A system and method for graded desulfurization of flue gas from a grate-rotary kiln pelletizing plant

Abstract

The present invention discloses a system and method for graded desulfurization of flue gas from a chain grate-rotary kiln pelletizer. The system comprises a chain grate, a rotary kiln, and a ring cooler connected in sequence. The inlet of the cooling fan of section I of the ring cooler is connected to the atmosphere, and the outlet is connected to the desulfurization and dust removal system in sequence through the ring cooler section I, the rotary kiln, the preheating section II, the medium- and high-temperature SCR denitrification system, the reheat fan, the exhaust drying section, and the exhaust section fan. The inlet of the cooling fan of section II of the ring cooler is connected to the atmosphere, and the outlet is connected to the bag filter in sequence through the ring cooler section II, the preheating section I, and the preheating section fan. The inlet of the cooling fan of section III of the ring cooler is connected to the atmosphere, and the outlet is connected to the bag filter in sequence through the ring cooler section III, the blower drying fan, and the blower drying section. The present invention separates high-sulfur flue gas from low-sulfur flue gas and adopts different treatment methods to achieve ultra-low emissions of flue gas discharged from the chain grate-rotary kiln pelletizer, while reducing the investment and operating costs of the flue gas treatment device.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental protection, and in particular to a system and method for graded desulfurization of flue gas from a chain grate-rotary kiln pelletizing plant. Background Art

[0002] Oxidized pellets are a common charge in blast furnace ironmaking, and the chain grate-rotary kiln process is the mainstream process for producing oxidized pellets in my country. In 2019, the Ministry of Ecology and Environment and five other departments jointly issued the "Opinions on Promoting the Implementation of Ultra-Low Emissions in the Steel Industry," which proposed ultra-low emission standards for pelletizing flue gas: Under operating conditions with a baseline oxygen content of 18%, the hourly average SO2, NOx, and particulate matter emission concentrations in pellet roasting flue gas shall not exceed 35, 50, and 10 mg / m, respectively. 3 .

[0003] The chain grate mainly consists of a blast drying section, an exhaust drying section, a preheating section I and a preheating section II. In the existing flue gas treatment process, the flue gas is discharged after staged treatment: the chain grate blast drying section is discharged separately after dust removal; the flue gas from the chain grate preheating section II is first passed through a medium and high temperature SCR denitrification system to remove nitrogen oxides, and then sent to the chain grate exhaust drying section through a heat recovery fan. The flue gas from the exhaust drying section and the preheating section I is collected by the main fan and sent to the desulfurization and dust removal system for treatment before discharge.

[0004] According to the actual production conditions of the chain grate, the green pellets are added from the blast drying section of the chain grate, and gradually heated through the blast drying section, exhaust drying section, preheating section I and preheating section II. The sulfur in the pellets is gradually released into the flue gas. In the existing technology, the flue gas discharged from the blast drying section is not desulfurized, which easily causes SO2 to exceed the standard; the high-sulfur flue gas from the exhaust drying section and the low-sulfur flue gas from the preheating section I are combined and discharged, causing the downstream desulfurization and dust removal system to handle a large amount of flue gas, and the project investment and operating costs are high. Summary of the Invention

[0005] The purpose of the present invention is to provide a system and method for graded desulfurization of flue gas from a chain grate-rotary kiln pelletizer. According to the characteristic that sulfur in the pellets is gradually released into the flue gas, the system separates high-sulfur flue gas from low-sulfur flue gas and adopts different treatment methods to achieve ultra-low emissions of flue gas discharged from the chain grate-rotary kiln pelletizer, while reducing the investment and operating costs of the flue gas treatment device.

