CA1049258A - Method of detecting abnormal conditions of blast furnaces - Google Patents
Method of detecting abnormal conditions of blast furnacesInfo
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- CA1049258A CA1049258A CA224,173A CA224173A CA1049258A CA 1049258 A CA1049258 A CA 1049258A CA 224173 A CA224173 A CA 224173A CA 1049258 A CA1049258 A CA 1049258A
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- furnace
- hot blast
- pipe
- pressure difference
- blast
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21B—MANUFACTURE OF IRON OR STEEL
- C21B5/00—Making pig-iron in the blast furnace
- C21B5/001—Injecting additional fuel or reducing agents
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- Chemical & Material Sciences (AREA)
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- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Blast Furnaces (AREA)
- Manufacture Of Iron (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The pressure difference of the hot blast blown into a blast furnace is continuously detected between the hot blast main or a bustle main pipe and respective hot blast branch pipes leading to tuyeres, and the abnormal condition of the furnace is detected in accordance with the condition of variation in the pressure difference. Where an abnormal condition is detected, the operation of the furnace is controlled so as to improve the operation.
The pressure difference of the hot blast blown into a blast furnace is continuously detected between the hot blast main or a bustle main pipe and respective hot blast branch pipes leading to tuyeres, and the abnormal condition of the furnace is detected in accordance with the condition of variation in the pressure difference. Where an abnormal condition is detected, the operation of the furnace is controlled so as to improve the operation.
Description
Back~round of the Invention This invention relates to a method of detecting abnormal conditions in a bla~t furnace.
As is well known in the art during the operation of a blast furnace such abnormal conditions as hanging, slip, scaffolding and irregular burden descending occur frequently. Such abnormal condition~ prevent normal stable operationæ of the furnace. Although many method of foreca~ting or detecting such abnormal conditions have been proposed, it has not yet been establi~hed an efficient m~thod that can promptly forecast or detect such abnormal conditions at high a~curacies. Thus, accordlng to certain prior art methods of detecting the abnormal conditions of a blast furnace, variation~ in the pres~ure or quantity of the air supplied by a blower is detected or the burden descendlng in the furnace is detected by a sounding rod ~or a scaled rod) mounted on the furnace top, or the temperature distribution or the composition di~tribution of the gas in the top or body of the furnace is detected by means of a probe or to assume the flow condition gas in accordance with the variation in the temperature of the furnace wall.
Since a number of factors exi~t concurrently in the furnace, with any one of these prior art ~ethods it has been impossible to detect or foreca~t the furnace condition since the analysis of the factor~ i8 extremely complicated. E~pecially, as the accuracy of detection of the abnormal conditlon~ based on ~uch in~ormation~ is not high it has been impos~ible to correctly determine the condition at any position in a modern large blast furnace. As a re~ult, the operation of the furnace becomes irregular thus rendering it impos~ible to operate the furnace stably and ~moothly.
As is well known in the art during the operation of a blast furnace such abnormal conditions as hanging, slip, scaffolding and irregular burden descending occur frequently. Such abnormal condition~ prevent normal stable operationæ of the furnace. Although many method of foreca~ting or detecting such abnormal conditions have been proposed, it has not yet been establi~hed an efficient m~thod that can promptly forecast or detect such abnormal conditions at high a~curacies. Thus, accordlng to certain prior art methods of detecting the abnormal conditions of a blast furnace, variation~ in the pres~ure or quantity of the air supplied by a blower is detected or the burden descendlng in the furnace is detected by a sounding rod ~or a scaled rod) mounted on the furnace top, or the temperature distribution or the composition di~tribution of the gas in the top or body of the furnace is detected by means of a probe or to assume the flow condition gas in accordance with the variation in the temperature of the furnace wall.
Since a number of factors exi~t concurrently in the furnace, with any one of these prior art ~ethods it has been impossible to detect or foreca~t the furnace condition since the analysis of the factor~ i8 extremely complicated. E~pecially, as the accuracy of detection of the abnormal conditlon~ based on ~uch in~ormation~ is not high it has been impos~ible to correctly determine the condition at any position in a modern large blast furnace. As a re~ult, the operation of the furnace becomes irregular thus rendering it impos~ible to operate the furnace stably and ~moothly.
- 2 -~THOD O~ DETECTING AB~ORM~L CO~JDITIONS
OF BLAST FURNAC~S
ABSTR~CT OF THE DISCLOSURE
The pressur~ difference of the hot blast blown lnto a blast furnace is continuously detected between the hot ~last main or a bustle main pipe and respective hot bla~t branch pipes lead~ng to tuyere~, and the abnormal conaition of the furnace is detected in accordance with the condition of variation in the pressure difference. Where an abnormal condition i~ detected, the operation of the furnace i~
controlled so as to improve the operation.
lO~9Z58 It is an object of this invention to provide a novel method of detecting the abnormal conditions of a blast furnace which can accurately and promptly detect or forcast various abnormal conditions of a blast furnace.
Another object of this invention is to provide an efficient method of detecting the abnormal conditions of a blast furnace which can stabilize the operation of the furnace and can improve the operating efficiency of the furnace by increasing the utilization factor and the amount of oil blown into the furnace.
According to this invention there is provided a method of detecting the abnormal condition of a blast furnace of the type wherein hot air is blown into the furnace from-a main air duct -- through an annular pipe connected to the main air duct and branchpipes branched from the annular pipe and leading to respective tuyeres of the furnace, characterized in that the pressure differ-ence of the hot air between the main air duct or the a~nular pipe and respéctive branch pipes is detected continuously and that the abnormal blast furnace is detected in accordance with the condition of variation of the detected pressure difference.
Although certaSn types of the abnormal conditions persist for a short interval whereas another type of the abnormal conditions persist over a relatively long period, the invention enables accurate detection of these two types of abnormal condi-tions because the manner of varying the pressure difference is continuously measured. Moreover, as the apparatus required to measure the pressure difference or abnormal conditions of the furnace are installed on the outside of the furnace the method of this invention can be readily carried out.
