Decomposition furnace deep self-denitration system with gasification furnace and two-stage combustion furnace and decomposition furnace deep self-denitration technology

Abstract

The invention relates to a deep self-denitration system and process for a decomposing furnace with a gasification furnace and a two-stage combustion furnace. The deep self-denitration system comprises a preheater, a rotary kiln, a kiln tail smoke chamber, the decomposing furnace and a tertiary air pipe, the decomposing furnace comprises a first-stage combustion furnace, a gasification furnace and a second-stage combustion furnace, the bottom of the first-stage combustion furnace is connected with the kiln tail smoke chamber, the bottom of the gasification furnace is connected with an outlet of the first-stage combustion furnace, an air inlet of the second-stage combustion furnace is connected with an outlet of the gasification furnace, and a final-stage cyclone inlet of the preheater is connected with an outlet of the second-stage combustion furnace; an air inlet of the second-stage combustion furnace is a volute type air inlet; the tertiary air pipe comprises a tertiary air lower branch pipe and a tertiary air upper branch pipe, the tertiary air lower branch pipe is connected with the side face of the lower portion of the first-stage combustion furnace, and the tertiary air upper branch pipe is connected with the bottom of the second-stage combustion furnace. The decomposition furnace is divided into the gasification furnace and the two-stage combustion furnace, the problem that fuel type NOx is gradually released in an extended range in the decomposition furnace and is difficult to deeply remove is solved through the graded design of tertiary air, pulverized coal and raw materials, and deep self-denitration is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of cement industry flue gas denitration, and in particular relates to a deep self-denitration system and process of a decomposition furnace with a gasification furnace and a two-stage combustion furnace. Background Art

[0002] Nitrogen oxides are gases produced when fossil fuels and air burn at high temperatures. They are highly toxic. Nitrogen oxide emissions affect air quality and have serious hazards to human living environment and health. The cement industry is the third largest emitter of nitrogen oxides after thermal power generation and automobile exhaust. At present, pulverized coal is a common fuel for cement kiln calcination. NOx in cement kiln flue gas is mainly produced during the combustion of pulverized coal in rotary kilns and decomposition furnaces. The type of NOx in cement rotary kilns is mainly thermal NOx, that is, NOx produced by oxidation of N2 in combustion-supporting air at high temperatures. During the combustion process, the higher the flue gas temperature, the faster the generation rate of thermodynamic NOx. The calcination temperature of cement clinker is generally as high as 1350-1450℃, and the concentration of NOx in the flue gas out of the kiln is often high, generally 800-1500ppm. After the rotary kiln flue gas is discharged from the kiln, it enters the decomposition furnace through the kiln tail smoke chamber. Reducing the NOx concentration in the flue gas out of the kiln is very important for improving the overall self-denitrification efficiency.

[0003] The calciner is used to realize the functions of raw material decomposition and fuel combustion. NO generated by combustion in the calciner x Fuel-type NO x Fuel NOx includes NO generated by N in the volatile matter. x and NO generated from the residual N in the coke x Two parts. Fuel type NO x It is mainly related to the nitrogen content in the coal powder and the combustion atmosphere. When the nitrogen content in the coal powder is high, the fuel type NO x Often higher. During the combustion of pulverized coal, volatiles are released quickly first, followed by the combustion of coke. Volatile nitrogen mainly includes HCN, NH3 and other initial products, which are the main precursors of NOx generation; there is also a part of nitrogen remaining in the coke, called coke nitrogen, which is released with the combustion of coal coke, and a part of it is directly oxidized to generate NO x A portion of it may be released in the form of HCN / NH3 and then further converted into NO x The coal powder in the decomposition furnace accounts for about 60% of the total coal powder in the burning system, and the combustion temperature is generally 900-1100℃, so the thermal NO x The amount of fuel NO generated can be ignored. x NO is generated by combustion in the decomposition furnace x The subject of.

[0004] Fuel combustion self-denitrification technology is a combustion technology that uses the control of fuel combustion characteristic parameters to inhibit the formation of NOx through the intermediate products formed during the combustion process without adding an external reducing agent (generally an amino reducing agent such as ammonia water and urea). With the improvement of environmental protection requirements, the denitrification operating costs of cement enterprises have further increased. Improving the efficiency of fuel combustion self-denitrification, reducing the denitrification operating costs and reducing secondary pollution are urgent tasks for the cement industry. Reducing NOx through the intermediate products of the combustion process is an environmental protection management method for source emission reduction, which is conducive to reducing the overall operating cost of denitrification. Chinese Patent Publication No. CN111750683A discloses a decomposition furnace zoned combustion self-denitrification system and process with adjustable oxygen concentration in the reduction zone. It uses part of the coal powder to burn in the kiln gas flue in the strong reduction zone with an oxygen coefficient of less than 0.8 to produce CO, and reduce the thermal NOx in the kiln flue gas. However, the coke in the pulverized coal leaving the reduction zone and another part of the pulverized coal continue to burn in the burnout zone. The coke N is continuously converted into NOx along the way in the burnout zone as the coke burns. However, there is no reducing atmosphere in the burnout zone, which causes the NOx concentration to rise again in the burnout zone, making it impossible to further reduce NOx emissions.

[0005] In summary, the problems existing in the prior art are:

[0006] (1) The staged combustion method of the decomposition furnace can reduce most of the thermal NOx generated in the rotary kiln, but it cannot reduce the fuel NOx generated by the combustion of coal powder in the decomposition furnace.

[0007] (2) After pyrolysis, pulverized coal produces volatile matter and coke. Under oxygen-deficient conditions, coke is difficult to ignite and burn. The coke then continues to burn in the burnout zone, and the coke N continues to generate NOx, causing fuel-type NOx to be gradually released during the decomposition furnace and difficult to remove deeply.

[0008] (3) After adopting graded combustion, the decomposition furnace cone is disconnected from the smoke chamber to increase the reduction zone. Since there is no kiln gas entering the bottom of the decomposition furnace, it is easy for the material to collapse into the rotary kiln.

