CA1092361A - Method for controlling exhaust gases in oxygen blown converter - Google Patents

Abstract

TITLE OF THE INVENTION
A METHOD FOR CONTROLLING EXHAUST GASES IN OXYGEN BLOWN
CONVERTER

ABSTRACT OF THE DISCLOSURE
A method for recovering unburnt exhaust gases in an oxygen converter, characterized by the control of an exhaust gas damper by a contorl signal obtained by signal-processing, in accordance with the set functional formulae, an exhaust gas damper control signal obtained from a pressure differential between throat pressure and atmospheric pressure, and an exhaust gas damper prediction control signal obtained by continuously detecting the quantity of oxygen fed, the quantity of secondary raw material charged, the composition of exhaust gases and the flow rate of exhaust gases to calculate the quantity of furnace generated gases and the quantity of combustion exhaust gases at throat.

Description

~a923~;~

BAC~GROIJND OF rl'iLlE I NVEN'I`I O~`i This invention rclates to a m~thod for control:ling exhaust gases in an oxygen blown converter.
In steel making in a converter using oxygen, as is known, ~ a method has been employed to recover combustible gases, such as carbon monoxide ~C0) produced by blast refining, in a state unburnt for re-use as the heat source.
, The unburnt gases have been recovered by employment o a ` method in which the pressure differential between throat pressure i.e. the pressure ~ithin the hood, and atmospheric pressure is detected, and an exhaust gas damper is automatically adjusted I through an adjusting meter or regulator so that said pressure ¦l differential assumes a predetermined Yalue. This method, however, 1:
Il unaYoidably poses problems such BS so-called blow-out, in which 15 1l the exhaust gases are emitted out of the throat, and so-called~ ;
intake phenomenon9 in which surplus air is sucked into the throat, 1, due to delay in detection or transmission~ of signals to r~pid ~ ~ ~¦~
¦, variation in quantity of exhaust gases and delay in responsel~ ~ I
of the adjusting meteir or the exhaust gas damper produced when ~20 il the quantity or flow rate of oxygen fed is changed~ when secondary material such as~iron ore etc. lS charged or~completed ; I to be charged, or when the quantity or feeding rate of secondary raw material charged is changed in the case where the absolute~ l , 1~ quantity of the charge is changed. This results in a waste ~ I
li of unburnt exhaust gases and a considerable economical loss due ~
to wasteful burning of the exhaust gases resultlng from intake ~ ;
o-f surplus~alr. ~ I
Thus, in the oxygen blown converter, the method has been I employed in~an~effor~to recove~ the combustible gases, such as ,I CO produced in conn~ection with the blast refining, in a state unburnt,~tAe method normally being called the m~thod for recover-

2-', . .
..
, .
~.. ~ ... .. .. . . . .

1(~923~

ing unbur~ exhaust gases. For example, see British Patent No.
1,187,530. A method as controlling means therefore, which is generally called the throat pressure control, is used in which the pressure differential between throat pressure, i.e., the pressure within the hood is detected, and atmospheric pressure.
A damper is controlled through a con~rol means so that said internal pressure assumes a predetermined level.
.Incidentally, a method is employed.to suck surplus air by suitably opening the dust collector damper in order to avoid the surging phenomenon of the draught fan for the exhaust gases despite ~he fact that the furnace generated gases are in a very small amount at the early stage and at the last stage of blast refining in the converter. This method, however, results in ~ a wasteful burning of unburnt gases, leading to a considerable ~- . .
economical loss.
Further, the aforementioned throat pressure controlllng .-~
method unavoidably involves delay in detection or transmission .
- of signals and delay in response of control means or damper drive means to rapid change in converter.reaction thereby in- .
evitably producing phenomenon (blow.-out phenomenon), in which the combustible gases are emit~ed out of the throat, or phenom- ~ :
enon (excessive intake phenomenon), in which surplus air is ~
~ - sucked into the throat, often resulting in an economical los~
: such as dissipation or.wasteful burning of the combustib~ gases.
In addition, the blow-out phenomenon is caused to produce ;.
emission of re~ fume~ which is not desirable in terms of environ- ~
mental health. ~ -SUMMARY OF T B INVENTION
It is an object of an aspect of the present invention to :

provide a method for recovering the unburnt exhaust gases with-out suffering from the blow-out or intake as previously mention-..:
. .

1~9236~L

ed, and to provide a method which has much adaptability to .
operating conditions and equipment conditionsO
An objeet of an aspect of the invention is to provide a method ~or controlling exhaust gases without suffering from the :
blow-out phenomenon or intake phenomenon in recovery of unburnt exhaust gases.
An object of an aspect of the invention is to enhance recovery rate of exhaust gases and to reduce cost.
Therefore, according to one featuxe o the present inyen-tion, there is provided a method of controlling exhaust gases in ~ -an oxygen hlown converter comprising the steps of: ~ :
~ a) detecting a pressure differential betwee~the pre!ssure within the hood of the converter and atmos-pheric pressure to ob~ain an exhaust gas damper control .
signal;
(b) detecting thè quantity of oxygen fed to the :~-converter, the quantity of secondary raw material charged to the converter, the composition of the exhaust gases and the flow rate of the exhaust gases to obtain an exhàust .
gas aamper prediction control signal;
: ~c) processing in.a conventional processor circuit both said gas damper control signal and said exhaust .
gas damper prediction control siynal in accorda-nce with :
the equation Z-f (X,Y) wherein Z is the optimum control signal, f is a function sign, X is the contr~l signal of : the exhaust gas damper obtained at (a) and Y is the predic ::~
tion control signal of the exhaust g~s damper obtained ~t (b), to obtain s~aid optimum control signal; and : (d) controlling an exhaust damper in said co~vertex on ~he basis o~ the thus obtained optimum control signal.

~- -4-~.. . . . . . . . . ...................... . .
.: , . . .