Upon detection of the abnormal condition suitable steps for eliminating the cause of the abnormal conditions are taken. Thus, by recording the variation with time of the detected pressure difference and by analyzing the record, the ~049ZS8 type of the abnormal condition can be determined. As the typ~
is determined, the operation of the furnace is controlled so as to eliminate the cause of the abnormal condition as by varying the pressure of the hot blast, varying the distribution of the charge and the diameter of the tuyeres, or by varying the hot blast flow rate for the furnace. Accordingly, it is possible to increase the wind volume, heavy oil for example, and the gas utilization factor which ultimately resulting in the improvement of the stability of the furnace operation, and of the productivity of pig iron.
In accordance with a preferred embodiment, a method of detecting an abnormal condition of a blast furnace of the type wherein hot blast is blown into the furnace from a hot blast main pipe, a bustle pipe connected to said hot blast main pipe and branch pipe branches from said bustle pipe and leading to respective tuyeres of said furnace, comprises: continuously detecting the time-varying pressure difference of the hot blast between respective branch pipes and at least one of said hot blast main pipe and said bustle pipe, recording the time-varying pressure difference pattern over a long period of time, and then controlling, in response to predetermined furnace condition indicating changes in said time-varying pressure difference pattern over a given period of time which is substantially shorter than said long period of time, at least one operating parameter of the furnace, to eliminate abnormal conditions in the blast furnace which are functions of said predetermined changes of said time-varying pressure difference pattern.
Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:
Fig. 1 is a diagrammatic representation of a portion including a hot blast main and a tuyere: I
~0492S8 Figs. 2 through 10 are reproductions of charts actually recorded for detecting the abnormal conditions of a blast furnace in accordance with the method of this invention;
in which:
Figs. 2 and 3 show hanging and its descending of the charge, Fig. 4 shows a burden slip condition, Figs. 5 and 9 show the tendency of hanging, ; Fig. 6 shows the occurrence of a channeling;
Figs. 7, 8 and 10 show abnormal conditions of burden descending; and Fig. 11 is a block diagram explaining the method of this invention as applied to the operation of a blast furnace.
As diagrammatically shown in Fig. 1, the hot blast from a hot stove (not shown) is conveyed to each tuyere 4 of a b~ast furnace through a hot blast main pipe 5, a bustle main pipe 2 and a hot blast branch pipe 3 in a method well known in the art. The branch pipe 3 comprises a blow pipe 6 connected to the tuyere 4 and a bent pipe 7 connected between the blow pipe 6 and the bustle pipe 2. According to this invention, the pressure difference between the hot blast main pipe 5 or the ! bustle pipe 2 and the branch pipe 3 is measured continuously.
Such pressure difference can be measured readily even when the variation in the furnace pressure is very small. Moreover, as the variation in the condition at various positions in the furnace appears in respective hot bl~ast branch pipes 3 it is possible to readily detect such variation on the outside of the furnace although such detection is impossible in the furnace. More advantageously is that the difference of the pressure drop (loss) caused by the different length from the hot blast main to each branch pipe is negligibly small, and according to this invention, as the pressure difference between the hot blast main and each C ~ 5 ~
. , ~
branch pipe is continuously measured, the result of measurement is not affected by the distance from the hot blast main pipe 5.
By detecting the furnace condition by measuring the variation in the pressure difference in this method the analysis and the assumption of the furnace condition becomes extremely simple.
Accordingly, it is possible to promptly take necessary measures when such abnormal conditions as hanging, slip, channeling and irregular burden descending occur. For example, hanging can be readily eliminated by varying the composition of the raw materials charged or by abruptly changing the hot blast flow rate.
Where the pressure difference between the hot blast main pipe 5 and the branch pipe 3 is measured, the result of measurement is affected by such factors as the cross-sectional area of the branch pipe 3, the length of the pipe along which the blast pressure is measured and the temperature drop of the hotblast in the bustle pipe 2 but the overall accuracy is within + 5% of the true value without the influence of such factors, so that the result of measurement is fairly high. On the other hand, where the pressure difference between the bustle pipe 2 and the branch pipe 3 is measured, the result of measurement is affected by the distribution of the static pressure in the bustle pipe in addition to various factors described above, but'the over-all accuracy is within + 10% of the true value without the influence of such factors, which value has been obtained by actual operation. Thus, such result of measurement can also be used practically without causing any serious trouble.
Where a large pressure difference is to be obtained it is necessary to measure the pressure difference at a pbint near the blow pipe. However, as the blow pipe is required to be frequently exchanged (the frequ~ncy of exchange is next to that of the tuyere 4), it is advantageous to select the pbint of measurement to be near the bustle pipe 2 or before the bent pipe .
~049Z58 7. In the latter case although the pressure difference is small its accuracy is high. In this manner, the point of measurement does not affect the measuring accuracy. By connecting suitable taps ~ and 8' tl the branch pipe 3 and the bustle pipe 2 or the hot blast main pipe 5, respectively, as shown by thin lines in Fig. 1 by using the branch pipe 3 whose cross-sectional area decreases gradually from the bustle pipe 2 toward the tuyere it becomes unneçessary to provide any Venturi pipe or nozzle of a particular construction in the branch pipe 3, etc.
The relationship between the pressure difference obtainec by the method of this invention and the variation of the pressure in the furnace is as follows. Denoting the pressure in the bustle pipe 2 by PO~ and the enthalpy thereof by io and assuming that the pressure loss is (100.~) % of the kinetic energy U2~2, then the enthalpy can be expressed by the following equation <(~U2/2) + U2/2 = io -i ................... (1) where i represents the enthalpy of jet at tuyere ahead.
The velocity of the hot blast flow rate through tuyere is expres-sed by U = ~ S .................................... (2) where q represents a mean flow rate per one tuyere, ; and S the cross-sectional area of the tuyere nozzle.
