JPH0660356B2 - Flue gas temperature control method for continuous heating furnace - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for controlling the temperature of waste gas in a flue of two systems in a continuous heating furnace.

[Conventional technology]

Continuous heating furnace with a recuperator for preheating combustion air to the heating furnace combustion burner in two flue channels that attract and discharge waste gas from both the left and right sides (widthwise sides) of the charging side of the material to be heated. In the above, the control of the damper installed in each flue is conventionally performed, for example, in Maruzen Co., Ltd., November 20, 1980 "3rd Edition Steel Manual, Section III (2) Steel bar, steel pipe, rolling common equipment".
As shown in FIG. 16-52, p. 1279, the difference between the measured value of the in-reactor pressure from the in-reactor pressure gauge and the target value is set to 0 in order to control the in-reactor pressure to a certain target value. Based on the above, only the parallel opening / closing control was performed, and the control of the temperature of the induced exhaust gas in each flue was not controlled.

[Problems to be solved by the invention]

Only in the case of controlling the furnace pressure, the material to be heated is charged into the continuous heating furnace, and in the case of an operation in which the center of the longitudinal direction of the furnace is aligned with the center of the furnace width direction, both halves in the furnace width direction are heated. Each heating load is equal, and there is almost no difference between the temperatures of the waste gas that is attracted to each flue that is openly connected to the left and right sides of the charging side, so the temperature of the waste gas at the maximum heating load in this operation is almost the same. Considering that the exhaust gas temperature on the inlet side of the recuperator does not exceed the upper limit of the allowable range for its protection, and the exhaust gas temperature on the outlet side of the recuperator does not fall below the lower limit of the range, the recuperator is placed in the flue. There is no problem if the specifications such as the position and the preheating ability of the combustion air of the recuperator are determined.
However, in the case of a heating operation in which the length of each material to be charged into the continuous heating furnace is not constant and the temperature at the rolling start tip is extracted to a predetermined value in response to a request from the next rolling process, the furnace is The position of the rolling start tip of each of the materials to be heated in the inner width direction is all charged in line with the rolling process side in the inner width direction of the furnace, so the position of the trailing end of each material to be heated becomes uneven, The heating load on the non-uniform side is smaller than the heat load on the non-uniform side. Therefore, the temperature of the waste gas attracted to the non-uniform side flue becomes higher than the temperature of the waste gas attracted to the non-uniform flue.

As a result, the inlet side exhaust gas temperature of the recuperator placed in the high temperature waste gas induction flue often exceeds the upper limit of its allowable range, and the outlet side exhaust gas temperature of the recuperator installed in the low temperature waste gas induction flue. Often occurs below the lower limit of the permissible range, which significantly shortens the life of the recuperator. If a highly efficient metallic recuperator is used as a recuperator to improve the thermal efficiency of the heating furnace, the allowable exhaust gas temperature range for its protection is greatly reduced, so more severe smoke is generated in such heating operations. Temperature control of waste gas in Hokkaido is required.

As a control of this waste gas temperature, when the waste gas temperature on the inlet side of the recuperator exceeds the upper limit of the permissible range, cool air is blown to the flue or the amount of combustion air sent to the recuperator is increased more than necessary and discarded. Temporary measures can be taken such as increasing the heat removal from the gas and lowering the temperature of the recuperator itself to within the permissible range, and releasing the excess amount of combustion air leaving the recuperator to the atmosphere, but thermal loss. Is not the preferred means. Further, when the temperature of the waste gas on the outlet side of the recuperator is below the lower limit of the permissible range, there is no countermeasure.

[Means for solving problems]

The present invention has been made to solve the above-mentioned problems, and its means is to provide a continuous heating furnace having two flues for attracting and discharging waste gas from both left and right sides of a material to be heated charging side, When the exhaust gas temperature at the inlet or outlet of the recuperator installed in each system flue is within the allowable temperature range of the recuperator, the reactor pressure control system controls the dampers of each flue in parallel to open and close each flue. When either one of the recuperator inlet side exhaust gas temperature exceeds the upper limit of the permissible temperature range, or when any one of the flue recuperator outlet side waste gas temperature is below the lower limit of the permissible temperature range The opening and closing control of one of the dampers of each of the flues by the furnace pressure control system, the other damper based on the inlet side exhaust gas temperature difference between the recuperators or the outlet side exhaust gas temperature difference,
It is characterized in that opening / closing control is performed so that a waste gas temperature above the upper limit or a waste gas temperature below the lower limit falls within the allowable range.