~9Z3~;~

BRI~F DESCRIPTION OF THE DRAWINGS
_ Figure 1 is a schematic block diagram of apparatus for embodying the method of the present invention;
Figure 2 schemakically illust:rates control of pressure : differential;
Figure 3 schematically illust:rates prediction control in accordance with the present invention;
. Figure 4 schematically illustrates signal processing in a signal processing circuit in accordance with the present inven-t;on;
Figures 5 (i) to ~) schematically illustrate the coefi- :
cient of coupling; ; :
Figures 6 and 7 illustrate a comparison of the recovered quantity of unburnt gases between the present invention and ~ -prior art method, in connection with an embodiment of a 170-t ;~ ~:
converter in accordance with the present invention;
Figure 8 illustrates variation with time in the control of :
throat pressure;

,'~

.

-4a~

. .
;, '~ ' ~923~

Figure 9 is a scl~ematic block diagram of apparatus ~or recover-~ing unburnt exhaust gases in a convcrter;
Figure 10 is a view of assistance in explaining prediction of tlle quantity of furnace generated ~ases; .-.
5Figure 11 illustrates variation with time of gas recovery in accordance wit]l the controlling method of the invention; and Figure 12 is a view of assistance in explaining operation of~a draught fan damper and a dust collector damper.

1~ DETAILED DESCRIPTION OF THE ~MBODIM. N_ .
ll Referring now to Figure 1, the re~erence numeral 1 designates a converter, the oxygen being introduced into steel ~ath by means ,of the blast refining oxygen lance 2. The exhaust gases produced from this converter 1 are passed through a collecting hood 3 .
Ilprovided with a vertically movable skir't'. 3' and:an exhaust gas '`lS i'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. ~ 1 IThe~exhaust gas damper 6 émployea could be any convlenient design~
,as long as it is possible to~control a quantity oE 10w. Secondary :~
- .';20 'raw materlal, whlch may include 1uxes.and co.o`lants'.are:.. : charged 1 ;~ ,into the converter~l from a secondary raw material hopper 9 ~ ~:~
I'~through a charging feeder 10. The pressure differential between pressure in ~the hood or throat pressure and atmospheric pressure ~ ~:
is measured by a prçssure differential oscillator OT regulator 11, 25 ~ the signal thereof being supplied t.o a throat pressure controlllng :, :`adjusting-meter or regulator.l2. This adjusting meter or controller ; ,`12 has the inteDded pressure dlfferential set value preset~the~reto, and from thls, the input signal of the aforesaid pressure differen-tial osciIlator or-transmitter.::ll can be compared with the:aoresaic pressure dlfferential set value so that the resultant corrected ~ .
I .
:

iOg~
signal is t-ransmitted in thc form of ~n exhaust gas damper control signal through a signal proc~ssor circuit 13 tlater described) to a scrvomechanism 14 for operating the damper 6 :in accordance ~ ~ith the conditions (later described) to thereby control the exhault gas damper 6.
In this case, if a correction of signal is not made by the signal processor circuit 13, the control based on the known pressure difference can naturally be attained. In accordance with ~ the present invention, in the case where a control system based l on prediction later described is not desirable or impossible to be used because of operation conditions involved or troubles in equipment, the aforesaid con-trol based on the pressure ' difference, i.e., feedback control may immediately be applied j' to thereby afford the advantages such as readiness of the control I based on the pressure differential and simpllcity of maintenance.
In addition, according to the invention, both the feedback control and predictive control may be carried out to thereby render i highly precise control possible.
Next, an operator or calculator 19 operates operations noted 1~ :
l~below on basis of an oxygen flow meter lS, a secondary raw material charge oscillator or regulator 16, an exhaust gas analyser 17, a quantity or flow rate of oxygen fed to be measured i' ~ continuously by an exhaust gas flow meter l8,~ a quantity of 1, secondary raw material charged, analysed va~ues of the exhaust ,I gases such as CO, CO2, 2' N2, H2, etc., and signal inputs of the exhaust gas flow.
(1) A quantity or flow rate of gases of formation formed by reactlon with oxygen supplied and the oxygen generated~as A
' result of decomposition of charged secondary raw material.
~l ~2) A quantity or flow rate of cracked and reacted gases resulting from decomposition ~fthe secondary raw material.

6 ~ ~

.

~09~3631

(3) ~ quantity or ~lo~ rate of combustion exhaust gases at throat burnecl and formed by air entered from the throat.
In the presellt invention, the abovementioned cluantity or flow rate of gases of formation and quantity or flow rate o cracked and reacted gases are referred to as "the qùantity of furnace generated gases".
In the case where the quantity of oxygen fed is varied as the operation progresses, that is, when the oxygen is begun to be fed and is increased or decreased in quantity to be fed, or ' when the secondary raw material is begun to be charged and is - `I varied in quantity to be charged and lS changed ln kind or stoppedto be charged, the quantity of furnace generated gases, i.e., I
gases produced within the hood abruptly varies. Thus, when~the I exhaust gas recovery system is delayed to be contrDlled, as~
previously mentioned, blow-out or excessive intake phenomenon occurs. To prevent such a phenomenon, the quantlty OT flow rate~
of urnace generated gases and the quantity or~flow rate of combustion exhaust gases~at throatl~resulting from variation~of~
, 1, the quantity~or fiou rate of oxygen~Eed and variation of the~
quantity~ of secondary raw material;~charg~ed as descrlbed above~ ~
are operated by~the operator~or~calculator l9 by~means;~of ~ ~ ;
~predlction, the result therefrom being supplied to~a prediction ;
control~adjustlng~meter or regulator 20. This adjustlng meter or ~ ~regulator 20 provldes a quantity of exhaust gas ~damper predictlon - 2S~ I control in~order to adjust opening of the exhaust gas damper 6 ~-~ to such a degr~ee as not to produce the blow-out or excessive intake as~described above,~and the control signal lS delivered to the operatlng servomechanism 14 through the slgnal processor~
circult~13 later described. Accordingly3 the~exhaust gàs damper ~æo ,16 is operated~to~be opened or closed in response to the increase or decrease of the quantlty of furnace generated~gases, i.e.~ gase ;
in the hood and the quantity of combustion exhaust gases at .

. - ' ~ .
., ' 1 :'~: ,. .

