DE1921963A1 - Method and device for regulating the fresh process with pig iron - Google Patents

Description

Center National de Recherches Me-fellurgiques Association sans but lucratif

47, rue Montoyer Brussels Belgium

Method and device for regulating the fresh process in pig iron.

The invention relates to a method and a device for controlling the hairdressing process in pig iron, the Refining takes place by blowing in an oxidizing gas from above onto or into the pig iron, and this is oxidizing Gas can be technically pure oxygen and contain slag-forming substances in suspension.

There are already numerous special methods known that a certain monitoring of a hot metal refining process using one or the other characteristic Allow factor of this process.

In this context, those methods which are based on the observation of the emission spectrum can be mentioned, for example the converter flame, on the observation of the sound spectrum the pig iron conversion, on analyzes of the converter exhaust gases, etc. are based. From these observations resp.

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Analyzes based on these methods can be used at A corresponding change in one or the other of these freshness conditions makes the "observed sizes easier." keep within the limits that must not be exceeded, if a proper process the freshening process should be guaranteed.

With this method very satisfactory results could be achieved so far, but the realization has become some of these methods, e.g. those based on gas analysis, have proven difficult, while others do than for the assessment of the freshening process running reactions have to be considered insufficient. '

To ensure control of the metallurgical reactions, one must know the distribution of the injected oxygen on the following c ^ ei conditions:

1) Decarburization of the metal pool with the formation of carbon monoxide (CO),

2) oxidation of the slag covering the level of the metal bath,

3) Combustion of carbon monoxide (CO) to form carbonic acid anhydride (CO ₂ ) inside the converter.

The present invention is very much aimed at providing one simple method for controlling the oxygen distribution as mentioned above, and not only with the aim of achieving a predetermined final composition of the slag and of the metal bath to achieve, but also with the further aim of increasing the heat balance and the iron yield from the process check.

The method according to the invention is essentially characterized marked that at every moment of the Irish process the total amount of oxygen blown into the converter is measured that the amount of oxygen in the gas .. The converter hood of the burnt carbon monoxide (CO) is determined to be based on this in the

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BATH ORIGINAL

The exhaust hood burned the amount of carbon monoxide (GO) speed of the metal bath, the instantaneous carbon content of the bath, the oxygen distribution on metal and slag, as well as the total amount of oxygen introduced into the slag, are calculated, and that these Invoice quantities can be used to determine optimal blowing conditions

In the course of the investigations carried out, one has one discovered new and unexpected fact, namely that the exhaust gas temperature measured in the exhaust hood of the converter can be used to determine the QQ quantity burned in this exhaust hood.

Under the converter hood is that “part of the system understood for the discharge of these gases, the converter hat begins and runs at least to the point where the measurement of the temperature of the exhaust gases flowing through the system is measured.

According to the invention, the heat balance is preferably of the gas emerging from the converter in the area of the exhaust hood set up to determine the CO-Kentje burned in this extractor hood and based on this for the calculation the cooling speed of the metal structure, the the current carbon content of the bath, the distribution of oxygen to metal and slag and the total amount of the oxygen introduced into the slag. .

Um, a picture of the importance of the heat balance of the hood To convey, the attached Figure 1 shows as an example to be understood in a non-restrictive sense a converter (1) and an extraction hood (2) for the gases escaping from the converter, as in the above defined · It should be noted that in the selected example the gases exiting the converter are in the extractor hood without cooling water dusting into the gases are exposed to complete combustion.

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The symbols in this figure have the following meanings:

! coI = the amount of carbon monoxide released from the converter (GO) in Nm / min.

CO _Q I = the amount of carbon leaving the converter

Lensic anhydride (CO ₂ ) »also in Nm / min.

^{= the C0} 2 ~ » ®2 ~ ^or * Og quantity in the hood (lim / min.)

T = the temperature of the gases exiting the converter in ⁰ C.

Τ _ψ = temperature of the exhaust gases (C)
™ Q ~ = the amount of exhaust gas (Nm / min.) "

0 = that given off by the exhaust gases in the hood

Tf

Warmth.

