CN115216625A

CN115216625A - Gas periodic interval injection auxiliary sintering method

Info

Publication number: CN115216625A
Application number: CN202111390081.7A
Authority: CN
Inventors: 周浩宇; 叶恒棣; 魏进超; 王业峰; 陈思墨; 李谦; 刘前
Original assignee: Zhongye Changtian International Engineering Co Ltd
Current assignee: Zhongye Changtian International Engineering Co Ltd
Priority date: 2021-11-22
Filing date: 2021-11-22
Publication date: 2022-10-21
Anticipated expiration: 2041-11-22
Also published as: CN115216625B

Abstract

A method for auxiliary sintering by periodically and alternately injecting gas is characterized in that: periodically blowing gas to the charge level of the sintering mixture at intervals, and enabling the gas to enter a sintering charge layer for combustion and heat supply; in the process of gas injection, the temperature of the sintering ore zone and the combustion zone area in the sintering material layer is controlled by adjusting the time length of gas injection in a single period. The invention skillfully controls the injection and the stop of the fuel gas through periodic interval injection, further enables the fuel gas to be repeatedly ignited and extinguished near the combustion zone, namely, certain cooling time is left for sintering finished ore in a specific area while supplementing heat through the fuel gas feed layer, so that the temperature of the combustion zone and the sintering ore zone can be controlled not to be too high.

Description

Gas periodic interval injection auxiliary sintering method

Technical Field

The invention relates to a gas injection auxiliary sintering process, in particular to a gas periodic interval injection auxiliary sintering method, and belongs to the technical field of sintering.

Background

Due to CO ₂ And due to greenhouse effect caused by gases, glaciers melt, sea level rises, natural ecology degeneration and natural disasters frequently occur, and the lives of human beings in partial regions are directly threatened. Along with the annual increase of the steel yield in China, the total carbon emission of the steel industry in China tends to rise year by year, the annual carbon emission is more than ten thousand, and CO in the steel industry ₂ Emission reduction tasks face tremendous pressure.

As a key link in the iron-making process in the iron and steel industry, the sintering process mainly has the main functions of mixing various powdery iron-containing raw materials with a proper amount of fuel and flux, adding a proper amount of water, mixing and pelletizing, enabling the materials to generate a series of physical and chemical changes on sintering equipment, sintering the materials into blocks, and conveying the blocks to a blast furnace for the next working procedure.

According to the relevant data, the carbon dioxide emission of sintering and blast furnace processes accounts for about 60% of the total industrial emission. In order to reduce carbon emission in the sintering process and the subsequent blast furnace smelting cost, the blast furnace usually has high strength and high reducibility on sintered ores. In the sintering process, the sintered ore is generally required to have higher strength, high yield, lower return fines rate and lower fuel consumption. The high-strength and high-reducibility sintered ore consumes less coke in the blast furnace smelting process, thereby reducing the emission of carbon dioxide.

After the pulverized coal of the upper material layer is ignited in the sintering process, the combustion heat release is used for sintering nearby raw materials and air draft type operation production, the heat of the upper part is brought into the lower material layer by gas through the self-heat-storage effect to participate in the sintering of the lower material layer, and therefore the heat required by the material layer from top to bottom is gradually reduced. Segregation distribution is adopted during distribution, the amount of coal powder distributed on the upper material layer is large, and the amount of coal powder distributed on the lower material layer is small. The quality index of the finished product can be greatly improved under the same fuel consumption index, or the fuel consumption index can be greatly reduced under the same finished product quality index, so that the aims of saving energy and reducing carbon emission are fulfilled.

However, due to the limitation of the device technology, the strict ideal layered segregation type fuel distribution is difficult to realize in the actual industrial production of the sintering plant, and the owners have to distribute the solid fuel according to the high value of the theoretical required fuel quantity in each layer. Meanwhile, some large-particle coke powder can roll to the bottom of the material layer when the sintering machine head is used for distributing materials, and the opposite situation that the solid fuel quantity at the lower part is high and the solid fuel quantity at the middle upper part is low can be caused. The problem that the upper material layer heat is insufficient and the middle and lower material layers heat is excessive can be caused in the sintering material layer during sintering production, the lower sintering material is easy to melt, and the like, so that energy and resource waste is caused and the generation of smoke pollutants is greatly intensified.

Under the large environment, the technology of 'sintering charge level gas fuel injection' developed by the Japan JFE company comes into force, natural gas fuel diluted to be below the lower limit of combustible concentration is injected above the sintering charge level at a distance behind an ignition furnace, and is combusted and supplied heat in a sintering charge layer, so that the solid carbon consumption and CO in the production of sintering ore are reduced ₂ And (4) discharging the amount. Meanwhile, the combustion of the gas fuel widens the width of a high-temperature belt of a sinter bed during production, so that the temperature time of the sinter at 1200-1400 ℃ is prolonged, and the strength and the porosity of the sinter of 5-10 mm are effectively enhanced.

In the initial sintering process, the material layer distribution in the sintering process is shown in fig. 3, and the material layers on the trolley mainly comprise a sintering ore belt, a combustion belt, a drying preheating belt, an over-wet belt and an original material belt from top to bottom in sequence, wherein the approximate temperature distribution is shown by a curve corresponding to 'no blowing' in fig. 4. The burning zone is at a high temperature because the coke powder in the sintering material layer is ignited, the physicochemical processes of melting, sintering and the like of minerals are realized at 1200-1400 ℃, finished sintering ore is formed (the burning zone is changed into a sintering ore zone), and the burning of the coke powder is finished at the moment. Due to the influence of the air draft, fresh air is continuously supplemented to the top of the material bed to cool the material bed, so that the temperature of the sintering ore zone is low at a position close to the top of the material bed and high at a position close to a combustion zone.