~ 9 Z3 throat before thesc gases increase or decrease. As a consequence, the exhaust gases are properly recovered, and -the pressure differential be~ween the throat pressure, i.e., the pressure in the hood and the atmosplleric pressure is also properly maintained to minimize :Eluctuation thereof. This will be further discussed in detail with reference to the drawings.
Figure 2 (a) to (h) include the axis of abscissas which represents the lapse of time, and the axis of ordinate which l'represents the quantity of variation with each item, showing the , contorl based on the pressure diferential between the throat pressure and the atmospheric pressure. In Figure 2 (a), assuming ¦
that the iron ore as the secondary raw material is begun to be , charged at time tSl, the furance generated gases begin to increase i after the lapse of to seconds, i-e., at time tS2. ~Fig- 2 ~b) ) ~ Then, the pressure differential between the throat pressure !
and the atmospheric pressure begins to increase at time tS3, the ~¦
pressure differential ~eing detect-ed by the pressure differential oscillator or regulator 11. When the pressure~differentlal I
increases, air entered through the throat decreases or the furnace ~ `
generated gases themselves begln to give out of the skir~ 3', as a consequence o~ which the quantity of furnace generated gases burned withln the throat will decrease. That 1S, the quantity of CO which burns with air entered at the throat among the quantity ~ of CO contained in the furnace~generated gases increases. If ~l' the ratio of the quantity~of CO in the furnace generated, i.e., ~!' gases produced in the hood to the quantity of CO which burns at the throat is expressed by the combustion rate, the combustion rate decreases~as in curve~dl shown in;Figure 2 (d). Slnce open-ing of the exhaus~t~gas damper 6 is set at the time when an increas ,,in the aforesaid pressure dif~erential has been detected as shown in Figure 2 ~e), the exhaust gas damper 6 will not be opened ., i I
' I

~09236~ 1 until time tS~ is reached as shol~n in Figllre 2 (f). Ihe quantity of exhaust gases to be suckef~ thus begins to increase at time tS4 as shown in Figure 2 (g). ~s pre~iously mentioned, however, the ~urnace generated gases increases at time tS2, and hence, the differential between the quantity OT flow rate of suction exhaust gases and the quantity or flow rate of furnace generated ~gases, i.e., the quantity of exhaust gases corresponding to a hatched line area hl in Figure 2 (h) is blown out of the throat and is dissipated outside the ex}laust gas recovery system.
IFurther, after the secondary raw material has been charged, the ,quantity of furnace generated gases is actually decreased at tS6 ,but is delayed in response so that the exhaust gas damper S
~remains opened until time tSg is reached thereby allowing air licorresponding in quantity to a hatched line area h2 to enter I5 lithrough the throat. The exhaust gases are burned by the thus ~
entered air to decrease thermal calorie of thè recovered exhaust ~ i ;
gases and to increase temperature of the exhaust g;ases simul~
taneously therewith, and as a result, extra ene~rgy is required~to~
cool the exhaust gases and the service llfe of thelmachlnery ~ , may be shortened.
In order to overcome the~response delay as noted~above~, the present invention may provide a predictive control as shown ~ I
in Figure 3 (a'3 to~(h'). In~Figure 3 (a'), at ore charging time ¦ ;
t~5l, an ore charge~starting signal is received from the secondary f, raw materlal~charge~osclllator or regulator 16, and lmmediately ll the openlng of~the exhaust gas damper 6 is set through the operator - ~, or calculatot~l9 and the prediction control adjustlng meter or~
!I regulator 20 at tlme between tSll and tSlz, the exhaust gas i damper G belng~opened at tlme tS13. Slnce time;~tsl3 is actually ~30 l~earlier than time t52~at which the furnace generated gases, i.e., gases generated in the hood begin to increase, the difference .
_ 9 _ ~ . ~

.

' ', `

~ L~)923fi~L I
bet~een the fulllace geller.lted gcls quantity or flow ratc and thc suction exhaust gas quantity or flow rate ls produced to thereby ~ j suck a small amoun-t of air corresponding to a hatched line area h'l as shown in Figure 3 (h'). ~lowcver, this is merely one example. Practically, the increase in the quantity or flow rate of furnace generated gases and adjustment of opening of the exhaust gas damper 6 may be well arranged whereby minimizing the above- .
mentioned suction to a degree such as to be out o question in actual operation. While the abovementioned suction sometimes 1~ turns the blow-out by suitable selection of the time difference between time tS13 and tS2 as pre~iously mentioned~ this can be l .
suitably selected in accordance' with the equipment conditions.
It will be noted in Figure 3 that the difference between , the quantity or flow rate of furnace generated gases and the !
1 quantity or flow rate of suction exhaust gases after the secondary raw material has been charged, i.e. ? the quantity corresponding ' to a hatched line portion h'2 in Figure 3 ~h') is the residual quantity or~flow rate of suction air which has not been burned. ' , It is natural in recovery of such exhaust gases~ that;control - 20 ~ involving neither blow-out nor excessive intake is better. ~
' However, it has a tendency to be one-sided to either mode though little depending upon equipment condition. In this case, it is better to adjust the control system relative to~the intake side in ~terms of both opera*ing environment and util;zing effect 25 ~ of exhaust gases, but this is ln no way restrictive. While ¦
,~ variation of the charging quantity of raw material has~been described particularly ln res~ect of iron ore charging in the ~
embodiment described above, it is to be understood that also I
" in other cases, similar procedure may be employed to achieve -30 ' similar effec~s. ~ ' Nextl a method for calculating the quantity or'flow rate of -10- I .
I .
.