[0006] To achieve the above-mentioned purpose, the technical solution of the present application is: a system for graded desulfurization of flue gas from a chain grate-rotary kiln pelletizer, comprising a chain grate, a rotary kiln and a ring cooler connected in sequence; the chain grate comprises a blast drying section, an exhaust drying section, a preheating section I and a preheating section II connected in sequence, the preheating section II is connected to the tail of the rotary kiln, the head of the rotary kiln is connected to the ring cooler, the ring cooler comprises a ring cooler section I, a ring cooler section II, a ring cooler section III and a ring cooler section IV connected in sequence, and also comprises a section I cooling fan for providing cold air to the ring cooler section I, a section II cooling fan for providing cold air to the ring cooler section II, and a section III cooling fan for providing cold air to the ring cooler section III;

[0007] The inlet of the cooling fan of section I is connected to the atmosphere, and the outlet is connected to the desulfurization and dust removal system through the ring cooler section I, rotary kiln, preheating section II, medium and high temperature SCR denitrification system, reheat fan, exhaust drying section, exhaust section fan;

[0008] The inlet of the cooling fan of section II is connected to the atmosphere, and the outlet is connected to the bag dust collector through the ring cooler section II, preheating section I, and the preheating section fan in sequence;

[0009] The inlet of the section III cooling fan is connected to the atmosphere, and the outlet is connected to the bag dust collector through the ring cooler section III, the blower drying fan, and the blower drying section in sequence.

[0010] Furthermore, pressure detection instruments are respectively provided in the blast drying section, exhaust drying section, preheating section I and preheating section II.

[0011] Furthermore, a low-nitrogen combustion burner is provided at the head of the rotary kiln.

[0012] Furthermore, high specific surface area calcium hydroxide (specific surface area ≥ 35m2) is sprayed into the bag filter inlet pipe. 2 / g; the injected calcium hydroxide stays in the pipeline for ≥1 second and then enters the bag filter together with the flue gas.

[0013] Furthermore, the desulfurization and dust removal system is a combination system of wet desulfurization and wet electrostatic precipitator.

[0014] The present invention also provides a method for graded desulfurization of flue gas from grate-rotary kiln pellets, comprising drying, preheating, roasting and cooling the pellets:

[0015] The green balls enter the blast drying section of the grate machine and are dried by hot air flow. After staying in this section for a period of time to remove surface moisture, they enter the exhaust drying section. After staying in this section for a period of time, they enter the preheating section I to continue drying and undergo initial oxidation and consolidation. After staying in this section for a period of time, the green balls enter the preheating section II to complete internal consolidation, hardening and oxidation. The temperatures of the blast drying section, exhaust drying section, preheating section I and preheating section II gradually increase.

[0016] The balls entering the rotary kiln tumble inside the kiln and move from the kiln tail to the kiln head. The low-nitrogen combustion burner at the kiln head provides heat to the rotary kiln and introduces the hot exhaust gas from the ring cooler section I into the kiln head. The roasting temperature in the rotary kiln is higher than that of the preheating section II, and the kiln is roasted for a period of time.

[0017] The roasted pellets are sent to the ring cooler for cooling. The cooling fans of section I, section II and section III send air from bottom to top into the ring cooler to cool the pellets. The ring cooler is divided into four sections. The hot exhaust gas of section I of the ring cooler enters the rotary kiln as secondary air; the hot air flow of section II of the ring cooler is introduced into the preheating section I of the chain grate as a heat source; the hot air flow of section III of the ring cooler is introduced into the blast drying section of the chain grate as a heat source through the blast drying fan; the exhaust gas of section IV of the ring cooler is discharged from the chimney of the ring cooler itself.

[0018] The pellets are cooled on the ring cooler for a period of time until the temperature of the pellets drops below the set value, and then the finished pellets are transported to the blast furnace for ironmaking.

[0019] Furthermore, the flue gas in the blast drying section and preheating section I is low-sulfur flue gas, and the flue gas in the exhaust drying section and preheating section II is high-sulfur flue gas.

[0020] Furthermore, the above method also includes the treatment of the flue gas in the grate drying section:

[0021] The hot exhaust gas from the ring cooler section I enters the rotary kiln as secondary air; the high-sulfur flue gas that passes through the rotary kiln and the chain grate preheating section II first passes through the medium and high temperature SCR denitrification system to remove NOx, and then is sent to the chain grate exhaust drying section through the reheating fan for preheating the raw balls. The exhaust gas discharged from the exhaust drying section is high-sulfur flue gas, and is finally sent to the desulfurization and dust removal system through the exhaust section fan for treatment before meeting the emission standards.

