BLOWING CONTROL METHOD FOR MAINTAINING MUSHROOM HEAD OF BOTTOM-BLOWING NOZZLE CONVERTER

Abstract

A blowing control method for maintaining a mushroom head of a bottom-blowing nozzle converter is disclosed. Considering the actual state of the mushroom head at the end of the bottom-blowing nozzle tip, the real-time molten steel overheating change during the blowing process, the process requirements of different stages of blowing conversion, and the macroscopic heat balance of the converter, the oxygen-carbon dioxide-lime powder blowing parameters of the inner tube of the bottom-blowing nozzle are dynamically adjusted during the converter smelting process of the bottom-blowing nozzle converter so as to control the cooling intensity, thus achieving precise control of the size of the mushroom head. The present invention maintains the basic stability of the size of the mushroom head at the end of the bottom-blowing nozzle tip, avoiding nozzle blockage caused by an oversized mushroom head and rapid erosion of the nozzle caused by an undersized mushroom head.

Claims

1. A blowing control method for maintaining a mushroom head of a bottom-blowing nozzle converter, comprising the following steps: (1) before smelting of the bottom-blowing nozzle converter, measuring a gas flow rate and a gas pressure of a narrow annuli channel blowing by a nozzle, and calculating a state coefficient of the mushroom head; (2) after smelting of the bottom-blowing nozzle converter, oxygen is used as a carrier gas to spray-blow a lime powder; after spray-blowing the lime powder, mixing the oxygen with a same amount of carbon dioxide to form a carbon dioxide-oxygen mixed gas and continuing spray-blowing until the end of the smelting process to maintain the mushroom head of the bottom-blowing nozzle converter; according to the state coefficient of the mushroom head and a blowing strength during, adjusting the blowing intensity of carbon dioxide in the smelting process; a molten steel overheating degree ΔT being calculated according to Formula 1:
ΔT=T−Tu  (Formula 1) wherein, T is a temperature of molten steel during the smelting process; Tu is calculated according to formula 2:
Tu=1536.6−88×ω[C]−8×ω[Si]−5×ω[Mn]−30×ω[P]  (Formula 2) wherein, ω[C] is a mass fraction of carbon in molten steel, ω[Si] is a mass fraction of silicon in molten steel, ω[Mn] is a mass fraction of manganese in molten steel, and ω[P] is a mass fraction of phosphorus in molten steel.

2. The method according to claim 1, wherein, in step (1), the gas flow rate is Q, the gas pressure is P, a ratio of Q and P is defined as actual flow pressure ratio ε.sub.A, a ratio of the actual flow pressure ratio ε.sub.A to a reference flow pressure ratio ε.sub.R is defined as mushroom head state coefficient η.

3. The method according to claim 2, wherein the reference flow pressure ratio
ε.sub.R=α×ε.sub.u, ε.sub.u is a flow pressure ratio of the end of the narrow annuli channel blowing by the nozzle freely; α ranges 0.6 to 0.7.

4. The method according to claim 1, wherein in step (2), a steelmaking control system is used to obtain a real-time composition and temperature T of the molten steel; the molten steel composition includes the mass fraction of carbon in molten steel ω[C], the mass fraction of silicon ω[Si], the mass fraction of manganese ω[Mn], and the mass fraction of phosphorus ω[P].

5. The method according to claim 1, wherein in step (2), oxygen is the carrier gas when spray-blowing the lime powder, a blowing intensity of oxygen ranges from 0.8 to 1.2 (Nm.sup.3/t/min), a blowing intensity of the lime powder ranges from 4 to 6 (kg/t/min).

6. The method according to claim 1, wherein, step (2) comprising, after blowing the lime powder, at the same time, spray-blowing carbon dioxide.

7. The method according to claim 1, wherein, in step (2), adjusting the blowing intensity of carbon dioxide comprises: if the molten steel is overheated at ΔT≤100° C., the blowing intensity of carbon dioxide is I=η×I.sub.R; if the molten steel is overheated at 100° C.<ΔT≤150° C., the blowing intensity of carbon dioxide is I=1.5×η×I.sub.R; if the molten steel is overheated at ΔT>150° C., the blowing intensity of carbon dioxide is I=2×η×I.sub.R; I.sub.R is a reference blowing intensity of carbon dioxide.

