Optimized chain grate-rotary kiln SCR denitrification system and its denitrification process

Abstract

The present invention relates to the technical field of chain grate-rotary kiln SCR denitrification, and specifically to an optimized chain grate-rotary kiln SCR denitrification system and a denitrification process thereof. The optimized chain grate-rotary kiln SCR denitrification system comprises a chain grate, a rotary kiln, an annular cooler, an SCR denitrification system, a multi-tube dust collector, and a circulating fan; the chain grate is segmented into a drying section I, a drying section II, and a preheating section in a "three-section and two-chamber" manner; two groups of SCR denitrification systems are arranged between the multi-tube dust collector and the circulating fan, and are distributed on both sides of the chain grate. The present invention provides an optimized chain grate-rotary kiln SCR denitrification system, which achieves stable and standard emission of nitrogen oxides in flue gas, promotes the optimization of pellet production process and the improvement of pellet quality, and provides technical support for the effective application of the SCR denitrification process in the chain grate-rotary kiln independent pellet production line, which has broad application prospects and promotion value. The present invention also provides its denitrification process.

Description

Technical Field

[0001] The invention relates to the technical field of chain grate-rotary kiln SCR denitration, and in particular to an optimized chain grate-rotary kiln SCR denitration system and a denitration process thereof. Background Art

[0002] At present, the more widely used pelletizing method is the chain grate-rotary kiln method. The main process of the chain grate-rotary kiln pelletizing production process includes batching, pelletizing, screening and distributing materials, drying and preheating, oxidative roasting and cooling. The finely ground iron ore concentrate powder with a small amount of additives is rolled into balls, and then evenly distributed to the chain grate bed after screening, and then enters the chain grate for drying and preheating, and then enters the rotary kiln for oxidative roasting, and finally enters the ring cooler for secondary oxidation and gradually cooled to room temperature.

[0003] Nitrogen oxides are one of the main harmful components in flue gas. Their harm to the environment and human body has gradually been paid attention to by people. Nitrogen oxides in the atmosphere mainly come from fuel combustion. Although there are many types of nitrogen oxides, the main ones produced by combustion are NO and NO 2 , where NO and NO 2 The volume ratio is about 90%-95%. In terms of NOx, there are three main ways of NOx generation: temperature type, fuel type, and rapid type. In the chain grate-rotary kiln pellet production process, the pellet oxidation roasting temperature with coal powder as fuel is about 1250℃-1300℃, and the flame temperature is about 1400℃-1500℃, which has the rapid generation conditions of thermal NOx. At the same time, fuel-type nitrogen oxides account for a certain proportion. SCR denitrification technology has a significant effect on flue gas NOx control, and can achieve a NOx removal efficiency of up to 80%-90%. It has the advantages of mature technology, high denitrification efficiency, small footprint, easy operation, stability and reliability. It is one of the main means of controlling NOx pollution in sintering flue gas and pelletizing flue gas in my country, and is more suitable for the chain grate-rotary kiln independent pellet production line denitrification technology.

[0004] Denitrification technology is widely used in the treatment of nitrogen oxides in industrial waste gas such as metallurgy, thermal power, and cement. With the increasing national and local standards for air pollutant emissions, the nitrogen oxide content in the flue gas of pellet production lines represented by chain grate-rotary kiln roasting process can no longer meet the emission standards, and it is imperative to add a denitrification process to the pellet production line. Since the application of denitrification technology to chain grate-rotary kiln independent pellet production lines started late and has not yet matured, the key technologies and methods to improve denitrification efficiency are still under continuous exploration.

[0005] CN108392984A discloses a chain grate rotary kiln denitrification system and a denitrification method. The denitrification method is to lead the flue gas in the second preheating section to the outside of the chain grate, and then use a reducing agent injection device to spray the reducing agent, and then use a denitrification reactor to denitrify the flue gas, and then send the denitrified flue gas to the exhaust drying section. The concentration of NOx in the flue gas of the first preheating section 13 is still very high, and no specific treatment is made, so a part of it will leak, and the method and device are relatively complex, the operation is complex, and the equipment requirements are high. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide an optimized chain grate-rotary kiln SCR denitration system, which can achieve stable emission of nitrogen oxides in flue gas up to standard without adding other denitration devices and heat energy supply devices, and promote the optimization of pellet production process and the improvement of pellet quality, and provide technical support for the effective application of SCR denitration process in chain grate-rotary kiln independent pellet production line, which has broad application prospects and promotion value. The present invention also provides its denitration process.