In an ideal fluid since the internal energy and the enthalpy are functions of only the temperature, following rela-tion holds: ~
- i ~
o Gc.J.C - - ----..................... (3) where, To: temperature of hot blast in the hot blast main pipe 30 - T: temperature of the hot blast close by the tuyere in the furnace Gc: gravity conversion factor i - 7 -. ~
J : mechanical equivalent of heat Cp: specific heat at constant pressure.
Further K-l p /p) K ,.,,,,,,,................. (4) where PO: pressure in the hot blast main pipe P : pressure near by the tuyere in the furances and K is expressed by the followlng equation 5 K = p .................................... (5) where Cv represents the specific heat at constant volume.
Equation 4 gives the pressure inside the furnace.
When the furnace inside pressure varies by ~P, the variation ~P in the pressure difference utilized for the measurement of the flow quantity can be expressed as follows ~(~ ) 2C [ 1 ] ( c p) , (KKl) , (T/P) . ~P (6) where C: a fixed number obtained by adding D to the pressure difference ~P of the case when the average flow rate q flows at the tuyere D: a fixed number used to define the relation-ship between the pressure difference ~P
and the flow rate q, which actually indicates the dynamic pressure in the hot blast main pipe.
Substitution of various values in equation 6 giveC; the relation-ship between the flow quantity of the blast flowing through a tuyere and the variation in the furnace inside pressure.
The followings are one example of the invention as applied to a blast furnace and one example of the pattern of detecting abnormal conditions. The blast furnace to which the , ~ , invention was applied had a capacity of 1728 m3. Suitable conditions of hot blast for this furnace are Wind rate QO = 3200 Nm3/min Blast pressure PO = 2.25 Kg/cm G
Blast temperature To = 1100C
Denoting the pressure in the bustle pipe 2 shown in Fig. 1 by 3.28 Kg/cm2 ab and the enthalpy by i j the pressure loss can be calculated as follows (1) Energy consumed by pressure loss ~Pfl + ~P
( ~ ) x Gc = 7,915 ......................... (7) where, ~Pfl: pressure loss between the hot blast main pipe and the point in the hot blast branch pipe where the pressure loss is detected ~Pf2: pressure loss between the point in the hot blast branch pipe where the pressure loss is detected and the inner furnace (2) Kinetic energy U = 26,900 ................................ (8) Since the ratio of (1) and (2) is equal to 0.3 the enthalpy can be expressed as follows (0.3)~~~ ~ + 2 = io ~ i .............
U = q = 3.83/0.0165 = 232 m/sec ............ (10) From equation 3, T - 1068C - 1341K and from equations 4 and 5, KKl _ 0.286, so that P = 3,018 Kg/cm2 ab - 1.99 Kg/cm2G
where, ab: absolute pressure G : gauge pressure P : pressure nearby the tuyere in the furnace.
Equation 6 representing the relationship between the variation ~P in the furnace inside pressure and the variation ~P in the ~f ~ _ g_ ' ~ ~I .
. . ~
measured pressure difference can be derived out from various equations described above.
By differentiating equation 9 1.3 U~U = - ~i ........................ (11) By differentiating equation 3 - G ~J.C
From equation 11 and 12 1.3 U~U = - Gc J Cp ~T ................ (13) By differentiating equation 4 2 ~T = ~ ( K ) (3.28) K . p-(l+ K ) . ~p (14) T
By arranging these equations, we obtain T
~T = 0.286 ( p ) ~P ................... (15) From equations 13 and 15, we obtain 1.3 U~U = - Gc-J-Cp~0.286 ( T )~p] ... (16) The relationship between the flow rate and the pressure difference is given by the following equation ~P = C( g )2 _ D ........................... (17) where, D: a fixed number used to define the relationship between the pressure difference ~P and the flow rate q, which actually indicates the dynamic pressure in the hot blast main pipe.
In the blast furnace under consideration various constants are as follows C = 675 mm H20 D = 74 mm H20 q = 3.83 m3/sec.
q = SU (actual flow rate at the tuyere) 9a -By differentiating equation 17, we obtain ~(AP) = 2C ( ~ ) . ~q .................. (18) By using - ~q = S~U~ ............................... (19) which is obtained by differentiating q = S~U~, equation 18 is modified as follows ~(~p) = 22 s'2 . U' ~U' ................ (20) q Assuming now that the density p is constance, S~U~ = SU
Accordingly, ~(~p) = 2CS U~U ........................ (21) q hence U~U = q ~(~P) .................................... (22) 2cs2 Equation 6 is obtained by substituting equation 22 into equation 16, thus obtaining equation 23 (-2C.S .G~ J C ) E0.286( p )8P]
-2 ~~ .. (23) 1.3(g ) When it is assumed that T = 1341K
P = 3.018 Kg/cm ab C = 675 mm H20 the equation for calculating the pressure in the blast furnace is given by the following equation ~P = - 2670 ~P ...................................... (24) where P : internal pressure in the furnace (Kg/cm ab) ~P : pressure difference (mm H20) Equation 24 shows that the variation in the pressure difference of 200 mm H20 at a tuyere flow rate q = q corresponds to the variation in the furnace inside pressure of 0.07 Kg/cm2. Such .. . .
rA~
relationship can also be obtained for each of various different operating conditions for various types of the blast furnace.
Some examples of the patterns obtained by measuring the pressure difference between the hot blast branch pipe and the hot blast main pipe and showing the abnormal condition of a blast furnace having a volume of 1728 m3 are illustrated ln Figs. 2 through 10 in which slightly curved vertical lines rep~esent time units in one hour, the spacing between two horizontal lines corresponds to a pressure of 20 mm H20 and the graphs were re-corded by moving the recording charts toward right as viewed inrespective figures, 90 that the time elapse of the operation pro-ceeded from right to the left. The graph shown in Fig. 2, shows that up to a time instant e, hanging was detected above and ahead of Nos. 15 and 17 tuyeres and then the hanging and impermeability have gradually grown during succeeding five hours with the result that the pressure difference decreased gradually. Although at time a the normal blast pressure of 2.25 Kg/cm G was reduced to 1.20 Kg/cm2G for about two minutes, the hanging was still noted.
