GB1568406A - Method for controlling exhaust gases in oxygen blown converter - Google Patents
Method for controlling exhaust gases in oxygen blown converter Download PDFInfo
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- GB1568406A GB1568406A GB5314176A GB5314176A GB1568406A GB 1568406 A GB1568406 A GB 1568406A GB 5314176 A GB5314176 A GB 5314176A GB 5314176 A GB5314176 A GB 5314176A GB 1568406 A GB1568406 A GB 1568406A
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- gases
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- damper
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/28—Manufacture of steel in the converter
- C21C5/38—Removal of waste gases or dust
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- Environmental & Geological Engineering (AREA)
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- Organic Chemistry (AREA)
- Carbon Steel Or Casting Steel Manufacturing (AREA)
- Waste-Gas Treatment And Other Accessory Devices For Furnaces (AREA)
Description
(54) A METHOD FOR CONTROLLING EXHAUST GASES
IN OXYGEN BLOWN CONVERTER
(71) We, NIPPON STEEL COR
PORATION, a Company organized under the laws of Japan, of 6-3, Otemachi, 2-chome, Chiyoda-ku, Tokyo, Japan, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a method for controlling the withdrawal of exhaust gases from an oxygen blown converter.
It is known, in steel making processes using oxygen, to recover combustible exhaust gases, such as carbon monoxide (CO) produced by blast refining, and to reuse them for heat generation.
In such known processes unburnt gases have been recovered using a method in which the pressure differential between throat pressure ie. the pressure within the hood adjacent the outlet of the converter, and atmospheric pressure is detected and the opening of an exhaust gas damper is automatically adjusted by an adjusting meter or regulator so that said pressure differential is brought to or maintained at a predetermined value.The disadvantages of this method are the so-called blow-out, in which the exhaust gases are emitted out of the hood, and the so-called intake phenomenon, in which excess air is drawn into the hood, which result from delayed response in detecting rapid variations in the quantity of exhaust gases being generated and from delayed response of the adjusting meter or the exhaust gas damper to changes in the quantity or flow rate of oxygen feed, and charge rate of secondary material such as iron ore. This results in a loss of combustible exhaust gases since they will burn with oxygen from indrawn excess air.
Attempts have been made to recover the combustible gases, such as CO produced in connection with the blast refining. For example, see British Patent Specification
No. 1,187,530 which describes a method in which a damper is controlled in response to the pressure differential between hood pressure, ie. the pressure within the hood, and atmospheric pressure so that the pressure within the hood assumes a predetermined level. Surplus air may be indrawn into the exhaust system by suitably opening the dust collector damper in order to avoid the surging phenomenon created by the draught fan used to withdraw the exhaust gases. This occurs because the quantity of furnace generated gases varies from time to time, being very small in the early stages and the last stages of the blast refining.This method, consequently results in the burning of combustible exhaust gases, representing an undesirable economical loss.
Further, the aforementioned hood pressure controlling method unavoidably involves the disadvantages of blow out and excessive intake mentioned above. It should also be noted that blow-out phenomenon may cause the emission of red fume, which is environmentally damaging.
According to the invention there is provided a method of controlling the withdrawal of exhaust gases from an oxygen blown converter, comprising continuously detecting the quantity of oxygen fed, the quantity of secondary raw materials charged, the composition of exhaust gases and the flow rate of the exhaust vases: continuously calculating future values of the quantity of the furnace generated gases and the flow rate of combustion exhaust gases at the converter hood on the basis of said detected values; and controlling the quantity of drawn exhaust gases on the basis of said future values.
At any one moment the gases actually generated are in dimensional terms, a quantity, which, if divided by time becomes, in dimensional terms, a flow rate.
For producing a control signal it is more suitable to operate in terms of flow rate, but generally in the practice of the invention, as described hereunder, either quantity or flow rate is equally applicable.
Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which:
Figure 1 is a schematic block diagram of an oxygen blown converter and exhaust system;
Figure 2 schematically illustrates the time sequence of factors involved in the control of exhaust gas;
Figure 3 schematically illustrates the time sequence as in Figure 2 but with reference to the exhaust system shown in Figure 1;
Figure 4 schematically illustrates a signal processing circuit in the exhaust system of
Figure 1;
Figures 5(i) to (1) schematically illustrate the coefficients of coupling;
Figures 6 and 7 illustrate a comparison of the quantity of recovered unburnt gases operating in accordance with the present invention and by a prior art method;
Figure 8 illustrates the variation with time of recovered exhaust gases;;
Figure 9 is a schematic block diagram of apparatus for recovering unburnt exhaust gases in a converter;
Figure 10 is a comparison of predicted and actual quantities of furnace generated gases during blast refining;
Figure 11 illustrates the variation with time of exhaust gas recovery; and
Figure 12 shows the variation of damper opening during blast refining.