~ 9 ~ 3 combustioll cxhaust gases ~-t throat to he sucked will be descrlbed in detail. (oncerItrations o exhaust gas analysed values CO, CO2, Il2 and N2 obtained :~rom the exhaus-t gas analyser 17 are ~e~pressed by Xco, Xco2, Xo2, X112 and Xn2 ~), respectively.
:IYith respect to Xn2 (~), in this case, it could be ruled that the N2 is one other than CO -to ll2. Since the gases generated within the converter comprise CO, C02 and ~l2, it may be considered that most of N2 ~itllin the exhaust gases are induced by air entered ,~lthrough the throat. It may also be considered that the greater part of 2 contained in air entered througll the throat burns with CO within the furnace generated gases and a small amount of : .
`remainder thereof is detected as Xo2% within the exhaust gases.
Accordingly, the apparent concentration Xo'2 of the 2 contained 'in air entered through the throat to the quantity of combustIon .
jlexhaust gases at throat can be calculated by equation (1) below from the concentration of the quantity of N2 contained in alr:
entered through the throat, i.e., the concentration Xn2~ of N2 ~ .
within the exhaust gases, '2 = 7~ '`n2 . .
From this,¦the apparent concentratlon Xo"2% of the quantIty:o~ O
connected in combustion of the furnace generated:gases within:the~ ~:
~`.collecting hood 3 to the quantity of combustion gases at throat : may~be obtained~by~equation (2) below Erom the quantity o 2 not ¦~ connected.in combus.tion, i.e., the conc.entration Xa2% f.2 wlthin~
Ithe exhaust gases, ;, ~
Xo 2 = X'2 ~ X2 ~ 2) ~
The CO within :the furnace genera~ted gases is oxldized into CO2 :
as indicated by equation~(3) below by the O2 connect~ed in :
,combustion, ~ ~ I
30 ~ i 2CO + 2 ~~~ 2CO2 . . . . . (3) . , .
. ' .

' 1, . - . - , 1~923~1 Tllus, ~ilC (:o prod~lce{l:ill tlle converter is partly oxi.dized by t}-le 2 ~ hin air entered throu~h the throat into the combustion exhaust gases at throat~ and as a consequence, the CO concentration decreases as compared to the furTIace generated gases while the CO
concentration increases. From the foregoing, the apparent concentrations Xco' and Xco'2~ of the quantities of CO, CO2, :respectively, produced within the converter to the quantity of combustion gases at throat may be obtained by equations (4) and 1 (5), respectively, Xco' = Xco ~ 2 . Xo"2 . . . . . ~3 '2 = Xco2 - 2. Xo't2 . . . . . (S) ,~From this, a ratio of air entered through the throat to the quantity of burning CO, among the quantity of CO produced in the ,, converter, i.e., the combustion rate ~ may be obtained by 15 ' equation (6) below, - h ~ = (Xco' - Xco) / X'co (6) ;Furt~er, the relation of variation in volume when the furnace ~ :
generated gasés turns the combustion exhaust gases at the throat I may:be obtained by equation (7) below? from wh-ch:the quantlty ~:20 or flow rate of combustion exhaust gases to be sucked may be calculated. ~ :
I Quantity_of combusti.on exhaust gases = 100 ` Quantity o ffurnace~generated gases~ (X'co + Xco2 + Xn2) (7), Next, the quantity of furnace generated gases, i.e., gase ~'.generated in the converter may be calculated in a manner as ifollows.
., .
If the total quantity of oxygen supplied to the converter 1 reacts !
with carbon w:ithin the steel bath as indicated by equation (8) :~,below, the volume ln quanti-ty of~gases of formation a-Eter reaction j : in a standard condition is twice:as much as the ~olume of the total .; ' I' -12- .

I
"

~09~:3~
quc~n-tlty of oxygen supplied, 2C ~ 2 -32C0 . . . (8) I-lo~ever, since a part of OXYgen is also reacted as indicated by equation (9) below, an increase in volume of gases of formation after reaction with respect to the total quan~ity of supplied oxygen is reduced by a produced amount of C02, 2C0 + 2--~ 2C02 . . . . . (9) Assuming now that the apparent ratio of the quantities of C0 and - C2 produced in the converter to the quantity of combustion '~ exhaust gases at throat is X'co and X'co2%, respectively, as ,prevlously mentioned and a rati.o ~f the quantity of C02 produced in the converter to the quantities of the furnace generated C0 . and C02 is y~, the y may be obtained by equation (10) below, ~; :

Y X'~o ~ X IOO , .... (10) ~ ~ ~

.l From this, the quantity or flow ratelof gasès:;~of~formation after;:~
reaction:to the total quantity of s.uppli~ed~oxygen may~be obtained~ 1 . by equation (11) below, Quantity.of gases produced~within : , ii~
nverter---a~te-~r rfeaC~pli-ed ~ ~-:
~oxygen within converter~ :
~Let~Fo2Nm3/Hr~be the quantity~o oxygen~fed obtalned~:~from the~ ¦~
.20~ ~:oxygen~10w~meter 15,~WlT/Hr the charge quaDtity of secondary~ ~ :
: ~raw materlal~which produces~02 resulting from cracklng amongl :~
the charge qUaDtity of~secoDdary raw material obtained from~the ~ ' : ~ ' secondary raw~materlal~ charge osci~llator or~regul;ator~l6,~1Nm /T I
the coefficlent of producing ~2~ W2T/Hr the ch~arge quantity ofl~` :
25~ ,~secondary~raw~material whlch~produces~cracked~ react~ion gases ~ ~ : .
; resultlng from cracking,~aDd a2Nm3/T the~ coefficient of produclng . gases thereof. :Then:FlNm3/Hr,~the quantlty of gases of formation;
produced~:resulting~from~re~acti~on~with oxygen wlthin~the converter,l F2Nm /Hr, the cracked reaction gas~es:produced resulting from ,i ~ 13~
, : ' 1.
.. .
~ , - I ,,.
, . . . ; . . . -: ~, .~ ~

~ 36 ~
cracking of the secondclry raw material, .Ind ~3Nm3/~lr, the quantity of furnace generated gases produced in the converter, which is the sum of PlNm3/~lr and P2Nm3/l-1r, are given by equa~ions (12), (13) and (14)~ respectively, 1 (2 100 ) ~P2 ~ ~l.W~ (12) F2 = a2-W2 . . . . . (13) P3 = Pl ~ P2 . . . . . ~14) ,The coefficients ~1 and ~2 can easily be obtained by the consti-`Itue3its of the respective secondary raw material.
10i Generally, however, in the iron ore, al : 150 to 250 Nm3/T, and in the raw dolomite) a2 : 150 to 250 ONm3/T.
Accordingly, the quantity or flow rate of combustion exhaust gases resulting from combustion at the throat to be sucked may .
,Ibe obtained easily by equation (7') below rather than the equation i(7) described above,