[0009] With the improvement of environmental protection requirements, the denitrification operating costs of cement enterprises have further increased. Improving the efficiency of self-denitrification by fuel combustion, reducing the operating costs of denitrification, and reducing secondary pollution are the top priorities of the cement industry. Reducing NOx through the intermediate products of the combustion process is an environmental protection method of source emission reduction, which is conducive to reducing the overall operating costs of denitrification. For this reason, a deep self-denitrification system and process of a decomposition furnace with a gasification furnace and a two-stage combustion furnace is proposed. Summary of the invention

[0010] In view of the problems existing in the prior art, the present invention provides a deep self-denitrification system and process of a decomposition furnace with a gasification furnace and a two-stage combustion furnace. The decomposition furnace is divided into a gasification furnace and a two-stage combustion furnace, and through the graded design of tertiary air, pulverized coal and raw meal, not only the thermal NOx in the flue gas leaving the rotary kiln is completely reduced, but also part of the pulverized coal in the decomposition furnace releases NOx in advance and is reduced, which greatly reduces the concentration of NOx leaving the furnace, realizes deep self-denitrification, and solves the problem that fuel-type NOx is gradually released during the extended process of the decomposition furnace and is difficult to be deeply removed. It not only improves the self-denitrification efficiency, but also does not reduce the combustion speed of the decomposition furnace fuel and the complete decomposition of the raw meal. It is of great significance to the promotion and application of high-efficiency and low-cost denitrification technology for cement kiln flue gas.

[0011] The present invention is implemented as follows: a decomposition furnace deep self-denitrification system with a gasification furnace and a two-stage combustion furnace, comprising a preheater, a rotary kiln, a kiln tail smoke chamber connected to the rotary kiln tail, a decomposition furnace, and a tertiary air duct;

[0012] The decomposition furnace comprises a primary combustion furnace, a gasification furnace and a secondary combustion furnace. The bottom of the primary combustion furnace is connected to the kiln tail smoke chamber, the bottom of the gasification furnace is connected to the outlet of the primary combustion furnace, the air inlet of the secondary combustion furnace is connected to the outlet of the gasification furnace, and the inlet of the final cyclone of the preheater is connected to the outlet of the secondary combustion furnace; a primary combustion furnace coal powder feeding point and a primary combustion furnace raw material feeding point are arranged on the primary combustion furnace, a gasification furnace coal powder feeding point and a gasification furnace raw material feeding point are arranged on the gasification furnace, and a secondary combustion furnace raw material feeding point is arranged on the secondary combustion furnace;

[0013] The tertiary air duct includes a tertiary air lower branch pipe and a tertiary air upper branch pipe, the tertiary air lower branch pipe is connected to the lower side of the first-stage combustion furnace, and the tertiary air upper branch pipe is connected to the bottom of the second-stage combustion furnace.

[0014] Preferably, the primary combustion furnace includes a primary combustion furnace bottom necking, a primary combustion furnace cone, and a primary combustion furnace column which are sequentially connected from bottom to top; the primary combustion furnace coal powder feeding point is located above the lower branch of the tertiary air duct; the coal powder fed into the primary combustion furnace is completely burned in sufficient air to generate fuel-type NOx; the primary combustion furnace raw meal feeding point is located above the primary combustion furnace coal powder feeding point.

[0015] Further preferably, the coal powder feeding point of the primary combustion furnace is located on the cone of the primary combustion furnace, and the number of the coal powder feeding points of the primary combustion furnace is 1 to 4.

[0016] Further preferably, the raw meal feeding point of the primary combustion furnace is located at the lower part of the primary combustion furnace column or on the primary combustion furnace cone; the number of the raw meal feeding points of the primary combustion furnace is 1 or 2.

[0017] Preferably, the gasifier includes a gasifier cone, a gasifier column, and a gasifier outlet air duct which are sequentially connected from bottom to top. The raw material feeding point of the gasifier is located above the coal powder feeding point of the gasifier. The coal powder fed into the gasifier produces reducing gas under extremely oxygen-deficient and high-temperature conditions, so that the gasifier forms a strong reducing atmosphere, reducing the NOx in the rotary kiln flue gas and the fuel-type NOx generated in the primary combustion furnace.

[0018] Further preferably, the coal powder feeding point of the gasifier is located on the cone of the gasifier or at the bottom of the column of the gasifier, and the number of the coal powder feeding points of the gasifier is 1 to 4.

[0019] Further preferably, the raw material feeding point of the gasifier is located at the bottom of the gasifier column, and the number is 1.

[0020] Preferably, the secondary combustion furnace includes a secondary combustion furnace bottom necking, a secondary combustion furnace cone, a secondary combustion furnace column, and a secondary combustion furnace air inlet volute connected in sequence from bottom to top; the secondary combustion furnace air inlet volute is connected to the gasifier outlet air duct; the secondary combustion furnace air inlet volute has a wrap angle of 360°, and the relative position of the secondary combustion furnace raw meal feeding point and the secondary combustion furnace air inlet volute is: the secondary combustion furnace raw meal feeding point on the vertical plane is located in the middle of the secondary combustion furnace air inlet volute, and the secondary combustion furnace raw meal feeding point on the horizontal plane is located at 90-270° clockwise from the secondary combustion furnace air inlet volute; the volute-type air inlet at the secondary combustion furnace air inlet volute allows the raw meal sprinkled into the secondary combustion furnace to be evenly mixed on the cross-section of the secondary combustion furnace under the action of the swirling gas out of the gasifier, and then moves upward.

[0021] Further preferably, the raw meal feeding point of the secondary combustion furnace is located on the cone of the secondary combustion furnace or at the bottom of the column of the secondary combustion furnace or at the connection between the cone of the secondary combustion furnace and the column of the secondary combustion furnace, and the number of the raw meal feeding point of the secondary combustion furnace is 1.

[0022] Further preferably, the secondary combustion furnace air inlet volute is located on the secondary combustion furnace cone or at the connection between the secondary combustion furnace cone and the column.

