CN112458237B

CN112458237B - Steelmaking method for reducing slag quantity and modifying slag components on line

Info

Publication number: CN112458237B
Application number: CN201910851443.4A
Authority: CN
Inventors: 刘浏; 佟溥翘; 胡砚斌; 贾志立
Original assignee: Jiangsu Jicui Metallurgy Technology Institute Co ltd
Current assignee: Jiangsu Jicui Metallurgy Technology Institute Co ltd
Priority date: 2019-09-06
Filing date: 2019-09-06
Publication date: 2022-05-24
Anticipated expiration: 2039-09-06
Also published as: CN112458237A

Abstract

A steelmaking process method suitable for a hot metal three-decarburization pretreatment and converter decarburization duplex process. It is characterized in thatThe molten iron 'three-removal' pretreatment process is adopted, the steel slag reaction efficiency is improved, the slag step cyclic utilization and the on-line slag modification are realized, the steel-making slag quantity is greatly reduced, and the free calcium oxide (CaO) in discharged slag is thoroughly eliminated_f) And (4) content. Adding high alkalinity final slag formed in desulfurization period of decarbonization furnace and three decarbonization furnaces in the desilication period according to the replacement ratio of 2:1 instead of lime]Oxidation to form a large amount of SiO₂Mixing with the added high-alkalinity final slag, melting and realizing on-line modification. Enriching the high alkalinity in CaO_fThe slag is converted into low alkalinity (R is less than or equal to 1.8) to completely eliminate CaO_fThe foamed slag is continuously discharged out of the furnace. Compared with the traditional steelmaking slagging process, the method can reduce the lime consumption by 50-60%; reducing the consumption of other slagging auxiliary materials (such as dolomite, ore or iron scale and the like) by 30-40%; the amount of the discharged steel-making waste slag is reduced to 40kg/t from 100-120 kg/t; thoroughly solves the problem of the CaO of the steel-making slag_fPowdering caused by more than or equal to 2.0 percent.

Description

Steelmaking method for reducing slag quantity and modifying slag components on line

Technical Field

The invention belongs to the field of converter steelmaking, and particularly provides a steelmaking method suitable for a hot metal three-decarburization pretreatment and converter decarburization duplex process. By improving the reaction efficiency of the slag steel, the step cyclic utilization of the slag and the on-line modification of the slag, the slag quantity of the steel-making furnace is greatly reduced, and the free calcium oxide (CaO) in discharged slag is completely eliminated_f) And (4) content.

Technical Field

The essence of steel making is an oxidation purification process, namely, impurities such as carbon, phosphorus, silicon, manganese, chromium, titanium, vanadium and the like in molten iron are subjected to oxidation reaction through oxygen blowing and slagging, and reaction products (except C) enter furnace slag to achieve the aim of purifying the molten steel. The traditional steelmaking method has the following technical problems:

(1) the steel slag has low reaction efficiency and large slag quantity. Taking dephosphorization as an example, the dephosphorization effect and the slag amount are determined by the distribution ratio (L) of phosphorus among slag steels_P＝(％P)/[％P]): when L is_PThe same end point [ P ] was reached for molten irons of the same phosphorus content, at 100 and 200]The former is required to have a slag amount 1 times larger than that of the latter. Similarly, desulfurization under reducing condition, slag-to-steel sulfur ratio (L)_S＝(％S)/[％S]) Is 1000; desulfurization under oxidizing conditions, L_SThe content of the sulfur is only 4-6, which means that the amount of the oxidized desulfurized slag is 160-200 times higher than that of the reduced desulfurized slag on the premise of the same desulfurization effect.

(2) The slag is inconvenient to pour, and the stepped utilization of the slag cannot be realized. The quantity of slag in the steel-making process is determined by the capacity factor and intensity factor of the chemical reaction, i.e.The slag amount is the capacity factor multiplied by the strength factor. Generally, the silicon content of molten iron is 10-20 times of the phosphorus and sulfur content, and silicon is a capacity factor; but the high alkalinity (R is more than or equal to 3.5) required for dephosphorization and desulfurization is 2.5 times of the alkalinity required for desiliconization slag, and the alkalinity is a strength factor. Therefore, the steel making in the conventional converter is the product of the maximum capacity factor and the maximum strength factor, so that the slag quantity is large and is 100-120 kg/t steel. The MURC process developed in Japan divides the steel-making process into two stages of desiliconization, phosphorus stage and decarburization stage, and deslagging is carried out in the middle, as shown in figure 1^[1]. The slag in the decarburization period is completely remained in the furnace for smelting in the next furnace, and the slag amount can be reduced by 20-30% compared with the traditional steelmaking process. But still has low reaction efficiency (L)_PThe improvement is not obvious), the blowing time is prolonged by 5min during intermediate deslagging, the production efficiency of the converter is reduced, and the like.