Referring to Figure 1, this shows a converter in the form of a steel bath 1, into which oxygen is introduced by means of the blast refining oxygen lance 2. The exhaust gases produced from converter 1 are passed through a collecting hood 3 provided with a vertically movable skirt 3' and an exhaust gas pipe 4 and are guided into a holder (not shown) or a smokestack (not shown) via a dust collector 5, an exhaust gas damper 6, a throat 7 provided with a flow detector, and a draught fan 8. The exhaust gas damper 6 can be any convenient design as long as it can be used to control the flow of exhaust gas.
Secondary raw material, which may include fluxes and coolants are charged into the converter 1 from a secondary raw material hopper 9 through a charging feeder 10. The pressure differential between pressure in the hood (referred to herein as hood pressure) and atmospheric pressure is measured by a pressure differential transmitter 11, the signal thereof being supplied to a hood pressure controlling adjusting-meter or regulator 12.This adjusting meter or regulator 12 has a predetermined pressure differential value preset therein, with which the input signal of the aforesaid pressure differential transmitter 11 can be compared so that a resultant corrected signal is generated and can be transmitted in the form of an exhaust gas damper control signal through a signal processor circuit 13 (later described) to a servomechanism 14 for operating the damper 6 in accordance with conditions (later described) to thereby control the exhaust gas damper 6.
In this state, if a correction of the signal entering signal processor circuit 13 is not carried out, control based on the pressure difference occurs as in known systems. In the present embodiment where a control system based on prediction of various gas quantities, described hereinbelow, is not desirable or is impossible due to operating conditions or difficulties with equipment, the aforesaid control based on the pressure difference, ie. feedback control may immediately be applied to the damper to thereby afford the possibility at least of control readiness and simplicity of maintenance. In addition, both the feedback control and predictive control may be carried out to permit more precise control.
A calculator 19 carries out the three operations noted below on the basis of inputs from an oxygen flow meter 15, a secondary raw material charge transmitter 16, an exhaust gas analyser 17, and an exhaust gas flow meter 18, and
1) it calculates the quantity or flow rate of gases formed by reaction with oxygen the feed in the converter and the oxygen generated as a result of decomposition of secondary raw material.
2) it calculates the quantity or flow rate of decomposed and reacted gases resulting from the decomposition of the secondary raw material.
3) it calculates the quantity or flow rate of combustion exhaust gases at the hood which react with air entering the hood.
The above mentioned quantity or flow rate of gases formed by reaction with oxygen feed in the converter and quantity or flow rate of decomposed and reacted gases are referred to herein as "the quantity of furnace generated gases".
In the case where the rate of oxygen feed is varied as the operation progresses, that is, when the oxygen feed is commenced and is increased or decreased, or when the secondary raw material charging is commenced and is varied, changed in kind or stopped, the quantity of furnace generated gases, ie. gases produced within the hood varies sharply. Thus, when control of the exhaust gas recovery system is delayed as previously mentioned, blow-out or excessive intake occurs. To prevent such a phenomenon, the flow rate of furnace generated gases and the flow rate of combustion exhaust gases at the hood resulting from variation of the oxygen feed rate and variation of the rate of secondary raw material charging as described above can be controlled through the calculator 19 computing the above mentioned information and supplying a signal to a prediction control adjusting meter or regulator 20.This adjusting meter or regulator 20 then provides the degree of exhaust gas damper prediction control necessary to adjust opening of the exhaust gas damper 6 to such a degree as to avoid blow-out or excessive intake as described above; the control signal is delivered to the operating servomechanism 14 through the signal processor circuit 13 later described.
Accordingly, the exhaust gas damper 6 will be opened or closed in response to an increase or decrease of the quantity of converter generated gases, ie. gases in the hood and the quantity of combustion exhaust gases at throat before the quantity of these gases increase or decrease. As a consequence, the exhaust gases can be recovered, and the hood pressure, can also be properly maintained to minimize the fluctuation thereof. This will be further discussed in detail with reference to the other drawings.
In Figure 2(a) to (h) the abscissas represent the lapse of time, and the ordinate represents the degree of variation of each item, showing the effect of control based on the pressure differential between the hood pressure and the atmospheric pressure. In
Figure 2(a), assuming that charging of the iron ore as the secondary raw material began at time tst, the generated gases begin to increase after to seconds, ie. at time t,2.
(Fig. 2(b)). Then, the differential between the hood pressure and the atmospheric pressure begins to increase at time tis3, the pressure differential being detected by the pressure differential transmitter 11. When the pressure differential increases in one direction, the amount of air entering through the hood decreases or, when it increases in the other direction the converter generated gases themselves begin to pass out of the skirt 3', as a consequence of which the quantity of converter generated gases burned within the hood will decrease. That is, the quantity of CO which burns with the air entered at the hood as a proportion of the quantity of CO contained in the furnace generated gases decreases.If the ratio of the quantity of CO generated in the converter, ie. gases passing into the hood, to the quantity of CO which burns at the hood is expressed by the combustion rate, the combustion rate decreases as in curve d, shown in Figure 2(d). Since opening of the exhaust gas damper 6 is set at the time when an increase in the aforesaid pressure differential has been detected as shown in Figure 2(e), the exhaust gas damper 6 will not be opened until time ts4 is reached as shown in Figure 2(f).