[0007] The optimized chain grate-rotary kiln SCR denitration system described in the present invention includes a chain grate, a rotary kiln), an annular cooler, an SCR denitration system, a multi-tube dust collector, and a circulating fan; the chain grate is divided into a drying section I, a drying section II, and a preheating section in a "three-section and two-chamber" manner; two groups of SCR denitration systems are arranged between the multi-tube dust collector and the circulating fan, and are distributed on both sides of the chain grate.

[0008] There is a partition wall A between the drying section I and the drying section II of the chain grate machine; there is a partition wall B1 between the drying section II and the preheating section, and there is a connecting window a1 on the partition wall B1; the area of ​​the connecting window a1 is 0.33m 2 .

[0009] Bellows 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 are arranged in sequence on the side of the grate machine close to the rotary kiln. The bellows are arranged in two symmetrical rows on both sides of the grate machine. Bellows 1-6 are in the preheating section, bellows 7-8 are in the drying section II, and bellows 9-12 are in the drying section I).

[0010] Flue gas outlets are respectively arranged on one side of the wind box of the preheating section and the drying section I. The flue gas outlet in the preheating section is connected to the inlet of the multi-tube dust collector, and the flue gas outlet in the drying section I is connected to the electrostatic dust removal device; on the other side, the drying section II is provided with a second-stage air inlet of the ring cooler, and the drying section I is provided with a flue gas inlet.

[0011] The outlet of the multi-tube dust collector is connected to the inlet of the SCR denitration system, the outlet of the SCR denitration system is connected to the circulation fan, and the circulation fan is connected to the inlet of the flue gas of the drying stage I.

[0012] A burner is arranged on one end of the rotary kiln near the ring cooler; the ring cooler is divided into the first ring cooling section, the second ring cooling section and the third ring cooling section from the end connected to the rotary kiln, and the first ring cooling section, the third ring cooling section and the second ring cooling section are respectively provided with 1# ring cooling fan, 2# ring cooling fan and 3# ring cooling fan; there are partition walls a, b and c between the first ring cooling section, the second ring cooling section and the third ring cooling section; the first ring cooling section is provided with a flat material pile, a windbreak wall and a discharge port in a counterclockwise direction.

[0013] The first ring cooling stage is connected to the rotary kiln, the second ring cooling stage is connected to the drying stage II through the second stage air inlet of the ring cooler of the drying stage II, and the third ring cooling stage is connected to the waste heat recovery device.

[0014] The denitration process of the optimized chain grate-rotary kiln SCR denitration system includes:

[0015] The air from the ring cooling section enters the rotary kiln to assist combustion, and the high-temperature flue gas after combustion enters the preheating section of the chain grate;

[0016] The hot air from the second ring cooling section enters the drying section II, and the hot air temperature is not less than 600℃. Part of the high-temperature flue gas is led to the drying section II through the connecting window a1 on the partition wall between the drying section II and the preheating section to dry the pellets. The flue of the preheating section is extended to the outlet of the No. 6 bellows, and the partition wall B1 is set between the No. 6 bellows and the No. 7 bellows. The flue gas from the preheating section enters the multi-tube dust collector after coming out, and enters the SCR denitrification system for treatment. After denitrification, it is led to the chain grate drying section I through the circulating fan, and then discharged into the atmosphere after dust removal and desulfurization by the electrostatic dust removal device.

[0017] The catalyst of the SCR denitrification system is a vanadium-titanium catalyst.

[0018] The circulating fan adopts variable frequency regulation, and the operating margin is not less than 20%; the inlet temperature of the SCR denitrification and denitrification system is between 300℃-400℃.

[0019] Specifically, the optimized chain grate-rotary kiln SCR denitration system includes a chain grate, a rotary kiln, an annular cooler, an SCR denitration system, a multi-tube dust collector, and a circulating fan; the chain grate is divided into a drying section I, a drying section II, and a preheating section in a "three-section and two-chamber" manner; two groups of SCR denitration systems are arranged between the multi-tube dust collector and the circulating fan, and are distributed on both sides of the chain grate; the operation guarantee rate of the multi-tube dust collector is not less than 95%, and the particulate matter emission of the SCR denitration reactor is less than 3g / m 3 .

[0020] The chain grate is divided into drying section I, drying section II and preheating section. After drying, dehydration and preliminary oxidation preheating, the green balls become preheated dry balls with a certain temperature and strength and enter the rotary kiln for high-temperature oxidation roasting.

[0021] The grate-rotary kiln pelletizing production line is equipped with dust removal and desulfurization systems that meet emission requirements, and the particulate matter emission is less than 10mg / m 3 , sulfur dioxide emissions less than 35mg / m 3 .