(3) The final slag discharged from the converter is difficult to use. In order to ensure dephosphorization and desulfurization effects, the alkalinity R is usually more than or equal to 3.5, and the rock phase structure of the slag is C₃S is the main. C₃S is unstable and is converted to CaO. SiO at low temperature₂Or 2 CaO. SiO₂And free calcium oxide CaO_fResulting in a large amount of CaO in the waste converter slag_fCaO, which is very hygroscopic, reacts with water_f+H₂O＝Ca(HO)₂And the volume expansion causes pulverization, so that the application prospect and the use value of the converter slag are limited. In order to solve the problem, steel slag is treated by adopting a slag smoldering process in China, and the effect is good. But for removing CaO_fHas poor effect (CaO after treatment)_fIs 2.63 to 3.27%)^[2](ii) a The 'steam pressure process' developed in Japan adopts a closed container to improve the steam pressure and further reduce CaO_fBut the slag treatment cost is high and the production efficiency is low. German Zernike's test of blowing SiO into the slag of an electric furnace after tapping₂Powder, namely, the high-alkalinity slag is modified into the low-alkalinity slag on line as shown in figure 2, but the industrial production is not realized^[3]。

(4) The large amount of waste high-basicity steel-making slag causes serious environmental pollution. Because the steel-making slag has large quantity and can not be recycled, and the waste slag contains a large amount of CaO_fEasy hydrolysis and pulverization, unstable performance and the like, so that a great amount of steelmaking slag can not produce cement clinker like blast furnace slagAnd can be completely recycled. The waste residues are accumulated or buried deeply, not only occupy a large amount of territorial area, but also form a large amount of fine white powder suspended in the air after pulverization, which is called as white pollution and seriously damages the ecological environment.

In order to solve the technical problems of the traditional steelmaking method, steelmaking workers all over the world seek to improve and optimize the traditional steelmaking process, further improve the reaction efficiency and reduce the slag amount; according to the characteristics of various elementary reactions, the step utilization of the slag is realized, and the CaO in the waste converter slag is thoroughly eliminated by the method of online modification in the furnace_fThe content of the slag improves the recycling value of the waste converter slag.

Disclosure of Invention

1. Principle of the invention

The invention decomposes the traditional converter steelmaking process into two stages of three-removal (namely desiliconization, dephosphorization and desulfurization) pretreatment of molten iron and converter decarburization, thereby realizing duplex production. On the basis, the following core technologies are adopted:

(1) improving the elementary reaction efficiency and reducing the slag quantity: the method utilizes the strong reduction potential under the condition of molten iron, improves the proportion of phosphorus and sulfur between slag and steel and reduces the amount of reaction slag by controlling oxygen blowing, adjusting slag components, strengthening molten pool stirring and other measures; the decarburization furnace adopts a less slag smelting process, and the slag amount is controlled to be less than or equal to 25kg/t steel.

(2) Realizing the stepped recycling of the slag: the technical characteristics of large capacity factor and low alkalinity requirement of the desiliconized slag are utilized, and the high alkalinity slag formed in the desulfurization period of the decarbonization furnace and the three desiliconization furnaces is added in the desiliconization period instead of lime. As the alkalinity R of the final slag of the decarburization furnace or the final slag of the desulfurization period of the three decarburization furnaces is more than or equal to 4.0, compared with the alkalinity R of the slag required by the desilication period of 1.7-1.8, the excess alkalinity is more than or equal to 2.0. Therefore, a 2-ton decarbonizing furnace or desulfurization final slag can be adopted to replace 1 ton of lime, and the addition amount of the lime is reduced.

(3) Realizing on-line slag modification treatment: the desiliconization period adopts an oxygen blowing desiliconization process, and the injected oxygen reacts with the molten steel to generate a large amount of SiO₂：2[O]+[Si]＝(SiO₂). SiO produced by the reaction₂Continuing to react with the slag:

CaO_f+SiO₂＝CaO·SiO₂

3CaO·SiO₂+SiO₂＝2CaO·SiO₂+CaO·SiO₂

2CaO·SiO₂+SiO₂＝2(CaO·SiO₂)

the high-alkalinity decarburization converter slag or the final desulfurization slag is converted into low-alkalinity desilicication slag, and free calcium oxide CaO which is easy to cause slag pulverization is thoroughly eliminated_fAnd (4) content.

