; under the condition of 200-500 kilo-pa of economic industrial water, the total area of the nozzle outlet cross-section is in the range of 6-18 square millimeters, which is sufficient for the calculation of the maximum amount of water injection corresponding to the air replacement period during the addition of carbon materials and / or organic materials during the tapping process; obviously, the single-sided single-channel single-nozzle injection is the simplest.

[0020] Advantages Compared with the prior art, the advantages of the present application are: 1) By continuously injecting water flow into the tapping stream and ladle, the water vapor generated by the evaporation of water in the physical space and action system formed by the tapping hole of the steelmaking furnace, the tapping stream, and the ladle is used to drive, displace, isolate, and dilute the ambient air, achieving less nitrogen increase or no nitrogen increase in the molten steel during the tapping process, which can be used to produce various low-nitrogen steels, and is suitable for producing low-nitrogen steels that require vacuum dehydrogenation, especially for producing low-carbon / ultra-low-carbon low-nitrogen steels that require vacuum decarburization, and can reduce the oxygen blowing amount in the subsequent vacuum decarburization process.

[0021] 2) For molten steel with increasingly lower blowing endpoint oxygen content and carbon-oxygen product as the steelmaking technology develops, the method of the present application is particularly significant for producing low-nitrogen steel with strict nitrogen content limitations, especially for low-carbon low-nitrogen steel.

[0022] 3) Compared with the prior art, due to the fact that the number of moles of water is less than half of that of argon, the mass required for the same displacement and dilution is greatly reduced, and in the case of inhibiting nitrogen increase, it also compensates for part of the heat absorption of water evaporation to some extent; also, due to the fact that large-flow water injection and large-scale adjustment of its flow can be easily achieved, the air replacement time during the air replacement period before tapping is greatly reduced.

[0023] 4) Due to the fact that the number of moles of water vapor is much lower than that of air, the driving of the rising water vapor generated by the evaporation of the injected water flow on the air above the molten steel surface in the ladle and the isolation effect of the air around the tapping stream are good.

[0024] 5) Adding carbon materials and / or organic materials to the water can limit the oxygen increase of the tapping molten steel, and the proportion of the added carbon materials and / or organic materials can be changed to effectively control the oxygen increase of the tapping molten steel.

[0025] 6) The limitation of oxygen increase in the molten steel can maintain the low oxygen content level of the molten steel in the steelmaking furnace after the completion of the tapping under the premise of low nitrogen, which not only reduces the consumption of deoxidizing alloy but also relatively reduces the amount of oxide inclusions in the molten steel.

[0026] 7) Compared with the scarce argon, the cost of water injection to inhibit the nitrogen increase of the molten steel is greatly reduced.

[0027] 8) The method is easy to operate, the device is simple, and the operation is convenient, only a little investment is needed, and there is almost no running and maintenance cost. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The schematic diagram of the injection device used in the method for suppressing nitrogen increase and regulating oxygen increase of molten steel during tapping, comprising: 1) a fixed / swingable injection lance with a spray head installed on a fixed / retractable base; 2) a spray head; 3) a water flow detection and adjustment system; 4) a carbon substance and / or organic matter concentrated slurry or premixed mixed water slurry pressurized delivery, flow detection and adjustment system; 5) a water and concentrated slurry mixing device; 6) a concentrated slurry of carbon substance and / or organic matter or premixed mixed water slurry on-site storage tank during tapping; 7) a ground-made and stored tank and delivery system of concentrated slurry of carbon substance and / or organic matter.

[0029] Figure 2 The schematic diagram of the channel outlet section of a single-channel spray head for three single-sided single-spray-head injection in the injection device of the method for suppressing nitrogen increase and regulating oxygen increase of molten steel during tapping. DETAILED DESCRIPTION

[0030] The method for suppressing nitrogen increase and regulating oxygen increase of molten steel during tapping of the present application uses an injection device to inject water flow or mixed water slurry containing carbon substance / organic matter into the ladle and / or the molten steel stream during the air replacement period before tapping starts and the tapping process, replaces and isolates air in the whole tapping system by evaporation of water vapor, suppresses nitrogen increase of molten steel during the tapping process, and regulates oxygen increase of molten steel during the tapping process by oxidative control of water vapor; specifically: First, water flow or mixed water slurry containing carbon substance / organic matter is injected into the ladle during the air replacement period, and the hot ladle lining stores heat to evaporate water vapor to drive and replace air in the empty ladle and the tapping channel above it.