[0022] The main exhaust fan of the independent chain grate-rotary kiln pelletizing production line has sufficient operating capacity, with an operating margin of about 20%.

[0023] There are partition walls between the grate drying section I and the drying section II, and between the drying section II and the preheating section. There is a connecting window on the partition wall B1, and the area of ​​the connecting window is 0.33m 2 .

[0024] The chain grate is equipped with bellows No. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 in sequence starting from the side close to the rotary furnace. The bellows are arranged in two symmetrical rows on both sides of the chain grate. Bellows No. 1-6 are in the preheating section, bellows No. 7-8 are in the drying section II, bellows No. 9-12 are in the drying section I. A roller screen is provided on the chain grate.

[0025] Flue gas outlets are provided on one side of the wind box of the preheating section and drying section I respectively, and the flue gas outlet of drying section I is connected to the electrostatic precipitator; a second-stage air inlet of the ring cooler is provided on the other side of drying section II, and an air inlet is provided in drying section I.

[0026] The flue gas outlet of the preheating section is connected to the inlet of the multi-tube dust collector, the outlet of the multi-tube dust collector is connected to the inlet of the SCR denitration reactor, the outlet circulation fan of the SCR denitration reactor is connected, and the circulation fan is connected to the air inlet of the drying stage I.

[0027] The catalyst of the SCR denitrification reactor is a vanadium-titanium catalyst.

[0028] The ring cooler adopts three-stage cooling and scientifically recycles and utilizes waste heat.

[0029] A burner is arranged on the rotary kiln near the side of the ring cooler; the ring cooler is divided into the first ring cooling section, the second ring cooling section and the third ring cooling section from the end connected to the rotary kiln, and there is a ring cooling fan on the first, second and third ring cooling sections respectively; there are partition walls between the first, second and third ring cooling sections; the first ring cooling section is provided with a flat material pile, a windbreak wall and a discharge port in a counterclockwise direction.

[0030] The air from the first ring cooling stage comes out from the first ring cooling stage outlet and enters the rotary kiln. The air from the second ring cooling stage comes out from the second ring cooling stage outlet and enters the second ring cooling machine air inlet of the drying stage II. The air from the third ring cooling stage is connected to the waste heat recovery device for recovery.

[0031] The denitration process of the optimized chain grate-rotary kiln SCR denitration system of the present invention comprises:

[0032] The heat required for oxidative roasting of pellets comes from the fuel sprayed by the burner at the head (discharging end) of the rotary kiln. The fuel of the chain grate-rotary kiln independent pellet production line is mainly based on relatively economical pulverized coal. Wind and flue gas are the main media for conducting heat energy. After the fuel is burned, high-temperature gas of 1300℃ is generated to oxidatively roast the pellets in the rotary kiln. The flue gas with a temperature of 950℃-1000℃ generated at the kiln tail directly enters the preheating section of the chain grate. The flue gas of the preheated pellets passes through the multi-tube dust collectors symmetrically on both sides of the chain grate, and is led to the drying section I of the chain grate by the corresponding circulating fans to dry the pellets.

[0033] After the hot pellets after oxidation roasting enter the ring cooler, the hot air temperature generated by the ring cooling section I reaches 1000℃-1100℃, and directly passes through the kiln head cover into the rotary kiln for recycling. The hot air temperature generated by the ring cooling section II is about 600℃-650℃, and is led to the chain grate drying section II through the ring hot air duct. The exhaust gas generated by the chain grate drying section II and the exhaust gas from the drying section I are led to the electrostatic dust collectors symmetrically distributed on both sides of the chain grate through the flues on both sides, and then led to the flue gas desulfurization system through the main exhaust fan to treat the pollutants and meet the emission standards.

[0034] The air from the ring cooling section enters the rotary kiln to assist combustion, and the high-temperature flue gas after combustion enters the preheating section of the chain grate;

[0035] The hot air from the second ring cooling section enters the drying section II, and the waste heat utilization is fully guaranteed. The hot air temperature is not less than 600℃. Part of the high-temperature flue gas is led to the drying section II through the connecting window on the partition wall between the drying section II and the preheating section to dry the pellets. The flue of the preheating section is extended to the outlet of the No. 6 bellows, and the partition wall is set between the No. 6 bellows and the No. 7 bellows. The flue gas from the preheating section enters the multi-tube dust collector and then enters the SCR denitrification system for treatment. After denitrification, it is led to the chain grate drying section I through the circulating fan, and then discharged into the atmosphere after further dust removal, purification and desulfurization.

[0036] The circulating fan adopts variable frequency regulation, and the operating margin is not less than 20%; the inlet temperature of the SCR denitrification reactor is between 300℃-400℃.