Accordingly, at point b the blast pressure was reduced to 1.00 Kg/cm2G for about 30 seconds. As a result, hanging was eliminated during the succeeding two hours and the normal operation was re-sumed. This is also true in the case of Fig. 3, which shows that hanging was created at the l9th and 20th tuyeres and that hanging was removed by decreasing the blast pres~ure in the same manner ~ as above déscribed.
; Graphs shown in Figs. 4 shows that burden slip was created at the l9th and ~Oth tuyeres for about one hour. However, the extent of the slip was relatively small and did not occur frequently the normal operation was continued until the normal operation was resumed.
The graph shown in Fig. 5 shows that there was a tendency of forming hanging. In the case shown in Fig. 6, channeling was noted at the 7th tuyere ahead and the operation of the furnace was stabilized by varying the distribution of the charge. Fig. 7 shows an abnormal burden descending due to the combined action of hanging, slip and channeling. Figs. 8 and 10 also show simi-lar phenomena. In each case, abnormal burden descending was detected near the each tuyere ahead. In the case shown in Fig. 7 the operation of the furnace was stabilized by decreasing the normal blast pressure of 2.25 Kg/cm G to 1.5 Kg/cm ~ ~t a point C shown in Fig. 7 and by changing the distribution of the charge.
The graph shown in Fig. 9 shows that the tendency of hanging simi-lar to those at the 7th tuyere shown in Fig. 5 was detected at the 15th and 17th tuyeres. In this case, the operation of the furnace was stabilized by varying the distribution of the charge at a point d.
Fig. 11 shows a block diagram of the operation of a blast furnace in which the furnace condition is judged by detect-ing the operation patterns as described above and the operation of the furnace is controlled in accordance with the judgement.
More particularly, upon detection of the varying conditions the informations regarding the characteristics of the raw materials, operating parameters, the temperature and composition of cast iron, etc. are combined with the detected varying conditions for judging the cause of the abnormal condition and then the opera-tion is controlled to eliminate such cause. On the other hand, variation in the enthalpy is determined from the variation in the measured value of the blast flow rate through a tuyere and the abnormal condition of the furnace is forecast by calculating the variation in the furnace pressure. The furnace operation is control~ed to prevent the occurrence of such forecast abnormal condition as well as sticking to the furnace wall. Further-more, the manner of charging the raw materials is modified to obtain adequate heat balance of the furnace.
r A ~ - 12 -~Q4~ZS8 The measures described above for overcoming various detected abnormal conditions such as hanging, slip, channeling, and irregular burden descending have been previously used in practice and include variation in the distribution of charge, variation in the diameter of the tuyere and hence the velocity of the hot blast and the control of the injected oil rate into the furnace. Variation in the distribution of the charge can be performed by changing the charging program, changing the position at which the charge is dropped from a charging bell, and by changing the composition of the charge. Among these, the variation in the blast pressure is temporary but others are permanent measures. Of course, one or suitable combinations of these measures can be used. Generally, the blast pressure is decreased for about 30 seconds to 5 minutes.
In another furnace having a capacity of 2828 m3, the furnace is usually operated under the following conditions.
Total blast moisture 5.0 g/Nm3 Hot blast flow rate 4690 Nm3/min Hot blast pressure 2.847 Kg/cm2G
Hot blast temperature 1186C
V/P 3.88 Coke rate ! ~14 Kg/pig, ton Oil rate 58 Kg/pig, ton V/P is an index indicating the permeability in the furnace, which is determined by dividing the flow rate (Nm /min) by the pressure difference (g/cm2) between the blast pressure and the pressure at the top of the furnace. While V/P has dimensions, it is ordinarily indicated without dimensions.
The CO/CO2 ratio in the furnace top gas is 1.06 and the rate of production of the pig iron amounts to 2.17 ton/m3~day.
On the other hand, where the pressure difference is measured and the furnace operation is stabilized by controlling the same in accordance with the result of measurement of this invention follow-ing operating conditions are suitable.
Total blast moisture 9.0 g/~m3 Hot blast flow rate 4861 Nm /min Hot blast pressure 2.913 Kg/cm2G
Hot blast temperature 1187C
V/P 3.88 Coke rate 416 Kg/pig, ton Oil rate 61.0 Kg/pig, ton In the latter case, since the content of blast moisture is approximately two times larger, the coke rate was increased somewhat but by slightly increasing the oil rate stable operation was obtained. The CO/CO2 ratio in the exhaust gas was measured as 1.00 proving a high utilization factor of the fuel. The pro-duction rate of pig iron was 2.25 t/m3/ day meaning that stable operation is possible at an increased production rate.
As has been described hereinabove, ac~ording to this invention, the pressure difference between the hot blast main pipe or a bustle pipe and each branch pipe leading to a tuyere 20 is detected continuously and by using the variation 1n the pres-sure difference the operation condition of a blast furnace is correctly detected and judged, which condition was impossible to determine correctly according to prior art technique. Such pressure difference also enables adequate measurement of the blast flow rate. Thus, according ! to this invention, it is possible to detect and forecast at high accuracies the abnormal conditions of the blast furnace thus enabling to be taken appro-priate measures for obviating such abnormal conditions.
~ ~.
OF BLAST FURNAC~S
ABSTR~CT OF THE DISCLOSURE
The pressur~ difference of the hot blast blown lnto a blast furnace is continuously detected between the hot ~last main or a bustle main pipe and respective hot bla~t branch pipes lead~ng to tuyere~, and the abnormal conaition of the furnace is detected in accordance with the condition of variation in the pressure difference. Where an abnormal condition i~ detected, the operation of the furnace i~
controlled so as to improve the operation.
lO~9Z58 It is an object of this invention to provide a novel method of detecting the abnormal conditions of a blast furnace which can accurately and promptly detect or forcast various abnormal conditions of a blast furnace.