(4) The molten iron three-removing pretreatment furnace has the function of continuous slag discharge in the blowing process. After oxygen blowing is started in the desiliconization period, the added slag rapidly reacts with molten iron to form foamed slag. The foaming slag containing a large amount of gas automatically overflows from the furnace door, so that the aim of continuously discharging slag is fulfilled. The slag discharge amount is generally required to be more than or equal to 40 percent of the added slag.

2. Technical invention

The invention is mainly used for the double production process of three-step pretreatment and decarburization converter of molten iron: the 'three-step' of molten iron is mainly used for purifying the molten iron and removing impurities such as sulfur, phosphorus, silicon, titanium and the like in the molten iron; the decarburization converter is mainly used for decarburization and temperature rise. The above two process stages are separately completed in two independent reactors.

The molten iron 'three-removal' reactor has a continuous slag discharge function, and can continuously discharge foam slag in the blowing process without stopping blowing and pouring slag. The decarburization furnace is the same as a conventional converter. The three-stage smelting in the three-removal furnace comprises the following steps: the first stage is a desiliconization stage, pure oxygen is blown and a slagging agent is added for slagging. The second stage and the third stage are dephosphorization and desulfurization stages respectively, and the alkalinity R of the slag is gradually increased and the FeO in the slag is gradually reduced by continuously discharging slag and making new slag. After the blowing of the three-decarburization furnace is finished, the treated molten iron (C is more than or equal to 3.5 percent, Si is less than or equal to 0.1 percent, P is less than or equal to 0.02 percent, S is less than or equal to 0.005 percent, and T is more than or equal to 1300 ℃) is added into a half ladle, and the molten iron is added into a decarburization furnace as soon as possible, oxygen is blown for decarburization, and the temperature is raised. Because the content of the [ Si ] in the molten iron is extremely low, a less-slag smelting process is adopted, the addition amount of lime is controlled to be less than or equal to 10kg/t, the addition amount of other auxiliary materials (such as iron oxide sheets, magnesium balls, light-burned dolomite, fluorite and the like) is controlled to be less than or equal to 10kg/t, the total slag amount is less than or equal to 20kg/t, and the final slag alkalinity R is more than or equal to 4.0. Typical final slag composition is shown in table 1. Tapping steel according to a conventional steel-making method after smelting, splashing slag to protect the furnace after tapping, and pouring out the slag splashed in the furnace. The amount of the slag poured is about 15 kg/t.

TABLE 1 typical composition of final slag of decarburization furnace (%)

CaO	SiO₂	TFe	MnO	MgO	P₂O₅	S	R
								53.75	10.49	21.19	2.08	9.30	2.78	0.057	5.37

The three-step molten iron furnace adopts a slag-remaining and iron-remaining eccentric bottom tapping mode. In order to reduce the slag amount during tapping, the iron content in the furnace is 5-10 tons, and the high-alkalinity desulphurization slag generated in the desulphurization period(R is more than or equal to 4.0, TFe is less than or equal to 5 percent) is completely remained in the furnace, and the weight is about 25-30 kg/t_{Iron (II)}And the slag is used as slag for the next furnace desiliconization period. The desulfurization slag reference composition is listed in table 2.

TABLE 2 typical composition of slag (%) -in desulfurization stage of molten iron "three-step" furnace

CaO	SiO₂	TiO₂	MnO	P₂O₅	S	MgO	TFe	R
									44.41	10.13	0.57	0.46	1.97	0.30	7.47	5.75	4.53

The 'three-step' furnace adopts common blast furnace molten iron as raw material, and the molten iron does not need to be subjected to pre-desiliconization or desulfurization treatment in advance. Before adding iron, adding a proper amount of scrap steel (the ratio of the scrap steel is 10-20%) and 15-20 kg/t of condensed final slag of the decarburization furnace, mixing the final slag with the residual desulfurization slag in the previous furnace, and blowing oxygen to form the desilication slag. When the [ Si ] of the molten iron is less than or equal to 0.4 percent, lime is not added in the desiliconization period; when [ Si ] is more than or equal to 0.4%, a small amount of lime is added properly. The desilication period generally does not need to add other auxiliary slagging materials.