[0037] The segmented technical transformation of the chain grate in the present invention effectively controls the escape of nitrogen oxides in the flue gas, and the SCR denitrification reactor is more fully utilized. In the normal production process, the emission concentration of nitrogen oxides is controlled at 15mg / Nm 3 Left and right (O 2 The content is about 18%), and the converted emission concentration is less than 45mg / Nm 3, the ammonia consumption is reduced by about 15% compared with the initial design; after the innovation of the chain grate segmentation technology, the space of the drying section II is reduced by one third, and the waste heat utilization level of the ring cooler section II is improved. Under the condition of meeting the pellet drying temperature requirements and the pellet cooling needs of the ring cooler section II, the cooling air volume can be reduced accordingly, which promotes the O 2 The content of 20% tantalum was reduced; the production process was further optimized, and the temperature level of the drying stage II was increased by about 50℃ on average year-on-year, and the linear temperature rise was more reasonable. The waste heat air volume from the ring cooler stage II to the drying stage II was reduced accordingly, which effectively promoted the formation of negative pressure in the rotary kiln, and the heat conduction was smoother. The temperature of the preheating stage was increased by 50℃-100℃, which improved the quality of the preheating of the pellets. The strength of the preheating dry ball was increased by 50N-100N, which reduced the ringing and agglomeration in the kiln. The quality of the pellets was significantly improved, and the problem of low compressive strength of the pellets was further improved on the basis of being effectively solved.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The chain grate segmentation technology optimized by the present invention performs SCR denitrification, and the denitrification effect is higher than expected, achieving nitrogen oxide emission standards, with a nitrogen oxide emission concentration of <45mg / Nm 3 , reduce the usage of ammonia water as a denitrification reducing agent;

[0040] (2) The optimized chain grate-rotary kiln SCR denitrification method of the present invention improves the utilization level of waste heat from the ring cooler II stage, and the O 2 The concentration decreased by 0.5% year-on-year;

[0041] (3) The optimized chain grate-rotary kiln SCR denitrification system of the present invention increases the temperature level of the drying stage II by an average of about 50°C year-on-year, makes the linear temperature rise more reasonable, effectively promotes the formation of negative pressure in the rotary kiln, increases the temperature of the preheating stage by 50°C-100°C, improves the preheating quality of the pellets, increases the preheating dry ball strength by 50N-100N, improves the quality of the pellets, and further increases the compressive strength of the pellets. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of the chain grate-rotary kiln pellet production process in Example 1;

[0043] Figure 2 Schematic diagram of the chain grate-rotary kiln structure in Example 1;

[0044] Figure 3 is a schematic diagram of the structure of the ring cooler in Example 1;

[0045] Figure 4 It is a schematic diagram of the chain grate-rotary kiln SCR destocking process in Example 1;

[0046] Figure 5 It is a schematic diagram of a non-completely disconnected partition wall between the drying section II and the preheating section of the grate machine in Example 1;

[0047] Figure 6 is a schematic diagram of the chain grate after segmentation in Example 2;

[0048] Figure 7 is a schematic diagram of the chain grate after segment optimization in Example 3;

[0049] Figure 8 It is a schematic diagram of the optimized non-completely disconnected partition wall between the chain grate drying section II and the preheating section in Example 3;

[0050] 1. Chain grate; 2. Drying section I; 3. Partition wall A; 4. Drying section II; 5. Partition wall B; 6. Preheating section; 7. Rotary kiln; 8. Burner; 9. Waste heat recovery device; 10. Annular cooler; 11. Multi-tube dust collector; 12. Circulating fan; 13. Electrostatic dust removal device; 14. Bellows; 15. SCR denitration system; 16. Connecting window a; 17. Partition wall B1; 18. Connecting window a1;

[0051] 10-01, first stage of circular cooling; 10-02, third stage of circular cooling; 10-03, second stage of circular cooling; 10-04, circular cooling machine; 10-05, 1# circular cooling fan; 10-06, first stage of circular cooling; 10-07, partition wall a; 10-08, second stage of circular cooling; 10-09, 2# circular cooling fan; 10-10, partition wall b; 10-11, third stage of circular cooling; 10-12, 3# circular cooling fan; 10-13, partition wall c; 10-14, discharge port; 10-15, windbreak wall; 10-16, flat material lump; 10-17, finished product belt. DETAILED DESCRIPTION

[0052] The present invention is described below with reference to the embodiments, but the present invention is not limited thereto.

