US3627857A

US3627857A - Heating controlling system in a multizone type continuously heating furnace

Info

Publication number: US3627857A
Application number: US798729A
Authority: US
Inventors: Hiroshi Matuno; Toshiya Morisue
Original assignee: Yawata Iron and Steel Co Ltd
Current assignee: Yawata Iron and Steel Co Ltd
Priority date: 1968-02-15
Filing date: 1969-02-12
Publication date: 1971-12-14
Anticipated expiration: 1988-12-14
Also published as: NL6902415A; DE1907551B2; FR2001974A1; BE728391A; GB1256561A; DE1907551A1

Abstract

A heating controlling system in a multizone-type continuously heating furnace having a preheating zone, heating zone and soaking zone in sequence for obtaining an object heated in the furnace which may be extracted from the soaking zone at any objected temperature by determining the temperature of the heated object at the inlet of the heated zone from the atmospheric temperature in the preheating zone and other factors, controlling quantity of fed heat in the heating zone from said temperature and then adjusting quantity of fed heat or moving velocity of the heated object in the soaking zone.

Description

[50] Field of 263/6. 52

[56] References Cited UNITED STATES PATENTS 2,620,l74 12/1952 Passafaro..................... 263/6 3,252,693 5/1966 Nelson 263/3 Primary Examiner-John J. Camby Anomey-Wenderoth, Lind & Ponack ABSTRACT: A heating controlling system in a multizone-type continuously heating furnace having a preheating zone, heating zone and soaking zone in sequence for obtaining an object heated in the furnace which may be extracted from the soaking zone at any objected temperature by determining the temperature of the heated object at the inlet of the heated zone from the atmospheric temperature in the preheating zone and 263/52 other factors, controlling quantity of fed heat in the heating 263/6 zone from said temperature and'then adjusting quantity of fed F27) 9/40 heat or moving velocity of the heated object in the soaking :zone.

Hiroshi Matuno; Toshlya Morisue, both of Kltakyushu, Japan Appl. No. 798,729

Feb. 12, 1969 Dec. 14, 1971 Yawata Iron 8; Steel Co., Ltd. Tokyo, Japan Feb. 15, 1968 Japan 43/9540 MULTIZONE TYPE CONTINUOUSLY HEATING FURNACE 1 Claim, 7 Drawing United States Patent [72] Inventors [22] Filed [45] Patented [73] Assignee [32] Priority [54] HEATING CONTROLLING SYSTEM IN A I a wmawazwe :52

20.82% 53 EEEE 93w Ill.

. wz Ckmm me. 41 masmk wzrEmI SOAKING ZONE 4 HEATING TEMPERATURE 9 G (DIMENSION 7 Eu zoCouGa 535E825 93m $520255 2555 m 20 5 12 85mm 9 30 5 GB HEATING ZONE: 2 HEATING TEMPERATURE DIMENSION PHYSICAL CONSTANT PS PHYSICAL CONSTANT PS PATENIEU DEC I 4 IIIII SHEET 1 BF 6 FIG. I I

FIG. III) FIG. 2

I I E $35825 HEATING I TEMPERATURE 9 G 3 3 9 SOAKING zoNE.4 emo wZCLum 304m Juan.

wzrrmw wank HEATING ZONE: 2

TEMPERATURE GmI T HEATING DIM E N s I ON PHYSICAL CONSTANT P DIM E N SIO N PHYSICAL CONSTANT P5 INVENTOR Ma funo Hiras/n' Tosh/ya Mar/sue wmzfilIoiLlikii uwdi ATTORNEY PATENIEU 115m 412m sum 2. HF 6 mohamiou INVENTOR S at/m0 H l'roshi M or/sue ATTORNEY SHEET 6 OF 6 UPPER J PART LOWER PART FIRST SECOND THIRD FOURTH FIFTH HEATING HEATING HEATING HEATING TI zoNE z oNE zoNE zoNE zoNE UPPER i ART Gs s STEEL I MATERIAL M t'c t CQ 0 ti ti+d i L E 'NLET OUTLET LOWER t'GB \dQiB PART INVENTORS HIRosHI MATUNO TosHIYA MORISUE BY fi 'y z ATTORNEYS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a continuously heating furnace and more particularly to a system for controlling the temperature of continuously heated steel materials to a temperature best adapted to a hot-rolling thereof.