The exhaust gas withdrawal thus begins at time ts4 as shown in Figure 2(g). As previously mentioned, however, the furnace generated gases increase at time tis2, and hence, the differential between the quantity or flow rate of suction exhaust gases and the quantity or flow rate of converter generated gases, ie. the quantity of exhaust gases corresponding to a cross-hatched area h1 in
Figure 2(h) is blown out of the hood and is dissipated outside the exhaust gas recovery system.Further, after the secondary raw material has been charged, the quantity of converter generated gases is actually decreased at time ts6 but the closing of the damper 6 is delayed in response so that the exhaust gas damper 6 remains opened until time ts9 is reached thereby allowing air corresponding in quantity to a crosshatched area h2 to enter through the hood.
The exhaust gases are burned by the thus entered air reducing the calorific value of the recovered exhaust gases and increasing the temperature of the exhaust gases simultaneously therewith; as a result, extra energy is required to cool the exhaust gases and the service life of the machinery may be shortened.
In order to overcome the response delay as noted above, a predictive control may be provided as shown in Figure 3(a') to (h'). In
Figure 3(a'), at ore charging time tsi, an ore charge starting signal is received from the secondary raw material charge transmitter 16, and immediately the opening of the exhaust gas damper 6 is set through the calculator 19 and the prediction control adjusting meter or regulator 20 at time between tsii and tri2, the exhaust gas damper 6 being opened at time tst3.Since time tst3 is actually earlier than time ts2 at which the converter generated gases, ie. gases passing into the hood begin to increase, the difference between the converter generated gas quantity or flow rate and the suction exhaust gas quantity or flow rate is produced to thereby draw in a small amount of air corresponding to a hatched line area h'l as shown in Figure 3 (h'). However, this is merely one example. Practically, the increase in the quantity or flow rate of converter generated gases and adjustment of the opening of the exhaust gas damper 6 may be arranged so as to minimize the above-mentioned indrawing of air to a degree such as to be negligible in actual operation.The above-mentioned indrawing may be altered to or substituted by blow out by suitable selection of the time difference between time tS13 and ts2 as previously mentioned, this can be suitably selected in accordance with the equipment and operating conditions.
It will be noted in Figure 3 that the difference between the quantity or flow rate of converter generated gases and the quantity or flow rate of indrawn exhaust gases after the secondary raw material has been charged, ie. the quantity corresponding to a hatched line portion 2h' in Figure 3(h') is the residual quantity or flow rate of indrawn air which has not been burned. It is desirable that the efficiency of control in preventing blow-out or excessive intake should be similar. However, there is a tendency for a slight bias to one mode or the other depending upon the particular kind of equipment and its condition. In the illustrated case, it has been found better to adjust the control system relative to the intake side in terms of improving both the operating environment and recovery of the exhaust gases, but this is in no way restrictive.While variation in the rate of charging of secondary raw material has been described particularly in respect of iron ore a similar procedure may be employed in respect of other raw material e.g. in the quantity of dolomite ore or other material, and quantity or flow rate of oxygen.
Next, a method for calculating the quantity or flow rate of combustion exhaust gases at the hood to be withdrawn will be described in detail. Concentrations in the exhaust gas of CO, CO2, H2 and N2 are obtained from the exhaust gas analyser 17 and are expressed as Xco, Xco2, Xo2, XH2 and XN2 (%), respectively. With respect to
XN2 ( Sn), since the gases generated within the converter comprise CO, CO2 and H2, it may be considered that most of the N2 within the exhaust gases results from air entering through the hood. It may also be considered that the greater part of O2 contained in air entering through the hood burns with the CO of the furnace generated gases and a small amount of the remainder thereof is detected as Xo2 within the exhaust gases.Accordingly, the apparent concentration Xo2, of the O2 contained in air entering through the hood to the quantity of combustion exhaust gases at the hood can be calculated by equation (1) below from the concentration of the quantity of N2 contained in air which has entered through the . hood, ie. the concentration XN2V0 of N2 within the exhaust gases,
21 To2,= . XN2 (1)
79
From this, the apparent concentration To2"% of the quantity of O2 used in combustion of the converter generated gases within the collecting hood 3 to the quantity of combustion gases at the hood may be obtained by equation (2) below from the quantity of O2 not used in combustion, ie. the concentration Xo2% of O2 within the exhaust gases, Xo21,=Xo2,-Xo2 (2)
CO within the converter generated gases is oxidized into CO2 as indicated by equation (3) below by the 02, 2CO+O22CO2 (3)
Thus, the CO produced in the converter is partly oxidized by the O2 of the air entering the hood and mixing with the combustion exhaust gases and as a consequence, the CO concentration decreases while the CO2 concentration increases.From the foregoing, the relationship between the apparent concentrations Xco' and Xco,'O/, of the quantities of CO, CO2, respectively, produced within the converter and the quantity of combustion gases at hood may be obtained by equations (4) and (5), respectively, Xco'=Xco+2. Xo2,, (4) Xco2,=Xco2-2 . Xo," (5) 100XH2 XH2,= (5') Xco'+Xco2,+XH2 We have found that XH2 can be utilized in place of XH2' in order to operate embodiments of the present invention with satisfactory accuracy. In the following description, therefore, XH2 has been used.
