CN104884641A - Molten iron pre-treatment method - Google Patents

Abstract

A molten iron pre-treatment method for performing desiliconization and dephosphorization of molten iron using a single converter-type refining furnace by supplying an oxygen source to the molten iron in the converter-type refining furnace to desiliconize same, then discharging some of the slag present in the furnace while retaining the molten iron inside the furnace, and subsequently supplying a CaO solvent and an oxygen source into the converter-type refining furnace and tapping the dephosphorized molten iron from the converter-type refining furnace. By analyzing the concentration of at least one carbon atom-containing gaseous species in suctioned gas drawn using an exhaust gas treatment device of the converter-type refining furnace during the desiliconization and determining the desiliconization completion time point on the basis of said analysis value, the subsequent dephosphorization process can be performed at low cost while limiting decreases in molten iron temperature.

Description

The pretreatment process of molten iron

Technical field

The present invention relates to the pretreatment process that use converter type refining furnace carries out the desiliconization process of molten iron and the molten iron of dephosphorization treatment continuously, and between desiliconization process and dephosphorization treatment, accompany middle deslagging operation.

Background technology

Be strongly required the quantity discharged of minimizing greenhouse gases in recent years, in steel industry, when carrying out dephosphorization treatment and Decarburising and refining etc. with the processing vessel such as converter, molten iron boiler, in the molten iron in stove, coordinate the cold iron sources such as iron filings, thus reduce the energy required for iron and steel manufacture.This is because, the cold iron source ferric oxide such from the iron ore be encased in blast furnace is different, it does not need reduction, therefore with the pig iron from blast furnace casting is carried out to refining to manufacture compared with molten steel, greenhouse gas emission amount that can be few, less with less energy consumption manufactures molten steel.

In addition, in recent years, before implementing the Decarburising and refining in converter, pre-treatment is implemented to molten iron, thus remove the method for refining (also referred to as " pre-dephosphorization treatment ") of the phosphorus in molten iron in advance, because the method is favourable in cost and in quality.In general, dephosphorization treatment is carried out as follows: add in molten iron by oxygenant (oxygen source such as oxygen) and dephosphorization refining agent (CaO system fusing assistant), utilize oxygenant that the phosphorus oxidation in molten iron is formed phosphorous oxides, in dephosphorization refining agent after making it absorb dregs again, from thermodynamics, for this dephosphorisation reaction, refining temperature is more low more favourable.That is, the molten iron stage that temperature is lower than the molten steel stage is easy carries out dephosphorisation reaction, can carry out dephosphorization treatment with less oxygenant and dephosphorization refining agent.Therefore, by carrying out above-mentioned pre-dephosphorization treatment, although treatment process increases to some extent, the slag generation of steel refining operation entirety processed can be reduced.

But contain the silicon of about 0.3 ~ 0.6 quality % from the molten iron of blast furnace casting, when carrying out dephosphorization treatment to the molten iron containing silicon, first oxidation removing silicon, the silicon concentration in molten iron is reduced to a certain degree, reoxidizes the phosphorus in removing molten iron.By the oxidation of above-mentioned silicon, generate with SiO ₂for the slag of principal constituent, this slag can hinder dephosphorisation reaction.This is because, in order to carry out dephosphorisation reaction, need basicity ([CaO (quality %)]/[SiO ₂(quality %)]) be more than 1.2 slag, and on the other hand, the SiO generated by the oxidation of silicon ₂there is the effect reducing basicity of slag.

For the Steel Refining operation be made up of the combination of blast furnace-converter, the melting thermal source of the cold iron sources such as iron filings is combustions heat of carbon in the sensible heat and molten iron had based on molten iron and silicon, substantially cannot melt a large amount of cold iron sources.And, when implementing as mentioned above as to the pretreated desiliconization process of molten iron and dephosphorization treatment, not only along with adding for the treatment of process, molten iron temperature is declined, and oxidized and reduce in above-mentioned desiliconization process and dephosphorization treatment as the carbon in the molten iron of combustion heat source and silicon, the melting therefore for the cold iron source in converter is more unfavorable.

Therefore, when carrying out hot metal pretreatment, in order to melt more cold iron source, in patent documentation 1, such as propose the pretreatment process of following molten iron: when use converter type refining furnace carries out desiliconization, the dephosphorization treatment of molten iron, first, the feed rate of CaO system fusing assistant is regulated to carry out desiliconization process, and the basicity of slag enters into the scope of 0.3 ~ 1.3 at the end of making desiliconization process, then make refining furnace deflection and discharge the slag generated in stove from fire door, then, the new CaO system fusing assistant that adds carries out dephosphorization treatment.In addition, the pretreatment process of following molten iron is proposed: when use converter type refining furnace carries out desiliconization, the dephosphorization treatment of molten iron in patent documentation 2, in end dephosphorization treatment after tapping molten iron, do not discharge slag and in refining furnace, load the molten iron of following core with the state remained in stove, desiliconization process is carried out for oxygen supply, after desiliconization process, brief interruption blowing be set and discharge the middle deslagging operation of slag, then proceeding dephosphorization treatment.

For the technology of above-mentioned patent documentation 1, by carrying out desiliconization process and dephosphorization treatment in a converter type refining furnace, can prevent the temperature caused because of the transfer of molten iron from declining; In addition, for the technology of patent documentation 2, except above-mentioned effect, the slag that dephosphorization treatment can also be produced in desiliconization process is (following, also referred to as " dephosphorization slag ") re-use, slag former is added in desiliconization treatment process and the temperature that causes declines therefore, it is possible to be reduced in.

That is, by adopting the technology of patent documentation 1, patent documentation 2, the thermosteresis in the pretreatment process of molten iron can be reduced, therefore, compared with the past, the mixing ratio of cold iron source can be increased, quantity discharged and the reduction manufacturing cost of cutting down greenhouse gases can be sought simultaneously.

Prior art document

Patent documentation

Patent documentation 1: Japanese Unexamined Patent Publication 10-152714 publication

Patent documentation 2: Japanese Unexamined Patent Publication 11-323420 publication

Summary of the invention

The problem that invention will solve

But there is following problem in above-mentioned prior art.

When carrying out desiliconization process, middle deslagging, dephosphorization treatment continuously in a converter type refining furnace as the technology disclosed in patent documentation 1, patent documentation 2, in order to make more than the set-point of the basicity of slag needed for dephosphorization, and reduce the CaO system fusing assistant that dephosphorization treatment uses, must discharge from converter type refining furnace more than specified rate generate in desiliconization process containing a large amount of SiO ₂slag (hereinafter also referred to as " desiliconization slag ").

During prior art above-mentioned from this viewpoint, for the technology of patent documentation 1, if control 0.3 ~ 1.3 by the basicity of slag at the end of desiliconization process, then slag shows sufficient mobility, fully can carry out the deslagging of desiliconization slag.But, only the basicity of desiliconization slag is controlled 0.3 ~ 1.3, the formation of slag is insufficient, mobility is also poor, is difficult to discharge slag in the short period of time and do not make molten iron flow out, or forms superfluous slag on the contrary, in desiliconization process, slag overflows from fire door, hinder operation etc. sometimes, therefore, be difficult to carry out letting cinder control fully.

In addition, in the technology of patent documentation 2, propose making that the basicity of desiliconization slag is 1.0 ~ 3.0, to carry out middle deslagging after reaching below 0.20 quality % be most suitable for silicon concentration in molten iron.But, its reason is, silicon concentration at the end of desiliconization process in molten iron is higher than 0.20 quality %, become too much containing CaO material in order to the basicity of slag during dephosphorization treatment by subsequent processing is adjusted to required for 2.0, cost is disadvantageous, and any consideration is not done for the deslagging of desiliconization slag.

Namely, there is following problems in above-mentioned patent documentation 1 and the technology disclosed in patent documentation 2: can not discharge desiliconization slag fully, to have to the usage quantity of CaO system fusing assistant increased in the dephosphorization treatment of subsequent processing, or the phosphorus concentration in molten iron after likely making dephosphorization treatment increases.

The present invention carries out in view of above-mentioned the problems of the prior art, its object is to the pretreatment process that a kind of molten iron is provided, the pretreatment process of this molten iron uses a converter type refining furnace to carry out desiliconization process and the dephosphorization treatment of molten iron continuously, and between desiliconization process and dephosphorization treatment, accompany middle deslagging operation, wherein, by improving the deslagging of the desiliconization slag generated in desiliconization process, the temperature of molten iron can be suppressed to decline and carry out the dephosphorization treatment of subsequent processing with low cost.

The method of dealing with problems

The 1st mode of the present invention developed to solve above-mentioned problem is a kind of pretreatment process of molten iron, the method comprises: to the molten iron supply oxygen source in converter type refining furnace after carrying out desiliconization process, under the state remaining in stove making molten iron, a part for the slag be present in stove is discharged from converter type refining furnace, then, in converter type refining furnace, supply CaO system fusing assistant and oxygen source and carry out dephosphorization treatment, again the molten iron after dephosphorization treatment is tapped a blast furnace from converter type refining furnace, thus use a converter type refining furnace to carry out desiliconization process and dephosphorization treatment to molten iron, wherein, in described desiliconization process, concentration for the gas the kind more than at least one in the intake-gas come with the waste gas treatment equipment suction of converter type refining furnace containing carbon atom is analyzed, and the end time of desiliconization process is decided based on its analytical value.

