JPS63241124A - Method for controlling temperature of circulating gas for sintering - Google Patents

Abstract

PURPOSE:To improve productivity of a sintering machine of an exhaust gas circulation system without degrading cold strength, by controlling a temp.of circulating gas by adjustment of steam pressure in an evaporation part of a waste heat boiler through which an exhaust gas is passed. CONSTITUTION:The exhaust gas is sucked from the sintering machine and after the gas is passed through the waste heat boiler 11, the gas is returned to the sintering machine. The temp. (t) of the circulating gas is measured by a thermometer 30 and a deviation DELTAt between the temp. (t) and optimum temp. t0 is calculated. The stored data on the relation between the temp. of the circulating gas and the steam pressure and the deviation DELTAt are compared and the steam pressure P0 necessary for decreasing the deviation DELTAt to 0 is computed. On the other hand, feed water B is preheated and is sent through a boiler drum 25a to an evaporator 11b. The steam pressure (p) in the drum 25a is measured by a pressure gage 35 and the deviation DELTAp from the pressure p0 is computed. The opening degree of a pressure control valve 34 is so controlled as to decrease the deviation to 0. The temp. of the circulating gas is thereby controlled according to the meltability of sintered ore.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention improves the production of sintered ore by changing the circulating gas temperature in accordance with the solubility of the sintered ore in an exhaust gas circulation type sintering machine. The present invention relates to a circulating gas temperature control method for improving performance.

[Conventional technology]

In recent years, as an energy-saving measure, waste heat boilers have been installed in sintering plants at steel mills, and exhaust gases drawn from the sintered layer are passed through this boiler and then returned to the sintered layer. In many cases, an exhaust gas i-ring system is adopted, which increases the amount of exhaust heat recovered.

To explain the conventional exhaust gas circulation system using Fig. 1, the sintering raw material is transferred from the hopper 1.2 to the pallet 4 via the chute.
After being charged to the top and ignited in the ignition furnace 5, it is sintered while passing through the pallet 4. The fired sintered ore is cooled while passing through the cooler 16 of the cooler 8.

Sintering machine is used for exhaust heat recovery7. The cooling process is performed on both sides of the cooling Wa8.

For exhaust heat recovery in the sintering machine 7, the exhaust gas discharged from the wind box 9 is transferred to the pre-duster 10 and the exhaust heat boiler 1.
1 into the hood 3 of the sintering machine 7. The exhaust gas near the ore discharge section 12 is around 350℃, and even after exhaust heat is recovered by the exhaust heat boiler 11, the temperature is 150~20℃.
It has a temperature of 0°C. This exhaust gas is transferred to the blower 203.
In addition to increasing the amount of steam generated in the exhaust heat boiler 11 and increasing the amount of exhaust heat recovered, the exhaust gas circulation system returns the exhaust gas to the sintering machine 7 again.
It is possible to reduce the amount of exhaust gas emitted from the engine and reduce the scale of pollution prevention equipment (electrostatic precipitator 13, desulfurization and denitrification equipment 14).

On the other hand, exhaust heat recovery in the cooler 8 is performed as follows.

The sintered ore fired in the sintering machine 7 is cooled in the cooler 16, but since the sintered ore temperature in the cooler population 17 is about 500°C, the exhaust gas temperature in the first half of the cooler 16 is 400°C.
It will be about ℃. This exhaust gas is recirculated from the hood 18 to the wind box 21 via the pre-duster 19, economizer 24, and blower 20b.

Further, since the exhaust gas temperature in the latter half of the cooler 16 is about 150°C, the exhaust gas is used to preheat the boiler feed water in the feed water preheater 22. The feed water preheated by the feed water preheater 22 comes out from A and enters B and B' separately.

The feed water entering from B enters the economizer 11a of the waste heat boiler 11 via the deaerator 23a by the pump 29a.
Here, it is preheated by the sintering machine circulating gas and enters the boiler drum 25a as a liquid.