On the basis of what is shown in this FIG. 1, this results the heat balance of the extraction hood - as follows:

. / CC / _c + C °° 2. T _c . | C0 ₂ | _c + 4H. jCSO

⁰ P · ^T f

In addition to the symbols explained above, the following also result:

πω cn f
Cf Cp 2f ^c = ^the specific heats of CO, CO ₂ or

of the exhaust gases based on the temperature T_ for CO and CO ₂ and the temperature T _f for the exhaust gases. These specific heats are generally expressed in Kcal per C and per Nm. . <

H = ■ the combustion of 1 Nm CO at

1600 C released heat.

The above equation of the heat balance for the deduction hood is set up under the following aspects:

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rf ^ "-

1) Amount of heat available at the entrance to the fume cupboard «η ο ι η ο ο

co ί ι ι y ^ ι y ο 3

a) sensible warmth of the CO = C ^ ^u . T _ß - [COl ₀

b) sensible heat of the CO ₂ = CCO ₂ .. _T * | coj | _e

e) Combustion of CO in the hood = H * fco | _e

The inherent heat of the combustion heat is negligible.

2) Amount of heat available at the outlet of the fume cupboard:

a) Heat inherent in the exhaust gases = CJ * * T- * Q _f

b) heat given off by the exhaust gases to the hood = Q _w . j

If one sets K =

| col _c + | co ₂ |

C.

for the proportion of CO in the gases CO + CO ₂ escaping from the converter, the heat balance Cl) can be written as follows:

^CT f ^Q f ^{+ Q} w

CO Λ V

C · ¹ P ψ 1 "λ ι λ

ρ c - ^ - ρ "C

This formula shows the very close relationship between the amount of CO leaving the converter and the temperature of the Exhaust gases passing through the hood. Thus, from T ^ based on the value ICO), provided the other factors

f ^c0 CO « ^C t»> ^c > C ² J ^ H, T, Q-, Q and K, their deviations in

only a small mass influence the value JCO) is known are.

Except for the above equations (1) and (2> when the CO is completely burned in the extractor hood, the reproduce the following relations:

= 0.266 | N ₂ | _h - 1/2 Icd |

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The rate of decarburization of the metal bath is thus obtained (in kg carbon per minute) using the formula below:. :

II ^{'12 12}

^e 22.4 22.4 K

The amount (in Nm) of the with the carbon of the metal bath expressing oxygen as follows:

⁰ C = 1 ^C0 2lc ⁺ V2 | CO | _C = - ² ^ | 00 /. _o (4)

Schli.esslich the amount -ausgedrückt in Nm- (0 _sc) of the determined by the difference between the τer and of the lance injected oxygen quantity (D) with the quantity w slag connecting oxygen (0 _c) of the with the carbon of the Metal bath of connecting oxygen »

0 _sc = D -O ₀ . (5)

According to the invention, it has proven to be expedient and advantageous to continuously monitor the exhaust gas temperature and amount, the amount of calories given off by the exhaust gases to the extractor hood, the temperature of the gases emerging from the converter, the amount of water dusted into these gases and the ratio:
K =

| co |

■ +

which is the percentage of GO in the from the converter escaping gases.

These last-mentioned equations (3), (4) and (5) also allow the calculation of the decarburization rate of the metal bath as well as the amount (O ₀₀ ): of the oxygen that binds with the slag, based on the temperature

f door (T ^) of the exhaust gases, provided that the values C,

Cp ⁰ , cr ^O 2,4H, T _c , Q _f , Q ^ ^ ^{10 K are} known.

909885/1028

The first five values are known to a good approximation j small deviations in these values have a only marginal influence on the \ 7ert Go | _.

What the amount of exhaust gas (Q ^) or the amount of combustion concerns combustion products with air sucked into the extractor hood, it can be assumed that that these during the prischungsvorgangs after a reproducible law varies from one melt to another.