2nd mode of the present invention relates to the pretreatment process of the molten iron of the 1st mode of the present invention, wherein, calculate the velocity of discharge of carbon in the waste gas of discharging from the converter type refining furnace described desiliconization process based on the concentration analysis value of gas kind containing carbon atom in described intake-gas and the under meter of described intake-gas, reach based on the velocity of discharge of carbon in the described waste gas calculated the end time that the variation diagram again increased after maximum value reaches mnm. again decides described desiliconization process.

3rd mode of the present invention relates to the pretreatment process of the molten iron of the 1st mode of the present invention, wherein, based on CO gas concentration, CO in described intake-gas ₂gas concentration and CO gas and CO ₂in the total concn of gas, the analytical value of any one concentration reaches the end time that the variation diagram again increased after maximum value reaches mnm. again decides described desiliconization process.

4th mode of the present invention relates to the pretreatment process of the molten iron of the 1st mode of the present invention, wherein, based on CO gas flow, CO in described intake-gas ₂gas flow and CO gas and CO ₂at least one flow in the total flux of gas reaches the end time that the variation diagram again increased after maximum value reaches mnm. again decides described desiliconization process, the CO gas flow in described intake-gas, CO ₂gas flow and CO gas and CO ₂the total flux of gas is by CO gas concentration, the CO in described intake-gas respectively ₂gas concentration and CO gas and CO ₂calculating of the analytical value of the total concn of gas and the flow of described intake-gas.

5th mode of the present invention relates to the pretreatment process of the molten iron of either type in of the present invention 2nd ~ 4, wherein, with described reach the value again increased in the variation diagram again increased after maximum value reaches mnm. again reach be more than 90% relative to maximum value and less than 150% to the time more than value of certainty ratio for benchmark, make the end time of described desiliconization process within the given elapsed time.

6th mode of the present invention relates to the pretreatment process of the molten iron of either type in of the present invention 2nd ~ 5, and wherein, reach in the variation diagram again increased after maximum value reaches mnm. again described, the difference of maximum value and mnm. is more than 10% of maximum value.

7th mode of the present invention relates to the pretreatment process of the molten iron of the 1st mode of the present invention, wherein, with CO gas concentration, CO in described intake-gas ₂gas concentration and CO gas and CO ₂in the total concn of gas, the analytical value of any one concentration reaches the time of more than given threshold value is benchmark, makes the end time of described desiliconization process within the given elapsed time.

8th mode of the present invention relates to the pretreatment process of the molten iron of the 7th mode of the present invention, wherein, described waste gas treatment equipment is the equipment of the function that the waste gas with described converter type refining furnace suction come reclaims as fuel gas, in described waste gas treatment equipment, the waste gas of converter type refining furnace aspirated together with air and make the burning at least partially of the CO gas in described waste gas, and, reach 2.0 more than volume % with the CO gas concentration in the intake-gas after described burning and more than the given threshold value of 18.0 below volume % time for benchmark, make the end time of described desiliconization process within the given elapsed time.

9th mode of the present invention relates to the pretreatment process of the molten iron of the 1st mode of the present invention, wherein, with CO gas flow, CO in described intake-gas ₂gas flow and CO gas and CO ₂the time that at least one flow in the total flux of gas reaches more than given threshold value is benchmark, makes the end time of described desiliconization process within the given elapsed time, the CO gas flow in described intake-gas, CO ₂gas flow and CO gas and CO ₂the total flux of gas is by CO gas concentration, the CO in described intake-gas respectively ₂gas concentration and CO gas and CO ₂calculating of the analytical value of the total concn of gas and the flow of described intake-gas.

10th mode of the present invention relates to the pretreatment process of the molten iron of the 1st mode of the present invention, wherein, the velocity of discharge of carbon in the waste gas of discharging from the converter type refining furnace described desiliconization process is calculated based on the concentration analysis value of gas kind containing carbon atom in described intake-gas and the under meter of described intake-gas, and reach the time of more than given threshold value for benchmark with this velocity of discharge, make the end time of described desiliconization process within the given elapsed time.

11st mode of the present invention relates to the pretreatment process of the molten iron of either type in of the present invention 1st ~ 10, wherein, residue in the state in stove more than the 30 quality % making the slag generated in the dephosphorization treatment of last furnace charge under, the molten iron of following core is loaded in converter type refining furnace, carries out desiliconization process.

12nd mode of the present invention relates to the pretreatment process of the molten iron of either type in of the present invention 1st ~ 11, wherein, at the end of described desiliconization process, by basicity ([CaO (the quality %)]/[SiO of slag be present in described converter type refining furnace ₂(quality %)]) control 0.80 ~ 1.50 scope.

The effect of invention

According to the present invention, when accompanying desiliconization process and the dephosphorization treatment of the molten iron of deslagging operation between use converter type refining furnace carries out continuously, analytical value based on the gas kind containing carbon atom in the intake-gas come by the suction of the waste gas treatment equipment of converter type refining furnace decides the end time of desiliconization process, therefore, significantly can reduce the deviation judging that desiliconization process terminates, thus can desiliconization slag be formed fully and under the state that mobility is high, carry out middle deslagging, can desiliconization slag be discharged fully with the short period of time and molten iron can not be made to flow out, and then the cost of the dephosphorization treatment after desiliconization process can be reduced, and reduce the inequality of phosphorus concentration in the molten iron after process.

Accompanying drawing explanation

[Fig. 1] is the figure of the example of the velocity of discharge change of carbon in the waste gas that desiliconization process is shown.

[Fig. 2] is the figure changed for illustration of the velocity of discharge of carbon in waste gas.

[Fig. 3] is the constructed profile of the converter type refining furnace used in the pretreatment process of molten iron of the present invention.

[Fig. 4] be desiliconization process is shown at the end of the figure of CO gas concentration in intake-gas and the relation between the deslagging of desiliconization slag.

[Fig. 5] is so that the schematic diagram of pretreatment process of the present invention to be described according to the order of operation.

[Fig. 6] is and previous methods by comparison illustrates the figure of the relation in middle deslagging time of method of the present invention and molten iron between Si concentration.

Nomenclature

1: converter type refining furnace

2: top-blown spray gun

3: bottom blowing nozzle

4: iron notch

5: molten iron

5a: the molten iron after desiliconization process

5b: the molten iron after dephosphorization treatment

6: desiliconization slag

7: dephosphorization slag

8: cold iron source

9: oxygen

10: bottom blown gas

11: coaming plate

12: flue

13: Gas sampling probes

14: gas analysis apparatus

15: charging pot

Embodiment

First, basic fundamental thought of the present invention is described.

The discharge of the desiliconization slag accompany desiliconization process between use converter type refining furnace carries out continuously to molten iron after is (following, also referred to as " middle deslagging ") desiliconization process and dephosphorization treatment when, in order to improve the deslagging of above-mentioned desiliconization slag, contriver etc. conduct in-depth research repeatedly for the various essential factors of the deslagging affecting desiliconization slag.

Its result is known, the deslagging of the desiliconization slag of middle deslagging is except the impact of the mobility by desiliconization slag itself, also by the formation situation considerable influence of desiliconization slag, become good to make the deslagging of desiliconization slag, the importantly abundant scorification of desiliconization slag and show good mobility when deslagging, slag is formed fully simultaneously, and loose density reduces.

The SiO that the desiliconization slag generated in desiliconization process is generated by the burning of silicon in molten iron ₂with add or the slag making materials scorification that remains in stove and being formed.At the desiliconization process initial stage that silicon concentration in, molten iron low at molten iron temperature is higher, preferentially carry out desilication reaction, the SiO in stove ₂amount increases thereupon, but in order to ensure mobility during deslagging, importantly adds or load the slag making materials containing CaO such as unslaked lime and steel slag processed in advance, the composition of slag is adjusted to suitable scope.

On the other hand, the formation speed of CO gas is in low level at the desiliconization process initial stage, but carry out along with desilication reaction and make the silicon concentration in molten iron be reduced to be less than 0.20 quality %, molten iron temperature to rise, decarburizing reaction comes to life, and the formation speed of CO gas increases gradually.In addition, at the desiliconization process initial stage that the silicon concentration in molten iron is high, the iron oxide concentration in slag is also lower, for lower than 10 quality %, but along with desilication reaction carry out, silicon concentration in molten iron reduces, slag amount increases, the iron oxide concentration in slag increases gradually.