[0053] Example 1

[0054] like Figure 1 As shown, this embodiment provides a chain grate-rotary kiln production process, and the main process of the chain grate-rotary kiln pellet production process includes batching, pelletizing, screening and distributing materials, drying and preheating, oxidation roasting and cooling. The finely ground iron ore concentrate powder with a small amount of additives is rolled into balls, and then evenly distributed to the grate bed of the chain grate after screening, and then enters the chain grate for drying and preheating, and then enters the rotary kiln for oxidation roasting, and finally enters the ring cooler for secondary oxidation and gradually cools to room temperature.

[0055] Grate-rotary kiln device, such as Figure 2As shown; after being dried, dehydrated and preliminarily oxidized and preheated in the chain grate 1, the green balls become preheated dry balls with a certain temperature and strength and enter the rotary kiln for high-temperature oxidation roasting; the chain grate 1 is usually divided into a drying section I 2, a drying section II 4, and a preheating section 6. There is a partition wall A3 between the drying section I 2 and the drying section II 4, and there is a partition wall B5 between the drying section II 4 and the preheating section 6; the ring cooler 10 is usually a three-stage cooling, including a ring cooling section I 10-06, a ring cooling section II 10-08, and a ring cooling section III 10-11, and the waste heat is scientifically recycled and utilized. The structure of the ring cooler 10 is as follows Figure 3 shown.

[0056] The heat required for oxidative roasting of pellets comes from the fuel sprayed by the burner 8 at the kiln head (discharging end) of the rotary kiln 7. The fuel of the chain grate-rotary kiln independent pelletizing production line is mainly economical pulverized coal. Wind and flue gas are the main media for conducting heat energy. After the fuel is burned, high-temperature gas of about 1300°C is generated to oxidatively roast the pellets in the rotary kiln 7. The flue gas (about 950°C-1000°C) generated at the kiln tail directly enters the chain grate preheating section 6. The flue gas of the preheated pellets passes through the multi-tube dust collectors 11 symmetrical on both sides of the chain grate 1, and is then led by the corresponding circulating fans 12 to the chain grate drying section I 2 to dry the pellets.

[0057] After the hot pellets after oxidation roasting enter the ring cooler 10, the temperature of the hot air generated by the first ring cooling stage 10-06 can reach 1000℃-1100℃, and directly enter the rotary kiln 7 through the kiln head cover for recycling. The temperature of the hot air generated by the second ring cooling stage 10-08 is about 600℃-650℃, and is led to the chain grate drying stage II 4 through the ring hot air duct. The tail gas generated by the chain grate drying stage II 4 and the tail gas of the drying stage I 2 are respectively led to the electrostatic dust removal devices 13 symmetrically distributed on both sides of the chain grate through the flues on both sides, and are led to the flue gas desulfurization system through the main exhaust fan to treat the pollutants and meet the emission standards; the heat generated by the third ring cooling stage 10-11 is recycled through the waste heat recovery device 9.

[0058] In the chain grate-rotary kiln pellet production process, the oxidative roasting temperature of pellets using coal powder as fuel is around 1250℃-1300℃, and the flame temperature is around 1400℃-1500℃, which has the conditions for the rapid generation of thermal NOx. At the same time, fuel-type nitrogen oxides account for a certain proportion. The generation of nitrogen oxides in the pellet production process is closely related to temperature changes.

[0059] The flue gas composition of the 600,000-ton chain grate-rotary kiln independent pelletizing production line was tested. The flue gas volume was measured at the existing total exhaust port, the outlet of the multi-tube dust collector before the circulating fan, and the working condition was wet basis. The actual oxygen content was 18.5-19.5%; the nitrogen oxides (NOx) in the flue gas were measured at the existing desulfurization outlet without oxygen content conversion; the sulfur dioxide (SO 2) is online data, the operating condition is 90% of the operating time is less than 35mg / Nm 3 , the test results are shown in Table 1:

[0060] Table 1 Flue gas composition of 600,000 ton chain grate-rotary kiln independent pelletizing production line

[0061]

[0062]

[0063] According to Shandong Province's "Standards for Air Pollutants in the Iron and Steel Industry" (DB 37 / 990-2019), starting from November 1, 2020, the limit of NOx emission concentration under the condition of 16% oxygen content is 50mg / Nm 3 At present, the total outlet nitrogen oxides of the pelletizing production line have an oxygen content of 18.5-19.5%, and the pollutant emission concentration reaches 70mg / Nm 3 Therefore, the flue gas emission system must be treated with higher standards of denitrification technology.