After the gas injection technology is adopted, the combustion of the gas fuel widens the width of a high-temperature zone of a sinter bed during production, and slows down the cooling speed of fresh air on sintered finished ore, so that the temperature of the position, close to a combustion zone, in the sinter ore zone is higher than that of the sinter ore zone without injection, and the effect is shown as a curve corresponding to injection in figure 4. The laboratory research and sintering process engineering practice shows that in a certain range, the larger the gas injection amount and the injection concentration are, the more heat released after the gas is absorbed into a material layer is, the larger the substituted solid fuel amount is, and therefore the lower coke consumption and CO are realized ₂ And (4) discharging. Generally, the higher the combustible gas concentration in the mixed gas is, the lower the ignition temperature is, and therefore, it can be found from the temperature distribution in the charge bed that, after increasing the injection amount of the gas and increasing the injection concentration, the position where the gas ignites in the charge bed moves from a position near the burning zone to the direction of the burning zone, and the temperature profile in the charge bed shows that the temperature is higher at the position near the burning zone as shown by the broken line in fig. 5. The 'red layer' is used for describing the region with the temperature in the sintering material layer being above about 1000 ℃, obviously, after the gas injection amount is increased, the thickness of the red layer in the material layer is obviously increased, and because the temperature in the red layer is high and liquid phase is generated, the excessively thick red layer can cause poor air permeability of the material layer and overlarge negative pressure of sintering air draft, influence the air quantity passing through the material layer and the sintering process, and reduce the yield and quality of sintering ores.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a method for auxiliary sintering by periodically and alternately injecting gas. The invention aims to solve the problems of poor air permeability of a material layer and sintering caused by the increase of the gas injection amount in the gas injection auxiliary sintering processThe maximum gas injection amount is realized under the condition of maintaining the air permeability of the material layer and normal air draft negative pressure, thereby more obviously improving the solid fuel substitution amount and reducing CO ₂ And (5) discharging.

The invention provides a method for periodically injecting fuel gas into a material layer of a sintering mixture by changing the original method for continuously injecting fuel gas and adopting periodic interval injection measures in the fuel gas injection process. The invention skillfully controls the injection and stop of the fuel gas through periodic interval injection, so that the fuel gas is repeatedly ignited and extinguished near the combustion zone, namely, a certain cooling time is left for sintering finished ore in a specific area while supplementing heat through the fuel gas feed layer, thereby controlling the temperature of the combustion zone and the sintering ore zone not to be overhigh. Therefore, the invention can improve the temperature change curve of the sintered ore zone and the area near the combustion zone, weaken the thickness of the red layer and ensure proper material layer air permeability and normal air draft negative pressure on the premise of maintaining the original fuel gas supplement amount.

According to an embodiment of the invention, a method of gas cycle interval injection assisted sintering is provided.

A gas periodic interval injection auxiliary sintering method is characterized in that gas is periodically injected at intervals to the charge level of a sintering mixture, and the gas enters a sintering charge layer to burn and supply heat. In the process of gas injection, the temperature of the sintering ore zone and the combustion zone area in the sintering material layer is controlled by adjusting the time length of gas injection in a single period.

Along the thickness direction of the sinter bed, the sinter bed on the sintering trolley mainly comprises a sinter ore zone, a combustion zone, a drying preheating zone, an over-wet zone and an original material zone from top to bottom in sequence.

In the invention, the control of the temperature of the sintering ore zone and the combustion zone area in the sintering material layer comprises the following steps:

1) And determining the cycle number of the injected gas, the time length of initially injecting the gas in a single cycle and the time length of initially stopping injecting the gas in the single cycle.

2) And calculating the injection amount of the fuel gas in unit time according to the total amount of the fuel gas to be injected into the sintering mixture in the sintering trolley.

3) And calculating the heat released by the combustion of the injected fuel gas in the sintering material layer in the fuel gas injection time of a single period.

4) And calculating the cooling quantity of the air to the sinter bed in the gas blowout stopping time of a single period.

5) And judging the temperature change condition of the sinter bed in a single period according to the heat released by the combustion of the injected gas and the cooling capacity of air on the sinter bed, thereby realizing the control of the temperature of the sinter band and the combustion band area in the sinter bed.

In the present invention, step 1) comprises the following substeps:

1a) Calculating the operation time t of the sintering pallet in the gas injection section according to the length L of the gas injection section on the sintering machine and the operation speed v of the sintering pallet, namely the total time t for injecting gas into the sintering mixture in the sintering pallet is as follows:

it should be noted that the total injection time of the sintering mixture in the sintering pallet includes the injection time and the injection stop time in each period.

1b) Setting the number of cycles for injecting gas into the sintering mixture in the sintering trolley to be N and the time length for initially injecting gas in a single cycle to be delta t ₁ Whereby the duration Deltat of the initial gas injection cut within a single cycle ₂ Comprises the following steps:

in the invention, in step 2), the total amount of gas to be injected into the sintering mixture in the sintering pallet is as follows:

in the formula: g is the total amount of gas to be injected into the sintering mixture in the sintering trolley. And m is the quality of the sintering mixture in the corresponding area of the gas injection section. Q _{Supplement device} The heat quantity needs to be supplemented for the sintering mixture of unit mass after the solid fuel proportion is reduced integrally. Wherein Q is _{Supplement device} Is determined by the types of sintering raw materials, the average particle size of sintering mixture, the solid fuel ratio and the like. H is the heat value of the fuel gas.

Preferably, in step 2), the calculating the injection amount of the fuel gas in unit time includes:

in the formula: s is the injection amount of the fuel gas in unit time.

In the invention, in step 3), the heat released by the combustion of the injected fuel gas in the sintering bed is calculated within the single period of fuel gas injection time, specifically:

in the formula: q _in Is Δ t ₁ The heat released by the combustion of the injected gas in the time.

In the invention, in step 4), the amount of cooling the sinter bed by air is calculated within the gas blowout stop time of a single period, specifically: the stop time delta t of a single cycle ₂ The cooling rate of the sinter bed by air cooling is q _co Namely, the following steps are provided:

q _co ＝h _co ·(T _{burning of} -T _∞ )·ξ·m·A............(6)。

In the formula: q _co Is Δt ₂ The cooling amount of the air to the sinter bed in the time. h is _co For the sinter bed cooling coefficient, determined empirically, h _co The value range of (a) is 50-60W/(m) ² ·℃)。T _{Burning of} The combustion temperature of the fuel gas in the sintering material layer is generally selected within the range of 1000-1200 ℃ according to experience. T is _∞ The air temperature is, for example, 30 ℃, 25 ℃, or 20 ℃. And m is the quality of the sintering mixture in the corresponding area of the gas injection section. A is the specific surface area of the combustion zone in the sintering material layer. Xi is the proportion of the combustion zone in the height direction to the height of the whole sinter bed, and the value range of xi is 0-1, preferably 0.01-0.1.

In the present invention, step 5) comprises the following substeps:

5a) According to the heat balance principle, calculating the temperature change value delta T of the sinter bed at the corresponding position in a single period:

c _p ·ξ·m·ΔT＝Q _in -Q _co ............(8)。

namely have

In the formula: c. C _p Is the average specific heat capacity of the sinter bed.