8. The method according to claim 1, wherein the reference blowing intensity of carbon dioxide ranges from 0.2 to 0.3 Nm.sup.3/t/min.

Description

EXAMPLES OF THE INVENTION

Detailed Description of the Examples

[0034] The invention is based on the actual state, variations of the molten steel overheating degree of the mushroom head during blowing process, the needs of the different blowing stages and the macro heat balance of the converter. The cooling intensity of the end of the bottom-blowing nozzle in stages is dynamically adjusted based on the actual state of the mushroom head, the change of molten steel superheat in the blowing process and the steelmaking process requirements, thereby controlling the growth rate of the mushroom head. The invention dynamically adjusts the cooling intensity of the bottom blowing nozzle according to the change in the degree of molten steel superheat, which can effectively stabilize the size of the mushroom head and reduce the amount of carbon dioxide used.

[0035] The bottom blowing of the bottom-blowing nozzle converter is a double-layer casing structure, in which the inner tube is used to blowing carbon dioxide, oxygen and lime powder, and the annular seam between the inner tube and the outer tube is used to blowing cooling media such as natural gas and nitrogen. The oxygen sprayed by the inner tube is the main source of heat release. The carbon dioxide and lime powder sprayed by the inner tube have different degrees of cooling effect. The present invention adjusts the bottom blowing nozzle by adjusting the mixed blowing parameters of oxygen, carbon dioxide and lime powder in the inner tube. The cooling strength of the end; but the mixing ratio and mixing timing of carbon dioxide and lime powder are very important, otherwise it will destroy the heat balance of the converter steelmaking and increase the consumption of raw and auxiliary materials for the converter steelmaking.

Example 1

[0036] The present invention was applied to a 120-ton bottom-spraying converter. The bottom-blowing nozzle was a double-layer casing structure. The inner pipe channel of the bottom-blowing nozzle was used to blowing oxygen, carbon dioxide and lime powder. The total blowing intensity of oxygen and carbon dioxide designed to be 1.0 Nm.sup.3/t/min, and the blowing intensity of lime powder was designed to be 6 kg/t/min; nitrogen as a cooling protection gas blowing by the narrow annuli channel, the blowing intensity of nitrogen was 0.2 Nm.sup.3/t/min. In addition, in order to increase the oxygen intensity and speed up the smelting rhythm, the converter uses a four-hole supersonic oxygen lance for top-blowing oxygen, and the top-blowing intensity of oxygen was 2.5 Nm.sup.3/t/min.

[0037] Testing the flow rate of narrow annuli channel was 24 Nm.sup.3/t/min before installing the bottom-blowing nozzle, the pressure was 0.8 MPa, the flow-pressure ratio (ε.sub.u) in the unobstructed state was 30, nitrogen as a cooling protection gas, the conversion factor α was 0.6, the reference flow pressure ratio ε.sub.R was 18, the reference blowing intensity of carbon dioxide I.sub.R was 0.3 Nm.sup.3/t/min. The smelting step of any of the furnaces of the converter was taken as an example. The specific steps were as follows:

[0038] (1) Before smelting of the bottom-blowing nozzle converter, reading the gas flow rate was 24 Nm.sup.3/t/min, and gas pressure was 1.0 MPa, the actual flow pressure ratio ε.sub.A was 24, the mushroom head state coefficient η=ε.sub.A/ε.sub.R=24/18=4/3, indicates that the size of the mushroom head was smaller.

[0039] (2) Before smelting of the bottom-blowing nozzle converter, the steelmaking control system calculates the total amount of lime powder this time according to structure and composition of the furnace charge M.sub.CaO was 30 kg/t steel.

[0040] After smelting of the bottom-blowing nozzle converter, oxygen was the carrier gas when spray blowing lime powder, the blowing intensity of oxygen was 1.0 Nm.sup.3/t/min, the blowing intensity of lime powder was 6 kg/t/min, cooling the bottom blowing nozzle uses the physical endothermic effect of the temperature rise of the lime powder. After 5 minutes of continuous powder spraying, the amount of lime powder blowing reaches the total amount of lime powder calculated by the steelmaking control system, and the lime powder spraying was stopped at this time.