Another object of this invention is to provide an efficient method of detecting the abnormal conditions of a blast furnace which can stabilize the operation of the furnace and can improve the operating efficiency of the furnace by increasing the utilization factor and the amount of oil blown into the furnace.
According to this invention there is provided a method of detecting the abnormal condition of a blast furnace of the type wherein hot air is blown into the furnace from-a main air duct -- through an annular pipe connected to the main air duct and branchpipes branched from the annular pipe and leading to respective tuyeres of the furnace, characterized in that the pressure differ-ence of the hot air between the main air duct or the a~nular pipe and respéctive branch pipes is detected continuously and that the abnormal blast furnace is detected in accordance with the condition of variation of the detected pressure difference.
Although certaSn types of the abnormal conditions persist for a short interval whereas another type of the abnormal conditions persist over a relatively long period, the invention enables accurate detection of these two types of abnormal condi-tions because the manner of varying the pressure difference is continuously measured. Moreover, as the apparatus required to measure the pressure difference or abnormal conditions of the furnace are installed on the outside of the furnace the method of this invention can be readily carried out.
Upon detection of the abnormal condition suitable steps for eliminating the cause of the abnormal conditions are taken. Thus, by recording the variation with time of the detected pressure difference and by analyzing the record, the ~049ZS8 type of the abnormal condition can be determined. As the typ~
is determined, the operation of the furnace is controlled so as to eliminate the cause of the abnormal condition as by varying the pressure of the hot blast, varying the distribution of the charge and the diameter of the tuyeres, or by varying the hot blast flow rate for the furnace. Accordingly, it is possible to increase the wind volume, heavy oil for example, and the gas utilization factor which ultimately resulting in the improvement of the stability of the furnace operation, and of the productivity of pig iron.
In accordance with a preferred embodiment, a method of detecting an abnormal condition of a blast furnace of the type wherein hot blast is blown into the furnace from a hot blast main pipe, a bustle pipe connected to said hot blast main pipe and branch pipe branches from said bustle pipe and leading to respective tuyeres of said furnace, comprises: continuously detecting the time-varying pressure difference of the hot blast between respective branch pipes and at least one of said hot blast main pipe and said bustle pipe, recording the time-varying pressure difference pattern over a long period of time, and then controlling, in response to predetermined furnace condition indicating changes in said time-varying pressure difference pattern over a given period of time which is substantially shorter than said long period of time, at least one operating parameter of the furnace, to eliminate abnormal conditions in the blast furnace which are functions of said predetermined changes of said time-varying pressure difference pattern.
Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:
Fig. 1 is a diagrammatic representation of a portion including a hot blast main and a tuyere: I
~0492S8 Figs. 2 through 10 are reproductions of charts actually recorded for detecting the abnormal conditions of a blast furnace in accordance with the method of this invention;
in which:
Figs. 2 and 3 show hanging and its descending of the charge, Fig. 4 shows a burden slip condition, Figs. 5 and 9 show the tendency of hanging, ; Fig. 6 shows the occurrence of a channeling;
Figs. 7, 8 and 10 show abnormal conditions of burden descending; and Fig. 11 is a block diagram explaining the method of this invention as applied to the operation of a blast furnace.
As diagrammatically shown in Fig. 1, the hot blast from a hot stove (not shown) is conveyed to each tuyere 4 of a b~ast furnace through a hot blast main pipe 5, a bustle main pipe 2 and a hot blast branch pipe 3 in a method well known in the art. The branch pipe 3 comprises a blow pipe 6 connected to the tuyere 4 and a bent pipe 7 connected between the blow pipe 6 and the bustle pipe 2. According to this invention, the pressure difference between the hot blast main pipe 5 or the ! bustle pipe 2 and the branch pipe 3 is measured continuously.
Such pressure difference can be measured readily even when the variation in the furnace pressure is very small. Moreover, as the variation in the condition at various positions in the furnace appears in respective hot bl~ast branch pipes 3 it is possible to readily detect such variation on the outside of the furnace although such detection is impossible in the furnace. More advantageously is that the difference of the pressure drop (loss) caused by the different length from the hot blast main to each branch pipe is negligibly small, and according to this invention, as the pressure difference between the hot blast main and each C ~ 5 ~
. , ~
branch pipe is continuously measured, the result of measurement is not affected by the distance from the hot blast main pipe 5.
By detecting the furnace condition by measuring the variation in the pressure difference in this method the analysis and the assumption of the furnace condition becomes extremely simple.
Accordingly, it is possible to promptly take necessary measures when such abnormal conditions as hanging, slip, channeling and irregular burden descending occur. For example, hanging can be readily eliminated by varying the composition of the raw materials charged or by abruptly changing the hot blast flow rate.
Where the pressure difference between the hot blast main pipe 5 and the branch pipe 3 is measured, the result of measurement is affected by such factors as the cross-sectional area of the branch pipe 3, the length of the pipe along which the blast pressure is measured and the temperature drop of the hotblast in the bustle pipe 2 but the overall accuracy is within + 5% of the true value without the influence of such factors, so that the result of measurement is fairly high. On the other hand, where the pressure difference between the bustle pipe 2 and the branch pipe 3 is measured, the result of measurement is affected by the distribution of the static pressure in the bustle pipe in addition to various factors described above, but'the over-all accuracy is within + 10% of the true value without the influence of such factors, which value has been obtained by actual operation. Thus, such result of measurement can also be used practically without causing any serious trouble.
Where a large pressure difference is to be obtained it is necessary to measure the pressure difference at a pbint near the blow pipe. However, as the blow pipe is required to be frequently exchanged (the frequ~ncy of exchange is next to that of the tuyere 4), it is advantageous to select the pbint of measurement to be near the bustle pipe 2 or before the bent pipe .