[0022] Furthermore, the above method also includes the treatment of the flue gas from the grate blast drying section and the preheating section I:

[0023] The hot air from the ring cooler section II is introduced into the grate preheating section I 103 as a heat source; the hot air from the ring cooler section III is introduced into the grate preheating section 103 as a heat source through the blower dryer fan; the low-sulfur flue gas from the preheating section I is drawn by the preheating section fan and merged with the low-sulfur flue gas from the blower dryer section, and high-specific surface area calcium hydroxide is sprayed into the flue downstream of the confluence point; the injected calcium hydroxide stays in the pipeline for ≥1 second; the reactions occurring during the desulfurization process are as follows:

[0024] Ca(OH)2+SO2→CaSO3+H2O

[0025] CaSO3+O2→CaSO4

[0026] After desulfurization, the flue gas enters the bag dust collector and meets the emission standards after removing particulate matter.

[0027] Furthermore, the above method also includes pressure control of each section of the chain grate: the value of the pressure detection instrument P2 of the exhaust drying section is lower than the value of the pressure detection instrument P1 of the blast drying section and the value of the pressure detection instrument P3 of the preheating section I; the value of the pressure detection instrument P4 of the preheating section II is lower than the value of the pressure detection instrument P3 of the preheating section I.

[0028] By adopting the above technical solution, the present invention can achieve the following technical effects:

[0029] 1. The high-sulfur flue gas in the exhaust drying section is treated separately, which can reduce the flue gas treatment volume of the downstream desulfurization and dust removal system, reducing project investment and operating costs.

[0030] 2. The exhaust gas from the blast drying section is treated with desulfurization and dust removal to meet ultra-low emission requirements;

[0031] 3. The low-sulfur flue gas from the preheating stage I and the low-sulfur flue gas from the blast drying stage are treated together. By spraying high-specific surface area calcium hydroxide into the flue, sulfur dioxide can be removed, reducing investment and operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of the system structure for grate-rotary kiln pelletizing flue gas graded desulfurization;

[0033] Explanation of the serial numbers in the figure: 1-chain grate, 101-blast drying section, 102-exhaust drying section, 103-preheating section I, 104-preheating section II, 105-partition wall; 2-rotary kiln, 201-low nitrogen combustion burner. 3-Annular cooler, 301-Annular cooler section I, 302-Annular cooler section II, 303-Annular cooler section III, 304-Annular cooler section IV, 305-Section I cooling fan, 306-Section II cooling fan, 307-Section III cooling fan; 4-Blower drying fan, 5-Preheating section fan, 6-Bag dust collector, 7-Medium and high temperature SCR denitrification system, 8-Reheat fan, 9-Exhaust section fan, 10-Desulfurization and dust removal system, P1-Blower drying section pressure detection instrument, P2-Exhaust drying section pressure detection instrument, P3-Preheating section I pressure detection instrument, P4-Preheating section II pressure detection instrument. DETAILED DESCRIPTION

[0034] In order to help those skilled in the art better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of this application.

[0035] Example 1

[0036] Reference Figure 1 This embodiment provides a system for chain grate-rotary kiln pelletizing flue gas graded desulfurization, comprising a chain grate 1, a rotary kiln 2 and an annular cooler 3 connected in sequence;

[0037] The chain grate comprises a blast drying section 101, an exhaust drying section 102, a preheating section I 103 and a preheating section II 104. Pressure detection instruments P1, P2, P3 and P4 are respectively provided in each section. Partition walls 105 are provided between the sections. A gap is provided between the bottom of the partition wall and the material surface in the chain grate.

[0038] A low nitrogen combustion burner 201 is provided at the head of the rotary kiln 2;

[0039] The ring cooler 3 includes a ring cooler section I 301, a ring cooler section II 302, a ring cooler section III 303, and a ring cooler section IV 304. It also includes a section I cooling fan 305 for providing cold air to the ring cooler section I 301, a section II cooling fan 306 for providing cold air to the ring cooler section II 302, and a section III cooling fan 307 for providing cold air to the ring cooler section III 303.