[0031] Secondly, for steel grades that want or do not care about oxygen increase, water flow is injected into the tapping stream and the ladle during the tapping process, water vapor is evaporated by the heat energy of molten steel to cover the molten steel surface in the ladle, wrap the molten steel stream during tapping, and fill the whole longitudinal columnar space from the molten steel surface of the ladle to the tapping port of the steelmaking furnace, isolating air while also using water vapor covering the molten steel surface and wrapping the molten steel stream to oxidize and increase oxygen in the molten steel.

[0032] In addition, for the steel grade that does not need to increase oxygen, before the molten steel begins to flow out of the taphole and during the subsequent tapping process, (1) continuously add carbonaceous matter and / or concentrated mixed water slurry of organic matter to the sprayed water, or (2) switch to pre-mixed water slurry containing carbonaceous matter and / or organic matter, while covering the molten steel surface in the ladle with water vapor evaporated by using the heat energy of the molten steel, wrapping the molten steel flow during tapping and filling the entire longitudinal columnar space between the molten steel surface of the ladle and the taphole of the steelmaking furnace to isolate air, the heat energy of the molten steel is also used to promote the pyrolysis, carbonization and reduction of water vapor / carbon dioxide of the added carbonaceous matter and / or organic matter, and by changing the total mass ratio of the added carbonaceous matter and / or organic matter in the mixed water slurry, the amount of reducing gas produced is adjusted to adjust the oxidizing property of the water vapor mixed gas, so as to realize the regulation and control of the oxygen increase of the molten steel during the tapping process.

[0033] Further, the flow rate Q and q of water in the air displacement period and the water flow or mixed water slurry during the tapping process are specifically calculated as: Q=Q0+A* (W-100) / 100 +B+C (L / min) and q=q0+ a * (W-100) / 100 +b+c (L / min); wherein W is the molten steel capacity of the ladle, A is a coefficient related to the volume of the ladle, a is a coefficient related to the area of the upper opening of the ladle and the distance between the taphole and the upper opening of the ladle, B and b are the sum of the strictness of the nitrogen increase limit of the steel grade, and C and c are the sum of the current transverse wind speed of the tapping environment (air flow displacement intensity); each coefficient and sum is specifically:

[0034] For a 80-350 ton steelmaking furnace, the water injection flow rate is approximately Q=7-22 L / min and q=3-11 L / min.

[0035] Further, 1) the time t of the air replacement period to pre-inject water flow into the ladle is determined according to the ladle steel holding capacity W (tons), the molten steel density p (tons / m3), the total flow rate Q (L / min) of the injected water flow, and the temperature T reduction of the ladle lining by about 50℃ when the molten steel is discharged after the completion of the steam pre-filling, and the fullness coefficient k is defined as 25%, 30%, 35%, and 40% of the ladle steel holding capacity volume for low, medium, high, and extremely high degrees of nitrogen content limitation requirements, respectively, and the pre-injection time of water flow into the ladle is calculated as t=k* (W / p) *1000 / ((Q / 18)*22.4*(T-50+273) / 298)*60 (seconds); 2) the time of injecting water flow or mixed water slurry into the tundish and the ladle during the tapping process is equivalent to the tapping process time; 3) after the molten steel flows out of the tapping hole, the flow rate Q is maintained for 2-5 seconds according to the nitrogen increase limitation strictness, and then the flow rate q is switched; 4) for steel grades that do not want to increase oxygen, the water is switched to mixed water slurry containing carbon substances and / or organic substances 3 seconds before the molten steel flows out of the tapping hole at the beginning of the tapping; the specific injection start-stop and carbon substance / organic slurry addition or switching can be interlocked with the angle of rotation of the steelmaking furnace during tapping.