2. Description of the Prior Art Generally, in the temperature control of a continuously heating furnace it is requisite that metal be uniformly heated to a temperature adapted to a rolling thereof and be able to be supplied corresponding to the rolling velocity required in the rolling. For this purpose, in a continuously heating furnace there has been adopted an automatic combustion controlling system, which is, however, to control the atmospheric temperature within the furnace, but is not to control the temperature itself of the object being heated. Consequently, by this known control system it is so difficult to control the operation of the heating furnace in response to the frequently varying dimension of the object to be heated, the variation of the kinds of objects and the fluctuation of the extracting velocity that at present only a fixed pattern control or an indirect control disregarding these variations is carried out and the significance of the automatic control in the true sense of the words is almost extinguished.

Therefore, the accurate control of the temperature within the heating furnace in response to such various variations of the object to be heated as mentioned above was to depend on the high degree of skill, very great efforts and carefulness of the heating furnace operators. That is to say, today the control of the temperature of the heated object in the furnace operation is made mostly by controlling the atmospheric temperature of each zone by measuring the surface temperature of the heated object by optical means. However, in such case, there exists no standard of judgement and the control is resort to experiences and intuition obtained for a number of years. Further, even in the case of a control by utilizing feedback information, there are various disadvantages, that there exists a time lag between the time of obtaining an information and the operation, because the operator can first obtain the information, when the operation proceeds already to sequent steps, that is, a crude rolling and finishing rolling, that the informations are not uniform in the state of defonnation and further that the steel material (heated object), on which information has been obtained, and the steel material (heated object) to be compensated on the basis of this information are not always of the samecharacteristics, which makes the compensation difficult.

Further, as regards the temperature of the heated object in a three-zone-type continuously heating furnace it is to note in general that, as the temperature of the heated object in the preheating zone is represented only as a function of the time required for the passage of the heated object and the residual temperature and the amount of the exhaust gas discharged out of the heating zone, that is, the quantity of the sensible heat of the exhaust gas, it is generally almost impossible to control the heating of the heated material and further, as the heated object does not come to be red hot, it is difficult to measure the temperature of the heated object even at the end of the preheating zone. However, in order to accurately control the heating in the heating zone so as to heat the object to a temperature adapted to a hot-working thereof, it is indispensable to accurately measure the temperature of the heated object at the end of the preheating zone, that is, at the inlet of the heating zone, which was, however, impossible according to any known method.

SUMMARY OF THE INVENTION In view of such actual circumstances as above-mentioned the present invention has for its object the control of combustion in each zone as in an independent state by determining the inlet temperature of the heated object in each zone, taking also the moving velocity, physical constant and dimension of the heated materials into consideration so that any desired rolling temperature of the heated object may be finally obtained.

Another object of the present invention is to carry out an economical operation by reducing personnel and saving fuel consumption by efficiently and automatically operating a continuously heating furnace so that the heated object may be extracted out of the heating furnace at any desired temperature. That is, the present invention is to provide a heating controlling system in a multizone-type continuously heating furnace, in which furnace a preheating zone, heating zone and soaking zone being formed in sequence, characterized by determining by calculation the temperature of a heated object at the inlet of the heating zone according to a relative formula of a predetermined temperature of the heated object from the controlled or uncontrolled atmospheric temperature in the preheating zone and the dimension, moving velocity and physical constant of the heated object, controlling the quantity of fed heat in the heating zone from the said determined temperature, the dimension, moving velocity and physical constant of the heated object and a predetermined rolling temperature and further adjusting the quantity of the fed heat or the moving velocity of the heated zone in the soaking zone from the difference between the above-mentioned predetermined rolling temperature and soaking zone inlet temperature and the dimension and physical constant of the heated zone.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 3 is a graph comparing the set values according to the 7 present invention and set values in actual operation.

FIGS. 4(a) and (b) show fuel (heavy oil) flow volumes (amounts of feed) in a continuously heating furnace controlled by the system of the present invention and in a continuously heating furnace not using the system of the present invention, in which (a) shows the former and (b) the latter.