From this, the ratio of air entering through the hood to the quantity of CO produced in the converter, ie. the combustion rate A may be obtained by equation (6) below, =(Xco'-Xco),Xco' (6)
Further, the relation of the change in volume when the converter generated gases in turn become the combustion exhaust gases at the hood may be obtained by equation (7) below, from which the quantity or flow rate of combustion exhaust gases to be withdrawn may be calculated as follows:
Quantity of combustion exhaust gases
Quantity of converter generated gases
Next, the quantity of converter generated gases, ie. gases generated in the converter may be calculated in a manner as follows.
If the total quantity of oxygen supplied to the converter 1 reacts with carbon within the steel bath as indicated by equation (8) below, the volumetric quantity of gases of formation after reaction calculated at standard conditions is twice as much as the volume of the total quantity of oxygen supplied.
2C+O2 < 2CO (8) However, since a part of oxygen is also reacted as indicated by equation (9) below, the volume of gases is reduced after reaction according to the amount of CO2 produced, 2co+o22C 2 (9)
Assuming now that the apparent quantities of CO and CO2 produced in the converter and the quantity of combustion exhaust gases at the hood are Xco' and Xco2'% respectively, as previously mentioned and the ratio of the quantity of CO2 produced in the converter to the quantities of the converter generated CO and CO2 is y which may be obtained by the following equations (10) and (10')::
When a calculation of y is carried out on the basis of carbon (C) distribution, y may be calculated by the equation (10) and designated y,, Xco2, 3'c= .100 (10)
Xco'+Xco2,
In another case, the calculation of y may
be carried out on the basis of O2 distribution
and y obtained therefrom designated as yO2, Xco2, YO2=- 100 (10') +Xco'+Xco2l Thus the ratio of the quantity or the flow
rate of gases being formed after reaction
with respect to the total quantity of supplied
oxygen may be obtained from the following
equations (11) and (11')::
Quantity of gases produced within the converter after reaction
Total quantity of supplied oxygen within the converter
In the following discussions of the preferred embodiment of the present invention, yo, is used as y, which is the ratio of the quantity of CO2 produced in the converter to the quantities of the converter generated CO and CO2.Let Fo2 be the quantity (in Nm2/hr) of oxygen feed obtained from the oxygen flow meter 15, WtT/Hr the charged quantity of O3 producing secondary raw material obtained from the secondary raw material charge transmitter 16, a,Nm3/T the coefficient of O production, W2T/Hr the charge quantity secondary raw material which produces decomposed reaction gases, and a2Nm3T the coefficient of producing gases thereof.
Then the quantity F1 (in Nm3/hr) of gases resulting from reaction with oxygen within the converter, the decomposed reaction gases F2 (in Nm3/hr) produced resulting from cracking of the secondary raw material, and the quantity F3 (in Nm3/hr) of generated gases produced in the converter, which is the sum of F1 and F2, are given by equations (12), (13) and (14), respectively,
F2=a2.W2 (13) F3=F1+F2 (14)
The coefficients a, and a2 can easily be obtained by analysis of the constituents of the respective secondary raw material.
Generally, however, in iron ores, a, is 150 to 250 Nm3,T, and in the raw dolomite, a2 is 150 to 250 Nm3/T.
Accordingly, the quantity or flow rate of combustion exhaust gases F4 (in Nm3/hr) resulting from combustion at the hood to be withdrawn may be obtained easily by equation (7') below rather than the equation (7) described above
Signal processing of the exhaust gas damper control signal based on the pressure differential between the throat pressure and the atmospheric pressure and the exhaust gas damper prediction control signal based on change in the quantity of oxygen feed and the quantity of secondary material charged in accordance with the present invention will be described in detail, by way of example, with reference to Figures 4 and 5.In Figure 4, the control signal SX of the exhaust gas damper 6 from the throat pressure controlling adjusting-meter 12 and the control signal Y from the prediction control adjusting meter 20 are supplied to signal processor circuit 13 which may be conventional. For example, Fig. 4 shows a combination of conventional potentiometers 13a, 13b and conventional adder 1 3c for carrying out the processing as shown in Fig. 5(i) and (j). Signal processor circuit 13, may operate for example, on the basis of equation (15) to provide a control signal Z: Z=aOX+bOY (15) where, a0 and b0 are the coefficients of coupling in 13a and 13b, respectively.In this case, control based only on the pressure differential between the hood pressure and the atmospheric pressure may be employed by setting the coefficients of coupling to aO=I; bo- as shown in Figure 5(i); this situation might arise, for example, due to operating problems necessitating partial shutdown of the apparatus.