[0023] Preferably, the tertiary air duct also includes a tertiary air vortex chamber, which is located below the bottom constriction of the secondary combustion furnace. The outlet of the tertiary air upper branch pipe is connected to the inlet of the tertiary air vortex chamber. The tertiary air vortex chamber is a 360° volute, and the flue gas leaving the gasification furnace and the tertiary air entering the secondary combustion furnace converge at the cone of the secondary combustion furnace.

[0024] Further preferably, a discharge bin and a material pipe connected to the discharge bin are provided below the tertiary wind vortex chamber, the other end of the material pipe is connected to the kiln tail smoke chamber, and a wind lock valve is provided on the material pipe.

[0025] Preferably, the tertiary air upper branch pipe and the tertiary air lower branch pipe are both provided with tertiary air valves.

[0026] Preferably, the number of stages of the preheater is 5 to 7, the discharge pipe of the last stage cyclone is connected to the kiln tail smoke chamber; the discharge pipe of the penultimate stage cyclone is respectively connected to the raw meal feeding point of the first combustion furnace, the raw meal feeding point of the gasification furnace, and the raw meal feeding point of the second combustion furnace.

[0027] The present invention also provides a deep self-denitrification process of a decomposition furnace with a gasification furnace and a two-stage combustion furnace, and the process is as follows:

[0028] The raw meal enters the preheater to complete preheating and gas-solid separation. After preheating, the raw meal enters the decomposition furnace for pre-decomposition. The feeding ratio of the preheated raw meal is adjusted to control the temperature in the primary combustion furnace at 850-1250℃, the temperature in the gasification furnace at 850-1100℃, and the temperature in the secondary combustion furnace at 850-1250℃;

[0029] The smoke from the rotary kiln enters the primary combustion furnace, and the pulverized coal is fed into the primary combustion furnace from the pulverized coal feeding point. The tertiary air distribution ratio of the tertiary air upper branch pipe is adjusted, and the wind speed of the tertiary air lower branch pipe entering the primary combustion furnace is not less than 10m / s. The excess oxygen coefficient in the primary combustion furnace is controlled to be 0.8-1.1, so that the volatile N and coke N in the pulverized coal are completely released to produce NOx;

[0030] The flue gas from the primary combustion furnace enters the gasifier, and coal powder is fed into the gasifier from the coal powder feeding point to control the excess oxygen coefficient in the gasifier to be less than 0.5. The coal powder produces reducing gas under extremely oxygen-poor and high-temperature conditions, so that a strong reducing atmosphere is formed in the gasifier, reducing the NOx in the flue gas of the rotary kiln and the flue gas from the primary combustion furnace, thus achieving deep self-denitrification.

[0031] The flue gas swirl from the gasification furnace enters the secondary combustion furnace, and the tertiary air swirl in the tertiary air upper branch pipe enters the secondary combustion furnace. The wind speed at the bottom of the secondary combustion furnace is controlled to be greater than 20m / s, and the excess oxygen coefficient in the secondary combustion furnace is greater than 1.0-1.2, so that the unburned volatile matter and coke in the pulverized coal can be fully burned in the secondary combustion furnace.

[0032] The present invention has the following advantages and beneficial effects:

[0033] 1. The decomposition furnace of the present invention comprises a gasification furnace and a two-stage combustion furnace, and through the hierarchical design of tertiary air, pulverized coal and raw meal, not only the thermal NOx in the smoke from the rotary kiln is completely reduced, but also part of the pulverized coal in the decomposition furnace is released in advance and reduced, thus realizing deep self-denitrification, solving the problem that fuel-type NOx is gradually released during the extended process of the decomposition furnace and is difficult to be deeply removed, thus improving the self-denitrification efficiency and not reducing the combustion speed of the decomposition furnace fuel and the complete decomposition of the raw meal; the present invention has no adverse effect on the cement clinker production process, has the advantages of reasonable system process, good reliability, strong adaptability, etc., can reduce the environmental protection management cost of the enterprise, can be promoted and applied in the new production line of cement engineering and the denitrification technical transformation of the old line, and has strong operability and practicality.

[0034] 2. The present invention divides the decomposition furnace into a primary combustion furnace, a gasification furnace, and a secondary combustion furnace. The coal powder is completely burned in the primary combustion furnace and the secondary combustion furnace to provide sufficient heat for the decomposition of raw materials. The coal powder is gasified in the gasification furnace to form a strong reducing atmosphere to reduce the NOx in the flue gas from the rotary kiln and the primary combustion furnace. Since the primary combustion furnace, the gasification furnace, and the secondary combustion furnace are independent of each other, the gas residence time can be adjusted to improve the coal powder burnout rate and self-denitrification efficiency, while improving the raw material decomposition rate, thereby achieving the purpose of environmental protection control and green production.

[0035] 3. The wrap angle of the volute of the air inlet of the secondary combustion furnace of the present invention is 360°, and by designing the relative position of the raw material feeding point of the secondary combustion furnace and the volute of the air inlet of the secondary combustion furnace, the raw material is first mixed evenly on the cross section of the secondary combustion furnace under the action of the swirling flue gas, and then suspended and flows upward. The swirling flow increases the contact time between the flue gas from the gasification furnace and the tertiary air, prolongs the residence time, and improves the fuel burnout rate; it also avoids the phenomenon of partial wind caused by only one raw material feeding point, and solves the problem of uneven combustion.

[0036] 4. The tertiary wind upper branch pipe of the present invention is provided with a tertiary wind vortex chamber, which can separate the tertiary wind flying sand into the kiln to avoid circulation in the secondary combustion furnace and increase the resistance of the secondary combustion furnace. In addition, the tertiary wind vortex chamber covers the tertiary wind swirl in the circumferential direction to avoid the material sliding down along the wall surface and short-circuiting the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a system schematic diagram of Embodiment 1 of the present invention;

[0038] Figure 2 Schematic diagram of the air inlet volute of the secondary combustion furnace of Example 1 of the present invention;

[0039] Figure 3 It is a schematic diagram of the tertiary wind vortex chamber of Example 1 of the present invention.