~049Z58 7. In the latter case although the pressure difference is small its accuracy is high. In this manner, the point of measurement does not affect the measuring accuracy. By connecting suitable taps ~ and 8' tl the branch pipe 3 and the bustle pipe 2 or the hot blast main pipe 5, respectively, as shown by thin lines in Fig. 1 by using the branch pipe 3 whose cross-sectional area decreases gradually from the bustle pipe 2 toward the tuyere it becomes unneçessary to provide any Venturi pipe or nozzle of a particular construction in the branch pipe 3, etc.
The relationship between the pressure difference obtainec by the method of this invention and the variation of the pressure in the furnace is as follows. Denoting the pressure in the bustle pipe 2 by PO~ and the enthalpy thereof by io and assuming that the pressure loss is (100.~) % of the kinetic energy U2~2, then the enthalpy can be expressed by the following equation <(~U2/2) + U2/2 = io -i ................... (1) where i represents the enthalpy of jet at tuyere ahead.
The velocity of the hot blast flow rate through tuyere is expres-sed by U = ~ S .................................... (2) where q represents a mean flow rate per one tuyere, ; and S the cross-sectional area of the tuyere nozzle.
In an ideal fluid since the internal energy and the enthalpy are functions of only the temperature, following rela-tion holds: ~
- i ~
o Gc.J.C - - ----..................... (3) where, To: temperature of hot blast in the hot blast main pipe 30 - T: temperature of the hot blast close by the tuyere in the furnace Gc: gravity conversion factor i - 7 -. ~
J : mechanical equivalent of heat Cp: specific heat at constant pressure.
Further K-l p /p) K ,.,,,,,,,................. (4) where PO: pressure in the hot blast main pipe P : pressure near by the tuyere in the furances and K is expressed by the followlng equation 5 K = p .................................... (5) where Cv represents the specific heat at constant volume.
Equation 4 gives the pressure inside the furnace.
When the furnace inside pressure varies by ~P, the variation ~P in the pressure difference utilized for the measurement of the flow quantity can be expressed as follows ~(~ ) 2C [ 1 ] ( c p) , (KKl) , (T/P) . ~P (6) where C: a fixed number obtained by adding D to the pressure difference ~P of the case when the average flow rate q flows at the tuyere D: a fixed number used to define the relation-ship between the pressure difference ~P
and the flow rate q, which actually indicates the dynamic pressure in the hot blast main pipe.
Substitution of various values in equation 6 giveC; the relation-ship between the flow quantity of the blast flowing through a tuyere and the variation in the furnace inside pressure.
The followings are one example of the invention as applied to a blast furnace and one example of the pattern of detecting abnormal conditions. The blast furnace to which the , ~ , invention was applied had a capacity of 1728 m3. Suitable conditions of hot blast for this furnace are Wind rate QO = 3200 Nm3/min Blast pressure PO = 2.25 Kg/cm G
Blast temperature To = 1100C
Denoting the pressure in the bustle pipe 2 shown in Fig. 1 by 3.28 Kg/cm2 ab and the enthalpy by i j the pressure loss can be calculated as follows (1) Energy consumed by pressure loss ~Pfl + ~P
( ~ ) x Gc = 7,915 ......................... (7) where, ~Pfl: pressure loss between the hot blast main pipe and the point in the hot blast branch pipe where the pressure loss is detected ~Pf2: pressure loss between the point in the hot blast branch pipe where the pressure loss is detected and the inner furnace (2) Kinetic energy U = 26,900 ................................ (8) Since the ratio of (1) and (2) is equal to 0.3 the enthalpy can be expressed as follows (0.3)~~~ ~ + 2 = io ~ i .............
U = q = 3.83/0.0165 = 232 m/sec ............ (10) From equation 3, T - 1068C - 1341K and from equations 4 and 5, KKl _ 0.286, so that P = 3,018 Kg/cm2 ab - 1.99 Kg/cm2G
where, ab: absolute pressure G : gauge pressure P : pressure nearby the tuyere in the furnace.
Equation 6 representing the relationship between the variation ~P in the furnace inside pressure and the variation ~P in the ~f ~ _ g_ ' ~ ~I .
. . ~
measured pressure difference can be derived out from various equations described above.
By differentiating equation 9 1.3 U~U = - ~i ........................ (11) By differentiating equation 3 - G ~J.C
From equation 11 and 12 1.3 U~U = - Gc J Cp ~T ................ (13) By differentiating equation 4 2 ~T = ~ ( K ) (3.28) K . p-(l+ K ) . ~p (14) T
By arranging these equations, we obtain T
~T = 0.286 ( p ) ~P ................... (15) From equations 13 and 15, we obtain 1.3 U~U = - Gc-J-Cp~0.286 ( T )~p] ... (16) The relationship between the flow rate and the pressure difference is given by the following equation ~P = C( g )2 _ D ........................... (17) where, D: a fixed number used to define the relationship between the pressure difference ~P and the flow rate q, which actually indicates the dynamic pressure in the hot blast main pipe.
In the blast furnace under consideration various constants are as follows C = 675 mm H20 D = 74 mm H20 q = 3.83 m3/sec.
q = SU (actual flow rate at the tuyere) 9a -By differentiating equation 17, we obtain ~(AP) = 2C ( ~ ) . ~q .................. (18) By using - ~q = S~U~ ............................... (19) which is obtained by differentiating q = S~U~, equation 18 is modified as follows ~(~p) = 22 s'2 . U' ~U' ................ (20) q Assuming now that the density p is constance, S~U~ = SU
Accordingly, ~(~p) = 2CS U~U ........................ (21) q hence U~U = q ~(~P) .................................... (22) 2cs2 Equation 6 is obtained by substituting equation 22 into equation 16, thus obtaining equation 23 (-2C.S .G~ J C ) E0.286( p )8P]
-2 ~~ .. (23) 1.3(g ) When it is assumed that T = 1341K
P = 3.018 Kg/cm ab C = 675 mm H20 the equation for calculating the pressure in the blast furnace is given by the following equation ~P = - 2670 ~P ...................................... (24) where P : internal pressure in the furnace (Kg/cm ab) ~P : pressure difference (mm H20) Equation 24 shows that the variation in the pressure difference of 200 mm H20 at a tuyere flow rate q = q corresponds to the variation in the furnace inside pressure of 0.07 Kg/cm2. Such .. . .
rA~
relationship can also be obtained for each of various different operating conditions for various types of the blast furnace.