4 (X'co ~ X'co2 ~ Xn ) F3 ~ 7') i Signal processing of the exhaust gas damper control signal based on the pressùre differential between the throat pressure ~
and the atmospherlc pressure and the exhaust gas damper prediction ,control signal based on change in the quantity oE oxygen fed and the quantity of secondary material charged in accordance with the , present inven~i~on will be described .in detail with reference to~
,Figures 4 and 5. In Figure 4, the control signal X of the exhaus~
,;gas damper 6 from the throat pressure controlling adjusting-''meter 12 and the control~signal Y rom the prediction controlad~usting meter 20 are suppl1ed to the conventional type of Isignal processor circuit 13. As~the signal processor circuit 13 ,Iwhlch is well-known~ for example,~-Fig. 4 shows a ~ombinati.on of conventional potentio meters 13a, 13a and conventional adder 13c : `

-14- I l ' .
, ' I 1' ~9Z3~
tor opera-ting tlle processes as shown in Fig 5 (i) and (j).
In the signal processor clrcuit 13, ~he operating process, for example, based on equation (15) below is carrie~ out to provide I .
a control signal Z.
Z = aOX -~ boY . . . . (15) where, aO and bo are the coeffic:ients of coupling, respectively. I
In this case, only the controlli.ng based on the pressure differen-i tial between the throat pressure and the atmospheric pressure . could be employed by setting the coefficient of coupling to ~ aO = 1, bo =

.as shown in Figure 5 (i) according to the equipment conditions, .
j for example, such as troubles in apparatus, or the operating conditions, or a method relying on the quantity of the exhaust Il gas damper prediction control could be employed by setting the 15 '' coefficient of coupling to ~ ~ .
,. aO = , bo = 1 :
I as shown in Figure 5 (j). : ~
Further, in the case where the control signal is in excess :
of a predetermined control slgnal~value YO:as shown in~Figure 5 ~1 ~k), linear coupling could be employe~d so as to have~the coeffici-¦
ent of coupling as shown below at that time, I
aO = 0,:bo = l ~ ~ I :
That is, the prediction control at the time of changing the aforementioned quantity or flow rate of oxygen fed and or the quantity of secondary raw material charged may easily be accomplished .by selecting the set control signal value YO so as to assume .' a sultable value. To achieve control with high accuracy, the coeffici:en-t of coupling aO may gradually be decreased and I conversely the coefficient of coupling bo may gradually be increased until the set~control signal value YO is reached, as shown in Flgure S (Q), then ~the coefficient of coupling are .

, I
!

.
~, ~ , . . . . . .

Z~6~

"O O, bo = :L
at tlle set con~rol signal value YO. ~ I
It l~ill be noted in the present invention tha~ hi~her linear couplings or couplings with other ~unctions may also be employed by using the equation, Z = f~X,Y) though not shown.
In the present invention, accomplishment of control in accordance with the signal process noted above is referred to as the control of exhaust gas damper i:n accordance with the con~rol signal obtained resulting -from signal processing in accordance ¦ .
with the set unctional equation. The abovementioned signal ¦
.processor circuit 13 comprises a combination of known control elements so that functional analysis in compliance~with the purpose may be obtained. For example, the processes as shown ~iin Figure 5 (i) and (i) can be carried out by the signal processor c~ircuit 13 of such a type as shown in Figure 4.
The processes as shown ln Figure 5 (k) and (Q3 can be ~accomplished by the signal processor circuit of:the conventional type including a comparator, functional generator etc. .
An embodiment in connection with a::170-t converter of the~ I
;.2.0 present invention is shown in Flgures 6 and 7. Figure 6 is a ~`graphic representation, in which variation in recovered quantity - .of unburnt exhaust gases,~which~has been:converted into the:: quantity of gases with a standard calorific power (2000 Kcal/~Nm3~, ~is illustrated in accordance with time (minute) passed after ¦ I
~ 25. .,commencement of charging iron ore~ the solid line (m) represent- ¦ I
: I,ing the example of the pres.ent inventi.on, the dotted line (n) ..
the example:of prior art method, and the hatched line area the ..
~lexample by which the recovered quantity of unburnt gases is .
lenhanced or the gas emission from the throat is decreased, i.e., I .
:30 enhancement:lby SOONm31in.this example. Figure 7 is a graphic :
representation, in which variation in recovered quantity of unburnt gases converted into calorific power at the time of . , .

. .

~ Z3~
coml)lcti~l~ o~ cllargillg iron ore is iLIustrclted in accordtlnce with time (minu-tc) passe~ after compLetion o.f chclrging iron ore, the solid line (m') r~prcsentillg the example of the present invention~
the dotted line (nl) the example oE prior art method, and the hatched line area the example by whlch the recovered quantity of unburnt gases is enhanced or entry of the surplus air from the throat is restrained, i.e., enhancement by 400Nm3 in this example.
Figure 8 is a schematic explanatory view of the exhaust gas recovery in the known throat pressure control, the axis of abscissa ~representing time while the axis of ordinate represent- I
ing the quantity of furn`ace generated gases, the quantity of ¦ I
exhaust gas flow, the quantity of oxygen fed, the quantity of iron ore charged, and the recovered quantity of exhaust gases, variation thereof with time being illustrated in the form of graphl.
~ At time Tl, blast refining begins, and the quantity of furnace generated gases varies with a lapse of time as shown by the solid line 21. Incidentally, since openings of the dust collector ; ~¦
damper and draught fan damper are set greater than the quantity ~
of furnace generated gases in fear of surging of the draught fan~ ¦
~`20 ~ as previously mentioned, the suction quantity of exhaust gases varies as shown by the dotted line 22. That is, the hatched line area 23 separated from the solid line 21 and dotted line 22 means the intake of surplus air from the throat portion, and hence, at an early stage of blast refining as indlcated at time Tl and , time T2, combustible gases or`CO gases are wastefully burned within a flue to fail to recover gases, and dust contained within he furnace generated gases-by combustion are formed lnto flne particles to decrease dust collecting efficiency. Gas reco~ering l normally begins when a content of CO i~ the exhaust gases reaches approximateIy 40%,~which is~determined from an economical point - of view in utilization of exhaust gases. If the intake of the surplus air could be reduced, the rate of gas recovery at time T
~ 1.

., - ~ I

.- . ~ ' ' . .: , .