[0040] In the figure:

[0041] A-cooling air; B-exiting preheater flue gas;

[0042] a-raw material;

[0043] 1- primary combustion furnace; 101- bottom constriction of primary combustion furnace; 102- cone of primary combustion furnace; 103- column of primary combustion furnace; 104- coal powder feeding point of primary combustion furnace; 105- raw meal feeding point of primary combustion furnace;

[0044] 2-gasifier; 201-gasifier cone; 202-gasifier column; 203-gasifier coal powder feeding point; 204-gasifier raw material feeding point; 205-gasifier outlet air duct;

[0045] 3-secondary combustion furnace; 301-secondary combustion furnace bottom conical opening; 302-secondary combustion furnace cone; 303-secondary combustion furnace column; 304-secondary combustion furnace raw material feeding point; 305-secondary combustion furnace air inlet volute;

[0046] 4- tertiary air duct; 401- tertiary air lower branch pipe; 402- tertiary air upper branch pipe; 403- tertiary air valve; 404- tertiary air vortex chamber;

[0047] 501-unloading bin; 502-material pipe; 503-air lock valve;

[0048] 6-kiln tail smoke chamber; 7-rotary kiln; 8-cooler;

[0049] 9-preheater; 901-last stage cyclone; 902-second to last stage cyclone; 903-electric dispensing valve; 904-first stage cyclone;

[0050] 10- kiln head burner; 11- clinker storage;

[0051] The solid line with arrows is the material flow direction, and the dotted line with arrows is the air flow direction. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0053] Example 1

[0054] See also Figure 1 to Figure 3 The present invention provides a decomposition furnace deep self-denitrification system with a gasification furnace and a two-stage combustion furnace, comprising a preheater 9, a rotary kiln 7, a kiln tail smoke chamber 8 connected to the rotary kiln tail, a decomposition furnace, a tertiary air duct 4, a cooler 8, and a clinker storage 11. The decomposition furnace comprises a primary combustion furnace 1, a gasification furnace 2, and a secondary combustion furnace 3.

[0055] The working principle of the present invention to achieve the deep self-denitrification function is as follows: the rotary kiln flue gas enters the primary combustion furnace 1 after passing through the kiln tail smoke chamber 6. Since the sintering temperature of cement clinker in the rotary kiln 7 is generally 1350-1450°C, the NOx concentration in the rotary kiln flue gas is often high, generally 800-1500ppm, the O2 content is low, generally within 5%, and the CO2 content is high. Coal powder is sprayed into the cone 102 of the primary combustion furnace, and the tertiary air valve 403 on the tertiary air lower branch pipe 401 is adjusted to introduce sufficient tertiary air into the primary combustion furnace 1 to meet the oxygen demand for coal powder combustion. The volatile matter N and coke N are completely released to generate fuel-type NOx, and the generated NOx concentration is 100-500ppm. The rotary kiln flue gas enters the gasification furnace 2 together with the flue gas generated in the primary combustion furnace 1. The remaining pulverized coal is sprayed into the gasifier cone 203. Since there is only a small amount of oxygen in the coal supply air and the flue gas from the first-stage combustion furnace in the gasifier 2, the pulverized coal is incompletely burned to produce reducing gases such as CO, forming a strong reducing atmosphere. Under the catalytic action of coke, raw materials, etc., the reducing gases such as CO will reduce the thermal NOx in the flue gas from the rotary kiln and the fuel NOx in the flue gas from the first-stage combustion furnace. At the same time, when the pulverized coal is burned in a reducing atmosphere, the volatile N released by the pyrolysis of the pulverized coal tends to generate N2, and the NOx generated by the combustion of the fuel in the gasifier is suppressed.

[0056] The primary combustion furnace 1 comprises a primary combustion furnace bottom constriction 101, a primary combustion furnace cone 102, a primary combustion furnace column 103, a primary combustion furnace coal powder feeding point 104 and a primary combustion furnace raw material feeding point 105, which are sequentially connected from bottom to top. The primary combustion furnace bottom constriction 101 is connected to the kiln tail smoke chamber 8.

[0057] The primary combustion furnace coal powder feeding point 104 is located on the primary combustion furnace cone 102, specifically above the lower branch pipe 401 of the tertiary air duct. The number of primary combustion furnace coal powder feeding points 104 is 1 to 4. The coal powder is sprayed into the primary combustion furnace cone 102 and contacts with the high-temperature tertiary air, which helps the coal powder to ignite. The coal powder fed into the primary combustion furnace coal powder feeding point will be completely burned in sufficient air to generate combustion products such as CO2. The volatile N and coke N in the coal powder are released in advance as the coal powder is pyrolyzed and the coke is burned to generate fuel-type NOx. The proportion of coal powder sprayed into the primary combustion furnace 1 to the coal powder sprayed into the decomposition furnace is 40 to 70%.

[0058] The primary combustion furnace raw meal feeding point 105 is located at the lower part of the primary combustion furnace column 103 or on the primary combustion furnace cone 102; the number of the primary combustion furnace raw meal feeding point 102 is 1 or 2, and is located above the primary combustion furnace coal powder feeding point 104. The temperature of the primary combustion furnace is controlled to 850-1250°C by controlling the amount of raw meal entering the primary combustion furnace raw meal feeding point 105, ensuring the decomposition of the raw meal without affecting the coal powder combustion speed, so that the N in the coal powder is quickly released.

[0059] The wind speed of the cross section of the constriction 101 at the bottom of the primary combustion furnace is greater than 20m / s, which is used to prevent the raw material from short-circuiting through the bottom of the primary combustion furnace and entering the kiln tail smoke chamber 6 to affect the quality of cement clinker.

[0060] The gasifier 2 includes a gasifier cone 201, a gasifier column 202, a gasifier outlet air duct 205, a gasifier coal powder feeding point 203 and a gasifier raw material feeding point 204, which are sequentially connected from bottom to top. The gasifier cone 201 is connected to the outlet of the primary combustion furnace 1.