Some examples of the patterns obtained by measuring the pressure difference between the hot blast branch pipe and the hot blast main pipe and showing the abnormal condition of a blast furnace having a volume of 1728 m3 are illustrated ln Figs. 2 through 10 in which slightly curved vertical lines rep~esent time units in one hour, the spacing between two horizontal lines corresponds to a pressure of 20 mm H20 and the graphs were re-corded by moving the recording charts toward right as viewed inrespective figures, 90 that the time elapse of the operation pro-ceeded from right to the left. The graph shown in Fig. 2, shows that up to a time instant e, hanging was detected above and ahead of Nos. 15 and 17 tuyeres and then the hanging and impermeability have gradually grown during succeeding five hours with the result that the pressure difference decreased gradually. Although at time a the normal blast pressure of 2.25 Kg/cm G was reduced to 1.20 Kg/cm2G for about two minutes, the hanging was still noted.
Accordingly, at point b the blast pressure was reduced to 1.00 Kg/cm2G for about 30 seconds. As a result, hanging was eliminated during the succeeding two hours and the normal operation was re-sumed. This is also true in the case of Fig. 3, which shows that hanging was created at the l9th and 20th tuyeres and that hanging was removed by decreasing the blast pres~ure in the same manner ~ as above déscribed.
; Graphs shown in Figs. 4 shows that burden slip was created at the l9th and ~Oth tuyeres for about one hour. However, the extent of the slip was relatively small and did not occur frequently the normal operation was continued until the normal operation was resumed.
The graph shown in Fig. 5 shows that there was a tendency of forming hanging. In the case shown in Fig. 6, channeling was noted at the 7th tuyere ahead and the operation of the furnace was stabilized by varying the distribution of the charge. Fig. 7 shows an abnormal burden descending due to the combined action of hanging, slip and channeling. Figs. 8 and 10 also show simi-lar phenomena. In each case, abnormal burden descending was detected near the each tuyere ahead. In the case shown in Fig. 7 the operation of the furnace was stabilized by decreasing the normal blast pressure of 2.25 Kg/cm G to 1.5 Kg/cm ~ ~t a point C shown in Fig. 7 and by changing the distribution of the charge.
The graph shown in Fig. 9 shows that the tendency of hanging simi-lar to those at the 7th tuyere shown in Fig. 5 was detected at the 15th and 17th tuyeres. In this case, the operation of the furnace was stabilized by varying the distribution of the charge at a point d.
Fig. 11 shows a block diagram of the operation of a blast furnace in which the furnace condition is judged by detect-ing the operation patterns as described above and the operation of the furnace is controlled in accordance with the judgement.
More particularly, upon detection of the varying conditions the informations regarding the characteristics of the raw materials, operating parameters, the temperature and composition of cast iron, etc. are combined with the detected varying conditions for judging the cause of the abnormal condition and then the opera-tion is controlled to eliminate such cause. On the other hand, variation in the enthalpy is determined from the variation in the measured value of the blast flow rate through a tuyere and the abnormal condition of the furnace is forecast by calculating the variation in the furnace pressure. The furnace operation is control~ed to prevent the occurrence of such forecast abnormal condition as well as sticking to the furnace wall. Further-more, the manner of charging the raw materials is modified to obtain adequate heat balance of the furnace.
r A ~ - 12 -~Q4~ZS8 The measures described above for overcoming various detected abnormal conditions such as hanging, slip, channeling, and irregular burden descending have been previously used in practice and include variation in the distribution of charge, variation in the diameter of the tuyere and hence the velocity of the hot blast and the control of the injected oil rate into the furnace. Variation in the distribution of the charge can be performed by changing the charging program, changing the position at which the charge is dropped from a charging bell, and by changing the composition of the charge. Among these, the variation in the blast pressure is temporary but others are permanent measures. Of course, one or suitable combinations of these measures can be used. Generally, the blast pressure is decreased for about 30 seconds to 5 minutes.
In another furnace having a capacity of 2828 m3, the furnace is usually operated under the following conditions.
Total blast moisture 5.0 g/Nm3 Hot blast flow rate 4690 Nm3/min Hot blast pressure 2.847 Kg/cm2G
Hot blast temperature 1186C
V/P 3.88 Coke rate ! ~14 Kg/pig, ton Oil rate 58 Kg/pig, ton V/P is an index indicating the permeability in the furnace, which is determined by dividing the flow rate (Nm /min) by the pressure difference (g/cm2) between the blast pressure and the pressure at the top of the furnace. While V/P has dimensions, it is ordinarily indicated without dimensions.
The CO/CO2 ratio in the furnace top gas is 1.06 and the rate of production of the pig iron amounts to 2.17 ton/m3~day.
On the other hand, where the pressure difference is measured and the furnace operation is stabilized by controlling the same in accordance with the result of measurement of this invention follow-ing operating conditions are suitable.
Total blast moisture 9.0 g/~m3 Hot blast flow rate 4861 Nm /min Hot blast pressure 2.913 Kg/cm2G
Hot blast temperature 1187C
V/P 3.88 Coke rate 416 Kg/pig, ton Oil rate 61.0 Kg/pig, ton In the latter case, since the content of blast moisture is approximately two times larger, the coke rate was increased somewhat but by slightly increasing the oil rate stable operation was obtained. The CO/CO2 ratio in the exhaust gas was measured as 1.00 proving a high utilization factor of the fuel. The pro-duction rate of pig iron was 2.25 t/m3/ day meaning that stable operation is possible at an increased production rate.
