JPS63153204A - Method for controlling preheating temperature of material to be reduced in reduction furnace - Google Patents

Abstract

PURPOSE:To control the preheating temp. of a material to be reduced so as to coincide with a target preheating temp. with high accuracy by dividing the discharge gas passages of a heat exchanger crossing the passage for the material to be reduced to plural blocks and controlling the temps. and flow rates of the exhaust gases to the respective blocks. CONSTITUTION:Iron powder 1 which is the material to be reduced and is supplied to a reduction furnace (not shown in figure) is allowed to flow down in the iron powder passage 9 of a heat exchanger 24 and the waste combustion gas is passed in the exhaust gas passage 10 crossing the passage 9 by which the inside of the passage is heated. The passage 10 is divided to the plural blocks 10a-10c and iron powder temp. detectors T1-T18 and exhaust gas temp. detectors Tg1-Tg3 are disposed in accordance with the respective blocks. The detected temps. therefrom and the target preheating temp. Ts of the iron powder from a setter 16 are inputted to a microcomputer 14 which computes the optimum heat patterns and the target iron powder temp. for each of the respective blocks 10a-10c. External air introducing dampers 6a-6c and exhaust gas flow rate control dampers 11a-11c are controlled via a control unit 15 in order to obtain the required temps. and flow rates of the exhaust gas based thereon.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for controlling the preheating temperature of iron powder in an iron powder reduction furnace for reducing iron powder, for example, and particularly to a method for controlling the preheating temperature of a material to be reduced. Regarding improvement.

[Conventional technology]

Generally, in a reduction furnace, a powdered material to be reduced, such as iron powder, is placed in the form of a strip on a conveying steel belt, and heated along a predetermined pattern while being conveyed through the furnace.

This is a thermal facility that performs reduction treatment by cooling.

Such iron powder reduction furnaces heat iron powder to a high temperature and hold it at this high temperature for a predetermined period of time, so the amount of energy required is extremely large, and there is a need to reduce the amount of energy consumed. There is.

Therefore, in order to reduce the above energy consumption, the present applicant has developed an iron powder preheating device that preheats iron powder using the combustion exhaust gas of the reduction furnace itself.

As shown in FIGS. 6 and 7, this preheating device is equipped with a heat exchanger 4 in the middle of a supply hopper 3 that supplies raw material powder 1 into the furnace body 2. An exhaust duct 5 for discharging the combustion exhaust gas from the burner 2a to the outside is connected to the exhaust duct 5, and an outside air introduction damper 6 is connected to the exhaust duct 5. It is configured so that the temperature of the four population parts is constant.

The heat exchanger 4 is of a multi-tube type, and the combustion exhaust gas is passed through a large number of pipes 4a, and the raw material powder 1 is passed through an iron powder passage perpendicular to the exhaust gas passage for indirect heating. method is adopted. Note that 8a is a conveying steel belt, which is wound around head pulleys 8b and 8c disposed before and after the furnace.

According to the above-mentioned preheating device, since the amount of heat corresponding to the preheating temperature of the iron powder can be recovered from the exhaust gas, the required amount of fuel is reduced by that amount, and the fuel consumption rate can be improved.

By the way, from the standpoint of improving fuel consumption, it is desirable to preheat the raw material powder to as high a temperature as possible.On the other hand, if the raw material powder is iron powder, for example, if the preheating temperature is 300°C or higher, its surface will oxidize rapidly. Therefore, the preheating completion temperature needs to be lower than a predetermined temperature. Therefore, in order to prevent the above-mentioned surface oxidation problem while obtaining a large preheating effect, it is required to improve the preheating accuracy.

[Problem that the invention seeks to solve]

However, the preheating device shown in Figures 6 and 7 above is intended only to improve the fuel consumption rate by preheating the iron powder, and is a device that preheats the iron powder by the same temperature while keeping the exhaust gas temperature constant. It is. Therefore, for example, if the iron powder temperature at the heat exchanger inlet changes, or if the amount of iron powder passing through the heat exchanger fluctuates due to changes in the operating conditions of the reduction furnace, the preheating completion temperature will not necessarily remain constant. Therefore, the above-mentioned request for improving preheating accuracy cannot be met.