[Action]

When the occupying areas of the heated material loaded in the continuous heating furnace in the furnace widthwise both halves are greatly different, and the heating load is significantly different, it is attracted to the flue on the low heating load side. The temperature of the waste gas is high and exceeds the upper limit of the allowable range for protecting the recuperator on the inlet side of the recuperator of this flue, or the temperature of the exhaust gas attracted to the flue on the high heating load side is low, and the recuperator of this flue is low. On the output side, the lower limit of the allowable range for recuperator protection is exceeded, or both occur simultaneously. Such a state is detected by providing exhaust gas temperature detectors on the inlet side and outlet side of the recuperator in each flue.
If each detected temperature value is within the allowable temperature range, the conventional furnace pressure control system causes the dampers of each flue to operate in parallel, that is, a control signal is sent to both dampers to perform the same opening / closing control, outside the allowable temperature range. If so, the simultaneous opening of the furnace pressure control system
One of the dampers of each flue which was controlled to be closed is used as an open / close control damper by the furnace pressure control system, and the other is used as an open / close control damper of the waste gas temperature control system. As described above, the exhaust gas temperature control system compares the exhaust gas temperature detection values on the inlet side or the outlet side of the recuperator of each flue by comparing the exhaust gas temperature detection value with the lower limit or the upper limit of the recuperator allowable range to obtain the difference, The damper is controlled to open / close to the damper opening degree that makes this difference 0.

When the detected temperature value is outside the allowable temperature range, for example, the damper of the low heating load side flue is the furnace pressure control system and the damper of the high heating load side flue is the waste gas temperature control system. When a situation occurs, the damper for the high heating load side flue is opened by the above-mentioned opening / closing control to increase the waste gas flow rate, while the damper for the low heating load side flue is aimed at the furnace pressure that is reduced by this. The closing operation is performed to increase the value to reduce the waste gas flow rate. Here, assuming that the amount of combustion air flowing in each recuperator is the same for each, the amount of heat recovered from the waste gas is substantially the same, and the amount of waste gas generated in the furnace does not change, the opening operation damper side The temperature of the waste gas on the inlet side or the outlet side of the recuperator is increased, and the temperature of the waste gas on the inlet side or the outlet side of the recuperator on the closing operation damper side is lowered to be balanced. As a result, even if the exhaust gas temperature on the inlet side and outlet side of each flue deviates from the allowable range for protection of the recuperator, cold air is blown into the flue and the amount of combustion air to the recuperator is increased as before. It can be immediately brought into the permissible range without causing a large heat loss such as supply and excessive dissipation.

〔Example〕

In the embodiment shown in the drawings, the slabs S of various lengths sent from the slab yard are arranged such that the position of the rolling start tip TP is the rolling process side in the width direction of the furnace (hereinafter referred to as the east side, and the opposite side is referred to as the west side). align the called) was charged from the charging hole I _N, spout E
It is an example applied to a continuous heating furnace RF that is extracted from _X and supplied to the rolling process in the direction of the arrow. The heating furnace PF includes flues E _E , E _W having inlet ports open-connected on both sides in the width direction of the furnace interior entrance side.
Each flue E _E , E _W is provided with a recuperator R _E , R _W and a damper D _E , D _W , respectively, and the outlet ends are joined together to communicate with one chimney 20. .

The first computing unit 1 sequentially introduces the measured in-furnace pressure value P detected by the furnace pressure gauge 2 and compares it with the target furnace pressure target value P ₀ from the upper-level computer 3 to find the deviation, and this deviation is always The opening / closing control signal ΔP of the same amount is output to the control units AC _E and AC _W of the opening / closing drive actuators A _E and A _W of the dampers D _E and D _W so that the dampers D _E and D _W become zero.

The first determination unit 8 each flue _E E, recuperator _R E of _{E W, R W} inlet side respectively disposed waste gas thermometer 4E, ₄ temperature measurement value T _INE from _W, introducing T _INW, these The judgment signal θ _u and the respective temperature measurement values T _INE and T _INW are set to the second value only when any one of the temperature measurement values exceeds the upper limit of the allowable range UD for protecting the recuperator which is preset. Output to the arithmetic unit 10.

The second determiner 9 is a recuperator R for each flue E _E , E _W.
E, R _W exit side respectively disposed waste gas thermometer 5E, temperature measuring value T _OUTE from 5w, introducing T _outW, recuperator protection temperature measurement value of any of these, which had been pre Ji because setting Only when the lower limit of the upper allowable range UD is exceeded, the determination signal θd and the temperature measurement values T _outE and T _outW are output to the second calculation unit 10.

The second arithmetic unit 10 receives the θ _u and T _INE from the first determiner 8 and
When T _INW is input, the actuator A _E
Output the signal OFF for instructing not to output the damper opening / closing control signal ΔP for controlling the furnace pressure only to the control unit AC _E , and perform the calculation of the following equation to notify the control unit AC _E of the exhaust gas temperature. The opening / closing amount Δθ of the damper for control is output.