5b) Calculating the actual final temperature T of the sinter bed at the corresponding position in a single period _co ：

T _co ＝T _{Burning of} +ΔT………(10)。

5c) Comparing the actual final temperature T of the sinter bed in a single cycle _co With a target temperature T _aim And further adjusting the duration of gas injection in a single period, thereby realizing the control of the temperature of the sintering ore zone and the combustion zone area in the sintering material layer.

Preferably, substep 5 c) is specifically:

if the actual final temperature T of the sinter bed in a single cycle _co = target temperature T _aim And controlling the temperature of the sintering zone and the combustion zone within a normal range in the period, and keeping the current injection parameters of the system to continue to operate.

If the actual final temperature T of the sinter bed in a single cycle _co > target temperature T _aim At the moment, the time length of gas injection in a single period is shortened, so that T _co ＝T _aim 。

If the actual final temperature T of the sinter bed in a single cycle _co < target temperature T _aim At the moment, the time length of gas injection in a single period is prolonged, so that T _co ＝T _aim 。

Preferably, in sub-step 5 c), said target temperature T _aim The value range of (A) is 600-1000 ℃, preferably 700-850 ℃, and more preferably 740-780 ℃.

Generally, in the initial sintering process, the material layers in the sintering process mainly comprise a sintering ore belt, a combustion belt, a drying preheating belt, an over-wet belt and an original material belt from top to bottom in sequence. Wherein, the burning zone has higher temperature because the coke powder in the sintering material layer is ignited, the physicochemical processes of mineral melting, sintering and the like are realized at 1200-1400 ℃, the finished product sintering ore is formed, namely, the burning zone is converted into a sintering ore zone, and the burning of the coke powder is finished. Due to the influence of air suction in the air suction type sintering, fresh air is continuously supplemented to the top of the material layer to cool the material layer, so that the temperature of the sintering ore belt is low at a position close to the top of the material layer and high at a position close to a combustion belt.

In the prior art, in order to reduce CO in the sintering process ₂ The technology of gas injection assisted sintering is proposed. Gas fuel diluted to below the lower limit of combustible concentration is sprayed above the sintering charge level and is combusted in the sintering charge layer to supply heat, so that the solid carbon consumption and CO in the production of sintered ore are reduced ₂ And (4) discharging the amount. In fig. 4, the temperature distribution of the sinter bed in the sintering process was compared between the case of using the gas injection technique and the case of not using the gas injection technique. The temperature distribution of the sinter bed not adopting the gas injection technology in the sintering process is shown by a curve corresponding to 'not adopting injection' in fig. 4, and the temperature distribution of the sinter bed adopting the gas injection technology is shown by a curve corresponding to 'adopting injection' in fig. 4. As can be derived from FIG. 4, use is made ofAfter the gas injection technology, the combustion of gas fuel widens the width of a high-temperature zone of a sinter bed during production, and slows down the cooling speed of fresh air on sintered finished ore, so that the temperature of the position, close to a combustion zone, in the sinter ore zone is higher than the temperature of the sinter ore zone when the injection is not adopted.

For further CO reduction ₂ The laboratory research and the sintering process engineering practice find that in a certain range, the larger the gas injection amount and the higher the injection concentration are, the more the heat released after the gas is absorbed into a material layer is, the larger the substituted solid fuel amount is, so that the less coke consumption is realized, namely, the less CO is realized ₂ And (5) discharging. The temperature distribution of the sinter bed after increasing the injection amount of the fuel gas and increasing the injection concentration is shown by the dotted line in fig. 5. As can be seen from fig. 5, after the injection amount of the fuel gas is increased and the injection concentration is increased, the position where the fuel gas ignites in the bed moves from the position near the burning zone to the direction of the burning zone, that is, the temperature of the burning zone is higher. The 'red layer' is used for describing the region with the temperature in the sintering material layer being above about 1000 ℃, obviously, after the gas injection amount is increased, the thickness of the red layer in the material layer is obviously increased, and because the temperature in the red layer is high and liquid phase is generated, the excessively thick red layer can cause poor air permeability of the material layer and overlarge negative pressure of sintering air draft, influence the air quantity passing through the material layer and the sintering process, and reduce the yield and quality of sintering ores. That is, the amount of solid carbon and CO in the production of sinter ore are reduced due to the increase of the gas injection amount in the gas injection auxiliary sintering process ₂ The discharge amount, but also brings new technical problems.

In the prior art, the conventional sintering-assisted method using a gas injection technology, or the sintering-assisted method using injection after increasing the injection amount of gas and increasing the injection concentration, both use a method of continuously injecting (or injecting) gas into the sintering charge level. The invention provides a method for auxiliary sintering by periodically and alternately injecting gas, aiming at the problems in auxiliary sintering by continuously injecting gas after increasing the injection amount and the injection concentration of the gas in the prior art. The method provides that the original persistence is changed in the gas injection processThe method for spraying fuel gas is changed into a periodic interval spraying measure, and the fuel gas is periodically sprayed into a material layer of the sintering mixture. As shown in FIG. 6, in the present invention, gas injection Δ t ₁ Shortly after the duration, stop spraying delta t ₂ Duration, then continue to blow Δ t ₁ Duration, spray stop Δ t ₂ The duration … … cycles through this. Wherein blowing is Δ t ₁ Duration + spray cut Δ t ₂ The duration is one injection period and is continuously repeated in the whole process of sintering and injecting the fuel gas. Blowing duration at single cycle Δ t ₁ Because of the injection of the fuel gas, the fuel gas is ignited and burnt at the position of the area near the burning zone and the sintering ore zone to release heat; duration of spray interruption Δ t in a single cycle ₂ In, because there is not the jetting of gas to mend, the position of gas burning then can put out a fire originally, and this district can receive the cooling of air this moment. That is to say, through the gas periodic injection, stop spouting, can control the sintering ore area and be close to near the position of burning zone and take place catching fire, the flame-out of gas repeatedly to guarantee that corresponding region can not appear the high temperature and cause too thick red layer, and then effectively avoided improving the technical problem such as the bed of material gas permeability is relatively poor, sintering convulsions negative pressure rises that brings behind the gas injection volume. Furthermore, the invention determines a proper injection system by adjusting parameters of the injected fuel gas (such as the cycle number of the injected fuel gas, the injection time in the cycle, the injection stop time in the cycle and the like), further realizes that the temperature change curve of the sintered ore zone and the area near the combustion zone is improved on the premise of maintaining the original fuel gas supplement amount (namely the existing increased fuel gas injection amount), the red layer thickness is weakened, the proper bed air permeability and the normal air draft negative pressure are ensured, and the maximum fuel gas injection amount is realized under the condition of maintaining the bed air permeability and the normal air draft negative pressure, thereby more obviously improving the solid fuel substitution amount, reducing the CO substitution amount, and reducing the CO ₂ And (5) discharging.