[0036] Further, the carbon substance is coal powder, graphite powder, carbon powder, or carbon black, and the organic matter is biomass, petrochemical product waste, or recycled material; the particle size or wire diameter of the processed various substances is not greater than 0.10 mm, and the concentrated slurry is mixed online after being mixed with water or pre-mixed into mixed water slurry with water; the amount of carbon substance and / or organic matter in the mixed water slurry is 10%-30% of the total mass of the mixed water slurry.

[0037] The application of the present application is further described below in combination with the embodiment scheme.

[0038] Example 1 Basic conditions: 300-ton top and bottom combined blown converter, low-oxygen and low-carbon oxygen product molten steel; production of high-grade non-oriented silicon steel, with extremely high nitrogen limitation requirements; ultra-low carbon steel, which needs to be vacuum decarburized after tapping, and wants to moderately increase oxygen; ladle temperature 700℃, industrial water pressure 600kPa, and large wind in the tapping environment.

[0039] Device condition: fixed seat spray gun can swing type single side single double channel spray, all are circular section liquid column flow spray head; D = 3.6 mm larger spray head jet drop point is the cross section center of 1 / 4 height of ladle; D = 2.7 mm smaller spray head jet drop point is the cross section center of 1 / 2 height of water flow drop point; The flow ratio of large and small spray heads is about 2:1; The total area of the outlet cross section of the spray head is 16 square millimeters; Two jets are accurately adjusted to intersect in the empty ladle, which can granulate water droplets through jet interference, reduce the adverse effects of air replacement period pre-spraying on drop point refractory; The system supports adding concentrated slurry containing carbonaceous substances and / or organic matter in the water line to become mixed water slurry with carbonaceous substance and / or organic matter content of 35%.

[0040] Implementation: only spray water; calculate and select Q = 20 liters / min, q = 9 liters / min, k = 40%; Air replacement period pre-spraying time is 14 seconds (water spraying starts simultaneously with the start of the steel tapping and the start of the steel furnace rotation), and the water flow is reduced from Q to q after a 5-second delay after the molten steel flows out of the taphole (the steel furnace is rotated to 78° when the molten steel flows out of the taphole, and the delay is 5 seconds).

[0041] Effect: the nitrogen content of the molten steel during tapping is less than 0.3 ppm, and the oxygen content is increased by 70 ppm.

[0042] Example 2 Basic conditions: 120 tons of top and bottom combined blowing converter, blowing low oxygen and low carbon oxygen product molten steel; production of low carbon high strength structural steel thick slab, with high requirement for nitrogen limitation; hope to reduce the oxygen increase during tapping as much as possible; ladle furnace desulfurization and vacuum degassing; ladle temperature 850℃; industrial water pressure 500kPa; slight wind in the workshop.

[0043] Device condition: fixed seat spray gun can swing type single side single double channel spray, all are circular section liquid column flow spray head; D = 3.6 mm larger spray head jet drop point is the cross section center of 1 / 4 height of ladle; D = 2.7 mm smaller spray head jet drop point is the cross section center of 1 / 2 height of water flow drop point; The flow ratio of large and small spray heads is about 2:1; The total area of the outlet cross section of the spray head is 16 square millimeters; Two jets are accurately adjusted to intersect in the empty ladle, which can granulate water droplets through jet interference, reduce the adverse effects of air replacement period pre-spraying on drop point refractory; The system supports adding concentrated slurry containing carbonaceous substances and / or organic matter in the water line to become mixed water slurry with carbonaceous substance and / or organic matter content of 35%.