[0040] The inlet of the cooling fan 305 of stage I is connected to the atmosphere, and the outlet is connected to the desulfurization and dust removal system 10 through a pipeline, which passes through the ring cooler stage I 301, the rotary kiln 2, the preheating stage II 104, the medium-high temperature SCR denitrification system 7, the reheating fan 8, the exhaust drying stage 102, and the exhaust stage fan 9. Preferably, the desulfurization and dust removal system 10 is a combination of wet desulfurization and a wet electrostatic precipitator.

[0041] The inlet of the section II cooling fan 306 is connected to the atmosphere, and the outlet is connected to the bag dust collector 6 through a pipeline through the ring cooler section II 302, the preheating section I 103, the preheating section fan 5.

[0042] The inlet of the section III cooling fan 307 is connected to the atmosphere, and the outlet is connected to the bag dust collector 6 through a pipeline through the ring cooler section III 303, the blower drying fan 4, and the blower drying section 101 in sequence.

[0043] In the present invention, high specific surface area calcium hydroxide is sprayed into the inlet pipe of the bag filter 6. Preferably, the specific surface area of ​​the high specific surface area calcium hydroxide is ≥35m 2 / g; the injected calcium hydroxide stays in the pipeline for ≥1 second and then enters the bag filter 6 together with the flue gas.

[0044] This embodiment also provides a method for graded desulfurization of flue gas from a grate-rotary kiln pelletizer, the method comprising:

[0045] (1) Drying, preheating, roasting and cooling of pellets:

[0046] The green balls enter the blast drying section 101 of the grate 1 and can be dried with a hot air flow at 200°C. The residence time of the green balls is about 3-5 minutes. After the surface moisture of the green balls is removed, they enter the exhaust drying section 102. The temperature of this section can generally be 360°C, and the residence time is about 3-5 minutes. After passing through the exhaust drying section 102, the green balls enter the preheating section I 103. The temperature of this section can generally be 575°C, and the residence time is about 3-5 minutes, so that the green balls continue to dry and are initially oxidized and consolidated. After passing through the preheating section I 103, the green balls enter the preheating section II 104. The temperature of this section can generally be 1000°C, and the residence time is about 8-10 minutes. At this stage, the green balls complete their own internal consolidation, hardening and oxidation, so that the green balls have a certain strength and can withstand the continuous impact of the balls in the rotary kiln 2 without breaking.

[0047] The pellets entering rotary kiln 2 tumble within the kiln, moving from the kiln's rear end to the kiln's front end. A low-nitrogen combustion burner 201 is installed at the kiln's front end to provide heat to the kiln 2. This burner also directs hot exhaust gas from the ring cooler's first stage 301 into the kiln's front end hood to maintain the required kiln temperature. The kiln's firing temperature is typically controlled at 1250°C, with a firing time of approximately 25-35 minutes.

[0048] The roasted pellets are fed into the ring cooler 3 for cooling. The pellet temperature entering the ring cooler is generally around 1250°C. Section I cooling fans 305, Section II cooling fans 306, and Section III cooling fans 307 deliver air from bottom to top into the ring cooler to cool the material. The ring cooler is divided into four sections. The hot exhaust gas from section I 301 enters the rotary kiln 2 as secondary air; the hot air from section II is introduced into the grate preheating section 103 as a heat source; the hot air from section III 303 passes through the blower fan 4 and is introduced into the grate blast drying section 101 as a heat source; and the exhaust gas from section IV 304 is discharged through the chimney of the ring cooler 3 itself.

[0049] The pellets are cooled on the ring cooler for about 40-50 minutes to reduce the temperature of the pellets to below 150℃. The finished pellets are then transported to the blast furnace for ironmaking.