In the invention, the method for the gas period interval injection auxiliary sintering firstly determines the initial parameters of the injected gas, wherein the initial parameters of the injected gas comprise the period number N of the injected gas, and the time length delta t of the initial injected gas in a single period ₁ Duration delta t of initial gas cut-off in a single cycle ₂ And a sheetThe injection amount S of the gas (i.e., the gas injection flow rate) in the time. After the initial parameters of the gas for injection are determined, the gas is periodically injected to the charge level of the sintering mixture at intervals according to the initial parameters, and the gas enters the sintering charge level for combustion and heat supply to assist in sintering. Then calculating the heat quantity Q released by the combustion of the injected fuel gas in the sintering material layer in a single period _in And air at Δ t ₂ Cooling quantity Q of sinter bed in time _co According to the heat balance principle, the temperature change condition of the sinter bed at the corresponding position in a single period is judged, and accordingly, the control of the temperature of the sinter band and the combustion band area in the sinter bed is realized. Wherein, the control to the sintering ore area in the sinter bed and the regional temperature of burning zone is realized according to the temperature change condition of sinter bed in single cycle, specifically includes: according to the heat balance principle, calculating the temperature change value delta T of the sinter bed at the position corresponding to the gas injection in a single period, and then calculating the actual final temperature T of the sinter bed at the position corresponding to the gas injection in the single period _co The actual final temperature T obtained by calculation _co With a target temperature T _aim And comparing the temperature of the sintering ore zone and the temperature of the combustion zone in the sintering material layer, and further adjusting the duration of gas injection in a single period, thereby realizing the control of the temperatures of the sintering ore zone and the combustion zone area in the sintering material layer and avoiding the conditions of overhigh temperature and over-thick red layer.

In the present invention, said target temperature T _aim The critical temperature value is obtained according to laboratory research and practical experience summary of sintering engineering, and can enable the gas in the sintering ore zone and the combustion zone area in a single period to be extinguished. The target temperature T _aim The value range of (A) is 600-1000 ℃, preferably 700-850 ℃, and more preferably 740-780 ℃. The invention determines a proper injection system by adjusting the cycle number of the injected fuel gas, the injection time length in a single cycle and the injection stop time length in a single cycle, namely the final temperature in the cycle of the sinter bed in the controllable type (10), thereby accurately controlling the trend of the temperature curve near the sinter band and the combustion band in the sintering process, and ensuring that the high-temperature retention time in the sintering process is prolonged by the supplemented fuel gas but is not limitedAs for the gas is continuously supplemented, the temperature is too slowly reduced, the thickness of a red layer is weakened, and the air permeability of a material layer and the air draft negative pressure are in the optimal state. In the invention, if the actual final temperature T of the sinter bed at the corresponding position in a single period _co = target temperature T _aim Namely, the actual final temperature of the sinter bed is in the range of the target temperature, and the gas at the position corresponding to the sinter bed is extinguished (namely the gas is extinguished at the position corresponding to the gas blowout stopping time interval) at the moment, which shows that the temperature of the sintering zone and the combustion zone area in the injection period is controlled in the normal range, the injection parameter at the moment is the proper injection parameter, and the system keeps the current injection parameter to continue to operate. If the actual final temperature T of the sinter bed at the corresponding position in a single period _co > target temperature T _aim The temperature of the sintered ore zone and the combustion zone area in the injection period is higher, and at the moment, the gas at the position corresponding to the sinter bed possibly has the condition of not extinguishing (namely the gas at the position corresponding to the gas stop time interval is not extinguished), so that the conditions that the gas permeability of the sinter bed is influenced and the air draft negative pressure is increased due to the excessively thick red layer possibly occur; the injection parameters need to be adjusted, for example, to shorten the time of injecting gas in a single period, or to increase the number of cycles of injecting gas, or to adjust the time of injecting gas and the number of cycles of injecting gas in a single period, so that T is _co ＝T _aim And further controlling the temperature of the sintering ore zone and the combustion zone to return to the normal range. If the actual final temperature T of the sinter bed at the corresponding position in a single period _co < target temperature T _aim At the moment, the gas at the position corresponding to the sinter bed is extinguished (namely, the gas is extinguished at the position corresponding to the gas blowout stopping time interval), but the temperature of the sintering zone and the combustion zone area in the blowing period is lower, so that the normal operation of sintering and the quality of sintering ore can be influenced; the injection parameters may need to be adjusted, for example, to extend the duration of gas injection in a single cycle, or to reduce the number of cycles of gas injection, or to adjust both the duration of gas injection and the number of cycles of gas injection in a single cycle, such that T is _co ＝T _aim And further controlling the temperature of the sintering ore zone and the combustion zone to return to the normal range.

It should be noted that, in the process of adjusting the duration of gas injection and/or the number of cycles of gas injection in a single cycle according to the present invention, when only the duration of gas injection in a single cycle is adjusted (extended or shortened), since the number of cycles of gas injection is not changed at this time, the duration of gas injection stoppage in a single cycle needs to be adjusted (shortened or extended) synchronously in the adjustment process. When only the number of cycles of injecting the gas is adjusted (increased or decreased), since the time length of injecting the gas in a single cycle is not changed at this time, the time length of stopping injecting the gas in a single cycle needs to be synchronously adjusted (shortened or lengthened) in the adjustment process. When the time length of gas injection and the cycle number of the gas injection in a single period are adjusted simultaneously, the time length of gas stop injection in the single period also needs to be adjusted synchronously. Further, according to the formula (4), the amount of gas injected per unit time

Therefore, when the time length of gas injection and/or the number of cycles of gas injection in a single cycle are/is adjusted, the injection amount of gas in unit time is synchronously adjusted correspondingly.