In the desiliconization period, oxygen is blown for about one minute, a large amount of foam slag is formed in the furnace, and slag begins to overflow from the furnace door. The foaming of the slag can be controlled by adjusting the lance position of the oxygen lance according to the slag amount in the furnace, the temperature of the molten pool and the melting rate of the slag, so that the reasonable slag overflow amount is ensured. Namely, the amount of the newly generated slag in the furnace is 40-50 kg/t, the amount of the overflowing slag is 50-60%, and the actual amount of the slag in the furnace is maintained at about 20 kg/t. Typical composition of the desiliconization stage is shown in Table 3.

TABLE 3 typical composition of slag discharged during desilication of molten iron "three-strip" furnace

CaO	SiO₂	TiO₂	MnO	P₂O₅	S	MgO	TFe	R
									29.46	20.01	1.42	1.77	2.06	0.061	10.47	18.39	1.56

In the subsequent dephosphorization period, 10-15 kg/t of lime and other auxiliary slag materials are added according to the reaction requirement, so that the slag amount is further increased, the alkalinity of the slag is increased, the TFe content in the slag is reduced, the foamability of the slag is greatly reduced, and a small amount of foam slag still overflows. As the oxygen blowing amount is reduced to stop oxygen blowing, the foamed slag disappears and the slag overflow is stopped, but the slag amount in the furnace is basically maintained at about 20 kg/t. 5kg/t of Mg/CaO desulfurizer is sprayed in the desulfurization period, and 25kg/t of residue is remained in the furnace.

Fig. 3 shows the variation of the slagging process scheme and the slag formation and discharge amount in the whole steel making process (including the decarburization furnace) under the condition that the [ Si ] of the molten iron is 0.4%. As can be seen from the figure: lime is added into the decarburization furnace at 10kg/t, other slagging auxiliary materials are less than or equal to 10kg/t, the total slag charge is less than or equal to 20kg/t, and the generated slag amount is about 20 kg/t. Wherein 15kg/t is recycled for smelting in a three-removal furnace. Meanwhile, 25kg/t of the desulfurized slag in the previous furnace is left in the furnace. The total amount of generated slag in the desilication period is 50kg/t, wherein 60 percent of slag overflows and is about 30 kg/t. Lime and auxiliary materials are added in the dephosphorization period to be less than or equal to 15kg/t, and the alkalinity of the slag is further increased until R is 2.0-2.5. Wherein the overflowing slag is about 10kg/t (the overflowing slag rate is about 50 percent). After powder injection and desulfurization, no slag overflow is caused, and the amount of slag left in the furnace is 25 kg/t.

Table 3 shows the comparison of the slagging process of the present invention with the conventional steelmaking process (0.4% for liquid iron [ Si ]).

Table 3 comparison of the slagging process of the present invention with the conventional steelmaking process (kg/t, molten iron [ Si ] ═ 0.4%)

As can be seen from the table, the consumption of the lime and the slagging auxiliary materials is respectively 20kg/t, the consumption of the desulfurizer is increased by 5kg/t, the slag is formed by 65kg/t, and the slag is discharged by 40 kg/t. Compared with the traditional steel making, the consumption of lime is reduced by 50 percent, and the consumption of auxiliary materials is reduced by 60 percent. The total discharged slag amount is reduced by 60-70%.

Because the furnace slag modification is carried out in the furnace, the final slag of the high-alkalinity decarbonization furnace and the desulfurization slag of the three-dehydration furnace are converted into the low-alkalinity desilicication slag, and the CaO in the slag is thoroughly eliminated_fThe content of the slag improves the usability of the slag.

Drawings

FIG. 1 schematic diagram of the Japanese MURC process

FIG. 2 shows the principle of the process of blowing oxygen and quartz sand into a slag bath to modify steel slag

FIG. 3 shows the slag-making process and slag-flow diagram (kg/t) of the present invention

Detailed Description

Example 1:

the invention carries out the thermal simulation experiment of the on-line modification of the furnace slag in the molten iron 'three-removal' furnace modified by the 0.5 ton induction furnace, and the converter slag and the desulfurized slag are directly used for the smelting in the desiliconization period of the 'three-removal' furnace instead of lime, and the smelting effect is shown in the table 4.

TABLE 4 thermal simulation test results of 0.5t of the present invention

The test results prove that: the process can realize on-line modification of slag, reduce high-alkalinity slag into low-alkalinity desiliconized slag (R is reduced from average 4.53 to 1.56), and eliminate all free calcium oxide CaO in slag_fSlag lithofacies of calcium silicate, pumice andRO phase is the main phase and is not easy to pulverize. The process adopts the returned slag to replace lime, and still has higher dephosphorization and desulfurization effects in the desiliconization period.