A method relying only on exhaust gas damper prediction control can be employed by setting the coefficients of coupling to aO=O; b0=1 as shown in Figure 5(j).
Further, in the case where the control signal is in excess of a predetermined control signal value Y0 as shown in Figure 5(k), a linear coupling may be employed so as to have the coefficients of coupling as shown below at that time, at=0; and bio=1 That is, the prediction control at the time of changing the oxygen feedrate and or the rate of charging of secondary raw material may be accomplished by selecting the set control signal value Y0 at a suitable value.
To achieve more accurate control, the coefficient of coupling a0 may gradually be decreased and conversely the coefficient of
coupling b0 may gradually be increased until the set control signal value Y0 is attained, as
shown in Figure 5(1), then the coefficients of
coupling are aO=O; b0=l at the set control signal value YO.
It will be noted that higher linear
couplings or couplings with other functions
may also be employed in accordance with
the equation, Z=f(SX,Y). The above
mentioned signal processor circuit 13
comprises a combination of known control
elements. For example, the conditions
shown in Figure 5(i) and (j) can be used in
the signal processor circuit 13 of the kind as
shown in Figure 4.
The conditions shown in Figure 5(k) and
(I) can be used by a conventional signal
processor circuit for example a comparator
or functional generator.
Results obtained when operating a 170
ton converter are shown in Figures 6 and 7.
Figure 6 shows the variation with time in the
amount of unburnt exhaust gases recovered,
in terms of standard calorific content (2000 Kcal/Nm3), after the commencement of
charging iron ore; the solid line (m)
representing an example in accordance with
the present invention, the dotted line (n) an
example in accordance with the prior art,
and the cross-hatched area highlights the
difference in the quantity of unburnt gases
which was recovered or gas which was
emitted from the hood by operating in
accordance with the invention, ie. an extra
500 Nm3. Figure 7 shows the variations in
the amount of unburnt gases recovered in
terms of calorific content at the time of
completion of charging iron ore, and after
completion of charging iron ore: the solid
line (m') represents an example in
accordance with the present invention, the
dotted line (n') an example in accordance
with a prior art method, and the cross
hatched area highlights the difference in the
amount of unburnt gases recovered or
surplus air restrained from entering the
hood by operating in accordance with this
invention, ie. by 400 Nm3 in this example.
Referring to Figure 8, which illustrates a prior art method, at time t,, blast refining begins, and the quantity of converter generated gases varies with time as shown by the solid line 21. The openings of the dust collector damper and draught fan damper are set to permit the passage of a quantity of gases greater than the quantity of converter generated gases to reduce the risk of surging carried by the draught fan as previously mentioned; the quantity of exhaust gases withdrawn varies as shown by the dotted line 22.The cross-hatched area 23 indicates the amount of surplus air indrawn at the hood and hence, at an early stage in blast refining by time t, and time t2, combustible gases or CO gases are being wastefully burned within the flue and dust contained within the converter generated gases by burning, are formed, into fine particles which reduces the dust collecting efficiency of the exhaust systems. Gas recovery is normally economical when the content of
CO in the exhaust gases reaches approximately 40O/o. If the intake of the surplus air could be reduced, the rate of gas recovery during time t, to t2 would be enhanced. Next, the converter generated gases abruptly increase in volume as reaction in the converter starts at time t2.
However, in the hood pressure control method, the quantity of withdrawn gases cannot rapidly follow the increase in the quantity of converter generated gases due to response time of the control system, and for this reason, as indicated by the crosshatched area 24, converter generated gases are blown out of the hood with consequential loss of CO.
Next, at the intermediate stage of blast refining, the quantity of converter generated gases will be stabilized and the quantity of withdrawn exhaust gases will also be stabilized accordingly. However, in the final stage of blast refining, when the rate of oxygen feed is increased at time t3 as shown by the solid line 25, to bring the carbon content in the steel to the desired level, the quantity of furnace generated gases may increase for a while but will abruptly decrease as the quantity of carbon in the steel decreases.Also, at this time, the quantity of withdrawn exhaust gases cannot follow the variation in quantity of converter generated gases due to the delay of the control system to produce the excessive intake of surplus air at the hood portion as shown by the cross-hatched area 26 this leads to wasteful combustion and gives rise to a problem similar. to that referred to above in relation to the hatched line area 23.
In Figure 8, the solid line 27 indicates the charging of secondary raw material or the like and represents the quantity of iron ore charged; the solid line 28 indicates the quantity of recovered gases in standard calorific content.
Figure 9, which illustrates an embodiment in accordance with the invention shows a plant having a converter 29, an oxygen lance 30, exhaust ducts 31 and 33, dust collectors 32 and 32', and a draught fan 34. In the blast refining, the secondary raw material is charged into the converter 29 through a charging chute 36 from the secondary raw material charging device 35, a signal corresponding to the charged quantity being sent from a secondary raw material charge transmitter 37 to an operation control device 38. A signal corresponding to the rate of oxygen is sent to the operation control device 38 from an oxygen flow meter 39 and a signal corresponding to the composition of the exhaust gases is sent thereto from an exhaust gas analyser 40.