In the invention, the total amount of fuel gas required to be injected into the sintering mixture in the sintering trolley

Wherein Q _{Supplement device} The total amount of gas to be injected into the sinter mix in the sintering pallet is related to the mass of the sinter mix, the type of the sinter material, the average particle size of the sinter mix, the proportion of solid fuel in the sinter mix, the type of gas, and the like, as can be seen from the formula. In the invention, the cooling rate q of the sinter bed by air cooling _co ＝h _co ·(T _{Burning of} -T _∞ ) ξ · m · a, the cooling rate of the sinter bed by air cooling and the sinter bed cooling coefficient, the combustion temperature of the fuel gas, the ambient air temperature, the internal surface area of the sinter bed, and the height of the combustion zone in the height direction relative to the entire sinter bedRatio, etc. In addition, in the present application, the specific values of the parameters related to the formulas (1) to (10) can be obtained by detection, calculation, or according to production experience.

It should be noted that the cycle number of the injected gas and the total amount of the gas to be injected into the sinter mix in the sintering pallet are both based on the sinter mix in the region corresponding to the gas injection segment. The cycle number of the injected gas refers to the number of times of injection and stop of injection when the sintering mixture passes through the gas injection section. The total amount of gas to be injected into the sintering mixture in the sintering trolley is based on the realization of the maximum gas injection amount, so that the solid fuel substitution amount is increased, and the CO is reduced ₂ On the premise of emission, the amount of gas required to be injected by the sintering mixture is increased.

In addition, since the "red layer" means a region in which the temperature in the sintering material layer is about 1000 ℃ or higher, and the region in which the temperature in the sintering material layer is 1000 ℃ or higher is mainly concentrated in the combustion zone and a partial region of the sintering ore zone close to the combustion zone, the present application realizes the control of the thickness of the red layer by controlling the temperatures of the sintering ore zone and the combustion zone region in the sintering material layer, and mainly controls the temperature of the upper region of the combustion zone and the temperature of the sintering ore zone close to the combustion zone within a reasonable range in the thickness direction of the material layer.

In the present application, the terms "gas combustion position", "position near gas combustion", and "corresponding position" have the same meaning.

Compared with the prior art, the invention has the following beneficial technical effects:

1. the invention changes the existing method for continuously spraying fuel gas, adopts periodic interval spraying measures, skillfully controls the spraying and stopping of the fuel gas through the periodic interval spraying, further ensures that the fuel gas is repeatedly ignited and extinguished near a combustion zone, and keeps a certain cooling time for sintering finished ore in a specific area while supplementing heat through a fuel gas feeding layer, thereby being capable of controlling the temperature of the combustion zone and the sintering ore zone without overhigh condition.

2. The invention selects and adjusts the cycle number of the injected fuel gas, the injection time length in a single cycle and the stop injection time length in a single cycle to determine a proper injection system, and the final temperature in the cycle of the sinter bed can be controlled, thereby accurately controlling the trend of the temperature curve near the sinter band and the combustion band in the sintering process, ensuring that the temperature reduction is too slow due to the continuous supplement of the fuel gas after the high temperature retention time in the sintering process is prolonged by the supplement of the fuel gas, further weakening the thickness of the red layer, and ensuring the air permeability of the bed and the air draft negative pressure to be in the optimal state.

3. The invention realizes the maximum gas injection amount in the sintering process under the condition of maintaining the air permeability of the material layer and the negative pressure of air draft, thereby realizing the substitution of solid fuel and CO with larger proportion ₂ And (5) emission reduction.

Drawings

FIG. 1 is a schematic diagram of a method for gas periodic interval injection assisted sintering according to the present invention;

FIG. 2 is a flow chart of a method of gas cycle interval injection assisted sintering according to the present invention;

FIG. 3 is a bed distribution diagram of a sinter mix;

FIG. 4 is a graph showing the temperature of the sinter bed in the case of gas injection and in the case of no gas injection;

FIG. 5 is a graph showing the temperature of a sinter bed in two cases of increasing the gas injection concentration and adopting the conventional gas injection;

FIG. 6 is a schematic view of the present invention with gas injected at periodic intervals;

FIG. 7 is a graph showing the temperature of the sinter bed in the case of the periodic interval injection of fuel gas and the case of the conventional continuous injection of fuel gas.

Reference numerals are as follows:

1: sintering the trolley; a1: sintering the ore belt; a2: a combustion zone; a3: drying the preheating zone; a4: an overwetting belt; a5: an original material tape.

Detailed Description

A method for auxiliary sintering by periodically and intermittently injecting gas includes periodically and intermittently injecting gas to the surface of sintered mixture, and burning the gas in the sintered mixture for supplying heat. In the process of gas injection, the temperature of the sintering ore zone and the combustion zone area in the sintering material layer is controlled by adjusting the time length of gas injection in a single period.

Along the thickness direction of the sinter bed, the sinter bed on the sintering trolley mainly comprises a sinter ore belt, a combustion belt, a drying preheating belt, an over-wetting belt and an original material belt from top to bottom in sequence.

In the present invention, step 1) comprises the following substeps:

it should be noted that the total duration of the gas injection into the sinter mix in the sintering pallet described herein includes the injection duration and the injection stop duration in each cycle.

1b) Setting the number of cycles for injecting gas into the sintering mixture in the sintering trolley to be N and the time length for initially injecting gas in a single cycle to be delta t ₁ Whereby the duration Deltat of the initial gas injection cut in a single cycle ₂ Comprises the following steps:

in the formula: s is the injection amount of the fuel gas in unit time.

In the invention, in step 4), the amount of cooling the sinter bed by air is calculated within the gas blowout stop time of a single period, specifically: spray-off time at of a single cycle ₂ The cooling rate of the sinter bed by air cooling is q _co Namely, the following steps are provided:

q _co ＝h _co ·(T _{burning of} -T _∞ )·ξ·m·A…………(6)。

In the formula: q _co Is Δ t ₂ The cooling amount of the air to the sinter bed in the time. h is a total of _co The cooling coefficient of the sinter bed is determined empirically, h _co The value range of (A) is 50-60W/(m) ² ·℃)。T _{Burning of} The combustion temperature of the fuel gas in the sintering material layer is generally selected within the range of 1000-1200 ℃ according to experience. T is _∞ The temperature is, for example, 30 ℃, 25 ℃ or 20 ℃ or the like. And m is the quality of the sintering mixture in the corresponding area of the gas injection section. A is the specific surface area of the combustion zone in the sintering material layer. Xi is the proportion of the height of the combustion zone in the height direction of the whole sintering material layer, and the value range of xi is 0-1, preferably 0.01-0.1.