[0041] (3) In the smelting of the bottom-blowing nozzle converter, using the steelmaking control system to obtain real-time composition and temperature T of molten steel; the mass fraction of carbon in molten steel ω[C], the mass fraction of silicon ω[Si], the mass fraction of manganese ω[Mn], and the mass fraction of phosphorus ω[P]. The steelmaking control system calculates the solidification temperature Tu (Formula 2) of molten steel according to the composition of the molten steel, and according to the temperature T of molten steel, calculates the real-time molten steel overheating degree ΔT (Formula 1).

ΔT=T−Tu  (Formula 1)

Tu=1536.6−88×ω[C]−8×ω[Si]−5×ω[Mn]−30×ω[P]  (Formula 2)

[0042] Start spraying carbon dioxide while stopping the lime powder spraying. The oxygen was replaced by the same amount of carbon dioxide. The real-time molten steel overheating degree was 90° C. The blowing intensity of carbon dioxide, I=η×I.sub.R=4/3×0.3=0.4 Nm.sup.3/t/min. Correspondingly the blowing intensity of oxygen was reduced from 1.0 Nm.sup.3/t/min to 0.6 Nm.sup.3/t/min; when the converter smelting time last for 11 min, the real-time molten steel overheating degree calculated by the bottom blowing control system over 100° C., the blowing intensity of carbon dioxide increases to I=1.5×η×I.sub.R=1.5×4/3×0.3=0.6 Nm.sup.3/t/min, Correspondingly the blowing intensity of oxygen was reduced to 0.4 Nm.sup.3/t/min; when the converter smelting time last for 16.5 min, the composition and temperature of the molten steel reach the tapping standard, the bottom blowing of oxygen and carbon dioxide was stopped, and the converter was tapped. During this period, the real-time molten steel overheating degree under 150° C. (over 100° C.), the bottom blowing of carbon dioxide was maintained at 0.6 Nm.sup.3/t/min.

[0043] After smelting, the actual flow pressure ratio of the narrow annuli channel ε.sub.A was reduced to 19. The implementation results show that the size of the mushroom head at the end of the bottom blowing nozzle increases after the blowing method of the present invention was used, which was close to the reference state, which avoids The nozzle was severely corroded due to the too small size of the mushroom head, which effectively protects the bottom blowing nozzle in time.

Control Example 1

[0044] Selecting the 120-ton bottom-spraying converter was as the same specifications with Example 1. The bottom-blowing nozzle specifications were the same, the reference flow pressure ratio ε.sub.R was 18. The actual flow pressure ratio ε.sub.A was 23; the molten steel was the same.

[0045] The existing method was adopted for smelting. The inner pipe channel of the bottom blowing nozzle was used to blowing oxygen and lime powder. The blowing intensity of lime powder was designed to be 6 kg/t/min, and the blowing intensity of oxygen was designed to be 1.0 Nm.sup.3/t/min, no carbon dioxide was blown during the whole process; the narrow annuli channel blowing by the nozzle was used to spray nitrogen which as a cooling protection gas, and the blowing intensity of nitrogen was 0.2 Nm.sup.3/t/min. In addition, in order to increase the oxygen intensity and speed up the smelting rhythm, the converter uses a four-hole supersonic oxygen lance for top-blowing oxygen, and the top-blowing intensity of oxygen was 2.5 Nm.sup.3/t/min.

[0046] Before smelting of the bottom-blowing nozzle converter, the steelmaking control system calculates the total amount of lime powder this time according to structure and composition of the furnace charge M.sub.CaO was 30 kg/t steel. After smelting, the actual flow pressure ratio of the narrow annuli channel ε.sub.A was reduced to 29. The actual flow pressure ratio was further increased, and it was close to the flow pressure ratio in the unobstructed state. It explained that the size of the mushroom head was too small to protect the bottom blowing nozzle.

Control Example 2

[0047] Selecting the 120-ton bottom-spraying converter was as the same specifications with Example 1. The bottom-blowing nozzle specifications were the same, the reference flow pressure ratio ε.sub.R was 18. The actual flow pressure ratio ε.sub.A was 24; the molten steel was the same.