Opening of a dust collector damper 41 (hereinafter referred to as a DC damper) disposed e.g. in the dust collectors 32 and 32' is similarly signal-supplied to the operation control device 38 from an opening oscillator 52 and the quantity of exhaust gas flow is signal-supplied thereto from a flow meter 53. DC damper 41 is operated by the operation control device 38 through a DC damper control device 44 and a draught fan damper 45 (hereinafter referred to as a SD damper) operated thereby through an SD damper control device 46. The information input device 46a is provided to supply the various bits of information required to predict the quantity of furnace generated gases, for example, quantity of hot metal, quantity of molten metal, quantity of scrap, temperature of hot metal, Si content, quantity of lime and hood pressure, to the operation control device 38.
A hood pressure transmitter 47 is provided to similarly supply the hood pressure signal to the operation control device 38.
The quantity of converter generated gases as the reference of control can be predicted in a manner as follows.
The concentrations as percentages, of
CO, CO2, 2, H2, N2 within the exhaust gases obtained from the exhaust gas analyser 40 are expressed by Xco, Xco2, Xo2,XH2, XN2 (O/,). The analysed values of exhaust gases as indicated by the concentrations Xco to Xn2(V0), the exhaust gas flow value (F) obtained by the exhaust gas flow meter 53, the quantity of furnace generated gases, and the concentration of gases thereof may be given as follows, utilizing equations (1), (2), (4) and (5);;
21 To2,= XN2 (1)
79 Xo2,1=Xo2,-Xo2 (2) Xco'=Xco+2Xo2,, (4)
The quantity F' of furnace generated gases is given by equation (16) below,
F'=F. (Xco'+Xco2,) (16)
The above equations (1), (2), (4) and (5) do not refer to H2 gas, which can be dealt with using equations similar to those used for CO gas.
For the prediction of F' i.e. the quantity of converter generated gases let Fn' be the value at time tn of the quantify F' of converter generated gases obtained by the equation (20).
Assuming that n=0 represents the instant time, n=-l, -2 etc. represents past time, and n=+l, +2, etc. represents future time, n can suitably be determined as follows. Referring to figure 10 this illustrates one embodiment, which predicts the quantity F+, of furnace generated gases (indicated by line 51) 30 seconds after the quantities F-;', F1,, For of converter generated gases (indicated by dotted line 50) have been determined.
Curve 50 as mentioned above designates the quantity F' of converter generated gases at 30 second intervals, and each point on the curve 51 designates the predicted value F1+, of the quantity of converter generated gases obtained from linear components of three points on the dotted curve, F2,, F~,', and F,'.
It is apparent that this method of prediction
Is quite accurate. It will however be noted that in order to further enhance accuracy, curve components such as a quadratic equations may also be employed or, prediction using time intervals of less than 30 seconds may be used.
If the quantity F' of converter generated
gases is obtained, the quantity Fex of
withdrawn exhaust gases can be obtained by
the following equation: Fex=K. F' (21) where K is the coefficient used to obtain the quantity of exhaust gases drawn by the draught fan from the quantity of converter generated gases, good results being obtained by setting such coefficient K equal to 1.2 according to our practical experience.
However, the coefficient K varies with the characteristics of the equipment, so that the range thereof may be assumed to range from 1.0 to 1.4.
The present invention will now be described by way of example only with reference to the graphs shown in Figures 11 and 12. In Figure 11, the gases ordinate represents the quantity of converter generated 21, the quantity of drawn exhaust gases 22a, (operating in accordance with the present invention) the quantity of oxygen fed 25, the quantity of other secondary raw material charged 27 (including an oxidation coolant), the recovered quantity of gases 28 (in standard calorific power) operating not in accordance with the method of the present invention, and the recovered quantity of gases 28a (in standard calorific power) operating in accordance with the method of the present invention, the abscissa represents time intervals to illustrate the variation thereof with time.
It is assumed that the step from the beginning of blast refining at time t, to charging of other secondary material (including the oxidation coolant) at time t2 i.e. from the desiliconizing reaction to the early decarburization reaction is period I; the step from a rapid increase in the quantity of converter generated gases to a subsequent mode of stabilization i.e., the step of rapid increase in the quantity of gases resulting from the charging of the oxidation coolant and other secondary raw material from time t2 to time t2 is period II; the step of a further mode of stabilization of the quantity of converter generated gases, i.e., the step from time t2, to time t3 is period III; the step of increasing the rate of oxygen feed to the sharp decrease in the withdrawal of exhaust gases, i.e., the step from time t3 to t4 is period IV; and the last stage of blast refining until oxygen feeding is stopped, i.e., time from t4 to t6 is period V.
During the period I, the quantity of converter generated gases is predicted but only a small amount of gases are produced during this period so that the quantity of exhaust gases to be withdrawn may be determined by consideration of the risk of surging carried by the draught fan.