[0061] The coal powder feeding point 203 of the gasifier is located on the gasifier cone 201 or at the bottom of the gasifier column 202, and the number of coal powder feeding points 203 of the gasifier is 1 to 4. The coal powder feeding point of the gasifier forms a strong reducing atmosphere by injecting coal powder. This stream of coal powder is pyrolyzed into volatile matter and coke under extremely oxygen-poor and high-temperature conditions. The volatile matter of the coal powder is first released quickly to generate reducing gases such as CO, CH4, C2H4, HCN, and NH3. The coke reacts with CO2 or a small amount of O2 in the flue gas from the first combustion furnace to produce CO reducing gas, which reduces the NOx in the rotary kiln flue gas and the fuel-type NOx generated in the first combustion furnace 1. When the coal powder is burned in a reducing atmosphere, the volatile matter N released by pyrolysis tends to generate N2, and the NOx generated by the combustion of coal powder in the gasifier 2 is suppressed.

[0062] The gasifier raw material feeding point 204 is located at the bottom of the gasifier column 202 and above the gasifier coal powder feeding point 203, and the number is 1. The temperature in the gasifier is controlled to be 850-1100°C by controlling the amount of raw material entering the gasifier raw material feeding point 204.

[0063] The secondary combustion furnace 3 includes a secondary combustion furnace bottom constriction 301, a secondary combustion furnace cone 302, a secondary combustion furnace column 303, and a secondary combustion furnace air inlet volute 305 and a secondary combustion furnace raw material feeding point 304, which are sequentially connected from bottom to top. The secondary combustion furnace air inlet volute 305 is connected to the gasification furnace outlet air duct 205, and the outlet of the secondary combustion furnace 3 is connected to the inlet of the final cyclone 901 of the preheater 9.

[0064] The secondary combustion furnace raw material feeding point 304 is located on the secondary combustion furnace cone 302 or at the bottom of the secondary combustion furnace column 303 or at the connection between the secondary combustion furnace cone 302 and the secondary combustion furnace column 303. The number of the secondary combustion furnace raw material feeding point 304 is one.

[0065] The wrap angle of the secondary combustion furnace air inlet volute 305 is 360°, and the secondary combustion furnace air inlet volute 305 is located on the secondary combustion furnace cone 302 or at the connection between the secondary combustion furnace cone 302 and the secondary combustion furnace column 303 .

[0066] The relative position of the secondary combustion furnace raw meal feeding point 304 and the secondary combustion furnace air inlet volute 305 is: on the vertical plane, the secondary combustion furnace raw meal feeding point 304 is located in the middle of the secondary combustion furnace air inlet volute 305; on the horizontal plane, the secondary combustion furnace raw meal feeding point 304 is located at the secondary combustion furnace air inlet volute 305 clockwise at 90-270°.

[0067] The flue gas from the gasifier passes through the secondary combustion furnace air inlet volute 305, first swirls along the inner wall of the secondary combustion furnace 3, and then swirls upward along the wall. The angle between the wind direction of the flue gas from the gasifier and the horizontal direction entering the secondary combustion furnace is within the range of ±30°. The raw meal fed from the raw meal feeding point 304 of the secondary combustion furnace is sprinkled into the secondary combustion furnace 3. Under the action of the swirling flue gas from the gasifier, the raw meal is first mixed evenly on the cross section of the secondary combustion furnace 3, and then moves upward. This arrangement can avoid the situation where there is only one raw meal feeding point, which causes the tertiary air entering the secondary combustion furnace to preferentially go upward from the furnace space without raw meal, resulting in a skewed wind phenomenon and uneven combustion.

[0068] The temperature of the secondary combustion furnace is controlled to 850-1200°C by controlling the amount of raw material entering the raw material feeding point 304 of the secondary combustion furnace. The wind speed of the cross section of the conical opening 301 at the bottom of the secondary combustion furnace is greater than 20m / s, so that the raw material in the cone 302 of the secondary combustion furnace is suspended to prevent material collapse caused by short circuit of the material.

[0069] The main functions of the decomposition furnace are fuel combustion and raw material decomposition. The present invention divides the decomposition furnace into a primary combustion furnace 1, a gasification furnace 2, and a secondary combustion furnace 3. The coal powder is completely burned in the primary combustion furnace 1 and the secondary combustion furnace 2 to provide sufficient heat for raw material decomposition. The coal powder is gasified in the gasification furnace 2 to form a strong reducing atmosphere to reduce the NOx in the flue gas of the rotary kiln 7 and the primary combustion furnace 1. Since the primary combustion furnace, the gasification furnace, and the secondary combustion furnace are independent of each other, the gas residence time can be adjusted to improve the coal powder burnout rate and self-denitrification efficiency, while improving the raw material decomposition rate.

[0070] The tertiary air duct 4 includes a tertiary air lower branch 401 and a tertiary air upper branch 402. The tertiary air lower branch 401 is connected to the side of the primary combustion furnace cone 102, and the tertiary air upper branch 402 is connected to the bottom constriction 301 of the secondary combustion furnace.

[0071] The tertiary air duct 4 also includes a tertiary air vortex chamber 404, which is located below the bottom constriction 301 of the secondary combustion furnace. The outlet of the tertiary air upper branch pipe 402 is connected to the inlet of the tertiary air vortex chamber 404, and the tertiary air vortex chamber 404 is a 360° volute. The flue gas leaving the gasification furnace and the tertiary air entering the secondary combustion furnace merge at the decomposition furnace cone 302.

[0072] The tertiary wind upper branch pipe 402 is provided with a tertiary wind vortex chamber 404, which can separate and settle the tertiary wind flying sand and enter the rotary kiln 7 to avoid circulation in the secondary combustion furnace 3 and increase the resistance of the secondary combustion furnace 3. The flying sand has a large particle size, generally 1 to 5 mm, and the tertiary wind carrying the flying sand will increase the resistance when flowing upward in the secondary combustion furnace 3. In addition, the tertiary wind vortex chamber 404 covers the tertiary wind vortex in the circumferential direction to prevent the material from sliding down the wall and short-circuiting the material.