And, if iron oxide concentration in slag increases and more than 10 quality %, then the eutectic of slag is revealed or the increase of liquid phase ratio becomes remarkable, to reveal or the increase of liquid phase ratio becomes significantly with under the interaction of the rising of in-furnace temperature, the mobility raising of slag at the eutectic of slag.In addition, by the ferric oxide in slag be rolled into molten iron is bathed or molten iron in slag drips reaction and the generation of CO gas that causes also comes to life, be surrounded by a large amount of CO gas bubbles in slag, become the state of so-called " slag formation ".Once formation slag, the oxygen-supplying amount to slag layer sending oxygen to cause from top-blown spray gun also increases, thus promote the oxidation of iron etc., therefore, send the difference of oxygen condition according to spray gun height etc., height of formation increases post and reaches so-called " splash (slopping) " sometimes.

If can control when the deslagging of desiliconization slag and remain on this slag to form state, the loose density of slag then can be made very little, even identical slag quality, also the large volume of about about 10 times can be become, when slag is flowed out from fire door, can promptly discharge slag and not make molten iron flow out.But if the slag in desiliconization process is formed excessive, then slag overflows from fire door, may hinder operation, therefore should be noted that.

But, in the prior art, not yet establish and the method controlling and keep and the technology being suitable for evaluating formation state and suitably judging the time transferring to middle deslagging from desiliconization process formed to above-mentioned slag.Therefore, the ash-retention efficiency of the desiliconization slag stably improved in middle deslagging is difficult to.

Contrivers etc. are for the formation state being suitable for evaluating slag in desiliconization process thus determine to terminate desiliconization process and start the method for the time of middle deslagging and repeatedly conduct in-depth research.It found that, in the desiliconization process using converter type refining furnace, in waste gas, the velocity of discharge of carbon shows specific variation diagram, simultaneously, in the specified range of its variation diagram, formation state is best suited for deslagging, and, terminate desiliconization process and start time of middle deslagging can be (following based on the intake-gas come by the suction of converter type refining furnace incidental waste gas treatment equipment, also be only called " intake-gas ") in the contained concentration analysis value comprising the gas kind of carbon atom decide, thus develop the present invention.

The molten iron that it is 0.35 quality % that Fig. 1 shows for the silicon concentration in molten iron carries out desiliconization process until the change (over time) of the velocity of discharge (carbon amounts contained in the waste gas that time per unit is discharged) of carbon contained in waste gas when silicon concentration is reduced to below 0.10 quality % in the condition easily forming desiliconization slag, and also show intake-gas flow, send CO gas concentration in oxygen speed and intake-gas and CO ₂the change of gas concentration sum, the change of the velocity of discharge (carbon amounts contained in the waste gas that time per unit is discharged) of carbon contained in described waste gas is CO gas concentration, CO based on being aspirated by the incidental waste gas treatment equipment of converter type refining furnace in the intake-gas come ₂gas concentration and intake-gas flow (standard state) calculate.

As known in the figure, when forming desiliconization slag, the special variation diagram that the velocity of discharge of carbon contained in waste gas shows below: rise along with the carrying out of desilication reaction (stage I) after desiliconization process starts, start to reduce after display maximum value and show mnm. (stage II), and then increasing (stage III).It should be noted that, strictly speaking, in above-mentioned waste gas, the velocity of discharge of carbon also comprises and is aspirated CO contained in the air come by waste gas treatment equipment ₂, the CO in air ₂owing to being micro-, the impact brought by it therefore can be ignored.

For the reason of the above-mentioned special variation diagram of velocity of discharge display of carbon in waste gas, contriver etc. think that its reason is as follows.

First, stage I be carry out along with desiliconization process and the molten iron temperature that causes rises and in molten iron silicon concentration decline and make the stage that the generation of CO gas rises gradually, decarburizing reaction starts the initial stage, the growing amount of desiliconization slag is also less, and temperature is low, do not form slag, as shown in Fig. 2 (a), CO gas can easily be discharged to outside stove through desiliconization slag layer.But, when desilication reaction carries out and arrives stage II, the generation of CO gas increases, the temperature of the slag of desiliconization simultaneously rises, reduced viscosity, therefore, as shown in Fig. 2 (b), the CO gas produced enters in desiliconization slag, cause formation slag, in waste gas, the velocity of discharge of carbon sees temporary transient minimizing in appearance.When desilication reaction carries out further and arrives stage III, cannot enter CO gas many like this in desiliconization slag, slag forms the state that reaches capacity, and as shown in Fig. 2 (c), CO gas is discharged to outside stove, and in waste gas, the velocity of discharge of carbon starts to rise again.

In addition, think that the variation diagram of the velocity of discharge of carbon is also relevant with following phenomenon in waste gas.

In the stage I of desiliconization process, the oxygen supplied by top-blown spray gun is mainly consumed in desilication reaction and decarburizing reaction, but after arriving stage II, generation slag amount increases, and the thickness of slag layer increases, and the iron oxide concentration simultaneously in slag raises, supply oxygen also consume by the oxidizing reaction of iron, therefore, the oxygen for decarburization decrease the part that consumes by the oxidizing reaction of iron, in waste gas, the velocity of discharge of carbon declines.Particularly, when slag starts formed and the thickness of slag layer is increased, accelerated to increase by the oxygen supply amount to slag layer sending oxygen to cause from top-blown spray gun, iron oxide concentration rises.Then, when reaching stage III, due to the ferric oxide in slag and molten iron reaction and produce CO gas, ferric oxide simultaneously in slag decreases the part of reacting with molten iron, ferric oxide in slag reaches break-even state, therefore, the generation speed of CO gas increases again, and in waste gas, the velocity of discharge of carbon starts to rise.

From above research, in waste gas, the velocity of discharge of carbon becomes mnm. from maximum value, again increased by mnm., if the stage being in the above-mentioned stage III of formation state at desiliconization slag terminates desiliconization process and starts middle deslagging, then can improve the ash-retention efficiency of desiliconization slag effectively.Also confirm in addition, the silicon concentration in the molten iron in this stage is stably reduced to below 0.10 quality %, and this concentration can reduce the usage quantity of dephosphorization refining agent and effectively carry out dephosphorization in the dephosphorization treatment of next carrying out.

In addition, the discoveries such as contriver, the specific region of above-mentioned stage III, when the maximum value of the velocity of discharge of carbon is more than 90% and terminates desiliconization process in the scope of less than 150% in relative to waste gas specifically, the ash-retention efficiency of desiliconization slag can be improved further.

Can think that its reason is as follows: as explained above, due to the carrying out of decarburizing reaction, the temperature of desiliconization slag rises, viscosity declines, mobility improves, in addition, owing to forming slag, the proportion of desiliconization slag from the appearance reduces, and the slag layer height (thickness) in molten iron bath increases, and easily flows out from fire door.In the offgas carbon the velocity of discharge relative to above-mentioned maximum value lower than 90% time terminate desiliconization process when, the formation of slag is insufficient, and the ash-retention efficiency of desiliconization slag is sometimes also insufficient.On the other hand, when relative to above-mentioned maximum value more than 150% time terminate desiliconization process, slag overflowed from fire door before end desiliconization process, may hinder operation.

The present invention develops based on above-mentioned new discovery like this, it is characterized in that a kind of pretreatment process of molten iron, the method comprises: after carrying out desiliconization process to the molten iron supply oxygen source in converter type refining furnace, the slag that is present in stove discharged (middle deslagging) at least partially from converter type refining furnace, then dephosphorization treatment is carried out to the molten iron supply CaO system fusing assistant in converter type refining furnace and oxygen source, tap a blast furnace, wherein, in above-mentioned desiliconization process, concentration for the gas kind containing carbon atom in the intake-gas come with the waste gas treatment equipment suction of converter type refining furnace is analyzed, and the end time of desiliconization process is decided based on its analytical value.

In the pretreatment process of the molten iron of the invention described above, use as shown in Figure 3 can the converter type refining furnace 1 of top and bottom complex blowing.Top blast carries out as follows: utilize and at the top-blown spray gun 2 of the inside of converter type refining furnace 1 lifting, can supply the oxygen-containing gas 9 as oxygen source from this top-blown spray gun 2 front end to molten iron 5.As above-mentioned oxygen-containing gas 9, the mixed gas etc. of oxygen (industrial pure oxygen), oxygen-rich air, air, oxygen and non-active gas can be used.

On the other hand, bottom blowing is carried out as follows: utilize the bottom blowing nozzle 3 be arranged at bottom converter type refining furnace 1, be blown into bottom blown gas 10 in molten iron.As above-mentioned bottom blown gas 10, can be the gas containing oxygen, may also be only the non-active gas such as argon gas, nitrogen.Bottom blown gas 10 promotes the stirring of molten iron 5 by being blown in molten iron, thus has the function promoting that cold iron source melts, and also can have the function as the conveying gas being blown into slag former from bottom blowing nozzle 3 in molten iron.