[0064] Combined with the characteristics of the chain grate-rotary kiln flue gas system, SCR technology has a significant effect on flue gas NOx control and can achieve a NOx removal efficiency of up to 80%-90%. It has the advantages of mature technology, high denitrification efficiency, small footprint, easy operation, stability and reliability. It is one of the main means of controlling NOx pollution in sintering flue gas and pelletizing flue gas in my country, and is more suitable for the denitrification technology of the chain grate-rotary kiln independent pelletizing production line.

[0065] SCR technology is a process in which NH 3 As a reducing agent, it reduces NOx to N in the temperature range of 250℃-410℃ 2 and H 2 O. In the chain grate-rotary kiln pelletizing process, the flue gas temperature at the inlet of the circulating fan is usually between 300℃ and 380℃. The SCR technology is suitable for installation in the flue between the multi-tube dust removal and the circulating fan. After denitrification, the flue gas is led to the chain grate drying section I through the circulating fan, and then discharged into the atmosphere after further dust removal, purification and desulfurization.

[0066] Schematic diagram of chain grate-rotary kiln SCR destocking process, such as Figure 4 shown.

[0067] Through the initial design scheme of applying the SCR combined denitrification process to the chain grate-rotary kiln independent pellet production, according to the grate-rotary kiln pellet production process requirements, the partition wall B5 between the chain grate drying section II 4 and the preheating section 6 is a non-completely disconnected partition. The purpose is to lead part of the high-temperature flue gas from the preheating section to the drying section II 4 through the connecting window a16, so as to solve the problem of no waste heat utilization in the second stage of the annular cooler in the initial stage of production operation or insufficient temperature of the second stage of the annular cooler during production, which affects the normal drying of the pellets.

[0068] The partition wall B5 between the drying section II 4 and the preheating section 6 of the chain grate 1 is as follows: Figure 5 shown.

[0069] Example 2

[0070] The chain grate-rotary kiln SCR denitrification process in Example 1 and the connecting window a16 on the partition wall B5 between the chain grate drying section II 4 and the preheating section 6 are set. The heat of the chain grate drying section II 4 comes from the waste heat of the second stage of the ring cooler. From the analysis of the temperature range and the properties of the heat source, the nitrogen oxides in the flue gas coming out of the drying section II can be ignored. However, due to the presence of the connecting window a16 on the partition wall B5 between the chain grate drying section II 4 and the preheating section 6, part of the high-temperature flue gas in the preheating section will enter the drying section II 4 due to the change in the pressure difference between the two sections. This part of the high-temperature flue gas cannot be denitrified by the SCR reaction system, and there is a phenomenon of nitrogen oxide escape, which directly affects the final nitrogen oxide emission index in the flue gas. Therefore, it is necessary to continue technical innovation in the segmentation technology of the chain grate.

[0071] The purpose of the chain grate segmentation technology innovation is to provide a technical means to optimize the SCR denitrification process of the chain grate-rotary kiln independent pelletizing production line and improve the denitrification efficiency through scientific and reasonable adjustment and technical improvement of the chain grate segmentation method.

[0072] The steps for implementing the chain grate segmentation technology innovation are:

[0073] (1) The nitrogen oxide content in the flue gas of the No. 6, 7, and 8 bellows of the drying section II 4 was tested; the testing steps were: first, the thermocouple jacks of the No. 6, 7, and 8 bellows of the chain grate drying section II 4 were selected as the flue gas testing points, and then the test was carried out during the normal production operation, and the data was recorded in detail. Finally, the data was analyzed, and the test results are shown in Table 2:

[0074] Table 2 Detection results of nitrogen oxide content in flue gas

[0075] Detection point Left bellows 6 Left bellows 7 Left bellows 8 Right bellows 6 Right bellows 7 Right bellows 8 average value Temperature(℃) 249 202 142 290 225 135 207 <![CDATA[NOx(mg / m 3 )]]> 82 27 61 116 73 77 73 <![CDATA[O 2 (℃)]]> 18 20.14 18.6 17 18.5 18.5 18.5

[0076] It can be seen from Table 2 that the average NOx content in the flue gas of the chain grate drying stage Ⅱ 4 is 73 mg / m 3, which is higher than the average value of the total discharge port. In particular, the NOx content of the flue gas in the wind box 6 close to the preheating section is relatively high, which fully demonstrates that the high-temperature flue gas in the preheating section can enter the drying section II 4 through the window connecting the partition wall.

[0077] (2) Redesign of chain grate segmentation scheme and result demonstration:

[0078] Solution 1: Reduce or directly block the connecting window a16 between the drying section II and the preheating section;

[0079] The necessity of setting up the interconnecting window and its size are obtained through process calculations and production practice. Once it is reduced or blocked, it will affect the drying quality of the pellets in the initial stage of resumption of production and daily production. This solution is not advisable.