In the present invention, step 5) comprises the following substeps:

c _p ·ξ·m·ΔT＝Q _in -Q _co …………(8)。

namely have

In the formula: c. C _p Is the average specific heat capacity of the sinter layer.

T _co ＝T _{Burning of} +ΔT………(10)。

Preferably, substep 5 c) is specifically:

If the actual final temperature T of the sinter bed in a single cycle _co > target temperature T _aim At this time, the time length of gas injection in a single period is shortened to make T _co ＝T _aim 。

Example 1

As shown in figure 1, in the method for auxiliary sintering by periodically and alternately injecting gas, gas is periodically and alternately injected to the charge level of a sintering mixture, and the gas enters a sintering charge layer to be combusted and heat is supplied. In the process of gas injection, the temperature of the sintered ore zone A1 and the combustion zone A2 in the sinter bed is controlled by adjusting the time length of gas injection in a single period.

As shown in fig. 3, the sinter bed on the sintering pallet 1 mainly includes, in order from top to bottom, a sinter bed A1, a combustion zone A2, a drying and preheating zone A3, an over-wetting zone A4, and an original material zone A5 along the thickness direction of the sinter bed.

Example 2

A method for auxiliary sintering by periodically and intermittently injecting gas includes periodically and intermittently injecting gas to the surface of sintered mixture, and burning the gas in the sintered mixture for supplying heat. In the process of gas injection, the temperature of the sintered ore zone A1 and the combustion zone A2 in the sinter bed is controlled by adjusting the time length of gas injection in a single period.

The method for controlling the temperature of the sintered ore zone A1 and the combustion zone A2 in the sinter bed specifically comprises the following steps:

5) And judging the temperature change condition of the sinter bed in a single period according to the heat released by the combustion of the injected gas and the cooling capacity of air on the sinter bed, and further realizing the control of the temperature of the regions of the sinter band A1 and the combustion band A2 in the sinter bed.

Example 3

As shown in fig. 2, the implementation of controlling the temperature of the sintering ore zone A1 and the combustion zone A2 in the sinter layer specifically includes the following steps:

Step 1) comprises the following substeps:

1b) Setting the cycle number of gas injection for the sintering mixture in the sintering trolley as N and the time length of initial gas injection in a single cycle as delta t ₁ Whereby the duration Deltat of the initial gas injection cut in a single cycle ₂ Comprises the following steps:

In step 2), the total amount of gas to be injected into the sintering mixture in the sintering trolley is as follows:

in the formula: g is the total amount of gas required to be blown by the sintering mixture in the sintering trolley. And m is the quality of the sintering mixture in the corresponding area of the gas injection section. Q _{Supplement device} The heat quantity needs to be supplemented for the sintering mixture of unit mass after the solid fuel proportion is reduced integrally. H is the heat value of the fuel gas.

The calculation of the injection amount of the fuel gas in unit time specifically comprises the following steps:

in the formula: s is the injection amount of the fuel gas in unit time.

3) In the single period of gas injection time, calculating the heat released by the injected gas in the sintering bed by combustion, specifically:

4) In the gas blowout stopping time of a single period, the cooling capacity of air to a sinter bed is calculated, and the method specifically comprises the following steps: spray-off time at of a single cycle ₂ The cooling rate of the sinter bed by air cooling is q _co Namely, the following steps are provided:

q _co ＝h _co ·(T _{burning of} -T _∞ )·ξ·m·A…………(6)。

In the formula: q _co Is Δ t ₂ The cooling amount of the air to the sinter bed in the time. h is _co Is the sinter bed cooling coefficient, h _co Is 60W/(m) ² ·℃)。T _{Burning of} The combustion temperature of the fuel gas in the sintering material layer. T is _∞ Is the air temperature. And m is the quality of the sintering mixture in the corresponding area of the gas injection section. A is the specific surface area of the combustion zone in the sintering material layer. Xi is the proportion of the combustion zone in the height direction to the height of the whole sinter bed, and the value of xi is 0.07.

Step 5) comprises the following substeps:

c _p ·ξ·m·ΔT＝Q _in -Q _co …………(8)。

namely have

T _co ＝T _{Burning of} +ΔT…………(10)。

5c) Comparing the actual final temperature T of the sinter bed in a single cycle _co With a target temperature T _aim And further adjusting the time length of gas injection in a single period, thereby realizing the control of the temperature of the sintered ore zone A1 and the combustion zone A2 in the sinter bed.

Example 4

Example 3 is repeated except that in substep 5 c), the target temperature T is _aim Is 700 ℃.

The substep 5 c) is specifically:

If the actual final temperature T of the sinter bed in a single cycle _co > target temperature T _aim At the moment, the time length of gas injection in a single period is shortened, so that T _co ＝T _aim ；

Example 5

Example 4 is repeated, except that in substep 5 c), the target temperature T _aim The value of (A) is 850 ℃.

Example 6

Example 4 is repeated, except that in substep 5 c), the target temperature T _aim The value range of (a) is 750 ℃.

Application example 1

Step 1) comprises the following substeps:

1a) Calculating the operation time t of the sintering pallet in the gas injection section according to the length L =16m of the gas injection section on the sintering machine and the operation speed v =2m/min of the sintering pallet, namely the total time t for injecting gas into the sintering mixture in the sintering pallet is as follows:

1b) Setting the number of cycles N =10 for injecting gas into the sinter mix in the sintering pallet, and the time length Deltat for initially injecting gas in a single cycle ₁ =30s, whereby the duration Δ t of the initial gas injection stoppage in a single cycle ₂ Comprises the following steps:

in the formula: g is the total amount of gas to be injected into the sintering mixture in the sintering trolley. m is the mass of the sintering mixture in the corresponding area of the gas injection section, and m =172800kg. Q _{Supplement device} The heat quantity, Q, is required to be supplemented for integrally reducing the sintered mixture of unit mass after the solid fuel is proportioned _{Supplement device} =12000kJ/kg. H is the heat value of the fuel gas, H =35588kJ/m ³ 。

in the formula: s is the injection amount of the fuel gas in unit time.