In addition, above converter type refining furnace 1, be provided with coaming plate 11 and coupled flue, described coaming plate covers the fire door of converter type refining furnace 1 by being elevated.The waste gas of discharging from converter type refining furnace 1 is aspirated by not shown waste gas treatment equipment by flue 12, after water spray dedusting, measures pumping velocity.When waste gas treatment equipment has the function reclaimed as fuel gas by the intake-gas that suction comes, intake-gas forms according to it and flow is recovered as fuel gas or is released, but because in desiliconization process, the generation speed of CO gas is low, usually can not be recovered as fuel gas.At this, next intake-gas is aspirated except the waste gas of being discharged by converter type refining furnace 1 by not shown waste gas treatment equipment, also comprise corresponding to and the gap size (after, also referred to as " coaming plate height ") of pressure reduction between normal atmosphere and converter type refining furnace 1 and coaming plate 11 and the air (air) that is sucked in coaming plate 11.

The waste gas of high temperature reacts with the oxygen in the air be sucked in coaming plate and the CO in waste gas and generates CO ₂, until any one in oxygen and CO is depleted in fact.In flue 12, be provided with the Gas sampling probes 13 for sampling analysis waste gas, be connected with gas analysis apparatus 14, for CO, CO in the intake-gas of being sampled by Gas sampling probes 13 with this Gas sampling probes 13 ₂, O ₂analyze Deng gas composition.That is, it is constructed as follows: measured for the gas composition of the intake-gas of being sampled by Gas sampling probes 13 continuously or off and on by gas analysis apparatus 14.It should be noted that also have the part passed through at the high-temperature gas of flue 12 grade that the situation of steam boiler is set.

When utilizing waste gas treatment equipment to be reclaimed as fuel gas by the waste gas of high temperature, the running of waste gas treatment equipment is usually according to making coaming plate height reduce as far as possible, thus the mode doing one's utmost to reduce the air be sucked is carried out.But due to the generation speed little (generation is few) of CO gas during desiliconization process, usually do not carry out the recovery as fuel gas, therefore, coaming plate height can set arbitrarily.Therefore, when such as flue 12 has the function of steam boiler, iting is desirable to carry out suction air energetically by making coaming plate 11 rise, making the CO gaseous combustion in waste gas, thus this combustion heat (heat energy) is reclaimed with the form of high pressure steam.On the other hand, when flue 12 does not have the function of steam boiler, in order to suppress the suction of air, the position that can reduce coaming plate 11 operates to make waste gas treatment equipment, thus, can alleviate the thermal load of flue 12 grade.

Aspirating by waste gas treatment equipment the one-tenth of intake-gas come is grouped into according to the feature of waste gas treatment equipment and operating condition thereof completely different.That is, when inhibit the aspiration of air in the position reducing coaming plate 11, CO and CO ₂concentration reach higher concentration, but when making coaming plate 11 rise energetically suction air, if more than not reaching to a certain degree ratio from the generation speed of the CO gas of converter type refining furnace 1 relative to the gas pumping velocity of waste gas treatment equipment (being specially about 30 more than volume %), then only detect CO when the analysis of intake-gas ₂, and do not detect CO.This is because, the O in the air that suction is next ₂effect under, the CO in waste gas is burned.In addition, CO and CO in intake-gas ₂concentration due to by N ₂dilute and be low concentration.In addition, although shown in Fig. 1 is have gas recovery function, but be used in the waste gas treatment equipment in flue without steam boiler, and the example of the operation carried out confirm waste gas igniting after desiliconization process starts after reducing coaming plate 11 and inhibit air to aspirate.

In addition, in the waste gas shown in above-mentioned Fig. 1, the velocity of discharge of carbon is based on CO gas concentration, the CO in intake-gas ₂the gas pumping velocity (intake-gas flow in normal conditions) of gas concentration and waste gas treatment equipment calculates, the CO gas concentration in described intake-gas, CO ₂gas concentration is measured by the Gas sampling probes 13 be arranged in the flue leading to the converter waste gas treatment facility shown in Fig. 3.CO, CO ₂the mensuration of gas composition usually use infrared absorbing type analyser, but this assay method is compared with mensurated gas composition flow, and response speed is slow, can produce the time of lag about tens seconds ~ tens seconds, therefore will be corrected each minute.In addition, in order to prevent the leakage of waste gas, the gas aspiration in waste gas treatment equipment more than the gas volume produced by converter type refining furnace when desiliconization process, carbonization treatment, therefore, air is sucked, the CO produced oxidized at least partially and be converted into CO between fire door and coaming plate ₂.

Therefore, in order to determine the end time of desiliconization process, by the CO concentration in mensuration intake-gas and CO ₂the method that the attraction speed (flow of standard state) of concentration and waste gas treatment equipment obtains the velocity of discharge of carbon in waste gas is effective.But, according to the experimental result of contriver etc., if the operating condition of converter waste gas treatment facility (coaming plate height, fire door pressure etc.) is constant, then can by CO gas concentration, the CO in intake-gas ₂gas concentration and CO gas and CO ₂any one concentration in the total concn of gas reaches the time that the variation diagram that again increases after maximum value reaches mnm. again replaces the velocity of discharge of carbon in waste gas to decide desiliconization process terminating.Now, under remaining the such operating condition of CO in, intake-gas fewer in the air capacity be sucked, can based on CO gas and CO ₂the variation diagram of the total concn of gas decides the time that desiliconization process terminates, but at the too large variation of the air capacity not making to be sucked, CO ₂when gas concentration is stable, also only can decide based on the variation diagram of CO gas concentration the time that desiliconization process terminates.In addition, under the operating condition of the CO perfect combustion in, waste gas abundant in the air capacity be sucked, can also only based on CO ₂the variation diagram of gas concentration decides the time that desiliconization process terminates.

In addition, can also by CO gas flow, the CO in intake-gas ₂gas flow and CO gas and CO ₂at least one flow in the total flux of gas reaches the time that the variation diagram that again increases after maximum value reaches mnm. again replaces the velocity of discharge of carbon in waste gas to decide desiliconization process terminating, the CO gas flow in described intake-gas, CO ₂gas flow and CO gas and CO ₂the total flux of gas is by the CO gas concentration in intake-gas and/or CO ₂calculating of the analytical value of gas concentration and the flow of intake-gas.Now, under remaining the such operating condition of CO in, intake-gas less in the air capacity be sucked, can based on CO gas and CO ₂the variation diagram of the total flux of gas decides the time that desiliconization process terminates, but at the too large variation of the air capacity not making to be sucked, CO ₂when gas concentration is stable, also only can decide based on the variation diagram of CO gas flow the time that desiliconization process terminates.In addition, under the operating condition of the CO perfect combustion in, waste gas abundant in the air capacity be sucked, can also only based on CO ₂the variation diagram of gas flow decides the time that desiliconization process terminates.

In addition, intake-gas flow based on the coaming plate height carried out before and after desiliconization process adjustment and significantly change (Fig. 1 reference), but as previously mentioned, because when the analysis with gas composition of the mensuration of intake-gas flow, response speed is different, if there is large variation in intake-gas flow, then when the change of the velocity of discharge measuring carbon in waste gas, it can become the reason producing error.Therefore, when judging above-mentioned maximum value and mnm., it is desirable to not make the intake-gas flow before and after generation maximum value and mnm. occur significantly to carry out operation with changing.In general, control coaming plate height and make the swabbing pressure of gas keep constant, or it is constant to control the maintenance of coaming plate height, in these cases, when judging maximum value and mnm., the variation of intake-gas flow is the level that can not have problems.

As mentioned above, can based on the velocity of discharge of carbon in waste gas or based on CO gas concentration, the CO in intake-gas ₂gas concentration, CO gas and CO ₂the total concn of gas, CO gas flow, CO ₂gas flow and CO gas and CO ₂any one measured value in the total flux of gas reaches the end time that the variation diagram again increased after maximum value reaches mnm. again decides desiliconization process, but wishes to judge the maximum value in above-mentioned variation diagram and mnm. when the difference of maximum value and mnm. is more than 10% of maximum value.Its reason prevents error detection effectively to ignore small variation, this is because, when above-mentioned difference is less than 10%, likely think it is form the relevant variation diagram of phenomenon to above-mentioned slag by mistake by resulting from the small variations of intake-gas flow variation etc.It should be noted that, wish not go identification when the maximum value of said determination value and the difference of mnm. are less than 10% of maximum value and the maximum value ignored in above-mentioned variation diagram and mnm., and continue to monitor that the variation of measured value is until occur that the difference of maximum value and mnm. reaches the variation diagram of 10% of maximum value.

In addition, with above-mentioned reach mnm. after the variation value that again increases be more than 90% relative to above-mentioned maximum value and less than 150% to the time more than value of certainty ratio for benchmark, wish that the end time of desiliconization process is within the scope of the given elapsed time.Give the value of certainty ratio as follows as the reason of threshold value the above-mentioned scope relative to maximum value: the region again increased after reaching mnm. in above-mentioned variation diagram be carry out desiliconization slag formation and make stove in must the region that sharply increases of slag height, but it is insufficient because slag is formed lower than the region of 90% relative to maximum value, the ash-retention efficiency of desiliconization slag may become insufficient, on the other hand, in the region more than 150%, existed before end desiliconization process, slag overflows from fire door and hinders the worry of operation.In addition, as long as the end time of desiliconization process can make above-mentioned variation value reach the time of more than threshold value, but in fact, even from this time through about the several tens of seconds needed for the operations such as the operation of necessity or device work after also no problem.Wish that the above-mentioned elapsed time is in the scope in 0 ~ 50 second, be more preferably in the scope in 0 ~ 30 second.As long as be the above-mentioned time scope in, would not exceedingly carry out slag formation and hinder operation, thus desiliconization process can be terminated carry out middle deslagging fully.