Therefore, it is an object of the present invention to accurately maintain the preheating temperature of the reductant to the target preheating temperature even when the temperature at the inlet of the raw material powder to the heat exchanger changes or the amount of raw material powder passing through the heat exchanger fluctuates. It is an object of the present invention to provide a method for controlling the preheating temperature of a material to be reduced, which can be easily brought to a boil.

[Means for solving problems]

The present invention provides a control method for preheating a powdered material to be reduced to a target preheating temperature, in which an exhaust gas passage of a heat exchanger is divided into a plurality of blocks in the direction of passage of the material to be reduced, and combustion exhaust gas is directed to each block. The inlet temperature and flow rate of the reductant are controlled so that the outlet temperature of each block of the material to be reduced becomes a predetermined temperature on the optimum heat pattern.

[Effect]

In the method for preheating temperature control of a material to be reduced in a reduction furnace according to the present invention, the exhaust gas temperature and flow rate are controlled for each block so that the outlet temperature of each block becomes the target outlet temperature of each block. Compared to controlling all at once, the responsiveness of the control is improved, and the control accuracy is improved accordingly.For example, when the temperature of the reductant at the heat exchanger inlet changes, or when the If the amount of material passing through fluctuates, the temperature at the outlet of each block for the raw material powder also tends to change, but in the present invention, the exhaust gas supplied to each block is adjusted according to the difference between the outlet temperature of each block and the target outlet temperature. Since the temperature and flow rate of the gas are adjusted, the effects on the target preheating temperature due to changes in the inlet temperature of the reductant and fluctuations in the throughput amount are suppressed by adjusting the exhaust gas temperature and flow rate, and as a result, the heat exchanger The outlet temperature can be brought down to the target temperature with high accuracy.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

1 to 4 are diagrams for explaining a method for controlling the preheating temperature of iron powder in an iron powder reduction furnace according to an embodiment of the present invention, and the same reference numerals as in FIG. 6 indicate the same or corresponding parts.

First, an apparatus for carrying out the method of this embodiment will be explained. In FIGS. 1 and 2, 24 is a plate type heat exchanger, which has an iron powder passage 9 through which iron powder l flows from above to below, and which is perpendicular to the passage 9 and sandwiching the iron powder passage 9. It is composed of a pair of exhaust gas passages IO. Each of the exhaust gas passages 10 has upper, middle,
It is divided into lower blocks 10a, 10b, and 10c, and each block 103 to 10C has an inlet header 17a to 17c on the inlet side, and an exit ladder 17 on the outlet side.
d is connected.

5 is a combustion exhaust gas duct, and this exhaust gas duct 5
The upstream portion of the heat exchanger 24 is branched into three ducts 5a, 5b, and 5c connected to each of the divided inlet headers 17a to 17c, and the downstream portion 5d connects the duct 17d to the outlet. It is connected to a chimney (not shown). Further, each of the ducts 5a, 5b, and 5c includes outside air introduction dampers 6a to 6C and exhaust gas flow rate adjustment dampers lla to 1, respectively.
1c is interposed.

T, ~T1. is an iron powder temperature detector that detects the temperature in each block loa, 10b, and 10c of iron powder 1 flowing in the iron powder passage 9, and each detector is connected to each block lOa to 10c as shown in FIG. They are arranged at the center and both ends of the iron powder passage 9 at the inlet and outlet portions of the iron powder passage 10c.

Tg+-Tgs, Tgs are each of the above exhaust gas ducts 5a,
This is an exhaust gas temperature detector that detects the temperature of the combustion exhaust gas flowing inside the heat exchanger 24, which flows through the insides of the combustion exhaust gases 5b and 5c.

16 is an iron powder target preheating temperature setting device that sets a target preheating temperature Ts of the iron powder 1 at the outlet of the heat exchanger 24.