[0080] Option 2: Extend the flue of preheating section 6 to the outlet of wind box No. 6, and keep the partition wall B117 in the original position between wind box No. 5 and wind box No. 6. The schematic diagram of the chain grate after segmentation is as follows: Figure 6 As shown;

[0081] According to the actual measurement results of the flue gas from the grate drying section Ⅱ 4, it was found that the NOx content in the flue gas from the No. 6 wind box near the preheating section 4 was relatively high. # After the bellows outlet, it can be led to the SCR denitrification system through a circulating fan for denitrification treatment. The scheme is theoretically feasible.

[0082] Scheme 2 was adopted to carry out SCR denitrification of the chain grate-rotary kiln independent pelletizing production line. The nitrogen oxide content in the flue gas of bellows 6, 7, and 8 of drying section II 4 was retested, and the strength after pelletizing was tested. The test results are shown in Table 3: The total discharge nitrogen oxide content and the strength of the finished pellets were tested, and the test results are shown in Table 4.

[0083] Table 3 Detection results of nitrogen oxide content in flue gas of drying stage II

[0084]

[0085]

[0086] Table 4 Total outlet nitrogen oxide content test results and finished pellet strength test results

[0087]

[0088] According to Table 3, the denitrification and denitrification effect of Scheme 2 can basically meet the expectations, but the stability of nitrogen oxide emission indicators is poor. More importantly, the compressive strength of pellets has dropped significantly, from the normal value of 2500N to below 2000N. The main reason for the instability of nitrogen oxide emission indicators and the decrease in compressive strength of pellets is that after the preheating section flue is extended to the outlet of the No. 6 wind box, the original operating state of the flue gas in the drying section II is broken, and the flue gas has two emission directions: the main exhaust fan and the circulating fan. In the normal production process, due to the actual operation needs, When the air volume of the main exhaust fan, circulating fan and the second stage of the ring cooler is adjusted, there is uncertainty in the direction of the flue gas in the drying stage II 4. When the suction force of the main exhaust fan is too large, the escape of nitrogen oxides increases, affecting the emission concentration; when the suction force of the circulating fan is too large, the flue gas in the drying stage II 4 is concentrated at the outlet of the No. 6 bellows, affecting the air flow distribution of the No. 7 and No. 8 bellows. The drying process of the pellets in this section is affected, and linear temperature rising drying preheating cannot be achieved. When the pellets instantly enter the high temperature zone for preheating and oxidation, a relatively solid "shell" is formed on the outside, and the strength inside and outside is different, resulting in a significant reduction in the compressive strength of the finished pellets.

[0089] Example 3

[0090] The scheme 2 in Example 2 cannot meet the requirements of stable nitrogen oxide emission indicators and high compressive strength of pellets, so the scheme 2 is continued to be optimized, the flue 6 of the preheating section is extended to the outlet of the No. 6 wind box, and the partition wall B117 is moved from between the No. 5 wind box and the No. 6 wind box to between the No. 6 wind box and the No. 7 wind box. The schematic diagram of the segmented optimization of the chain grate is as follows: Figure 7 As shown;

[0091] Thus, the drying section II 4 and the preheating section 6 are effectively separated, the space of the drying section II 4 is reduced, the smoke in this section is only discharged in the main extraction direction, the air flow distribution is uniform and stable, and the pellet drying process is not affected;

[0092] After the drying section Ⅱ 4 is shortened, the space of drying section Ⅱ is reduced by one third, the capacity is reduced accordingly, and the heat demand required for preheating section compensation is reduced accordingly. The area of ​​the connecting window a118 set on the partition wall B117 is increased from the original area of ​​the connecting window a16 by 0.5m 2 Reduced to 0.33m 2 , the amount of flue gas entering the drying section II 4 from the preheating section is reduced, and the escape of nitrogen oxides is further reduced. The schematic diagram of the optimized non-completely disconnected partition wall between the chain grate drying section II 4 and the preheating section 6 is as follows: Figure 8 shown.

[0093] According to the optimized plan, the SCR denitrification of the chain grate-rotary kiln independent pelletizing production line was carried out, and the nitrogen oxide content in the flue gas of the 6th, 7th and 8th bellows of the drying section II 4 was retested. The test results are shown in Table 5; and the total discharge nitrogen oxide content and the strength of the finished pellets were tested. The test results are shown in Table 6.

