CN110684898B - Method for circulating waste gas in pelletizing production process of chain grate-rotary kiln-circular cooler three-machine system - Google Patents
Method for circulating waste gas in pelletizing production process of chain grate-rotary kiln-circular cooler three-machine system Download PDFInfo
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- 239000002912 waste gas Substances 0.000 title claims abstract description 100
- 238000000034 method Methods 0.000 title claims abstract description 38
- 238000004519 manufacturing process Methods 0.000 title claims description 23
- 238000005453 pelletization Methods 0.000 title claims description 4
- 238000001816 cooling Methods 0.000 claims abstract description 129
- 239000008188 pellet Substances 0.000 claims abstract description 39
- 238000011282 treatment Methods 0.000 claims abstract description 23
- 238000001035 drying Methods 0.000 claims abstract description 10
- 238000007599 discharging Methods 0.000 claims abstract description 3
- 238000010792 warming Methods 0.000 claims abstract 2
- 239000007789 gas Substances 0.000 claims description 22
- 230000000630 rising effect Effects 0.000 claims description 15
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 14
- 239000001301 oxygen Substances 0.000 claims description 14
- 229910052760 oxygen Inorganic materials 0.000 claims description 14
- 238000004064 recycling Methods 0.000 claims description 9
- 238000007254 oxidation reaction Methods 0.000 claims description 6
- 230000003647 oxidation Effects 0.000 claims description 4
- CBENFWSGALASAD-UHFFFAOYSA-N Ozone Chemical compound [O-][O+]=O CBENFWSGALASAD-UHFFFAOYSA-N 0.000 claims description 3
- 238000006477 desulfuration reaction Methods 0.000 claims description 3
- 230000023556 desulfurization Effects 0.000 claims description 3
- 238000007605 air drying Methods 0.000 claims description 2
- 238000007664 blowing Methods 0.000 claims description 2
- 239000000446 fuel Substances 0.000 abstract description 12
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 10
- 229910052742 iron Inorganic materials 0.000 description 5
- 239000002918 waste heat Substances 0.000 description 5
- SZVJSHCCFOBDDC-UHFFFAOYSA-N iron(II,III) oxide Inorganic materials O=[Fe]O[Fe]O[Fe]=O SZVJSHCCFOBDDC-UHFFFAOYSA-N 0.000 description 4
- 238000000746 purification Methods 0.000 description 4
- 239000002994 raw material Substances 0.000 description 4
- 238000005265 energy consumption Methods 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 239000003344 environmental pollutant Substances 0.000 description 3
- 231100000719 pollutant Toxicity 0.000 description 3
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 2
- 229910000831 Steel Inorganic materials 0.000 description 2
- 238000005054 agglomeration Methods 0.000 description 2
- 230000002776 aggregation Effects 0.000 description 2
- 239000003245 coal Substances 0.000 description 2
- 239000003034 coal gas Substances 0.000 description 2
- 238000002485 combustion reaction Methods 0.000 description 2
- 125000004122 cyclic group Chemical group 0.000 description 2
- 238000004134 energy conservation Methods 0.000 description 2
- 239000003546 flue gas Substances 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 239000010959 steel Substances 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000009851 ferrous metallurgy Methods 0.000 description 1
- 239000003779 heat-resistant material Substances 0.000 description 1
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N iron oxide Inorganic materials [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B1/00—Preliminary treatment of ores or scrap
- C22B1/14—Agglomerating; Briquetting; Binding; Granulating
- C22B1/16—Sintering; Agglomerating
- C22B1/20—Sintering; Agglomerating in sintering machines with movable grates
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B1/00—Preliminary treatment of ores or scrap
- C22B1/14—Agglomerating; Briquetting; Binding; Granulating
- C22B1/16—Sintering; Agglomerating
- C22B1/216—Sintering; Agglomerating in rotary furnaces
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B1/00—Preliminary treatment of ores or scrap
- C22B1/26—Cooling of roasted, sintered, or agglomerated ores
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Geology (AREA)
- Life Sciences & Earth Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Manufacture And Refinement Of Metals (AREA)
Abstract
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.
Description
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=QⅠ×[1+(0.2~0.3)Qc/QⅡ]
wherein,
QⅠfor setting the standard exhaust gas quantity, Nm, of the cooling section I before the cooling section3;
QcIn order to circulate the standard exhaust gas quantity, Nm3;
QⅡTo 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.