The feed water that has entered the drum 25a is sent to the evaporator 11b of the boiler 11 by the pump 29b, and after being reheated by the sintering machine circulating gas, it returns to the drum 25a, where it is vaporized and sent to the consumer 26.

The feed water entering from B' enters the deaerator 23b, and is further circulated by pumps 29c and 29d between the economizer 24, which is heated by the cooler circulating gas, and the boiler drum 25b, where it is vaporized and sent to the consumer 26. Sent.

Further, since the exhaust gas in the wandering part hood 27 is about 150° C., it is returned to the sintering machine outlet hood 28.

[Problem that the invention seeks to solve]

By the way, in such an exhaust gas circulation type sintering machine, the circulating gas at 150 to 200° C. is returned to the sintering machine 7, as described above. Sintering of such relatively high temperature circulating gas [? When refluxed, the heat capacity of the gas for the same actual volume increases by the higher temperature, and as a result, heat is accumulated in the sintered layer during firing, and the sintered layer begins to melt.
The melting area of the sintered layer at 100° C. or higher will increase.

Figure 2 shows the change in productivity (%) when circulating gas temperature (1) is changed, and Figure 3 shows the effect of circulating gas temperature on cold strength (S1%) and ore melting rate (%). ) is shown as a parameter, and Figure 4 shows the relationship between ore melting rate (%) and cold strength (51%). Table 1 shows the blending conditions of the sintering raw materials used in the investigation. According to these investigation results, it is clear that the conventional exhaust gas circulation system has the following problems.

Table 1 ■ When the temperature of the circulating exhaust gas is 150 to 200°C, the air permeability during firing deteriorates and productivity decreases (Figure 2).

■ 1100 in the range of circulating gas temperature 150 to 200℃
The cold strength (S1%) increases because the melting area above ℃ increases and the melting rate (%) of the ore increases (Figure 3). However, the amount of melted ore differs depending on the type of ore, and when using ore that melts easily, it becomes overmelted, causing uneven burning and lowering the u4 yield.

■ As the cold strength increases, the meltability of the ore increases (
Figure 4).

That is, as the circulating gas temperature increases, the cold strength increases and sintered ore desirable for use in blast furnace operation is obtained, but on the other hand, productivity decreases due to overmelting.

The present invention aims to solve this problem and improve productivity without impairing cold strength.

[Means for solving the problem] The present invention sucks exhaust gas from the sintering machine 7 and connects it to the exhaust heat boiler 1.
In the exhaust gas circulation system, the temperature of the circulating gas flowing back to the sintering machine 7 is adjusted by adjusting the steam pressure in the evaporation section of the exhaust heat boiler 11. The gist of this paper is a sintering circulating gas temperature control method that is controlled according to the solubility of ore.

That is, the temperature of the circulating gas returned to the sintering machine 7 is as follows:
As mentioned above, the temperature ranges from about 150 to 200°C. This is because the temperature of the circulating gas changes depending on the pressure of the steam generated by the waste heat boiler 11. For example, if the ordered steam is low pressure steam of 8 atm, the temperature of the circulating gas after passing through the exhaust heat boiler 11i11 is about 150°C, whereas if the generated steam is medium pressure steam of 27 atm,
Exhaust heat boiler 1liI! The v11 ring gas temperature after
The temperature will be around 0℃.

The present invention focuses on the point that the temperature of the circulating gas returned to the sintering machine 7 changes depending on the steam pressure of the exhaust heat boiler 11 as described above, and the steam pressure of the exhaust heat boiler 11 is adjusted to melt the sintered ore. By actively adjusting the temperature of the reflux gas to the sintering machine 7, the temperature of the reflux gas to the sintering machine 7 can be controlled to achieve the above objective.

[For production]

By adjusting the steam pressure in the evaporator section of the waste heat boiler 11, the saturated steam temperature changes and the temperature of the circulating gas flowing back to the sintering machine 7 can be adjusted over a wide range.