As has been described hereinabove, ac~ording to this invention, the pressure difference between the hot blast main pipe or a bustle pipe and each branch pipe leading to a tuyere 20 is detected continuously and by using the variation 1n the pres-sure difference the operation condition of a blast furnace is correctly detected and judged, which condition was impossible to determine correctly according to prior art technique. Such pressure difference also enables adequate measurement of the blast flow rate. Thus, according ! to this invention, it is possible to detect and forecast at high accuracies the abnormal conditions of the blast furnace thus enabling to be taken appro-priate measures for obviating such abnormal conditions.
~ ~.
Claims (14)
1. A method of detecting an abnormal condition of a blast furnace of the type wherein hot blast is blown into the furnace from a hot blast main pipe, a bustle pipe connected to said hot blast main pipe and branch pipe branches from said bustle pipe and leading to respective tuyeres of said furnace, said method comprising:
continuously detecting the time-varying pressure dif-ference of the hot blast between respective branch pipes and at least one of said hot blast main pipe and said bustle pipe, recording the time-varying pressure difference pattern over a long period of time, and then controlling, in response to predetermined furnace condition indicating changes in said time-varying pressure difference pattern over a given period of time which is sub-stantially shorter than said long period of time, at least one operating parameter of the furnace, to eliminate abnormal con-ditions in the blast furnace which are functions of said pre-determined changes of said time varying pressure difference pattern.
continuously detecting the time-varying pressure dif-ference of the hot blast between respective branch pipes and at least one of said hot blast main pipe and said bustle pipe, recording the time-varying pressure difference pattern over a long period of time, and then controlling, in response to predetermined furnace condition indicating changes in said time-varying pressure difference pattern over a given period of time which is sub-stantially shorter than said long period of time, at least one operating parameter of the furnace, to eliminate abnormal con-ditions in the blast furnace which are functions of said pre-determined changes of said time varying pressure difference pattern.
2. The method according to claim 1, wherein each branch pipe includes a blow pipe and the pressure difference is detected continuously between said blow pipe and at least one of said hot blast main pipe and said bustle pipe.
3. The method according to claim 1, wherein the pressure difference is detected continuously between a point along said branch pipe near said bustle pipe and at least one of said hot blast main pipe and said bustle pipe.
4. The method according to claim 1, wherein fuel oil is injected into said furnace, and wherein said controlling step comprises increasing the injected fuel oil rate for decreasing the CO/CO2 ratio, thus increasing the gas utilization factor as well as the production rate of pig iron, in accordance with the detected abnormal condition.
5. The method according to claim 1, comprising controlling the operation of the furnace only at given tuyeres of the furnace responsive to said predetermined changes in said time-varying pressure difference pattern.
6. The method according to claim 1, wherein said controlling step comprises varying the pressure of the hot blast of said blast furnace.
7. The method according to claim 1, wherein said controlling step comprises varying the hot blast flow rate for said blast fur-nace.
8. The method according to claim 1, wherein said controlling step comprises increasing the wind volume in said hot blast fur-nace.
9. The method according to claim 1, wherein said controlling step comprises increasing the gas utilization factor of said blast furnace.
10. The method according to claim 1, wherein said controlling step comprises controlling the temperature of the hot blast of said hot blast furnace.
11. The method according to claim 7 wherein said controlling step comprises abruptly changing the hot blast flow rate.
12. The method according to claim 1 wherein said controlling step comprises varying the composition of the raw materials charged into said hot blast furnace.
13. The method according to claim 12 comprising varying at least one of the quality and proportion of the materials charged into said hot blast furnace.
14. The method according to claim 1 wherein said controlling step comprises varying the diameter of said tuyeres and hence the velocity of the hot blast of said hot blast furnace.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3984074A JPS5611729B2 (en) | 1974-04-10 | 1974-04-10 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1049258A true CA1049258A (en) | 1979-02-27 |
Family
ID=12564147
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA224,173A Expired CA1049258A (en) | 1974-04-10 | 1975-04-09 | Method of detecting abnormal conditions of blast furnaces |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS5611729B2 (en) |
| CA (1) | CA1049258A (en) |
| DE (1) | DE2515704A1 (en) |
| FR (1) | FR2274692A1 (en) |
| GB (1) | GB1461242A (en) |
| ZA (1) | ZA752290B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5897324A (en) * | 1981-12-04 | 1983-06-09 | 松下電器産業株式会社 | Cooking machine |
| USRE33857E (en) * | 1983-02-22 | 1992-03-24 | Weyerhaeuser Company | Imaging of hot infrared emitting surfaces obscured by particulate fume and hot gases |
| JPH03162808A (en) * | 1990-07-19 | 1991-07-12 | Sanyo Electric Co Ltd | Mixer |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS526844B2 (en) * | 1972-03-15 | 1977-02-25 |
-
1974
- 1974-04-10 JP JP3984074A patent/JPS5611729B2/ja not_active Expired
-
1975
- 1975-04-09 CA CA224,173A patent/CA1049258A/en not_active Expired
- 1975-04-10 DE DE19752515704 patent/DE2515704A1/en active Pending
- 1975-04-10 GB GB1472175A patent/GB1461242A/en not_active Expired
- 1975-04-10 ZA ZA00752290A patent/ZA752290B/en unknown
- 1975-04-10 FR FR7511214A patent/FR2274692A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| FR2274692A1 (en) | 1976-01-09 |
| JPS50133111A (en) | 1975-10-22 |
| JPS5611729B2 (en) | 1981-03-17 |
| DE2515704A1 (en) | 1975-10-23 |
| FR2274692B1 (en) | 1978-02-03 |
| ZA752290B (en) | 1976-03-31 |
| GB1461242A (en) | 1977-01-13 |
| AU8000575A (en) | 1976-10-14 |
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