10923~
, ~ I
to l`2 wou:ld be enhanced. Next, the furllace generated gases abruptly increase in volume as reaction in the converter violently takes place at time T2. Ilowever~ in tlle throat pressure control me~hodJ the quantity of drawn gases cannot follow an increase in quanti-ty of furnace generated gases due to response delay o~ the control system, and for this reason, in the hatched line area 24, the furnace generated gases are blown out of the throat to wastefully lose C0 gases leadlng to a loss thereof, resulting in an adverse efect also in terms of environmental health.
Next, at a middle stage of blast refining, the quantity of furnace generated gases will be stabilized and the quantity of drawn exhaust gases will also be stabilized accordingly. However, ~at a final stage of blast refining, when operation lS made so as ~increase the quantity of oxygen fed at time T3 as shown by the solid line 25 fDr the purpose of approaching the quantity of carbon in steel to its goal, the quantity of furnace generated;
`gases may increase for a while but abruptly decreases as the quantity of carbon in steel decreases. Also, at this tlme, the ~ quantity of drawn exhaust gases cannot follow the variation in~
quantity of furnace generate~d gases due to the delay of the~control system to produce the excessive intake of surplus-air from the - ~` throat portion-as shownlby the hatched line area 26 leading to ~a wasteful combustion, thus givlng rise to a problem entirely ~ simiIarlto that produced in the abovementioned hatched line l area 23. ~
In Figure 8, the solid line 27 indicates charging of seconda-, ry raw materlal~or the like representative of the quantity of 'I iron ore charged, and the so~lid line 28~indlcates~the recovered quantity of gases in standard calorific power.
The present~in~ention may provide a control method without suffering from the difficulties noted above with respec~ to prior ., ~

~o~z361 1 alt e.~llaust gas cont~ols, and principa:lly compri~es pred:icting tlle cluanti-ty o~ furnace generated ~ses as proviously mentioned~ !
and varying the qu~ntity of dra~n exhaust gases. ~Vhen the qu~ntity oE ~urnace generated gases is expected to be increased or decreasedl opening of the dust collector damper is opera~ed beforehand so that the quantity of drawn exhaust gases may synchronously be increased or decreased in response to increase or decrease of the quantity of furnace generated gases as previous ly mentioned.
The method of the present invention will now be described' .,by way of embodiment. ' In Figure 9, the reference numeral' 29 designates a converter, 30 an oxygen lance, 31 and 33 exhaust ducts~ 32 and 32l dust . collectors~ and 34 a draugh.t fan. In the blast refining~ the ;. secondary raw material is charged into the converter 29 througX .
, a charging chute 36 from the secondary raw material charging '-device 35, the charged quantity being applied from a secondary i, ~
, raw material charge oscillator 37 to an operation control device 38. The quantity of oxygen fed is applied to the operation'' ~

~ control device 38 from an oxygen flow meter 39 and the composltion .

'~ of exhaust gases applied thereto from an exhaust gas analyser 40.

~, Opening of.a~dust collector damper 41 (hereinafter referred to '~ as a DC damper) disposed in the dust collectors 32 and 32' is ;
s:imilarly.~applied to:the operation control device 38 ~rom an i , :
1' opening oscilLator 42 and the quantity of exhaust gas flow applied .', thereto from a~flow meter~43. :A DC damper 41 is operated by the operation~control~devlce~.3~8~through a DC damper control device .

,i 44 and a draught fan damper 45 ~hereinafter referred to as a ii -, SD damper) operated thereby through an SD damper control device : .
30 ,l:46. An applied-~lnfo.rmation input device indicated as at 46a i .

, is provided to apply various informati.on required to predict the I :
.

.. . . . . . . .

~ Z 36 ~ I
clu~ntity of Eurllace generat~l gasc~ or ~xampl~, such as quantity, oE ho~ me~al, quallti~y of mold metal, quantity of scrap3 tempera-ture oC hot metal~ content o:f S-i, quantity of lime, throat pressure, etc. to -the operation control device 38. A throat pressure oscillator indicated as at 47 is provided to similarly 1 1 apply the throat pressure signal to the operation contTol device l ¦
38.
The method of the present invention may be carried out ¦
through the devices as just mentioned~ and the quantity of furnace generated gases as the reference of control can be predicted in a manner as follows.
Concentrations of CO~ CO2, 2' H2, N2 withln the exhaust gase obtained from the exhaust gas analyser 40 are expressed by Xco, ¦
Xco2, Xo2, Xh2, Xn2 (%). With ~espect to Xn2 (%), in this case, it could be ruled that the N2 is one other than CO, CO2, H2.
1 The gases produced in the converter comprise CO, CO2 and H2 and il are burned with air at the throat. Then, the analysed values of exhaust gases as indicated by the concentratlons Xco to Xn2(%), ~ the exhaust gas flow value F obtained by the exhaust gas flow meter 43, the quantity of furnace generated gases, and the ~ I
i concentration of gases thereof may be given by equations~ (l6) to ~203 That is, let X'co, X'co2 and X'h2 be the concentrations of furnace~generated gases, X'o2 the ratio of the quantity of I oxygen from the air entered the throat to the quantity of exhaust gases, and X"o2 the reaction oxygen at the throat.
Then equations are ~
: : :
X~2 = 7~ . Xn2 , . (16) X"o2 =~X'o2;-- Xo2~ . . . . (17) 30 ~ X'co = Xco ~ 2 . X"o2 . . . . . (18 ~L092361 X'co2 = Xco2 - 2.X"o2 . . (19) Thc quantity F' of :~urnace gcnerclted gases is given by equation ~20) belo~
F' = F . (X'co ~ X'~o2) . . . . . (20) The abovedescribed equations (16) to (20~are not concerned ..
~ith ll2 gas, the ~l2 gas being handled similarly to CO gas.
Next~ prediction o-f ~he quantity F' of furnace generated gases will be described. Let F'n be the value at time tn of the quantity F' of furnace generated gases obtained by the equation ~20).
It is now assumed that present is expressed by n = 0, time prior to present expressed by n = ~ 2 . . ., and time after a lapse .
of given time from present expressed by n = ~ 2 . . . The .n can suitably be determined. Figure 10 illustrates one embodiment which predicts the quantity P +l of furnace generated gases 30 seconds after the quantities F' 2~ F' 1~ F~o of furnace generated gases at three times at intervals of 30 seconds, : .
~ n = -2, -1, and 0 at an early-stage of decarburization reaction.
`~n Figure 10, curve 50 designates the dotted row of the . .
quantity F' of furnace generated gas~es every 30 seconds, and ~
~ curve 51 designates the dotted row of the predicted value F'+l .
of the quantity of furnace generated gases obtained by linear ~components~-from three dotted~rows, F' 2~ F' 1~ and F'o. ~As is ~ :
: obvious from the figure, this predicting method is very high in accuracy. It will however be noted that.in order to further ~
25 enhance accuracy, curve components such as a quadratic equation I ;
may also be employed or~ prediction at suitable time selected : out of l~to:30 seconds instead of.every 30 seconds may be accomplished:
. That is, if:the quantity F':of furnace generated gases is :30 obtained1:the;~quantity ~FeX of drawn exhaust gases can easily be obtained by equation, F = X . Fi ~ . . . . . (21) 1' r.

