阅读说明：本技术 一种链篦机-回转窑-环冷机三机系统生产球团过程中废气循环的方法 (Method for circulating waste gas in pelletizing production process of chain grate-rotary kiln-circular cooler three-machine system ) 是由 甘敏 曹风 范晓慧 胡兵 季志云 陈许玲 黄晓贤 袁礼顺 王鑫 朱亮 于 2019-08-09 设计创作，主要内容包括：本发明公开了一种链篦机-回转窑-环冷机三机系统生产球团过程中废气循环的方法,链篦机由进料端至回转窑依次分为鼓风干燥段、抽风干燥段、预热升温段和预热段,所述环冷机由回转窑至出料端依次分为冷却I段、冷却II段、冷却III段,本发明主要改进在于：将链篦机的预热升温段分为前段、中段和后段三个区域,且将环冷机的冷却II段分为循环冷却段和冷却ii段,循环冷却段设置在冷却I段和冷却ii段之间；将链篦机的预热升温段的中段废气循环至环冷机循环冷却段。本发的方法可使回转窑中燃料的使用量降低3％～10％,废气处理量减少15％～25％。(The invention discloses a method for circulating waste gas in the process of producing pellets by a chain grate-rotary kiln-circular cooler three-machine system, wherein the chain grate is sequentially divided into a blast drying section, a draft drying section, a preheating and warming section and a preheating section from a feeding end to a rotary kiln, and the circular cooler is sequentially divided into a cooling I section, a cooling II section and a cooling III section from the rotary kiln to a discharging end, and the invention mainly improves the following steps: dividing a preheating and temperature raising section of the chain grate machine into a front section, a middle section and a rear section, and dividing a cooling II section of the circular cooler into a circulating cooling section and a cooling II section, wherein the circulating cooling section is arranged between the cooling I section and the cooling II section; and circulating the middle-section waste gas of the preheating and temperature raising section of the chain grate machine to the circulating cooling section of the circular cooler. The method can reduce the usage amount of fuel in the rotary kiln by 3-10 percent and reduce the waste gas treatment amount by 15-25 percent.)

1. The method for circulating the waste gas in the pelletizing production process of the chain grate-rotary kiln-circular cooler three-machine system is characterized in that the chain grate is sequentially divided into a blowing drying section, a preheating warming section and a preheating section from a feeding end to a rotary kiln, and the circular cooler is sequentially divided into a cooling I section, a cooling II section and a cooling III section from the rotary kiln to a discharging end, and the method is characterized in that: dividing a preheating and temperature raising section of the chain grate machine into a front section, a middle section and a rear section, and dividing a cooling II section of the circular cooler into a circulating cooling section and a cooling II section, wherein the circulating cooling section is arranged between the cooling I section and the cooling II section; and circulating the middle-section waste gas of the preheating and temperature raising section of the chain grate machine to the circulating cooling section of the circular cooler.

2. The method for recycling the exhaust gas generated in the pellet production process of the three-machine system of the grate, the rotary kiln and the circular cooler, as claimed in claim 1, is characterized in that: the oxygen content of the middle section waste gas of the preheating and temperature rising section of the chain grate machine is not lower than 19 percent, the CO content is not higher than 30ppm, and the circulating amount accounts for 30 to 50 percent of the total volume of the waste gas of the preheating and temperature rising section.

3. The method for recycling the exhaust gas generated in the pellet production process of the three-machine system of the grate, the rotary kiln and the circular cooler, as claimed in claim 1, is characterized in that: the pellet temperature of the circulating cooling section is 650-950 ℃.

4. The method for recycling the exhaust gas generated in the pellet production process of the three-machine system of the grate, the rotary kiln and the circular cooler, as claimed in claim 1, is characterized in that: the cooling waste gas that the recirculated cooling section came out and the cooling waste gas that the II sections of cooling came out lead to the preheating section that rises to the chain grate, and the cooling waste gas that the I section of cooling came out leads to the rotary kiln, and the cooling waste gas that the III sections of cooling came out leads to the forced air drying section of chain grate.