It should be noted that, the end time of the desiliconization process determined as described so can be set as that any one measured value above-mentioned reaches the time more than to the value of certainty ratio relative to maximum value, also can be the time that have passed through from this time after the given treatment time.But, in the latter case, it is desirable to be set as that the time being no more than 150% relative to maximum value in any one measured value above-mentioned terminates desiliconization process.

In addition, for the method for the end time of decision desiliconization process, except deciding except the method for the end time of desiliconization process based on above-mentioned such variation diagram, with the velocity of discharge of carbon in waste gas for benchmark or with CO gas concentration, the CO in intake-gas ₂gas concentration, CO gas and CO ₂the total concn of gas, CO gas flow, CO ₂gas flow and CO gas and CO ₂the time that any one measured value in the total flux of gas reaches more than given threshold value is that benchmark is set as that the method within the scope of the given elapsed time is also effective.Wherein, as described above, the elapsed time from the time that said determination value reaches more than threshold value till the end time of desiliconization process is preferably in the scope in 0 ~ 50 second, and more hope is in the scope in 0 ~ 30 second.

But, when these methods, need to make not show said determination value reach more than threshold value in the intermediate stage of desiliconization process, the maximum value part such as seen at the variation diagram of the carbon velocity of discharge shown in Fig. 1.For this reason, wish to be set as after the moment of the oxygen of 1.2 times that supply to give required oxygen amount on chemical theory, preferably 1.5 times, above-mentioned measured value reaches the time of more than given threshold value, and on described chemical theory, required oxygen amount is calculated by the Si concentration in the molten iron after the desiliconization process of the Si concentration in desiliconization molten iron before treatment and target.In addition, above-mentioned threshold value can be the numerical value of rule of thumb trying to achieve, also can be the value that the variographs such as the Si concentration such as used in molten iron temperature, molten iron calculate, but deslagging situation in the middle of preferably considering during deslagging, with and subsequent the actual effect of dephosphorization treatment determine.

At this, for in following situation, the example that the deslagging of desiliconization slag is investigated is illustrated as follows, described situation is: waste gas treatment equipment has the function reclaimed as fuel gas by the waste gas of converter type refining furnace, and there is the flue possessing steam boiler, and, when making waste gas treatment equipment to aspirate air energetically in desiliconization process, the mode of burning at least partially of the CO gas in waste gas be operated, the situation of the end time of desiliconization process is decided based on above-mentioned illustrated threshold value, the situation of the end time of desiliconization process is decided specifically based on the CO gas concentration in intake-gas.

In this example, the desiliconization slag of the silicon concentration made in desiliconization molten iron before treatment and generation quality substantially constant and under the condition that when making deslagging, the angle excursion of converter type refining furnace is constant, the deslagging of amount to desiliconization slag based on the desiliconization slag of being discharged by converter type refining furnace is evaluated.Specifically, by be discharged to the quality by the desiliconization slag in slag container accepting slag immediately below converter type refining furnace be the average evaluation of more than 50% of the quality of the desiliconization slag be present in stove is " deslagging is excellent ", above-mentioned value is more than 30% and the average evaluation being less than 50% is " deslagging is good ", above-mentioned value is less than the average evaluation of 30% for " deslagging is bad ".

Shown in Fig. 4 is above-mentioned investigation result.As known in the figure, the CO gas concentration at the end of desiliconization process in intake-gas is higher, and the deslagging of desiliconization slag improves, and in addition, when the CO gas concentration at the end of desiliconization process in intake-gas is 6.0 more than volume %, does not produce " deslagging is bad ".Namely, the end of desiliconization process can be decided based on the CO gas concentration in intake-gas in desiliconization process, and known, in this case, be preferably the threshold value of value as the end time of decision desiliconization process of 6.0 more than volume % using CO gas concentration in intake-gas.

It should be noted that, in the refining furnaces such as converter type refining furnace, implement refining with intermittent type to the molten iron in stove, molten steel, this 1 unit refining is called " furnace charge ", and what the furnace charge number in Fig. 4 represented is its number of times.In addition, in desiliconization process, the generation of waste gas is few, therefore due to the air sucked between the fire door and coaming plate of converter type refining furnace, the CO gas concentration in intake-gas is changed, but the threshold value of " CO gas concentration is 6.0 more than volume % " in above-mentioned intake-gas obtains under operating condition (sending oxygen amount, coaming plate height, fire door pressure etc.) is set to the operating condition of a certain steady state value.Therefore, as long as under this condition, just can make full use of as threshold value.

In addition, as the suitable value of above-mentioned threshold value, different according to operating conditions such as appointed condition and oxygen supply speed such as the suction capactities of waste gas treatment equipment.When waste gas treatment equipment there is the function that reclaimed as fuel gas by the waste gas of converter type refining furnace and in desiliconization process energetically suction air and make the CO burning in waste gas, as the threshold value of the end time of decision desiliconization process, the CO gas concentration preferably in intake-gas is 2.0 more than volume % and rule of thumb selectes suitable value based on ash-retention efficiency during middle deslagging and the practical situation of deslagging time in the scope of 18.0 below volume % to use.If the threshold value of CO gas concentration is 2.0 more than volume %, even if then only use the measured value of CO gas concentration to replace the variation diagram of the velocity of discharge of carbon in above-mentioned waste gas, also the situation of the misidentification judged when fully promoting slag formation can be reduced, on the other hand, if the threshold value of CO gas concentration is 18.0 below volume %, then can prevent the operating barrier that the excessive formation due to slag causes, and precision can judge for effectively carrying out deslagging formation state well.

As described above, situation can be formed by means of only the information obtained by intake-gas to the slag judging in desiliconization process and be applicable to terminating desiliconization process and time of middle deslagging, by the necessary oxygen amount of the silicon blow calculated by operating condition obtained in advance, spent air temperture, slag is from the ejection situation of fire door, slag is from the outflow situation of tap hole, the change of the vibration of production line or supplement production line, the information such as change of the sound in oxygen blowing, or combined with the technology etc. utilizing known method to estimate slag level, the precision of above-mentioned decision condition can be made higher.

Then, to use the pretreatment process of situation to molten iron of the present invention of the converter type refining furnace shown in Fig. 3 to be described particularly.

First, for the pretreatment process of molten iron of the present invention, as shown in Fig. 5 (a), in the converter type refining furnace 1 being incorporated with the cold iron sources such as iron filings 8, load the molten iron 5 (molten iron loading operation) before molten iron, the namely pre-treatment not carrying out desiliconization process and dephosphorization treatment by charging pot 15.

Then, as shown in Fig. 5 (b), to the molten iron 5 in this converter type refining furnace 1 supply as oxygen source oxygen-containing gas or supply oxygen-containing gas and ferric oxide implement desiliconization process (desiliconization treatment process).Now, contained in molten iron 5 silicon and the oxygen supplied react and carry out desilication reaction (Si+O ₂→ SiO ₂).Under the effect of the combustion heat of the silicon of this desilication reaction, molten iron temperature rises, and promotes the melting of the cold iron source 8 in molten iron.

Then, along with the carrying out of above-mentioned desiliconization process, silicon concentration in molten iron slowly reduces and produces CO gas, if but desiliconization process is carried out further, the growing amount of desiliconization slag increases, molten iron temperature raises, then the composition transitivity of slag also changes, and causes generation slag due to produced CO gas.

At this, in order to prevent the phosphorous oxides (P contained from dephosphorization slag 7 described later in desiliconization process ₂o ₅) to decompose and the phosphorus that generates is transferred in molten iron 5 and (this phenomenon is called " returning phosphorus "), preferably make the basicity of desiliconization slag 6 after desiliconization process terminates ([CaO (the quality %)]/[SiO generated by above-mentioned desiliconization process ₂(quality %)]) be more than 0.80.It should be noted that, about the higher limit of the basicity of desiliconization slag 6, from desilication reaction, there is no need to be specified.But basicity is high means that CaO is relative to generated SiO ₂ratio high, the amount of desiliconization slag 6 increases, and therefore, preferably its upper limit is about 1.50.More preferably less than 1.30, preferred lower than 1.20 further.

It should be noted that, the basicity of desiliconization slag 6 is adjusted in above-mentioned scope and can be undertaken by adding the fusing assistants such as CaO system fusing assistant before desiliconization process and in desiliconization process in stove.But when the initial stage of desiliconization process adds CaO system fusing assistant, it is generated SiO that the basicity of desiliconization slag 6 reaches the minimum time ₂amount reaches maximum desiliconization process end times, and therefore, if make the basicity at the end of desiliconization process be more than 0.80, then the basicity in desiliconization process before this must be more than 0.80.In addition, when the CaO contained by the dephosphorization slag 7 by means of only the last furnace charge remained in stove just can make the basicity at the end of desiliconization process be more than 0.80, substantially without the need to adding the fusing assistants such as CaO system fusing assistant.