In cases where the extraction hood for the gases escaping from the converter is moved into the deadening system without cooling the exhaust gases, the amount of this is measured Exhaust gases

In the other case, namely when the exhaust gases are cooled by dust Water, the amount of dusted water is continuously measured and at every moment a corresponding Correction of the law, which establishes the relationship between the amount of exhaust gas and the injection, made, whereby this law or this rule once and for all through calibration for a given system to collect the gases exiting the converter.

One can also make a correction to the law, which is the ratio between the injection and the gas extractor hood (s)

of the exhaust gases passing through, make by for each melt calculates the balance of the carbon emitted with the exhaust gases and this with the balance of the dem Metal bath compares withdrawn carbon, the calculation of this last-mentioned balance taking into account the composition and the analysis of the used Materials and cast steel.

In the same way, it is possible, for example, on the Based on the amount of water heated and injected into the hood, the amount of calories Qw given to the hood to investigate. Practice has shown that this amount is in

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In many cases it is proportional to the exhaust gas temperature T ^.

The last value to be determined below is the value K. As in practice shows, this value K increases extremely quickly in the first few minutes of the injection, and finally around itself to stabilize to a value between 0.7 and 0.9. FIG. 2 shows such a development as a function of K of the blowing-in time. *

Although the "fluctuations in the value K have only a slight influence on the calculation of the amount icol" burned in the extractor hood, they still have a direct influence on the values V, 0 and 0 calculated according to equations 3-5.

A good control of V, O ₀ and 0 thus sets a good one. Knowledge of the value K and keeping it constant to a large extent.

TJm to show the influence of K on the factors V, 0 and 0, for example, the two melts are discussed according to the following conditions:

1) same weight,

2) same starting composition,

5) which the deviation of the exhaust gas temperatures in the range of The curve representing the hood as a function of time is for the two melts from the first to ) identical to the fifth minute of the injection,

4) the mean of the coefficient K is 0.9 for one melt and 0.8 for the other.

Under these conditions, the calculation of the amounts of carbon released from the metal bath and of the oxygen bound to the carbon of the metal bath on the one hand (0) and the oxygen bound to the slag (0 _gc ) on the other hand gives the following results

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the prerequisite that an oxygen injection rate of 500 fm / min. can be assumed to be constant:

O ₂ .gee. Means free. O ₀ 0 _{02/0 gc} C ₁₅ K carbon st.
in kg

I 7500 0.9 4575 4675 1825 2.55 1.12 %

II 7500 0.8 4950 5550 1450 3.80 O.92 fo

WHEREBY:

C-jc = the carbon content of the metal bath after 15 'blowing time assuming that a batch of 180 tons contains 6600 kg of carbon.

So it can be determined for the same exhaust gas temperature curve, that in the case of melt II the decarburization took place more quickly and that the slag has not received enough oxygen at this stage, with the result that the danger is that the final levels of phosphorus and sulfur come into play. With continuous freshening on the same At the end of the blow-in process, the carbon content of the metal bath is too low and this is the result Insufficient oxygen content in the slag. In contrast, the freshening process with blowing in a Saueratof excess for the purpose of feeding the missing amount of oxygen into the slag continued, so designed the'heat balance is irregular.

In examining the various factors that are likely to have an influence on the coefficient K, one comes to the following conclusions:

1) K is "dependent on the respective or current altitude the lance over the bath surface, because it has always been found that with increasing distance between the lower end of the lance and

- 10 -r

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the metal bath level is reduced by the coefficient K, v / uh- " rend all other conditions remain the same.

2) K depends on the temperature inside the converter.

This dependency can be determined based on the release of heat-generating and other elements as well as the Calculate the Y / poor state of the converter. So is for example the resumption of production with a cold crucible must be taken into account i ^ -Ti.

From cKm above it follows that the coefficient K as a function of the current height of the lance above the bath level as well as the level inside the converter seeing temperature changes.

After the influence of K is known, it must be sought after this value either by making corrections the mean value of K from one melt to another or by correcting this coefficient K im To keep the course of "pouring constant."