[0050] (2) Treatment of flue gas in the exhaust drying section of the grate machine:

[0051] Hot exhaust gas from the ring cooler section 1 301 enters the rotary kiln 2 as secondary air. Low-nitrogen combustion burners 201 are installed at the kiln head of the rotary kiln 2, allowing sulfur in the fuel to enter the flue gas during combustion. Sulfur in the green pellets primarily enters the flue gas during medium- and high-temperature roasting in the rotary kiln 2 and preheating in the grate preheating section 2 104. The flue gas passing through the rotary kiln 2 and grate preheating section 2 104 contains high concentrations of SO2 and NOx, with temperatures ranging from 350 to 400°C. It first passes through the medium- and high-temperature SCR denitrification system 7 to remove NOx. The gas is then delivered to the grate exhaust drying section 102 via a reheat fan 8 for preheating the green pellets. The exhaust gas from the exhaust drying section 102 is high in sulfur and is then delivered to the desulfurization and dust removal system 10 via the exhaust fan 9 for treatment before reaching emission standards. The desulfurization and dust removal system 10 is preferably a combination of wet desulfurization and a wet electrostatic precipitator.

[0052] (3) Treatment of flue gas from the drying section and preheating section I of the grate machine

[0053] The hot air flow from the ring cooler section II is introduced into the grate preheating section I 103 as a heat source; the hot air flow from the ring cooler section III 303 is introduced into the grate blast drying section 101 as a heat source through the blast drying fan 4. Since the reaction temperatures of the preheating section I 103 and the blast drying section 101 are relatively low, a small amount of sulfur in the raw materials will enter the flue gas, so the flue gas produced by the above two sections is low-sulfur flue gas. The flue gas from the preheating section I 103 is extracted by the preheating section fan 5 and merged with the flue gas from the blast drying section 101, and high specific surface area calcium hydroxide is sprayed into the flue downstream of the confluence point; the residence time of the injected calcium hydroxide in the pipeline is ≥1 second. Compared with ordinary calcium hydroxide, the specific surface area of ​​high specific surface area calcium hydroxide is ≥35m 2 / g, which increases the porosity and significantly enhances the adsorption capacity of SO2. The reaction during the desulfurization process is:

[0054] Ca(OH)2+SO2→CaSO3+H2O

[0055] CaSO3+O2→CaSO4

[0056] After desulfurization, the flue gas enters the bag filter 6, where particulate matter is removed before being discharged in compliance with emission standards.

[0057] (4) Pressure control of each section of chain grate

[0058] Since the flue gas in the blast drying section 101 and preheating section I 103 is low-sulfur flue gas, and the flue gas in the exhaust drying section 102 and preheating section II 104 is high-sulfur flue gas, in order to prevent the flue gas from leaking through the gaps at the bottom of the partition wall, pressure control is required in each section of the chain grate when the system is running.

[0059] In order to prevent the high-sulfur flue gas in the exhaust drying section 102 from leaking into the blast drying section 101 and the preheating section I 103, the value of the pressure detection instrument P2 needs to be controlled to be lower than the values ​​of the pressure detection instruments P1 and P3;

[0060] In order to prevent the high-sulfur flue gas in the preheating section II 104 from leaking into the preheating section I 103, the value of the pressure detection instrument P4 needs to be controlled to be lower than the value of the pressure detection instrument P3.

[0061] Example 2

[0062] To further illustrate the effect of the present invention, a 3 million tons / year chain grate-rotary kiln pelletizing production line is used as an example for illustration;

[0063] The sulfur in the green pellets comes from iron ore concentrate, with a consumption of 420 t / h and a sulfur content of 0.27%. The sulfur in the fuel comes from bituminous coal used in the rotary kiln low-nitrogen combustion burner 201, with an hourly consumption of 9.47 t / h and a sulfur content of 0.26%.

[0064] The sulfur content of the pellets at the outlet of green balls, blast drying section 101 outlet, exhaust drying section 102 outlet, preheating section I 103 outlet, preheating section II 104 outlet and rotary kiln 2 outlet was tested respectively. See the table below for details:

[0065] Table 1: Sulfur content of pellets at the outlet of each section of the grate-rotary kiln pelletizing process and the proportion of sulfur in the incoming flue gas

[0066]

[0067] As shown in Table 1, a small portion of the sulfur in the pellet feedstock enters the flue gas during the blast drying section 101, the exhaust drying section 102, and the preheating section I 103. As the temperature rises, the majority of the sulfur in the pellet feedstock enters the flue gas during the high-temperature roasting process in the preheating section II 104 and the rotary kiln 2.