[0048] The inner pipe channel of the bottom blowing nozzle was used to blowing oxygen, carbon dioxide and lime powder. The blowing intensity of lime powder was designed to be 6 kg/t/min, and the blowing intensity of oxygen and carbon dioxide were designed to be 1.0 Nm.sup.3/t/min, wherein the blowing intensity of oxygen was 0.4 Nm.sup.3/t/min, the blowing intensity of carbon dioxide was 0.6 Nm.sup.3/t/min. The mixture ratio of oxygen and carbon dioxide remains unchanged during the blowing process. The narrow annuli channel blowing by the nozzle was used to spray nitrogen which as a cooling protection gas, and the blowing intensity of nitrogen was 0.2 Nm.sup.3/t/min. In addition, in order to increase the oxygen intensity and speed up the smelting rhythm, the converter uses a four-hole supersonic oxygen lance for top-blowing oxygen, and the top-blowing intensity of oxygen was 2.5 Nm.sup.3/t/min.

[0049] Before smelting of the bottom-blowing nozzle converter, the steelmaking control system calculates the total amount of lime powder this time according to structure and composition of the furnace charge M.sub.CaO was 30 kg/t steel. After smelting, the actual flow pressure ratio of the narrow annuli channel ε.sub.A was reduced to 14. This means that the bottom-blowing nozzle was partially blocked; at the same time, carbon dioxide causes an increase in heat loss of the molten steel, and the molten steel temperature decreased by 32° C. when the steel was discharged.

Example 2

[0050] The present invention was applied to a 300-ton bottom-spraying converter. The bottom-blowing nozzle was a double-layer casing structure. The inner pipe channel of the bottom-blowing nozzle was used to blowing oxygen, carbon dioxide and lime powder. The total blowing intensity of oxygen and carbon dioxide designed to be 1.0 Nm.sup.3/t/min, and the blowing intensity of lime powder was designed to be 5 kg/t/min; nitrogen as a cooling protection gas blowing by the narrow annuli channel, the blowing intensity of Gas was 0.1 Nm.sup.3/t/min. In addition, in order to increase the oxygen intensity and speed up the smelting rhythm, the converter uses a six-hole supersonic oxygen lance for top-blowing oxygen, and the top-blowing intensity of oxygen was 2.4 Nm.sup.3/t/min.

[0051] Testing the flow rate of narrow annuli channel was 30 Nm.sup.3/t/min before installing the bottom-blowing nozzle, the pressure was 0.65 MPa, the flow-pressure ratio (ε.sub.u) in the unobstructed state was 46, nitrogen as a cooling protection gas, the conversion factor was 0.7, the reference flow pressure ratio ε.sub.R was 32, the reference blowing intensity of carbon dioxide I.sub.R was 0.2 Nm.sup.3/t/min.

[0052] The smelting step of any of the furnaces of the converter was taken as an example. The specific steps were as follows:

[0053] (1) Before smelting of the bottom-blowing nozzle converter, reading the gas flow rate was 30 Nm.sup.3/t/min, and gas pressure was 1.2 MPa, the actual flow pressure ratio ε.sub.A was 25, the mushroom head state coefficient η=ε.sub.A/ε.sub.R=25/32=0.78, indicates that the size of the mushroom head was over big.

[0054] (2) Before smelting of the bottom-blowing nozzle converter, the steelmaking control system calculates the total amount of lime powder this time according to structure and composition of the furnace charge M.sub.CaO was 28 kg/t steel.

[0055] (3) In the smelting of the bottom-blowing nozzle converter, using the steelmaking control system to obtain real-time composition and temperature T of molten steel; the mass fraction of carbon in molten steel ω[C], the mass fraction of silicon ω[Si], the mass fraction of manganese ω[Mn], and the mass fraction of phosphorus ω[P]. The steelmaking control system calculates the solidification temperature Tu (Formula 1) of molten steel according to the composition of the molten steel, and according to the temperature T of molten steel, calculates the real-time molten steel overheating degree ΔT (Formula 2).

ΔT=T−Tu  (Formula 1)

Tu=1536.6−88×ω[C]−8×ω[Si]−5×ω[Mn]−30×ω[P]  (Formula 2)

[0056] (4) After smelting of the bottom-blowing nozzle converter, oxygen was the carrier gas when spray blowing lime powder, the blowing intensity of oxygen was 1.0 Nm.sup.3/t/min, the blowing intensity of lime powder was 5 kg/t/min, cooling the bottom blowing nozzle uses the physical endothermic effect of the temperature rise of the lime powder. After 5.6 minutes of continuous powder spraying, the amount of lime powder blowing reaches the total amount of lime powder calculated by the steelmaking control system, and the lime powder spraying was stopped at this time.