[0094] Table 5 Detection results of nitrogen oxide content in flue gas of drying stage II

[0095]

[0096] Table 6 Total outlet nitrogen oxide content test results and finished pellet strength test results

[0097]

[0098] According to Tables 5 and 6, it can be seen that the optimized chain grate-rotary kiln SCR denitrification system has achieved the expected denitrification effect, and the nitrogen oxide emission indicators are stable, and the compressive strength of the pellets is greater than 2500N.

Claims

1. An optimized chain grate-rotary kiln SCR denitrification system, characterized by: The invention comprises a chain grate machine (1), a rotary kiln (7), an annular cooler (10), an SCR denitration system (15), a multi-tube dust collector (11), and a circulating fan (12); the chain grate machine is divided into a drying section I (2), a drying section II (4), and a preheating section (6) in a "three-section and two-chamber" manner; two sets of SCR denitration systems (15) are arranged between the multi-tube dust collector (11) and the circulating fan (12), and are distributed on both sides of the chain grate machine (1); The chain grate (1) is provided with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 wind boxes (14) in sequence starting from the side close to the rotary kiln (7). The wind boxes are arranged in two symmetrical rows on both sides of the chain grate. Wind boxes No. 1 to 6 are in the preheating section (6), wind boxes No. 7 to 8 are in the drying section II (4), and wind boxes No. 9 to 12 are in the drying section I (2). The outlet of the multi-tube dust collector (11) is connected to the inlet of the SCR denitration system (15), the outlet of the SCR denitration system (15) is connected to the circulation fan (12), and the circulation fan (12) is connected to the flue gas inlet of the drying stage I (2); There is a partition wall A (3) between the drying section I (2) and the drying section II (4) of the chain grate machine; there is a partition wall B1 (17) between the drying section II (4) and the preheating section (6), and there is a connecting window a1 (18) on the partition wall B1 (17); the area of ​​the connecting window a1 is 0.33m 2 ; A burner (8) is provided on one end of the rotary kiln (7) near the annular cooler (10); the annular cooler (10) is provided with an annular cooling section (10-06), an annular cooling section (10-08), and an annular cooling section (10-11) in sequence from the end connected to the rotary kiln (7); the annular cooling section (10-05), the annular cooling section (10-09), and the annular cooling section (10-12) are provided with a 1# annular cooling fan (10-05), a 2# annular cooling fan (10-09), and a 3# annular cooling fan (10-12) respectively; partition walls a (10-07), a partition wall b (10-10), and a partition wall c (10-13) are provided between the annular cooling section (10-06); a flat material block (10-16), a windshield wall (10-15), and a discharge port (10-14) are provided in sequence counterclockwise direction on the annular cooling section (10-06); The first ring cooling section (10-06) is connected to the rotary kiln (7), the second ring cooling section (10-08) is connected to the drying section II (4) through the second ring cooling machine air inlet of the drying section II (4), and the third ring cooling section (10-11) is connected to the waste heat recovery device (9).

2. The optimized chain grate-rotary kiln SCR denitrification system according to claim 1 is characterized in that: A flue gas outlet is provided on one side of the wind box of the preheating section (6) and the drying section I (2), respectively. The flue gas outlet of the preheating section (6) is connected to the inlet of the multi-tube dust collector (11), and the flue gas outlet of the drying section I (2) is connected to the electrostatic dust removal device (13). A second-stage air inlet of the ring cooler is provided on the drying section II (4) on the other side, and a flue gas inlet is provided on the drying section I.

3. A denitration process of the optimized chain grate-rotary kiln SCR denitration system according to any one of claims 1 to 2, characterized in that: include: The air from the ring cooling section (10-06) enters the rotary kiln (7) to assist combustion, and the high-temperature flue gas after combustion enters the preheating section (6) of the chain grate (1); The hot air from the second ring cooling section (10-08) enters the drying section (4), and the hot air temperature is not less than 600°C. A part of the high-temperature flue gas is introduced into the drying section (4) through the connecting window a1 (18) on the partition wall between the drying section (4) and the preheating section (6) to dry the pellets. The flue gas from the preheating section (6) is extended to the outlet of the No. 6 wind box (14), and the partition wall B1 (17) is set between the No. 6 wind box (14) and the No. 7 wind box (14). The flue gas from the preheating section (6) enters the multi-tube dust collector (11) and enters the SCR denitration system (15) for treatment. After denitration, the flue gas is introduced into the chain grate drying section (2) through the circulating fan (12), and then discharged into the atmosphere after dust removal and desulfurization by the electrostatic dust removal device (13). The catalyst of the SCR denitration system is a vanadium-titanium catalyst; The circulating fan (12) adopts variable frequency regulation, and the operating margin is not less than 20%; the inlet temperature of the SCR denitration and denitration system is between 300°C and 400°C.

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