FIG. 5 is a graph showing the measured temperatures of the heated object (slab) at the soaking zone outlet in the case of the control by the system of the present invention.

FIG. 6 shows a simplified model of a continuously heating furnace.

FIG. 7 shows a heat balance model of a heated object in any heating zone according to FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention shall now be explained with reference to an embodiment in the following. First, the contents of the present invention shall be explained with reference to a threezone-type heating furnace for example.

In FIG. 1 in which is a schematic view of a three-zone-type continuously heating furnace, l is a preheating zone, 2 and 3 are respectively an upper heating zone and lower heating zone, 4 is a soaking zone and 5 is a part of objects to be heated. Further, in FIG. 2, 6 is an outlet of the heating zone and 8 is an inlet of the same. 7 is an inlet of the soaking zone and 13 is an outlet of the same. 9 is a heating zone fuel inflow volume. 10 is a combustion air volume. 11 is a heating furnace set temperature. 12 is a thermometer.

The temperature of the heated object at the end of the preheating zone 1 can be represented by the following formula as a function of the quantity of sensible heat of the exhaust gas from the heating zone and the time of the passage of the heated object through the preheating zone:

wherein time is a mean temperature of the heated object at the outlet of the preheating zone,

is an atmospheric temperature in the preheating zone,

6 is a volume of flow of the exhaust gas,

V is a moving velocity of the heated object,

P is a physical constant of the heated object,

D is a dimension of the heated object and C is a specific heat of the exhaust gas.

Therefore, the temperature at the end of the preheating zone, that is, at the inlet of the heating zone can be determined 10 by calculation by the above-mentioned formula from the physical constant and dimension of the heated object given in advance by detecting the atmospheric temperature in the preheating zone and the moving velocity of the heated object. One of the features of the present invention is to determine the temperature at the preheating zone outlet of the heated object.

The thus determined average temperature at the preheating zone outlet of the heated object is then used for the base of the heating control of the heating zone.

The heating of the object is mostly carried out in the upper heating part and lower heating part with the heated object path in the heating zone as a boundary between both parts. The control of the heating zone and soaking zone shall be described with reference to FIG. 2 in the following.

The control of the heating in the heating zone 2 is mostly carried out with the heating temperature, independently of the control of the soaking zone 4 following the heating zone 2. First of all, the temperature of the heated object at the outlet of the heating zone 2, h that is, at the inlet 7 of the soaking zone is so set as to coincide with the temperature required for the hot-working in the subsequent step. The temperature of the heated object 5 in the heating zone 2 is controlled by controlling the heating temperature as mentioned above. The temperature 0 mo of the heated object at the above-mentioned heating zone outlet 6 is represented by the following formula as a function of the heatingzone heating temperature 0 heated object moving velocity V heated object temperature 67ml at the heating zone inlet 8, heated object dimension D and physical constant P of the heated object:

l( 6s! s; 0771i, s, s) Therefore, when V 0mi,D and P are given, the optimum atmospheric temperature for passing the heated object 5 through the heating zone outlet 6 at an objective temperature, that is, the heating furnace set temperature 11 can be determined by the formula fi =r,' omo, V amt, P P when the atmospheric temperature is determined, the fuel inflow volume 9 and combustion air volume 10 can be readily determined. Therefore, if the combustion is controlled by using these values as set values, the temperature of the heated object in the heating zone can be made the optimum temperature.

If the control of the heating in the heating zone is properly accomplished, the actual temperature m0 of the object thus heated in the heating zone and the temperature m!" of the soaking zone inlet 7 should be ideally equal to each other. However, the temperature of the heated object leaving the heating zone is measured with the thermometer 12 in anticipation of the case that, due to any external disturbance, the actual temperature Hmo of the heated object 5 might not reach the predetermined temperature at the soaking zone inlet.

in such case, when the temperature of the heated object 5 deviates from the predetermined temperature, there must be made a necessary heating correction as is described later, in order to obtain the objective temperature at the soaking zone outlet. However, in case the heating zone outlet temperature is the predetermined temperature, heat is fed for soaking.