~09~:36~ 1 ~hel~e ~ is the coef:Eicient used to obtain the cluantity of exhclust gascs dral~n by the drallght fan from the quankity of furnace generated gases, the good result being obtained by setting the coefEicient to 1.2 according to experience of the present inventor. ~lo~ever, the coefficient K varies with the characteristics of equipment, the range thereof being considered from 1.0 to 1.4.
The embodiment of the control method in accordance with the present in~ention will now be described with reference to graphs shown in Figures 11 and 12. In Figure 11, the axis of ordinate represents the quantity of furnace generated gases 21,.the quantity of drawn exhaust gases 22a in accordance ..
with the present method, the quantity of oxygen fe.d 25, the ilquantity of other secondary raw material charged 27 including lS l an oxidation coolant, the recorered quantity of gases 28 in -standard calorific power not in accordance wl~h the present ~
I`method, and the recovered quanti:ty of gases 28a in standard~ I 1 f'' calorific power in accordance~withf~the present method, whereas l the axis of abscissa represents~a lapse of time, illustrating :¦
~arlation thereof with time~
.Next, lt is~assumed~that: the step from the beginning of blast reflning~iat:~time Tl~to charging of~other secondary raw -~ material includlng the oxldatlon coolant at tlme T2,~l.e~ from:~
il deslliconizing reaction:i:to~:e~arly de:carburization reacti~on is: :
: ~25 period I; the steplfrom a rapld increase in~the~quantity of : ¦
I Eurnace generated gases to a subsequent mode. of stabilizatlon, ::
i.e., the~ste:p of rapid~lincr:ease in the~quantity of gases~result-ng from charglng of the;oxldatlon coolant and~other~:secondary raw materlal~from ti~e T2 to tlme T'2 is perio~d II;~the step of~
~130 ~a..further mode o r: s t~ab~ilL~ation~olf~ the~quantlty~of~furnace ~-generated gas~es, i.e.,:the step from time T'z to tlme T3 lS period : -2Z-~

~09Z3~ 1 lll; the stcll Or i~creasirlg the cluantity of oxygen Çed to tempo-rclrily increclse the quantity of furnace generated gases, i.e., t}le step from time T3 to l~ is period IV; and the step of the last stage o:E blast refinil-g until oxygen feeding is stopped, i.e.
time from T~ to T6 is period ~. I
During the period I, the quantity of furnace generated gases ¦
is predicted but the gases are not much produced during this period so that the quantity of drawn exhaust gases may be determined in consideration of surging of the draught fan.
10 1 Figure 12 illus~rates operation of opening of the draught fan damper and the dust collector damper. That is, at the time o~ starting blast refining the opening of the draught fan damper is set to SDl, and as the quantity of furnace generated gases ~ increases, the opening of the dust collector damper is windened.
1 At the time when said opending is reached a given value, the opening of the draught fan damper is reset to SD2 (SD2 >SDl) and at the same time, the opening of the~dust collector damper is , narrowed in accordance with the required quantity of exhaust , gases. This operation is repeated one or several tlmes until -~20 ; the opening of the draught fan damper is 100 %, then the dust collector damper is independently controlled. During the period ln which~the furnace~generated~gases are decreased at the last ; stage of~blast refining, the damper operation reverse to that of the gas~increasing period as mentioned above is c~arried out.
Next, a~method for~the control-of time relative to the blast refining will be described. In control at the period I~ the draught fan damper is restr~icted to reduce the intake amount, whereby increasing an un~burnt portion ln the exhaust gases.
I That is, the quantity of furnace generated gases is predicted , as~previously mentioned, and the resultant value and the pre- ¦
obtained formula between the draught fan damper, the dust collector ~ -23-I .

1~39Z361 1 1 d~lml)er and th~ ~lo~ r~te of the exhaust gases are uscd to obtain opening of the dclmper to thercby sc~ openlngs of the draught fan daml)er and thc dust collcctor damper beforchand.
~t the period II, the quantity of furnace genera~ed gases is rapidly varied so that future variation in quantity of furnace genera-ted gases resulting from charging of the secondary raw material is predicted and mean~hile, the dust collector damper is operated beforehand so as to obtain the quantity of drawn ~exhaust gases corresponding thereto. That is, controlling is 11 ¦
made so as not to produce delay in actual variation, and at this period II, the draught fan damper is placed in fully ope-n state so as to produce no harm in sucking the exhaust gases. Then~ at the period III, the quantity of furnace generated ~ases is rich ' and stabilized so that controlling in principal consideration ~ of the throat pressure can be made. Principally, the dust collector damper is independently controlled.
Next, at the period IV, when the quantity of oxygen fed is increased, future variation in quantity of furnace generated ' gases resulting from increase in quantity o~ oxygen fed is ¦
predicted with high accuracy, and the dust collector damper should be operated beforehand in accordance with the prediction attained.
That is, ~at~the~lperiod IV, employment of controlling principally based on the throat pressure control is not desirable since the blow-out phenomenon occurls. At the period V, the quantity of furnace generated gases is rapidly reduced, and hence, the same I! .
consideration as that of the period I is necessary. That lS ?
controlling is made in consideration of surging of the d~aught fan damper and simultaneous controlling of the dust collector damper and ~he~draught fan damper lS made to ~ary the quantity of ~ drawn exhaust~gases.
In accordance with the abovementioned control, the quantity of drawn exhaust gases 22a comes very close to the quantity of 1 , .,. .~ . .