14 is a microcomputer, which is connected to each of the temperature detectors T + -T l @ l T g 1 to T g
The detected iron powder temperature, detected exhaust gas temperature, and target preheating temperature Ts from 3 are input, and from these detected temperatures, the amount of heat received in each block 10a, 10b, and 10c is calculated, and from this amount of heat received and the target preheating temperature Ts, Calculate the optimum heat pattern in the range below the powder upper limit temperature, and calculate each block lOa, 10 b, 10 on the heat pattern.
The iron powder temperature TaxTc at the outlet of block c is set as the target outlet temperature, and the set exhaust gas temperature Tgsl to Tgs to achieve the target outlet temperature Ta-Tc is calculated, and the exhaust gas temperature Tg to each block is calculated. +~Tg3 to the above set exhaust gas temperature Tgs, xTgs, -wl(s is calculated as the opening degree of the exhaust gas flow rate adjustment dampers lla~llc and the outside air introduction dampers 6a~6c, and this is used to control the damper opening/closing. Output to unit 15.

The control unit 15 controls each damper lla.
The opening/closing control is performed so that the opening degrees of ~llc and 6a~6C correspond to the opening signals from the microcomputer 14.

Next, a case will be described in which the method of this embodiment is implemented using the above-mentioned apparatus.

First, an overview of the operation of the present device will be described. After the iron powder 1 is preheated by the main heat exchanger 24, it is placed on the conveying steel belt 8a in the furnace 2, and is subjected to a reduction treatment while being conveyed. Further, the heat exchanger 24 is supplied with combustion exhaust gas from the burner 2a.

In this case, the damper opening/closing control unit 15
However, the outside air introduction dampers 6 of the exhaust ducts 5a, 5b, 5c are installed so that each target preheating temperature Ta-Tc of the iron powder 1 can be achieved.
a~6C and exhaust gas flow 1lll damper lla~II
Open/close C to the opening degree from microcomputer I4 01? Have sex.

Next, the operations of the microcomputer 14 and the damper opening/closing control unit 15 will be explained along the flowchart of FIG. 3.

The target preheating temperature T s set by the target preheating temperature setting device 16 for the iron powder 1, and the detected iron powder temperature T1 at the center and both ends at the inlet and outlet of each block 10a to IOc.
~T4. The detected exhaust gas temperatures Tg r to Tg in each exhaust duct) 5a, 5b, and 5c are input (step Sl), and the iron powder temperature is determined from the iron powder temperature at the center and both ends of each block 103 to 10c. The temperature distribution in the thickness direction is approximated to a quadratic curve, and thereby the amount of heat received is calculated (step S2). From the amount of heat received in each block 102 to 10C and the target preheating temperature Ts, the temperature of the iron powder at any part is calculated. The optimum heat pattern is calculated within a range that does not exceed an upper limit value, for example, 300° C. (step 33).

Then, the temperature at the outlet portion of each block loa to 10C of the iron powder 1 on the above heat pattern is set to the target outlet temperature Tax.
Tc and step S4), the target outlet temperature Ta-T
Set exhaust gas temperature Tgs, zTgs to realize c
, is calculated (step S5).

Here, Fig. 4 is a characteristic diagram showing the relationship between the optimum heat pattern and the set exhaust gas temperature. In the figure, A shows the optimum heat pattern, and B shows the set exhaust gas temperature. Once the heat pattern A is determined, the set exhaust gas temperatures Tg s+, TgSt, to achieve the target outlet temperatures Ta, Tb, Tc of each block on the pattern A
TgS3 is determined.

and the above-mentioned set exhaust gas temperature Tg3. ~Tgs, the opening degree Kl''Ks of each damper lla~llc, 6a~6C is calculated, and the opening degree K is calculated.

~ to the damper opening/closing control unit) 15 (steps S6 and S7), and the detected outlet temperature Tao-Tco in each block 103 to 10c of the iron powder l
and target outlet temperature Ta-Tc, and if they do not match, set exhaust gas temperature Tgs,
~Tg 33 is corrected and the process returns to step S6 (steps S8 and S9), and when the two match, the process returns to step S1.