That is to say, the control of the heating or soaking in the soaking zone 4 is carried out by utilizing the following relative formula in the same manner as in the heat control in the heating zone:

5m is an objective temperature for extracting the heated object,

0 is a heating temperature in the soaking zone,

Omi' is a temperature of the heated object at the soaking zone inlet,

P is a physical constant of the heated object and D is a dimension of the heated object.

From this relative formula, the moving velocity V of the heated object for extracting it at the object extracting temperature is determined as k V ,=F,(0 Omo', a t", D P Therefore, the temperature of the heated object at the outlet of the soaking zone is controlled by the moving velocity on the basis of the relation of the above formula.

Further, in case the moving velocity of the heated object in the soaking zone, that is, the extracting velocity of the heated object is given by an external factor, for example, a rolling velocity in a roll, the objective temperature of the heated object is controlled by adjusting the soaking zone heating or soaking temperature,'asis determined by The above-mentioned is of the case of a three-zone type which has no burner in the preheating zone and therefore in which the heated object cannot be controlled in the preheating zone. However, generally, even in the case of a multizone type having a burner, the independent furnace set heating temperature or moving velocity for the heated object to pass through the outlet at the objective temperature can be determined by regarding the preheating zone, heating zone and soaking zone respectively as independent furnaces and measuring or calculating the temperature of the heated object at the inlet of the independent furnace or from the above-mentioned formula model if the objective temperature at the outlet is determined. Therefore, a temperature adapted to roll the heated object can be obtained automatically and accurately by carrying out the same operation for each independent furnace.

In the following the present invention shall be further explained in detail by giving a calculation example to concretely realize thereby the fundamental idea of the present invention, particularly with reference to FIGS. 6 and 7.

In FIG. 6 there is shown a usual continuously heating furnace, the interior of which is divided into five parts, that is, the first, second, third, fourth and fifth heating zones, seen from the inlet for charge at the left end, each of which being regarded as an independent furnace and being divided into an upper part and a lower part respectively.

In the heating furnace of such a construction as above mentioned the fifth heating zone may be regarded as a soaking zone, and the temperature in each upper part and lower part of the respective zones can be controlled separately.

In view of a heat balance relating to a very small section of a heated object in a zone i.e., the i-zone, as shown in FIG. 7, while supposing that the furnace temperatures in the upper and lower parts of respective heating zones of such a heating furnace as above mentioned are constant for each part, the heat transmissions to the upper and lower parts in said small section of the heated object in FIG. 7, dQ,, dQ are given by the following formulas respectively:

QI I 'GS c) I Qs sK GB c) As the sum of the above formulas (dQ,=dQ,'+dQ comes to the quantity of heat to be given to the heated object, the following equation can be obtained.

I JUG c)+ B ('GB c)] c+ c) 'c'1 wherein,

M: Treated amount of a heated object in the i-heating zone (kg/hr.)

Cf: Specific heat of a heated object in the i-heating zone (K- cal./KG. C.)

1': Length of heated objects in the i-heating zone (m) X: Distance of a heated object in the i-heating zone from the inlet thereof (m) H,=h +h n' m+ cn' wherein,

h h Radiation heat transfer coefficient of the upper and lower parts of the i-heating zone respectively (KcaL/m. hr. C.)

h,,', h Convection heat transfer coefficient of the upper and lower parts of the i-heating zone respectively (KcaL/m. hr. C.)

Further, as a linear radiation heat transfer coefficient is introduced the following formulas (5) results:

0-: 4.88(Stephan Boltzmann constant) 1,": Average temperature of a heated object in the i-heating zone C.)

wherein,

L,-: Furnace length of the i-heating zone (m) Then, the temperature of a heated object at the inlet of the iheating zone is supposed to be r,,' that is,

tc X=0=r,., (7) and further the relation between the furnace temperature in the upper part and that in the lower part is supposed to be, as shown in the following formula (8):

GB GI ()t' is the temperature ratio between the upper part and lower part of the i-heating zone).

When a solution of the formula (3) is sought under these conditions as above mentioned, there can be obtained the following equation:

From the formula (9) it is possible to calculate the furnace temperatures of the upper and lower parts of the i-heating zone. 1 I at which temperatures the heated object which has passed through inlet of the i-heating zone with a temperature of t,,'( C.) may pass through the outlet of the same zone with a temperature of t C.