[0068] The source of sulfur dioxide in the flue gas downstream of the grate blast drying section 101 is the oxidation of a small amount of sulfur in the raw balls during the drying process. The flue gas volume in this section is 350,000 Nm 3 / h, sulfur dioxide concentration is 241mg / m 3 .

[0069] The sources of sulfur dioxide in the flue gas downstream of the grate exhaust drying section 102 are: sulfur oxidation in the fuel of the low-nitrogen combustion burner 201 of the rotary kiln; and most of the sulfur oxidation in the green balls during the roasting in the rotary kiln 2 and the grate preheating section 103. The flue gas volume in this section is 440,000 Nm 3 / h, sulfur dioxide concentration is 4755mg / m 3 .

[0070] The source of sulfur dioxide in the flue gas downstream of the chain grate preheating section I 103 is: a small amount of sulfur oxidation of the raw materials during the preheating process. The flue gas volume in this section is 407000Nm 3 / h, sulfur dioxide concentration is 206mg / m 3 .

[0071] If the existing technology is used for treatment, the flue gas discharged after dust removal from the grate drying section 101 will cause the sulfur dioxide emission to exceed the standard; the flue gas from the exhaust drying section 102 and the preheating section I 103 will be treated together, and the flue gas treatment capacity of the downstream desulfurization and dust removal facilities is 847,000 Nm 3 / h, sulfur dioxide concentration 2569mg / m 3 , the investment and operating costs of treatment facilities are high.

[0072] According to the system and method of Example 1, the flue gas from the grate-rotary kiln pelletizing was graded for desulfurization: the flue gas from the grate blast drying section 101 and the flue gas from the preheating section I 103 were both low-sulfur flue gases, and after being combined and treated, the sulfur dioxide concentration was 222 mg / m 3 By spraying high specific surface area calcium hydroxide into the flue, sulfur dioxide can be removed, saving investment in the desulfurization system.

[0073] The high-sulfur flue gas from the grate exhaust drying section 102 is treated separately by a combination of wet desulfurization and wet electrostatic precipitator. The air volume of the treatment facility is 440,000 Nm 3 / h, which is only 52% of the existing technology, and the investment and operating costs of treatment facilities are greatly reduced.

[0074] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A system for graded desulfurization of flue gas from pelletizing using a grate and a rotary kiln, comprising a grate, a rotary kiln, and an annular cooler connected in sequence; the grate comprises a blast drying section, an exhaust drying section, a preheating section I, and a preheating section II connected in sequence, the preheating section II being connected to the rear of the rotary kiln, and the head of the rotary kiln being connected to the annular cooler, characterized in that: The ring cooler includes a ring cooler section I, a ring cooler section II, a ring cooler section III, and a ring cooler section IV which are connected in sequence, and also includes a cooling fan of section I for providing cold air to the ring cooler section I, a cooling fan of section II for providing cold air to the ring cooler section II, and a cooling fan of section III for providing cold air to the ring cooler section III; The inlet of the cooling fan of section I is connected to the atmosphere, and the outlet is connected to the desulfurization and dust removal system through the ring cooler section I, rotary kiln, preheating section II, medium and high temperature SCR denitrification system, reheat fan, exhaust drying section, exhaust section fan; The inlet of the cooling fan of section II is connected to the atmosphere, and the outlet is connected to the bag dust collector through the ring cooler section II, preheating section I, and the preheating section fan in sequence; The inlet of the cooling fan of section III is connected to the atmosphere, and the outlet is connected to the bag dust collector through the ring cooler section III, the blower dryer, and the blower dryer section in sequence; A low nitrogen combustion burner is provided at the head of the rotary kiln; Spray high specific surface area calcium hydroxide into the bag filter inlet pipe, with a specific surface area of ​​≥35m 2 / g; the injected calcium hydroxide stays in the pipe for ≥1 second and then enters the bag filter together with the flue gas; Pressure detection instruments are respectively provided in the blast drying section, exhaust drying section, preheating section I and preheating section II.