Figure 12 illustrates the operation of opening of the draught fan damper and the dust collector damper. That is, at the commencement of blast refining the opening of the draught fan damper is set at
SD,; and as the quantity of converter generated gases increases, the opening of the dust collector damper is widened. At the time when said opening reaches a given value, the opening of the draught fan damper is reset to SD2 (SD2 SD,) and at the same time, the opening of the dust collector damper is reduced in accordance with the required quantity of exhaust gases.
This operation may be repeated once more or several times until the opening of the draught fan damper is 100%, after which the dust collector damper is independently controlled. During the period in which the converter generated gases decrease in the last stage of blast refining, the above damper operation is reversed.
In exercising control in period I, the draught fan damper is restricted to reduce the amount of gas withdrawn and thus the amount of air drawn into the hood, thereby increasing the proportion of unburnt gas in the exhaust gases.
The quantity of converter generated gases can be predicted as previously mentioned, and the resultant value and the pre-obtained formula between the draught fan damper, the dust collector damper, and the flow rate of the exhaust gases can be used to determine the required opening of the damper, of the draught fan damper and the dust collector damper to be set before an increase or decrease in the quantity of gases occurs. In period II, the quantity of converter generated gases rapidly varies.
The future variation in the quantity of converter generated gases resulting from charging of the secondary raw material can be predicted and the dust collector damper operated beforehand so as to withdraw a quantity of exhaust gases corresponding thereto. Thus, control is carried out so as not to cause a delay in the expected variation of the quantity of furnace generated gases, and at this period II, the draught fan damper is placed in fully open state. At period III, the quantity of furnace generated gases produced is relatively large and stable so that direct control of the hood pressure can be carried out. The dust collector damper is usually independently controlled.
In period IV, when the rate of oxygen feed is increased, future variation in quantity of converter generated gases resulting from increase in rate of oxygen feed can be accurately predicted, and the dust collector damper should be actuated beforehand in accordance with the predicted values for the converter generated gases. Control based principally on the hood pressure control is not desirable in this period since the blow-out phenomenon can occur. In period V, the quantity of converter generated gases rapidly decreases, and hence, the same consideration as that in period I is applicable.
In carrying out the above described control operation, the quantity of withdrawn exhaust gases 22a can be brought very close to the quantity of converter generated gases 21 with little time lag between the generation and withdrawal of gases and a reduced risk of blow-out or intake phenomenon. The comparison of the quantity of gases recovered expressed in standard calorific power in Figure 11 shows that the quantity of gases 28a recovered by a preferred method in accordance with the present invention is materially great in the period I, period II, period IV, and period V, for example, as seen from the quantity recovered reaching 10Nm3/ton steel, than the gas recovered using the known constant hood pressure control and the saving of electric power may for example be 0.3
KWH/ton steel.
WHAT WE CLAIM IS:
1. A method of controlling exhaust gases in an oxygen blown converter comprising continuously detecting the quantity of oxygen fed, the quantity of secondary raw materials charged, the composition of exhaust gases and the flow rate of the exhaust gases; continuously calculating future values of the quantity of the furnace generated gases and the flow rate of combustion exhaust gases at the converter hood on the basis of said detected values; and controlling the quantity of drawn exhaust gases on the basis of said future values.
2. A method according to Claim 1, wherein said calculated future values are used to control an exhaust gas damper, thereby to control the quantity of drawn exhaust gas.
3. A method according to Claim 1, wherein said calculated future values are used to produce a first signal and the pressure differential between the converter hood and the atmosphere is used to generate a second signal, the two said signals being processed to generate an exhaust gas damper control signal.
4. A method according to any one of the preceding claims, which comprises controlling a dust collector damper and a draught fan damper, either dependently or independently of each other, using said calculated future values or said processed signals, such that the quantity of drawn exhaust gases approximates to the quantity of converter generated gases.
5. A method according to Claim 2, wherein said future values are supplied to an adjusting meter or regulator which controls an exhaust gas damper so as to avoid or substantially avoid blow out or excessive intake.
6. A method according to any one of
Claims 2 to 5, wherein the quantity of combustion exhaust gases to be withdrawn is determined in accordance with the following equation:
Quantity of combustion exhaust gases 100
Quantity of converter generated gases Xco'+Xco2,+XH2
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (10)
1. A method of controlling exhaust gases in an oxygen blown converter comprising continuously detecting the quantity of oxygen fed, the quantity of secondary raw materials charged, the composition of exhaust gases and the flow rate of the exhaust gases; continuously calculating future values of the quantity of the furnace generated gases and the flow rate of combustion exhaust gases at the converter hood on the basis of said detected values; and controlling the quantity of drawn exhaust gases on the basis of said future values.
2. A method according to Claim 1, wherein said calculated future values are used to control an exhaust gas damper, thereby to control the quantity of drawn exhaust gas.
3. A method according to Claim 1, wherein said calculated future values are used to produce a first signal and the pressure differential between the converter hood and the atmosphere is used to generate a second signal, the two said signals being processed to generate an exhaust gas damper control signal.