It should be noted that, the addition means of above-mentioned CaO system fusing assistant can be drop into granular and block CaO system fusing assistant from the loading hopper stove, or is dropped into the method for CaO system fusing assistant of powdery by top-blown spray gun 2, is not particularly limited.

In addition, the basicity of desiliconization slag 6 can calculate based on following formula (1).

Basicity=[(in stove residual CaO amount (kg/ molten iron-t))+(the interpolation CaO in desiliconization process measures (kg/ molten iron-t))]/[(residual Si O in stove ₂amount (kg/ molten iron-t))+(SiO generated in desiliconization process ₂amount (kg/ molten iron-t))] ... (1)

It should be noted that, the SiO generated in desiliconization process in above-mentioned formula ₂amount is calculated by the change of the silicon concentration in molten iron before and after desiliconization process.

In addition, as the oxygen source for desiliconization process, can be only the oxygen 9 supplied by top-blown spray gun 2, in addition, also above-mentioned oxygen 9 can be combinationally used with ferric oxide (not shown).But, melt from the viewpoint of the more cold iron sources 8 that makes as an object of the present invention, be not preferably used in the ferric oxide of heat absorption when heating up and decompose.Therefore, preferably avoid as far as possible using ferric oxide as oxygen source.

In addition, as an embodiment of the invention, due to based on obtain when the velocity of discharge of carbon contained in the waste gas of being discharged by converter type refining furnace during desiliconization process is measured, the velocity of discharge of carbon reaches the end time that the variation diagram again increased after maximum value reaches mnm. again decides desiliconization process, therefore, reach maximum value and minimizing period in the velocity of discharge of above-mentioned carbon, wish that as far as possible the feed speed of oxygen source being kept constant carries out operation.It should be noted that, in common operation, in order to complete desiliconization process at short notice, carry out increasing the operation sent oxygen speed or drop into ferric oxide at the initial stage of desiliconization process, therefore, can in maximum value and the mnm. thereafter by making oxygen supply constant airspeed stably measure the velocity of discharge of carbon.

After as mentioned above molten iron enforcement desiliconization process also being determined to terminate desiliconization process, make top-blown spray gun 2 increase immediately and terminate desiliconization process, but the end time of the desiliconization process of reality be generally terminate desiliconization process from above-mentioned decision moment through about several tens of seconds after, this elapsed time is time needed for action of the operations such as necessary operation and device.Then, immediately as shown in Fig. 5 (c), make converter type refining furnace 1 to the opposition side deflection of side being provided with iron notch 4, from the fire door of converter type refining furnace 1 discharge that desiliconization process produces containing a large amount of SiO ₂the desiliconization slag 6 (middle deslagging operation) of low alkalinity.It should be noted that, in Fig. 5 (c), in order to be distinguished with desiliconization molten iron 5 before treatment, the molten iron after desiliconization process is expressed as 5a.

In order to effectively carry out dephosphorisation reaction in dephosphorization treatment operation described later with the usage quantity of less CaO system fusing assistant, in above-mentioned middle deslagging operation, the ash-retention efficiency of desiliconization slag 6 is preferably set to more than 30 quality %.In addition, in order to make the total amount to the CaO system fusing assistant used between ensuing Decarburising and refining operation from hot metal pretreatment fewer than the existing method not implementing middle deslagging operation, the ash-retention efficiency of more than 50 quality % is preferably stably guaranteed.

But if to discharge desiliconization slag 6 more than 80 quality %, then in ensuing dephosphorization treatment operation, the slag of the new CaO system fusing assistant added suffers damage, and may hinder dephosphorisation reaction.Therefore, in the present invention, preferably the ash-retention efficiency of desiliconization slag 6 is controlled the scope at 50 ~ 80 quality %.

It should be noted that, above-mentioned ash-retention efficiency following formula (2) definition.

Ash-retention efficiency (quality %)=(discharging slag quality) × 100/ [(the slag quality generated in desiliconization treatment process)+(the residual slag quality of last furnace charge)] (2)

After above-mentioned middle deslagging, as shown in Fig. 5 (d), supply CaO system fusing assistant and oxygen source to carry out dephosphorization treatment (dephosphorization treatment operation) to the molten iron 5a after the desiliconization process remained in converter type refining furnace.At this, preferably the basicity of the dephosphorization slag 7 generated in stove is made to be adjusted to the scope of 1.2 ~ 3.0 in above-mentioned dephosphorization treatment operation.If basicity is more than 1.2, then the dephosphorizing capacity of slag is suitable scope, can reduce the phosphorus concentration in molten iron with less slag amount.On the other hand, if basicity is less than 3.0, then makes the mobility of slag be that suitable scope carries out dephosphorisation reaction, and the scorification of CaO system fusing assistant can not be damaged.

Wherein, same with desiliconization process, the oxygen source used in above-mentioned dephosphorization treatment operation is based on the oxygen 9 from top-blown spray gun 2, but ferric oxide also can be used as part oxygen source.Wherein, because an object of the present invention is the use increasing cold iron source 8, therefore, the ferric oxide of a small amount of heat absorption when heating up and decompose preferably is used as far as possible.For this reason, preferably will oxygen condition, spray gun height etc. be sent to control as suitable and regulate the T.Fe concentration of dephosphorization slag 7, thus promote the scorification of CaO system fusing assistant and do not rely on the use of ferric oxide.

In addition, as the CaO system fusing assistant used in dephosphorization treatment, unslaked lime (CaO), Wingdale (CaCO can be used ₃), slaked lime (Ca (OH) ₂) etc., but be not limited to these, such as, also can use as CaO system fusing assistant by the material using the CaO containing more than 40 quality % and as required containing other composition such as fluorine and aluminum oxide.It should be noted that, for the addition means of above-mentioned CaO system fusing assistant, same with adding CaO system fusing assistant in desiliconization process, can be drop into granular and block CaO system fusing assistant from the loading hopper stove, or the method for CaO system fusing assistant of powdery is dropped into by top-blown spray gun 2, be not particularly limited.

In this dephosphorization treatment operation, oxidized and form phosphorous oxides (P under the effect of the oxygen of the phosphorus in molten iron in supplied oxygen source ₂o ₅), enter into the dephosphorization slag 7 playing the effect of dephosphorization refining agent formed by the scorification of CaO system fusing assistant, form the compound (3CaOP of stable state ₂o ₅), thus carry out the dephosphorization of molten iron 5a.It should be noted that, the end of dephosphorization treatment can be set as the dephosphorization treatment time have passed through preset time after moment, or also can be set as that dephosphorisation reaction carries out and makes the phosphorus concentration of molten iron 5a be reduced to the moment of below set-point.

After dephosphorization treatment terminates, as shown in Fig. 5 (e), make converter type refining furnace 1 to the direction deflection contrary with middle deslagging, via iron notch 4, the molten iron 5b in converter type refining furnace 1 is tapped a blast furnace to not shown molten iron maintenance container (operation of tapping a blast furnace).It should be noted that, in Fig. 5 (e), in order to desiliconization process after molten iron 5a distinguished, the molten iron after dephosphorization treatment is expressed as 5b.After the end of tapping a blast furnace of molten iron 5b, as shown in Fig. 5 (f), converter type refining furnace 1 is overturn, makes fire door upward, terminate to tap a blast furnace.

It should be noted that, tap a blast furnace in operation above-mentioned, be blended in sometimes the molten iron 5b flowed out from iron notch 4 and flow out dephosphorization slag 7, although the outflow of this dephosphorization slag 7 is inevitable, but its amount is a small amount of, thus clearly distinguishes with the discharge of the dephosphorization slag described later of discharging wittingly.Therefore, in the converter type refining furnace 1 after terminating that taps a blast furnace, the dephosphorization slag 7 of a small amount of molten iron 5b (not shown) do not tapped a blast furnace and almost whole amount left behind.

It should be noted that, this dephosphorization slag 7 is high due to phosphoric acid concentration, if directly used as the desiliconization slag of following core, then may cause and returns phosphorus and cause the phosphorus concentration in molten iron to rise.Therefore, after above-mentioned operation of tapping a blast furnace terminates, the dephosphorization slag of whole amount has been carried out deslagging in the past.But, if the dephosphorization slag of whole amount is discharged, then increase for the usage quantity generating the slag making materials of required desiliconization slag in the desiliconization process of following core, thus cause auxiliary material cost to raise.Therefore, in the present invention, refining condition in preferred adjustment desiliconization process prevents from returning phosphorus from dephosphorization slag, and after middle deslagging, carry out dephosphorization treatment, then molten iron is tapped a blast furnace, then make more than the 30 quality % residued in the dephosphorization slag in converter type refining furnace remain in stove, the part as the desiliconization raw slag of following core uses.Residual dephosphorization slag is more preferably more than 50 quality %.