In an effort to keep the coefficient K constant from melt to melt, the equations are added Calculation of the batches or /. Inserts for the freshening process expediently those indicators that enable a control with regard to excessive reduction or increase "enable this coefficient, and if you change the injection scheme, i.e. the development of the predetermined injection conditions for the subsequent melt such that the value of the coefficient K is precisely adapted to the respective melt.

According to the invention, the value of the coefficient can also be determined K in an advantageous manner by means of a continuous measurement of the sound strength in the vicinity of the converter specify, whereby this coefficient K is given by corresponding

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9 0 9 8 8 5/1028 ■ "'

Rapid adaptation of the blowing conditions during the freshening process can be kept constant at the setpoint.

The level of the from the freshening equipment accruing- ' The curve representing noises shows various characteristic sections in its general course: according to to FIG. 3 as appended in the appendix, section I corresponds to the period of progressive slag formation as well as the dissolution of the lime used, section II begins in your moment, as the entire slag becomes responsive, and the section III corresponds to the different values of K, the different curves 1, 2, 3 correspond to the increasing values of K.

According to an operational embodiment of the invention is used to change the blowing conditions so that the value of the coefficient K is a predetermined curve follows, the continuous measurement of the strength of the sound emitted by the converter is used.

Injection conditions are to be understood as the quantity of injected oxygen, the height of the lance and the total amount of oxygen injected up to the moment of penetration O

According to the invention, it is also advantageous to use the blow-in conditions ; e.g. the lance height, the amount of oxygen blowing, the up to sun: Auger, t lick of penetrating or acting to regulate the total amount of oxygen blown in so that the metal bath decoction rate is the current one Carbon content of the bath, the oxygen distribution on metal and slag and that introduced into the slag total amount of oxygen according to predetermined principles be achieved.

To ensure the speed and accuracy of the invoices and any impacts during the freshening process the measured values obtained are expediently increased

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into a computer, preferably a digital computer, given with the aim of having the calculations carried out and those suitable for the respective programming Get results.

In order to exclude any external influence, the commands of the devices for regulating the operating conditions subordinate to the signals generated by the computer as a result of the measured values and the calculation made according to the programming.

In this context it should be pointed out that when processing batches with a larger slag weight ψ, a slightly larger proportion of oxygen must be added to this slag. The best solution is to increase the coefficient K slightly, but there is also the possibility of slightly increasing the blowing time.

With increasing steel weight, more oxygen has to be blown through the egg the freshening process takes a little longer. In this case the best means of adapting the exhaust gas temperature curve must be determined.

The present invention also relates to a device for implementing the method described above.

The plant system according to the invention is essentially characterized by a converter as well as all -required to carry out the oxygen-freshening of a pig iron bath Accessory devices, through an extractor hood to catch the during the freshening from the converter escaping gases, by devices for measuring the temperature of the gases passing through this hood, as well as using devices to determine the decarburization rate of the metal bath on the basis of the measured values, the current carbon content of the metal bath, the

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distribution to metal and slag as well as the in to calculate the total amount of oxygen introduced into the slag.

Each of an expediently modified embodiment according to the invention is thereby the device used marked that it is a link between the Devices for measuring the exhaust gas temperature and the Computing elements comprises such that each intermediate link between these two groups of devices is not applicable.

According to the invention, the computer elements also consist of an electronic computer that is as digital as possible.

! ⁿ times a further advantageous embodiment of the invention the device is characterized in that it comprises means for the means for regulation of the operating conditions to assign the computer elements! whereby a management and control of the freshening process is possible without any external influence.

To clarify the given example with regard to the heat balance an extractor hood for gases escaping from the converter with complete combustion in this hood The operating conditions are without cooling water atomization in the gases determined as follows:

1) converter ■ '■

It is a converter with a capacity of 180 tons, which is charged with 150 tons of pig iron with 4-p4 fo carbon content. The blowing time is 19 minutes «, ~.

2) Development of the amount of exhaust gas depending on the side

Q = A- -L- ..B

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909885/102 8

V / OBEI s A = 4800 F B =

t = 19 minutes as blowing duration or time s

t = an instantaneous value for the injection.