4. A method according to any one of the preceding claims, which comprises controlling a dust collector damper and a draught fan damper, either dependently or independently of each other, using said calculated future values or said processed signals, such that the quantity of drawn exhaust gases approximates to the quantity of converter generated gases.
5. A method according to Claim 2, wherein said future values are supplied to an adjusting meter or regulator which controls an exhaust gas damper so as to avoid or substantially avoid blow out or excessive intake.
6. A method according to any one of
Claims 2 to 5, wherein the quantity of combustion exhaust gases to be withdrawn is determined in accordance with the following equation:
Quantity of combustion exhaust gases 100
Quantity of converter generated gases Xco'+Xco2,+XH2
and the quantity of converter generated following equations: gases is determined in accordance with the
Quantity of converter generated
gases after reaction V =(2 Total quantity of oxygen feed 100 where Xco2, P= .100 +Xco'+Xco2, or
Quantity of converter generated
gases after reaction 2
Total quantity of oxygen feed Vc 1+
100 Xco2,
yc= 100
XCO+XCO2 wherein Xco', Xco2, and XH2 are detected concentrations of CO, CO2, and H2 respectively in the exhaust gas.
7. A method according to any one of
Claims 2 to 5, wherein the quantity (F4) of combustion exhaust gases to be withdrawn which results from combustion at the inlet to the exhaust system is determined in accordance with the following equation: 100 F4 . F3 (Xco'+Xco2,+XH2) wherein Xco', Xco2, and XH2, are as defined in Claim 6 and F3 is the quantity of gases produced in the converter.
8. A method according to Claim 3 or any one of Claims 4 to 7 when appendent to
Claim 3, in which the first signal (SX) and the second signal (Y) are supplied to a signal processor circuit which generates an optimum exhaust gas damper control signal (Z) in accordance with the equation
Z=f(SX . Y).
9. A method according to Claim 8, in which
Z=aoSX+boY the values of coefficients ao and bo being predetermined.
10. A method of controlling the withdrawal of exhaust gases in an oxygen blown converter according to Claim 1, substantially as hereinbefore described, with reference to Figs. 1 to 5, or Fig. 6 or
Fig. 7 or Fig. 8 or Fig. 9, or Fig. 10 or Figs.
11 and 12.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP15228175A JPS5289503A (en) | 1975-12-20 | 1975-12-20 | Recovery of uncombustive exhaust gas from converter |
| JP7510876A JPS531110A (en) | 1976-06-25 | 1976-06-25 | Control of exhaust gas of converter |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB1568406A true GB1568406A (en) | 1980-05-29 |
Family
ID=26416252
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB5314176A Expired GB1568406A (en) | 1975-12-20 | 1976-12-20 | Method for controlling exhaust gases in oxygen blown converter |
Country Status (6)
| Country | Link |
|---|---|
| CA (1) | CA1092361A (en) |
| DE (1) | DE2657540C2 (en) |
| ES (1) | ES454305A1 (en) |
| FR (1) | FR2335604A1 (en) |
| GB (1) | GB1568406A (en) |
| IT (1) | IT1065692B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112195302A (en) * | 2020-10-16 | 2021-01-08 | 中冶赛迪技术研究中心有限公司 | Method and device for predicting electric precipitation explosion risk of primary flue gas of converter |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AT511806B1 (en) * | 2011-09-28 | 2013-03-15 | Siemens Vai Metals Tech Gmbh | METHOD AND DEVICE FOR INFLUENCING THE GENERATION OF REACTION GASES IN A METALLURGICAL VESSEL |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1549489A (en) * | 1967-10-31 | 1968-12-13 |
-
1976
- 1976-12-14 CA CA267,837A patent/CA1092361A/en not_active Expired
- 1976-12-16 ES ES454305A patent/ES454305A1/en not_active Expired
- 1976-12-17 IT IT3059976A patent/IT1065692B/en active
- 1976-12-18 DE DE19762657540 patent/DE2657540C2/en not_active Expired
- 1976-12-20 FR FR7638411A patent/FR2335604A1/en active Granted
- 1976-12-20 GB GB5314176A patent/GB1568406A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112195302A (en) * | 2020-10-16 | 2021-01-08 | 中冶赛迪技术研究中心有限公司 | Method and device for predicting electric precipitation explosion risk of primary flue gas of converter |
| CN112195302B (en) * | 2020-10-16 | 2023-05-12 | 中冶赛迪技术研究中心有限公司 | Method and device for predicting primary flue gas electric dust removal explosion risk of converter |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2335604A1 (en) | 1977-07-15 |
| DE2657540C2 (en) | 1983-02-17 |
| FR2335604B1 (en) | 1980-11-07 |
| DE2657540A1 (en) | 1977-06-30 |
| IT1065692B (en) | 1985-03-04 |
| CA1092361A (en) | 1980-12-30 |
| ES454305A1 (en) | 1977-12-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PS | Patent sealed | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19951220 |