Z36~
furnace(l gellerilted gases 21 to produce no time lag and to minimise.
the aforemcntioned blow-out or .intake pllenomenon. It has been ~ I
proved from a comparison :in ef:fect bet~een the present invention l ¦
and the prior art Wit}l respec-t to the recovered quant;ty o~ gases in standard calorific po~er in F:igure ll that the recovered quantity of gases 28a in accordance with the present invention is materially great in the period I, period II, period IV, and ~ .
period V, for example, such as seen from an increase in the re- I
covered quantity reaching 10 Nm3/T.S in one example~ as compared ¦
to the known constant throat pressure control not in accordance !
with the method of the present invention, which recovered quantity of gases is indicated at 28. In addition, according to the invention, electric power saving has been achieved, as for example, 0.3 KWH/T.6.

' .
:, ., . ~ . ~ . ,;

Claims (7)

CLAIMS:

1. A method of controlling exhaust gases in an oxygen blown converter comprising the steps of:
(a) detecting a pressure differential between the pressure within the hood of the converter and atmos-pheric pressure to obtain an exhaust gas damper control signal;
(b) detecting the quantity of oxygen fed to the converter, the quantity of secondary raw material charged to the converter, the composition of the exhaust gases and the flow rate of the exhaust gases to obtain an exhaust gas damper prediction control signal;
(c) processing in a conventional processor circuit both said gas damper control signal and said exhaust gas damper prediction control signal in accordance with the equation Z=f (X,Y) wherein Z is the optimum control signal, f is a function sign, X is the control signal of the exhaust gas damper obtained at (a) and Y is the predic-tion control signal of the exhaust gas damper obtained at (b), to obtain said optimum control signal; and (d) controlling an exhaust damper in said converter on the basis of the thus obtained optimum control signal.

2. The method for controlling exhaust gases in an oxygen blown converter, according to claim 1, wherein said processing in a conventional processor circuit is carried out to provide said optimum control signal for controlling the degree of opening the damper in said converter, said operation being carried out in accordance with the equation z=a0 X + b0 Y wherein Z is the optimum control signal, X is the control signal of the exhaust damper, Y is the prediction control signal of the exhaust gas damper and a0 and b0 are coefficient of coupling in the signal processor circuit and vary from zero to one.

3. A method of controlling exhaust gases in an oxygen blown converter for recovering the exhaust gases in an unburnt state, comprising the steps of:
(a) providing means including a hood for recovering gases generated within the said converter in the unburnt state;
(b) providing a duct means communicating with the said hood for sucking the said gases;
(c) providing at least one damper means mounted in the said duct for adjusting the flow rate of the said gases;
(d) providing means for cleaning the said gases sucked through the said duct and for eliminating dust contained in the said gases;
(e) providing means for preventing air from penetrating into the said converter between the said hood and a furnace throat of the said converter to enhance the efficiency in the recovery of the said gases;
(f) providing a charge information input means for supplying a charge information signal consisting of the quantity of hot metal, the quantity of scrap metal, the temperature of the hot metal, and the silicon content;
(g) detecting the flow rate of oxygen supplied to the converter to obtain a first flow rate signal;
(h) detecting the amount of secondary raw material charged to the converter to obtain a secondary raw material charge signal;
(i) analyzing the composition of the gases passing through the said duct to obtain an analysis signal;
(j) detecting the flow rate of the gases passing through the said duct to obtain a second flow rate signal;

(k) combining the said charge information signal, the said secondary raw material charge signal, the said analysis signal, the said first flow rate signal, and the said second flow rate signal and computing by calculation the amount of the generated gases after reaction, the amount of gases resulting from the decomposition reaction and the amount of combustion gases at the furnace throat;
(l) providing means for calculating a prediction control variable by using the output from step (k);
(m) detecting the pressure difference between the gas pressure within the said hood and atmospheric pressure to obtain a pressure differential signal;
(n) providing a pressure controlling adjusting means for receiving the said pressure differential signal and comparing it with a predetermined reference value to obtain an exhaust damper control signal for reducing the difference between the said pressure differential signal and the said reference value; and (o) determining the optimum control signal to adjust the degree of opening of the said damper by combining said damper control signal from said pressure controlling adjusting means and the output signal from the said prediction control variable calculating means in a signal processing circuit, wherein each of said output signals is multiplied by a respective coupling coefficient, said coefficient being responsive to equipment operational conditions and varying from zero to one, and transmitting the said optimum control signal from the said signal processing circuit to a servo mechanism for operating the said damper to minimize blow out and intake phenomena at the furnace throat of the said converter.

4. The method as defined in claim 1, wherein the quantity of furnace generated gases and the quantity of combustion exhaust gases at throat resulting from variation of the quantity of oxygen fed and variation of the quantity of secondary raw material charged are calculated for predic-tion control, the result thereof being supplied to a predic-tion control adjusting meter or regulator which provides a quantity of exhaust gas damper prediction control in order to adjust opening of the exhaust gas damper to such a degree as not to produce the blow-out or excessive intake phenomenon.

5. The method as defined in claim 1, wherein the quantity (F4) of combustion exhaust gases resulting from combustion at the throat to be sucked is calculated by the following equation:

wherein X'co, X'co2, and Xn2 are concentrations of exhaust gas analyzed values CO, CO2, and N2, respectively, and F3 is the quantity of furnace generated gases produced in the converter.

6. The method as defined in claim 3, the quantity of combustion exhaust gases to be sucked is calculated by the following equation:

and the quantity of furnace generated gases is calculated by the following equations:
wherein Xco, Xco2 and Xn2 are concentrations of exhaust gas analyzed values CO, CO2 and N2, respectively.

7. The method as defined in claim 3, wherein the quantity (F4) of combustion exhaust gases resulting from combustion at the throat to be sucked is calculated by the following equation:

wherein X'co, X'co2, and Xn2 are concentrations of exhaust gas analyzed values CO, CO2, and N2, respectively, and F3 is the quantity of furnace generated gases produced in the converter.