[0057] (5) Start spraying carbon dioxide while stopping the lime powder spraying. The oxygen was replaced by the same amount of carbon dioxide. The real-time molten steel overheating degree was 83° C. The blowing intensity of carbon dioxide, I=η×I.sub.R=0.78×0.2=0.156 Nm.sup.3/t/min. Correspondingly the blowing intensity of oxygen was reduced from 1.0 Nm.sup.3/t/min to 0.844 Nm.sup.3/t/min; when the converter smelting time last for 10.5 min, the real-time molten steel overheating degree calculated by the bottom blowing control system over 100° C., the blowing intensity of carbon dioxide increases to I=1.5×η×I.sub.R=1.5×0.78×0.2=0.234 Nm.sup.3/t/min, Correspondingly the blowing intensity of oxygen was reduced to 0.766 Nm.sup.3/t/min; While the converter smelting time last for 16 min, the real-time temperature of the molten steel overheating over 150° C., the bottom blowing of carbon dioxide was increased at I=2×η×I.sub.R=2×0.78×0.2=0.312 Nm.sup.3/t/min, correspondingly the blowing intensity of oxygen was reduced to 0.688 Nm.sup.3/t/min; While the converter smelting time last for 17.5 min, the composition and temperature of the molten steel reached the tapping standard and the stopped blowing oxygen and carbon dioxide, steel production from the converter.

[0058] After smelting, the actual flow pressure ratio of the narrow annuli channel ε.sub.A was raised to 31. The implementation results show that the size of the mushroom head at the end of the bottom blowing nozzle was reduced after adopting the blowing method of the present invention, which was close to the reference state. Avoid nozzle clogging due to oversized mushroom heads, and maintain the basic stability of mushroom head size.

Example 3

[0059] The present invention was applied to a 120-ton bottom-spraying converter. The bottom-blowing nozzle was a double-layer casing structure. The inner pipe channel of the bottom-blowing nozzle was used to blowing oxygen, carbon dioxide and lime powder. The total blowing intensity of oxygen and carbon dioxide designed to be 1.0 Nm.sup.3/t/min, and the blowing intensity of lime powder was designed to be 6 kg/t/min; nitrogen as a cooling protection gas blowing by the narrow annuli channel, the blowing intensity of nitrogen was 0.2 Nm.sup.3/t/min. In addition, in order to increase the oxygen intensity and speed up the smelting rhythm, the converter uses a four-hole supersonic oxygen lance for top-blowing oxygen, and the top-blowing intensity of oxygen was 2.5 Nm.sup.3/t/min.

[0060] Testing the flow rate of narrow annuli channel was 24 Nm.sup.3/t/min before installing the bottom-blowing nozzle, the pressure was 0.8 MPa, the flow-pressure ratio (ε.sub.u) in the unobstructed state was 30, nitrogen as a cooling protection gas, the conversion factor was 0.6, the reference flow pressure ratio ε.sub.R was 18, the reference blowing intensity of carbon dioxide I.sub.R was 0.3 Nm.sup.3/t/min.

[0061] Taken the first furnace smelted after the converter was replaced with a new bottom blowing nozzle as an example. The specific steps were as follows:

[0062] (1) Because a newly replaced bottom blowing nozzle, there was no mushroom head covering the end of the bottom blowing nozzle before the first furnace was smelted. It was in the unobstructed state, so the actual flow pressure ratio ε.sub.A was 30, the mushroom head state coefficient η=ε.sub.A/ε.sub.R=30/18/5/3.

[0063] (2) Before smelting of the bottom-blowing nozzle converter, the steelmaking control system calculates the total amount of lime powder this time according to structure and composition of the furnace charge M.sub.CaO was 30 kg/t steel.

[0064] After smelting of the bottom-blowing nozzle converter, oxygen was the carrier gas when spray blowing lime powder, the blowing intensity of oxygen was 1.0 Nm.sup.3/t/min, the blowing intensity of lime powder was 6 kg/t/min, cooling the bottom blowing nozzle uses the physical endothermic effect of the temperature rise of the lime powder. After 5 minutes of continuous powder spraying, the amount of lime powder blowing reaches the total amount of lime powder calculated by the steelmaking control system, and the lime powder spraying was stopped at this time.