[0044] Implementation: Q=10 L / min, q=5.5 L / min, k=40% are selected after calculation, 1) lignite fine powder with particle size less than 0.09 mm is used to make concentrated slurry, the water content of lignite concentrated slurry is 40%, and the mass ratio of 20% lignite powder in the mixed water is selected for pre-injection, or 2) recycled gutter oil residue is used, and the mass ratio of 30% gutter oil residue in the mixed water is selected for pre-injection; the pre-injection time of the air replacement period is 12 seconds (water injection starts when the steel tapping begins and the steelmaking furnace rotates to 15°), and the injection gun is swung up and down during the process to reduce the adverse effects on the refractory material at the jet drop point, and the water flow rate is reduced from Q to q after the molten steel enters the ladle for 4 seconds (the flow rate is switched when the steelmaking furnace rotates to 78° of the outflow of the tundish, and the molten steel flows out for 4 seconds); 40% water-containing lignite concentrated slurry / gutter oil residue is added to the injection water 4 seconds before the molten steel starts to flow out of the tundish (the concentrated slurry starts to be added when the steelmaking furnace rotates to 60°).

[0045] Effect: The nitrogen content of the molten steel increases by less than 0.5 ppm during the tapping process, and the oxygen content increases by not more than 10 ppm.

[0046] Example 3 Basic conditions: 300 tons of top and bottom combined blowing converter, low oxygen and low carbon oxygen product molten steel; production of medium and high grade non-oriented silicon steel, high requirement for nitrogen limitation; ultra-low carbon steel, vacuum decarburization after tapping, and moderate oxygen increase is expected; ladle temperature 700°C; industrial water pressure 400 kPa; wind in the tapping environment.

[0047] Device condition: telescopic and swing single-sided single-channel nozzle gun, using a water droplet-shaped cross-section liquid column flow nozzle at the outlet; nozzle outlet D=2.8 mm, d=1.0 mm, H=9 mm; jet drop point is the cross-sectional center of 1 / 4 height of the ladle; the total cross-sectional area of the nozzle outlet is 16 mm2; the system supports switching water to pre-mixed mixed water slurry containing carbon and / or organic matter.

[0048] Implementation: only water injection; Q=19 L / min, q=7.5 L / min, k=35% are selected after calculation; the pre-injection time of the air replacement period is 12 seconds, and the injection gun is swung up and down during the process to reduce the adverse effects on the refractory material at the jet drop point, and the water flow rate is reduced from Q to q after the molten steel flows out of the tundish for 4 seconds.

[0049] Effect: The nitrogen content of the molten steel increases by less than 0.6 ppm during the tapping process, and the oxygen content increases by 60 ppm.

[0050] Example 4 Basic conditions: 100 tons of electric arc furnace with bottom blowing stirring system, low oxygen and low carbon oxygen product molten steel; production of CQ grade low carbon sheet steel, with limited nitrogen content requirement, but the limitation requirement is low, k=25%; hoping to reduce the oxygen increase during tapping; direct continuous casting after tapping; industrial water pressure 600 kPa, no wind in the tapping environment.

[0051] Equipment specifications: Fully fixed spray gun; dual-sided single-nozzle spray, both with circular cross-section liquid jet nozzles; the larger nozzle with a diameter of 2.2 mm has a jet landing point at the center of the cross-section of 1 / 4 of the ladle height; the smaller nozzle with a diameter of 1.7 mm has a jet landing point at the center of the cross-section of 1 / 2 of the ladle height; the flow rate ratio of the large and small nozzles is approximately 2:1; the total cross-sectional area of ​​the nozzle outlet is 6.07 square millimeters; the system supports switching water to a premixed water slurry containing carbonaceous materials and / or organic matter.

[0052] Implementation plan: After calculation, Q=8 liters / minute, q=3 liters / minute, k=25% are selected; a premixed water slurry is prepared by diluting concentrated papermaking waste liquor with water, wherein the filament diameter of organic materials such as lignin and hemicellulose is 0.05mm and their mass ratio is 10%; the pre-spraying time during the air replacement period is 9 seconds, and the spray water flow rate is reduced from Q to q after the molten steel flows out of the outlet for 2 seconds; 3 seconds before the molten steel flows out of the outlet, the water is switched to contain the premixed water slurry diluted with papermaking waste liquor.