[0073] A discharge bin 501 and a material pipe 502 connected to the discharge bin 501 are provided below the tertiary wind vortex chamber 404, and the other end of the material pipe 502 is connected to the kiln tail smoke chamber 6. When an accident occurs and the machine is shut down, the material in the secondary combustion furnace 3 can fall into the discharge bin 501 under the action of gravity, and enter the kiln tail smoke chamber 6 through the material pipe 502, and then enter the rotary kiln 7, without the need for manual cleaning of the material. A lock valve 503 is provided on the material pipe 502 to prevent or reduce the kiln smoke in the kiln tail smoke chamber 6 from entering the secondary combustion furnace 3 through the material pipe 503.

[0074] A tertiary air valve 403 is provided on each of the tertiary air upper branch pipe 402 and the tertiary air lower branch pipe 401. The tertiary air valve 403 is adjusted to control the tertiary air volume on the corresponding branch pipe.

[0075] The number of stages of the preheater 9 is 5 to 7. The discharge pipe of the last stage cyclone 901 is connected to the kiln tail smoke chamber 6; the discharge pipe of the penultimate stage cyclone 902 is respectively connected to the raw material feeding point 105 of the first combustion furnace, the raw material feeding point 204 of the gasification furnace, and the raw material feeding point 304 of the second combustion furnace. The discharge pipe of the penultimate stage cyclone 902 is equipped with two electric distributing valves 903 to ensure stable and uniform distributing.

[0076] In summary, the decomposition furnace of the present invention comprises a gasification furnace and a two-stage combustion furnace, and through the hierarchical design of tertiary wind, coal powder and raw materials, part of the coal powder is first completely burned in the primary combustion furnace to release NOx, and then the remaining coal powder is sprayed into the gasification furnace without supplementing the tertiary wind, forming a strong reducing atmosphere, reducing the thermal NOx in the flue gas out of the kiln and the fuel NOx generated in the primary combustion furnace, and finally the coal powder continues to burn in the secondary combustion furnace, thereby realizing deep self-denitrification, not only completely reducing the thermal NOx in the flue gas out of the rotary kiln, but also making part of the coal powder in the decomposition furnace release NOx in advance and be reduced, solving the problem that the fuel NOx is gradually released in the decomposition furnace and is difficult to be deeply removed, and improving the self-denitrification efficiency, and not reducing the combustion speed of the decomposition furnace fuel and the complete decomposition of raw materials. The present invention has no adverse effects on the cement clinker production process, has the advantages of reasonable system process, good reliability, strong adaptability, etc., can reduce the environmental protection cost of enterprises, can be promoted and applied in the new production line of cement engineering and the denitrification technical transformation of old lines, and has strong operability and practicality.

[0077] Example 2

[0078] The above system is used to carry out the deep self-denitrification process of the decomposition furnace with a gasification furnace and a two-stage combustion furnace as follows: the raw material a after crushing, pre-homogenization, grinding and homogenization enters the preheater 9 to complete preheating and gas-solid separation; the flue gas B from the preheater enters the waste heat recovery system, and the material enters the decomposition furnace for pre-decomposition, and then enters the rotary kiln 7 through the kiln tail smoke chamber 6. The fuel is sent to the kiln head burner 10 to provide heat. The material undergoes rapid decomposition and a series of solid-phase reactions in the rotary kiln 7 to produce cement clinker. The high-temperature clinker discharged from the rotary kiln 7 falls onto the grate bed of the cooler 8, and is distributed along the entire length of the grate bed to form a material bed of a certain thickness. Under the action of the cooling air A blown into the grate bed below the cooler 8, the high-temperature clinker is cooled to a suitable temperature, and the low-temperature clinker is obtained and transported to the clinker warehouse 11. After the cooling air A cools the high-temperature clinker, the high-temperature secondary air obtained enters the rotary kiln 7; the tertiary air enters the secondary combustion furnace 3 after the tertiary air vortex chamber 404 settles the flying sand, and the flying sand enters the rotary kiln 7 after separation and sedimentation, avoiding circulation in the secondary combustion furnace 3 and increasing the resistance of the secondary combustion furnace 3. The flying sand particle size of the tertiary wind is large, generally 1 to 5 mm, and the tertiary wind carrying the flying sand flows upward in the secondary combustion furnace 3, which will increase the resistance. In addition, the tertiary air vortex chamber 404 covers the tertiary air swirl in the circumferential direction to prevent the material from sliding down the wall and short-circuiting the material.

[0079] The sintering temperature of cement clinker in the rotary kiln is generally 1350-1450°C. The NOx concentration in the rotary kiln flue gas is often high, generally 800-1500ppm, the O2 content is low, generally within 5%, and the CO2 content is high, at 15%-20%. The flue gas from the rotary kiln enters the primary combustion furnace 1. Coal powder is fed from the primary combustion furnace coal powder feeding point 104, and the air distribution ratio of the tertiary air is adjusted through the tertiary air valve 403 to control the excess oxygen coefficient in the primary combustion furnace 1 to be 0.8-1.1, so as to meet the oxygen demand for coal powder combustion, so that the volatile N and coke N in the coal powder are completely released to produce NOx, and the fuel type NOx concentration is about 100-500ppm. In order to avoid the problem of crusting caused by excessive temperature in the primary combustion furnace 1 due to coal powder combustion, and at the same time not affecting the coal powder combustion speed, the amount of raw material entering the primary combustion furnace raw material feeding point 105 is controlled to control the temperature in the primary combustion furnace 1 at 850-1250°C. The proportion of pulverized coal injected into the primary combustion furnace 1 to the pulverized coal injected into the decomposition furnace is 40-70%. The main reactions involved in the primary combustion furnace are:

[0080] CxHy+O2→CO2+H2O

[0081] Fuel N+O2→NOx

[0082] C+O2→CO2

[0083] The flue gas from the primary combustion furnace 1 enters the gasifier 2. Pulverized coal is fed from the pulverized coal feeding point 203 of the gasifier to control the excess oxygen coefficient in the gasifier to be less than 0.5. Under extremely oxygen-deficient conditions, the volatile matter in the pulverized coal is first released rapidly to produce reducing gases such as CH4, C2H4, CO, HCN, and NH3; under a reducing atmosphere, volatile N such as HCN and NH3 in the volatile matter tends to be converted into N2, which inhibits the generation of fuel NOx. The temperature in the gasifier 2 is controlled at 850-1100°C by controlling the amount of raw material entering the raw material feeding point 204 of the gasifier. The decomposition of raw material will produce metal oxides such as CaO, Fe2O3, and Al2O3. Coke, CO, CH4, HCN, and NH3 can all reduce NOx to N2. Under the catalytic action of metal oxides and coke, CO can quickly and efficiently reduce NOx, so that both thermal NOx in the flue gas from the rotary kiln and fuel NOx in the flue gas from the primary combustion furnace are reduced. The CO concentration in the gasifier 2 is 1-2%. The NOx concentration at the outlet of the gasifier is less than 50ppm. The main reactions involved in the gasifier are:

[0084] CxHy+O2→CO+H2O

[0085] HCN+O2→NO+CO+H2

[0086] C+CO2→CO

[0087] CxHy+NOx→HCN+CO+N2

[0088] HCN+NO→CO2+N2

[0089] CO+NOx→CO2+N2 (metal oxides in coke and raw materials as catalysts)

[0090] The flue gas from the gasifier enters the secondary combustion furnace 3 in a cyclone. The excess oxygen coefficient of the secondary combustion furnace 3 is controlled to be greater than 1.0-1.2. The tertiary air enters the secondary combustion furnace 3 in a cyclone from the tertiary air upper branch pipe 402, and the unburned volatile matter and coke in the pulverized coal are fully burned in the secondary combustion furnace 3 to ensure the decomposition of the raw material. The average temperature in the secondary combustion furnace 3 is controlled at 850-1250°C. Since the reducing gas in the gasifier 2 has reduced the NOx released by the volatile matter N and coke N in the pulverized coal in the primary combustion furnace 1, the coke N injected into the pulverized coal in the gasifier will greatly reduce the NOx released in the secondary combustion furnace 3 along with the combustion of coke, thereby effectively reducing the NOx concentration out of the decomposition furnace, so that part of the pulverized coal in the decomposition furnace releases NOx in advance and is reduced, realizing deep self-denitrification, and solving the problem that fuel-type NOx is gradually released during the extended process of the decomposition furnace and is difficult to remove deeply. The NOx concentration in the flue gas leaving the secondary combustion furnace 3 is 150-250ppm, the O2 content is less than 3%, and the CO content is less than 1000ppm.

[0091] The cross-sectional wind speed at the bottom shrinkage of the first-stage combustion furnace and the bottom shrinkage of the second-stage combustion furnace is greater than 20m / s, and the wind speed entering the furnace from the tertiary wind lower branch pipe is not less than 10m / s, which can suspend the raw material in the decomposition furnace and prevent material collapse caused by short circuit.

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A decomposition furnace deep self-denitrification system with a gasification furnace and a two-stage combustion furnace, comprising a preheater, a rotary kiln, a kiln tail smoke chamber connected to the kiln tail of the rotary kiln, a decomposition furnace, and a tertiary air duct; characterized in that: The decomposition furnace comprises a primary combustion furnace, a gasification furnace and a secondary combustion furnace. The bottom of the primary combustion furnace is connected to the kiln tail smoke chamber, the bottom of the gasification furnace is connected to the outlet of the primary combustion furnace, the air inlet of the secondary combustion furnace is connected to the outlet of the gasification furnace, and the inlet of the final cyclone of the preheater is connected to the outlet of the secondary combustion furnace; a primary combustion furnace coal powder feeding point and a primary combustion furnace raw material feeding point are arranged on the primary combustion furnace, a gasification furnace coal powder feeding point and a gasification furnace raw material feeding point are arranged on the gasification furnace, and a secondary combustion furnace raw material feeding point is arranged on the secondary combustion furnace; The tertiary air duct includes a tertiary air lower branch pipe and a tertiary air upper branch pipe, the tertiary air lower branch pipe is connected to the lower side of the first-stage combustion furnace, and the tertiary air upper branch pipe is connected to the bottom of the second-stage combustion furnace.

2. The deep self-denitrification system of a decomposition furnace with a gasification furnace and a two-stage combustion furnace according to claim 1 is characterized in that: The primary combustion furnace includes a primary combustion furnace bottom necking, a primary combustion furnace cone, and a primary combustion furnace column which are sequentially connected from bottom to top; the primary combustion furnace coal powder feeding point is located above the lower branch of the tertiary air duct; the coal powder fed into the primary combustion furnace is completely burned in sufficient air to generate fuel-type NOx; the primary combustion furnace raw meal feeding point is located above the primary combustion furnace coal powder feeding point.

3. The deep self-denitrification system of a decomposition furnace with a gasification furnace and a two-stage combustion furnace according to claim 2 is characterized in that: The coal powder feeding point of the primary combustion furnace is located on the cone of the primary combustion furnace, and the number of the coal powder feeding points of the primary combustion furnace is 1 to 4.

4. The deep self-denitrification system of a decomposition furnace with a gasification furnace and a two-stage combustion furnace according to claim 2 is characterized in that: The raw material feeding point of the primary combustion furnace is located at the lower part of the primary combustion furnace column or on the primary combustion furnace cone; the number of the raw material feeding points of the primary combustion furnace is 1 or 2.

5. The deep self-denitrification system of a decomposition furnace with a gasification furnace and a two-stage combustion furnace according to claim 1 is characterized in that: The gasifier includes a gasifier cone, a gasifier column, and a gasifier outlet air duct which are connected in sequence from bottom to top. The raw material feeding point of the gasifier is located above the coal powder feeding point of the gasifier. The coal powder fed into the gasifier produces reducing gas under extremely oxygen-poor and high-temperature conditions, so that the gasifier forms a strong reducing atmosphere, reducing NOx in the rotary kiln flue gas and fuel-type NOx generated in the primary combustion furnace.