Example 1
Aiming at the magnetite raw material, the middle-section waste gas of the preheating and temperature raising section is used for circulation, and the quantity of the circulating waste gas is 3.2 ten thousand Nm3And h, accounting for 30 percent of the total amount of the waste gas in the preheating and temperature rising section. The oxygen content in the circulating waste gas is 19.6 percent, the CO content is 25ppm, the temperature is 200 ℃, and the circulating waste gas is pumped to a circulating cooling section with the temperature of 700-900 ℃ of balls in the cooling section by a circulating cooling fan. The air volume of the cooling section I and the cooling section II before circulation is respectively 12 ten thousand Nm310 ten thousand Nm/h3H is used as the reference value. The position of the cooling section II before the part of the circulating waste gas replacement is divided into a circulating cooling section and a cooling section ii, and after waste gas circulation is adopted, the air volume Q of the cooling section I is as follows: the air volume in the cooling ii section was adjusted to 6.8Nm3H, the total air volume of the circulating cooling section and the cooling section II is 10Nm3The/h remained unchanged or increased (see Table 1). After the hot waste gas circulation is adopted, the fuel usage amount in the rotary kiln is reduced by 6 percent, and the output and the quality of finished pellet ore can be ensured to be basically unchanged. Meanwhile, the amount of the discharged waste gas needing purification treatment is reduced by 15 percent compared with that before circulation.
Example 2
Aiming at the magnetite raw material, the middle-section waste gas of the preheating and temperature raising section is used for circulation, and the quantity of the circulating waste gas is 5.3 ten thousand Nm3And h, accounting for 50 percent of the total amount of the waste gas in the preheating and temperature rising section. The oxygen content in the circulating waste gas is 19 percent, the CO content is 30ppm, the temperature is 180 ℃, and the circulating waste gas is pumped to a circulating cooling section with the temperature of 650-950 ℃ of balls in a cooling section by a circulating cooling fan. The air volume of the cooling section I and the cooling section II before circulation is respectively 12 ten thousand Nm310 ten thousand Nm/h3H is used as the reference value. The position of the cooling section II before the part of the circulating waste gas replacement is divided into a circulating cooling section and a cooling section ii, and after waste gas circulation is adopted, the air volume Q of the cooling section I is as follows: the air volume in the cooling ii section was adjusted to 4.7Nm3H, the total air volume of the circulating cooling section and the cooling section II is 10Nm3The/h remained unchanged or increased (see Table 1). After the hot waste gas circulation is adopted, the fuel consumption in the rotary kiln is reduced by 10 percent, and the output and the quality of finished pellet ore can be ensured to be basically unchanged. Meanwhile, the amount of the discharged waste gas needing purification treatment is reduced by 25 percent compared with that before circulation.
Example 3
Aiming at the magnetite raw material, the middle-section waste gas of the preheating and temperature raising section is used for circulation, and the quantity of the circulating waste gas is 4.3 ten thousand Nm3And h is 40 percent of the total amount of the waste gas of the preheating and temperature rising section. The oxygen content in the circulating waste gas is 19.3%, the CO content is 27ppm, the temperature is 192 ℃, and the circulating waste gas is pumped to a circulating cooling section with the temperature of a ball group being 680-920 ℃ in a cooling section through a circulating cooling fan. The air volume of the cooling section I and the cooling section II before circulation is respectively 12 ten thousand Nm310 ten thousand Nm/h3H is used as the reference value. The position of the cooling section II before the part of the circulating waste gas replacement is divided into a circulating cooling section and a cooling section ii, and after waste gas circulation is adopted, the air volume Q of the cooling section I is as follows: the air volume in the cooling ii section was adjusted to 5.7Nm3H, the total air volume of the circulating cooling section and the cooling section II is 10Nm3The/h remains unchanged. After the hot waste gas circulation is adopted, the fuel consumption in the rotary kiln is reduced by 7 percent, and the output and the quality of finished pellet ore can be ensured to be basically unchanged or improved to some extent (see table 1). Meanwhile, the amount of the discharged waste gas needing purification treatment is reduced by 18 percent compared with that before circulation.
TABLE 1 pellet index after exhaust gas recirculation according to the invention
Scheme(s) | Compressive strength/N | Drum strength/% | FeO content/%) |
Before exhaust gas circulation | 2614 | 92 | 0.71 |
Example 1 | 2689 | 93 | 0.64 |
Example 2 | 2715 | 93 | 0.42 |
Example 3 | 2673 | 92 | 0.58 |
The content shows that compared with the process method for not recycling the hot waste gas at the preheating and temperature rising section, the method provided by the invention fully considers the appropriate ranges of the oxidation of magnetite, the secondary combustion of CO, the circulating position of the hot waste gas and the like, realizes the efficient utilization of the hot waste gas at the pellet preheating and temperature rising section, greatly reduces the waste gas treatment capacity, has universality and is suitable for various pellet processes. The device has simple structure and lower investment and operation cost.
Claims (5)
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; 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 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 circulation amount accounts for 30-50 percent of the volume total amount of the waste gas of the preheating and temperature rising section;
the cooling air volume of the cooling I section of the circular cooler is increased to Q:
Q=QⅠ×[1+(0.2~0.3)Qc/QⅡ]
wherein,
QⅠfor setting the standard exhaust gas quantity, Nm, of the cooling section I before the cooling section3;
QcIn order to circulate the standard exhaust gas quantity, Nm3;
QⅡTo 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.
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 pellet temperature of the circulating cooling section is 650-950 ℃.
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: and 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.
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 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.
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: and carrying out ozone oxidation denitration and semi-dry desulfurization treatment on the waste gas of the partial preheating and temperature raising section.
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