FIG. 5 shows the change in circulating gas temperature when the drum pressure in the boiler drum 25a, which is the evaporation section of the waste heat boiler 11, is changed from 25 kg/ajg to 8 kg/clig.

When the drum pressure is 27 kg/aJ g, as shown by the solid line, the circulating gas that entered the waste heat boiler 11 at about 400°C exchanges heat with the water supplied to the boiler and returns to the waste heat boiler 11 at about 200°C. exit. The water supplied to the boiler is heated by VA ring gas and becomes steam at approximately 200°C. On the other hand, when the drum pressure is 8 kg/c+Jg, as shown by the broken line, the circulating gas at about 400°C decreases in temperature to 150°C while passing through the waste heat boiler 11, and the temperature of the circulating gas decreases to 150°C while passing through the waste heat boiler 11.
The temperature of the circulating gas refluxed to can be reduced by 50°C.

Then, by using the relationship between the steam pressure change and the Wi ring gas temperature change to adjust the circulating gas temperature to match the solubility of the sintered ore, the cold strength can be improved without causing any problems.
Over-melting of the ore is prevented, making it possible to improve productivity.

For example, in Figure 3, the cold strength is 87%, which is the control value.
In order to maintain the circulating gas temperature at 125°C when the ore melting rate is 89%, 150°C when the ore melting rate is 88%, and 175°C when the ore melting rate is 87%, this means that the ore melting rate is high. When blending ores that are easy to use, overmelting can be prevented without affecting cold strength by lowering the circulating gas temperature as much as possible within the cold strength control value.

As described above, the present invention improves productivity without causing overmelting of the ore by controlling the temperature of the circulating gas flowing back into the sintering Ja7 according to the solubility of the ore by adjusting the steam pressure. and can maintain a practically sufficient cold strength.

〔Example〕

Hereinafter, a concrete implementation procedure of the present invention will be explained using the steam pressure regulating system illustrated in FIGS. 6(a) and 6(b).

According to the example in FIG. 6(a), sintering II? The circulating gas passes through the pre-duster 10 and enters the waste heat boiler 11, and then enters the economizer 113 in the boiler 11 and the evaporator 11.
After passing through b, it is refluxed to the sintering machine 7 via the blower 20a.

On the outlet side of the blower 20a, the temperature t of the circulating gas flowing back to the sintering machine 7 is measured by a thermometer 30, and is input to the first comparator 32 together with the signal from the temperature setting device 31.

The temperature setting device 31 inputs the optimum reflux gas temperature t0 for the sintered ore, that is, the lowest reflux gas temperature (FIG. 3) within a range that does not fall below the cold strength control value, to the first comparison calculator 32. The first comparator 32 calculates the deviation Δt between the measured temperature t output by the thermometer 30 and the optimum temperature t output by the temperature setting device 31 and outputs it to the pressure setting device 33 .

The pressure setting device 33 stores in advance the relationship between the circulating gas temperature and the steam pressure (FIG. 5), and compares the temperature deviation Δt inputted from the first calculator 33 with the stored data to determine the temperature deviation Δ.
The steam pressure p0 required to make t equal to O is calculated.

On the other hand, the feed water entering from B passes through the deaerator 23a and enters the economizer 118 by the pump 29a, where it is preheated by circulating gas and enters the boiler drum 25a.

The feed water that has entered the boiler drum 25a is sent to the evaporator 11b by the pump 29b, where it is heated by circulating gas, returns to the drum 25a, becomes steam, and is sent to the customer 26 via the pressure control valve 34. It will be done.

In the boiler drum 25a, the steam pressure p is measured by a pressure gauge 35 and inputted to a second comparator 36. The second comparator 36 compares the steam pressure p input from the pressure gauge 35 and the steam pressure p0 input from the pressure setting device 33, calculates the deviation Δp,
Output to 7.