3) Specific heat of CO and C0 "

TC ^ ⁰ = 0.310 + '. 0.002

= 0.405 + -. O.ülO

4) Heat released by "burning 1 Fm ^J CO at 1600 C:

H = 3000 Kcal / Km ⁵ CO

5) temperature of the. Converter escaping gas:

T ₀ = a + B (K - K ₀ ) WHERE:

a = 1400 b = K ₀ = 0.700

6) Heat given off to the hood:

Q _w = ET _f

ViOBEI: E = 1000

7) Change in the coefficient K as a function of time:

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909885/1028

It can be made one or the other of the following hypotheses use:

a) K = K ₀ + tG- for ο £ »t 6» * t.

• tr ir -Pitt »+ ■ ^ - +

^K - ¹ W, ^iur S

TOBEI:

K ₀ = 0.700
G- = 0.05
_t = 5 minutes
0.95

^b > ^K = ^K max - ^K o · ^e " ^{X t}

In the latter case, the change in K is expressed by an exponential function, with the course the curve representing this change in the attached Figure 4 ;; ee "is ebc-n.

8) Development of the exhaust gas temperature inside the extractor hood as a function of time:

The development of the exhaust gas temperature within the The curve representing the hood as a function of time is shown in FIG. 5 attached. This development is obtained by setting initially the corresponding lance height and then by setting the amount of oxygen accordingly.

9) Evaporated Was Mixture:

The amount of water that evaporated was in the order of magnitude of 30 tons per melt, the corresponding amount of heat in the order of 18,000.OCO Kcal / melt.

It can be assumed that the evaporated water is proportional to the temperature of the exhaust gases in the hood, which is also proven and confirmed in detail by practice is.

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909885/1028

Since the gases emit an average of approx. 900,000 Kcal / min and the mean temperature is about 900-C to be written:

Q _w = 1000 T _f .

Under the aforementioned conditions, the decoloration speed can be set at any moment in accordance with the example given calculate using the formula:

-ρ

12 ° p * ¹ f '^ f

C η η λ ir π GO m, 1 - K π ^^ η _ηχ

The development of the rate of decarburization is dependent The speed of the time is shown in the accompanying FIG. 6 and is used for the oxygen mixing of pig iron (LD method) to be considered classic.

In this example it can be calculated »that the total amount of carbon removed from the metal bath is 6600 kg. '*

In practice für.eine pig iron charge falls of 150 tons with a carbon content of 4.4 i ° a withdrawn from the metal carbon amount of 6600 kg of · Thus, there is a very good correlation between the calculated in dependence on the exhaust gas temperature (T _f) in the hood Decarburization rate and the "effectively burned amount of carbon _{β in the course of a melt."}

It turns out that the method described above and specifically the given equations are applied and used with the aim of regulating the metallurgical results of a refining treatment of pig iron, ■ whereby changes in the steel weight, des Slag weight, coefficient K etc. can be taken into account.

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Claims (1)