2. The system for graded desulfurization of flue gas from a grate-rotary kiln pelletizing plant according to claim 1, characterized in that: The desulfurization and dust removal system is a combination system of wet desulfurization and wet electrostatic precipitator.

3. A method for implementing pellet flue gas staged desulfurization in the system according to claim 1 or 2, characterized in that: Including drying, preheating, roasting and cooling of pellets: The green balls enter the blast drying section of the grate machine and are dried by hot air flow. After staying in this section for a period of time to remove surface moisture, they enter the exhaust drying section. After staying in this section for a period of time, they enter the preheating section I to continue drying and undergo initial oxidation and consolidation. After staying in this section for a period of time, the green balls enter the preheating section II to complete internal consolidation, hardening and oxidation. The temperatures of the blast drying section, exhaust drying section, preheating section I and preheating section II gradually increase. The balls entering the rotary kiln roll in the kiln and move from the kiln tail to the kiln head. The burner at the kiln head provides heat to the rotary kiln and introduces the hot exhaust gas from the ring cooler section I into the kiln head. The roasting temperature in the rotary kiln is higher than that of the preheating section II, and the kiln is roasted for a period of time. The roasted pellets are sent to the ring cooler for cooling. The cooling fans of section I, section II and section III send air from bottom to top into the ring cooler to cool the pellets. The ring cooler is divided into four sections. The hot exhaust gas of section I of the ring cooler enters the rotary kiln as secondary air; the hot air flow of section II of the ring cooler is introduced into the preheating section I of the chain grate as a heat source; the hot air flow of section III of the ring cooler is introduced into the blast drying section of the chain grate as a heat source through the blast drying fan; the exhaust gas of section IV of the ring cooler is discharged from the chimney of the ring cooler itself. The pellets are cooled on the ring cooler for a period of time until the temperature of the pellets drops below the set value, and then the finished pellets are transported to the blast furnace for ironmaking.

4. The method for implementing pellet flue gas staged desulfurization according to claim 3, characterized in that: The flue gas in the blast drying section and preheating section I is low-sulfur flue gas, and the flue gas in the exhaust drying section and preheating section II is high-sulfur flue gas.

5. The method for implementing pellet flue gas staged desulfurization according to claim 3, characterized in that: The above method also includes the treatment of flue gas from the grate exhaust drying section: The hot exhaust gas from the ring cooler section I enters the rotary kiln as secondary air; the high-sulfur flue gas that passes through the rotary kiln and the chain grate preheating section II first passes through the medium and high temperature SCR denitrification system to remove NOx, and then is sent to the chain grate exhaust drying section through the reheating fan for preheating the raw balls. The exhaust gas discharged from the exhaust drying section is high-sulfur flue gas, and is finally sent to the desulfurization and dust removal system through the exhaust section fan for treatment before meeting the emission standards.

6. The method for implementing pellet flue gas staged desulfurization according to claim 3, characterized in that: The above method also includes the treatment of the flue gas from the grate blast drying section and the preheating section I: The hot air from the ring cooler section II is introduced into the grate preheating section I as a heat source; the hot air from the ring cooler section III is introduced into the grate blast drying section as a heat source through the blast drying fan; the low-sulfur flue gas from the preheating section I is drawn by the preheating section fan and merged with the low-sulfur flue gas from the blast drying section, and high-specific surface area calcium hydroxide is sprayed into the flue downstream of the confluence point; the injected calcium hydroxide stays in the pipeline for ≥1 second; the reactions occurring during the desulfurization process are as follows: Ca(OH)2+SO2→CaSO3+H2O CaSO3+O2→CaSO4 After desulfurization, the flue gas enters the bag dust collector and meets the emission standards after removing particulate matter.

7. The method for implementing pellet flue gas staged desulfurization according to claim 3, characterized in that: The above method also includes pressure control of each section of the chain grate: the value of the pressure detection instrument P2 of the exhaust drying section is lower than the value of the pressure detection instrument P1 of the blast drying section and the value of the pressure detection instrument P3 of the preheating section I; the value of the pressure detection instrument P4 of the preheating section II is lower than the value of the pressure detection instrument P3 of the preheating section I.

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