4) In the gas blowout stopping time of a single period, the cooling capacity of air to a sinter bed is calculated, and the method specifically comprises the following steps: the stop time delta t of a single cycle ₂ The cooling rate of the sinter bed by air cooling is q _co Namely, the following steps are provided:

q _co ＝h _co ·(T _{burning of} -T _∞ )·ξ·m·A…………(6)。

In the formula: q _co Is Δ t ₂ The cooling amount of the air to the sinter bed in the time. h is _co Is the sinter bed cooling coefficient, h _co ＝50W/(m ² ·℃)。T _{Burning of} The combustion temperature, T, of the combustion gas in the sinter bed _{Burning of} ＝1200℃。T _∞ Is the air temperature, T _∞ =30 ℃. m is the mass of the sintering mixture in the corresponding area of the gas injection section, and m =172800kg. A is the specific surface area of a combustion zone in the sintering material layer, and A =0.02326m ² (ii) in terms of/g. Xi is the proportion of the height of the combustion zone in the height direction in the whole sinter layer, and xi =0.05.

Step 5) comprises the following substeps:

5a) According to the heat balance principle, calculating the temperature change value delta T of the sinter layer at the position close to the gas combustion in a single period:

c _p ·ξ·m·ΔT＝Q _in -Q _co …………(8)。

namely have

In the formula: c. C _p Is the average specific heat capacity of the sinter bed, c _p ＝1.1kJ/(kg·℃)。

5b) Calculating the actual final temperature T of the sinter bed at the position close to the gas combustion in a single period _co ：

T _co ＝T _{Burning of} +ΔT＝1200℃+(-448℃)＝752℃…………(10)。

5c) Comparing the actual final temperature T of the sinter bed in a single cycle _co And the targetTemperature T _aim And further adjusting the duration of gas injection in a single period, thereby realizing the control of the temperature of the sintered ore zone A1 and the combustion zone A2 in the sinter bed.

Due to the target temperature T _aim =752 ℃, obviously with T _co ＝T _aim In the period, the temperature of the sintering ore zone A1 and the combustion zone A2 is controlled in a normal range, and the system keeps the current injection parameters to continue to operate.

Application example 2

The method for controlling the temperature of the sintering ore zone A1 and the combustion zone A2 in the sintering material layer specifically comprises the following steps:

Step 1) comprises the following substeps:

1b) Setting the number of cycles N =10 for injecting gas into the sinter mix in the sintering pallet, and the time length Deltat for initially injecting gas in a single cycle ₁ =30.3s, whereby the duration Δ t of the initial gas injection stoppage in a single cycle ₂ Comprises the following steps:

in the formula: s is the injection amount of the fuel gas in unit time.

q _co ＝h _co ·(T _{burning of} -T _∞ )·ξ·m·A…………(6)。

In the formula: q _co Is Δ t ₂ The cooling amount of the air to the sinter bed in time. h is _co Is the sinter bed cooling coefficient, h _co ＝50W/(m ² ·℃)。T _{Burning of} The combustion temperature, T, of the gas in the sinter bed _{Burning of} ＝1200℃。T _∞ Is the air temperature, T _∞ =30 ℃. m is the mass of the sintering mixture in the corresponding area of the gas injection section, and m =172800kg. A is the specific surface area of a combustion zone in the sintering material layer, and A =0.02326m ² (ii) in terms of/g. Xi is the proportion of the height of the combustion zone in the height direction in the whole sinter layer, and xi =0.05.

Step 5) comprises the following substeps:

c _p ·ξ·m·ΔT＝Q _in -Q _co …………(8)。

namely have

T _co ＝T _{Burning of} +ΔT＝1200℃+(-77)℃＝1123℃…………(10)。

5c) Comparing within a single cycleActual final temperature T of the sinter bed _co With a target temperature T _aim And further adjusting the duration of gas injection in a single period, thereby realizing the control of the temperature of the sintered ore zone A1 and the combustion zone A2 in the sinter bed.

Due to the target temperature T _aim =752 ℃ i.e. having T _co ＞T _aim It is explained that the temperature of the sintering zone and the combustion zone area is higher in the injection period, and the gas in the sintering material layer is not extinguished in the interval time of stopping injecting the gas, so that the condition that the red layer is too thick to influence the permeability of the material layer and cause the rising of the air draft negative pressure occurs, at the moment, the time length of injecting the gas in a single period is shortened, and the T is enabled to be higher _co ＝T _aim And further controlling the temperature of the sintering ore zone and the combustion zone to return to the normal range.

Application example 3

Step 1) comprises the following substeps:

1b) Setting sintering in a sintering palletThe number N =10 of the periods of the mixture gas injection, and the time length delta t of the initial gas injection in a single period ₁ =29.7s, whereby the duration Δ t of the initial gas injection stoppage in a single cycle ₂ Comprises the following steps:

In the step 2), the total amount of gas to be injected into the sintering mixture in the sintering trolley is as follows:

in the formula: s is the injection amount of the fuel gas in unit time.

in the formula: q _in Is Δ t ₁ Heat released by combustion of gas injected over time。

q _co ＝h _co ·(T _{burning of} -T _∞ )·ξ·m·A…………(6)。

In the formula: q _co Is Δ t ₂ The cooling amount of the air to the sinter bed in the time. h is _co Is the sinter bed cooling coefficient, h _co ＝50W/(m ² ·℃)。T _{Burning of} The combustion temperature, T, of the gas in the sinter bed _{Burning of} ＝1200℃。T _∞ Is the air temperature, T _∞ =30 ℃. m is the mass of the sintering mixture in the corresponding area of the gas injection section, and m =172800kg. A is the specific surface area of a combustion zone in the sintering material layer, and A =0.02326m ² (ii) in terms of/g. Xi is the proportion of the combustion zone in the height direction accounting for the height of the whole sinter bed, and xi =0.05.

Step 5) comprises the following substeps:

c _p ·ξ·m·ΔT＝Q _in -Q _co …………(8)。

namely have

T _co ＝T _{Burning of} +ΔT＝1200℃+(-819)℃＝381℃…………(10)。

5c) Comparing the actual final temperature T of the sinter bed in a single cycle _co With a target temperature T _aim And further adjusting the duration of gas injection in a single period, thereby realizing the control of the temperature of the sintered ore zone A1 and the combustion zone A2 in the sinter bed.

Due to the target temperature T _aim =752 ℃, i.e. having T _co ＜T _aim The lower temperature of the sintering zone and the combustion zone area in the injection period possibly influences the normal operation of sintering and the quality of sintering ore, and at the moment, the duration of gas injection in a single period is prolonged, so that T is _co ＝T _aim And further controlling the temperature of the sintering ore zone and the combustion zone to return to the normal range.