5. The method for recycling the exhaust gas generated in the pellet production process of the three-machine system of the grate, the rotary kiln and the circular cooler, as claimed in claim 1, is characterized in that: the cooling air volume of the cooling I section of the circular cooler is increased to Q:

Q＝Q_Ⅰ×[1+(0.2～0.3)Q_c/Q_Ⅱ]

wherein the content of the first and second substances,

Q_Ⅰfor setting the standard exhaust gas quantity, Nm, of the cooling section I before the cooling section³；

Q_cIn order to circulate the standard exhaust gas quantity, Nm³；

Q_ⅡTo set the standard exhaust gas quantity, Nm, of the cooling section II before the cooling section³，

And (3) standard state conditions: temperature 273.15K, pressure 101.325 KPa.

6. The method for recycling the exhaust gas generated in the pellet production process of the three-machine system of the grate, the rotary kiln and the circular cooler, as claimed in claim 1, is characterized in that: the total amount of the waste gas in the standard state of the circulating cooling section and the cooling section ii is equal to the amount of the waste gas in the standard state of the cooling section II before the circulating cooling section is arranged.

7. The method for recycling the exhaust gas generated in the pellet production process of the three-machine system of the grate, the rotary kiln and the circular cooler, as claimed in claim 1, is characterized in that: and carrying out ozone oxidation denitration and semi-dry desulfurization treatment on the waste gas of the partial preheating and temperature raising section.

Technical Field

The invention relates to a method for recycling waste gas in a pellet production process, in particular to a method for realizing energy conservation and emission reduction of a pellet process by using recycling in a grate-rotary kiln-circular cooler three-machine system in a pellet generation process, and belongs to the field of preparation of ferrous metallurgy pellets and energy conservation and emission reduction.

Background

The pellet is used as an important raw material for blast furnace iron making, has better metallurgical performance and lower pollution load compared with sintering, and is more suitable for the current situation of iron ore resources mainly comprising concentrate in China, so compared with other iron ore agglomeration technologies, the pellet production technology is a more reasonable and effective agglomeration technology. With the development of the steel industry, the yield of the pellet ore in China also tends to increase year by year.

Compared with other pellet production processes, the grate-rotary kiln-circular cooler pellet production process has lower requirements on heat-resistant materials and fuel calorific values, is more suitable for the current situation of China, and is relatively good in quality of finished ore due to relatively uniform rolling of pellets in the roasting process of the rotary kiln, so that the grate-rotary kiln-circular cooler pellet production process can still be the most main production process in pellet production of China within a certain period of time. However, in the existing process for producing pellets of a grate-rotary kiln-circular cooler, the amount of discharged waste gas is large, so that the treatment cost of the waste gas is high, and the waste heat utilization degree of a large amount of discharged hot waste gas is not enough, so that the waste of energy is caused.

For the current chain grate-rotary kiln-circular cooler air flow system and waste gas treatment process in China, the discharged waste gas mainly comprises waste gas in a blowing drying section, waste gas in an exhausting drying section and waste gas in a preheating temperature rise section. The waste gas discharged from the blast drying section has high water vapor content and low pollutant content, and can be directly discharged. At present, hot waste gas in an air draft drying section and a preheating temperature raising section is combined and is discharged after being purified. The temperature of the part of the exhaust gas is high, the components are complex, and the part of the exhaust gas contains a large amount of pollutants such as NOx, SOx and the like, so that the hot exhaust gas in the section needs to be subjected to treatments such as desulfurization, denitrification and the like.

The exhaust gas volume of the air draft drying section and the preheating temperature raising section is large, along with the implementation of the ultra-low emission policy, the treatment cost for treating the part of hot exhaust gas is higher and higher, and meanwhile, because the temperature of the hot exhaust gas in the preheating temperature raising section is higher, if the hot exhaust gas is not utilized, only the exhaust gas is treated, so that a large amount of resources are wasted.