[0065] (3) In the smelting of the bottom-blowing nozzle converter, using the steelmaking control system to obtain real-time composition and temperature T of molten steel; the mass fraction of carbon in molten steel ω[C], the mass fraction of silicon ω[Si], the mass fraction of manganese ω[Mn], and the mass fraction of phosphorus ω[P]. The steelmaking control system calculates the solidification temperature Tu (Formula 1) of molten steel according to the composition of the molten steel, and according to the temperature T of molten steel, calculates the real-time molten steel overheating degree ΔT (Formula 2).

ΔT=T−Tu  (Formula 1)

Tu=1536.6−88×ω[C]−8×ω[Si]−5×ω[Mn]−30×ω[P]  (Formula 2)

[0066] Start spraying carbon dioxide while stopping the lime powder spraying. The oxygen was replaced by the same amount of carbon dioxide. The real-time molten steel overheating degree was 90° C. The blowing intensity of carbon dioxide, I=1.5×η×I.sub.R=5/3 0.3=0.5 Nm.sup.3/t/min. Correspondingly the blowing intensity of oxygen was reduced from 1.0 Nm.sup.3/t/min to 0.5 Nm.sup.3/t/min; when the converter smelting time last for 11 min, the real-time molten steel overheating degree calculated by the bottom blowing control system over 100° C., the blowing intensity of carbon dioxide increases to I=1.5×η×I.sub.R=1.5×5/3×0.3=0.75 Nm.sup.3/t/min, correspondingly the blowing intensity of oxygen was reduced to 0.25 Nm.sup.3/t/min; when the converter smelting time last for 16.5 min, the composition and temperature of the molten steel reach the tapping standard, the bottom blowing of oxygen and carbon dioxide was stopped, and the converter was tapped. During this period, the real-time molten steel overheating degree under 150° C., the bottom blowing of carbon dioxide was maintained at 0.75 Nm.sup.3/t/min.

[0067] After smelting, the actual flow pressure ratio of the narrow annuli channel ε.sub.A was reduced to 22. It shows that the end of the bottom-blowing nozzle had been covered by the mushroom head, which can form protection for the bottom blowing nozzle and inhibit its erosion; in addition, the actual flow pressure ratio at the end of the first furnace smelting was still slightly larger than the benchmark flow pressure ratio, and the blowing control method of the present invention can be continued in the subsequent furnace times to effectively regulate the mushroom head size to the benchmark state and basically keep it stable.

[0068] The implementation results show that the size of the mushroom head at the end of the bottom blowing nozzle increases after the blowing method of the present invention was used, which was close to the reference state, which avoids that the nozzle was severely corroded due to the too small size of the mushroom head, which effectively protects the bottom blowing nozzle in time.

[0069] After adopting the blowing method of the present invention, the life of this bottom-blowing powder converter reached more than 2000 furnaces (still available at 2000 furnaces), which were more than 500 furnaces higher than the traditional blowing method (the same new bottom-blowing nozzle converter).

[0070] The specific examples described above provide a quantitative and detailed description of the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above-mentioned were only specific examples of the present invention and were not intended to limit the present invention.

[0071] In the present invention, nearby the bottom blowing nozzle, the heat source was the reaction exothermic heat between the inner tube O.sub.2 and molten steel, the convective heat transfer of high temperature molten steel, and the cold source was the heat absorption of the reaction between the inner tube CO.sub.2 and molten steel, and the temperature of the inner tube lime powder The physical endothermic, the reaction endothermic of the cracking of natural gas in the annular joint, and the physical endothermic of the heating of the annular joint nitrogen, promote the condensation of molten steel into metal mushroom heads by limiting the injection parameters of the cold source and the heat source; a large number of research and production practices had shown that in the converter during the blowing process, the degree of superheat of the molten steel changes. The present invention dynamically adjusted the cooling intensity of the bottom blowing nozzle according to the change of the degree of superheat of the molten steel, which can effectively stabilize the mushroom head size and reduced the amount of carbon dioxide used, which solved the prior art due to the endothermic characteristics of CO.sub.2 reaction, CO.sub.2 blowing would reduce the problem of excess heat in the converter.