6. The deep self-denitrification system of a decomposition furnace with a gasification furnace and a two-stage combustion furnace according to claim 5 is characterized in that: The coal powder feeding point of the gasifier is located on the cone of the gasifier or at the bottom of the column of the gasifier, and the number of the coal powder feeding points of the gasifier is 1 to 4.

7. The deep self-denitrification system of a decomposition furnace with a gasification furnace and a two-stage combustion furnace according to claim 5 is characterized in that: The raw material feeding point of the gasifier is located at the bottom of the gasifier column, and the number is 1.

8. The deep self-denitrification system of a decomposition furnace with a gasification furnace and a two-stage combustion furnace according to claim 1 is characterized in that: The secondary combustion furnace includes a secondary combustion furnace bottom constriction, a secondary combustion furnace cone, a secondary combustion furnace column, and a secondary combustion furnace air inlet volute which are connected in sequence from bottom to top; the secondary combustion furnace air inlet volute is connected to the gasifier outlet air duct; the secondary combustion furnace air inlet volute has a wrap angle of 360°, and the relative position of the secondary combustion furnace raw material feeding point and the secondary combustion furnace air inlet volute is: the secondary combustion furnace raw material feeding point is located in the middle of the secondary combustion furnace air inlet volute on the vertical plane, and the secondary combustion furnace raw material feeding point is located at 90-270° clockwise from the secondary combustion furnace air inlet volute on the horizontal plane; the volute-type air inlet at the secondary combustion furnace air inlet volute allows the raw material sprinkled into the secondary combustion furnace to be evenly mixed on the cross-section of the secondary combustion furnace under the action of the swirling gas out of the gasifier, and then move upward.

9. The deep self-denitrification system of a decomposition furnace with a gasification furnace and a two-stage combustion furnace according to claim 8 is characterized in that: The raw material feeding point of the secondary combustion furnace is located on the cone of the secondary combustion furnace or at the bottom of the column of the secondary combustion furnace or at the connection between the cone of the secondary combustion furnace and the column of the secondary combustion furnace. The number of the raw material feeding point of the secondary combustion furnace is one.

10. The deep self-denitrification system of a decomposition furnace with a gasification furnace and a two-stage combustion furnace according to claim 8, characterized in that: The secondary combustion furnace air inlet volute is located on the secondary combustion furnace cone or at the connection between the secondary combustion furnace cone and the column.

11. The deep self-denitrification system of a decomposition furnace with a gasification furnace and a two-stage combustion furnace according to claim 1, characterized in that: The tertiary air duct also includes a tertiary air vortex chamber, which is located below the bottom constriction of the secondary combustion furnace. The outlet of the tertiary air upper branch pipe is connected to the inlet of the tertiary air vortex chamber. The tertiary air vortex chamber is a 360° volute. The flue gas leaving the gasification furnace and the tertiary air entering the secondary combustion furnace converge at the cone of the secondary combustion furnace.

12. The deep self-denitrification system of a decomposition furnace with a gasification furnace and a two-stage combustion furnace according to claim 11, characterized in that: A discharge bin and a material pipe connected to the discharge bin are arranged below the tertiary wind vortex chamber, the other end of the material pipe is connected to the kiln tail smoke chamber, and a wind lock valve is arranged on the material pipe.

13. The deep self-denitrification system of a decomposition furnace with a gasification furnace and a two-stage combustion furnace according to claim 1, characterized in that: The tertiary air upper branch pipe and the tertiary air lower branch pipe are both provided with tertiary air valves.

14. The deep self-denitrification system of a decomposition furnace with a gasification furnace and a two-stage combustion furnace according to claim 1, characterized in that: The number of stages of the preheater is 5 to 7, the discharge pipe of the last stage cyclone is connected to the kiln tail smoke chamber; the discharge pipe of the penultimate stage cyclone is respectively connected to the raw material feeding point of the first combustion furnace, the raw material feeding point of the gasification furnace, and the raw material feeding point of the second combustion furnace.

15. A deep self-denitrification process of a decomposition furnace with a gasification furnace and a two-stage combustion furnace, using the self-denitrification system according to any one of claims 1 to 14, characterized in that: The process is as follows: The raw meal enters the preheater to complete preheating and gas-solid separation. After preheating, the raw meal enters the decomposition furnace for pre-decomposition. The feeding ratio of the preheated raw meal is adjusted to control the temperature in the primary combustion furnace at 850-1250℃, the temperature in the gasification furnace at 850-1100℃, and the temperature in the secondary combustion furnace at 850-1250℃; The smoke from the rotary kiln enters the primary combustion furnace, and the pulverized coal is fed into the primary combustion furnace from the pulverized coal feeding point. The tertiary air distribution ratio of the tertiary air upper branch pipe is adjusted, and the wind speed of the tertiary air lower branch pipe entering the primary combustion furnace is not less than 10m / s. The excess oxygen coefficient in the primary combustion furnace is controlled to be 0.8-1.1, so that the volatile N and coke N in the pulverized coal are completely released to produce NOx; The flue gas from the primary combustion furnace enters the gasifier, and coal powder is fed into the gasifier from the coal powder feeding point to control the excess oxygen coefficient in the gasifier to be less than 0.

5. The coal powder produces reducing gas under extremely oxygen-poor and high-temperature conditions, so that a strong reducing atmosphere is formed in the gasifier, reducing the NOx in the flue gas of the rotary kiln and the flue gas from the primary combustion furnace, thus achieving deep self-denitrification. The flue gas swirl from the gasification furnace enters the secondary combustion furnace, and the tertiary air swirl in the tertiary air upper branch pipe enters the secondary combustion furnace. The wind speed at the bottom of the secondary combustion furnace is controlled to be greater than 20m / s, and the excess oxygen coefficient in the secondary combustion furnace is greater than 1.0-1.2, so that the unburned volatile matter and coke in the pulverized coal can be fully burned in the secondary combustion furnace.

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