Disclosure of Invention

The invention aims to provide a method for recycling waste gas in the process of producing iron ore oxidized pellets by a grate-rotary kiln-circular cooler three-machine system, which can ensure the stability of thermal parameters such as system temperature, air volume, air pressure and the like, and can fully utilize the waste heat of a preheating temperature rise section to ensure that the thermal circulation of the system is more reasonable, namely, the reduction of the waste gas treatment capacity and the reduction of fuel consumption are realized under the condition of ensuring the production quality index.

In order to achieve the technical purpose, the invention provides a method for circulating waste gas in a pelletizing production process of a chain grate-rotary kiln-circular cooler three-machine system, wherein the chain grate is sequentially divided into a blast drying section, a draft drying section, a preheating temperature raising section and a preheating section from a feeding end to a rotary kiln, and the circular cooler is sequentially divided into a cooling I section, a cooling II section and a cooling III section from the rotary kiln to a discharging end, and compared with the prior art, the method is mainly improved in that: the preheating and temperature raising section of the chain grate machine is sequentially divided into a front section, a middle section and a rear section, and a cooling II section of the circular cooler is divided into a circulating cooling section and a cooling II section, wherein the circulating cooling section is arranged between the cooling I section and the cooling II section; and circulating the middle-section waste gas of the preheating and temperature raising section of the chain grate machine to the circulating cooling section of the circular cooler.

In a preferable scheme, the oxygen content of the middle-section waste gas of the preheating and temperature rising section of the chain grate is not lower than 19 percent, the CO content is not higher than 30ppm, and the circulating amount accounts for 30 to 50 percent of the total volume of the waste gas of the preheating and temperature rising section. The method for circulating the waste gas in the process of producing the pellets by using the three-machine system of the chain grate machine, the rotary kiln and the circular cooler skillfully utilizes the difference of oxygen content and CO content in different areas of the preheating and temperature rising section, circulates the middle-section waste gas with the oxygen content not lower than 19% and the CO not higher than 30ppm between the cooling I section and the cooling II section and replaces part of bellows positions of the cooling II section, can fully utilize the waste heat of the preheating and temperature rising section to ensure that the heat circulation of the system is more reasonable, namely realizes the reduction of the waste gas treatment capacity and the reduction of the fuel consumption under the condition of ensuring the production quality index.

In the preferable scheme, the pellet temperature of the circulating cooling section is 650-950 ℃. A small amount of CO in the waste gas can be combusted secondarily in the circulating process, and the concentration of CO in the circulating waste gas is strictly controlled, so that the safe and reliable cyclic utilization of the waste gas is realized.

Preferably, the cooling waste gas from the circulating cooling section and the cooling waste gas from the cooling section ii are introduced into a preheating and temperature raising section of the chain grate, the cooling waste gas from the cooling section i is introduced into the rotary kiln, and the cooling waste gas from the cooling section iii is introduced into a forced air drying section of the chain grate.

In the preferable scheme, the cooling air volume of the cooling section I of the circular cooler is increased to Q:

Q＝Q_Ⅰ×[1+(0.2～0.3)Q_c/Q_Ⅱ]

wherein the content of the first and second substances,

Q_Ⅰfor setting the standard exhaust gas quantity, Nm, of the cooling section I before the cooling section³；

Q_cIn order to circulate the standard exhaust gas quantity, Nm³；

Q_ⅡTo set the standard exhaust gas quantity, Nm, of the cooling section II before the cooling section³；

And (3) standard state conditions: temperature 273.15K, pressure 101.325 KPa.

According to the invention, more heat enters the rotary kiln by increasing the cooling air volume of the cooling section I. Thus, not only the thermal processes of oxidization and the like of the pellets in the circulating cooling section are ensured, but also the use of part of fuel in the rotary kiln can be reduced.

Preferably, the total amount of the exhaust gas in the standard state (temperature 273.15K and pressure 101.325KPa) of the circulation cooling section and the cooling section ii is equal to the amount of the exhaust gas in the standard state of the cooling section II before the circulation cooling section is arranged.

Preferably, the waste gas of the partial preheating and temperature raising section is subjected to ozone oxidation denitration and semi-dry desulfurization treatment. Greatly reducing the flue gas treatment capacity and the treatment cost.