Δθ = K * (T _INW −T _INE ) ... (1) where K: conversion coefficient for converting the waste gas temperature difference into the damper opening / closing amount Δθ required to eliminate this.

The second arithmetic unit 10, second from the judging unit 9 the θd and T _OUTE, controller AC _E only the furnace pressure control damper opening control signal when inputting a T _outW first arithmetic unit 1 to the actuator A _E performs the following calculation to output a signal OFF for commanding that ΔP is not outputted, and outputs the damper opening and閉量Δθ for the waste gas temperature control to the control unit AC _E.

_{Δθ = K * (T outW -T} outE) ...... (2) controller AC _E inputs the [Delta] [theta] from the second calculation unit 10 when the value is positive, i.e., (T _INE <T _INW) or (T _outE <
When the T _outW), the damper D _E opening and closing operation of the actuator A _E allowed to Δθ minute opening operation while detecting the degree of opening of the damper D _E. As a result, the exhaust gas flow rate on the flue side E _E gradually increases and the furnace pressure P gradually decreases, but this fluctuation of the furnace pressure is caused by the damper by the furnace pressure control system of the control unit AC _W by the living first computing unit 1. The waste gas flow rate is reduced by the closing operation of D _W to prevent it and to return to the target furnace pressure set value P ₀ .

Now it made to increase the waste gas flow rate of E _E side of the flue E _W moved down the recuperator R _W entry side temperature T _INW flue E _W exceeding the upper limit placed within the permissible range (T _INE ≒
And T _INW), or those that have raised the recuperator R _E delivery temperature T _OUTE flue E _E which Shitamawa' the lower limit placed within the permissible range _(T outE ≒ T _outW).

Further, the control unit AC _E controls the damper D _E opening / closing operation of the actuator A _E when Δθ input from the second computing unit 10 is negative, that is, (T _INE > T _INW ), or (T _outE > T _outW ). While detecting the opening degree of D _E, the closing operation is performed by Δθ. As a result, the exhaust gas flow rate on the flue E _E side is gradually reduced and the furnace pressure p is gradually increased. This gradual increase in the furnace pressure causes the furnace pressure control system of the control unit AC _W by the living first computing unit 1. Due to the opening operation of the damper D _W by the above, the exhaust gas flow rate is increased to prevent it and to return to the target furnace pressure set value P ₀ .

With this, the exhaust gas flow rate on the E _E side of the flue E _W is reduced, and the recuperator R _E inlet side temperature T _INE of the flue E _E that exceeds the upper limit value is lowered to fall within the allowable range [T _INE
≉T _INW ], or by increasing the recuperator R _W outlet temperature T _outW of the flue E _W below the lower limit to bring it into the allowable range [T _{outE ≉T outW} ].

〔The invention's effect〕

Thus, the present invention, the occupying area of the material to be heated in the furnace width direction both halves of the continuous heating furnace is greatly different, the heating load is also greatly different accordingly, the charging side widthwise both sides Even if the temperature at the inlet or outlet of the recuperator exceeds or falls below the allowable range for protecting the recuperator, there is a large difference in the temperature of the waste gas that is attracted to each open flue, and the reactor pressure does not fluctuate. By simply changing the exhaust gas flow rate ratio to the flue, the exhaust gas temperature on the side above the lower limit can be reliably changed and controlled within the allowable range to significantly extend the life of the recuperator, and to cool air blowing etc. Since it is not necessary at all, the heat removal effect from the waste gas of the recuperator is stabilized at a high level,
The thermal efficiency of the heating furnace can be improved significantly.

[Brief description of drawings]

Drawing is a block diagram showing an example of a control device for carrying out one example of a control method of the present invention. Figure S is a material to be heated, RF continuous heating furnace, _{I N} is _SoIrigawa, E E, _{E W flue,} R E, _{R W} is recuperator,
D _E and D _W are dampers.

Claims (1)

[Claims] 1. A continuous heating furnace having two flues for attracting and discharging waste gas from the right and left sides of the side to which the material to be heated is loaded, and the waste gas at the inlet or outlet of the recuperator installed in each flue. When the temperature is within the allowable temperature range of the recuperator, the damper control of each flue is controlled in parallel by the furnace pressure control system, and the recuperator inlet side exhaust gas temperature of any one of the above flues is within the allowable temperature range. If the upper limit of the above, or if the exhaust gas temperature of the recuperator exit side of any one of the above flues is below the lower limit of the allowable temperature range,
Opening and closing of one of the dampers of each of the above flues was controlled by the furnace pressure control system, and the other damper was exceeded based on the inlet side exhaust gas temperature difference or the outlet side exhaust gas temperature difference between the recuperators. A method for controlling a flue waste gas temperature of a continuous heating furnace, comprising controlling opening / closing so that a waste gas temperature or a waste gas temperature below a lower limit falls within the allowable range.