[0053] Results: Nitrogen increase during steel tapping is less than 1.0 ppm, and oxygen increase is no more than 20 ppm.

[0054] Example 5 Basic requirements: 300-ton top and bottom blowing converter, blowing low-oxygen, low-carbon oxygen molten steel; producing IF steel, with high nitrogen restriction requirements; ultra-low carbon steel, which requires vacuum decarburization after tapping, so moderate oxygenation is desired; ladle temperature 700℃; industrial water pressure 600 kPa; light ventilation in the plant.

[0055] Device specifications: Fixed base with swingable spray gun; single-sided single-nozzle spraying, selected as an inverted T-shaped cross-section liquid jet nozzle, D=3 mm, H=13 mm, G=2.3 mm, g=1.0 mm, H / D=4.3, G / g=2.5; total nozzle outlet cross-sectional area is 18 square millimeters; basic jet landing point is the center of the bottom surface of the ladle; the system supports spraying mixed water slurry containing carbonaceous materials and / or organic matter.

[0056] Implementation plan: Water only; after calculation, Q=16 liters / min, q=7 liters / min, k=30; after 4 seconds of molten steel flowing out of the outlet, Q is adjusted to q; during the pre-spraying of the air replacement period, the spray gun is slightly oscillated up and down to reduce the adverse effects on the refractory material at the landing point; Results: Nitrogen increase during steel tapping is less than 0.7 ppm, and oxygen increase is 60 ppm.

[0057] Example 6 Base conditions: 300 tons top and bottom combined blown converter, low oxygen and low carbon oxygen product liquid; production of non-oriented silicon steel, limited nitrogen, strictness medium; need to vacuum decarburization after tapping, do not mind oxygen increase; ladle temperature 700°C; industrial water pressure 400 kilo pascal; tapping environment wind.

[0058] Device conditions: fixed base swing lance, single side single channel nozzle spray, using outlet isosceles trapezoidal cross section liquid column flow nozzle; nozzle outlet D=2.8mm, d=1.0mm, H=9mm; jet drop point is water drop point is the cross section center of 1 / 4 height of ladle; system supports spray mixed water slurry containing carbon and / or organic matter.

[0059] Implementation: only with water; after calculation, select Q=15L / min, q=7L / min, k=30%; air replacement period pre-spray time 11s, after the liquid steel flows out of the tapping hole, delay 3s, spray water flow rate from Q to q, in the process, the lance swings up and down to reduce the adverse effects on the jet drop point refractory.

[0060] Effect: nitrogen increase during tapping process is less than 1ppm.

[0061] The present application is described in detail in connection with specific exemplary embodiments. However, it should be understood that various modifications and variations can be made without departing from the scope of the application as defined by the appended claims. The detailed description and drawings are merely illustrative of the disclosure, rather than limiting, and the scope of the present application should be determined with the term of the appended claims. Any associated modifications and adjustments, without affecting the effects and purposes of the present application, should still fall within the scope of the disclosed technology. Meanwhile, the terms such as "up", "down", "left", "right", "middle" and the like in the specification are only for the convenience of clear description, and are not intended to limit the scope of implementation. The change or adjustment of the relative relationship, without substantially changing the technical content, is also considered as the implementation scope of the present application. In addition, the background is intended to explain the status and significance of the technology, and is not intended to limit the application of the present application or the application field of the present application. More specifically, although the exemplary embodiments of the present application have been described herein, the present application is not limited to these embodiments, but includes any and all embodiments that can be recognized by those skilled in the art according to the foregoing detailed description. The limitations in the claims can be widely interpreted according to the language used in the claims, and are not limited to the examples described in the foregoing detailed description or during the implementation of the application, which should be considered as non-exclusive. Any steps listed in any method or process claim can be performed in any order and is not limited to the order presented in the claim. Therefore, the scope of the present application should be determined only by the appended claims and their legal equivalents, rather than by the description and examples given above. It should be understood that the term "and / or" used herein is a description of the association relationship of the associated objects, which is defined as representing three possible relationships, for example, a and / or b can represent three cases: a exists alone, a and b exist together, and b exists alone; the character " / " in this paper is defined as representing the "or" relationship of the associated objects before and after.