The invention reduces the energy consumption of pellets and the treatment capacity of waste gas in the subsequent purification process by circulating part of hot waste gas (mainly meaning that the oxygen content is not lower than 19 percent and the CO content is not higher than 30ppm) in the preheating temperature rising section to the circular cooler and optimizing the operation parameters of the chain grate machine, the rotary kiln and the circular cooler.

The circular cooler is additionally provided with a circulating cooling section which is mainly arranged at the position of the original cooling section II, the original cooling section II is partially used as the circulating cooling section, namely the space of the cooling section I and the cooling section III is kept unchanged, and the position of the cooling section II is reduced for the circulating cooling section.

After the waste gas circulation is adopted, the consumption of fuels such as coal gas or coal powder and the like in the rotary kiln can be reduced, for example, the volume proportion of the coal gas or the mass proportion of the coal powder is reduced by 3-10%.

The method for recycling the waste gas of the iron ore pellets skillfully utilizes the difference of oxygen content and CO content in different areas of the preheating and temperature rising section, and recycles the middle section waste gas which meets the requirements that the oxygen content is not less than 19% and the CO content is not more than 30ppm to the position between the cooling I section and the cooling II section and replaces part of the positions of the air boxes of the cooling II section. And then, increasing the cooling air quantity of the cooling section I to ensure that more heat enters the rotary kiln. Thus, not only the thermal processes of oxidization and the like of the pellets in the circulating cooling section are ensured, but also the use of part of fuel in the rotary kiln can be reduced. Finally, the content of the waste gas to be treated is greatly reduced, the treatment pressure of the waste gas is relieved, and the treatment cost is saved.

Compared with the prior art, the invention has the advantages that:

(1) the invention improves the heat utilization efficiency, reduces the energy consumption of the pellet production process and reduces the energy consumption by 3 to 10 percent on the premise of not influencing the yield and the quality of pellets by circulating a part of waste gas of the preheating and temperature rising section of the grate, utilizing the waste heat in the waste gas and integrally optimizing the pellet production process; and the treatment capacity of the discharged waste gas is reduced, the waste gas is reduced by 15-25%, and the investment cost and the operation cost of waste gas treatment can be reduced.

(2) According to the invention, the waste gas is circulated to the ring cooling machine section with the pellet temperature of 650-950 ℃ by controlling the circulation position of the waste gas, so that a small amount of CO in the waste gas can be combusted secondarily in the circulation process, and the concentration of CO in the circulating waste gas is strictly controlled, thereby realizing safe and reliable cyclic utilization of the waste gas.

(3) The invention circulates the hot waste gas between the cooling section I and the cooling section II to replace part of the air quantity of the cooling section II, thereby increasing the air quantity of the cooling section I, leading more heat to enter the rotary kiln and reducing the heat required by fuel combustion.

(4) The invention ensures that the waste gas circulation does not influence the oxidation of the pellet production process and reduces the oxygen content in the discharged waste gas by circulating the waste gas with high oxygen content, and the invention stipulates the suggestion about the ultra-low emission of the advancing and implementing steel industry that the standard oxygen content of the production facility of the grate-rotary kiln pellet production process is 18 percent, and reduces the oxygen content after circulation, so that the requirement of ultra-low emission can be more easily met.

(5) The waste gas circulation of the invention also comprehensively considers the pollutant treatment method of the discharged waste gas, and the temperature and the components of the discharged flue gas are more beneficial to adopting the high-efficiency treatment process of ozone denitration and dry desulphurization through the waste gas circulation.

The system of the invention considers the balance of thermal parameters such as temperature, air quantity, air pressure and the like of each process after circulation, and can fully utilize the waste heat of the preheating and temperature rising section to ensure that the thermal circulation of the system is more reasonable, thereby realizing the reduction of waste gas treatment capacity and the reduction of fuel consumption on the premise of ensuring the production quality index.

Drawings

FIG. 1 is a process flow diagram of a wind system in the process of producing pellets by a chain grate-rotary kiln-circular cooler three-machine system.

Detailed Description

The following examples are intended to illustrate the invention in further detail without limiting the scope of the invention as claimed.