Comparative example 1

A method for assisting sintering by continuously blowing gas is characterized in that gas is continuously blown to the charge level of a sintering mixture, and the gas enters a sintering charge layer to burn for supplying heat and assist sintering. Wherein, aiming at the sintering mixture in the corresponding area of the gas injection section, the total amount G of the continuously injected gas ₁ ＝58266.83m ³ Here, total amount of gas G continuously injected ₁ The total amount of gas injected at periodic intervals in application example 1 was equal to G. According to the length L of a gas injection section on a sintering machine ₁ =16m, running speed v of sintering pallet ₁ =2m/min, calculating the total time t for blowing gas into the sintering mixture in the sintering trolley ₁ ＝L ₁ /v ₁ =480s, where the total duration t of the gas injection into the sinter mix in the sinter car is ₁ The total time t (including the injection time period and the spray stopping time period) for injecting the fuel gas into the sintering mixture in the sintering pallet in the application example 1 is equal. In comparative example 1, the gas injection flow rate, that is, the injection amount S of gas per unit time ₁ ＝G ₁ /t ₁ ＝121.39m ³ /s。

The temperature of the sinter layer during sintering was measured, and the temperature change curves of the sinter layer of application example 1 and comparative example 1 were plotted, as shown in fig. 7. The relevant test data for application example 1 and comparative example 1 are recorded as follows:

the invention changes the existing method for continuously spraying fuel gas, and adopts periodic interval spraying measures to spray the fuel gas into the sintering material layer. As can be seen from the above table in conjunction with FIG. 7, the present invention can achieve the maximum gas injection amount to ensure a large proportion of solid fuel substitution and CO substitution while maintaining the original gas supply amount ₂ On the premise of emission reduction, the temperature change curve of the sintered ore zone and the area near the combustion zone is improved, the thickness of a red layer is weakened, and proper material bed air permeability and normal air draft negative pressure are ensured, so that the yield and the quality of the sintered ore are improved.

Claims

1. A gas period interval injection auxiliary sintering method is characterized in that: periodically blowing gas to the charge level of the sintering mixture at intervals, and enabling the gas to enter a sintering charge layer for combustion and heat supply; in the process of gas injection, the temperature of the sintering ore zone and the combustion zone area in the sintering material layer is controlled by adjusting the time length of gas injection in a single period.

2. The method of claim 1, wherein: the method for controlling the temperature of the sintering ore zone and the combustion zone area in the sintering material layer specifically comprises the following steps:

1) Determining the cycle number of gas injection, the time length of initial gas injection in a single cycle and the time length of initial gas stop in a single cycle;

2) Calculating the injection amount of the fuel gas in unit time according to the total amount of the fuel gas to be injected into the sintering mixture in the sintering trolley;

3) Calculating the heat released by the combustion of the injected fuel gas in the sintering bed within the fuel gas injection time of a single period;

4) Calculating the cooling capacity of air to a sinter bed in the gas spraying stopping time of a single period;

3. The method of claim 2, wherein: step 1) comprises the following substeps:

1a) According to the length L of a gas injection section on the sintering machine and the running speed v of the sintering trolley, the running time t of the sintering trolley in the gas injection section is calculated, namely the total time t for injecting gas to the sintering mixture in the sintering trolley is as follows:

4. a method according to claim 2 or 3, characterized in that: in step 2), the total amount of gas to be injected into the sintering mixture in the sintering trolley is as follows:

in the formula: g is the total amount of gas to be blown by the sintering mixture in the sintering trolley; m isThe quality of the sintering mixture in the corresponding area of the gas injection section; q _{Supplement device} The heat quantity needs to be supplemented for the sintering mixture of unit mass after the solid fuel proportion is reduced integrally; h is the heat value of the fuel gas.

5. The method of claim 4, wherein: in step 2), the calculating the injection amount of the fuel gas in unit time specifically includes:

in the formula: s is the injection amount of the fuel gas in unit time.

6. The method according to claim 4 or 5, characterized in that: in step 3), calculating the heat released by the combustion of the injected fuel gas in the sintering bed within the single-period fuel gas injection time, specifically:

7. The method according to any one of claims 3-6, wherein: in step 4), the cooling capacity of the air to the sinter bed is calculated within the gas blowout stop time of a single period, specifically: the stop time delta t of a single cycle ₂ The cooling rate of the sinter bed by air cooling is q _co Namely, the following steps are provided:

q _co ＝h _co ·(T _{burning of} -T _∞ )·ξ·m·A............(6)；

In the formula: q _co Is Δ t ₂ The cooling capacity of the air to the sinter bed in time; h is _co Is the sinter bed cooling coefficient, h _co The value range of (A) is 50-60W/(m) ² ·℃)；T _{Burning of} The combustion temperature of the fuel gas in the sintering material layer; t is _∞ Is the air temperature; m is the mass of the sintering mixture in the corresponding area of the gas injection section; a is the specific surface area of a combustion zone in a sintering charge layer; xi is the proportion of the height of the combustion zone in the height direction of the whole sintering material layer, and the value range of xi is 0-1, preferably 0.01-0.1.

8. The method of claim 7, wherein: step 5) comprises the following substeps:

5a) According to the heat balance principle, calculating the temperature change value delta T of the sinter bed at the gas combustion position in a single period:

c _p ·ξ·m·ΔT＝Q _in -Q _co ............(8)；

namely have

In the formula: c. C _p Is the average specific heat capacity of the sinter bed;

T _co ＝T _{Burning of} +ΔT............(10)；

9. The method of claim 8, wherein: the substep 5 c) is specifically:

if the actual final temperature T of the sinter bed in a single cycle _co = target temperature T _aim Description of the firing in this periodControlling the temperature of the ore deposit zone and the combustion zone within a normal range, and keeping the current injection parameters of the system to continuously operate;

if the actual final temperature T of the sinter bed in a single cycle _co >Target temperature T _aim At the moment, the time length of gas injection in a single period is shortened, so that T _co ＝T _aim ；

If the actual final temperature T of the sinter bed in a single cycle _co <Target temperature T _aim At the moment, the time length of gas injection in a single period is prolonged, so that T _co ＝T _aim 。

10. The method according to claim 8 or 9, characterized in that: in sub-step 5 c), the target temperature T _aim The value range of (A) is 600-1000 ℃, preferably 700-850 ℃, and more preferably 740-780 ℃.