The valve controller 37 controls the opening of the pressure regulating valve 34 so that this deviation Δp becomes zero.

Thus, the temperature of the circulating gas returned to the sinterer 7 matches the optimum temperature t0.

At this time, it goes without saying that an appropriate heat transfer area should be given to the feed water preheater 22 (FIG. 1) to prevent evaporation in the economizer 113 and to ensure proper evaporation in the evaporator 11b.

In the system shown in FIG. 6(a), the steam obtained by exhaust heat recovery is reduced in pressure by the pressure regulating valve 34 and sent as is to the consumer 26.

In this case, the pressure reduction loss caused by the pressure regulating valve 34 becomes large, resulting in a disadvantage in terms of energy recovery rate.

Therefore, as shown in the example of FIG. 6(b), the pressure regulating valve 3
It is also possible to provide a pressure regulating valve 38, a back pressure turbine 39, and a generator 40 in parallel to the pressure regulating valve 34, and recover the pressure reduction energy by the pressure regulating valve 34 as motive power/electrical energy, thereby increasing the energy recovery rate. Since this example is the same as the example shown in FIG. 6(b) except that the decompression energy is recovered, the same parts are given the same numbers and detailed explanations will be omitted.

Furthermore, when the demand for steam is low, it is also possible to use a condensing turbine to recover energy and adjust the steam pressure.

Table 2 shows how the drum pressure can be adjusted from 27 kg/cal g to 8 kg/cal g in the steam pressure adjustment system shown in Figure 6 (a).
This shows a comparison of operational data when changing to ajg.

As is clear from the table, circulating gas 15000Nrd/
By reducing the drum pressure from 27ksr/cdg to 8kg/aJg in a minute operation, the circulating gas temperature decreased from 200°C to 150°C, which increased the production from 9600t7d to 10200td/day. ,
Electric power consumption ranges from 26.0 kw h/ton to 25.0
kw h/ton, and no overmelting occurred at all. In addition, the amount of steam generated is 47 tons/hour to 58 tons/hour.
The cold strength of sintered ore (31%
) decreased from 88.0% to 87.5%, but the control value (
31≧87%), there was no problem.

Table 2 [Effects of the Invention] According to the present invention, by adjusting the circulating gas temperature, it is possible to obtain operating conditions that correspond to the brand of the sintering raw material ore, the operating status of the exhaust heat recovery equipment, etc., and the cooling of the sintered ore is improved. This method has a significant effect on maintaining the quality of sintered ore and improving productivity by sufficiently increasing productivity while maintaining mechanical strength.

[Brief explanation of drawings]

Figure 1 is a system diagram showing the exhaust gas circulation system of the sintering machine, Figure 2 is a diagram showing the relationship between circulating gas temperature and productivity change, and Figure 3 is a diagram showing the relationship between circulating gas temperature and productivity change.
The figure is a diagram showing the relationship between circulating gas temperature and cold strength.
The figure is a diagram showing the relationship between ore melting rate and cold strength, Figure 5 is a diagram showing the relationship between steam pressure and circulating gas temperature, and Figures 6 (a) and (b) are diagrams showing the relationship between ore melting rate and cold strength. 1 is a system diagram illustrating a suitable steam pressure regulation system; FIG. In the figure, 7: sintering machine, 8: cooling machine, ll: exhaust heat boiler,
25 boiler drum, 30: thermometer, 34: pressure control valve, 35: pressure gauge. Circulating gas temperature (°C) Figure 2 Melting rate (%) Figure 4 Circulating gas temperature (°C) Figure 3 Figure 5

Claims (1)

[Claims] (1) The exhaust gas is sucked from the sintering machine (7) and the exhaust heat boiler (
11), the exhaust gas is returned to the sintering machine (7) by adjusting the steam pressure in the evaporation section of the waste heat boiler (11). A sintering circulating gas temperature control method characterized by controlling the temperature of the circulating gas according to the solubility of sintered ore.