Example 2:

the semi-industrial test of the invention was carried out on a conventional 100t electric furnace: the furnace charge structure of 80 percent of molten iron and 20 percent of scrap steel is adopted, and the electric furnace smelting is divided into a desiliconization period, a dephosphorization period and a decarburization period. The high-alkalinity slag generated in the decarburization period is completely used for smelting in the desilication period, so that the addition amount of lime in the desilication period is reduced, and a large amount of slag is discharged through the foamed slag in the desilication period. As shown in table 5, the results of the test showed that the in-furnace modification of the high-basicity final slag was completed with a decrease in lime consumption, and the basicity of the discharged slag was 0.89 on average.

Table 5100 t electric furnace slag modification test results

Blowing period	SiO₂	Al₂O₃	MgO	MnO	TiO₂	P₂O₅	CaO	T.Fe	R	L
											Final slag of decarburization stage	8.48	1.30	3.88	1.81	0.46	1.30	25.79	41.10	3.09	62.9
Desilication period	14.48	2.04	1.59	3.36	0.98	1.60	13.34	45.82	0.89	12.3

Claims

1. A steel-making method for reducing slag quantity and modifying slag components on line adopts a molten iron 'three-removal' pretreatment process to improve slag steel reaction efficiency, realize slag step cyclic utilization and on-line slag modification, greatly reduce steel-making slag quantity and thoroughly eliminate free calcium oxide CaO in discharged slag_fThe content is characterized in that:

(1) the decarburization furnace adopts 'triple decarburization', namely desilication, dephosphorization and desulfurization molten iron less-slag smelting, the slag amount is less than or equal to 25kg/t, 15-20 kg/t of final slag is remained after slag splashing, the final slag is added into the 'triple decarburization' furnace along with the scrap steel after cooling, and as the alkalinity R of the final slag of the decarburization furnace is more than or equal to 4.0, and the excess alkalinity is more than or equal to 2.0 compared with the alkalinity R of the slag in the desilication period which is 1.8, 1 ton of lime is replaced by 2 tons of slag;

(2) the 'three-step-removing' furnace is smelted in three stages, namely a desiliconization stage, a dephosphorization stage and a desulfurization stage, the slag alkalinity is increased along with smelting, the TFe in the slag is gradually reduced, finally, low FeO desulfurization reducing slag with the high alkalinity R being more than or equal to 4.0 is formed, the mode of slag-remaining and iron-remaining eccentric bottom tapping is adopted, all the desulfurization slag in the furnace is reserved in the desiliconization stage of the next furnace to be used instead of lime, and the replacement ratio is 2: 1;

(3) the slag modification is realized on line in the desiliconization period, and the CaO rich in free calcium oxide with high alkalinity R being more than or equal to 4.0_fThe final slag and the desulfurized slag of the decarburization furnace are modified into the desilicated slag with low alkalinity R less than or equal to 1.8, and CaO in the slag is thoroughly removed_f；

(4) The three-de-aeration furnace has the function of automatically discharging slag and blowing oxygen into the iron oxide water during the de-aeration period]Formation of SiO₂The slag is melted and modified to form foam slag mainly containing calcium silicate, a pumice and an RO phase, and the foam slag automatically overflows from a furnace mouth, and the slag discharge amount is more than or equal to 40 percent of the slag.

2. The steelmaking method for reducing the on-line modification of the slag quantity and the slag components as claimed in claim 1, wherein the steelmaking slagging process is provided with the following specific characteristics:

(1) adding all the residual final slag in the decarburization furnace in the desilication period of the third decarburization furnace according to the replacement ratio of the slag to the lime of 2: 1;

(2) replacing part of lime by all the residual semi-liquid desulfurized slag in the desulfurization period of the third desulfurization furnace according to the ratio of 2:1 to the lime;

(3) when the silicon content in the molten iron is less than or equal to 0.4 percent, no slag-making material is added in the desiliconization period; when the content of [ Si ] is more than 0.4%, a small amount of lime and other auxiliary slag-making materials are added;

(4) oxygen blowing iron oxide water [ Si ] in desiliconization period]Formation of SiO₂Mixing with various added slags, reacting to modify the slags on line to form low basicity R less than or equal to 1.8 and free calcium oxide CaO_fDischarging the desiliconized slag;

(5) the foam slag generated by oxygen blowing in the desiliconization period is utilized to carry out continuous slag discharge in the blowing process, and the slag foaming is controlled by adjusting the lance position of an oxygen lance, so that the slag discharge rate of the overflowed slag is ensured to be more than or equal to 40 percent.