Claims 1. A method for regulating the fresh process in pig iron, characterized in _{that 3} in each. At the moment of the frying process, the total amount of oxygen blown into the converter is measured, that the amount of carbon monoxide (CO) burned in the gas hood of the converter is determined, that based on this amount of carbon monoxide (CO) burned in the hood, the decarburization rate of the bath, the oxygen distribution on metal and slag as well as the total amount of oxygen introduced into the slag can be calculated, and that these calculation parameters are used to determine optimal injection conditions. 2. The method of claim 1, characterized in that ₃ to determine which is in the gas hood of the converter CO amount burned measured in this hood exhaust temperature used. 3. The method according to claims 1 and 2, characterized in that for calculating the decarburization rate of the metal bath, the current carbon content of the bath, the distribution of oxygen on metal and slag and the total amount of carbon introduced into the slag, the heat balance for the gas - ■ the converter hood is installed. H. The method according to claims 1 to 3, characterized ₃ that continuously the exhaust gas temperature and amount, the amount of calories released by the exhaust gases to the hood, the temperature of the gases emerging from the converter, the amount of water dusted into this and the ratio 909885/102 8 co K = co _Λ + co, " c ic .,. can be determined, the latter ratio representing the percentage of CO in the gases CO + CO ₂ emerging from the converter. i. Method according to Claims 1 to H, characterized in that in those cases where the extraction hood for the gases escaping from the converter is operated without cooling the exhaust gases by means of water atomization, the amount of these exhaust gases is measured. fc 6. Method according to claims 1 to ¹ ^, characterized in that in the cases where the exhaust hood for the gases escaping from the converter is driven with cooling of the exhaust gases by spraying water, the amount of dusted water is continuously measured and At every moment a corresponding correction of the law, which establishes the relationship between the amount of exhaust gas and the blow-in, is made, this law or this rule being established once and for all by calibration for a given system for collecting the gases emerging from the converter. 7. The method according to claims 1 to H, marked thereby distinguished ₃ that a correction of the law, which establishes the relationship between the blowing and the amount of the gas hood passing exhaust gases, is made by nan for each melt, the balance of the Calculates the carbon released from the exhaust gases and compares this with the balance of the carbon removed from the metal bath, the calculation of this last-mentioned balance taking into account the composition and analysis of the materials used and the cast steel. 909885/1028 8. The method according to claims 1 to 7, characterized in that in order to keep the coefficient K constant from one melt to the other in the equations for calculating the batches or inserts for the freshening process, such indicators are used which allow a control with regard to allow this coefficient K to be reduced or increased too great, and that the injection scheme, ie the development of the predetermined injection conditions for the subsequent melt, is changed in such a way that the value of the coefficient K is precisely adapted to the respective melt. 9. The method according to claims 1 to 7, characterized in that the value of the coefficient K is specified by means of a continuous measurement of the sound intensity in the vicinity of the converter, whereby this coefficient K can be kept constant at the target value by appropriate adjustment of the blowing conditions during the Irish process . 10. The method according to claims 1 to 7, characterized in that to change the injection conditions in such a way that the value of the coefficient K follows a predetermined curve, the continuous measurement of the strength of the sound emitted by the converter is used. 11. The method according to claims 1 to 10, characterized in that the injection conditions such as the lance height, the amount of oxygen blowing, the total amount of oxygen blown in until the moment of action are regulated so that the metal bath decarburization rate, the current carbon content of the bath, the Oxygen distribution to metal and slag and the total amount of oxygen introduced into the slag forwards t. certain regularities can be achieved. 909885/102 8 12. The method according to claims 1 to 11, characterized in that to increase the speed and accuracy of the calculations and any effects during the freshening process, the measured values obtained are entered into a computer, preferably a digital computer, with the aim of performing the calculations to be carried out and to obtain the results suitable for the respective programming. 13. The method according to claims 1 to 12, characterized in that, in order to avoid any external influence, the commands of the devices for regulating the operating conditions are subordinate to those signals that are sent by the computer as a result of the entered measured values and the respective Programming employed calculation are sent. IH. Device for implementing the method described in claims 1 to 13, characterized by a converter and all the accessories required to carry out the oxygen refining of a pig iron bath, by a hood to collect the gases escaping from the converter during refining, by devices for measuring the temperature of the gases passing through this vent, as well as by means of devices to determine the decarburization rate of the metal bath based on the measured values obtained. Calculate the oxygen distribution on metal and slag as well as the total amount of oxygen introduced into the slag. IS. Device according to claim 1H, characterized in that it includes a connection between the devices for measuring the exhaust gas temperature and the computer elements in such a way that there is no need for any intermediate link between these two groups of devices. 909885/1028 16. Device according to claims 14 and 15, characterized in that the computer elements consist of an electronic computer. 17. The device according to claim 16, characterized in that the electronic computer used is a digital computer. _Λ that it comprises means subordinate to the means for controlling the operating conditions of the machine elements, whereby a guide lind control of the refining process without any external influence is possible 18. Device according to claims 14 to 17, characterized. 909885/1028 Blank page