Claims

1. A method for suppressing nitrogen pickup and regulating oxygen pickup of liquid steel during tapping, characterized by: In the air replacement period before the beginning of the tapping of the steelmaking furnace and the tapping process, a water stream or a mixed water slurry containing carbon substances / organic matter is sprayed into the ladle and / or the tapping liquid stream by using a spraying device, the air in the tapping system is replaced by evaporated water vapor, and the external air is isolated, the nitrogen increase of the liquid steel in the tapping process is inhibited, and the oxygen increase of the liquid steel in the tapping process is also regulated by the oxidative control of the evaporated water vapor, specifically: 1) For the steel grade that wants or does not care about the oxygen increase, (1) water stream is sprayed into the ladle in advance in the air replacement period, the air in the empty ladle and the tapping channel above it is driven and replaced by the heat storage and evaporation of water vapor in the hot ladle lining, (2) water stream is sprayed into the tapping stream and / or the ladle in the tapping process, the water vapor is evaporated by the heat energy of the liquid steel to cover the liquid surface in the ladle, wrap the tapping liquid stream and fill the entire longitudinal columnar space from the liquid surface of the ladle to the tapping hole of the steelmaking furnace, (3) while isolating the air to inhibit the nitrogen increase of the liquid steel, the water vapor covering the liquid surface and wrapping the tapping stream is also used to oxidize and increase the oxygen of the liquid steel; 2) For the steel grade that does not want to increase oxygen, (1) water stream or mixed water slurry containing carbon substances and / or organic matter is sprayed into the ladle in advance in the air replacement period to drive and replace the air in the empty ladle and the tapping channel above it, (2) when only water is sprayed in the air replacement period, carbon substances and / or organic matter are added to the water to become a mixed water slurry or the pre-mixed mixed water slurry is switched to be sprayed before the liquid steel flows out of the tapping hole at the beginning of the tapping, (3) the mixed water slurry is continuously sprayed in the entire tapping process, the water vapor is used to cover the liquid surface in the ladle, wrap the tapping liquid stream and fill the entire longitudinal columnar space from the liquid surface of the ladle to the tapping hole of the steelmaking furnace to isolate the air and inhibit the nitrogen increase of the liquid steel, while the heat energy of the liquid steel is used to promote the pyrolysis and carbonization of the mixed carbon substances and / or organic matter, the water vapor and a small amount of carbon dioxide are reduced, and by changing the total mass ratio of the added carbon substances and / or organic matter in the mixed water slurry, the amount of the reduced gas product is correspondingly produced to adjust the oxidizability of the water vapor mixed gas, so as to realize the regulation and control of the oxygen increase of the liquid steel in the tapping process.

2. The method of claim 1, wherein the method is characterized by: The flow rate Q and q of water in the water stream or mixed water slurry sprayed in the air replacement period and the tapping process are specifically calculated and considered as Q=Q0+A* (W-100) / 100 +B+C (L / min) and q=q0+ a * (W-100) / 100 +b+c (L / min); wherein, W is the steel ladle capacity, A is a coefficient related to the volume of the ladle, a is a coefficient related to the area of the upper opening of the ladle and the distance between the tapping hole and the upper opening of the ladle, B and b are the sum of the strictness of the nitrogen increase limit of the steel grade, and C and c are the sum of the current transverse wind speed of the tapping environment (air flow replacement intensity); each coefficient and sum is specifically:

3. A method and apparatus for controlling nitrogen pickup and oxygen pickup of liquid steel during tapping according to claim 1, wherein: 1) The time t of the air replacement period to inject water flow or mixed water slurry containing carbonaceous matter / organic matter into the ladle is based on the ladle steel volume W (tons), the molten steel density p (tons / m3), the total flow rate Q (L / min) of the injected water flow, and the assumption that the steam temperature is about 50℃ lower than the inner lining temperature T of the ladle before tapping after the pre-filling is completed, and the fullness coefficient k is defined as 25%, 30%, 35% and 40% of the volume of the ladle steel, respectively, which is determined by the low, medium, high and extremely high degree of nitrogen content limit requirements of the steel grade, and the corresponding pre-injection time of water flow into the ladle is calculated as t=k* (W / p)*1000 / ((Q / 18)*22.4*(T-50+273) / 298)*60 (seconds); 2) The time of injecting water flow or mixed water slurry containing carbonaceous matter / organic matter into the ladle and / or the tapping molten steel stream during the tapping process is equivalent to the tapping process time; 3) After the molten steel starts to flow out of the tapping hole, the flow rate Q is maintained for 2-5 seconds according to the nitrogen increase limit strictness, and then switched to the flow rate q; 4) For the case of not wanting to increase the oxygen content of the steel grade, the concentrated slurry containing carbonaceous matter and / or organic matter is added to the water or the water is switched to the pre-mixed mixed water slurry containing carbonaceous matter and / or organic matter before the molten steel starts to flow out of the tapping hole 3 seconds before.

4. The method of claim 1, wherein the method is characterized by: The carbonaceous matter is coal powder, graphite powder, carbon powder or carbon black, and the organic matter is biomass, petrochemical product waste or recycled material; the particle size and wire diameter of the processed various substances are not greater than 0.10 mm, and the concentrated slurry is mixed online after being mixed with water or is pre-mixed into a mixed water slurry with water; the amount of carbonaceous matter and / or organic matter in the mixed water slurry is 10%-30% of the total mass of the mixed water slurry.

5. The method of controlling nitrogen pickup and oxygen pickup of liquid steel during tapping according to claim 1, wherein: The basic structure of the injection device is: 1) a fixed / oscillating lance with a nozzle mounted on a fixed / extendable base for injecting water flow or mixed water slurry into the tapping stream and the ladle and positioning and adjusting the landing point; 2) a nozzle for injecting water flow or mixed water slurry into the tapping stream and the ladle; 3) a water flow detection and adjustment system; 4) a carbonaceous matter and / or organic matter concentrated slurry or pre-mixed mixed water slurry pressurized delivery, flow detection and adjustment system for pressurizing the concentrated slurry or pre-mixed mixed water slurry when preparing the mixed water slurry and metering and regulating the flow; 5) a water and concentrated slurry mixing device for improving the uniformity of the mixed water slurry; 6) a concentrated slurry or pre-mixed mixed water slurry of carbonaceous matter and / or organic matter on-site storage tank at the tapping site; 7) a ground-made and stored tank and delivery system for concentrated slurry or pre-mixed mixed water slurry of carbonaceous matter and / or organic matter.

6. The method of claim 5, wherein the method is characterized by: The nozzle is divided into single / dual nozzles for single-sided injection or single nozzles for double-sided injection, and the single-sided single nozzle nozzle is further divided into single-channel or double-channel nozzles.

7. The method of controlling nitrogen pickup and oxygen pickup of liquid steel during tapping according to claim 6, wherein: The single-sided single-jet spray uses a single-channel nozzle with a liquid column flow nozzle with a reverse T-shaped or drop-shaped / isosceles trapezoidal outlet, the cross-sectional shape of the outlet and the size relationship thereof are shown in FIG. 2 of the specification, wherein H / D≥3, D>d, G≥g, the total sum of the outlet cross-sectional area of the nozzle ranges from 6 to 18 square millimeters corresponding to the calculated amount of possible maximum sprayed water during the air displacement period; the various forms of nozzles for various other modes of spraying are all circular cross-section outlet liquid column flow nozzles corresponding to the calculated amount of possible maximum sprayed water during the air displacement period, and the total sum of the outlet cross-sectional area of the nozzle ranges from 6 to 18 square millimeters.

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