It should be noted that, as the Slagoff method making dephosphorization slag residual as above, same with the Slagoff method of the slag usually carried out, can be make the body of heater after tapping a blast furnace to iron notch opposition side deflection and discharge from fire door time, regulate angle excursion residue in the method for carrying out in stove discharging with making slag parts.It should be noted that, in order to make the mobility of dephosphorization slag be suitable for deslagging, preferably the basicity of the slag after dephosphorization treatment being adjusted to the scope of 1.2 ~ 1.8, and the concentration of ferric oxide is adjusted to more than 10 quality %.

Then, when making the dephosphorization slag 7 of whole amount residue in the stove of converter type refining furnace 1, after above-mentioned operation of tapping a blast furnace, discharge section dephosphorization slag 7 from converter type refining furnace 1, now, can as shown in Fig. 5 (f), after forming the state making converter type refining furnace 1 upright, in converter type refining furnace 1, undersized cold iron source 8 is loaded from the loading hopper stove, or make deflection several before and after converter type refining furnace 1, the dephosphorization slag 7 remained in stove is solidified (dephosphorization slag curing process), makes the molten iron 5b remained in stove solidify thus.This dephosphorization slag curing process is for flowing into the inside of bottom blowing nozzle 3 by making to remain in dephosphorization slag 7 in stove and molten iron 5b and prevent the operation of bottom blowing nozzle 3 obturation, preferably at least spraying bottom blown gas 10 from bottom blowing nozzle 3 before dephosphorization slag 7 and molten iron 5b solidify/solidify.But, when sustainable supply bottom blown gas, also this operation can be omitted.

After this dephosphorization slag curing process, again return the molten iron shown in Fig. 3 (a) and load operation, implement desiliconization process and the dephosphorization treatment of following core according to above-mentioned operation.

According to the present invention of above-mentioned explanation, a converter type refining furnace can be used to carry out desiliconization process and dephosphorization treatment continuously, and between desiliconization process and dephosphorization treatment, accompany middle deslagging, be thermal source for melting cold iron source therefore, it is possible to refining vessel to be changed the loss hotwork caused and effectively utilize.In addition, according to the present invention, based on be sucked into converter type refining furnace waste gas treatment equipment intake-gas (waste gas) in the concentration of gas kind containing carbon atom decide end time of desiliconization process, thus middle deslagging can be carried out through the state that loose density is little, mobility is high of desiliconization slag of being everlasting, therefore, it is possible to stably improve the ash-retention efficiency of desiliconization slag.

It should be noted that, in above-mentioned explanation of the present invention, continuously desiliconization process and dephosphorization treatment are carried out to molten iron for use converter type refining furnace, and accompany between desiliconization process and dephosphorization treatment the desiliconization slag after desiliconization process discharge (after, also referred to as " middle deslagging ") situation be illustrated, but in this situation, the converter type refining furnace of more than 2 is preferably used when the refining of molten iron 5, at least one converter type refining furnace 1 is wherein used for hot metal pretreatment of the present invention, remaining at least one converter type refining furnace 1 ' is for the Decarburising and refining implementing the molten iron after above-mentioned hot metal pretreatment of the present invention.

Embodiment 1

The converter type refining furnace of the capacity 300 tons of scales shown in Fig. 3 of use, by top-blown spray gun to the 300 tons of molten iron spray refining oxygen be accommodated in above-mentioned stove, and in molten iron, be blown into stirring nitrogen by the bottom blowing nozzle being arranged at furnace bottom, desiliconization process and dephosphorization treatment are implemented to molten iron, implements hot metal pretreatment.Specifically, above-mentioned hot metal pretreatment comprises following a series of operation: in the converter type refining furnace shown in Fig. 3, load iron filings, then molten iron is loaded, add the unslaked lime as CaO system fusing assistant more as required, carry out desiliconization process by top-blown spray gun oxygen gas-supplying, after a part for desiliconization slag is discharged, by top-blown spray gun oxygen gas-supplying, the unslaked lime added as CaO system fusing assistant carries out dephosphorization treatment, is then tapped a blast furnace by molten iron, is subsequently discharged by the dephosphorization slag of whole amount.

It should be noted that, the molten iron implementing above-mentioned hot metal pretreatment uses the molten iron that temperature is 1250 ~ 1320 DEG C, silicon concentration is 0.20 ~ 0.55 quality %, phosphorus concentration is about 0.12 quality %.In addition, the target silicon concentration in the molten iron after above-mentioned desiliconization process is set as 0.03 quality %, desiliconization process terminate after the target basicity of desiliconization slag be set as 0.6 ~ 0.9 scope.In addition, target molten iron temperature at the end of above-mentioned desiliconization process is set to 1300 ~ 1340 DEG C, the control of target molten iron temperature is carried out as follows: making chip Intake Quantity constant is 80kg/t, according to the molten iron temperature loaded, add as the cold iron source of cooling material and/or iron ore or the carbon material added as thermal source and/or ferro-silicon at the initial stage of desiliconization process, and to their addition with give oxygen amount adjustment.

In addition, in the dephosphorization treatment of next carrying out, the presumed value based on the desiliconization slag amount remained in stove and composition thereof adjusts the usage quantity of unslaked lime, makes the basicity of dephosphorization slag be the scope of 1.6 ~ 2.0.

In above-mentioned hot metal pretreatment, 2 following methods are utilized to decide the end time of desiliconization process.

Method 1: calculate by the silicon concentration in the molten iron before pre-treatment with corresponding to the desiliconization oxygen efficiency (empirical value) of its concentration the time that the silicon concentration terminated in supply molten iron reaches the necessary oxygen amount of 0.03 quality %, and is set to the method (comparative example) in the past of the end time of desiliconization process this time

Method 2: as shown in Figure 1, the time reaching more than above-mentioned maximum value with the velocity of discharge of the carbon again risen after showing maximum value mnm. in the variation diagram of the velocity of discharge of carbon in the offgas decides the end of desiliconization process for benchmark, by the above-mentioned moment after about 20 seconds the velocity of discharge of carbon relative to above-mentioned maximum value more than 100% and the method (example) of the end of extent (EOE) desiliconization process of less than 150%

It should be noted that, any one method all makes the oxygen constant airspeed that send from top-blown spray gun be 30000Nm ³/ hr, and with 1200Nm ³the speed that the is blown into bottom blowing nitrogen of/hr.

In addition, decide the hot metal pretreatment of the end time of desiliconization process by utilizing aforesaid method 1 and these two kinds of methods of method 2 and implement tens furnace charges by respective method respectively, and the ash-retention efficiency of the desiliconization slag of the middle deslagging of each method is compared.

Now, the deslagging (middle deslagging) of the desiliconization slag after above-mentioned desiliconization process terminates carries out as follows: after desiliconization process terminates, make top-blown spray gun increase immediately, then body of heater deflection is started the deslagging of desiliconization slag, cause obstacle slag can not be accepted to the slag pot on the mobile handcart be arranged under stove, and in the scope not making molten iron flow out, the angle excursion strengthening converter type refining furnace as far as possible carries out middle deslagging, the end time of middle deslagging is set as any one following moment: to weigh the moment that value can confirm sufficient bed drain purge, only make slag flow out and do not make molten iron flow out the moment becoming difficulty, and the deslagging time reaches the moment of the maximum duration that operation allows.In addition, the utilization weighing device be arranged on the mobile handcart under stove measures the quality of the desiliconization slag received in above-mentioned slag pot, and has obtained the ash-retention efficiency of the desiliconization slag in above-mentioned middle deslagging according to following formula (2).

Ash-retention efficiency (quality %)=(discharging slag quality) × 100/ [(the slag quality desiliconization treatment process generates)+(the residual slag quality of last furnace charge)] (2)

The above results is shown in table 1.It can thus be appreciated that, for deciding for method (comparative example) in the past that desiliconization process terminates by the Si concentration in molten iron, the ash-retention efficiency of the desiliconization slag after desiliconization process is dispersed in the scope of 20 ~ 70 quality %, average ash-retention efficiency is 37 quality %, on the other hand, for being decided for the present invention's example that desiliconization process terminates by the velocity of discharge of carbon in waste gas, the ash-retention efficiency of the desiliconization slag after desiliconization process is the scope of 50 ~ 80 quality %, average ash-retention efficiency is 67 quality %, stably can realize the ash-retention efficiency of more than 50 quality %.In addition we know, by improve the ash-retention efficiency of middle deslagging in this wise, the usage quantity of the slag making materials added in dephosphorization treatment can also significantly be cut down.

In addition, Fig. 6 shows the figure of relation between the Si concentration in the time needed for middle deslagging and the molten iron before pre-treatment, and the activity duration required for middle deslagging of known example of the present invention can significantly foreshorten to less than 10 minutes.By shortening this deslagging time, the process of hot metal pretreatment can be foreshortened to process almost peer-level interval with the carbonization treatment of subsequent processing interval, therefore, hot metal pretreatment can be implemented for the molten iron of almost whole amount.