In this way, the outside air of each duct 5a, 5b, 5C is adjusted so that the detected outlet temperature TaoxTco of each block 102 to 10c of iron powder l becomes TaxTC, and the outlet temperature of the heat exchanger 24 becomes the target preheating temperature Ts. Introduction dampers 6a-5
c, the opening degree of the exhaust gas flow MHi 1-node damper 1la-11C, and thus the exhaust gas temperature Tg+ to Tg are controlled.

As described above, in this embodiment, the exhaust gas passage 10 of the heat exchanger 24 is divided into three blocks, and in each block, the iron powder temperature is set to the target outlet temperature T a - on the optimum heat pattern.
Exhaust gas temperature to be T c.

Since the flow rate is suppressed, the upper limit temperature is not exceeded in any part of the iron powder, and the target temperature as a whole can be maintained accurately.As a result, surface oxidation due to overheating is prevented. In addition, in this case, the iron powder passage 9 of the heat exchanger 24
Since the iron powder temperature is detected at the center and both wall surfaces in the thickness direction, the amount of heat received by the iron powder 1 can be calculated accurately, and controllability can be improved from this point as well.

In addition, since the control is divided into multiple blocks, the temperature at the inlet of the heat exchanger 24 of the iron powder 1 or the amount of iron powder passing through the heat exchanger 24 may fluctuate due to changes in operating conditions, for example. Also, since the exhaust gas temperature Tg+=Tgs can be changed with good responsiveness in accordance with this, the above fluctuation can be absorbed and the preheating temperature can be approximated to the target temperature.

In the above embodiment, a case has been described in which the heat exchanger is configured such that the iron powder passage is sandwiched between a pair of exhaust gas passages, but in the present invention, the heat exchanger of the above embodiment as shown in FIG. It can be applied to heat exchangers with a structure in which multiple exchangers are connected, and it can also be applied to shell-and-tube heat exchangers. It is sufficient to control the exhaust gas temperature and flow rate.

〔Effect of the invention〕

As described above, according to the method for preheating temperature control of a material to be reduced in a reduction furnace according to the present invention, the exhaust gas passage is divided into a plurality of blocks, and the temperature and flow rate of the exhaust gas to each block are controlled by
Since the outlet temperature of each block of the material to be reduced is controlled to be the target outlet temperature on the optimum heat pattern, the control accuracy of the preheating temperature can be improved.

[Brief explanation of the drawing]

1 to 4 are diagrams for explaining a method for preheating temperature control of iron powder in a reduction furnace according to an embodiment of the present invention, and FIG. A configuration diagram of the control device, FIG. 2 is a plan view thereof, FIG. 3 is a flowchart thereof, FIG. 4 is a characteristic diagram showing the relationship between the optimum heat pattern and the set exhaust gas, and FIG. 5 is a modification of the above embodiment. A perspective view showing an example, FIG. 6 is a configuration diagram of a conventional preheating device, and FIG. 7 is a configuration diagram of its main parts. In the figure, 1 is iron powder (material to be reduced), 2 is the reduction furnace main body,
24 is a heat exchanger, 9 is an iron powder passage (reducing agent passage), 10 is an exhaust gas passage, 10a, 10b. 10c is a block, and Tg+, Tgt, and Tgs are exhaust gas temperatures.

Claims (1)

[Claims] (1) The powdered material to be reduced to be supplied to the reduction furnace is caused to flow through the reducing material passage of the heat exchanger, and the combustion exhaust gas is caused to flow through the exhaust gas passage which intersects with the reducing material passage. In a preheating temperature control method for preheating a material to a target preheating temperature, the exhaust gas passage of the heat exchanger is divided into a plurality of blocks in the flow direction of the reductant material, and the temperature and flow rate of the combustion exhaust gas to each block are controlled by controlling the temperature and flow rate of the combustion exhaust gas to each block. A method for preheating temperature control of a material to be reduced in a reduction furnace, characterized in that the temperature at the exit of each block of the reducing material is controlled to be a target exit temperature on an optimal heat pattern.