If a quantity of heat Qf (KcaL/hr.) which is necessary for the heated object, is composed of a quantity of heat Q, (1(- cal./hr.) which flows in from the upper surface and a quantity of heat Q (KcaL/hr.) which flows in from the lower surface, Q=Q.+QB

On the other hand, Q}, Q, can be obtained by substituting the formula (9) and integrating the substituted over a range of 0 to L In the preheating zone having no combustion equipment an average temperature of a heated object is calculated according to the formula (9), while in the heating zone and soaking zone it is possible to calculate temperatures set in the furnace or quantity of fed heat by utilizing the formulas l0) and l 1 On the other hand, if the maximum set temperature which is realizable in the upper part of the heating zone is made t the maximum treated amount of a heated object M corresponding to said maximum set temperature can be obtained by modifying the formula 10).

B'M(82%.... n )/(fiz bm sq)l Further, the shortest treating pitch in in the i-heating zone P,,, which can afford said maximum heating capacity is calculated by the following formula l5 that is,

P 36OOl d L- Jam (1 wherein,

(l :Thickness of a. steel material (m), :l)ensity of a. heated object (kg/m3), fnlNumber of operating furnace, k

mzFirst value ofj which satisfies the relation of E i= (sum of widths of u slab from an extracting port) ZL On the other hand, the time that a heated object stays in the soaking zone (fifth zone), T (minute), which may secure the minimum soaking degree and may eliminate skid marks to such a degree as would not impede a subsequent hot rolling, is obtained by the analysis of heat transfer. That is,

LFT

wherein,

L Total length of Furnace.

Therefore, a treating pitch in the soaking zone P, is given by the formula l7).

60LF (d4:0) fn-W- T (m is the first value of k which satisfies the relation of an independent furnace and consequently the heat controlling is carried out for each zone separately, such set heating temperature and moving velocity of a heated object in the zone can be determined according to the above-mentioned formulas as the heated object may pass through the outlet of the zone with an objective temperature to be obtained, if the temperature of the heated object at the inlet of the zone is measured or calculated and the objective temperature at the outlet thereof is determined.

An actual operation example according to the system of the present invention shall be described in the following.

F IG. 3 shows the case of the operating a continuously heating furnace by the system of the present invention. In the graph, shown with the solid line are planned values by the system of the present invention and shown with the dotted line are corrected values (actual operation values) based on the differences between said planned values and actual values. As evident from this graph, a very accurate control can be made.

Further, FIG. 4 comparatively shows the amounts of fuel (heavy oil) fed to the upper heating zones in a continuously heating furnace controlled by the system of the present invention and in a continuously heating furnace not using the system of the present invention. As evident from this graph, in case the system of the present invention is used, a far more precise control can be made and the fuel consumption can be made efficient.

FIG. 5 shows the results of measuring the temperature of the heated object (slab) at the soaking zone outlet in the case that the system of the present invention was worked. It is found that said temperature varied depending on the thickness of the heated object but was substantially constant for the same thickness and that therefore the control was made properly and accurately.

Thus, accordingly to the present invention, a continuously heating furnace can be operated automatically under optimum condition so that the heated object may be extracted at a fixed temperature, therefore the operation can be carried out efficiently and its effect is very high.

What is claimed is:

l. A process for controlling the direct heating of a steel material in a multizone type continuously heating furnace, in which furnace a preheating zone, a heating zone and a soaking zone are formed in sequence, comprising the steps of measuring the atmospheric temperature in said preheating zone, determining the temperature of said heated steel material at an inlet of said heating zone from said measured value of said atmospheric temperature in said preheating zone and the dimension, moving velocity and physical constant of said heated steel material, controlling the fuel inflow volume and combustion air volume in said heating zone from said temperature, simultaneously adjusting the quantity of heat fed to or the moving velocity of said heated steel material in said soaking zone from the difference between a predetermined rolling temperature and the measured value of the temperature of said heated steel material at the inlet of said soaking zone and the dimension and physical constant of said heated steel.