[table 1]

Embodiment 2

Load under the dephosphorization slag after the dephosphorization treatment of whole amount is remained in the state of not carrying out deslagging in stove following core molten iron and the basicity of slag in desiliconization process is controlled 0.9 ~ 1.2 scope to prevent the phosphorus that returns from dephosphorization slag, in addition, implementing hot metal pretreatment with the condition that the method 2 by embodiment 1 decides the example of the end time of desiliconization process same, and this experiment is being implemented 10 furnace charges continuously.

Its result, can make the 6.0kg/ ton molten iron (table 1 reference) when of the present invention example of the usage quantity of CaO system fusing assistant (unslaked lime) in desiliconization process by embodiment 1 significantly be reduced to 2.0kg/ ton molten iron.In addition, substantially detrimentally affect can not be brought because making the dephosphorization slag of last furnace charge remain in stove to the phosphorus concentration in the molten iron after the unslaked lime usage quantity in dephosphorization treatment and process, therefore, it is possible to directly enjoy the advantage of the unslaked lime usage quantity reduction in above-mentioned desiliconization process.

Embodiment 3

Following comparative example and example is utilized to compare experiment, described comparative example is as follows: decide the end time of desiliconization process except the method same according to the method 1 with embodiment 1 and make the unslaked lime usage quantity in dephosphorization treatment be except 7.0kg/t, under condition similarly to Example 2, implementing hot metal pretreatment.Described example is that the determining method of the desiliconization process end time in this comparative example is changed to method 3 described later.

Specifically, as shown in Figure 5, iron filings 8 are loaded in the converter type refining furnace 1 that whole amount is not residual by dephosphorization slag 7 deslagging generated in the hot metal pretreatment of last furnace charge, then, molten iron 5 is loaded in above-mentioned converter type refining furnace 1, add unslaked lime as required again, by top-blown spray gun 2 oxygen gas-supplying 9 after having carried out desiliconization process, a part for desiliconization slag 6 is discharged, then unslaked lime is added, continue to carry out dephosphorization treatment by top-blown spray gun 2 oxygen gas-supplying 9, and be repeated such hot metal pretreatment.It should be noted that, the waste gas treatment equipment of this converter type refining furnace 1 has equipment intake-gas being reclaimed function as fuel gas, when blowing, under the state making coaming plate 11 increase, has 90000 ~ 100000Nm ³the suction capactity of about/hr.In addition, possess steam boiler (heat extraction boiler) in flue 12, in desiliconization process, do not carry out the recovery of intake-gas, therefore, coaming plate 11 is risen and aspirates air, make the CO gaseous combustion in waste gas energetically and form the steam of high pressure, thus having carried out the recovery of energy.

Now, as the determining method of the end time of above-mentioned desiliconization process, the method (comparative example) identical with the method 1 of embodiment 1 and these two kinds of methods of following method 3 (example) are used to compare.

Method 3: oxygen amount required on the chemical theory calculated by the Si densitometer in the molten iron after the desiliconization process of the Si concentration in desiliconization molten iron before treatment and target, after the moment of 1.2 times terminating oxygen amount required on the above-mentioned chemical theory of supply, the time reaching 6.0 more than volume % with the CO gas concentration in waste gas decides the end of desiliconization process for benchmark, and from the above-mentioned moment after about 20 seconds CO gas concentration terminate the method (example) of desiliconization process in the scope of 18.0 below volume % at 6.0 more than volume %

Aforesaid method 1 and these two kinds of methods of method 3 are utilized to implement the hot metal pretreatment of 100 furnace charges respectively, phosphorus concentration after desiliconization process being terminated to the average ash-retention efficiency of the desiliconization slag of rear middle deslagging and hot metal pretreatment in molten iron is studied, and the results are shown in table 2.

From this result, method same is utilized to decide in the method 1 of desiliconization process end time, the average ash-retention efficiency of desiliconization slag is 47 quality %, on the other hand, utilization is suitable for method of the present invention and decides in the method 3 of desiliconization process end time, and the average ash-retention efficiency of desiliconization slag is significantly increased to 62 quality %, in addition, accompany therewith, the phosphorus concentration in the molten iron after hot metal pretreatment significantly reduces, and its degree of scatter (standard deviation) also significantly reduces.

[table 2]

Claims (12)

1. the pretreatment process of a molten iron, the method comprises: to the molten iron supply oxygen source in converter type refining furnace after carrying out desiliconization process, under the state remaining in stove making molten iron, a part for the slag be present in stove is discharged from converter type refining furnace, then, in converter type refining furnace, supply CaO system fusing assistant and oxygen source and carry out dephosphorization treatment, again the molten iron after dephosphorization treatment is tapped a blast furnace from converter type refining furnace, thus use a converter type refining furnace to carry out desiliconization process and dephosphorization treatment to molten iron, wherein

In described desiliconization process, the concentration for the gas the kind more than at least one in the intake-gas come with the waste gas treatment equipment suction of converter type refining furnace containing carbon atom is analyzed, and decides the end time of desiliconization process based on its analytical value.

2. the pretreatment process of molten iron according to claim 1, wherein, calculate the velocity of discharge of carbon in the waste gas of discharging from the converter type refining furnace described desiliconization process based on the concentration analysis value of gas kind containing carbon atom in described intake-gas and the under meter of described intake-gas, reach based on the velocity of discharge of carbon in the described waste gas calculated the end time that the variation diagram again increased after maximum value reaches mnm. again decides described desiliconization process.

3. the pretreatment process of molten iron according to claim 1, wherein, based on CO gas concentration, CO in described intake-gas ₂gas concentration and CO gas and CO ₂in the total concn of gas, the analytical value of any one concentration reaches the end time that the variation diagram again increased after maximum value reaches mnm. again decides described desiliconization process.

4. the pretreatment process of molten iron according to claim 1, wherein, based on CO gas flow, CO in described intake-gas ₂gas flow and CO gas and CO ₂at least one flow in the total flux of gas reaches the end time that the variation diagram again increased after maximum value reaches mnm. again decides described desiliconization process, the CO gas flow in described intake-gas, CO ₂gas flow and CO gas and CO ₂the total flux of gas is by CO gas concentration, the CO in described intake-gas respectively ₂gas concentration and CO gas and CO ₂calculating of the analytical value of the total concn of gas and the flow of described intake-gas.

5. the pretreatment process of the molten iron according to any one of claim 2 ~ 4, wherein, with described reach the value again increased in the variation diagram again increased after maximum value reaches mnm. again reach be more than 90% relative to maximum value and less than 150% to the time more than value of certainty ratio for benchmark, make the end time of described desiliconization process within the given elapsed time.

6. the pretreatment process of the molten iron according to any one of claim 2 ~ 5, wherein, reach in the variation diagram again increased after maximum value reaches mnm. again described, the difference of maximum value and mnm. is more than 10% of maximum value.

7. the pretreatment process of molten iron according to claim 1, wherein, with CO gas concentration, CO in described intake-gas ₂gas concentration and CO gas and CO ₂in the total concn of gas, the analytical value of any one concentration reaches the time of more than given threshold value is benchmark, makes the end time of described desiliconization process within the given elapsed time.

8. the pretreatment process of molten iron according to claim 7, wherein,

Described waste gas treatment equipment is the equipment of the function that the waste gas with described converter type refining furnace suction come reclaims as fuel gas, in described waste gas treatment equipment, the waste gas of converter type refining furnace aspirated together with air and make the burning at least partially of the CO gas in described waste gas

Reach 2.0 more than volume % with the CO gas concentration in the intake-gas after described burning and more than the given threshold value of 18.0 below volume % time for benchmark, make the end time of described desiliconization process within the given elapsed time.

9. the pretreatment process of molten iron according to claim 1, wherein, with CO gas flow, CO in described intake-gas ₂gas flow and CO gas and CO ₂the time that at least one flow in the total flux of gas reaches more than given threshold value is benchmark, makes the end time of described desiliconization process within the given elapsed time, the CO gas flow in described intake-gas, CO ₂gas flow and CO gas and CO ₂the total flux of gas is by CO gas concentration, the CO in described intake-gas respectively ₂gas concentration and CO gas and CO ₂calculating of the analytical value of the total concn of gas and the flow of described intake-gas.

10. the pretreatment process of molten iron according to claim 1, wherein, the velocity of discharge of carbon in the waste gas of discharging from the converter type refining furnace described desiliconization process is calculated based on the concentration analysis value of gas kind containing carbon atom in described intake-gas and the under meter of described intake-gas, and reach the time of more than given threshold value for benchmark with this velocity of discharge, make the end time of described desiliconization process within the given elapsed time.

The pretreatment process of 11. molten iron according to any one of claim 1 ~ 10, wherein, residue in the state in stove more than the 30 quality % making the slag generated in the dephosphorization treatment of last furnace charge under, the molten iron of following core is loaded in converter type refining furnace, carries out desiliconization process.

The pretreatment process of 12. molten iron according to any one of claim 1 ~ 11, wherein, at the end of described desiliconization process, by basicity ([CaO (the quality %)]/[SiO of slag be present in described converter type refining furnace ₂(quality %)]) control 0.80 ~ 1.50 scope.